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JOURNAL

OF

MORPHOLOGY

FounDEpD By C. O. WHITMAN

EDITED BY

Ve Wo LINER hia x7
University of Illinois
Urbana, III.

WITH THE COLLABORATION OF

Gary N. CALKINS Epwin G. CoNKLIN C. E. McCiune
Columbia University Princeton University University of Pennsylvania

W. M. WHEELER WILLIAM PATTEN
Bussey Institution, Harvard University Dartmouth College

VOLUME 29
1917

THE WISTAR INSTITUTE OF ANATOMY AND BIOLOGY

PHILADELPHIA

Bey ir ee)

COMPOSED AND PRINTED AT THE
WAVERLY PRESS
By tHe WittrAMs & WiLkins COMPANY
Batrrmorg, Mp., U.S.A.

CONTENTS

No: 1.. JUNE

B. H. Buxton. Notes on the anatomy of arachnids. Eight diagrams and

ERC CEDIA CHS Pe eerny score tele oct « - «x. CREE On here bake nae Sn eb orm 1
N. E. McInpoo. The olfactory organs of Lepidoptera. Ten figtires.......... 33
Waro Naxanara. On the physiology of the nucleoli as seen in the silk-gland

cells of certain insects. Nine figures (two plates)......................... 55
JessE LERoy Cone. The urogenital system of Myxinoids. Eighty-five figures

(ATEELAEl TELE TPS) EOE ED Cb riots 6 cae eh ani y's 2 nr 75
Jay ArtHuR Myzrs. Studies on the syrinx of Gallus domesticus. Eighteen

| WERT DEL 2 2 SLA SA 2 tie acd ee =, tn 2 ee arr 165
S. Sacucur. Studies on ciliated cells. One text figure and four plates........ PAL?

No. 2. SEPTEMBER

Ropert J. Terry. The primordial cranium of the cat. Thirty figures (twelve

LUE CE EE ee ee ee Ae NB sn: «as, aes oe em 5 stan te 281
Naouipe Yatsu. Note on the structure of the maxillary gland of Cypridina
Balcendortat.) (Bour eres. oe Moral ec os... sx ce ee ae ee Dial 2d ore 435

BENJAMIN HarRIsOoN Pratt AnD J. A. Lone. The period of synapsis in the egg
of the white rat, Mus Norvegicus Albinus. Two text figures and one

(ERG oc itso Be cto cic Beto: i IS cc 05 441
Haroutp Heatu. The early development of a starfish, Pateria (Asterina)
Wiaeatan PMVeMtGUnenre 5 ac acl... . ..:5 nee eek cri sd Snes 4 erngee as 461

D. H. Wenricu. Synapsis and chromosome organization in Chorthippus
(Stenobothrus) Curtipennis and Trimerotropis Suffusa (Orthoptera).

“Teategay jel EMSS I steed oto ARMS ©. =o rca ch cg ey a 471
CuarENcE E. McCuiune. The multiple chromosomes of Hesperotettix and

Menmirias(Orvhoptera)=s bicht platesaaaeerreeric eee atic ose ess ce. 519
CaroutinE M. Hour. Multiple complexes in the alimentary tract of culex

pigiens: selhinty-phreesicures, (fOunsplaNtes) nace sss, deca scieaee ses = ces ae 607

ili

NOTES ON THE ANATOMY OF ARACHNIDS
B. H. BUXTON

EIGHT DIAGRAMS AND THREE PLATES

PART I
THE COXAL GLANDS OF THE ARACHNIDS

This paper is a continuation and extension of one published
in the Zoologische Jahrbiicher of July, 1913, since which time
I have had an opportunity of adding to the number of species
examined. —

It was shown in the previous paper that there are two very
distinct groups of the arachnids as regards the construction of
the coxal glands. In Group I may be placed the scorpions,
pedipalps and spiders, which have been more particularly
studied. The Phalangids certainly, and the Pseudoscorpions
-most probably, also belong to this group, but as they have not
been made a subject of special study, will not be described in
detail. In Group II were placed the Solifugae, and to these
can-now be added the Palpigrades.

The component parts of the coxal glands of Group I consist
of (1) the terminal sac, or saccule, lined with a very delicate
cubical or flattened epithelium which has the property of ex-
creting solid particles such as carmine when injected subcuta-
neously. Solid particles, probably urates, can also frequently
be observed normally in the cells lining the walls of the saccule.
From (2) the saccule, a short duct, or collecting tubule, leads
into (3) the labyrinth, which consists of a single, usually coiled,
tube, the walls of which are lined with excretory epithelium
having the usual striated base indicative of excretory functions,
but solid particles are never excreted by these cells. At the
distal end of the labyrinth there is sometimes a vesicular swell-
ing which can be regarded as (4) the bladder; and from the

1

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1
JUNE, 1917

2 B. H. BUXTON

bladder (5), a short exit tubule lined with cells derived from the
hypodermis leads to (6) the outlet! on the external surface,
either on segments III or V, or on both of these segments,
just posterior to the appendage.

In Group II the same arrangement holds good except that
between the collecting tubule and the labyrinth there is a large
sac lined with secretory epithelium, and the outlet is on segment
if bs

It was pointed out in the previous article that the coxal
glands of Group I appear to be homologous with the large ne-
phridia on segments VI and VII of Peripatus, whereas the coxal
glands of Group II show homology with the salivary gland of
Peripatus, the outlet of which is situated on segment II.

GROUP I. I. SCORPIONS AND SPIDERS

Several genera, both of scorpions and of Theraphosid spiders
from the East Indies, have been recently examined, but there
is nothing further to add to the description which has already
been published of the coxal glands of certain American, Euro-
pean and African genera.

It may be recalled that the coxal gland of the scorpions lies —
in segments V and VI with an outlet at the base of the posterior
surface of appendage V.

The eoxal glands of the spiders show considerable differences.
That of the Theraphosid spiders has two saccules and two
outlets, one of each on segment III and the other on segment
V with a large and complicated labyrinth apparently common
to both saccules and outlets. The Araneae verae have lost
the coxal gland of segment V, retaining only that of segment
III; and, with the exception of the six-eyed spiders, the Sica-
riids and Dysderids (to which can now be added the Oonopids),
the coxal glands of the higher spiders show various stages of
degeneration, or perhaps simplification.

1 There is always an outlet on the external surface, both in immature and
adult specimens. The arrangement of special muscle fibers around the exit
tubule indicates that it can be closed or opened at will.

ANATOMY OF ARACHNIDS 3

II. PEDIPALPS

Pocock has divided the Pedipalps into two distinct orders,
the Uropygi and the Amblypygi. The former group consists
of the Thelyphonides and Tartarides, and the latter of the
Phrynides. This separation seems to be justified on exam-
ination of the coxal glands, which differ very widely in these
two groups. |

Amblypygi

The description of the coxal glands of the Phrynides given in
the previous article was based upon two species of Tarantula
from Central and South America. Since then I have had an
opportunity of examining several species of Phrynicus and of
the Charontini family from India and the Malay Peninsula.

Phrynini Phrynicus ceylonicus, Ceylon.
Phrynicus nigromanus (Gravely), India.?
Charontini Charon grayi (Simon), Manila.*
Stygophrynus, caves in Malay Peninsula.
Sarax, caves in Malay Peninsula.
Phrynicho-Sarax singapurae (Gravely), Lang-
kawi Island, Kedah.
Charinides bengalensis (Gravely), Bengal.’

The coxal glands of Phrynicus are precisely similar to those
of Tarantula as previously described; i.e., there is a saccule on
segment III from which a very extensive coiled labyrinth tube
leads backwards to segment VI, where the tube loops forward
and runs anteriorly as a long straight tubule to the outlet on
segment III, just below the saccule and posterior to appendage
Ill (diagram 1, fig, 1). The labyrinth is peculiar in that the
- central portion is lined with a basophil epithelium which ap-
pears to be secretory, and it was suggested that the secretion
might be used for salivary purposes as there is no distinct sali-

2 Specimens collected and fixed for me by Mr. F. H. Gravely of the Indian
Museum, Calcutta.

3 Specimens given by M. Eugéne Simon of Paris. They had been kept in
alcohol for twenty years, but were in fairly good condition.

4 B. H. BUXTON

vary gland in Tarantula such as is found in the scorpions and
the spiders.

The Charontini, like Tarantula and Phrynicus, have a large
coxal gland with saccule and outlet on segment III, the laby-
rinth of which also possesses special secretory epithelium in its
middle portion; but the labyrinth of this large coxal gland does
not extend quite so far back as in Tarantula and Phrynicus.

Ss

Diagram 1 Coxal glands of the Amblypygi. Fig. 1 Tarantulini and Phry-
nini. Saccule on segment III from which the labyrinth extends posteriorly to
segment VI, from which point it loops forward and runs as a single tubule to the
outlet behind appendage ITI.

Fig. 2 Charontini. In addition to the large coxal gland on segment III
there is a small one, complete in itself, on segment V. S, saccule; CL, laby-
rinth of coxal gland; HT, exit tubule.

On segment V there is a second, very much smaller gland, com-
plete in itself, with saccule, labyrinth and outlet behind ap-
-pendage V, but the labyrinth possesses no secretory epithelium
(diagram 1, fig. 1).

The presence of this small, apparently disappearing, coxal
gland indicates that the Charontini are more primitive than
Phrynicus, before which they are probably giving way. The

ANATOMY OF ARACHNIDS 5

larger genera of the Charontini: Stygophrynus, Charon and
Sarax, are found only in caves, while those found in the open,
such as Charinides bengalensis and Phrynicho-sarax, some of
which I found on Langkawi Island, are very small, insignificant-
looking animals. Langkawi Island lies off the coast of Kedah
in the Malay Peninsula, and seems to possess a rather primitive
arachnid fauna, as I shall also have occasion to remark in a note
on the distribution of the Uropygi. Phrynicho-Sarax is quite
abundant in the jungle on Langkawi Island, but no Phrynicus
at all were found there.

Uropygt

Thelyphonides. The carapace of the older Thelyphonides is
very hard and difficult to section, but these animals live very
well n captivity, and among a number of specimens, kept in
small cages and supplied with grasshoppers, one wil! moult now
and then, immediately after which the chitin is thin and soft,
and even the mature animal can be readily sectioned. At this
stage, also, there is much turgescence of the tissues; the organs
are all actively functioning and therefore in a favorable condi-
tion for observation.

Species of Thelyphonides examined:

Thelyphonus linganus Malay Peninsula
Thelyphonus sepiaris Ceylon (Plains)
Labochirus crassimanus Ceylon (Hills)
Hypoctonus kraepelini Langkawi Island, Kedah

The coxal glands of all of the above representatives of this
family are precisely alike and resemble those of Tarantula in
that the coils of the labyrinth extend well back into segment VI,
and are not concentrated as in the scorpions; but nevertheless,
the gland differs greatly from that of Tarantula, for there are
two saccules—one on segment IV and-another on segment V.
The saccules, moreover, are elongated and flattened, not roughly
spherical like those of Tarantula and the other Amblypygi. In
the case of the Amblypygi (and this applies also to the more or
less spherical saccule of the scorpions and spiders) the surface

6 B. H. BUXTON

of the saccule is increased by blood capillaries which push in
the wall of the saccule and break up its lumen into tortuous
channels (figs. 1 and 2). The elongated and flattened saccules
of Thelyphonus have sufficient surface of themselves and are
not invaded by capillaries in this way. The saccule of Thely-
phonus appears tubular in sections, and the tubules can be dis-
tinguished from those of the labyrinth only by the nature of the
epithelium lining the walls. The cubical epithelium of the sac-
cule has very delicate outlines and the cytoplasm often contains
solid particles—probably urates—which are never found in the
coarser striated epithelium of the labyrinth. On injecting car-
mine the particles are taken up by the cells of the saccules, but
never by those of the labyrinth.

= s

Diagram 2 Coxal gland of the Thelyphonides. Two saccules, one on seg-
ment IV, and another on segment V, with a labyrinth common to both saccules
and an outlet behind appendage III. S, saccule; CL, labyrinth; ET, exit tubule.

From each of the two saccules of Thelyphonus a short but
wide collecting duct leads into a tubule of the labyrinth directed
posteriorly, so that the tubule from the saccule on segment V
extends posteriorly into segment VI where it forms coils which
ultimately pass forward again. Similarly the tubule from the
saccule on segment IV extends backwards into segment V where
it joins the main coils. The coils coalesce at some hitherto un- -
determined point, and the coiled labyrinth tubule passes forward
to a point opposite the anterior saccule, where the coiling comes
te an end and the labyrinth runs forward as a single straight
tubule to its outlet just posterior to appendage III (diagram 2).

The outlet, therefore, is in the same position as that of Taran-
tula, but the saccules, instead of being in segment III only, or
in III and V as in the Charontini, are in segments IV and V.
Moreover, the entire coxal gland is evidently formed by fusion

ANATOMY OF ARACHNIDS v4

and modification of three originally distinct glands on segments
III, IV and V, whereas the two coxal glands of the Charontini
are entirely distinct organs belonging to segments III and V,
one of which has been lost in Tarantula and Phrynicus.

Tartarides.
Species examined:
Schizomus peradeniyensis, Peradeniya, Ceylon.
Schizomus vittatus (Gravely), Peradeniya, Ceylon.
Schizomus perplexus n.sp. (Gravely), Plains, Ceylon.
Schizomus modestus (Hansen), Kedah, Malay Peninsula.

It is only within the last four or five years that any collector
has been able to obtain large numbers of the Tartarides.
Messrs. Green and Gravely, in the botanical gardens of Pera-
deniya in Ceylon, used a sieve with which they sifted fallen
leaves and débris over a large sheet of stiff paper, the Tartarides
and small insects falling through the meshes. Adopting this
method I was fortunate enough to secure, not only at Pera-
deniya, but also on the plains of Ceylon and in the Malay Penin-
sula, nearly 500 specimens of these interesting little animals,
of which more than 50 were fixed on the spot and sectioned
later. The type species—S. crassicaudatus—can not be col-
lected in this way, as it occurs under stones and bricks. <A few
specimens were secured in Ceylon but they were not sectioned.

Owing to their small size and the minuteness of their organs
and individual cells it is not easy to determine the details of the
coxal glands, but from a comparison of a large number of speci- ~
mens one may conclude that the fundamental arrangements of
the organ are precisely similar to those obtained in the Thely-
phonides. There are two flattened tubular saccules, one in
segment IV and another in appendage V, from each of which
a collecting duct, consisting of five or six minute cells, leads into
a labyrinth tubule running posteriorly to segments V and VI
respectively. The labyrinth, lined with striated cells, coils very
little and is much simpler in construction than that of Thely-
phonus, but nevertheless it has not been found possible to deter-
mine just where coalescence of the two tubules takes place be-

8 B. H. BUXTON

fore the labyrinth runs forward as a single tubule from segment
IV to the outlet on segment III. :

Note on the distribution of the Uropygi. Gravely (’12) suggests
that Hypoctonus of Burma is hemmed in and is being gradually
displaced by the more highly specialized Thelyphonus sepiaris
of India on the one hand, and Thelyphonus linganus of the Malay
Peninsula on the other; the latter being closely allied to other
species found in the Malay Archipelago, where he supposes that
this branch of Thelyphonus originated.

The Hypoctonus kraepelini found on Langkawi Island is
rather small, with red legs; the species having been previously
unknown to M. Eugéne Simon, to whom I gave some specimens.
There is one specimen in the Indian Museum at Calcutta, from
the northern (Siamese) region of the Malay Peninsula, found
and named by Annandale some years ago, but I do not know of
any other, nor is any other species of Hypoctonus known to occur
outside of Burma.

In Perak and Kedah, British controlled States of the Malay
Peninsula, Thelyphonus linganus is very common; but I found
only one specimen of Hypoctonus kraepelini, in the jungle far
removed from any settlement, near the Siamese border. On
Langkawi Island, only a few miles from the Kedah coast, there
are no Thelyphonus, but everywhere in the primaeval jungle
one can collect numbers of Hypoctonus kraepelini, although
they do not occur where the jungle has been cleared. The
‘species seems to have been left undisturbed on the island, but on
- the mainland it has become very scarce, owing to pressure by
‘Thelyphonus linganus.

It may also be noted that Tartarides (Schizomus modestus)
are very common in Kedah and Perak on the mainland, but dur-
ing a month’s stay in Langkawi I did not find a single specimen.

GROUP II. III. SOLIFUGAE AND PALPIGRADES
Solifugae

The coxal gland of the Solifugae was fully described in the
previous monograph, and a study of a considerable number of
additional specimens goes to confirm the results already ob-

ANATOMY OF ARACHNIDS 9
tained. Stress was laid on the peculiar nature of the saccule,
the lumen of which is filled with a pulpy mass of cells instead of
the walls being merely lined with a single layer of delicate epi-
thelium, which is the usual arrangement. This part of the
organ had never previously been described, and the opinion ex-
pressed, with some reservation, that it is actually the saccule,
has since been proved by the injection of carmine into a number
of specimens during a visit to Biskra in 1912. The carmine was
injected in minute quantities under the thoracic carapace. The
animals very quickly recovered from the effects of the inocula-
tion and were killed afterwards at varying intervals of time—
from six hours to one month. The carmine is very quickly
taken up by the cells of the saccule, and seems to remain there
for a ‘ong time—even up to a month. No carmine is ever found
in any other part of the organ.

The saccule is situated in segment II, the connecting tubule
opening into a long narrow sac (labyrinth sac) which extends
posteriorly into segment IV, where, after making several coils,
it ends blindly. The walls of this part of the gland are lined
with secretory epithelium. At a point in proximity to the sac-
cule there is an opening from the labyrinth sac into the true
labyrinth, which consists, as in group I, of a long single coiled
tubule lined throughout with striated epithelium. The laby-
rinth extends back as far as segment VI, where it forms several
coils and then runs forward again to the exit tubule and outlet
on appendage II (diagram 3 fig. 1). In connection with the
exit tubule there is a squirting apparatus, apparently intended
to force a stream of the secretion towards the prey held in front
of the mouth by the chelicerae, but this part of the organ need
not be described again in detail. The probable homology of.
the coxal gland of the Solifugae with the salivary gland of Peri-
patus was considered and discussed in detail, and I have since
seen no reason for changing my opinion.

Palpigrades

Koenenia mirabilis. In the spring of 1914 I was able, with
the help of Mr. C. Borner of Metz, to collect in the olive groves

10 B. H. BUXTON

.

of Palmi in Calabria about sixty specimens of Koenenia mirabi-
lis, almost all of which were fixed and sectioned for microscopic
study. In addition I was able to examine five specimens which
had been sectioned and described by Mr. Borner some years pre-
viously. The coxal gland had already been observed by Grassi,
the original discoverer of Koenenia, (’85), and Borner (’04) de-
scribed it as a single tube running anteriorly from the second

Diagram 3 Coxal gland of group II. Fig. 1 Coxal gland of the Solifugae.
Saccule on segment II opening into the long labyrinth sac. From the latter
there is an opening into the true labyrinth, running back and then forward again
to the outlet on appendage II. In the neighborhood of the saccule the labyrinth
sac is pouched and the labyrinth coils a little. For the sake of clearness these
pouches and coils are omitted in the diagram.

Fig. 2 Coxal gland of Koenenia. Saccule on segment II opening into the
long labyrinth sac. The true labyrinth is represented only by the vesicle, the
outlet from which is on appendage IT. S,saccule;CSL, labyrinthsac; CL, laby-
rinth; ET, exit tubule; V, vesicle.

abdominal (genital) segment to an outlet just posterior to ap-
pendage II. This description is correct so far as it goes, but
Bérner overlooked the saccule and did not appreciate the sig-
nificance of the tube being single and not double. He was not
acquainted with the anatomy of the Solifugae and his efforts
were chiefly directed towards grouping Koenenia with the
Pedipalps.

ANATOMY OF ARACHNIDS 11

As Koenenia is exceedingly rhinute, its organs and the cells
composing them are all on a correspondingly minute scale, so
that it is not by any means easy to make out the different parts
of the gland, and it is only by studying a large number of speci-
mens that one can come to satisfactory conclusions. There is a
small circular saccule in segment II consisting of eight or ten
fairly well defined cells enclosing a lumen, from which a short
collecting duct of five of six cells leads into a long narrow sac
which extends posteriorly into the abdomen to segment VIII
(genital), where it forms a short loop and ends blindly. As al-
ready observed by Borner, the cells of this posterior loop differ
from those of the straight part of the sac, and he quite rightly
remarks that none of the cells, either in the loop or in the straight
part of the sac, have a striated base; i.e., they are secreting, not
excreting cells such as one finds in the true labyrinth of the
arachnids. Just below the point at which the collecting tubule
or duct changes to the long sac, there is an opening leading into
a dilated vesicle, and from the vesicle there is a short exit tubule
leading to the outlet just posterior to appendage II (diagram 3,
fig. 2).

It seems obvious that this organ must be homologous with
the coxal gland of the Solifugae rather than with that of the
scorpions and spiders. The saccule and outlet are on the same
segment (II), and we also find the same long sac with a coil at
its posterior extremity extending far back and lined with secret-
ing cells. In Koenenia, however, the true labyrinth has prac-
tically disappeared as such, being represented merely by the
vesicle, which probably only acts as a reservoir for the products
of secretion, having no excretory functions, since the walls of
the vesicle do not appear to be lined with striated epithelium.

- It may be further remarked that if this long sac represented
the true labyrinth, not only should it be lined with striated cells
but it would necessarily have to loop forward on itself and run
forward again to the outlet, thus forming a double tubule on
cross section at any point; but it is a single tube throughout and
has been correctly so described by both Grassi and Borner.

12 B. H. BUXTON

The coxal glands of the Arachnids have always been described
as being located in such and such a segment, but it is probable
that fundamentally each coxal gland represents two segments
instead of one. There seems little doubt that in the saccule
we have the last traces of the coelom, which would belong to
the segment anterior to that of the main part of the coxal gland.
One may reflect that in the worms the coelom of one segment is
connected with the segment next posteriorly to it by means of a
funnel represented by the collecting tubule of the arachnids.
The funnel leads through the partition into a coiled nephridium
situated in the next segment; the coiled tubule of the nephridium

Diagram 4 Four segments of a worm, showing the nephridia.

having an outlet near the anterior partition of the segment
(diagram 4). When, therefore, dealing with the arachnids, we
say, as for instance with Phrynicus, that the saccule lies in seg-
ment III and the gland has its outlet on segment III just behind
appendage III, it should be borne in mind that the saccule and
collecting duct represent the coelom and funnel of segment II],
while the labyrinth and outlet belong in reality to segment IV;_
the labyrinth having encroached upon and suppressed the coxal
glands immediately posterior to itself—a process of encroach-
ment which is still in progress in the Charontini, the small pos-
terior gland of which is composed of the coelom and funnel of
segment V and the nephridium of segment VI.

ANATOMY OF ARACHNIDS 13

PART AL
THE GANGLIA OF THE ARACHNID

If the cephalothorax of an arachnid such as the scorpion or
Thelyphonus be sectioned sagitally through the median line, the
ganglia composing the large suboesophageal ganglion can be
clearly distinguished, the suboesophageal ganglion being mapped
out into a number of neuromeres, separated from each other by
a small artery whose course can be very readily determined.
Each of these neuromeres represents one of the individual gan-
glia of which the whole is composed. In the same way also it
can sometimes be recognized that the abdominal ganglia are
composed of more than one individual ganglion. By enu-
merating the ganglia in this way it is determined that there are
eighteen ganglia in each of the four orders which go to form
group I of the arachnids: scorpions, spiders, Uropygi and Ambly-
pygi. One of these eighteen ganglia (the cheliceral) has moved
up and fused with the supracesophageal ganglion; the other
seventeen being found in the suboesophageal ganglion and in
the abdomen.

GROUP I. IV. SCORPIONS

The nervous system of the scorpions is less concentrated than
that of the other arachnids. The suboesophageal ganglion con-
sists of nine neuromeres, the ninth neuromere supplying the '
abdomen as far as the first lung (fig. 5). In the abdomen itself
there are three single ganglia supplying lungs 2, 3 and 4. In
the post-abdomen are four ganglia, of which the last is double,
having two neuromeres. The entire ventral nerve chain, there-
fore, consists of seventeen ganglia which, with the cheliceral
ganglion, fused with the brain, would make eighteen.

14 B. H. BUXTON

V. PEDIPALPS
Amblypygi

The ganglia are all concentrated in the cephalothorax, the
suboesophageal ganglion containing seventeen neuromeres. The
photograph is taken from the only section I have which shows
the whole of the neuromeres in one field, but in a large number
of specimens it has been found easy to detect the whole seven-
teen by making a composite drawing from several sections in
series. The Tarantulini Phrynini and Charontini are precisely
similar as regards this arrangement of the ganglia (figs. 3 and 4).

Uropygt

Thelyphonides. Both in young and adult specimens the sub-
oesophageal ganglion contains only twelve neuromeres, but at
the posterior end of the abdomen there is a large additional
ganglion with five neuromeres, representing the last five abdom-
inal segments.

The eggs of Thelyphonus (linganus, the species studied) are
carried in a packet attached to the underside of the abdomen of
the mother. Just after hatching out, the larvae, white and
inert, are carried wrapped around the body of the mother to
which they are firmly attached by a gummy substance. At this
stage the suboesophageal ganglion consists of nine neuromeres;
the other eight ganglia being paired and strung out separately
along the abdomen. In a few days, however, and before the
next moult, the ganglia have become concentrated; the three
anterior pairs becoming fused in the median line and passing for-
ward to join the suboesophageal ganglion, while the five pos-
terior pairs also fuse in the median line and with each other to
form the abdominal ganglion as in the more mature animals.
Strubell (92), for Thelyphonus Caudatus, described six pairs
of ganglia in the cephalothorax and ten pairs in the abdomen—
his specimens probably representing a slightly earlier stage than
I had an opportunity of observing; but there are certainly sev-
enteen ganglia altogether, and not sixteen as he described.

ANATOMY OF ARACHNIDS 15

Tartarides. The arrangement of the ganglia in the Tartarides
at first sight appears to differ fundamentally from that in the Thel-
yphonides, since there is, in addition to the suboesophageal, a
large ganglion situated in the anterior part of the abdomen in the
neighborhood of the genital segment instead of at the posterior
endof the abdomen. Microscopical examination, however,shows
that there are nine neuromeres in the suboesophageal ganglion and
eight in the abdominal ganglion, making seventeen in all—the
same number as in the Thelyphonides—and it may be presumed
that the Thelyphonides and Tartarides became differentiated
from a common ancestor at a stage when there were still eight
separate paired ganglia in the abdomen; a stage now represented
in the larval Thelyphonides. On further specialization the
ganglia in the Tartarides became concentrated into a single an-
terior abdominal ganglion, while in the Thelyphonides two
groups of three and five ganglia respectively were formed, the
first group passing forward to join the suboesophageal ganglion
and the latter remaining in the posterior part of the abdomen.

It may be recalled that, apart from their external affinities,
which have led to placing these two groups in the same order,
the close relationship of the Thelyphonides and Tartarides is
clearly established by the similarity of the coxal glands—a fact
which makes it easier to accept this explanation of the appar-
ently fundamental difference in the arrangement of the ganglia.

VI. SPIDERS

In all spiders there appear to be twelve neuromeres in the sub-
oesophageal ganglion, although with the Araneae verae it is
not often possible to make them out except in larval and quite
young specimens, but the Theraphosid spiders show the neuro-
meres more clearly, always to the number of twelve.

In young and adult spiders there are no abdominal ganglia,
nor have I ever found any trace of them in larval specimens of
the Araneae verae; but in 1913 I was fortunate enough to find
in Sumatra a cocoon of a large Chilobrachys (Theraphosid)
containing nearly a hundred larvae just after hatching, and

16 _B. H. BUXTON

these I was able to keep alive for two months, fixing four or five
for sectioning every few days. In the larval stage the spiders
were very inert, with distended abdomen containing a large
amount of yolk. They were not pigmented and remained
quiescent in the cocoon. At the end of a month they all
moulted simultaneously and left the cocoon, passing from the
larval to the immature stage. They were now pigmented, Jong-
legged, with small abdomen, and very active, remaining so until
the last of them had been killed for sectioning a month later.
These points are merely mentioned to show that the spiders were
in a normal condition, at any rate in the early stages.

In the youngest specimens five abdominal ganglia were clearly
distinguishable, but the ganglia rapidly disappeared and in
about a week there were no traces left. I do not think that any
observation of these transient abdominal ganglia in spiders has
ever been recorded.

In specimens killed at once and two days later, the suboeso-
phageal ganglion contains twelve neuromeres very clearly mapped
out. From its posterior end two parallel nerve cords pass
through the pedicle, beyond which they separate, running later-
ally and ventrally in the abdomen. On either side of the abdo-
men are three very clearly defined, large ganglia, connected io-
gether by the nerve cord. The nerve cord can be traced a little
beyond the third ganglion, where it is lost, but more posteriorly
there are two very much smaller ganglia ‘ying in the neighbor-
hood of the intestinal tract, which has so far only partially been
formed. The rest of the abdomen is filled with yolk (diagram 5).

In specimens fixed three days later (five days after finding the
cocoon) the nerve cord was no longer traceable into the abdo-.
men; the two posterior ganglia had disappeared and the three °
anterior were greatly diminished in size.

On the seventh day there were some traces of one or two
ganglia, but it was difficult certainly to identify them, and this
was the last trace of them that could be found. If the series
had begun at this stage the ganglia would certainly have been
overlooked or not recognized as such.

ANATOMY OF ARACHNIDS wa

With the twelve neuromeres of the suboesophageal ganglion
these five paired evanescent ganglia in the abdomen make up
the usual number of seventeen for group I of the arachnids,
which may here be tabulated.

BRAIN Pee cae ABDOMINAL GANGLIA
AGEAL
TOTAL
Chelicerae ped se Anterior Posterior

orax
SCOLPIONSHE: ceca: oe. NE 1 9 161 1 1h tl 18
LSirlollig oi (oilee o, 6 oe 1 iL7/ 0 0 18
Thelyphonides...2.....i2... 1 12 0 5 18
ileSitigs 0 (es), ee 5 ae a 1 9 8 0 18
SPICES rn... eee Os 1 12 Cie LT) 18

(Transient)
6 segments 7 segments 5 segments

GROUP II. VII. SOLIFUGAE AND PALPIGRADES

The Solifugae being tracheate animals, there are no blood
channels to divide the neuromeres, although in the cephalo-
thorax their place seems to be taken to some extent by tracheae.
By means of the tracheae and the nerves proceeding from the
suboesophageal ganglion, one can determine that the suboeso-
phageal ganglion is composed of five neuromeres supplying ap-
pendages II to VI. The nerve supply to appendage VI, on
which the racquet organs are situated, is very abundant, and is
supplemented by a number of secondary ganglia at the roots of
the racquets themselves.

With the neuromeres supplying appendage VI, however, the
suboesophageal ganglion appears to come to an end, and from
this point there is a large nerve cord leading into the anterior
part of the abdomen where it swells into a large single ganglion
in the region of the genital segment. The nerve cord emerges
from this ganglion posteriorly, and can be traced a short dis-
tance after which it becomes distributed into small filaments
and gradually disappears. There is no trace of any ganglion
in the abdomen other than the one mentioned, nor does this
ganglion show any evidence of being divided into neuromeres.
It is simply one solid ganglionic mass (diagram 6, fig. 1).

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 1

18 B. H. BUXTON

Palpigrades

Koenenia, the coxal gland of which has been shown to be
closely related to that of the Solifugae, also shows a very simi-
lar arrangement of the ganglia. In the suboesophageal ganglion
there are five swellings on either side, one for each corresponding
appendage, and from the posterior end of the ganglion a nerve
cord passes to the abdomen, in the anterior part of which there

Diagram 5 Evansecent abdominal ganglia of Chilobrachys. Five ganglia
on either side of the abdomen, the first three of which are connected by a nerve
cord running through the pedicle from the suboesophageal ganglion. Ent,
intestine.
are three distinct ganglionic swellings, beyond which the nerve ©
cord can not be traced. These three ganglionic swellings in the
genital region appear to correspond to the abdominal ganglion
of the Solifugae, in which they have become concentrated into
a single mass (diagram 6, fig. 2).

Note on the segmentation of the arachnids. To return to group
I, we find in each case that there are eighteen ganglia, and the
question naturally arises—to what extent do these ganglia
represent segments?

ANATOMY OF ARACHNIDS 19

The supraoesophageal ganglion, with its sense organs, need
not be considered as having any segmental value except in so
far as the ganglion for the chelicerae is concerned—a ganglion
which in the earliest stages is obviously suboesophageal and on
later development moves over and becomes fused with the
brain.

Diagram 6 The ganglia of group II. Fig. 1 Frontal view of the ganglia of
the Solfugae. The five neuromeres of which the suboesophageal ganglion is
composed are indicated, and below is the large single abdominal ganglion,
connected by a nerve cord with the suboesophageal.

Fig. 2. Frontal view of the ganglia of Koenenia. Resembling that of the
Solifugae, but showing three abdominal ganglia instead of a single one.

The five anterior ganglia of the suboesophageal mass supply
appendages II to VI, which, with the chelicerae, represent the
six segments of which the cephalothorax is composed. This
number of segments of the cephalothorax obtains in all orders
of this group and Jeaves twelve abdominal segments to be ac-
counted for, each with its attendant ganglion.

20 B. H. BUXTON

Pedipalps

In the Pedipalps, both Uropygi and Amblypygi, the relations
are clear enough. There is a small first abdominal segment
(VII), after which comes the second abdominal, or genital seg-
ment (VIII); posterior to the genital segment are ten more
segments, making twelve abdominal segments in all; the num-
ber of segments therefore corresponding to the number of gan-
glia—six for the cephalothorax and twelve for the abdomen.

Spiders

In the ordinary spiders all trace of segmentation of the abdo-
men is lost, but the pedicle is taken to represent a first abdomi-
nal segment (VII) after which comes the genital organ repre-
senting segment VIII. Liphistius has nine tergal plates on the
abdomen, each of which is presumed to represent a segment, so
there are still three segments wanting. McBride (’14), quoting
Kishinouye, says that in the earlier stages of development of
Theridion ten segments are marked out in the abdomen, of
which the tenth is not always distinct, nor does it always de-
velop a coelomic cavity. There is no proof, therefore, of corre-
spondence between the number of ganglia and segments in the
spiders, although, since the rudiment of the tenth abdominal
segment is not always laid down, it is possible that an eleventh
and a twelfth segment may have originally existed but have now
entirely disappeared.

Scorpions

There is not complete correspondence between the ganglia
and the segments in the scorpions, although the total number
of eighteen is the same. The cephalothorax is composed of
six segments as usual, and the abdomen of twelve, but the first
abdominal segment (VII) has disappeared, leaving the genital
as the first abdominal segment, posterior to which are the seg-
ments bearing the pectens, the four lungs and the last abdomi-
nal segment—making seven in all—while beyond this comes the
post-abdomen with five segments forming the tail. There are,

ANATOMY OF ARACHNIDS 21

therefore, eleven post-genital segments instead of ten as in the
Pedipalps.

The first abdominal segment has disappeared, although Brauer
(95) found a transient rudiment corresponding to it in the em-
bryo scorpion.

On examination of the suboesophageal ganglion it is found
that the neuromeres 1 to 5 supply appendages II to VI; the
seventh neuromere supplies the genital organ, the eighth neuro-
mere the pectens and the ninth the first lung—leaving the sixth
neuromere, which should supply the missing segment VII, to
be accounted for. This sixth neuromere is clearly mapped out
and is quite normal in size, but I have not been able to trace
nerves preceding from it. It seems probable, however, that it
may be used as supplementary to the pectens, for the nerve
supply of which there is a secondary paired nervous mass lying
ventrally to the suboesophageal ganglion as shown in diagram 7.

Just ventrally to the eighth neuromere, on either side of the
median line, there is a large mass of nerve fibers from which a
cord runs posteriorly and joins the nerve from the eighth neuro-
mere, and another cord runs anteriorly to a point opposite the
sixth neuromere where there is another large swelling. I have
not been able to detect any direct connection between the sixth
neuromere and the nerve mass just ventral to it, but it seems
probable that there must actually be some such connection and
that the sixth neuromere, after the disappearance of segment
VII, became utilised as a secondary source of supply for the
pectens.

In the Buthidae, but not in the Scorpionidae, Chactidae, or
Vejovidae, there is a further extension of this ventral nerve
mass anteriorly to about opposite the second neuromere, where
there is another small swelling but no direct connection with
the suboesophageal ganglion itself. (This extension is shown
in diagram 7.)

Whatever may be the true function of the sixth neuromere, it
is clear that it is interpolated between the fifth and seventh
without having any corresponding segment to supply. Seg-
ment VII has disappeared, but the ganglion which originally
supphed it remains.

Laps B. H. BUXTON

Turning now to the abdomen we find twelve segments, of
which the first is the genital, but there remain only eleven gan-
glia to supply them since we have already disposed of seven
gangla (segments I to VII) (VII being transitory). The gan-
glia of the genital organ (VIII), pectens (IX) and first lung (X)
are fused L with the suboesophageal ganglion. Next comes a

Intestine

Diagram 7 Sagittal view of the suboesophageal ganglion of the scorpion,
showing nine neuromeres, the destination of the nerves proceeding from them;
and the ventral nerve mass secondarily supplying the pectens. It is under-
stood that all these structures can not be seen in one section. The neuromeres
can only be distinguished in sections through the median line, whereas the
nerves running to the appendages and the secondary nerve mass for the pectens
are paired structures which appear in sections on either side of the median line.

series of three single ganglia for lungs 2, 3 and 4 (XI, XII, XIID),
posterior to which is the last abdominal segment (XIV). In
the post-abdomen there are five segments and four ganglia, of
which the last, situated in the fourth segment, is double (hav-
ing two neuromeres) and clearly supplies segments 4 and 5.
The last segment in the abdomen, therefore, appears to be with-
out a ganglion. The first ganglion of the post-abdomen is cer-

ANATOMY OF ARACHNIDS 23

tainly single,* but it lies in the anterior part of this segment and
extends anteriorly through the constriction into the last segment
of the abdomen in the egg just before hatching. I have not
had an opportunity of examining earlier stages. The suggestion
may be put forward that the last abdominal and first post-
abdominal segments represent in reality a single segment which
has become secondarily divided into two in order to give to the
base of the tail greater strength than could be obtained by
utilizing the division between two primary segments. This
suggestion seems to recelve some support from Brauer’s figures
of the development of the scorpion, a part of one of which is
reproduced in diagram 8. Brauer, in his text, treats segments
XIV and XV (first post-abdominal) as if they are two distinct
segments, but it appears from his figures as if segment XIV folds
over on itself to form the base of the tail, without at first any
segmentation at the point of the fold.

That such a division is possible is indicated by the secondary
division between the fifth post-abdominal segment and the
poison gland, which corresponds to the telson of Limulus and
the Eurypterides. The telson is not considered as representing
an original segment, since it always lies behind the anus. There
is no ganglion for the poison gland in the scorpion. Similarly
the Uropygi and Koenenia have a tail jointed to the last abdom-
inal segment, but the tail is not recognized as a segment, nor
has it any corresponding ganglion.

The scorpion-like Eurypterides of the Silurian have ten post-
genital segments—one less than the scorpion; the pre-genital
segment (VII) being recognizable on the dorsal surface, but on
the ventral surface it is fused with the genital plate. On the
other hand, the Silurian scorpion, Palaeophonus, appears to
have the same number of segments as the modern scorpions.

The general conclusion is that in group I of the arachnids the
number of ganglia corresponds to the number of segments—
eighteen of each—obvious in the Pedipalps; not so clear, but
probable, in the scorpions; in the spiders possible but not proven.

*T have looked in vain through scores of specimens for some indication of
division of this ganglion into two neuromeres.

24 B. H. BUXTON

In regard to group I, since the large abdominal ganglion of
the Solifugae is a single, solid mass, without any evidence of
neuromeres, nothing definite can be said about it. It may
represent a fusion of all the original abdominal ganglia, or it
may be composed of one or more of the original ganglia which
have suppressed and taken over the functions of others. The
same may be said of the three abdominal ganglia of the Palpi-

Diagram 8 From Brauer. Development of the tail of the scorpion. Be-
tween segments XIV (last abdominal), and XV (first post abdominal), there is no
evidence of segmentation. Segment XIV seems to double over on itself to form
the base of the tail. In the tail itself only three out of the five segments have
been cut out at this stage.

grades. In neither of these two orders can any relation between
the abdominal segments and ganglia be determined. In this
respect they differ again from group I; and a still further differ-
ence between the two groups can be pointed out; in each of
these two orders of group II there are nine post-genital seg-
ments instead of ten, as is probable in all the orders composing
group 1.

ANATOMY OF ARACHNIDS 25

Tabulation of differences between group I and group II

Group II Group [
Woxcltolandisaceley aaa ace ee oa: Segment II | Segments III, IV, V
CoxaleclandiouGletitas. 26sec ss oe. Sse. Segment II | Segments III, V
Coxalvcland labyrinth sac...5.5.--.+---- - Present Absent
Gandhi 334 Sos Goes Ce eee eee 7 or 9 Always 18
GangliagmeuromeneSss: +3 2sc0-se55+ os c.e-- Doubtful Clearly marked
Seements, post genitals. =... .-2e- «sc - 9 10

My best thanks are due to Professor Pruvot for permission to
work in his laboratory of comparative anatomy at the Sor-
bonne, and also to M. Eugéne Simon and Mr. F. H. Gravely
for specimens and suggestions. The diagrams were made for
me by Miss G. E. Carver.

LITERATURE CITED

Bo6rNER 1904 Beitrag zun Kenntniss der Pedipalpen. Zoologica.
BravER 1595 Zeit. fiir wiss. Zoologie, vol. 59, p. 360.

Buxton 1913 Zoologische Jahrbiicher Abt. Anat. July Supplement.
Grassi 1885 Naturaliste Siciliano.

GRAVELY 1912 Records of the Indian Museum, Calcutta.

McBriprt 1914 Textbook of Embryology, vol. 1, p. 224.

STRUBELL 1892 Annals and Mag. Nat. Hist., vol. 10.

PLATE 1

EXPLANATION OF FIGURES

1 Tarantula palmata. Saccule of the coxal gland. X 175. The drawing
is outlined from a photograph, the cells being drawn in semi-diagramatically,
to show more clearly than is possible in photograph the differences between
the cells of the saccule, the collecting duct and the labyrinth. The lumen of
the saccule is broken up into channels by blood capillaries or rather lacunae)
which push in the walls, and thus increase the surface of the saccule. In the
diagrams this feature of th saccule is not shown. S, saccule; CD, connecting
duct; CL, labyrinth; E7, commencement of exit tubule; 7, muscle and con-
nective tissue indicated by horizontal broken lines; BC, blood capillaries indi-
cated only by vertical broken lines; GL, suboesophageal ganglion.

2 Vejovis flavescens. Photograph of coxal gland of scorpion. X 100. With
the help of figure 1 the constituent parts can be made out. In the center is the
saccule; its lumen, broken up by inhanging capillaries, opening on the right
into the labyrinth, whose tubules in this case completely surround the saccule
except at one point (CA) where the blood supply enters. At HT is the com-
mencement of the exit tubule, but the tubule itself is not shown. The coxal
gland rests posteriorly (right) upon the diaphragm D which separates the
cephalothorax from the abdomen. C, caeca of the intestine; NV, nerve supply-
ing appendage VI; WM, muscle; CA, coxal artery; #7, exit tubule; D, diaphragm.

ANATOMY OF ARACHNIDS PLATE

B. H. BUXTON

_— &
= fs = <e
— — M Ss
oe if ee
2 = LFF H hi I<
ee nw Wi es NG tae Z
= anes Dees
oS. Ss gy
we .; ; Ee
UE = ETT TE ee :
Le i, ES a
Uy NP, AS
AS (0415) AN SE
SEC Na
> 1 AS,

= B ae
ee ty

PLATE 2

1 Tarantula palmata. Neuromeres of the suboesophageal ganglion. X 60
Sagittal secton through median line of cephalothorax outlined from the photo-
graph showing 17 neuromeres. Anterior to the suboesophageal ganglion the
tissues are broken up on account of extraction of the chelicerae, which are too
hard to section. ART, artery, the branches from which run between the neuro-
meres; CH, chitin of external surface; C7, muscle and connective tissue indicated
by broken horizontal lines; NA, nerve to abdomen.

Fig. 2. Photograph from which the drawing was outlined.

ANATOMY OF ARACHNIDS

PLATE 2
B. H. BUXTON

SUCKING
CHAMBER

009
0,

t

6

£

Oo net

Cnr

29

PLATE 3

1 Immature scorpion. Buthus occitanus. Neuromeres of the suboesopha-
geal ganglion. X 40. Sagittal section through median line of cephalothorax
outlined from the photograph showing 9 neuromeres, of which the 6th is well
defined and normal in size. A, artery from which branches run between neuro-
meres; BR, brain; C, caeca of the intestine; CT, connective tissue and muscles;
GSO, suboesophageal ganglion; GAi, 1st abdominal ganglion; HT, heart; INT,
intestine; OLS, oesophagus; O, median eye.

2 Photograph from which the above drawing was outlined.

PLATE 3

ANATOMY OF ARACHNIDS
B. H. BUXTON

OES

GSO

ol

THE OLFACTORY ORGANS OF LEPIDOPTERA

N. E. McINDOO
Bureau of Entomology, Washington D. C.

TEN FIGURES

CONTENTS

EEO Y MOT ANG TMCLNOOS:c.,..0c. Be occ + ac «0 code SEMI Mn 0's ab age oe ba ae wanes 33
MPTEROILACC ORV RDOLES Ma ati ais iia cs ss Gis. cun, a onelebertnteiate le ore eo cinee oat See ae 35
LOSSES )S TU Ss eek eM Re eo rs ec. eh: ani iM, eS 35

eS OPED IMON Opry ape ie Soe) or 2-a's k «pd eRe os fais oe 35

pm UHCIESWECLER ee ooh bite aan ieyé 5 b=... Scegs OME amok > » oa ee 38

c. Generic, specific and sexual variations... 05.0. 0.....¢ aoa. oe. 41

SIHCUOH UTE us oO SS ote ea’ eal ers Di eae ie ae eR See IN Oe CORR ON 44

Ae LeP na SyMMet Ure na. set ish ied. souls aad Selabaes © «a SERRE oe 44
Peppa PS tC GUTS) Sos hen e155) 2 sore a. ene vores Sek w Soar td. to SMES geet os 44

Pete ear EOE CAE er ME Ses Ph Sook we oa nie ees Ro 50
LDS CCSATOG AS 3 Geocrcnc ih SRE OID eee el 51
SUIS TO Yc Sekt nts. as ee en Seen a. ¢ | ee ae 52

SOV RUTTETSe, SSA cee Ny Rl ee Tate Med
ise HUN CRCELE ee ee ri se a Sie. oyak eid 9s oe o's 6 A es A 54

INTRODUCTION AND METHODS

In the investigation herein recorded a careful study of the
morphology of the olfactory pores of Lepidoptera has been made
in order to determine whether these organs are better adapted
anatomically than the antennal organs to receive olfactory
stimuli.

The investigators who have performed experiments on but-
terflies and moths with mutilated antennae have concluded
that these appendages bear the olfactory organs, regardless of
whether or not the antennal organs are anatomically fitted to
receive olfactory stimuli. Since these investigators failed to
study sufficiently the behavior of the insects investigated, it is
possible that the responses observed misled them in determining
‘the seat of the olfactory organs (see the author’s paper, ’14 ¢).

33

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 1

34 N. E. McINDOO e

In 1857 Hicks discovered pore like organs on the wings of
Lepidoptera and called them vesicles. He says: “‘In moths they
are very apparent, being greatest in the noctuae [Noctuidae] and
Bombycidae. There are about 100 vesicles on the upper sur-
face of the posterior wing, and half that number beneath, be-
sides some few on the nervures [veins]. In the butterfly they
are smaller, but arranged in more definite groups, about three in
number.’ In 1860 Hicks discovered them on the legs of Lepi-
doptera, and the present writer (14a and b, 715 and 716) has
made a comprehensive study of these organs in Hymenoptera
and Coleoptera, and since he proved experimentally that they
receive olfactory stimuli, they were called olfactory pores. On
account of other investigations, the writer has not had time to
determine the physiology of these organs in Lepidoptera and for
this reason the present paper deals with only their morphology.

To obtain material for the study of the disposition of the
olfactory pores, dried museum specimens were mostly used. In
regard to preparing the specimens with caustic potash and to
bleaching them with chlorine gas, the reader is referred to the
writer’s work on Hymenoptera (’14b, p. 295).

To obtain material for the study of the internal anatomy of the
organs herein discussed, moths emerged a short time from the
cocoons and a butterfly were used. The material was fixed in
Carnoy’s fluid (equal parts of absolute alcohol, chloroform,
glacial acetic acid, with corrosive sublimate to excess) and was
embedded in celloidin and paraffin. The sections were cut five
and ten microns in thickness and were stained with Ehrlich’s
hematoxylin and eosin.

All the drawings were made by the writer and all are original
except figure 10, which represents the antennal organs of a
moth and was copied from Schenk (’02). The drawings were
made at the base of the microscope with the aid of a camera
lucida.

The museum specimens were secured through the courtesies
of Dr. L. O. Howard and Mr. August Buseck, and the writer is
also grateful to Mr. Carl Heinrich for verifying the identification
of all the Lepidoptera used.

OLFACTORY ORGANS OF LEPIDOPTERA 35

THE OLFACTORY PORES

Before making a study of the anatomy of the organs, called
the olfactory pores by the writer (’14 a), the distribution and
number of them were first investigated.

Disposition

In making a comparative study of the disposition of the
olfactory pores in Lepidoptera, 40 species, belonging to 36 genera
and representing 19 families, were used. In most cases only
one specimen of each species was employed, and whenever a
portion of an appendage or an entire appendage was missing or
was badly mutilated in being prepared for study, the supposed
number of pores on this portion or entire appendage was regarded
the same as the number found on the corresponding portion or
entire appendage on the opposite side of the body. Since the
pores on only one specimen for each species were counted, the
total number of pores recorded can not be a fair average. Be-
sides this error, there is also another small probable error for
each species, because a few of the pores were probably over-
looked, and often, as on the tibiae, it was impossible to distin-
guish the olfactory pores from hair sockets. Only the legs,
wings and mouth parts were examined, although in two or three
instances the chitinous parts of the reproductive organs were
also examined, but no olfactory pores were seen on them. The
mouth parts of more than one-half the specimens were either
missing or were so mutilated that the pores on them could not
be counted; nevertheless, regardless of all the errors, the total
numbers of pores recorded are probably not far from being accu-
rate, but they are perhaps always slightly less than the numbers
actually present. The sex of the species, except in tour cases,
was not determined.

a. Bombyx mort @. Since the silkworm moth, Bombyx mori,
is conveniently studied and, as its olfactory pores are typical for
most of the moths examined, the disposition of them will be
described in detail, and then the variations found in the other
species will be given.

36 ‘N. E. McINDOO

The wings have dorsal and ventral surfaces, and the legs may
be divided for description into two surfaces. The inner surface
faces the body of the insect and the outer surface is directed
away from it. On the specimen examined, four groups of pores,
besides many scattered pores, were found on each front wing;
three groups, besides several scattered pores, on each hind wing;
and four groups, besides two isolated pores on each leg.

Fig. 1 Wings of silkworm moth, Bombyx mori 9, showing location of groups
of olfactory pores as indicated by the numbers 1 to 7, and disposition of scat-
tered pores on the veins as represented by dots, X 3. A and B, dorsal and ven-
tral surfaces of right front wing respectively; and C and D, dorsal and ventral
surfaces of right hind wing respectively. 1 to 3 A, first to third anal veins; C,
costa; ci to 2, first and second cubital veins; M, media; m1 to 8, first to third
medial veins; #, radius; ri to 5, first to fifth radial veins; Sc, subcosta.

For descriptive purposes in locating the olfactory pores on
the wings, the veins at the bases of the wings may be called
costa (fig. 1 A-D, C), subcosta (Sc), radius (R), media (M),
and anal vein (1 to 3 A); the names, given by Comstock (manual,
01) to the distal ends of these veins, are also appended, so that
no confusion may arise. The groups and scattered pores are
located as follows: Groups nos. 1 to 7 lie on the bases of the
wings, nos. 1 to 4 being on the front wing and nos. 5 to 7 on the
hind wing; nos. 1, 2, 3, 5 and 6 are found on the dorsal surfaces
while nos. 4 and 7 lie on the ventral surfaces. Nos. 1 to 3 (fig.

OLFACTORY ORGANS OF LEPIDOPTERA 37

1 A) seem to lie on the union of the radius and media, but cross
sections (figs. 6 A and 9 C) show that nos. 1 and 2 lie on the
media while no. 3 lies on the radius. No. 4 (fig. 1 B) lies on the
broad portion of the subcosta which unites with the radius and
media. No. 5 lies on the radius and no. 6 (fig. 1 C) on the
media, but perhaps no. 6 lies more correctly on the union of the
radius and media (fig. 6B). No. 7 (fig. 1 D) is located on the
broad portion of the subcosta.

The number of pores in groups nos. 1 to 7 on the right wings
are as follows: No. 1—11, no. 2—52, no. 3—56, no. 4—67, no.
5—128, no. 6—44, and no. 7—12; on the left wings: no. 1—10,
no. 2—50, no. 3—52, no. 4—74, no. 5—148, no. 6—51, and no.
7—11. On the dorsal surface of the right front wing, the scat-
tered pores are located as follows: 2 at the distal end of the costa
(fig. 1 A), 10 extending the full length of the subcosta, 2 near the
base and 5 at the distal ends of the radial branches, 6 at the
distal ends of the medial branches, and 2 at the distal end of the
anal vein; on the ventral surface of the same wing: 8 extending
one-half the length of the costa (fig. 1 B), 5 near the middle of
the radius and 8 at the distal ends of its branches, 6 at the distal
ends of the medial branches, and 2 at the distal end of the
radial vein. On the dorsal surface of the right hind wing, the
scattered pores are as follows: 3 near the base of the subcosta
(fig. 1 C), 1 at the distal end of a radial branch, 6 near the
base of the media, and 6 on the medial branches; on the ventral
surface of the same wing: 1 near the base of each the costa and
subcosta (fig. 1 D), 1 at the distal end of a radial branch, 4 on a
medial branch, and 2 at the distal end of the second branch of
the anal vein. The. disposition of the scattered pores on the
left wings is very similar to that just given for the right wings.
_ Groups nos. 8 and 9 of the olfactory pores lie on the outer sur-
face of the trochanter (fig. 2 E) of each leg near the anterior
margin, while no. 10 is located on the inner surface of the same
segmeut (fig. 2F). No. 11 lies at the proximal end of the
femur (fig. 2 F) of each leg on the inner surface near the posterior
margin, and the two isolated pores (fig. 2 E, a) lie at the same
position on the outer surface of each leg.

38 N. E. McINDOO

The number of pores in each group on the right leg is as follows:
Front leg, no. 8—10, no. 9—8, no. 10—9, no. 11—9; middle leg,
no. 8—11, no. 9—6, no. 10—6, no. 11—8, hind leg, no. 8—11,
no. 9—6, no. 10—8, and no. 11—8. The variation in the num-
ber of pores on the left legs is very similar to that just given.

Fig. 2. Portions of legs of Bombyx mori 9, showing location of groups nos.
8 to 10 of olfactory pores on the trochanters, no. 11 and a on the femurs, X 192.
A and B, outer and inner surfaces of right front leg respectively; C and D, same
of right middle leg; and E and F, same of right hind leg.

All six legs of the specimen of Bombyx mori 2 examined bear
218 olfactory pores; the front wings carry 423 pores, and the
hind wings carry 420 pores; no pores were observed on the
mouth parts; all of these combined make 1061 olfactory pores.

b. Other species. The greatest variation found in the olfactory
pores of the other species examined is in regard to the total num-
bers of the pores. On the average, butterflies have only two-
thirds as many pores as have moths; this difference is due solely

OLFACTORY ORGANS OF LEPIDOPTERA 39

to the smaller number of pores on the wings of butterflies, and
chiefly to the smaller number on their hind wings. The preced-
ing conclusion was derived from the following data: The total
number of pores on the legs of moths vary from 71 to 240, with
140 as an average; on the legs of butterflies from 73 to 196, with
141 as an average; on the front wings of moths from 52 to 662,
with 399 as an average; on the front wings of butterflies from
206 to 404, with 303 as an average; on the hind wings of moths
from 45 to 663, with 382 as an average; on the hind wings of
butterflies from 130 to 228, with 197 as an average; on the
mouth parts of moths from 0 to 59, and on the same appendages
of butterflies from 0 to 34. The total number of pores on moths
vary from 222 to 1422, with 930 as an average; and on butter-
flies from 514 to 784, with 645 as an average.

As a general rule, all the other insects hitherto examined for
olfactory pores by the writer showed that the larger the species
the greater was its total number of pores. Relative to Lepidop-
tera this ruling is not true, because the larger species have
about the same number of pores as have the smaller species
(table 1, p. 43).

The other variations, most of which are small, pertain chiefly
to the distribution of the olfactory pores. For sake of brevity,
instead of using the long scientific names of the Lepidoptera ex-
amined, the species will be numbered from 1 to 48, and those
interested in associating the names of the species with the varia-
tions described may do so by referring to the names and num-
bers of the species in the table on page 43.

No wing was found devoid of olfactory pores, although they
are reduced in number on the rudimentary wings of the females
of Hemerocampa and Alsophila (nos. 10 and 16). These wings
will be discussed under sexual variations on page 41. The
disposition of the pores on the wings of the other specimens is
more or less similar to that already described for Bombyx mori.
The number of groups of pores on a wing depends on how
closely the pores lie to one another. At a given place on one
wing the pores may be scattered and therefore do not consti-
tute a group, while on another wing at the same place, the

40 N. E. McINDOO

pores are well grouped. ‘This fact chiefly explains the variation
in the number of groups of pores. ‘Two specimens examined
(Nos. 16, 18) have only two groups on each front wing and one
group on each hind wing; three specimens (nos. 15, 17, 26)
have three groups on each front wing and two on each hind
wing; 11 specimens (nos. 1, 3, 5, 6, 8, 9, 11, 12, 19, 20, 43) have
three groups on each front wing and three on each hind wing;
one specimen (no. 25) has four groups on one front wing and two
on the other, two groups on one hind wing and one on the other
hind wing; two specimens (nos. 10, 22) have four groups on
each front wing and two on each hind wing; six specimens (nos.
13, 14, 21, 28, 24, 28) have four groups on each front wing and
three on each hind wing; ten specimens (nos. 7, 27, 31, 33 to
37, 41, 42) have four groups on each front wing and four on
each hind wing;. two specimens (nos. 39, 40) have four groups on
each front wing and five on each hind wing; three specimens
(nos. 29, 30, 32) have five groups on each front wing and three
on each hind wing; two specimens (nos. 2, 4) have five groups
on each front wing and four on each hind wing; and one speci-
men (no. 38) has seven groups on each front wing and four on
each hind wing. Of the 15 specimens of butterflies examined
it is thus seen that each of 15 has 16 or more groups of pores
on both pairs of wings, while of the 28 specimens of moths ex-
amined each of 24 has 14 or less groups on both pairs of wings.
This indicates that the olfactory pores in butterflies are the
more highly developed.

Practically every specimen examined has at least a few scat-
tered pores on the wings, and, as a rule, the fewer the groups of
pores the greater is the number of scattered pores. It is com-
mon for the pores to extend the full length of one or more veins
and to terminate at the distal ends of the veins in pairs as shown
in figure 1.

Every leg of the specimens examined bore pores, but the more
the legs are reduced in size the fewer the pores they bear. The
disposition of the pores on the trochanters and femurs of a few
of the species is similar to that of the honey bee, but only occa-
sionally are pores found on the proximal ends of the tibiae and

OLFACTORY ORGANS OF LEPIDOPTERA 41

never on the tarsi, as observed in the Hymenoptera. A few
pores, usually near the distal ends of the tibiae, were seen in 21
of these specimens (nos. 1, 2, 3, 5, 7, 8, 11, 12, 19, 22 to 26, 33
to 35, 37, 38, 40, 48), and pores were observed in the tibial spines
of 12 individuals (nos. 1, 2, 6, 15, 16, 22 to 26, 28, 43). Rela-
tive to the isolated pores on the femurs at the position marked
a in figure 2 E, one pore was found at this position in 28 speci-
Mens). 2, 3, 6, 10'to 12; 15 to 17, 19/23) 26; 28, 30 to 41, 43);
two pores were found at this position in three specimens (nos.
5, 13, 14); four pores at this position in one specimen (no. 42).

c. Generic, specific and sexual variations. The generic and
specific variations are considerable when the total number of
pores is considered. The noctuids (Nos. 4 to 9, table 1, p.
43) well illustrate the generic variation and the three species
of Pontia (nos. 35 to 37) illustrate the specific variation. The
total number of pores of the noctuids vary from 852 to 1422,
with a difference of 570 pores, and the species of Pontia from
632 to 784, with a difference of 152 pores.

Excluding the females with rudimentary wings, the sexual
variation is insignificant. The male each of Bombyx (nos. 13
and 14) and of Sanninoidea (nos. 19 and 20), the peach-tree
borer, has 13 more pores than has the female of the same species.

The male of the tussock moth, Hemerocampa leucostigma, was
not examined, but the number of pores on the rudimentary wings
of the female (no. 10) does not seem to be greatly reduced. The
front wings are plainly visible to the unaided eye, but the hind
wings are not, and both pairs are nothing less than thick pads
in which the veins are not distinct. As in Bombyx, three groups
of pores (nos. 1 to 3) lie on the dorsal surface of each front wing
(fig. 3 A) and one (no. 4) on the ventral surface; nos. 5 and 6
are present on the dorsal surface of the hind wing (fig. 3 B),
but no. 7, usually present on the ventral surface of the hind wing,
is absent. The scattered pores on the front wings are twice,
and those on the hind wings are three times as large as the ones
in the groups; ordinarily the scattered pores are little, if any,
larger than those of the groups.

42 N. E. McINDOO

Both pairs of wings of the female geometrid moth, Alsophila
pometaria (no. 16), are invisible to the unaided eye, and are so
greatly reduced that the front wing (fig. 3 D) is only about three-
fourths as large as the tegula (7g) and no larger than the patagia
(fig. 3C) on the prothorax. The hind wing (fig. 3 E) is about
one-third as large as the front wing. No pores are present on the
ventral surfaces of the wings, and only two groups lie on the
dorsal surface of the front wing and only one on the hind wing;

- A

Fig. 3 Wings, tegule (Tg) and patagia of so-called wingless female moths,
showing location of groups of olfactory pores and scattered pores on dorsal
surfaces of wings. A, tegula and front wing and B, hind wing of tussock moth,
Hemerocampa leucostigma, X 21; C, patagia, D, tegula and front wing and E,
hind wing of the geometrid, Alsophila pometaria, X 53.

a few scattered pores were also seen on each wing. All of these
pores are larger than usual.

To determine the individual variation in the total number of
pores, three specimens of the lesser wax moth, Achroia grisella
(no. 22), were examined. The total numbers of pores on the
legs and wings of these moths are 1112, 1168 and 1238. A
part of this variation may be attributed to sex, because the sex
of each individual was not determined.

The following table (p. 483) includes the family, number and
name of the species, the number of olfactory pores on the legs,

TABLE 1

Number of olfactory pores on legs, wings and mouth parts of Lepidoptera

FAMILY NUMBER AND NAME OF SPECIES
Sphingidae 1 Phlegethontius quinquemaculata
2 Ceratomia catalpae
Arctiidae 3 Apantesis sp.
Noctuidae 4 Prodenia arnithogalli
5 Lycophotia margaritosa
6 Agrotis unicolor
7 Cirphis unipunctata
8 Alabama argillacea ;
9 Caenurgia erechtea
Liparidae 10 Hemerocampa leucostigma
Lasiocampidae |11 Tolype velleda
12 Malacosoma americana
Bombycidae 13. Bombyx mori
14 Bombyx mori 92
Geometridae 15 Alsophila pometaria
16 Alsophila pometaria
17 Synchlora aerata
Psychidae 18 Thyridopteryx ephemeraeformis
Aegeriidae 19 Sanninoidea exitiosa
20 Sanninoidea exitiosa
Pyralidae 21 Loxostege obliteralis
22 Achroia grisella
23 Ephestia cautella
Pterophoridae |24 Oxyptilus tenuidactylus
Olethreutidae |25 Laspeyresia pomonella
26 Eucosma scudderina
Yponomeutidae |27 Atteva aurea
Tineidae 28 Tinea pellionella
Nymphalidae [29 Argynnis cybele
30 Grapta interrogationis
31 Euvanessa antiopa
32 Junonia coenia
Lycaenidae 33 Heodes hypophlaeas
34 Everes comyntas
Pieridae 35 Pontia monuste
? 36 Pontia protodice
37 ~Pontia rapae
38 Callidryas eubule
39 Eurema nicippe
40 Eurema euterpe
Papilionidae 41 Papilio polyxenes
42 Papilio troilus
Hesperiidae 43 Eudamus proteus
VESTER IGS Been aaah ae eee eee oor ane ae

NUMBER OF PORES ON e
ele] | bs
eds fell = a
130] 453} 306 889
184] 502] 363| 00 | 1049
138] 392] 367 897
95| 442| 478] 37 | 1052
105} 500) 545 1150
107| 485] 448} 4 | 1044
83| 662] 663] 14 | 1422
74| 432| 499 1005
127| 387| 338 852
160| 318] 238] 00 | 716
188] 336] 366 890
143| 389] 344] 8 | 884
240] 433] 401] 00 | 1074
218} 423] 420) 00 | 1061
126] 284] 198 608
125] 52) 45 222
134] 278) 128 540
195] 262] 241 698
156] 468]. 379] 30 | 1033
146| 398] 445] 31 | 1020
120} 466] 416 1002
141] 496] 539] 59 | 1235
166| 486] 634] 14 | 1300
135] 272] 284 691
147| 476| 376| 14 | 1013
159| 432] 242 833
71| 507| 402| 14 | 994
138] 384] 354 76
168} 281] 182 631
113] 337] 208 658
73| 340| 216] 34] 663
104] 269] 198 571
160] 224] 168) 00 | 552
178| 206] 130 514
134] 298} 200 632
166] 390] 228 784
167} 301] 194 662
134] 404] 228 766
113] 312] 202) 4] 631
125] 258] 206 589
161| 350] 218) 21 | 750
196] 331} 160 687
122] 248} 220 590
7152 |45—|00—|| 222——
240| 662) 663] 59 | 1422

44 N. E. McINDOO

wings, mouth parts, and the total number of pores on each of the
43 specimens examined. In the preceding pages the insects are
usually referred to in this table by their respective numbers.
The blank spaces in the fourth column mean that the mouth
parts were either missing or so badly mutilated that the pores
on them could not be counted. Owing to the rudimentary con-
dition of the mouth parts, no attempt was made to identify
accurately the various mouth appendages, but most of the pores
recorded were found on the bases of the palpi, as is best illus-
trated in the lesser wax moth (no. 22). The only pores found on
the mouth parts of Euvanessa antiopa and Papilio polyxenes
(nos. 31 and 41) lie in two groups at the base of the proboscis,
on the dorsal surface, in the same position as recently stated for
the honey bee by the writer (16).

Structure

The preceding pages deal with the disposition of the olfactory
pores, and a discussion of the anatomy of these organs is given
in the following pages.

a. External structure. When the superficial ends of the olfac-
tory pores are examined under a high-power lens with a strong
transmitted light, the pores appear as small bright spots, each
of which is surrounded by darker chitin, the pore border (fig.
4K, PorB) and by the pore wall (PorW). The pore aperture
(PorAp) is usually oblong, but may be round; its size depends
upon the focusing level of the microscope, showing that it is
funnel-shaped. ‘The size of the pores vary considerably, as may
be seen by referring to figure 4.

b. Internal structure. The olfactory pores have been called
dome-shaped organs, but the domes are not always present as is
shown in figures 5C and 8 C; in those sections in which the
domes are not visible the microtome knife probably passed
through the organ too far from the pore aperture. The domes
(fig. 5B and D, D) in the wings and legs of moths, and in the
wings (fig. 9 A) of a butterfly rise slightly above the surface of
the surrounding chitin, while in the legs of the same butterfly

OLFACTORY ORGANS OF LEPIDOPTERA 45

the domes (fig. 9B, D) lie below the surface of the surrounding
chitin. Neither Guenther (’01) nor Freiling (09), who have
studied the anatomy of these organs, saw the sense fibers pass
through the domes, and consequently they speculated about the
function of these pores. Owing to the small size of the pore
apertures and to the great thickness of the domes the present

Se. | or O ©} Po
© } ; i ©&
@ oO} © Eas QO © = a 1» aia ©
© © © © © bee Oo a Gn © © tPA S) &
: ®

Fig. 4 External view of olfactory pores of Bombyx mori 9, showing varia-
tions in size, X 320. A, group no. 1; B, 6 of group no. 2; C, 10 of group no. 3;
D, 12 of group no. 4; E, 15 of group no. 5; F, 8 of group no. 6; G, group no. 7;
H, group no. 8; I, group no. 9; J, group no. 10; K, group no. 11; L, group a and
a hair socket (HrSk); and M, a hair (Hr), 4 hairs sockets and 4 pores from tip of
hind wing on ventral side. Hr, hair, called S. trichodea on antenna; HrSk,
hair socket; PorAp, pore aperture; PorB, pore border; PorW, pore wall.

writer has not been able to find a pore which well illustrated the
sense fiber running into the pore aperture, nevertheless four
pores (figs. 5 A and D, 8 A and E) were found, each of which
had a light streak passing through the dome (D). A few sec-
tions cut obliquely clearly show the sense fibers (figs. 7 and 8B)
connecting with the pore apertures, so that in the present writer’s
opinion there can be no doubt about the peripheral ends of the
sense fibers coming in direct contact with the external air.

46 N. E. McINDOO

All the olfactory pores studied are more or less flask-shaped
structures, although the width of the flask is often equal to its
height, and the mouths of such flasks are quite flaring; this is
particularly true for the pores in the legs (fig. 5D and E) of
Bombyx, but in the wings (fig. 5 A and B) of the same insect the
pores are more flask-shaped.

Fig. 5 Cross sections, showing internal anatomy of olfactory pores of Bombyx
mori, X 506. A, from front wing; B, from hind wing, showing dome (D); C
and D, from trochanter; and E, from femur. Con, chitinous cone of olfactory
pore; D, dome; Hyp, hypodermis; N, nerve; NB, nerve branch; NF, nerve fiber;
PorAp, pore aperture; SC, sense cell; SF, sense fiber; Tr, trachea.

Cones are usually present and are of three types: The external
boundary of the most common type (fig. 5 E, Con) is convex,
that of the second type (fig. 8 C) is almost flat, and that of the
third type (fig. 5 A) is concave. The first type is found both
in the legs and wings while the other two types are found in only
the wings; only the first and second types are present in the
wings of Achroia, the second type being the more common.

The sense cells (fig. 5 A and E, SC) are more spherical and
therefore less spindle-shaped than those found hitherto in other

OLFACTORY ORGANS OF LEPIDOPTERA 47

insects. The nerve fibers (fig. 5A, NF) run directly to the
nerves which lie surrounded by blood and the tracheae (7’r.)
The sense fibers (fig. 5 D and E, SF) are easily traced to the cones,
but seldom through them. Sometimes they are surrounded by

Fig. 6 Semidiagrammatic drawings of cross sections of wings of Bombyx
mori, showing internal anatomy at bases of wings and groups nos. 2, 4, 6 and 7
of olfactory pores, X 80. A, from front wing and B, from hind wing. BlSin,
blood sinus; C, costa; M, media; N, nerve; NF, nerve fiber; P, isolated olfactory
pore on costa; R, radius; SC, sense cell; Sc, subcosta;.77r, trachea.

the hypodermal secretion (fig. 8 A, C and D, HypS) which has
formed the cones.

To understand the anatomy of the wings at the position where
the olfactory pores are located, the reader is referred to figure ©
6 A and B, which are semidiagrammatic drawings taken from
sections across the bases of the wings, A being from the front

48 N. E. McINDOO

and B from the hind wing. At once it is seen that instead of
the surfaces of the wings being smooth, as is generally believed,
they are more or less corrugated, the elevations being formed by
the veins and the depressions usually by the flexible chitin be-
tween the veins. The position of a vein on one side of a wing
seldom corresponds exactly to the position of the same vein on the
other side of the wing, and consequently it is difficult to identify

Fig. 7 Semidiagrammatie drawing of an oblique section through femur,-
trochanter and coxa of Bombyx mori, showing internal anatomy at this loca-
tion in leg, and groups nos. 8, 10 and 11 of olfactory pores, no. 10 being shown
partially from a superficial view, X 106. BlSin, blood sinus; Hr, hair, called
S. trichodea on antenna; Me, muscle; N, nerve; NB, nerve branch; SC, sense
cell; Tr, trachea.

the veins in cross-sections; but after making a study of the
serial sections this difficulty was alleviated. The identification
of the veins then makes it easy to recognize the groups of pores.
The sections illustrated passed through groups nos. 2 and 4
on the front wing and nos. 6 and 7 on the hind wing. The sense
cells (SC) lie in thickened portions of the hypodermis and are
constantly bathed with blood. The nerve fibers (NF) spread
out fanlike from the nerves and unite with the sense cells. It
is to be noted that a nerve (NV) and one or more trachez (T7'r)

OLFACTORY ORGANS OF LEPIDOPTERA 49

lie in each vein, and that one of the sections passed through an
isolated pore in the costa of the hind wing (fig. 6 B, P).

To understand the anatomy of the legs at the position where
the olfactory pores lie, the reader is referred to figure 7, which is
a semidiagrammatic drawing taken from one section cut obliquely
across the femur, trochanter and coxa. In dead insects the femur

Fig. 8 Cross sections, showing internal anatomy of olfactory pores of other
moths, X 506. A to G, from wings; H, from trochanter; and I, from femur.
A, B and H, from catalpa sphinx, Ceratomia catalpe. B is cut obliquely; C,
D and I, from lesser wax moth, Achroia grisella; E, from Prodenia ornithogalli;
F, from Atteva aurea; and-G, from front wing of tussock moth. HypS, hypo-
dermal secretion forming cone; N, nerve; NB, nerve branch; PorAp, pore aper-
ture; Tr, trachea.

and trochanter form a right angle with the coxa, and this fact
explains how an oblique section may be cut passing through all
three segments. This section passed through groups nos. 8,
10 and 11, no. 10 being shown partially in cross section and
partially from a superficial view. Most of the muscles (Me)
are cut longitudinally, but those near the sense cells (SC) run
transversely, leaving a space, the blood sinus (BlSin), in which
the sense cells lie. The nerve branch (NB) leaves the nerve

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

50 N. E. McINDOO

(NV), runs to the hypodermis (figs. 7 and 9 B), and then divides
into nerve fibers which unite with the sense cells.

Figure 9 C is similar to figure 6 A, but represents a section
cut obliquely through the base of the front wing of a butterfly,

Fig. 9 Cross sections of wing and leg of cabbage butterfly, Pontia (Pieris)
rape, showing internal anatomy of these appendages at positions where olfac-
tory pores are located. A, from front wing and B, from trochanter, xX 506.
C is a semidiagrammatic drawing from an oblique section cut in direction of line
a in figure 1A and B, showing groups nos. 2, 3 and 4, of olfactory pores, X 106.
C, costa; D, dome; HrSk, hair socket; Hyp, hypodermis; M, media; N, nerve;
NB, nerve branch; R, radius; SC, sense cell; Sc, subcosta; Tr, trachea.

Pontia, in the direction of the line a in figure 1 A and B. The
section passed through groups nos. 2, 3 and 4 and longitudinally
through the nerve (N) for a short distance.

THE ANTENNAL ORGANS

Several investigators have studied the morphology of the
antennal organs in Lepidoptera, but since Schenk’s work (’02)

OLFACTORY ORGANS OF LEPIDOPTERA 51

seems to be the latest and perhaps the best, most of the preceding
discussion will be taken from his paper.

Disposition

Schenk has carefully studied the antennal organs in both sexes
of the following moths: One geometrid (Fidonia piniaria), two
bombycids (Orgyia antiqua and Psyche unicolor), and one
zygaenid (Ino (Atychia) pruni). He found the following five
sense organs on the antennae of both sexes: (1) Pit pegs (Sen-
silla coeloconica), (2) pegs (S. basiconica), (3) end pegs (S. stylo-
conica), (4) bristle-like hairs (S. saetica) and (5) ordinary hairs
(S. trichodea). In regard to the disposition of the above five
types of sense hairs on the feathered antennae of the males and
on the non-feathered ones of the females, the following may be
said: These sense organs not only lie on the shafts of both types
of antennae, but also on all the barbs of the male antennae.
The total number of sense hairs of each type found on the an-
tennae of the four moths examined by Schenk is tabulated as
follows:

TABLE 2

Number of sense organs on antennae of moths (after Schenk)

FIDONIA ORGYIA PSYCHE INO
TYPE OF SENSE — si
ORGAN
Male Female Male Female Male Female} Male Female
Pit pegs....... 350 100 600 75 |Numer-| O | Numer-| Numer-
ous ous ous
End pegs..... 2F 16 50 30 0 0 0 0
Bristle like
arse ts. 117 105 80 42 | Present} 0 120 120
Ordinary hairs| Numer-| Scarce} Numer-} Scarce| Numer-| 0 | Numer-} Scarce
" ous ous ous ous
Regstente ce 0 5 0 0 0) 0 0 0

Hicks (’59) and Hauser (’80) saw the same organs, particularly
the pit pegs, in the antennae of the butterflies, Argynnis and
Vanessa. Hauser says that each segment of the antennal knob
of Vanessa carries about 50 pits bearing pegs.

je N. E. McINDOO

It is thus seen that in Lepidoptera pore plates, common to
most insects, are entirely absent, while the pegs are practically
wanting; however the pegs seem to be replaced by the end pegs.
Of the five sense organs on the antennae of Lepidoptera, only the
pit pegs and end pegs are regarded as olfactory organs. Since
the end pegs are totally absent in Psyche and Ino, it does not
seem reasonable that they can be olfactory organs for any
lepidopteron, and, providing, there is no sexual difference in the
size of the pit pegs, the male of Fidonia smells three and one-
half times as well as the female of the same species; the male of
Orgyia eight times as well as the female of that species, and while
the male of Psyche smells well, the female of the same species
can not smell at all. It also seems doubtful that the pit pegs can
function as olfactory organs.

Now let us inquire if any of these organs are really adapted
anatomically to receive olfactory stimuli.

Structure

The ventral side of the shaft (fig. 10 A) of the antenna of
Fidonia bears more sense organs than does the dorsal side, and
the terminal segment bears more pit pegs (PPg) than does any
other segment. Observed from the side under a high-power
lens, the pit pegs look like pits lined with hairs, but when viewed
from the tops of the pits, the organs resemble small wheels in
that the hairs form the spokes and the base of the peg the hub.
Two of the pit pegs thus viewed are shown on the segment third
from the last one. :

A longitudinal section of a pit peg shows that a peg (fig. 10 B,
PPg), surrounded by a crown of pseudo-hairs (H7r'), arises from
the bottom of the pit and that the base of the peg is connected
with a sense cell group (SCG). The end pegs (fig. 10 C, E Pg)
are nothing more than short, stubby hairs supported on stout
projections, called styles (St), which are innervated. The
bristle-like hairs (fig. 10 D), ordinary hairs (fig. 10 E, Hr) and
pegs are also innervated.

Other authors who have studied the anatomy of these organs

describe them as similarly to the preceding account, except the

OLFACTORY ORGANS OF LEPIDOPTERA 53

Fig. 10 Antennal organs of the geometrid moth, Fidonia piniaria, copied
from Schenk (’02). A, ventral view of terminal segment of male antenna, show-
ing disposition of pit pegs (PPg), end pegs (H Pg), supported on the styles (St),
bristlelike hairs (Br) and ordinary hairs (Hr) in solid black, X 145; B, longi-
tudinal section through a pit peg, X 570; C, two end pegs, supported on a style,
X 220; D, section of a bristlelike hair, X 220; and E, longitudinal section of
three ordinary hairs, one-half schematic. Br, bristlelike hair (Sensilla saetica)
on antenna; EPG, end peg (S. styloconica) on antenna; Hr, hair, called S. tri-
chodea on antenna; Hr!, pseudo-hair in pit peg; N, “nerve; PPg, pit peg (8S.
coeloconica) on antenna; SC, sense cell; SCG, sense cell group in antenna; St,
style supporting end peg.

pit pegs and end pegs vary slightly in structure. The pit pegs
sometime consist of compound pits instead of single pits, and the
shape of the styles supporting the end pegs vary more or less.

Since the peripheral ends of the sense fibers are covered with
the hard chitin forming the walls of all the antennal organs, it
does not seem reasonable that the outside air carrying odoriferous
particles can pass through the chitin in order to stimulate the
nerves within.

S

54 N. E. McINDOO

SUMMARY

The disposition of the olfactory pores of Lepidoptera is similar
to that of Hymenoptera and Coleoptera, but resembles the former
more closely. The structure of these pores is also similar to that

~ of those found in other insects, but differs slightly in three fol-

lowing respects: The external ends of those in Lepidoptera are
dome-shaped and the only other dome-shaped ones found by the
writer are in the lady-beetle, Epilachna borealis. The external

.boundary of the cones may be convex, almost flat, and concave,

but hitherto it has always been convex. The sense cells are
more spherical than usual. |

Compared with the antennal organs, the olfactory pores are
better adapted anatomically to receive olfactory stimuli, be-
cause the peripheral ends of their sense fibers come in direct
contact with the external air, while those in the antennal organs
are covered with hard chitin.

LITERATURE CITED

FrEILING, Hans H. 1909 Duftorgane der weiblichen Schmetterlinge nebst
Beitrigen zur Kenntnis der Sinnesorgane auf dem Schmetterlings-
fligel und der Duftpinsel der Minnchen von Danais und Euploea.
Zeitsch. f. wiss. Zool., Bd. 92.

GUENTHER, Konrap 1901 Uber Nervenendigungen auf dem Schmetterlings-
fligel. Zool. Jahrb., Anat., vol. 14.

Hauser, Gustav 1880 Physiologische und histologische Untersuchungen iiber ©
das Geruchsorgan der Insekten. Zeitsch. f. wiss. Zool., Bd. 34.

Hicks, J. B. 1857 On a new organ in insects. Jour. Linn. Soc., London,
ZOO lemvOl. 1. :

1859 On a new structure in the antenne of insects. Trans. Linn.

Soc., London, vol. 22.

1860 On certain sensory organs in insects, hitherto undescribed.

Jour. Linn. Socy., London, vol. 23. Z
McInpoo, N. E. 1914a The olfactory sense of the honey bee. Jour. Exp.

Zool., vol. 16. d

1914b The olfactory sense of Hymenoptera. Proc. Phila. Acad. Nat.
Sci., vol. 66.

1914 The olfactory sense of insects. Smithsonian Misc. Collec.,
vol. 63, no. 9.

1915 The olfactory sense of Coleoptera. Biol. Bul., vol. 28.
1916 The sense organs on the mouth-parts of the honey bee. Smith-
sonian Mise. Collec., vol. 65, no. 14.

ScHENK, Orro 1902 Die antennalen Hautsinnesorgane einiger Lepidopteren
und Hymenopteren, mit besonderer Beriicksichtigung der sexuellen
Unterscheide. Zool. Jahrb., Bd. 17.

ON THE PHYSIOLOGY OF THE NUCLEOLI AS SEEN IN
THE SILK-GLAND CELLS OF CERTAIN INSECTS

WARO NAKAHARA
Cornell University, Ithaca, N. Y.

NINE FIGURES (TWO PLATES)

CONTENTS
il, LinROCeIOMS Jobb ooo ae Se ae ce eR 6 Sta oH Sen eNMIES te 55
IL, Aleaiererial scuavel saovenel an ofs ISeSte Slane cb cee eee ee cP alos: cits aS eM einer 8 Fed yf
ite Obsenvationstand: considerations...) :...9....c0ahee.. oo. 2... VE 57
Aen Warp nolo gicalpssterntsse tara Sethi). ii). Leek |. eee eo 57
Do JENSIGL Tei aited Rye) neers <1 Teemememee tS 0 ESS 57
PeeINGuRonTaemosticas Walkers! (02). 00.) tne sd eee are 61
Ge (SATUS ee Bee ceed oh ROE ee PCE IPO) enies eN Ate 63
IBS QOlaverrevi alll, ie eee nd Bt I ek eR AROS S| 2208 ai BIND 64
PE Gon ChustOngemresteer Waa crt: Lf ibir nace ors bi sass. ikea « sed So RE ce: a DAE: 66
[EG] MN OyRRRAY OLIN sete eto c coielcl es cog enER GRRE bro 1s Oh ce eer eR es choc = o CS ERC 67

I. INTRODUCTION

The peculiarly shaped nucleus and the unusually large num-
ber of the nucleoli in the cells of silk-glands of certain. insects
have attracted the attention of previous workers on the his-
tology of these organs, but detailed cytological work done in
connection with the process of silk secretion is rather limited.

Marshall and Vorhies (’06) published a comparative study
of the cell-structure of the silk-glands of Platyphylax desig-
natus, a caddis-worm, under different physiclogical conditions;
Vorhies (08) demonstrated the fact that the multiple nucleoli
are derived from a single nucleolus of the ordinary type in the
nucleus of the same insect, and noted the increase of the nucleolar
material with the growth of the nucleus. These two works
have shown that the nucleoli may take some important part -
in the metabolism of the silk-gland cell, but the exact réle they

5d

Ley ae WARO NAKAHARA

play has remained unsuggested until the appearance of Maziar-
ski’s (711) paper, in which he stated that the nucleoli migrate
in certain forms into the cell-body, and he regarded these as
giving the material for the silk secretion.

Considering the cytological aspect of the phenomenon of secre-
tion in general, the cases in which the secretion granules are de-
rived from the nucleoli are very few, if any. Such authors as
Garnier (’00), for the salivary gland of the rat, Maximow (’01),
for the similar gland of the dog, claim that the migrated ‘ Nucleo-
lekGrper’ are metabolized into secretion products, but this theary
does not seem to be as yet satisfactorily established. The ob-
servations on the nucleolar migration by Carlier (99, ’06) in the
stomach and liver cells of the newt, by Page and Walker (’08)
in the mammalian nerve cells, by Walker and Embleton (’08)
in the cells of Hydra, and by Walker and Tozer (’09) in vegetative
cells of various plants and animals seem opposed to the view that
the nucleolar material can be considered playing a role in the
formation of the secretion substance. On the other hand, al-
‘though not completely established, there is a considerable body
‘of evidence that the chondriosomes, which are widely distrib-
uted in the cells of secretory nature, give rise to the secretion
granules, as shown by Arnold (05), Hoven (10, ’11), and
Schultze (11).

In view of the fact that the nucleoli are now generally consid-
ered as passive by-products of the nuclear activity, and that,
so far as the more reliable of previous observations indicate,
the active réle of the nucleoli in the formation of the secretion
products is much to be doubted, it has seemed very advisable
to study the phenomenon of the migration of this nuclear
element in the silk-gland cells of some insects in greater detail.

The present paper gives a condensed account of my observa-
tions, both morphological and chemical, upon the subject.
Before proceeding further, I wish to express my sincere thanks
to Professor William A. Riley for his stimulating encourage-
ment and valuable advice rendered me during the progress of
this work.

PHYSIOLOGY OF THE NUCLEOLI GY

II. MATERIAL AND METHODS

As the material for this study, I used the larvae of the com-
mon cabbage butterfly, Pieris rapae Linn., and those of a large
eaddis-fly, Neuronia postica Walker.

Usually the silk-glands were taken out by the decapitation
method before being placed in the fixing agent; sometimes a dis-
section in normal salt solution was made and the silk-glands
obtained by this method also proved to be as good material.
Some other specimens, especially of very young stages, were
fixed in toto. Flemming’s chromo-aceto-osmic (strong formula)
and Hermann’s platino-aceto-osmic mixtures were used with
- good result for fixing the material. Gilson’s mercuro-nitriec also
proved to be a very good fixative. Sections were cut from 3
to 5 micra thick, and the majority of them were stained on the
slide with Ehrlich’s triacid or Flemming’s triple stains. A
number of other stains were tried to bring out the changes in the
staining reaction of the migrating nucleoli.

III. OBSERVATIONS AND CONSIDERATIONS

A. Morphological

a. Pieris rapae Linn (Plate 1). The silk-glands of Lepidop-
tera have been studied by Helm (’76), Van Liadth de Jeude
(78), Joseph (80), Carnoy (84), Blane (’89), Gilson (’90),
Tanaka (711) and Ito (15) from different standpoints. More
cytological are the papers of Korschelt (96, ’97) and Meves
(97), and especially the interesting cytological paper on the
process of silk-secretion by Maziarski (711).

In his earlier work, Korschelt (’96) noticed two stainable ma-
terials within the nucleus, and called them macrosomes and
microsomes. He described the former as large round,’ rregu-
larly angular, or spindle-shaped bodies, and the latter as small
particles which always stained darker than the former. The
macrosomes, according to this view, represent the chromatin,
and the microsomes are nothing but the nucleolar material.

58 WARO NAKAHARA

However, Meves (’97), employing various stains, has shown
that the microsomes are chromatin and the macrosomes are to
be considered as nucleoli, and, although Korschelt (97) adhered
to his previous view in his later paper, the results of subsequent
researches by Flemming (’97) and Henneguy (’04) seem to sup-
port the view of Meves.

Maziarski (’11) in the silk-gland cells of different lepidop-
terous larvae, observed that the nucleoli migrate from the
nucleus into the cell-body, either as separate bodies or in the
form of droplets of ‘prosécrét,’ being dissolved within the
nucleus and accumulated in vacuoles. This, although’ he does
not give any evidence except that this material and the silk-
fiber in the lumen of the gland show similar reaction to certain
stains, he regards as the source of the silk-secretion.

I found the following conditions in the silk-glands of larvae of
Pieris rapae. In the larva just hatched (figs. 1 and 2), the
- nuclei of the silk-glands are more or less round, showing almost
no sign of branching. Such nuclei contains a number of the
nucleoli and chromatin granules. The nucleoli are of varying
sizes and some of them show such a shape as to suggest that
they are in the process of division. They are scattered in the
nucleus or sometimes grouped together into a loose mass. Not
rarely one or two of them lie close to the border of the nucleus.
The chromatin granules are imbedded in the linin reticulum.
The nuclear membrane can easily be demonstrated in most
cases. However, at places where the nucleoli are approaching
closely to the border of the nucleus, it has been impossible for
me to detect a nuclear membrane.

The cytoplasm is homogenous; but granules of different sizes
are to be noted more or less surrounding the nuclei. While
most of the granules are somewhat scattered, I find a few almost
always occur at the outer border of the nucleus, or contiguous
to the nuclear membrane, when this is demonstrable. Now,
taking into account the facts of the close approach of the nucleoli
to the border of the nucleus and of the partial disappearance
of the nuclear membrane, we can conceive that a portion of the
nucleoli migrate from the nucleus into the cell-body, forming

PHYSIOLOGY OF THE NUCLEOLI 59

the granules we have just observed. The granules of the mi-
grated nucleoli increase in amount as the development advances,
and, in a little older larva, the entire of the cytoplasmic area is
filled with the granules (fig. 3).

In the larva a little older than those considered above (fig. 4),
a mass of the secreted substance occurs in the lumen of the
gland. It is apparent, therefore, that the gland is already func-
tional at this stage. Here the nucleus begins to show its branch-
ing, and the amount of the chromatin and of the nucleolar ma-
terial seem to have been increased. The process of the multi-
plication of the nucleoli is apparently proceeding rapidly. Along
the border of the nucleus and the cell-body are many masses
of the nucleolar material, indicative of the rather rapid process
of nueleoli migration occurring (fig. 5).

The cytoplasmic area shows some elongate vacuoles of vary-
ing sizes (fig. 4). Gilson (90), working on the silk-glands of
various lepidopterous larvae, found vacuoles present in the cell-
body and also in the nucleus of the cell, and he interpreted them
as containing secretory material. Matheson and Ruggles (’07)
stated in their work on the similar glands of Apanteles glomeratus
that ‘‘numerous vacuoles are present in the cytoplasm, becom-
ing most abundant during the time of glandular activity,’ and
that ‘‘the contents of the vacuoles remain unstained by any of
the coloring agents used.’”’ Such vacuoles have been observed
also in the silk-glands of caddis-worms, not only by Gilson (’96),
but also by Marshall and Vorhies (’06), but the latter authors
do not think that they contain secretory material. Their ob-
servations would show that the cytoplasm in the normal gland
cell ‘‘presents an appearance free from vacuoles,” while after
the activity of the gland for two and one-half hours, “‘a num-
ber of fairly large vacuoles are seen along the outer margin of
the cell, and such vacuoles persist in the cell-body of the gland
which has been active for longer periods (at least up to 250
hours).” .

It is rather inconceivable that the amount of the secretion
material (supposed to be contained in the vacuoles) in the cell
increases, instead of decreases, after the cell has discharged,

60 WARO NAKAHARA

and that the normal gland cell, which must naturally be loaded
preparatory to discharging, contains no ‘secretion material.’
These together with the fact that the vacuoles contain no stain-
able material seem to make Gilson’s opinion untenable.

According to Maziarski’s (11) observations, at the height
of the secretory activity of the cell, the nucleolar material is
discharged from the nucleus, not only as separate bodies, but
also as accumulations in vacuoles in the form of droplets of
‘prosécrét,’ being dissolved within the nucleus. I have gone
over my slides with special attention to this point, but the result
was negative. The appearances shown in his figures 13 to 27
do not occur in any of my slides, except those that apparently
show artificial conditions. I am, therefore, rather doubtful as
to whether the conditions observed by Maziarski, which led him
to conclude that on certain occasions the nucleoli become dis-
solved within the nucleus, and carried by vacuoles to the cell-
body, were normal. Even if they be normal conditions, we
should think that they indicate phenomena that occur very
rarely.

The granules of migrated nucleoli appear to be somewhat
reduced in number, and some of them begin to show more or
less elongated masses at this stage. These granules may natur-
ally be supposed to havé something to do with the secretion of
the cell, since Gilson’s ‘vacuole-therory’ is to be discarded, and
as far as my observations go, there are no other special granules
to be detected in the cell-body. Maziarski (11) claims that
basophile granules, which he interprets as derived from chro-
matin, are also present in the cytoplasm. I have observed such
eranules only in the degenerating glands obtained from prepupae!-

Maziarski (’11) considers the migrated nucleoli as the source
of the secretion of the cell, because these and the silk materials
in the lumen of the gland show similar color reaction. The fact
of the increase in their amount preparatory to the discharging
of the cell and its reduction as the cell discharges, also suggest
that the granules derived from the nucleoli may be the material
source of the silk-secretion.

PHYSIOLOGY OF THE NUCLEOLI 61

As the stage advances, the nucleus shows more and more the
feature of branching; its contents, both the nucleoli and the
chromatin, are apparently being increased in amount with it.
The migration of the nucleoli is to be demonstrated as occurring
very frequently.

b. Neuronia postica, Walker (Plate 2). The silk-glands of
caddis-worms have been discussed by Carnoy (’84), Gilson (’96)
and Vorhies (05) to a certain extent. It remained, however,
for Marshall and Vorhies (’06) to attempt a minute comparative
study of the gland-cells under different physiological conditions.
Quoting from their conclusions, Marshall and Vorhies found
that:

1. The even optical structure of the cytoplasm in the cells of most
normal glands become decidedly changed after activity.

2. The activity of the gland causes the membrane on that surface
of the nucleus which les nearest the outer margin of the gland to
become irregular, the most noticeable feature of its irregularity being
the pointed processes extending into the cytoplasm.

3. This nuclear membrane may often become indistinct.

4. The secretory activity does not cause the nuclei to become
swollen. :

_5. No plasmasoma or other structure is formed in the nucleus during
secretion.

6. As a result of activity the ‘nucleolus’ becomes very irregular in
shape.

As has been said in the preceding section, there has been a
considerable difference of opinions as to the nature of the two
stainable materials in the nucleus of the silk-gland cells of in-
sects, since Korschelt (’96, ’97) insists that the larger granules are
the chromatin, and nucleoli are represented by smaller particles,
while Meves (97), Flemming (’97), Henneguy (’04) and Mar-
shall and Vorhies (’06) express opinions that are exactly opposite
to that of Korschelt.

Vorhies’ (08) work on the development of the nucleus has
finally settled the question in favor of the view that. the nucleoli
are represented by smaller particles, and at the same time, his
studies enabled him to suggest that the ‘“‘nucleolar material bears
a direct relation to the glandular activity,” since he observed the

62 WARO NAKAHARO

increase of the material with the growth of the nucleus. He,
however, did not enter into a detailed discussion of the matter.

The nucleus contains many nucleoli and chromatin granules.
The former are of different sizes, distributed in most cases, fairly
evenly throughout the nuclear area and sometimes containing
vacuoles. The chromatin granules are very fine, and lie im-
bedded in the linin reticulum. As has already been said by
Marshall and Vorhies, the changes occurring in the nucleus dur-
ing the secretion are not great, and the nucleus retains the appear-
ance here described for the entire history of the secretory activity
of the gland. In the cytoplasmic area, however, some remark-
able changes are noted to occur.

Figure 6 shows a cross section of a resting gland, ie., the
gland which has not yet discharged the secretion material, and
figure 8 one which has apparently done some discharging. One
will notice that the granules of different sizes fill the entire area
of the cell-body in the resting gland, while in the case of the
other one, the amount of the granules is much reduced.

The granules in question are apparently identical with those
in the case of Pieris, and we can naturally expect them to be:
derived from the nucleolar material. Close examination of the
nuclei with special reference to the nucleoli indicates that this
supposition is not incorrect.

As has been observed by Marshall and Vorhies, the nucleus
become very irregular in shape, especially on the side facing
the outer margin of the cell. Not infrequently, the condition
as shown in figure 9 is to be observed, in which the nuclear mem-
brane apparently has disappeared at some part of the surface
of the nucleus, and some of the nucleoli are apparently migrating
into the cell-body.

Marshall and Vorhies described the appearance of small
dark colored areas scattered irregularly in the cell-body, after
glandular activity of five hours. They say that after twenty-
four hours of activity, small and somewhat elongated masses
of dark colored cytoplasm, running parallel to the vacuoles
appeared, while in some cases the masses were also noticed along
the inner border of the nucleus. Other very significant state-
ments from their paper are the following:

PHYSIOLOGY OF THE NUCLEOLI 63

‘‘In many places, the nuclear membrane is quite difficult to
distinguish, being lost in the adjacent cytoplasm; this is espe-
cially true in the nuclei along whose outer border the dark
cytoplasmic areas are numerous” (after one hundred and twenty
hours of activity).

fee These (the areas of darkened cytoplasm) are
here mostly in close proximity to the outer boundary of the
nucleus, but exceptionally present along the inner border of
the nucleus” (after an activity of two hundred and forty hours).

Their so-called “darkened areas of cytoplasm” are practi-
cally identical with what I consider as the nucleolar material
extruded into the cell-body or remaining in the nucleus but
ready to migrate. They attempted no explanation of the
significance of the appearance of the ‘“‘darkened areas of cyto-
plasm.” If my interpretation be correct, there is no doubt that
ten years ago they observed the phenomenon of the migration
of the nucleoli in the silk-gland cell of caddis-worms.

The case of the migration of the nucleoli in the silk-gland cells
of caddis-worms supports the theory that the extruded nucleolar
material is metabolized into the secretion products, since the
granules, which are the migrated nucleoli, are in such large num-
ber as to render it rather improbable that they represent a
degenerating product, and since, moreover, the quantitative
relation of the granules to the different physiological conditions
of the cell is such as to be naturally expected for the material
prepared for secretion.

c. Summary. The foregoing observations on Pieris and
Neuronia seem to justify the following statements as regard the
morphological changes of the nucleoli in the silk-gland cells of
the insects studied:

1. The nucleoli multiply by division of the preexisting ones,
and they increase in amount as the gland becomes more
functional. |

2. Before the gland becomes functional, a portion of the
nucleoli begins to migrate from the nucleus in considerable
number into the cell-body.

64 WARO NAKAHARA

3. The migration of the nucleoli is continued throughout the
entire history of the functional cell.

4. The number of the nucleolar masses in the cell-body de-
creases after some amount of secretion has been discharged from
the cell.

The facts enumerated above seem to lead to the conclusion
that the nucleoli constitute at least a part of the source of the
secretion products of the cell dealt with.

B. Chemical

Perhaps no one has paid more attention to the staining reac-
tion of the nucleoli and the changes in the reaction after the
material has passed out into the cell-body, than Walker and
other students of his school.

In their paper on the migration of the nucleoli in the nerve
cells of mammals, May and Walker (’08) stained the material
with (A) basic fuchsin, followed by methylen blue and Unna’s
orange tannin, or (B) safranin, followed by methelyn blue and
Unna’s orange tannin. In method A the nucleoli within the
nucleus stained blue or violet. They stain purple or red as they
pass through the opening in the nuclear membrane, bright red
or pink as they come to lie definitely outside of the nucleus, and,
as they travel away from the nuclear membrane, they are
always stained pink or red. Using the second method, they
observed that the nucleoli within the nucleus stain brilliant
scarlet, become reddish orange as they migrate, and turn pale
orange or yellow when they are completely extruded into the
cell-body. ‘‘This suggests strongly,” the authors say, ‘that
some important chemical or physical change takes place in the
nucleolus when it passes into the cytoplasm.”

Walker and Embleton (’08) also made a similar observation
on the nucleolus of the cells of Hydra, employing the same com-
binations of stains, as Page May and Walker did.

Working on the nucleoli of the vegetative cells of different
plants and animals, Walker and Tozer (’09) have made more
general statements as regard the staining reaction of the nucleoli
as compared to that of other elements of the cell. |

PHYSIOLOGY OF THE NUCLEOLI 65

The contents of the nucleolus seem always less susceptible to the
basic stain than is the chromatin. While in the nucleus, however, the
nucleolar contents show a more basic reaction than the cytoplasm and
this tendency remains for some time after it has left the nucleus. But
in most cases the extruded nucleolus takes less of the basic and more
of the acid stain, until it is quite as deeply or even more deeply colored
by it than is the surrounding cytoplasm.

Studying the phenomenon of the migration of the nucleoli
in the silk-gland cells of lepidopterous larvae, Maziarski paid no
special attention as we might desire, to this sort of changes.

In order to throw some additional light upon this phase of the
subject, I stained the secretions of the silk-glands obtained
from the larvae of Neuronia postica and Pieris rapae, with dif-
ferent combinations of the stains. From this I got results simi-
lar in the main to those obtained by Walker and others in the
ease of various other cells.

Delafield’s or Mayer’s haematoxylin,

CORN 40 Seoo Os weato Cabo SSeS eee eee Salmon Salmon
Iron haematoxylin, orange-G............. Black Dark orange
arin WCHL PLUM: 255.00. .' ote) 2. 25 Red Greenish
Borax carmine, blue de Lyon............. Red Bluish
Delafield’s or ee s haematoxylin,

picrofuchsin.. Lea E Re eA cata Salmon Pale clay yellow
Ehrlich’s pened onEE Risse Sty is CO Ee Pink Pink
Biomuming str ple Stal. 22s cece elses. Red Orange

Thus we see that:

(1) The nucleoli within the nucleus are stained more or less
energetically by the acid as well as certain of the basic stains,
while

(2) The migrated nucleoli always stain with acid stains
but they have no or very little affinity, if any, for the basic
stains.

In the field of the cellular chemistry, it has been already
made known by Miescher, Kossel, Altmann, Hoppe-Seyler, etc.,
that the ‘nucleins’ form a series leading downward from the pure

66 WARO NAKAHARA

nucleic acid according to the higher percentages of phosphorus
and the lesser percentages of albumen contained in those com-
pounds, and the fact that it is the nucleic acid that determines
the staining of the nuclear substance is shown by Lilienfeld,
Kossel, and others (Wilson, ’00, Mann, ’02, Jones, 714).

In 1893, Zacharias (later, Heidenhain, ’94) showed that in
staining the preparations of the nucleins containing different
amounts of phosphorus, with alcoholic solution of acid-fuchsin
and methyl green, the nucleic acid takes a pure green color,
but that the nuclein poorer in phosphorus and that poorest in
the same element stained bluish violet and pure red respectively.

Heidenhain (’94) applied this to the case of certain granules
in the nucleus of the leucocytes and demonstrated that these
granules may show different color reactions by combining with
or giving off phosphorus, although they are all exactly alike in
morphological characters. The very interesting case of the
changes in color reactions (as well as in sizes) of chromosomes
in the eggs of Pristiurus, first described by Rickert (’93) has
been beautifully explained by Wilson (’00) in similar manner.

Applying these principles to-the case under discussion, and
taking into account the interpretations of somewhat similar
changes in chromatic bodies by the previous authors, we may
say that the nucleoli originally contain some amount of phos-
phorus, but as they migrate into the cell-body, the phosphorus
seems to be given off from their composition. The migrated
nucleoli may, therefore, be considered as albuminous granules,
almost or entirely free from phosphorus.

Considering the chemical composition of the silk-fiber, we see
that this statement on the chemistry of the migrated nucleoli
is perfectly acceptable as that of a constituent of the former,
provided that there may be some other substance given off, in
addition to the nucleoli, for the formation of the silk-fibers.

IV. CONCLUSIONS

1. In the silk-gland cells of insects studied, a portion of the
nucleoli migrates into the cell-body, and it forms at least a part
of the secretion products of the cell.

PHYSIOLOGY OF THE NUCLEOLI 67

This shows that although the nucleolus may originally be a
passive by=product of the nuclear activity, 1 may also take an
umportant part in the secretory activity of the cell in certain cases.

2. As the nucleoli migrate from the nucleus, they seem to give
off phosphorus to form themselves one of the lowest members of the
nuclein series.

This statement on the chemical change may hold true for the
migrating nucleoli in different other cells.

BIBLIOGRAPHY

ARNOLD, J. 1905 Uber Bau und Sekretion der Driisen der Froschhaut; zugleich
ein Beitrag zur Plasmosomen-Granulalehre. Arch. f. mikroskop.
Anat., 65.

Buanc, L. 1889 Etude sur la sécrétion de la soie et la structure du brin et de
bave dans le Bombyx mori. Rap. Lab. d’étud. soie, Lyon.

Caruier, KE. W. 1899 Changes that occur in some cells of the newt’s stomach
during digestion. La Cellule, 16.
1905 Concerning the secretion of ferments by the liver cells and
some of the changes observable in them during digestion. La Cellule,
22.

Carnoy, J. B. 1884 La biologie cellulaire. Etude comparée de la cellule dans
les deux regnes. Paris.

FLemMinc, W. 1896 Zelle. Merkel u. Bonnet’s Ergebn. d. Anat. u. Entw. 5.

GarRNIER, C. 1900 Contribution 4 |’ étude de la structure et du fonctionnement
des cellules glandulaires séreuses. Du réle de l’ergastoplasme dans
la sécrétion. Journ. Anat. et la Physiol., 36.

Gitson, G. 1890 Recherches sur les cellules sécrétantes. I. Lepidoptera. La
Cellule, 6.
1896 Recherches sur les cellules sécrétantes. II. Trichoptera. La
Cellule, 10.

HEIDENHAIN. 1894 Neue Untersuchungen iiber die Centralkérper und ihre
Beziehungen zum Kern- und Zellenprotoplasma. Arch. f. mikroskop.
Anat., 43.

Hem, F. E. 1876 Uber die Spinndriisen der Lepidopteren. Zeit. f. wiss.
Zool., 26.

Hennecuy, L. 1904 Les Insectes. Paris.

Hoven, H. 1910 Contribution 4 l’étude du fonetionnement des cellules gland-
ulaires. Du role du chrondriome dans la sécrétion. Anat. Anz., 37.
1911 Du rédle du chrondriome dans l’élaboration des produits de
sécrétion de la glande mammaire. Anat. Anz., 39.

Iro, H. 1915 On the metamorphosis of the silk glands of Bombyx mori. Bull.
Imp. Tokyo Sericultural Coll., 1.

Jones, W. 1914 Nucleic acids, their chemical properties and physiological
conduct. London, New York.

68 WARO NAKAHARA

Josepu, G. 1880 Vorliufige Mitteilungen tber Innervation und Entwicklung
der Spinnorganen bei Insekten. Zool. Anz. 3.

Korscuett, E. 1896 Uber die Struktur der Kerne in den Spinndriisen der _

Raupen. Arch. f. mikroskop. Anat., 47.
1897 Uber die Bau der Kerne in den Spinndriisen der Raupen. Arch.
f. mikroskop. Anat., 49.

vaAN LipTH DE JEuDE, T. W. 1878 Zur Anatomie und Physiologie der Spinn-
driisen der Seidenraupe. Zool. Anz., 1.

Mann, G. 1902 Physiological histology, method and theory. Oxford.

MarsHALL, W.S. AnD Voruigs, C. T. 1906 Cytological studies on the spinning
glands of Platyphylax designatus Walker. Intern. Monatschr. f.
Anat. u. Physiol., 23.

Marugson, R. AND Ruaetes, A. G. 1907 The structure of the silk-glands of
Apanteles glomeratus L. Amer. Nat., 41.

Maximow, A. 1901 Beitrige zur Histologie und Physiologie der Speichel-
driisen. Arch. f. mikroskop. Anat., 58.

MaziarskI, S. 1911 Recherches cytologiques sur les phénoménes sécrétoires
dans les glandes filiéres des larves des Lépidoptéres. Arch. f. Zell-
forsch., 6.

Meves, F. 1897 Zur Struktur der Kerne in den Spinndriisen der Raupe.
Arch. f. mikroskop. Anat., 48.

Montcomery, T. H., Jr. 1899 Comparative cytological studies, with especial
regard to the morphology of the nucleolus. Jour. Morph., 15.

Pacr, May W. anp WALKER, C. E. 1908 Note on the multiplication and mi-
gration of the nucleoli in the nerve cells of mammals. Quart. Journ.
Exp. Phys:, 1.

Rickert, J. 1893 Zur Entwicklungsgeschichte des Selachereies. Anat. Anz., 7.

Scuutrzn, O. 1911 Uber die Genese der Granula in den Driisenzellen. Anat.
Anz., 38.

Tanaka, Y. 1911 Studies on the anatomy and physiology of the silk-produc-
ing insects. J. On the structure of the silk-gland and silk formation
in Bombyx mori. Journ. Coll. Agr. Tohoku Imp. Univ., 4.

Voruies, C. T. 1905 Habits and anatomy of the larva of the caddis-fly,
Platyphylax designatus Walker. Trans. Wisconsin Acd. Sci. Arts,
Letters, 15.
1908 The development of the nuclei of the spinning gland cells of
Platyphylax designatus Walker. Biol. Bull., 15.

Watker, C. E. anp Emsieton, A. L. 1908 Observations on the nucleoli in the
cells of Hydra fusca. Quart. Journ. Exp. Phys., 1. :

Waker, C. E. anp Tozrer, F. M. 1909 Observations on the history and pos-
sible function of the neuleoli in the vegetative cells of yarious plants
and animals. Quart. Journ. Exp. Phys., 2.

Witson, E. B. 1900 The cell in development and inheritance. Revised ed.
New York.

i

PLATES

PLATE 1

EXPLANATION OF FIGURES
All the figures are drawn with camera lucida.

Pieris rapae, L.

1 A cross section of a silk-gland of a larva just hatched. X 250.

2 A eross section of a silk-gland of a larva just hatched, a part of the cell.
X 1200.

3 A cross section of a silk-gland of a little older larva. X 250.

4 A cross section of a silk-gland of a little older larva, representing the
condition after a moderate discharge of the secretion. > 250.

5 A part of the gland-cell of a fairly grown larva. X 1200.

70

- PHYSIOLOGY OF THE NUCLEOLI
WARO NAKAHARA

PLATE 1

71

PLATE 2

EXPLANATION OF FIGURES ©

Neuronia postica, Walker

6 A cross section of a normal silk-gland of a young larva. X 250.

7 An enlarged portion of a cell shown in figure 6. X 1200.

8 A portion of a cross section of an active silk-gland of a full grown larva.
X 250.

9 An enlarged portion of a cell shown in figure 8. X 1200.

“I
i)

PHYSIOLOGY OF THE NUCLEOLI PLATE 2
WARO NAKAHARA

73

THE UROGENITAL SYSTEM OF MYXINOIDS!
JESSE LE ROY CONEL

EIGHTY-FIVE FIGURES (TWELVE PLATES)

CONTENTS

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PV enrOGMehivc: BYyNbelieee Is ke his cc acs. dss cee es oteals duke 120
LAST DOS, cae ais es ee ee RR cS Os 120
INSTA. Fae Ree oe eno ¢ tole tees 6 do ba omar 120
INI s 66) eo OOS IEE ee lene Ie teis io creme ties cs 0 c/o ciateaar esc 126
LEGalilnsiois0s 28 Sy, Geet oeete ae en en Arciricien, =~. db ieaeee tae 128
INGEN Oso stde sree ice Coe ene een eo oo onoclamem aoe 128
IMO Ge St ep ne ee ee IE TC ond clap ea me ote 130
Protandric hermapliroditism in Myxinoids...................-.- 131
AMER DV EE ee Oe RASS CEE Cais Sees se ok we as 6 Re rere ie a 134
LENG TRIN Nae 9A lee NE LARC ote oe ee. co. AEA mets: Rea rae ee 136

INTRODUCTION

As is well known, Johannes Miiller was the first to investigate
the urogenital system of the Myxinoids, describing briefly both
male and female of Bdellostoma forsteri and the European Myxine
glutinosa. Since his day much has been written regarding this
subject. The investigators of the excretory organs include W.
Miller (75), Kirkaldy (94), Semon (96), Spengel (97), and
Maas (’97), all of whom worked upon the Myxine found in Euro-
pean waters.

Weldon (’84) and Price (’10) are the only ones who have pub-
lished a description of the excretory apparatus of Bdellostoma.

1 Contribution from the Zoological Laboratory of the University of Illinois.
No. 92.

75

76 JESSE LE ROY CONEL

The former investigated Bdellostoma forsteri, the latter Bdello-
stoma stouti. Both of these descriptions are confined almost en-
tirely to the structure and probable function of the pronephros,
and are comparatively incomplete. Scarcely anything is said
about the mesonephros. Price (96a, ’96b, ’97, 710) has, how-
ever, given a detailed account of the development of the excre-
tory system in Bdellostoma stouti, which throws much light
upon the adult condition. Semon (’96) devotes one paragraph
to a comparison between the pronephroi of Myxine glutinosa and
Bdellostoma bischofi.

After J. Miller, Thompson (’59) and Streenstrup (’63) were
the next writers upon the generative organs of the Myxinoids,
each giving a short account of the mature ova of the European
Myxine. W. Miiller (’75) contributed many points regarding
oogenesis in Myxine and gave the first description of the minute
structure of the testis. In 1886 Cunningham added a few more
points regarding the reproductive elements of Bdellostoma for-
steri and in 1887 he published the first detailed description of
the sexual organs and products of Myxine glutinosa, introducing
the subject of protandric hermaphroditism. Nansen (’87) sup-
- plemented Cunningham’s description with the results of further
investigations, which led him to agree with Cunningham that
Myxine glutinosa is a protandric hermaphrodite. Cunningham
(92) next contributed a rather lengthly discussion of spermato-
genesis in Myxine. Ayers (’93) published the first description of
the reproductive system of Bdellostoma stouti, and soon after
Dean (99) gave an account of the structure of the eggs and
development of the embryo. The latest articles which have ap-
peared regarding this subject are those by A. and K. EK. Schréiner
(04, ’05, ’08) which consist of a description of the generative ele-
ments of Myxine glutinosa and a very thorough discussion of
spermatogenesis in Myxine glutinosa and Bdellostoma burgeri.
Besides the foregoing investigators, there are several who have
made minor contributions to our knowledge of the genital appara-
tus in Myxinoids.

The literature contains only a very meagre description of the
mesonephros and the reproductive elements of Bdellostoma and

UROGENITAL SYSTEM OF MYXINOIDS 77

practically nothing regarding the urogenital system of the North-
American Myxine. The latter animal differs from the European
Myxine glutinosa sufficiently to cause some writers to regard the
two as different species. Girard (’58) found specific differences
‘in the external aspect of the snout and buccal aperture, the
insertion and proportional development of the tentacles, the form
of the body, and . . ._._ the presence of a membraneous
fin-like expansion along the abdomen,” and proposed the name
Myxine limosa for the North-American species. Putnam (’73),
who compared specimens obtained off the north-eastern Atlantic
coast, from the straits of Magellan, and in the Museum of Com-
parative Zoology, collected off the English coast, however, consid-
ers the American animal as merely a variety of Myxine glutinosa.
The writer has been unable to obtain specimens of the European
animal for comparison. Judging from the literature, there is a
great difference in the sizes of the two animals. Putnam’s speci-
mens from Liverpool measured 1034 to 12 inches long (26 to 30
em.). Nansen, using animals caught near Bergen, and Schreiner,
who caught hundreds in Drodbaksfjord, reported the largest
adults as 35 em. long. From Cunningham’s account it is to be
inferred that the largest adults caught by him off the English
coast and near Bergen were from 25 to 42 cm. long, most of them
being from 33 to 35 cm., these containing the largest eggs. None
of the investigators of the European Myxine -report animals
longer than 42 em. The single North-American specimen used
by Girard was 114 inches long (about 29.25 em.), and the one ex-
amined by Putnam was 12 inches (about 30.5 em.). The writer
has been unable to find in the literature any other measurements
‘of the North-American Myxine. The adult animals used in the
present study range from 50 to 79 cm. in length, averaging 62
cm., which is almost twice the length reported for the adult
European Myxine. Three specimens, measuring in length 31,
33, and 36.5 em., respectively, are in a very young stage, the geni-
tal ridge being only 2 to 3 mm. wide along its entire course and
the eggs being nothing more than dots. Size alone, of course, is
not a specific character, but such a great difference as the above
is suggestive.

78 JESSE LE ROY CONEL

In view of the fact that only two comparatively short descrip-
tions of the pronephros of Bdellostoma have been published, and
that the mesonephros of Bdellostoma and the entire urogenital
system of the North-American Myxine are still undescribed, it
seems desirable:

First, That the pronephros of Bdellostoma be re-examined, in
order, if possible, to collect additional data which may illuminate
some of the uncertain or disputed points in regard to its structure;

Second, That the mesonephros of Bdellostoma be described
more fully;

Third, That the entire excretory and reproductive systems of
the North-American Myxine be described and compared with
those of Bdellostoma and of the European Myxine, in order to
ascertain whether they present any specific differences or add
anything to our comprehension of the urogenital system in
Myxinoids.

MATERIAL AND METHODS

The Myxine used in this study consist of 20 specimens which
were caught at South Harpswell, Maine, during the summers of
1914 and 1915. ‘Three of the animals are immature females, nos.
7, 17 and 18, measuring 36.5, 33, and 3l-cm., respectively. All
the other specimens are adults ranging from 50 to 79 cm. and av-
eraging 62 cm. in length. Only one specimen is 50 cm. long and
the largest eggs in it are 8 mm. long. The next longest specimen
measures 55 cm. and its largest eggs are 22 mm. long.

Twenty-four specimens of Bdellostoma stouti, 9 males and
15 females, which were caught at Pacific Grove, California, com-
prise the Bdellostoma material. The smallest is an immature
male 33 em. long. The other males are adults, ranging from 36
to 42 em. in length, and all the females are adults which range
from 34 to 40 cm.

All the animals were killed and preserved in 10 per cent forma-
lin, and later were transferred to 70 per cent alcohol.

The study of the pro- and mesonephros was made from sec-
tions stained in Delafield’s haematoxylin and eosin. Toto
mounts of these organs, cleared in xylol and imbedded in damar,
were also used.

UROGENITAL SYSTEM OF MYXINOIDS 79

The work was done in the Zoological Laboratories of the Uni-
versity of Illinois under the guidance of Dr. J. S. Kingsley. I
wish to acknowledge my sense of obligation to Dr. Kingsley for
his kindly interest and helpful suggestions, always willingly
given.

OBSERVATIONS

]. EXCRETORY SYSTEM

The investigation of the excretory apparatus is based upon
Bdellostoma stouti, and the results will be presented by describ-
ing the organs of this animal and by interjecting, from time to
time, comparative notes regarding the same organs in the
American Myxine. Unless, therefore, it is specifically stated
otherwise, the content of the following discussion refers to
Bdellostoma stouti.

Pronephros

The right pronephros lies in the right pericardial cavity imme-
diately dorsal to the portal heart and along the dorso-lateral
surface of the alimentary canal, parallel to the dorsal aorta. In
figures 1 and 3, which illustrate the position of the right pro-
nephros of Bdellostoma and Myxine, respectively, in the peri-
cardial cavity, the lateral wall of the cavity has been cut away,
but the edges of the pericardium which form the pericardo-
peritoneal foramen are shown. The pronephros lies along a
large diverticulum extending posteriorally from a vein which
is called by Jackson (01) the anterior portal and by Cole (14)
the right anterior cardinal vein. I have had no opportunity to
examine injected specimens, but from a study of serial sections
the writer agrees with Price (’10) that this vessel is merely a
diverticulum with no posterior outlet. In Myxine glutinosa,
however, Cole (14) has shown that this vein extends posteriorly
after leaving the pronephros and enters the supra-intestinal
vein. In a single poorly injected specimen of the North-Ameri-
can Myxine the writer found a small twig extending posteriorly
from this vein toward the supra-intestinal vein and a larger

80 JESSE LE ROY CONEL

branch going to and entering the right postcardinal vein. In
Bdellostoma the vein varies in diameter from 0.35 by 0.40 mm. to
0.65 by 0.85 mm. at a point about the middle of the pronephros.
The vein is always between the two folds of pericardium, by
means of which the pronephros is attached to the dorsal aorta
and to the wall of the alimentary tract (fig. 5).

The pericardium completely envelopes the pronephros. It en-
circles each tubule where the latter extends into the pericardial
cavity. At the distal end of each tubule the pericardium is con-
tinuous with the columnar epithelium which lines the tubule.
This enveloping pericardium extends farther down between the
tubules in Bdellostoma than in Myxine..

In all the specimens examined the right pronephros was lo-
cated in somites 31 and 32, counting the somite in which the eye
is located as the first. In only one specimen, a young female,
did the pronephros occupy but one somite. In all the other
specimens it began in somite 31 and projected into somite 32.

The left pronephros lies in the left pericardial cavity immedi-
ately dorsal to the auricle and along the dorso-lateral surface of
the alimentary tract, parallel to the dorsal aorta. The left pro-
nephros, also, is connected to the aorta and to the alimentary
tract by a fold of pericardium (fig. 5). The line of attachment
of this fold of pericardium embraces from one-fourth to one-half
of the width, and about three-fourths of the length of the median-
lateral surface of each pronephros. In all the specimens the left
pronephros was slightly posterior to the right, usually lying in
somites 32 and 33. Both right and left pronephroi lie about one
millimeter to the right and left of the dorsal aorta, as shown in
figures 45 and 46.

The left pronephros lies along a vein extending posteriorly
from the left anterior cardinal. From his sections the writer
could not trace this vein to any posterior connection in Bdello-
stoma, and concludes, with Price (’10), that it is merely a diver-
ticulum. In Myxine, however, the writer found that this vein
continues posteriorly and enters the large vein formed by the
union of the two posterior cardinals (fig. 4), the left ductus
Cuvieri of Cole (’14). Like the right vein, this vein along the

UROGENITAL SYSTEM. OF. MYXINOIDS S81

left pronephros hes between the folds of pericardium which
attach the pronephros to the dorsal aorta and to the digestive
tract. Since no name has been given to these veins, hereafter
in this discussion they will be referred to as the right and left
pronephric veins. The position of the left pronephros in the -
pericardial cavity is represented in figures 2 and 4.

In shape the pronephros is never exactly the same in any two
specimens nor on both sides of the same specimen. In most
cases, however, it is somewhat three-sided, though it is sometimes
flat on the attached side only and the remaining surface is
rounded. The ends always taper more or less, the anterior end
usually being the more pointed. This is due to the fact that at
its anterior end the pronephros always invariably consists of
only one or two small lobules, while the posterior end is usually
composed of several lobules crowded together. in a compact
mass. Figures 7 to 11 represent pronephroi taken at random
and illustrate the variation that may occur in the shape. Figure
lla represents a cross section of a pronephros and illustrates
the three-sided form. When three-sided the head-kidney is
more or less wedge-shaped, flattened dorso-ventrally with the
sharp edge of the wedge opposite the point of attachment. In
this condition the pronephros has the appearance of having
been subjected to pressure, probably due to the distended portal
heart and auricle pushing it against the dorsal body-wall.

The size of the pronephros is also quite variable, as the follow-
ing few measurements will indicate:

PEG e SIDE LENGTH aca
NUMBER i
Dorsal Ventral Lateral
mm. mm, mm. mim.
5 Right 6.0 5) es 25
Left 5.0 2.0 2.0 0.75
7 Right Dee Was 1 7s 0.75
Left 5.0 ilbeey 1 Oe 0.75
16 Right 6.0 2.25 2.0 1.0
Left 5.0 IL 5 rounded
18 Right 5.0 BAD) 2.0 | 1.0
Left HO 2.0 2.0 5

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 1

82 JESSE LE ROY CONEL

It was observed that the right pronephros is usually slightly
larger than the left. In none of the specimens was a pronephros
found even one-half as large as those of Bdellostoma forsteri, as
reported by Weldon (’84), namely 20 to 25 by 5to7mm. There
‘is no correlation between the size of the pronephros and the
length of the animal in Bdellostoma. Weldon does not give the
length of the animals examined by him, hence we do not know
whether the great difference in the sizes of the pronephroi of
Bdellostoma stouti and Bdellostoma forsteri may be explained
by a difference in the length of the two animals. The adult
Bdellostoma used in the present investigation range from 33 to
42 em. long, averaging 38 em. The pronephroi represented by
the above table are all from adult animals.

The writer has been able to find only one statement re-
garding the size or shape of the pronephros in the adult Euro-
pean Myxine. W. Muller (’75) mentions that they are ‘ling-
lich,’ 3 to 4 mm. long. Following is a table of dimensions of a
few pronephroi of the North-American Myxine:

: F SURFACES
SPECIMEN LENGTH OF ere LENGTH OF

NUMBER ANIMAL PRONEPHROS
Dorsal Ventral Lateral
cm. : mm. mm. mm. mm.
2 58 Right 5.9 2.0 2.0 0.75
Left 0.0 2.0 2.0 0.75
6 61 Right 7.0 2.5 3.0 1.5
Left 6.0 2.0 a 1.0
13 63 Right 8.5 Dae 2245 0.5
Left 7.0 2.0 2.20 eS
1 63 Right 9.0 4.0 4.0 2.5
Left 8.5 3.0 3.0 3.0
3 64 Right 9.0 3.0 3.0 1.0
Left 8.0 2.0 2.0 1.0
i 67 Right 6.0 2.0 2.0 eW)
Left 10.0 2.0 2.0 1.0
10 68 Right 10.25 10) AS Ee 4.5
Left 8.5 5.0 5.0 2.0

As is indicated by the above tables, the pronephroi of Myxine
are considerably larger than those of Bdellostoma. This is to
be expected from the great difference in the size of the adult ani-

UROGENITAL SYSTEM OF MYXINOIDS 83

mals. The writer found that there is a correlation between the

,size of the pronephros and the length of the animal in Myxine,
but not a sufficiently large number of specimens was available
to prove this to be constant. The largest pronephroi (those of
Myxine no. 10) are in an animal which has the appearance of
being quite old. The skin is darker than usual, very thick,
wrinkled and hard, the muscle fibers in the body wall are large
and coarse; the walls of the alimentary canal are very thick, the
liver and gall bladder are very large and coarse. In this speci-
men the pronephroi are a very dark brown color; in all the other
specimens and in all the Bdellostoma examined the pronephros
is gray. It is probable that the size of the pronephroi is more
correlated with the age than with the length of the animal.
The right pronephros of Myxine was almost always larger than
the left.

Price (04) found that at some stage of embryonic development
of Bdellostoma stouti an excretory tubule appears in each somite,
from the 11th to 13th to the 79th to 82d. That is to say, in
the embryo pronephric tubules are present in the same seg-
ments with gills. As the gills shift posteriorly (Dean, 97) these
pronephric tubules are pushed along behind them and eventually
become crowded together in a ‘‘small, compact body, the pro-
nephros of the adult, in the region a little posterior to the thir-
tieth segment”’ (Price, p. 132). Price does not mention anything
in regard to the history of the veins connected with the tubules
in this movement posteriorly.

As would be expected, there is a limitless variety in the minute .
structure of the pronephroi. It is well known that each proneph-
ros 1s composed of a large number of small tufts or lobules of
tubules which open separately into the pericardial cavity. Usu-
ally there are fewer of these lobules at the anterior than at the
posterior end, and one or two lobules may be entirely separated
anteriorly from the rest of the pronephros. Figure 12 repre-
sents a reconstruction on millimeter paper of the right proneph-
ros of Bdellostoma no. 15. This pronephros was cut in trans-
verse sections, each 10 microns thick, and it will be used as a

84 JESSE LE ROY CONEL

basis for the description of the minute structure of the head-
kidney of Bdellostoma, as follows: ;
Histology. The tubules in each of the two most anterior lob-
ules anastomose inwardly and form a single tubule which unites
with one similarly formed from the other lobule, and the singles
tube thus formed constitutes the central duct of the pronephros.
The first appearance of the central duct occurs in the 10th sec-
tion from the anterior end of the pronephros. All of the pro-
nephroi of Bdellostoma stouti examined by the writer have a
central duct, which is so evident that it can not possibly be in-
terpreted as anything else. Price (10) found a central duct in
the head-kidney of Bdellostoma stouti, and Weldon (84) de-
scribed one for Bdellostoma forsteri. Semon (’96) thought that
Weldon was mistaking the venous sinus (pronephric vein) for a
central duct, but Weldon’s description of the duct coincides so
nearly with the condition in Bdellostoma stouti that it seems
very probable that Bdellostoma forsteri has a central duct in the
pronephros. In the 10th section from the anterior end of the
pronephros the lumen of the duct is 0.02 mm. wide, but t en-
larges immediately and is 0.15 mm. at the widest part. The
duct proceeds posteriorly, entering the pronephric vein in sec-
tion 20 and ending blindly in the vein in section 48. From its
beginning this short segment of the central duct is surrounded
by a mass of large, deeply stained nuclei, which will be referred
to hereafter in this discussion as the ‘central mass’ and which
will be described in detail later. This mass is distributed some-
. what regularly around the central duct, now more on one side,
now more on the other. Some idea of its gross appearance may
be had from figure 12. At its widest part the mass measures
0.21 mm. from its outer edge to the lumen of the duct, and it
extends 0.14 mm. beyond the posterior end of the duct.
No trace of the central duct is again seen until section 52 is
reached. Here the tubules of one lobule unite into a single
tube, and the latter forms the beginning of the central duct.
The lumen of this segment of the duct is 0.05 mm. in diameter
at first, but measures 0.09 mm. at the widest part. The duct
proceeds posteriorly to section 60, receiving in its course the tube

UROGENITAL SYSTEM OF MYXINOIDS 85

from another lobule. In section 60 the duct enters the proneph-
ric vein, and remains in it to section 80 where it ends blindly.
From its beginning this segment of the duct is also surrounded by
a central mass like the one around the first segment of the duct.
In transverse section the mass is circular in outline and is dis-
tributed somewhat regularly around the lumen of the duct. At
its widest part the mass measures 0.16 mm. from its outer sur-
face to the lumen of the duct. Only two lobules of the proneph-
ros are connected with this segment of the central duct.

The third segment of the duct appears in section 90, and is
formed by the main tube of one lobule. In this section the
lumen of the duct is 0.05 mm. in diameter, but becomes as wide
as 0.20 mm. This segment of the duct extends to section 150
and there breaks up to form the tubules of three lobules. Alto-
gether there are four lobules connected with this segment. The
duct runs parallel to the pronephric vein, and up to section 115
is separated from the latter by a wide layer of connective tissue.
In this distance one vein 1 mm. wide and another 3 mm. wide
permit blood to flow into the pronephric vein from capillaries
which run between the tubules of the pronephros. At section
115 the duct widens abruptly and extends downward in the pro-
nephric vein. In the vein the duct becomes sheathed in a cen-
tral mass which resembles in all respects the masses which
surround the first and second segments of the duct. In section
117 the duct opens through the central mass into the lumen of
the pronephric vein. This opening is 0.05 mm. wide. Another
such opening 0.09 mm. wide occurs in section 250, and a third
0.04 mm. wide in section 320. These openings are not breaks
or tears, but are natural apertures lined by a single layer of
squamous epithelium which is continuous with the columnar
epithelium of the duct on the one hand and with the endothelium
of the pronephric vein on the other. Figure 20 represents one
of these openings. At least one, often more, such opening con-
necting the lumen of the central duct with the lumen of the
pronephric vein was found in every pronephros of Bdellostoma
exdmined. These openings occur only through the central mass,
never through the walls of the central duct when not surrounded
by the central mass.

86 JESSE LE ROY CONEL

To return to the description, the duct remains in the central
mass to section 137 where it leaves the vein and breaks up into
the tubules of three lobules. The central mass, however, con-
tinues in the lumen of the vein independent of the duct, and in
section 147 the fourth segment of the central duct appears in it.
The central mass projects into the pronephric vein as indicated
in figure 12 and has a cylindrical shape. Between sections 137
and 147 it is 0.80 by 0.40 mm. in transverse section.

The fourth segment of the central duct begins as the result of
the anastomoses of the tubules of four lobules whose main tubes
unite near section 150 and form the central duct. In this sec-
tion the duct is 0.05 mm. wide. At first the duct lies in the con-
nective tissue at the base of the pronephros, but in section 157
it bends toward and enters the central mass in the vein. Here
the lumen of the duct -is 0.27 mm. wide. In this segment one
side of the duct remains closely applied to the connective tissue
at the base of the pronephros and retains its columnar lining,
while the other side extends along the central mass to section
200 where it bends toward its fellow, thus narrowing the lumen
of the duct considerably, and the segment ends by the duct
branching into the tubules of a single lobule. There are eleven
lobules connected with this segment of the duct. The central
mass continues without interruption in the pronephric vein to
section 240 where the fifth segment of the duct enters it. That
is to say, the central mass extends from section 200 to section
240 (a distance of 0.40 mm.) entirely disconnected from the cen-
tral duct. In the region of the fourth segment the central mass
resembles in every respect that around the preceding segments
of the duct. In the portion between sections 200 and 240, how-
ever, the mass changes its shape in transverse section from cir-
cular to elongated, measuring 0.15 by 0.55 mm. in the largest
portion. Figure 20 represents the shape of the mass at this place.
This figure also indicates the relation of the size of the mass to
the lumen of the vein. In this particular pronephros the duct
and the mass together in the largest parts never occupy more
than about one-half of the lumen of the vein as viewed in trans-
verse section. In one specimen, however, the central duct was

UROGENITAL SYSTEM OF MYXINOIDS 87

so large that it, together with the central mass, almost entirely
obstructs the lumen of the vein. Between sections 205 and 230
the pronephric vein opens directly between the tubules as a large
sinus (fig. 20), and another such sinus lies between sections 255
and 300. At all other places, however, there is a strip of con-
nective tissue from 0.01 to 0.05 mm. wide, or even wider, be-
tween the pronephros and the vein. In one specimen, though,
the vein opens directly into the spaces between tubules along the
entire base of the pronephros. But even here the pronephros
stands upon the vein as illustrated in figure 20, so that in no
sense can the head-kidney be said to lie buried within the vein,
a misleading statement which occurs very frequently in the lit-
erature. Where the vein opens between the tubules as a sinus,
the capillaries, which otherwise carry the blood between the
tubules, have broken down and only the pericardial sheath and
the endothelium of the sinus confine the blood in the intertubular
space. These vascular spaces between the tubules aré not ‘sinu-
soids’ according to Minot’s use of the term. The pronephric
tubules do not invade the vein, for, as Price (10) has shown,
the branching to form new tubules always occurs in a direction
away from the pronephric vein, ‘‘just back of the nephrostomes.”’

The fifth segment of the central duct begins in section 212
where the tubules of one large lobule unite into a single tube
which widens to form the duct. The latter extends posteriorly
in the connective tissue at the base of the pronephros parallel to
the pronephric vein to section 240, increasing gradually in width
from 0.04 mm. to 0.15mm. _ In this section the duct bends down-
ward so that one side enters the central mass, which still remains
in the vein. The wall of the duct which les toward the proneph-
ros retains its columnar structure, but the wall which lies in
the central mass breaks down completely soon after entering
the mass and presents a jagged appearance, and the nuclei bor-
dering the lumen have no definite arrangement. In sections 243
to 255 the central duct opens through the central mass into the
lumen of the vein. The mass is similar in all respects to that
surrounding the preceding segments of the duct. In section 260
the duct divides, one branch entering a lobule and breaking up

88 JESSE LE ROY CONEL

into tubules, the other continuing posteriorly in the central mass
and ending blindly in it at section 274. In section 276 the duct
begins again as a part of the sixth segment, just opposite the
blind ending of the fifth segment. There are six lobules con-
nected with the fifth segment of the duct. ;

The sixth segment of the duct arises in section 273 from the
union of the tubules of one lobule. The duct enters the central
mass in the vein in section 300, and is here 0.12 mm. wide. A
small twig extends anteriorly in the mass to section 276 where it
ends blindly and is separated by only one section from the end
of the fifth segment of the duct. Undoubtedly at one time the
fifth and sixth segments of the duct were connected at this point.
The sixth segment extends posteriorly through the central mass
to section 380 where it ends as a single tubule which runs out of
the vein and opens into the pericardial cavity. In sections 318
to 323 the duct opens through the central mass into the pro-
nephric vein, and in this region the duct and neighboring tubules
contain many blood corpuscles. In section 350 the duct leaves
the central mass and the columnar cells of the walls of the duct
become double their usual length and are thrown into longitudi-
nal folds like those of the mesonephric duct, to be described later.
This folded condition of the epithelial walls of the duct contin-
ues to section 370; then the cells diminish in Jength to the nor-
mal size for the tubules, and the duct here ends as a single tubule,
as explained. There are six lobules connected with the sixth
segment of the duct.

The seventh segment of the central duct begins in the central
mass in section 340 beside the sixth segment. It continues in
the mass, which still lies in the pronephric vein, to section 365
where it leaves the mass and vein and divides into two branches,
one of which ends by branching into the tubules of a lobule and
two-single tubules, the other breaks up into the tubules of the four
most posterior lobules -of the pronephros. The lobules con-
nected with this segment of the duct are in such a compact mass
that they can not be counted with any degree of certainty.

The eighth and last segment of the central duct arises in the
central mass in section 370 beside the seventh segment. The

UROGENITAL SYSTEM OF MYXINOIDS 89

mass continues around the duct to section 380 and there ends,
remaining in the lumen of the vein. The duct proceeds posteri-
orly, and in section 385 divides into three tubules, each of which
leaves the pronephric vein and enters the Bowman’s capsule of
the Malpighian body of the pronephros, opening into the capsule
by a nephrostome. There are no lobules connected with the
eighth segment of the duct.

Price (14) suggests that perhaps each lobule of the pronephros
represents a single original tubule and its secondary branches.
This is scarcely probable, for there is a total of 31 lobules con-
nected with the first six segments of the duct in the above de-
scribed pronephros, while those of the seventh segment could
not be counted with accuracy but there are at least four. If the
most anterior original tubule lay in somite 11, then there could
be only 21 tubules at most to and including somite 32, the defin-
itive position of the tubules after they have been pushed pos-
teriorly by the gills. In the pronephros under discussion, how- .
ever, there are at least 35 lobules.

In Bdellostoma none of the tubules in any of the pronephroi
examined by the writer show any signs of degeneration, and the
lumen. of each tubule opens into the pericardial cavity at one end
and is continuous, either directly or indirectly, with the lumen
of the central duct. The lumen of almost every tubule is filled
with a coarsely granular coagulum which is more or less shredded
into long processes resembling flagella (fig. 16). These processes
are attached at one end to the columnar cells, usually one to a
cell, and the free end extends inward toward the base of the tu-
bule, that is, toward the central duct. The lumen of the central
duct sometimes contains a comparatively small amount of this
coagulum. The writer was unable to demonstrate cilia in the
phonephric tubules, but it is probable that his material was
not suitably preserved to permit these to be seen if present.

The tubules are very simple in structure. Each is a cylinder
consisting of a single layer of columnar cells, which are continu-
ous at the.mouth with the pericardium and, at the base, with the
columnar cells of the central duct. The mouths of the tubules
are sometimes funnel-shaped (fig. 13), but are usually constricted

90 JESSE LE ROY CONEL

(fig. 14). The columnar cells which constitute the wall of the
tubules are approximately the same size in all the tubules, vary-
ing somewhat around 0.0135 mm. high by 0.004 mm. wide.
The nucleus is always at the base of the cell and occupies the en-
tire width and from one-half to two-thirds its length. At the
base of the cells the cell-walls fuse to form a thin basal membrane,
the outer limit of the tubule. When connective tissue occupies
the space between the tubules, it lies next to the basal membrane,
and when a blood sinus fills the inter-tubular space, the endo-
thelium of the sinus usually lies against the basal membrane,
completely surrounding the tubule (fig. 15). The lumen is prac-
tically the same in diameter in all of the tubules, and the outside
diameter of the tubules is ikewise approximately the same for
all tubules.

The specimens of Bdellostoma examined were within a few
centimeters of being the same length, and the dimensions of the
. tubules are about the same in all the pronephroi examined. At
the mouth of the tubule the lumen narrows slightly, but other- °
wise is approximately the same diameter throughout. Often,
however, a tubule is constricted in one or two places. The lu-
men is approximately 0.0216 mm. wide, and the outside diameter
of the tubule is about 0.054 mm.

The protoplasm of the columnar cells of each tubule is coarsely
granular, and the boundary of the cell facing the lumen is usually
marked by many granules and one or two long processes which
consist of granules (fig. 16). The nuclei are more or less oval and
always contain many large deeply stained bodies. The cells of
the tubules are continuous with those of the central duct at the
proximal end, and with those of the pericardium at the distal
end.

The cells of the central duct are also columnar and are usually
longer than those of the tubules. The character of the cytoplasm
and nuclei in the duct cells is practically the same as in the tu-
bules, and the basal membrane of the latter is continuous with the
basal membrane of the former. The cells of the duct in a given
pronephros vary in length at different points, but any increase
or decrease is gradual. They may be as long as 0.0324 mm. in

UROGENITAL SYSTEM OF MYXINOIDS 91

the midregion of the pronephros. The diameter of the lumen of
the duct varies widely in an individual specimen. It may be as
small as a tubule in places, then increase to several times that
width. The duct and its lumen may be continuous throughout
the entire length of the pronephros or may be broken up into dis-
connected segments. The most continuous duct was found in a
young male. The duct in this specimen also has the least amount
of central mass connected with it, and the mass is almost entirely
confined to the posterior end of the duct.

The structure which has been referred to as the ‘central mass’
was first described by Kirkaldy (’94) for Myxine, and the writer
has adopted his name for it. It is possible that Weldon’s lym-
phatic tissue may have been the same thing as this central mass,
but his short description does not enable us to be positive. This
mass of tissue has been the subject of much discussion by investi-
gators of the pronephros of Myxinoids. Weldon (’84) described
a mass of lymphatic tissue which he found at the posterior end
of the head-kidney of Bdellostoma forsteri. He states that the
central duct ends posteriorly ‘‘ina mass of tissue . . . . re-
sembling the trabecular supporting tissue of a lymphatic gland.”
Into this mass strands of blood vessels pass from the glomerulus
which lay beside it. Upon the basis of this lymphatic tissue
Weldon thinks the pronephros becomes transferred into and func-
tions as a suprarenal body. Kirkaldy found a difference in the
mass, in animals without ova and those with them. In the former
the mass was divided into separate parts, and each part was re-
garded as a glomerulus supplied with a capsule, inside of which
was a characteristic loop (his fig. 2). In an animal with ova he
found no central duct or glomerulus in the pronephric vein, but
their former position was occupied by a mass of small cells with
small nuclei and larger cells with large, round, and deeply stained
nuclei (his fig. 7). Capillaries were numerous in this mass.
Kirkaldy regards the mass as the degenerating central duct of
earlier stages, hence Myxinoids may be considered as representing
a stage in the phylogenetic reduction of the head-kidney, and the
latter may represent the mesoblastic part of the supra-renal

bodies.

92 JESSE LE ROY CONEL

Semon (’97) regards this mass as the glomeruli of the head-
kidney. Eventually, however, the pronephros becomes trans-
formed into a suprarenal body. He found the mass rich in blood
vessels.

Spengel (’97) thinks this mass was never glomerular, but that
it is either a suprarenal body or a lymph organ, and that it is
the result of a metamorphosis of the inner ends of the pronephric
tubules.

Maas (’97) thinks the mass differs distinctly from a glomerulus.
Blood vessels occupy only a little space in it, and it is greatly
dissimilar to tubule epithelium. It resembles stages in the de-
. velopment of the Miillerian duct of higher animals, especially
reptiles. It is also not unlike the medulla of suprarenals.

Price (10) evidently saw this mass, but does not describe it.
He states that ‘‘in places the wall of the duct may become
ereatly thickened by an increase in the number of epithelial
cells. These change their shape, and become much more loosely
arranged, so that the tissue loses entirely the structure of colum-
nar epithelium.’ Price adds that these thickenings are not
supplied with arteries.

In specimens with a duct which is continuous throughout the
entire length of the pronephros, the central mass appears only
in the posterior third of the pronephros where it surrounds the
duct and hes in the pronephric vein. In most of the specimens,
however, the duct is broken up into segments which are not con-
nected with each other, and that part of each segment which
lies in the vein is surrounded by the central mass. The mass is
found only in the pronephric vein (a very small quantity may be
connected with the duct immediately before it enters the vein).
A typical distribution of the mass is represented by figure - 12.
It may project. into the vein like a glomus, one side remaining in
contact with the base of the pronephros, or it may lie in the lu-
men of the vein, completely surrounded by blood, and may be
attached to the base of the pronephros at one end only. The
central mass is found only in connection with the central duct
and is always attached to the latter, though one end of the mass
may extend in the pronephric vein some distance (as much. as

UROGENITAL SYSTEM OF MYXINOIDS 93

40 sections, 0.4 mm.) beyond the end of the lumen of the duct.
The mass is more or less cylindrical, though in places it may be
considerably widened as if bent upon itself, and then it is elon-
gated in transverse section. In none of the specimens does it
entirely fill the lumen of the vein. In those pronephroi in which
the duct is almost continuous, however, the lumen is so great in
diameter, that the duct, together with the central mass surround-
ing it, almost entirely fills the lumen of the vein, leaving only a
very narrow space between the mass and the vascular endothel-
ium. The endothelium of the pronephric vein is continuous
around the mass (figs. 17 and 22), but is here much thinner than
when lining the vein, and its nuclei can be observed only now and
then. The surface of the mass is smooth and convoluted.
Figure 18 represents a transverse section through the central
mass, and illustrates the typical condition in Bdellostoma. It is,
composed of a large number of cells, the nuclei of which are more
or less oval in shape. The latter are of various sizes, the largest
and most numerous averaging 0.0054 by 0.0108 mm. These
nuclei are not distributed in any regular manner, large, small
and intermediate sizes are mingled in all parts of the mass. Also,
there is no regularity in the manner of their arrangement; some
are isolated completely from surrounding neighbors, others are
collected in groups of two or three, and again six or eight may be
closely crowded together in a mass. There is no definite cellular
structure observable in the central mass. Most of the nuclei
contain many large, deeply stained granules, but many have only
a nuclear membrane with no granules inside. Many of the nu-
clei have no cytoplasm surrounding them, while others are im-
bedded in what resembles the granular cytoplasm in the cells
of the central duct and tubules. This granular cytoplasmic
ground-work is scattered throughout the central mass and, in
places, is drawn out into slender processes which resemble those
found in the tubules. There is no connective tissue in the cen-
tral mass. In an occasional transverse section of the mass there
are one to three or four giant nuclei, but these are not frequent
in Bdellostoma. About one hundred sections of the mass were
examined before a section containing one of these giant nuclei

94 JESSE LE ROY CONEL

was found. Occasionally such nuclei occur in the walls of the
duct or of the tubules near the central mass. These giant nuclei
are much more deeply stained than are the other nuclei of the
mass, and the cytoplasm, which always surrounds them, stains
like that of blood corpuscles, but much more deeply. These
giant cells are interpreted as greatly enlarged blood corpuscles.
They do not have the elongated characteristic shape of the blood
_ corpuscles, but are usually rounded and quite irregular in out-
line. In the central mass they are surrounded by a very thin
membrane which is interpreted as endothelium, although no nu-
clei were observed in it. In the walls of the duct or tubules,
however, nuclei occur in the membrane surrounding the giant
blood corpuscles and here it is undoubtedly endothelium. These
giant cells are also frequently seen in capillaries which occur in
the connective tissue surrounding the mesonephrie duct, and
here there is no doubt that they are in blood vessels.

Excepting the giant corpuscles just described, the writer
rarely found a blood corpuscle or blood vessel in the central mass.
An attempt was made to find blood vessels entering the mass,
but without success. The blood corpuscles have a distinctly
characteristic shape and appearance, and the cytoplasm stains
more deeply in eosin than that of any of the other cells in the
pronephros, hence the corpuscles are easily discerned in any tis-
sue. ‘There are many spaces in the central mass, but they are
not lined by endothelium and never contain blood corpuscles.
Furthermore, the writer found no vessels leaving the central
mass to enter the vein or any surrounding tissue. Also, natural
appertures in the endothelial wall of the mass were diligently
but vainly sought; the mass is completely shut off from the blood
in the vein. One series of sections is especially well stained to
demonstrate this fact. The blood corpuscles are stained a deep,
yellowish-red, which is strikingly different from the pale blue of
the central mass. The blood corpuscles surround the latter as a
dense mass which almost fills the lumen of the vein. On account
of the striking contrast in stain, a single blood corpuscle inside
the central mass would be instantly recognized if present. But

UROGENITAL SYSTEM OF MYXINOIDS 95

none was found. Price (’10), also, found no blood vessels in the
central mass in Bdellostoma.

When not surrounded by the central mass, the central duct
retains its columnar walls, but loses them upon entering the
mass. The walls break down completely and the cells become
scattered in the mass. The lumen of the duct may continue in
the mass, but it has no organized lining and is bordered by nuclei
and strands of cytoplasmic ground-work (fig. 29). The colum-
nar lining of the central duct is never continuous with the epi-
thelial sheath around the central mass. In view of this fact,
it is difficult to regard, as Semon (’96) does, the central mass as a
series of glomeruli into whose Bowman’s capsules the tubules of
the pronephros enter through their ‘Innentrichter,’ for Semon
(96, °97) himself has shown that, in the mesonephros, the col-
umnar wall of the tubule of a Malpighian body is continuous
with the squamosal epithelial wall of the Bowman’s capsule.
Furthermore, in Bdellostoma, the writer never found a tubule
entering the central mass. The tubules enter the central duct
and the latter alone enters the central mass, hence in Bdello-
stoma Semon’s ‘Innentrichter’ of the pronephric tubules really
open into the central duct. Therefore, the inner ends of the
pronephric tubules cannot correspond to that end of the tubule
of a mesonephric Malpighian body which opens into the Bow-
man’s capsule, and hence the central mass of the pronephros can-
not correspond to the glomerulus of a Malpighian body of the
mesonephros.

In every pronephros of Bdellostoma examined by the writer
the central mass has one or more openings, through which the
central duct communicates with the lumen of the pronephric
vein (figs. 12, 20, 21, 22). These openings are natural, and the
endothelial sheath which surrounds the central mass lines the
sides of the openings. In the lumen of the duct near these open-
ings, or even projecting into them, there is almost always a
rounded collection of nuclei and granules, which is more deeply
stained than the central mass. The nuclei and granules do not
resemble blood corpuscles, but have the appearance of waste
particles. These openings do not occur in the central duct at

O6 JESSE LE ROY CONEL

any place where the latter is not surrounded by the central mass,
nor do they occur in all those segments of the duct which are
ensheathed by the central mass. There is no regularity in the
location of these openings, except that they are always confined
to the posterior half of the pronephros. As is shown by figures
20, 21 and 22, by means of these openings the lumen of the pro-
nephric vein is in actual communication with the pericardial
cavity through the central duct and the tubules. Near the open-
ings blood corpuscles are numerous in the lumen of the central
duct, and they extend far up the tubules toward the openings of
the latter into the pericardial cavity. In one specimen blood
plasma extends from the central duct two-thirds of the entire
length of four or five tubules. The pericardial cavity communi-
cates with the peritoneal cavity through the large pericardo-peri-
toneal foramen, and the peritoneal cavity opens into the cloaca
through the genital pore, hence we have in Myxinoids the strange
condition of the vascular system being open to the exterior of
the body. The writer found no traces of blood in the pericardial
cavity. Since there are many hundreds of tubules in each adult
pronephros, it is difficult to explain why blood is not poured into
the pericardial cavity. Price (’10) found that carmine. grains
injected into the peritoneal cavity through the genital pore of
living animals were present later in abundance in the blood taken
from different parts of the body. He presumed that the carmine
grains gained admission to the blood stream through the cili-
ated pronephric tubules, that is to say any current in the tubules
which is caused by ciliary action is from the exterior toward the
interior. This inference is corroborated by the fact that, in al-
most all the tubules examined by the writer, the free ends of the
granular processes extending from the epithelial cells of the
tubules are directed inward toward the central duct.

In his description of the development of the pronephros Price
(04, p. 137) states that the manner in which the central duct
becomes shortened as the tubules are crowded together is a point
which has not been worked out; bending of the duct will not ac-
count for all of it. Kirkaldy (’94, p. 356) thinks the duct breaks
down and becomes the central mass. Morphological evidence

UROGENITAL SYSTEM OF MYXINOIDS 97

supports this hypothesis somewhat. The diffused condition of
the cells of the duct where the latter is in contact with the cen-
tral mass suggests that the duct is breaking down, and the en-
larged nuclei in the mass, which are without granules, are suggest-
ive of disintegrating cells, while the rounded masses of small
nuclei and granules found in the lumen of the duct may be inter-
preted as nuclei which have been broken down. These may
either be ejected into the body cavity through the tubules and
pericardial cavity, or, what is more probable, they may be swept
into the blood stream and be engulfed by leucocytes. These
masses occur only in or near the openings in the central mass
which connect the central duct with the pronephric vein. In one
specimen, however, a small ball of these nuclei was observed in a
tubule. Furthermore, in those pronephroi in which the central
duct is most continuous there is no central mass in the anterior
part of the duct where its columnar walls remain entire, but the
mass is limited to the posterior region where the walls of the duct
have lost their columnar structure and the lumen of the duct is
surrounded by the mass of nuclei. Also in those specimens in
which the duct is broken up into segments and the palisade wall
has broken down, each segment, anterior as well as posterior, is
surrounded by the central mass, but even in these specimens the
bulk of the central mass is found at the posterior end of the pro-
nephros, where the crowding of the original tubules is the great-
est. On the other hand, the quantity of the central mass in the
older animals seems greater than would be the case if it were
all derived from merely a crowding-together of the central duct,
especially if it were disintegrating all the while.

The central mass is the same in appearance and structure
_ wherever it occurs in Bdellostoma stouti. No lymphatic tissue
such as Weldon (’84) describes is present at the posterior end of
the pronephros of Bdellostoma stouti, unless he refers to the cen-
tral mass around the duct.

The pronephros of Myxine differs strikingly from that of
Bdellostoma in the fact that it contains much more connective
tissue. The pericardial sheath around the tubules is farther from
the wall of the tubule than in Bdellostoma, and the intervening

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

98 JESSE LE ROY CONEL

space is usually filled with connective tissue. Also, there is
much more connective tissue at the base of the pronephros, sepa-
rating the latter from the pronephric vein, than in Bdellostoma,
and bands of connective tissue even extend into the vein and into
the central mass. In the older animals there is often considerable
connective tissue between the walls of the tubule and the sur-
rounding sheath of pericardium (figs. 23 and 24). The pericar-
dial sheath is heavier and its nuclei larger than in Bdellostoma.
Figure 25, a cross section of one lobe of a pronephros of an adult
female, shows the proportion of connective tissue with reference
to the size of the tubules which it surrounds. Not all of the
tubules in the pronephroi of this animal, however, have connec-
tive tissue between their walls and the pericardial sheath. In
the youngest specimen examined,a young female 31 cm. long (no.
18), there js very little, and often no connective tissue at all,
near the distal ends of the tubules. In the oldest specimen
(Myxine no. 10) the connective tissue around the tubules and in
the entire pronephros is more abundant than in any of the other
animals and contains many blood vessels. In this specimen
there is, in transverse section of almost every large tubule, a
single large vessel which partially or entirely surrounds it (fig.
26). A blood sinus, which completely fills the space between
the tubules, as is frequent in Bdellostoma, is rare in Myxine.
The blood around the tubules is almost always confined in ves-
sels which he in the connective tissue surrounding the tubules.
Unlike Bdellostoma, the tubules in an adult Myxine are not
all of the same size (fig. 27). They are practically of the same
size in the youngest specimen examined (Myxine no. 18), but in
the older animals there is a gradually increasing number of tu-
bules which are slightly larger than others, and in the oldest speci-
men (Myxine no. 10) there are present, in the pronephros, tubules
which range in size from the smallest to very large ones. | In Myx-
ine no. 18 the average dimensions of the tubules are: Width of
lumen 0.0162 mm., width of each wall 0.0189, outside diameter
0.054 mm. Only a few of this size are present in the pronephros
of Myxine no. 10, many approximating the following dimen-
sions: Width of lumen 0.108 mm., width of each wall 0.027, out-

UROGENITAL SYSTEM OF MYXINOIDS 99

side diameter 0.1620 mm. One tubule in Myxine no. 10 is very
large, the outside diameter being 0.675 hy 1.1475 mm. before it
breaks up into smaller branches. The smaller tubules have
practically no connective tissue between the walls and the peri-
cardial sheath, the medium size tubules a little, while the large
ones usually have a comparatively large quantity of connective
tissue around them. The smaller tubules have the appearance
of being recent branches from the larger ones.

Kirkaldy (’94) states that, in a Myxine with large eggs, the
tubules at the posterior end of the pronephros are entirely differ-
ent from those of a Myxine without eggs in that the former are
considerably degenerated. The writer is of the opinion that
this degeneration of the tubules is not so much a matter of be-
ing with or without eggs as one of age. Kirkaldy does not state
whether the animal without eggs was young or old. In all the
pronephroi of Myxine examined by the writer the inner ends of
almost all the tubules have disintegrated, only occasionally is one
found whose walls remain intact to its opening at the inner end.
Only in the oldest specimen (Myxine no. 10), which does not
have any eggs, are there tubules which have the appearance of
degeneration. Some of the largest tubules alone are degenerating,
and answer to the description given by Kirkaldy. The nuclei
are enlarged, here and there, in the walls, while some of them
are attenuated and almost fibrous, and connective tissue is re-
placing the palisade cells. These degenerating tubules are not
numerous and are not limited to the posterior end of the pro-
nephros. They are surrounded by many smaller tubules which
give no evidence whatever of degeneration, but on the other
hand look like recently formed branches. The cells of the lat-
ter are more uniform in size and shape and stain more deeply
than those of the large tubules.

One of the most striking differences between the pronephroi of
Bdellestoma and Myxine is that in the latter the disintegrating
process of the interior has proceeded further than in the former.
In Bdellostoma the inner ends of the tubules are always entire,
while in Myxine they are seldom so. In places only dense lines
of nuclei indicate where the inner ends of tubules have been, and

100 JESSE LE ROY CONEL

these lines are always streaming toward a more or less large,
loosely arranged mass of nuclei, bordering or lying in the pro-
nephric vein.

Investigators do not agree as to the existence of a central duct
in the pronephros of Myxine. W. Miller and Kirkaldy affirm,
while Semon, Spengel and Maas deny the presence of the duct.
After studying the pronephros of Bdellostoma, it is inevitable
for one to conclude that a central duct at one time existed and
that fragments of it still exist in Myxine. It is not at all promi-
nent and might easily be overlooked except in a comparative
study. Along the entire extent of the pronephros the inner ends
of the tubules, as stated above, end as a loosely arranged mass of
nuclei in which a cavity frequently appears (fig. 28). This cav-
ity is the remains of the lumen of the central duct. In occasional
places it opens into the lumen of the pronephric vein, and blood
corpuscles occur in it and in the tubules near it (fig. 29). Here
and there the central duct is cut in longitudinal section and is
then unmistakable (fig. 30). The youngest specimen (Myxine
no. 18) shows the duct but imperfectly (fig. 31). Likewise, in
the oldest animal examined (no. 10) the duct has almost entirely
disappeared, the lumen being visible for only a short distance in
the posterior part of the pronephros and having but a small piece
of columnar wall (fig. 32). Extending along the wall of the vein
next to the pronephros is a large number of heavily stained nu-
clei, which are interpreted as remains of the central mass; or,
in other words, remains of the central duct and the inner ends
of the tubules. Waste particles, nuclei, and granules are occa-
sionally seen in the lumen of the duct and in the tubules. The
tubules are filled with a coagulum which is more or less drawn
out into granular processes, and these are almost always directed
inwards. In only a few places do the walls of the duct still re-
main entire (fig. 33). Where the duct has entirely disappeared,
the tubules often border directly on the vein and their inner
ends are degenerated.

The central mass in the pronephros of Myxine is decidedly dif-
ferent from that in Bdellostoma. In the young, immature ani-
mals (Myxine no. 18) it approaches in structure and appearance

UROGENITAL SYSTEM OF MYXINOIDS 101

the condition existing in Bdellostoma (fig. 34). Here the mass
contains the more or less oval nuclei, no blood corpuscles, but the
cytoplasmic groundwork is replaced by connective tissue. Also,
one side of the mass projects into the lumen of the pronephric
vein and has a more or less rounded form, while the other side
remains attached to the base of the pronephros, but is not as
compact as in Bdellostoma. The mass is distributed along the
entire length of the vein, from the anterior to the posterior end
of the pronephros, and extends behind the posterior end of the
latter about 0.18 mm. in one specimen. This posterior exten-
sion of the mass is cylindrical, has a tubule which ends blindly in
it, and contains several large blood corpuscles in capillaries.

In the older animals the central mass is much more unlike that
of Bdellostoma. In the anterior part of the pronephros it con-
sists of a loose collection of nuclei which extends along the base
of the tubules, embracing their inner ends, either lying outside
the vein or projecting slightly into it. The mass is not at all
compact, and has no definite form. Many of the nuclei are dis-
tributed in an irregular manner along the sides of the vein. At
the base of the pronephros the mass is more or less exposed to the
blood in the vein, even though it does not project into the lumen
of the latter. In occasional places the lumen of the vein opens
through the mass (fig. 32) and communicates with the lumen of
the central duct, and here blood corpuscles are present in the
duct, but are rarely found in the tubules. In the posterior part
of the pronephros the central mass becomes cylindrical and com-
pact, and projects into and extends posteriorly in the lumen of the
vein, completely surrounded by blood. It is bound to the sides
of the vein-by broad bands of connective tissue which extends
from the side of the mass here and there (fig. 35). Blood vessels
run from the connective tissue at the base of the pronephros into
these bands of connective tissue. The fibers of the latter con-
tinue to the center of the cylindrical mass, and enlarged nuclei
and blood capillaries are arranged in a cellular structure around
this central core of fibers. The giant blood corpuscles are rounded
in shape and are contained in capillaries. They are very num-
erous in the central mass in Myxine (as many as fifteen in one sec-

102 JESSE LE ROY CONEL

tion taken at random) and average 0.0081 mm. in diameter. Be-
sides the giant corpuscles, there are many large nuclei in the cen-
tral mass which are stained about the same as the nuclei of the
tubules and which contain very many small granules. The giant
blood corpuscles resemble those in Bdellostoma, but, in the lat-
ter animal, they are not nearly as numerous as in Myxine. In
this posterior region of the pronephros of Myxine the central
mass resembles a lymphatic structure.

Another striking difference between the pronephros of Myxine
and that of Bdellostoma is the presence of broad bands of con-
nective tissue which extend across the lumen of the pronephric
vein from side to side, and partially or completely divide the
lumen longitudinally in two parts (fig. 36). These bands are
present in all the pronephroi of Myxine, from the youngest to
the oldest, and are not confined to any particular region of the
pronephros. In one place, near the Malpighian body of the
pronephros, a large, isolated, thick-walled duct begins blindly in
such a band, continues in it for 16 sections and ends blindly.
This duct has, on one side, the columnar cells characteristic of
the central duct, on the other the appearance of a Malpighian
body. From its posterior end a small tubule is given off which
extends alongside the duct for five sections then ends blindly.
The entire structure measures 0.24 mm. long by 0.195 mm. wide.
In another Myxine a similar duct arises in one of these bands of
connective tissue, extends posteriorly in it for 24 sections (0.36
mm.) and ends blindly at the side of a structure represented in
figure 38, without connecting with a tubule which extends from
the posterior end of the latter. These structures in the bands of
connective tissue are interpreted as degenerating Malpighian
bodies. Bowman’s capsule is still present, and the tubules-are
connected with this, but the glomerulus is almost entirely gone.

Malpighian body of the pronephros. At least one Malpighian
bodyis always found lying beside the posterior end of the proneph-
ros of Bdellostoma and Myxine. Investigators of the head-
kidney of Myxinoids differ as to what part of the excretory sys-
tem this Malpighian body belongs. W. Miiller’s figure 2 shows
two of them in the pronephros. He failed to state directly

UROGENITAL SYSTEM OF MYXINOIDS 103

whether he thought they belong to the pronephros or to the meso-
nephros. Kirkaldy seems to consider the Malpighian body as
belonging to the head-kidney. Semon (’96) thinks it is the first
Malpighian body of the mesonephros. Spengel (’97) is of the
opinion that this is, in fact, the glomus of the pronephros in Myx-
ine. From his investigation of very young Myxine Maas (97)
concludes that it is the glomus of the pronephros formed by the
‘concentriren’ of the most posterior ‘Gefissnetze’ which surround
the original segmental pronephric tubules. Price (’04, 710) re-
gards this Malpighian body in Bdellostoma as belonging to the
‘pronephros,’ and from embryological study concludes that it
arises by the fusion of glomeruli which are formed in connection
with some of the most posterior original tubules of the pronephros
before they are crowded together by the posterior movement of
the gills. Since, in the embryo, only two or three of the original
tubules which take part in the formation of the head-kidney
have glomeruli, then the definitive pronephros represents the
fusion of not more than two or three glomeruli.

The adult condition of the Malpighian body in Myxine and
Bdellostoma supports the conclusions of Maas and Price in regard
to the manner in which it is formed. The pronephros of both
shows evidence of being the result of fusion of two or three glom-
eruli. The following description is for both Bdellostoma and
Myxine, and any variations which either shows will be noted.

The Malpighian body is always located beside the posterior
half of the pronephros, usually at the extreme posterior end. It
is always imbedded in the connective tissue beside the pronephric
vein and is separated from the pronephros by the sheath of its
Bowman’s capsule and the pericardium, as well as by a more or
less wide strip of the pericardial cavity (fig. 39). Quite fre-
quently the Malpighian body is followed immediately by a sec-
ond, the anterior end of which may lie beside the last few tubules
of the pronephros (fig. 12). Ordinarily, however, this second
Malpighian body is located back of the posterior limits of the
pronephros. The capsules of the two Malpighian bodies shown in
figure 12 are connected by a very narrow duct, the short colum-
nar cells of which do not have as much cytoplasm as those of the

104 JESSE LE ROY CONEL

pronephric tubules and they absorb much stain. The second
Malpighian body is interpreted as being the first Malpighian
body of the mesonephros. It is connected by a tubule to a short
piece of the segmental mesonephric duct which les in the lumen
of the pronephric vein. The vein ends blindly with this piece of
‘the mesonephric duct a few sections posterior to the Malpighian
body. Furthermore, two pronephric tubules, which open into
the capsule of the Malpighian body of the pronephros, extend
into the pronephric vein, unite and enter the piece of mesonephric
duct. Surrounding the base of these tubules, just before they
enter the mesonephric duct, is a small amount of the central
mass. This short piece of duct contains waste particles through-
out its entire extent. The continuous duct of the mesonephros,
in this specimen, begins 5 mm. posterior to this short piece and
there is no connection whatever between them. When there is
but one Malpighian body it usually ends blindly, although the
capsule may be drawn out posteriorly into the very small duct
which ends in the connective tissue.

In shape the Malpighian body of the pronephros of both
Bdellostoma and Myxine is usually an elongated oval, although
it may be almost round or flattened somewhat laterally. In
Myxine one end is, as a rule, more pointed than the other.

The glomerulus of the Malpighian body in Bdellostoma is
comparatively compact and uniform in structure. The surface
is smooth but slightly convoluted, and is covered by the epithelial
lining of Bowman’s capsule. There are lines of division which
separate the glomerulus here and there into lobes (fig. 40), and
in almost every specimen are one or more small cavities, inside
of which are blood corpuscles or blood plasma.

In appearance the glomerulus of the youngest Myxine (no.
18) is very similar to that of Bdellostoma. In the older speci-
mens, however, the lobed condition is more apparent, it is much
less compact and has a more or less shriveled appearance, and
the spaces in the glomerular mass are more numerous and larger.
Webs and strands of connective tissue appear everywhere in the
glomerulus and around the outside of the lining of Bowman’s
capsule. In the oldest Myxine (no. 10) these changes are most

UROGENITAL SYSTEM OF MYXINOIDS 105

advanced (fig. 41). As this figure shows, one large blood sinus
has appeared in the glomerulus. This sinus contains corpuscles
and blood plasma, and extends almost the entire length of the
glomerulus. It has an epithelial lining, outside of which are sev-
eral concentric layers of connective tissue. On the opposite
side of the glomerulus there is a large space with comparatively
few nuclei, but entirely filled with slender fibers of connective
tissue. This space also extends almost the entire length of the
glomerulus. The lining of Bowman’s capsule is an epithelium
surrounded by a broad band of concentric layers of connective
tissue.

In one Bdellostoma and one young Myxine the glomerulus of
the pronephros is double; two distinct glomerular masses are con-
tained in the same Bowman’s capsule. In the Bdellostoma the
capsule is constricted to one-half its width at the point of union
between the two glomerular masses, while in the young Myx-
ine there is but a slight constriction in one side of the capsule
(fig. 42).

In all the pronephroi of both animals, one or more pronephric
tubules open into the cavity of Bowman’s capsule of the Mal-
pighian body. The capsule in every specimen of Bdellostoma is
connected with the pericardial cavity by a more or less long, very
narrow duct (approximately one-half as wide as a pronephric
tubule). In addition to this duct there may be one or more
very small openings through the wall of the capsule which con-
nect the cavity of the latter with the pericardial cavity. The’
capsule of the specimen represented by figure 12 has seven such
openings. In none of the specimens of Bdellostoma are these
openings into the pericardial cavity greater than two or three
one-hundredths of a millimeter in diameter.

Spengel (’97) considers the glomerulus of the pronephros to
be really a glomus because it hangs freely in a cavity which he
found communicated with the pericardial cavity through a very
large aperture; in one specimen the opening extended through
nineteen sections each 30 microns thick, or 0.57 mm. Semon
(97) never saw in his preparations a communication as wide as
Spengel described. Maas (’97) also considers the glomerulus a

106 JESSE LE ROY CONEL

true glomus. In each of his youngest Myxine he found a very
large opening connecting the capsule with the pericardial cavity;
it extended through almost as many sections as the glomus it-
self. But in advanced stages, by a folding of the epithelial wall,
a capsule is formed around the glomus, and only a slit-like com-
munication with the pericardial cavity is left, and even this may
be completely closed. The glomerulus of the youngest Myxine
examined by the writer (no. 18) lies directly exposed to the peri-
cardial cavity through an opening 0.156 by 0.192 mm. and re-
sembles a glomus (fig. 43). The opening in Myxine no. 15, an
adult, measures 0.0195 by 0.105 mm., and that of Myxine no.
10, the oldest specimen, is 0.195 by 0.120 mm.

The glomerulus of the head-kidney is not always as large in
comparison with the glomeruli of the mesonephros as would be
expected if it were formed by the fusion of two or three glomeruli,
as the following measurements will indicate; see opposite page.

The figures 1, 2, 3, 4 in the column under ‘Glomerulus’ repre-
sent the number of the glomerulus, counting that of the head-
kidney as 1; glomeruli 2, 3, and 4 are the first, second and third
glomeruli, respectively, of the mesonephros immediately follow-
ing the glomerulus of the pronephros. All the glomeruli which
lie posterior to the glomerulus of the pronephros are considered
as belonging to the mesonephros. The glomeruli of the latter,
posterior to the most anterior three or four gradually diminish
in size. None of the anterior glomeruli of the mesonephros of
Myxine were sectioned, therefore no measurements of these are
given in the above table. As the table shows, the glomerulus of
the pronephros does not always exceed or even equal in size some
of the most anterior glomeruli of the mesonephros.

As has already been noted, the Malpighian body of the pro-
nephros of one Bdellostoma (fig. 12) is connected by tubules to a
fragment of the segmental duct of the mesonephros, which is en-
tirely disconnected from the continuous part of the duct. No
other case of a communication between the Malpighian body of
the pronephros and the duct of the mesonephros was found in
either Bdellostoma or Myxine. In a young male Bdellostoma
(no. 22), however, the mesonephric duct on each side continues

UROGENITAL SYSTEM OF MYXINOIDS 107

SPECIMEN SIDE GLOMERULUS WIDTH LENGTH
1 0.46 0.78
: 2 0.34 0.75
aeht 3 0.60 1.04
4 0.48 0.92
Bdellostoma no. 4.........
( 1 0.50 0.95
2 0.39 0.65
Bett 3 0.49 1.03
4 0.47 0.785
( 1 0.39 0.66
Right 2 0.4485 0.60
3 0.468 0.66
Bdellostoma no. 6.........
1 0.390 0.675
Left 2 0.4485 0.705
3 0.30 0.4875
1 0.41 0.60
; DZ, O27 0.2925
Bdellostoma no. 10..........] Right 3 0.2925 0. 405
4 0.41 0.60
( 1 0.39 1.10
: i, 0.40 0.30
ia 3 0.40 0.50
4 0.65 0.65
Bdellostoma no. 15........
: 1 0.4485 0.88
: 2 0.39 0.40
ba 3 0.40 0.60
4 0.53 0.84
1 0.41 0.60
2 0.2925 0.45
Bdellostoma no. 16..........| Left 3 0.2995 0.45
4 0.39 0.51
Mirxaime mossy. a ause Jon. s|), Right 1 1.2675 1.305
Miyxitte NO: Pl. .2.s¢2%..+..| Left 1 0.8775 0.975
IMivexame Onl Sees ale Left 1 0.6825 0.84
Mivsxiiie moO sSss-meeee tele Left 1 0.4095 0.348

108 JESSE LE ROY CONEL

to the posterior end of the pronephros, as is shown in figures 1
and 2. When the anterior ends or the ducts of this animal were
sectioned, it was found that the lumen of the right duct ends be-
side the posterior end of the Bowman’s capsule of the Malpighian
body of the pronephros, but there is no communication between
them. Some of the sections of the left duct were scraped off the
slide in this region, hence the duct could not be followed. Im-
mediately posterior to the pronephros the lumen of the right
duct of this animal abruptly enlarges, becoming a cavity which
measures 0.4875 by 0.6240 by 1.335mm. This cavity is almost
entirely filled with a rounded, loose mass of nuclei which re-
sembles a disintegrating glomerulus. This mass is connected
here and there to the lining of the duct by narrow strands of
nuclei, but no blood vessels could be seen in them. The lining of
the duct here does not resemble that of a Bowman’s capsule,
and is composed of short columnar cells like those of the proneph-
ric, tubules. If this be a disintegrating glomerulus, it is dif-
ficult to explain why it should be in the lumen of the mesonephric
duct. Immediately posterior to this enlarged cavity the duct
becomes narrowed to a diameter of 0.117 mm.

Mesonephros

Bdellostoma. Mesonephric ducts. Except in specimen 22, the
mesonephric ducts of the Bdellostomae examined begin’ from
2 to 10 mm. back of the posterior end of the pronephros. Small
strands of tissue, resembling in structure the outer wall of the
duct, extend from the anterior end of the duct toward the pro-
nephros. Sometimes a lumen is present in one of these strands
for a varying, but short, distance. These strands may be the
only trace of pro- or mesonephric elements between the posterior
limit of the pronephros and the anterior end of the ducts, or, in
addition to these, there may be one or more isolated tubules or
traces of glomeruli in this intermediate region.

The anterior ends of the right and left ducts in an individual
are seldom opposite each other. The duct does not start abruptly,
but is always narrowest at the anterior end, and presents the

UROGENITAL SYSTEM OF MYXINOIDS 109

appearance of having at one time extended farther forward.
There is no uniformity in the diameter of the duct at its anterior
end, except that it is always smallest here, varying in width from
a mere thread to 1 mm.

The left duct usually bends abruptly laterad at its anterior
end, until it assumes a position close beside the left postcardinal
vein, and retains this position to the end of the body cavity. The
right ducts bends only slightly laterad at its anterior end to
assume a similar position beside the right postcardinal vein.
The right duct is invariably closer to the dorsal aorta than the
left. .

In adults of the same size, the ducts of the males are lafger
and longer than those of the females. There is not much varia-
tion in the size of the two ducts of a given animal, nor in the ducts
of all the adult animals of the same sex. Each duct is smallest
at its anterior end, and gradually increases to its largest size at
the posterior end of the body cavity, where it is from 1.5 to 2 mm.
wide in females and from 3.5 to 4 mm. in males.

Each duct is flattened dorso-ventrally throughout its entire
length, being most flattened at the posterior end of the body
cavity. The outer surface of the ducts is smooth. When a
duct is stained, cleared and examined under the microscope the
surface appears longitudinally striated, due to the occurrence of
ridges formed in the lumen of the duct by the columnar epithelial
lining.

The ducts lie immediately ventral to the notochord, separated
from the latter by a small cavity which extends the entire length
of the ducts. By cutting the peritoneum along the dorsal body
wall at the sides of each duct, the ducts, together with the post-
cardinals and the dorsal aorta, can easily be removed.

The mesonephric ducts of the adult male are unlike those of
the adult female in some respects. Those of the former are not
only larger, but are longer, by reason of lateral bendings or con-
volutions. Figure 45, a dorsal view, represents the typical ap-
pearance of the male ducts, and figure 46 those of the female.
At their anterior ends the ducts of the male are only slightly con-
voluted, but, beginning about ten somites posterior to the ante-

110 JESSE LE ROY CONEL

rior ends, the convolutions become quite pronounced and regular.
There is but one convolution in each somite; the ducts bend lat-
erad at the interseptal lines and mediad between these lines.
The convolutions continue to the posterior end of the body
cavity, but in the last five or six somites they diminish in extent.
The greater size of the male duct is caused principally by the
fact that its lumen is larger than that of the female. The walls
of the male duct, however, are somewhat coarser than those of
the female.

No such convolutions occur in the ducts of the females. The
ducts bend laterad more or less slightly at the interseptal lines,
but there is no suggestion of the convoluted condition of the
male ducts.

At their posterior ends, the ducts of both males and females
have the same gross structure and appearance. The two ducts
leave the peritoneal cavity at its posterior end, approach each
other and continue a short distance (5 to 10 mm.) along the dor-
sal surface of the genital chamber, then converge sharply. At
the point of convergence the ducts bend ventrad and laterad,
and become abruptly narrowed to very small tubes (figs. 47 and
48). The latter continue posteriorly, bend sharply ventrad at
the posterior end of the cloaca, and open in this region of the
cloaca on a papillary enlargement on a prominent ridge which
extends along the dorsal wall of the genital chamber and cloaca.
The two openings lie alongside, but one is usually chee pos-
terior to the other.

The ducts of young males (fig. 49) are not convoluted at any
place, and resemble in appearance and gross structure those of
adult females.

Histology. Figures 50 and 51 are camera lucida drawings of
transverse sections of a male and female duct, respectively,
taken from the mid-region of the body cavity. The’ section of
the male duct was selected where there is the smallest possible
effect on the internal structure because of convolution. As
the figures show, the ducts consist of an inner epithelium and an
outer envelope of connective tissue.

UROGENITAL SYSTEM OF MYXINOIDS i

The epithelium is composed of columnar cells, and is arranged
in a series of longitudinal folds or ridges. Wax models show that
these ridges branch and anastomose freely, but are always longi-
tudinal and the branching is dichotomous. The two branches
may run parallel to each other for a short distance and then
unite, or may unite with another ridge, or may end without
union to other ridges. A ridge may be only a fraction of a
millimeter long and be entirely unattached to any other ridges.
When free, the ends of the ridges rise gradually from the normal
height of the epithelium.

The ridges are present in all parts of the duct, from the an-
terior to the posterior end, but at the former end, where the duct
is small, they may be only two or three in number (fig. 52). As
the duct becomes larger, the ridges increase in number, and are
most numerous at the posterior end where the duct reaches its
maximum width. The ridges vary in number in a transverse
section in corresponding regions in different adult specimens, as
is indicated by the following table:

cencre eee | ae
Bdellostoma no. 15, female......... 0.546 x 1.0725 20 0.1365
Bdellostoma no. 17, female......... O).ainl sx IL wae 29 0.0780
Bdellostoma no. 16, male.......... 0.780 x 2.4875 26 0.390

There is considerable variation in the height of the ridges in
the same transverse section and in different parts of the same
duct. Figures 50 and 51 show the variation in the same sec-
tion. For a given duct the ridges are lower at the ends than in
the mid-region.

The columnar epithelial cells which form the walls of the duct
are shortest between the ridges. The nucleus is always located
about one-third the length of the cell from the basal membrane.
The cytoplasm is very granular throughout the entire cell body,
the granules being especially numerous and large at the distal
ends of the cells. Along the surface of the distal ends of the
cells are agglutinations of granules which project into the lumen
of the duct and resemble the mass of waste material which is

ba JESSE LE ROY CONEL

seen in the center of the lumen of the duct throughout its entire
length. Toward the distal ends of the cells are numerous ‘small
and large, yellowish, round or oval bodies of homogeneous struc-
ture, which resemble oil droplets. Some of these are minute
granules, while others are as large as the nucleus of the cell.
They are especially numerous and large in the cells on top of the
ridges, and are distributed in no definite manner. Only a few
are found in the cells between ridges. These bodies are prob-
ably what V7. Miller described as yellowish pigment granules.
The larger bodies do not resemble pigment granules, however.

The long, columnar cells are always arranged on the ridges
in the shape of a fan, as illustrated in figure 53. To form a
ridge, the entire layer of epithelial cells bends into the lumen of
the duct, and the connective tissue outside the basal membrane
of the epithelium makes a core which fills the concavity beneath
each ridge (fig. 53).

The ridges are more numerous in the adult male ducts than in
the adult female. They are also higher, but the cells are no
longer than those of the female. The greater height is due to
the fact that the epithelial layer extends farther into the lumen
of the duct in the males. Wide ridges are more numerous in
the male than in the female, some of them being flat on top.
The concavities formed by the infoldings of the epithelial layers
are larger in the male than in the female, and are also filled by a
core of connective tissue.

Maas (’97) has suggested that the mesonephric ducts are not
simply excretory, but they may have a secretory function as
well. The distribution of the blood vessels, the presence of cilia,
the folded epithelium, the enlarged condition of the ducts in
comparison to the small tubules of the Malpighian bodies of the
mesonephros have been mentioned in the literature as indicative
of such a possibility. The many large foldings or ridges of epi-
thelium certainly increase the epithelial surface far beyond what
would seem necessary for excretion alone. The enlarged, con-
voluted condition of the ducts in the males is very peculiar.
The presence of the small and very large, yellowish bodies near

UROGENITAL SYSTEM OF MYXINOIDS 113

' the distal ends of the epithelial cells, especially in the large
cells of the ridges, is suggestive of secretion.

The envelope of connective tissue surrounding the duct con-
sists of two parts, a loose web containing blood vessels and a
more or less compact stratified layer. The loose web lies next
to the basal membrane of the epithelium. It follows closely
the outline of this membrane, and fills the concavities under the
ridges, as shown in figure 53. Some of the blood vessels in this
connective tissue contain giant blood corpuscles,. like those
found in the central mass.

The compact stratified layer consists of fibers arranged in
concentric rings around the duct, and is usually thicker along
the median surface of the duct. The peritoneum lies next to
the stratified layer.

The writer was unable to identify in Bdellostoma the three
layers which W. Miiller describes as forming the connective
tissue envelope around the duct of Myxine. Nowhere is there
a layer that can be called the ‘membrana propria.’ The two
layers observed by® the writer correspond to the ‘adventitia’
and the layer which contains blood vessels, as designated by
Miller.

Malpighian bodies. Price has shown that at one time in the
development of Bdellostoma the mesonephric duct is continuous
with the central duct of the pronephros, but that, later, a short
piece of the duct posterior to the pronephros degenerates, to-
gether with its Malpighian bodies. The amount which degener-
ates is not always the same, hence in the adult there is consider-
able variety in the structure of the anterior ends of the ducts
and in the location of the first few Malpighian bodies of the
mesonephros. The most anterior Malpighian body of the
Mesonephros may be located immediately posterior to the Mal-
pighian body of the headkidney and may be attached to the
latter and to a short, isolated piece of the mesonephric duct
(fig. 12); or it may be completely isolated in the space between
pro- and mesonephros. Not only one, but two or three of the
mesonephric Malpighian bodies may be in the intermediate space,
entirely disconnected from each other and from the mesonephric

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

114 JESSE LE ROY CONEL

duct. Again, the first Malpighian body of the mesonephros
may be located at the anterior end of the duct, and its tubule
may be widened to form the beginning of the duct, or the latter
may extend slightly anterior to the Malpighian body, in which .
case the tubule enters the duct at the side. Two or three Mal-
pighian bodies may be crowded close together around the anterior
end of the duct, but their tubules always enter the lumen of the
duct separately and in consecutive order (fig. 54, a drawing of
the anterior ends of the ducts of Bdellostoma 4). On the left
side Malpighian bodies 1, 2, and 3 are very close together.
The first two are in one somite, 3 occupying the next segment.
When the Malpighian bodies are thus crowded together at the
anterior end of the duct, the arteries which supply them arise
from the aorta at successive points close to the posterior end of
the pronephros, a condition which suggests that these Malpigh-
ian bodies have been pushed back from a more anterior loca-
tion. For example, the point of origin of the artery which sup-
plies the first Malpighian body of the right duct of Bdellostoma
no. 15 is 3.5 mm. anterior to the Malpighian’ body, and the latter
is only 5 mm. posterior to the caudal end of the pronephros.
Except where the Malpighian bodies are occasionally crowded
together at the anterior end of the duct, there is but one in each
somite to somite 60-65. The ducts usually begin in somite
33-35, and the body cavity extends to somite 75-79, hence the
posterior third of the ducts have no Malpighian bodies. Price
learned that in embryos excretory tubules are present in the
most posterior somites, but they later degenerate in the last 19
or 20 segments. The most posterior Malpighian bodies in the
adult show signs of degeneration. They are small, often not
visible to the unaided eye, frequently in a shriveled condition,
and parts of them may be lacking; for example, in one case the
tubule only is‘present. This degeneration is of unequal extent
in different animals and on both sides of the same animal.
Except an occasional one at the anterior end, all the Malpigh-
ian bodies lie along the median side of the duct. There is no
regularity in the orientation of the bodies with reference to the
somites; they may be located at either anterior or posterior side

UROGENITAL SYSTEM OF MYXINOIDS H15

or near the middle of the somite. Those of a side are not sepa-
rated from each other by equal intervals, but, as a rule, are
arranged in pairs, a greater distance occurring between two pairs
than between the two bodies of a pair (figs. 55 and 56). This
paired condition is in some way connected with the arterial
supply, as is shown by figure 56. Each of the Malpighian bodies
represented in this figure is in a separate somite. The two
arteries which supply the two Malpighian bodies of one of these
pairs are usually branches from_a somatic artery, as shown by
figure 56, but sometimes one of the arteries arises directly from
the dorsal aorta, close beside the somatic artery. When a
Malpighian body is not one of a pair, its artery comes directly
from the dorsal aorta. Seldom are the two Malpighian bodies
of corresponding somites on each side of the body opposite each
other, as is shown by figure 55.

The Malpighian bodies and their tubules usually extend ante-
riorly to the point where the tubule empties into the mesonephric
duct. When, however, each Malpighian body in two adjacent
somites is supplied by a branch from the same somatic artery,
the anterior one is doubled back upon its tubule so that the
distal end points posteriad toward the origin of the artery
which supplies it. .

Each Malpighian body has a tubule which enters the meso-
nephric duct. There are two types of these tubules which differ
distinctly and which will be designated as ‘plain’ and ‘compound’
tubules. All the tubules of a given animal are of one type
only.

The plain tubules are composed of very short, columnar cells
which have very little cytoplasm, as shown in figure 57. These
cells are all approximately the same size. Their nuclei stain
much more deeply than either the nuclei of the connective tissue
or those of the mesonephric duct, hence the tubules are very
distinctly differentiated from surrounding tissues. At the
proximal end the cells of the tubule are directly continuous with
those of the mesonephric duct, and at the distal end with the
cells of the single layer of squamous epithelium which lines
Bowman’s capsule. The basal membrane of the mesonephric

116 JESSE LE ROY CONEL

duct is continuous with that of the tubule. The tubules vary
in length, the shortest averaging 0.07 mm., the longest 0.2 mm.
When long, they are more constricted than when short, the out-
side diameter of the narrowest tubule measured being 0.04 mm.
The size of the opening where the tubules enter the duct varies,
but approximates 0.12 mm. in diameter. Figure 58 is a diagram-
matic reconstruction of a plain tubule.

The compound tubule is strikingly different from the plain, as
is shown by figure 59, which is a reconstruction of a Malpighian
body with a tubule of this type. It consists of two parts, a
neck and a trunk. All of the Malpighian bodies of all the speci-
mens examined, except the one described above, have this type
of tubule. The neck is that part of the tubule which joins the
Bowman’s capsule, and in structure and appearance it is exactly
like the plain tubules. It consists of short, columnar cells of
approximately equal height and which have very little cytoplasm.
The nuclei stain much more deeply than those of surrounding
tissues, so that the epithelium of the neck is easily distinguished
from that of the trunk. The cells of the neck gradually decrease
in height as they approach Bowman’s capsule, and are continu-
ous with the cells of the single layer of squamous epithelium which
lines the capsule. The neck is variable in width and length
within narrow limits in different specimens and in different
tubules of the same specimen. An idea of the dimensions may be
had from one specimen: Outside diameter at entrance to trunk of
tubule, 0.35 mm., and at entrance to capsule, 0.078 mm.; length,
0.4mm. The neck is sometimes as much as twice this length,
however. At the proximal end of the neck the epithelial cells
and basal membrane are continuous with the cells and basal
membrane, respectively, of the trunk-of the tubule. The tran-
sition from the cells of the neck to those of the trunk is eradual,
as shown in figure 60.

The trunk of the compound tubule is exactly like the mesoneph-
ric duct in structure. It consists of an epithelium of high colum-
nar cells which are arranged in ridges, and cells and ridges are
of approximately the same height as those of the duct. At the
anterior end of the duct this portion of the tubule is often as
large in diameter as the duct itself. Farther posteriorly, how-

UROGENITAL SYSTEM OF MYXINOIDS 117

ever, where the duct is larger, the trunk of the tubules is only
from one-fourth to one-third as large as the duct. At the
opening of the trunk of the tubule into the duct, the epithelial
cells of both are continuous with each other, including their
basal membranes (fig. 61). When the trunk of the tubule lies
close beside the duct, each has its own envelope of connective
tissue, but the two are bound together by a compact band of
connective tissue arranged in concentric layers. The trunk of
the compound tubules varies somewhat in length, but is not
more than a fraction of a millimeter, approximating 0.75 mm.
The trunk and neck together are about 1.5 mm.long. In some
cases the neck may be longer than the trunk, but it is usually
much shorter.

Waste granules resembling those in the duct are present in
large quantity in the lumen of both the plain and compound
tubules along their entire length. The short columnar cells of
the plain tubules and of the necks of the convoluted tubules
lack the yellowish bodies which are found in the cells of the duct,
but the long columnar cells of the trunk of the compound tubules
have more or less of them.

Each glomerulus almost entirely fills its Bowman’s capsule.
The squamous epithelial lining of the capsule continues around
the glomerular mass. The capsule is usually oval in shape.
The glomeruli are usually largest at the anterior end of the
duct, and diminish in size gradually toward the posterior, the
most posterior being the smallest. For instance, the following
are measurements of glomeruli from different regions of the
duct:

REGION SIDE WIDTH LENGTH
mm, mm.
eens Right 0.640 0.680
NTNSIOIR 4s Reise oS tae Oe Bee ee eee Left 0.600 0.830
Right 0.500 0.630
VINE Cena. epee eee eet ee ee,

eee Left 0.480 |: 0.645
+ ( Right 0.345 0.351

oy a ) g
OSKELIOUA ERT ae et. oh ee Left 0 331 0.405

118 JESSE LE ROY CONEL

The tubules of| the Malpighian bodies, also, are smallest
and shortest at the posterior ends of the duct. In one speci-
men the most posterior trace of a Malpighian body is a com-
pound tubule, the base of which opens into the duct, and the neck
ends blindly. The neck is 0.06 mm. long by 0.105 mm. wide,
and the trunk is 0.15 mm. long by 0.21 mm. wide.

Each Malpighian body is surrounded by a compact stratified
connective tissue band which is arranged in concentric rings and
which is closely applied to the epithelium of the capsule. Out-
side this band of connective tissue there may be a more or less
loose web of connective tissue which envelopes the Malpighian
body and the mesonephric duct. In one section, which shows
the short plain tubule opening into both the duct and the cap-
sule, the broad band of stratified connective tissue surrounding
the duct continues around the tubule and the Bowman’s cap-
sule. Here the tubule is very short and narrow. Figure 62
shows the relation of these tissues when both glomerulus and
the basal portion of the tubule are present in the same section
with the duct. From this figure it will be observed that the
glomerulus and the distal end of the tubule are not entirely sepa-
rated from the mesonephric duct, but that they are bound to the
latter by either a band or a web of connective tissue which
envelopes both duct and Malpighian body.

Myxine

Mesonephric Ducts. The mesonephric ducts of Myxine are
like those of Bdellostoma in so many respects that a detailed
description of them would be needless repetition, hence only
points in which they differ will be noted.

The ducts are longer in Myxine, of course, and are a fracuan
of a millimeter narrower than the female ducts of Bdellostoma.
The ducts of the latter are gray and opaque, while those of
Myxine are approximately of the same color as the flesh and are
somewhat. transparent.

The-anterior ends of the ducts are farther removed from the
pronephros in Myxine, being 10 to 20 mm. posterior to it. No

UROGENITAL SYSTEM OF MYXINOIDS 119

bendings or convolutions were present in the ducts of any of the
specimens. The laterad bending at the interseptal lines is some-
what less than in Bdellostoma, which may be due to the fact
that the somites are larger in Myxine. In the adult Bdellostoma
the somites are approximately 5 mm. wide, while in Myxine
they are about 6.5 mm.

The histology of the ducts of Myxine is practically the same
as those of Bdellostoma. The long columnar cells are arranged
in longitudinal ridges. In the youngest specimen studied
(Myxine no. 18) the ridges are not formed in the same manner
as in Bdellostoma. The basal membrane of the epithelium does
not bend inward, toward the lumen of the duct, at the base of
the ridges, hence no concavities are formed under the latter.
Also, the nuclei of the epithelial cells remain at the same level
around the entire circumference of the duct and turn inward
only very slightly at the base of the ridges. The ridges are
formed solely by the elongation of the epithelial cells. The
longest cells are approximately 0.0675 by 0.0081 mm. The
majority of the nuclei are round, although many are short
ovals. There are approximately fifteen ridges in each duct in
the mid-region of the body.

In all the adult Myxines the ridges in the ducts are more
numerous, shorter and narrower than in Bdellostoma. Their
shape is slightly different from those of the latter animal, and
much more uniform. They are usually narrower in the middle
than at the ends, and never have a wide, flat surface such as
are frequent in Bdellostoma. In one specimen, which has eggs
12 mm. long, the duct is 0.39 by 1.2675 mm., and has 54 ridges,
each approximately 0.039 by 0.117 mm. The duct of another
animal measures, at one place in the mid-region selected at ran-
dom, 0.2925 by 0.975 mm., and has 53 ridges, each approxi-
mately 0.029 by 0.105 mm. The ridges present a finger-like
appearance, as shown in figure 63.

The epithelial ridges in the ducts of adult animals do not
have concavities beneath them, but the nuclei at the base of the
ridges are arranged in a small heap (fig. 63).

120 | JESSE LE ROY CONEL

The nuclei of the epithelial cells in the ducts of Myxine are
much nearer the bases of the cells than in Bdellostoma. Most
of them are round, but some are oval. All the cells have much
cytoplasm, and as a rule they are narrower at the middle than
at the ends.

A very striking difference between the epithelial cells of
Myxine and those of Bdellostoma is the quantity and distribution
of the yellowish bodies. These are present in every ridge in
Myxine, more in some ridges than in others of the same section,
and more in some sections than in others. They are almost en-
tirely confined to the center of the ridge, forming a narrow core
which extends from the nuclei at the base of the cells to the top
of the ridge (fig. 64), but not to the very distal ends of the
cells. At the top of the ridges these yellowish bodies are in
rows, which spread out in the shape of a fan, following the ar-
rangement of the cells. The bodies vary in size from tiny gran-
ules to a diameter exceeding the width of a cell, and large and
small are intermingled in an irregular manner in all parts of
fheicore:

There is much less connective tissue around the mesonephric
ducts and Malpighian bodies in Myxine than in Bdellostoma.
The Malpighian bodies are confined to the anterior two-thirds
of the duct, one in each somite. They are approximately the
same size as those of Bdellostoma, the largest at the anterior
end of the ducts and the smallest toward the posterior. Only
the compound type of tubules were found in Myxine, and these
are usually shorter than the compound tubules of the Malpighian
bodies in Bdellostoma.

2. REPRODUCTIVE SYSTEM
Myxine

Female. The following is a general description of the female
generative apparatus in Myxine. It is not strictly applicable to
any one specimen, for there is much variation within certain
limits. Schreiner (04) has given a very detailed account of the
ovary in the European Myxine, and examination shows that

UROGENITAL SYSTEM OF MYXINOIDS {23

the North-American Myxine does not present any striking
differences.

The single ovary occurs on the right side, and extends from
the region of the gall bladder to the posterior end of the coelomic
cavity, and is approximately (within 2 or 3 cm.) one-half the
entire length of the animal. It is suspended in the body cavity
by a single mesovarium, which is attached along its proximal
margin to the mesentery where the latter joins the dorsal sur-
face of the alimentary canal, to the right of the supra-intestinal
vein. In young animals the mesovarium presents a perfectly
flat surface, but in specimens which have eggs 5 mm. long or
more it becomes folded transversely, being most folded in the
oldest females. The distal margin of the mesovarium does not
take part in this folding, but remains straight, therefore the two
margins are much shorter than the rest of the mesovarium, a
condition which causes the mesovarium to bulge out laterally.

For about 10 mm. at the anterior and posterior ends, the
mesovarium is merely a line along the dorsal surface of the
digestive tract, then increases more or less abruptly to its aver-
age width. At the posterior end it decreases more or less gradu-
ally to a line on the dorsal surface of the alimentary canal, and
ends at the genital pore. Even in the youngest females, where
the mesovarium is simply a flat sheet, its width varies at dif-
ferent points along its course (fig. 65). In successive older
stages these inequalities in width are more and more pronounced,
the widest points being where the eggs are attached. In the
youngest specimens (no. 18) the mesovarium is 2 mm. wide
at the widest points, and in Myxine no. 2, which has eggs 22
mm. long, it is as wide as 30 mm. where the large eggs are at-
tached. Between these large eggs the mesovarium is from 10
to 20 mm. wide. The weight of the eggs doubtless stretches the
mesovarium, for it is drawn out into an elongated strand where
each egg is suspended. Frequently these strands are inter-
twined and even tied in knots. In specimen no. 20 the meso-
variun is 25 to 30 mm. wide and the strands to which the corpora
lutea are attached extend only 3 or 4 mm. beyond the general
width of the mesovarium. In one of the oldest females the

122 JESSE LE ROY CONEL

mesovarium is approximately 15 mm. high along its entire course,
except at the ends, and its distal margin is not folded, but is
comparatively straight. Another old specimen has a mesovarium
which is 20 to 25 mm. wide, and its distal margin is also straight.
It is probable that, after losing the eggs, the distal margin of
the mesovarium tends to become straight again and the exces-
sive width caused by stretching where the eggs were suspended
is taken up by much transverse folding. As stated above, the
distal margin of the mesovarium does not take part in this folding.

The eggs seldom occupy more than the distal third of the mes-
ovarium, never extending entirely to the proximal margin. In
the adult animals they are distributed throughout the distal
half of the mesovarium, even to the outermost margin, but in one
of the young specimens (fig. 65) the most distal millimeter of the
mesovarium is entirely without eggs. The smallest eggs are
always most distal, successively larger stages extending prox-
imally, the largest being most proximal (fig. 66).

The eggs are comparatively evenly distributed along the length
of the mesovarium, except that there are few, if any, in the
most posterior 20 to 30 mm. Eggs larger than 10 mm. long,
when present, usually occur at fairly regular intervals along the
mesovarium from within 2 to 5 cm. of its anterior end to 3 to
10 cm. from the posterior end. Often from three to four or
five large eggs are found together in a cluster, due to the inter-
twining of the long strands of mesovarium by which they are
suspended.

In each female which has normal eggs there are all grada-
tions of sizes of these from mere dots to those 2mm. long. When
eggs longer than 2 mm. are present there are no intermediate
sizes between the 2 mm. eggs and the large ones, and all of the
latter are within 1 or 2 mm. of being of equal size. The largest
eggs found in any of the specimens measure 7 to 8 by 24 to 25 mm.
_ In immature females the smallest eggs are crowded close to-
gether along the entire distal margin of the mesovarium. In
older specimens the smallest eggs are much less numerous;
clusters of them are separated by more or less wide intervals.
Eggs 2 mm. long average approximately one for every 5 to 10

UROGENITAL SYSTEM OF MYXINOIDS 123

mm. of mesovariun in young females, and even less in adults.
The following table shows the number of larger eggs present in a
few individuals:

NUMBER OF SPECIMEN LENGTH OF ANIMAL SIZE OF EGGS NUMBER OF EGGS
cm. mm
16 50 1.5-2.0-x 620- 7.0 37
8 56 3.0-3.5 x 10.0-11.0 35
6 61 3.0-4.0 x 13.0-15.0 45
4 61 OO —Pa0) o< ile (=I). 33
2 58 8.0-8.5 x 19.0-20.0 20
14 58.5 7.0-8.0 x 21.0-22.0 28
11 55 8.0-9.0 x 21.0-22.0 26
3 64 7.0-8.0 x 24.0-25.0 30

None of the eggs are so far advanced as to have hooks at the
ends. .

In shape, the eggs are round until they reach a diameter of
about 1.5 mm., then they begin to elongate, and become oval.
Eggs 2 mm. long ae1to1.5 mm. wide. The eggs are developed
between the two layers of peritoneum which form the meso-
varium, as shown in figure 74. When the eggs begin to assume
the oval shape, the pointed ends project beyond the place of
attachment to the mesovarium, and one end evidently grows more
rapidly than the other for the largest eggs are usually attached
between one end and the equator, leaving the ends free (fig. 67).

Other structures besides eggs may be present in the mes-
ovarium. Specimen no. 20 has 33 empty egg envelopes, the
‘corpora lutea’ (fig. 68). The largest eggs in this animal are
approximately 1 by 1.5 mm. Specimen no. 2 has, besides the
27 large eggs, two corpora lutea, each of which is the same size
as the envelopes around the eggs (8.5 by 20 mm.), and which
has been opened along one side (fig. 69). The corpora lutea in |
Myxine no. 20 are much smaller (4 by 6 mm.) and are shrunken
into a compact mass. Myxine no. 5 has 25 or 30 of these corpora
lutea which are still smaller (2 by 3 mm.) than those of speci-
men no. 20, as shown in figure 70. The largest eggs of specimen
no. 5 are 1.5to2 by 0.5tol mm. Specimen no. 1 has several even

124 JESSE LE ROY CONEL

smaller corpora lutea. The writer is unable to explain what is
the final fate of the corpora lutea, unless they form some of the
small brown oval bodies which will be described later. It seems
improbable that they are completely absorbed. The fact that,
as noted above, there are no intermediate stages between eggs
about 2 mm. long and the large ones, and that also in animals
which have corpora lutea, the eggs present do not exceed 2 mm.,
is interpreted to mean that as soon as some eggs exceed 2 mm.
in length all the other eggs are arrested in development until
the larger ones have matured and have been passed from the
body, and their corpora lutea are well along in the process of
degeneration.

Distributed comparatively uniformly along the entire mes-
ovarium, wherever eggs occur, are numerous brown oval bodies
which measure approximately 0.5 by 1 mm. They are some-
what flattened laterally, and are located proximally to the
smallest eggs. None of these brown bodies are present in the
youngest specimens, but they occur in all adult females, being
most numerous in the older ones. In the mesovaria of some
of the latter, for example specimen no. 9, there are no eggs, but
many of these brown bodies. Since only comparatively a few
eggs become larger than 2 mm., many eggs do not attain com-
plete development, but degenerate. The brown bodies are the
degenerated eggs and their envelopes. Intermediate stages of
degeneration between the brown bodies and the normal eggs occur
occasionally. It is possible that some of the brown bodies repre-
sent degenerated corpora lutea, though none were found whose
structure would indicate this. As shown in figures 71, 72 and
73, representing sections of three stages of these, the mesovarium
envelopes the brown bodies in the same manner as it does the
small eggs (fig. 74), but the walls of the envelope around the
former are much thicker. Also, numerous blood capillaries occur
between the envelope and the former membranes of the egg,
which have been converted into convoluted strands of connec-
tive tissue. ‘The center of the brown bodies is filled with round
nuclei and dark-yellowish granules which may be the remains
of the yolk and which cause the brown color.

UROGENITAL SYSTEM OF MYXINOIDS 125

Along the posterior 25 or 30 mm. the mesovarium of young
animals has a narrow band (0.5 mm. wide) of testis lobes, as
shown in figure 65, but there are no traces of such testis lobes
in any of the nine adult females which have normal eggs. A
few small eggs are occasionally found in the mesovarium proxi-
mad to these testis lobes, but only at the anterior end of the testis
band. The posterior end of the mesovarium in adult females
with normal eggs may contain a few small eggs or brown bodies,
but it is usually without any reproductive elements.

Sections were made of portions of the bands of testis lobes found
in two of the young animals, viz., no. 18, no. 7. Figure 75 is a
transverse section of the band in Myxine no.18. The structure is
similar to that of the young European Myxine as described by
Nansen (87), Cunningham (’87 and ’92), and Schreiner (’05).
The testis band consists of a large mass of stroma cells and
many primitive germ cells which lie among the stroma cells.
The band is attached to the digestive tract by the continuation
of the mesovarium, though here it may perhaps be called more
properly the mesorchium. Here and there, in a transverse
section of the band, is a small follicle formed by a single layer
of stroma cells, inside of which are from four to two or three
dozen spermatogonia. No mitotic figures are present in any of
the spermatogonia. On the contrary, the cells are in a resting
stage, the nucleolus being visible in most of them. The entire
mass is surrounded by the squamous epithelium of the
mesorchium.

Myxine no. 7 is older than no. 18, and its testis lobes are more
advanced in development, as is shown by figure 76. The follicles
are more numerous, are larger, and contain more spermatogonia.
The stroma cells are much less numerous. No mitotic figures
are present, but the chromatin of many of the spermatogonia is
scattered throughout the cell and the nucleolus has disappeared.
The epithelium which surrounds the testicular mass js thicker,
and here and there it turns inward, thus cutting the testis band
into lobes. Small eggs occur along the entire distal margin of the
mesorchium anterior to the testis band. The follicles of neither
no. 18 nor no. 7 contain any spermatozoa. These specimens are

126 JESSE LE ROY CONEL

not sufficiently advanced in development to indicate whether
they will eventually be male or female.

Male. Myxine no. 15, an animal 62 cm. long, has a testis
band 5 mm. wide along the distal margin of the posterior 9.5
em. of the mesorchium. Anterior to this band the mesorchium
is of comparatively uniform width (about 7 mm.) all the way to
the anterior end, and contains along its distal margin numerous
brown bodies (degenerated eggs) but no normal eggs. No brown
bodies, however, are present in the portion of the mesorchitum
which is occupied by the testis band. The mesorchium is not
folded, but is straight and flat (fig. 82). There are no indications
that this animal ever produced large eggs, and it is considered
as an almost mature male. Only about one-half of the follicles
contain cells which show mitotic figures, but no spermatozoa
were found. <A transverse section of the testis band (fig. 77)
shows that, in this specimen, the large follicles are larger than
the largest ones in specimens no. 18 and no. 7, but they range in
size from small to large and are closely crowded together, so
that the stroma cells are limited to narrow strips between the
follicles or between the latter and the mesorchial sheath. AlI-
most every stage of mitosis is represented. Not all the cells of
an individual follicle show mitotic figures, but what figures are
present are approximately in the same stage (fig. 78).

A striking difference between the testis band of Myxine no.
15 and those of specimens no. 18 and no. 7 is the fact that the
single layer of squamous mesorchial epithelium which envelopes
the entire band has been here and there converted into a columnar
epithelium. The long, spindle-shaped cells of the mesorchial
sheath become shortened and arranged in palisade order. These
columnar cells have not entirely surrounded the testis band, but
in places the squamous epithelium is still present aor forms the
sheath of the band.

In two other specimens, no. 12 and no. 13, this process of con-
version of the mesorchial sheath into columnar epithelium has
advanced until the entire testis band is enveloped byit. The
band in these two animals is very different from that of any
other specimen. In the first place, the band extends the entire

UROGENITAL SYSTEM OF MYXINOIDS 127,

length of the mesorchium (fig. 83). Specimen no. 12 has the
general appearance of being older than no. 13. At the anterior
end of the genital fold the width of the mesorchium and the
testis band together is 4 mm., and it increases at once to 5 mm.,
then fluctuates between 4 and 5 mm. to a point about 7 cm.
from the extreme posterior end. At this point the combined
width of the band and the mesorchium increases to 7 mm. and
remains this to the posterior end of the mesorchium. The testis
band is suspended from the distal end of the mesorchium, and
at the anterior end it is 1 mm. wide by 0.5 mm. thick. The
band increases gradually in both width and thickness as it pro-
ceeds posteriorly, and at mid-region it is 2 mm. wide by 0.75
mm. thick. At a point 7 cm. from the posterior end it reaches
its maximum size, 6 mm. wide by 1 mm. thick, and retains these
dimensions to the extreme posterior end, immediately in front
of the genital pore. The testis band of specimen no. 13 is neither
as high nor as thick as that of no. 12, the widest part being 5
mm. Also, it is not as lobulated as the band of no. 12, and it is
yellowish in color instead of reddish as in no. 12. In the latter
the small lobules give a granular appearance to the band, which
is especially pronounced in the posterior region. There is not
the slightest trace of eggs, normal or degenerated, at any place
in the mesorchium of either no. 12 or no. 13. -Myxine no. 12 is
67 cm. and the testis band is 36 cm. long. Specimen no. 13 is
63 cm. long and its testis band measures 35 em.

Transverse sections, cut in all parts of the testis bands of these
two animals, reveal the fact that the bands are of uniform and
peculiar structure. They do not resemble the testis bands of
younger Myxine, nor those of Bdellostoma, as figures 80 and 81
show. The squamous mesorchial epithelium has been completely
converted into the palisade layer of columnar cells. In trans-
verse section the band is cone-shaped, and deep notches in the
sides cut it into triangular lobes, leaving a central core of stroma.
The latter has been entirely converted into fibrous connective
tissue which contains many blood capillaries. Nowhere in the
bands is there the slightest trace of primitive germ cells or fol-
licles. Figure 81, a transverse section from the posterior end

128 JESSE LE ROY CONEL

of the band. of Myxine no. 12, shows another peculiar condition.
At the base of the band, in a pocket formed between the lobes,
there is a tangled skein of columnar epithelium which is of the
same width as the columnar epithelium around the band. Here
and there this skein is continuous with the epithelium which
envelopes the band. It extends through all the sections cut
in the posterior region of the testis band of Myxine no. 12, but
occurs nowhere else. The writer has been unable to explain
what this tissue may be.

Myxine no. 12 and no. 13 are old animals, as is indicated by
their general conditions, viz., the thick, hard skin, the reddish,
coarse fibers of the muscular tissue, the enlarged, coarse, dark-
brown liver, the great diameter of the body, etc. The peculiar
condition of their testis, bands is interpreted as due to their
having become’ completely sterile with old age. Myxine no. 18
and no. 7, young, immature males, have many primitive germ
cells, a few follicles and very little connective tissue in the testis
band. Myxine no. 15, and adult male, has few germ cells, many
follicles, and much connective tissue around and between the
follicles in the testis lobes. In places the squamous epithelial
covering of the band has been converted into a columnar epi-
thelium, but sufficient squamous epithelium remains to permit
easy rupture of the follicles when they are ripe. The band is
notched only slightly here and there. In specimens no. 12 and
no. 13 the germ cells and follicles have entirely disappeared,
and the bands are completely filled with fibrous connective tissue
and blood capillaries, and all the squamous mesorchial sheath
has been converted into a columnar epithelium. The testis
bands are deeply notched in all parts so that they are cut up
into lobes. The testis bands in these two animals have lost. their
power of functioning and are completely sterile.

Bdellostoma

Female. The generative organs of Bdellostoma closely re-
semble those of Myxine in many respects. The ovary is single,
occurring on the right side only, and is suspended in the body

UROGENITAL SYSTEM OF MYXINOIDS 129

cavity from a mesovarium which extends from the region of the
gall bladder to the posterior end of the body cavity, a distance
which is approximately one-half the entire length of the body.
Unlike Myxine, however, the proximal margin of the mesovarium
is always attached to the mesentery about one-third the width
of the latter from the alimentary canal. The mesentery and
mesovarium are more delicate than in Myxine.

In the females which have eggs 2 mm. long or longer, the
mesovarium is approximately 10 to 15 mm. wide. Where the
large eggs are attached, the mesovarium is stretched into strands
which are 25 to 30 mm. long, and between the eggs it is 10 to 20
mm. wide.

The distribution of the eggs is very similar to that in Myxine.
There are all gradations of sizes of young eggs from mere dots to
those 2 mm. long in adult females, but there are no intermediate
sizes between the latter and any larger eggs or corpora lutea that
may be present.

The following table will give some conception in regard to the
number of large eggs which may occur in an adult female:

NUMBER OF SPECIMEN SIZE OF EGGS NUMBER OF EGGS
mim.
25 IWAl.® x¢ Be Ol 77
17 2.5-3.0 x 10.0-11.0 20
1 3.0-3.25 x 12.0-13.0 28
23 3.0-8.5 x 13.0-14.0 10
24 3.0-3.5 x 14.0-15.0 10
4 3.0-3.5 x 14.0-15.0 23
15 9.0-6.0 x 20.0-21.0 31

Two of the specimens of Bdellostoma contain corpora lutea,
one having eleven, the other twenty-four, and all show signs of
degeneration. Small brown ovals, representing degenerated
eggs, are scattered irregularly among the eggs.

In all the females, the eggs extend to within 1 or 2 em. of the
posterior end of the mesovarium (fig. 84), and there are sometimes
a few very small eggs in this most posterior part. No testis

JOURNAL OF MORPHOLOGY, VOL. 29, NO. J

130 JESSE LE ROY CONEL

lobes are present in any part of the mesovarium of any of the
females, not even in the posterior region.

Male. No female elements occur in any of the males, and
none of the mesorchia presents the appearance of ever having
contained eggs. The general structure and appearance of the
mesorchium js very similar in all the specimens. It extends
from the region of the gall bladder to the caudal end of the body
cavity, and is attached to the mesentery along a line which is
about one-third the width of the latter from the alimentary
canal (fig. 85). At the anterior end the mesorchium is merely a
line along the dorsal surface of the digestive tract. At a point
opposite the posterior end of the gall-bladder it leaves the ali-
mentary canal and gradually ascends in the mesentery to its
definitive position. Immediately behind the gall-bladder it is
from 1 to 3 mm. wide, and retains this width to the testis lobes
at the posterior end, usually decreasing slightly in width just
before reaching the lobes. In most of the males the mesorchium,
which is very delicate, contains no genital elements in the ante-
rior and mid-regions, but in some individuals very small testis
lobes are scattered along the distal margin of the mesorchium
from the extreme anterior end to the band of lobes at the posterior
end. One male has a single lobe about 0.5 mm. in diameter at
the anterior end of the mesorchium and no others excepting
those in the testis band at the posterior end. Other specimens
have two or three such small lobes, still others a dozen or more,
while one animal has so many that they look as though at one
time they formed a continuous narrow band along the distal
margin of the mesorchium.

The large mass of testis lobes is confined to the posterior end
of the mesorchium, and consists of a great many lobules closely
crowded together into a band, which varies in length, in the
seven males examined, from 3 to 8 em. and in width from 2 to
7mm. There is no correlation between the length of the testis
band and the length of the animal, as is shown by the following
table:

UROGENITAL SYSTEM OF MYXINOIDS esi)

TESTIS BAND
SPECIMEN NUMBER LENGTH
Width Length
cm. mm. cm
6 33.0 2 (aye)
10 36.0 2 2.0
21 36.5 2 6.0
10 36.5 5 3.5
1 38.5 a) 4.5
2 40.5 a 6.5
8 42.0 5 7 oh

In the longer, i.e., the older, animals the testis band is wider
and thicker than in the younger males.

The testis bands are folded more or less in the young males
and considerably in the older animals. In all, the bands have a
very granular appearance (fig. 85). The bands in the younger
males are light gray in color, and yellowish in older animals.

Transverse sections of the testis bands show that in minute
structure they are very similar to those of Myxine. Single germ
cells and follicles of all sizes, from very small to large, are pres-
ent. In a single section all stages of mitotic figures may occur,
and many of the follicles contain spermatozoa (fig. 79). Each
follicle has for its wall a single row of stroma cells, arranged end
to end, and outside this are two or more concentric layers of
fibrous connective tissue. Capillaries occur here and there in
the connective tissue and stroma between the follicles. The
primitive germ cells are limited to the distal end of the band,
and here the follicles are smaller, their walls are not so promi-
nent and there is less connective tissue than in the proximal
part, where the large follicles are located. The entire band is
covered by a single layer of squamous epithelium which is a
continuation of that of the mesorchium. In no place is there
columnar epithelium around the testis band as is described for
Myxine.

Cunningham (’87) and Nansen (’87) have advanced the theory
that Myxine is a protandric hermaphrodite, functioning as a
male when young (28 to 32 em. long) and as a female when older

132 JESSE LE ROY CONEL

(32 to 35 em.). Nansen thinks the change in sex occurs when
the animal reaches a body length of about 32 or 33 em. Out of
hundreds of specimens examined by each of these investigators,
only a few males were found (Cunningham 8, Nansen ‘very
few’) and most of these were immature. Nansen regards the
males as merely transformed hermaphrodites and found all
transition stages between males and common hermaphrodites.
Cunningham found that in ‘‘nearly all specimens with very im-
mature eggs the posterior portion of the sexual organ had the
same structure as the testis,’ and that ‘‘in all specimens with
well-developed ovarian eggs . . . . with one exception, no
testicular portion was present in the sexual organs,” then he
concluded ‘‘that in the young state the females are nearly, but
not quite always hermaphrodite, and that the testicular portion
normally disappears as the eggs become more mature.’ Nan-
sen states that “‘on opening large specimens of Myxine, we gen-
erally find well developed ova in their sexual organs. If we,
however, take smaller specimens, of about 28 to 32 em. in length,
and examine their sexual organs, we generally find that the
anterior portion is but slightly prominent, and contains very
small and young ova, whilst the posterior portion is often very
broad and prominent, is lobate, and has a distinct whitish colour
along its margin, and has, in all respects, the appearance that
we would expect to find in a testis; and that it really is.” He
concludes that ‘“Myxine is generally, or always (?), in its young
state, a male; whilst at a more advanced age it becomes trans-
formed into a female. Indeed, I have not yet found a single
female that did not show traces of the early male stage.”
Schreiner found only 19 pure males out of 2500 specimens
examined, and they were seldom over 33 cm. long, the majority
of them being 30 to 31 em. In a quite preponderating number
of individuals which were longer than 33 cm. there was a more
or less well-developed ovary and the testis part was sterile, and
in the males there was a more or less well-developed testis and
an abnormal or rudimentary ovary. In the females, the ovary
was well-developed and the testis part was usually rudimentary
or occasionally completely sterile. The testis was always ab-

UROGENITAL SYSTEM OF MYXINOIDS be

normal in both young and old females. In addition to func-
tional males and females, Schreiner found individuals in which
both testis and ovary were degenerated, and these he classed as
sterile animals. He also found normal females 22 em. long and
less, and states that, “‘lisst sich das hiufige Vorkommen von
jungen Weibchen unméglich mit der Annahme eines protan-
drischen Hermaphroditismus bei diesem ‘Tiere vereinigen.’’
Schreiner believes that Myxine is dioecious.

It is well known that Bdellostoma is an animal ‘of separate
sexes. The fifteen adult females examined by the writer have no
trace of testis lobes in any part of the mesovarium, and no
female elements occur in the mesorchium of any of the eight
adult males. The females range in length of body from 34 to
40 cm., and the males from 36 to 42 cm. That is to say, in this
particular lot of animals some of the functional males are larger
than the adult females, hence it is certain that Bdellostoma is
not a protandric hermaphrodite. It is improbable, to say the
least, that of two animals so closely related as Bdellostoma and
Myxine, the one should have normal, separate sexes while the
other should possess such a peculiar method of reproduction as
protandric hermaphroditism.

Furthermore, as Dean (’99) has suggested, the occurrence of
large males would also discredit the theory that Myxine is a pro-
tandric hermaphrodite. Myxine no. 15, described above,- is
undoubtedly a normal male, in which the only female sexual
products are small, completely degenerated eggs, and specimens
no. 12 and no. 13 are males which have become sterile with age
and which have no female elements whatever. Myxine no. 15
is 62 cm. long, no. 12 is 67 cm., and no. 13 is 63 cm. The
average length of the females with large eggs, from 18 to 25 mm.
long, is 59 em., the longest being 64 em. Here, then, we have
one normal and two sterile males which are longer than the
average female with large eggs. In view of these facts, it seems
impossible that Myxine can be a protandric hermaphrodite.

134 JESSE LE ROY CONEL

SUMMARY

1. A central duct is present in the pronephros of both Bdello-
stoma and the North American Myxine, but it is in a state of
degeneration in both animals. This degeneration is more ad-
vanced in Myxine than in Bdellostoma, so that it includes the
inner ends of the pronephric tubules and all parts of some of the
largest tubules.

2. The ‘central mass,’ which lies in the pronephric vein, is not
a series of glomeruli, but represents the disintegrated central
duct (including the inner ends of tubules in Myxine).

3. The Malpighian body of the pronephros in both Bdellos-
toma and Myxine is located at the posterior end of the pro-
nephros, and in appearance and structure closely resembles the
Malpighian bodies of the mesonephros. It is formed by the
fusion of two or more glomeruli.

4. The glomerulus of the pronephros in young Myxinoids is
exposed to the pericardial cavity through a large opening, thus
resembling a glomus. This opening becomes constricted to a.
small tubule in adult animals.

5. The large vein which extends along the base of each pro-
nephros communicates with the lumen of the central duct through
large natural openings. The pronephric tubules connect the
lumen of the duct with the pericardial cavity, and the latter
opens into the peritoneal cavity through the large pericardo-
peritoneal foramen, while the body cavity opens into the. cloaca
through the genital pore. Thus, the vascular system is in com-
munication with the exterior of the body.

6. The morphology of the pronephros does not reveal any
positive indications as to its function. The granular coagulum
in the tubules and duct suggests excretion. This question can
probably be determined only by physiological methods.

7. The tubules of the pronephroi of adult Bdellostoma are
approximately the same diameter, while those of Myxine vary
in size.

8. Each tubule in the pronephros does not represent an
original pronephric tubule.

UROGENITAL SYSTEM OF MYXINOIDS 35

9. The mesonephric ducts of Myxinoids probably possess. a
secretory as well as an excretory function, as is suggested by the
long epithelial cells, the increased surface of these by ridges, the
large granules at the distal ends of the cells, and the yellowish
bodies in the cells. Also, isolated pieces of the duct contain
‘waste particles like those present in all parts of the continuous
portion. of the duct.

10. The mesonephric ducts of adult male Bdellostomae are
larger than thosé of adult females, and the epithelial ridges
within them are larger.

11. The mesonephric ducts of Myxinoids open separately
into the cloaca.

12. The tubules of the mesonephric Malpighian bodies in
Bdellostoma are structurally of two types.

13. When some eggs in the ovary of Myxinoids attain a size
exceeding about 2 mm. in length, all the smaller eggs are ar-
rested in growth until the large eggs reach maturity and have
been passed from the body. :

14. Many of the small, young eggs in Myxinoids degenerate,
forming the ‘brown bodies.’

15. When a mature egg passes from the ovary it leaves at-
tached to the mesovarium a ‘corpus luteum,’ composed of the
outer envelope of mesovarium which surrounded the egg. The
corpora Jutea degenerate.

16. After the testis of old males ceases to function, the peri-
toneal epithelium which covers the testicular band becomes
changed from squamous to columnar; the empty testicular fol-
licles completely disappear, and the band becomes converted
into a mass of connective tissue penetrated by blood vessels.

17. Neither Bdellostoma nor Myxine is a protandric her-
maphrodite.

18. The urogenital system of the North American Myxine
does not present any specific differences from that of the Euro-
pean animal. On the other hand the great difference in size of
mature individuals from the two sides of the Atlantic would
appear to support the distinctness of M. limosa of Girard from
the M. glutinosa of Linneaus.

136 JESSE LE ROY CONEL

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stitut zu Wiirzburg, Bd. 2; pp. 167-509.

SPENGEL, J. W. 1897a Die Excretionsorgane von Myxine. Anat. Anz., Bd.
13; pp. 49-60. :

1897 b Semon’s Schilderung des Mesonephros von Myxine. Anat.
Anz., Bd. 13; pp. 211-216.

138 JESSE LE ROY CONEL

Weser, Max 1887 Erwiderung an Herrn Cunningham. Zool. Anz., Bd. 10,
no. 253; p. 318-321. ;

Wetpon, W.F. R. 1884 On the headkidney of Bdellostoma, with a suggestion
as to the origin of the suprarenal bodies. Quart. Journ. Micr. Sci.,
vol. 24; pp. 171-182. ;

Worruineton, Jutia 1905 Contribution to our knowledge of the Myxinoids.
Amer. Natural., vol. 39; pp. 625-663.

UROGENITAL SYSTEM OF MYXINOIDS

ABBREVIATIONS

a, dorsal aorta

ac, anterior cardinal vein

al, alimentary canal

an, anus

au, auricle

b, Bowman’s capsule

be, trunk of compound tubule

bm, basal membrane

bs, blood sinus

c, connective tissue

cb, band of connective tissue

cd, central duct

ce, columnar epithelium

cl, corpora lutea

clo, cloaca

cm, central mass

co, blood corpuscle

cp, common portal vein

d, distal margin of mesovarium or
mesorchium

dc, ductus Cuvieri

dm, degenerated Malpighian body

do, degenerated ova, ‘brown bodies’

e, connective tissue envelope

eb, epithelium of base of compound
tubule of mesonephros

el, epithelium of plain mesonephric
tubule

em, epithelium of mesonephric duct

en, epithelium of neck of compound
mesonephric tubule

eo, endothelium

ep, epithelium

f, funnel-shaped mouth of pronephric
tubule

fl, testicular follicle

g, glomerulus

gb, gall bladder

gc, giant blood corpuscle

gp, process composed of granules

7, intertubular space

liv, liver

lp, left posteardinal vein

m, Malpighian body of mesonephros

md, mesonephric duct

mi, mesoderm of peritoneum

mn, mesonephros .

mp, Malpighian body of pronephros

mr, mesorchium

ms, mMesovarium

mt, tubule of Malpighian body

n, nucleus

ne, neck of compound mesonephric
tubule

nu, nuclear mass

0, ovary

op, opening of central duct into pro-
nephric vein

ov, Ova

p, plain mesonephric tubule

pe, pericardium

pec, pericardial cavity

pf, pericardo-peritoneal foramen

pg, primitive germ cell

ph, portal heart

pn, pronephros

pnr, pronephros

pt, epithelium of peritoneum

pv, pronephric vein

ra, renal artery

rac, right anterior cardinal vein

rp, right posteardinal vein

rpv, right pronephric vein

s, stoma cells

sa, somatic artery

sc, skein of columnar epithelium

se, Squamous epithelium

st, supra-intestinal vein

so, somite

ss, sheath of stroma cells around testic-
ular follicle

st, septum transversum

t, pronephric tubule

tb, testis band

tu, mesonephric tubule

v, blood vessel

w, waste granules

y, yellowish granules

z, pericardial attachment to dorsal
aorta and alimentary canal.

PLATE 1

EXPLANATION OF FIGURES

1 Right pronephros of Bdellostoma no. 6, showing its position in the pericar-
dial cavity. Natural size.

2 Left pronephros of Bdellostoma no. 6, showing position in the pericardial
cavity. Natural size.

3 Right pronephros of Myxine no. 5, showing position in the pericardial
cavity. Natural size.

4 Left pronephros of Myxine no. 5, showing position in the pericardial
Cavity. X15.

5 Transverse section through the right pronephros of Bdellostoma no. 6.
Camera, X 25.

7 Left pronephros of Bdellostoma no. 16. X 4.

8 Left pronephros of Bdellostoma no. 18. X 4.

9 Left pronephros of Bdellostoma no. 7. X 4.

10 Right pronephros of Bdellostoma no. 16. X 4.

11 Right pronephros of Bdellostoma no. 18. X 4.

140

UROGENITAL SYSTEM OF MYXINOIDS
JESSE LE ROY CONEL

PLATE 1

ETE : liv = au

141

PLATE 2

EXPLANATION OF FIGURES

lla Transverse section of the right pronephros of Bdellostoma no. 10, illus-
trating the three-sided shape.

12 Millimeter paper reconstruction of the right pronephros of Bdellostoma
no.15. X 25.

13. Pronephric tubule with funnel-shaped mouth.

14 Pronephric tubules in longitudinal and transverse section. Bdellostoma
no. 1d.

15 Transverse section through two pronephric tubules showing relation of
the vascular endothelium to the tubules when a blood sinus occupies the space
between the tubules. Bdellostoma no. 15.

PLATE 2

\g » & y a
log BN, ia (/

lS — ox
‘Srnt LUE,

re OD ppl een

CQ veel aed OTL 0 (BTC Y eal

UROGENITAL SYSTEM OF MYXINOIDS

JESSE LE ROY CONEL

143

PLATE 3

EXPLANATION OF FIGURES

16 Enlarged drawing of columnar epithelial cells of a pronephric tubule.
Bdellostoma no. 15.

17. Transverse section through pronephros of Bdellostoma no. 10, showing
the endothelium of the pronephric vein continuing around the central mass.

18 Transverse section through the central mass. Bdellostoma no. 15.

19 Enlarged drawing of the central mass. Bdellostoma no. 15.

20 Transverse section through pronephros of Bdellostoma no. 15, showing
communication between the central duct and the pronephric vein, with nuclear
mass in the opening; also shows pronephric vein opening into the space between
the tubules, thus making a blood sinus. Not all the pronephric tubules are in-
cluded in the drawing.

21 Transverse section in another part of pronephros of Bdellostoma no. 15,
which also shows the central duct communicating with the pronephric vein and
the opening filled with the nuclear mass. Not all of the tubules are shown.

22 Transverse section through pronephros of Bdellostoma no. 6, showing the
central duct in communication with the pronephric vein through a large opening
which is filled with a nuclear mass.

23 Transverse section through a pronephric tubule of Myxine no. 10, showing
connective tissue surrounding the epithelium.

144

UROGENITAL SYSTEM OF MYXINOIDS

PLATE 3
JESSE LE ROY CONEL

Oe sWersren
CEPA

tS) Pon af
ZS pakke> Hi ‘dus
7h ge

145

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

PLATE 4

EXPLANATION OF FIGURES

24 ‘Transverse section through a pronephric tubule of Myxine no. 11, showing
connective tissue.

25 Section through some tubules of pronephros of Myxine no. 15, showing the
large amount of connective tissue around the tubules.

26 Transverse section through a pronephric tubule of Myxine no. 10, showing
blood sinus around the tubule.

27 ‘Transverse section through some tubules of pronephros of Myxine no.
10, showing difference in size of the tubules.

28 Transverse section through pronephros of Myxine no. 11, showing the
central duct in the central mass.

29 Transverse section through pronephros of Myxine no. 11, showing central
duct in communication with the pronephric vein. Camera lucida, x 50.

146

PLAIE 4

UROGENITAL SYSTEM OF MYXINOIDS

JESSE LE ROY CONEL

_unnTSONg

3

es

SOT

147

PLATE 5

EXPLANATION OF FIGURES

30 Longitudinal section through the central duct in pronephros of Myxine
no. 11. Camera lucida, X 50.

31 Longitudinal section through the central duct of-one of the youngest
specimens, Myxine no. 18. Camera, X 90. ae

32 Transverse section through pronephros of Myxine no. 10, showing the
central duct. Not all the tubules are included in the sketch. Camera lucida,
x 30.

33 Transverse section through pronephros of Myxine no. 11, showing the
central duct with its columnar walls intact. Camera lucida, < 50.

34 Transverse section through pronephros of one of the youngest specimens.
Myxine no. 18, showing the central mass. Camera lucida, X 50.

35 Longitudinal section through the central mass in pronephros of Myxine
no. 11. Camera lucida, X 90.

148

UROGENITAL SYSTEM OF MYXINOIDS
JESSE LE ROY CONEL

eZ

Bru ie =

EXE
(| Leh gs

Oger” z
oS lbiieN
SZ ast TCEANANSS

KS

3 // STAD
N Se

149

PLATE 5

PLATE 6

EXPLANATION OF FIGURES

36 Section pronephros of Myxine no. 15 which shows a broad band of connec-
tive tissue extending from the base of the tubules into the pronephric vein.
Camera, X 50.

37 Transverse section through a degenerated Malpighian body immediately
posterior to the left pronephros Myxine no. 15. Camera lucida, X 90.

38 Transverse section through a degenerated Malpighian body immediately
posterior to the left pronephros of Myxine no. 11, with a blind tubule beside it.
Camera, X 90.

39 Transverse section through pronephros of Bdellostoma no. 15, showing
Bowman’s capsule of the Malpighian body opening into the pericardial cavity.
Camera lucida, x 50.

40 Transverse section through the Malpighian body of the left pronephros of
Bdellostoma no. 16, showing lobulated structure of the glomerulus and the open-
ing of Bowman’s capsule into the pericardial cavity. Camera, X 90.

UROGENITAL SYSTEM OF MYXINOIDS

PLATE 6
JESSE LE ROY CONEL

— es
ABS
SC!

151

PLATE 7

EXPLANATION OF FIGURES

41 Section through the Malpighian body of one of the oldest specimens
(Myxine no. 10), showing degeneration of the glomerulus. Camera lucida, X
19.

42 Section through the Malpighian body of pronephros of a young Myxine
(no. 18), showing double glomerulus. Camera lucida x 50.

43 Section through Malpighian body of pronephros of a young Myxine (no.
18), showing the glomerulus exposed to the pericardial cavity through a large
opening and resembling a glomus. Camera lucida, 50.

44 Transverse section through mesonephros of Bdellostoma no. 17, cut in
mid-region of body cavity, showing relation of the ducts to blood vessels and
peritoneum.

45 Dorsal view of the excretory system of Bdellostoma no. 16. One-half
natural size. Male.

46 Dorsal view of the excretory system of Bdellostoma no. 15. One-half
natural size. Female.

47 Dorsal view of posterior ends of mesonephric ducts of Bdellostoma no.
16. Natural size.

48 Side view of posterior end of left mesonephric duct of Bdellostoma no 16.
Natural size.

—

UROGENITAL SYSTEM OF MYXINOIDS PLATE 7
JESSE LE ROY CONEL

rpv a

. ATS I ays os m1
Delhi (OBS oe
SN) SOT
Shes < (= = SSiy
np ONS \ \ \ SS nt

PLATE 8

EXPLANATION OF FIGURES

49 Ventral view of excretory system of a young male, Bdellostoma no. 6.
One-half natural size.

50 Transverse section through the mesonephric duct of an adult male, Bdell-
ostoma no. 16, cut in the mid-region of the body cavity. Camera lucida, X 19.

51 Transverse section through the mesonephric duct of an adult female,
Bdellostoma no. 15, cut in the mid-region of the body cavity. Camera lucida,
a9:

52 Transverse section through the anterior end of a mesonephric duct of
Bdellostoma no. 6, X 90.

53 Enlarged sketch of a ridge in the epithelial lining of a mesonephric duct.
Bdellostoma.

54 Enlarged sketch of the anterior ends of the mesonephric ducts of Bdello-
stoma no. 4, mounted in damar.

55 Enlarged veneral view of the mesonephric ducts of Bdellostoma no. 8,
showing location of the Malpighian bodies with reference to the somites.

56 Enlarged sketch of mesonephric ducts of Bdellostoma no. 16 showing
the distribution of the arteries to the Malpighian bodies.

57 Longitudinal section through the tubule of a Malpighian body of the
mesonephros, Bdellostoma no. 17. ‘Plain’ type of tubule. Camera lucida, X
90.

154

UROGENITAL SYSTEM OF MYXINOIDS PLATE 8
JESSE LE ROY CONEL .

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=

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j
y iy

=
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a

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PLATE 9

EXPLANATION OF FIGURES

58 Reconstruction of a ‘plain’ mesonephric tubule of Bdellostoma; diagram-
matic.

59 Diagrammatic reconstruction of a ‘compound’ mesonephric tubule of
Bdellostoma.

60 Sketch showing transition between the cells of the neck and those of the
trunk in a ‘compound’ tubule. X 250.

61 Transverse section of a ‘compound’ tubule showing opening of the trunk
into the mesonephric duct. Camera, X 50.

62 Transverse section through mesonephric duct of Bdellostoma no. 15, show-
ing a Malpighian body and its tubule. Camera lucida, x 30.

63 Transverse section through mesonephric duct of Myxine no. 12. Camera
lucida, X 50.

64 Enlarged sketch of epithelial ridges in mesonephric duct of Myxine no. 12,
showing core of yellowish granules.

65 Sketch of ovary of one of the youngest specimens of Myxine (no. 18).
Natural size.

PLATE 9

UROGENITAL SYSTEM OF MYXINOIDS

JESSE LE ROY CONEL

vu rep)

: un
is MiMNGGRMEG RU AGUsRRUGNA PEGE THOM CUUERENN AL]
pee NAMM tere eebaoae ce

Theis

Deer

(wy

PLATE 10

EXPLANATION OF FIGURES

66 Enlarged portion of ovary of an adult Myxine (no. 16), showing distribu-
tion of eggs. XX 2.

67 Sketch of large egg in Myxine no. 2. Natural size.

68 Portion of mesovarium containing ‘corpora lutea.’ Myxine no. 20. Nat-
ural size.

69 A large corpus luteum from Myxine no. 2. Natural size.

70 Small corporea lutea from Myxine no. 5. Natural size.

71, 72, and 73 Sections of ‘brown bodies’ from Myxine showing three stages
in the degeneration of eggs. Camera lucida, X 30.

74 Section through small eggs from Myxine no. 8. Camera lucida, X 30.

UROGENITAL SYSTEM OF MYXINOIDS
JESSE LE ROY CONEL

PLATE 10

PLATE 11

EXPLANATION OF FIGURES

75 Transverse section through the testis band at the posterior end of the
mesovarium of a young Myxine (no. 18). Camera lucida, X 50.

76 Transverse section through the testis band at the posterior end of the
mesovarium of an older, but immature Myxine (no. 7). Camera lucida, X 30.

77 Transverse section through the testis band of Myxine no. 15, a normal
male. Camera lucida, < 50.

78 Enlarged sketch of a transverse section through a follicle in the testis of
Myxine showing the spermatogonia in the metaphase stage.

79 Transverse section through a follicle in the testis band of Bdellostoma no.
7, showing spermatozoa.

80 Transverse section through the anterior region of the testis band of Myx-
ine no. 12. Camera lucida, * 30.

81 Sketch of a portion of transverse section through the posterior region of
the testis band in Myxine no. 12. Camera lucida, X 30.

160

UROGENITAL SYSTEM OF MYXINOIDS
JESSE LE ROY CONEL

PLATE 11

161

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163

STUDIES ON THE SYRINX OF GALLUS DOMESTICUS

JAY ARTHUR MYERS

Department of Anatomy, University of Minnesota

EIGHTEEN FIGURES

CONTENTS

ELS Se DS oa ei Abe ee oe Se hea tee 165
RENDITIONS ashe sed a Gat Bebe 6 en ano nee ces oo Sane aa 167
fee naOHny Or TNS LOUlh SVHNK........ 0... bs ase sdeeereeer etree eae 167
Pen ee COS eNEGHOTTINT EAS Oe /5. 5. 95 ax. avave 2a A A ono ee 167
Be Chena RAINE WOT Kens oc) <0 y2)2-5 «0 4's Ae ene ss ae 168
b. Vibrating membranes........... 4 A se em eee 172
@s. MUSOU TITRE, Se Ae 2 ie Ae een ai cee leet Ali BO iss teseeg es 174
deeb GIereEnCEs... .)).. 020.62... 0 anes. RAE tier 1 175
amy CRC COP Gy MEISE ROE: 6) 2.502) 2° 025s wi. « ic 2.6 Slap ge bin dachie aepeee ee 176
Lo, LD GRAEIOTINSN, 2.2 RS oR es ee eer ane eaniree Ae as 179
HPVINICOUS pT EAT Gk see yse a. ox vis. <0s eye eo eee 181
Pe GaniilacinOuseskeletOMes 25.5: 52 ss .4> Pas ae eee eer 184
SSU DUN COSAtE a eeins fate. basa ~ Oss 3 os Hh St ees. See 189
Al. IMMMS CONE AINE. Coie Bate dog 6 20a eee ee io. sn oon oaras noe 190
Peiueresri ll acimous MeMbPrANES.......... -..,-- > -cneeeeee soe eee 191
Ga pubematy Of Gevelopment...............-. sete se ene ee 192
EE ROCHE UOMMERIIC UOLISe 15) oe ial). kt... as. sce SM eo eee 195
TL T DISS SE ARE RS | a ne ne een | eae 199
PP VEUTENSicee VS PE ti Do tA ee 199
Ls PTE, PUTED GIL Sees oiR aia 2 0.1 ee hgh Zr 200
PIDGIN Se ESR Ee? > os LS ae a eas | eee 201

INTRODUCTION

The songs of birds have served to inspire various classes of
people for ages, but not until the last three or four centuries
do we have any record of scientists becoming interested in them
to the extent of studying the organs concerned in their pro-
duction.

Competent authorities, such as Duvernoy, Cuvier, Johannes
Miiller, and others, early observed that birds possess two larynges

165

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

166 JAY ARTHUR MYERS

—an upper and a lower. From their observations these early
investigators concluded that it was in the lower larynx that the
voice is produced. Regarded as a voice organ, the syrinx has
aroused much interest and has been the subject of numerous
researches. These researches deal chiefly with its function,
structure, and comparative anatomy. Its embryology has been
quite neglected, and it was this fact that prompted the present
investigation. At the outset it was thought best to confine this
study to some single species of bird, and to work out the de-
velopment of the voice organ, stage by stage, in this one form.
It was found, however, that many anatomical details of the
syrinx and its related structures had also been neglected. There-
fore, before the embryological study could be undertaken, it
became necessary to inquire more minutely into its anatomy.
Somewhat incidentally the function of the syrinx, too, has been
considered, and experiments performed to determine whether
the lower larynx is, in truth, the voice-producing organ.

This investigation was undertaken on the suggestion of Prof.
H. D. Reed of Cornell University, and was carried on, under his
supervision in the Laboratories of Comparative Anatomy at that
University until September, 1913, when it was transferred to
the Anatomical Laboratories of the University of Missouri.
To Dr. Reed of the former university the author is deeply in-
debted for many valuable suggestions and criticisms. At the
latter university, the author is obligated to Dr. F. P. Johnson
for his keen interest in the embryological division of these
studies, and to Thos. J. Heldt for his aid and criticism.

For the early literature the reader is referred to L. Wunder-
lich (’84), who gives an excellent historical sketch of the work
previous to his own. He includes a very complete résumé of
all work dealing with the syrinx as studied in numerous species
of birds.

In his text book entitled ‘‘The development of the chick”
Lillie ’08, treats the respiratory system quite fully, but states
that very little is known concerning the development of the voice
organ in the chick. :

THE SYRINX OF GALLUS DOMESTICUS 167
OBSERVATIONS

In this investigation Gallus domesticus was used for two
reasons. First, adults are accessible at all seasons of the year.
Second, developmental stages are easily obtained and controlled.

I. ANATOMY OF THE ADULT SYRINX
1. Gross anatomy

Birds differ from mammals in possessing two larynges, an
upper and a lower. The latter, known also as the syrinx, was
described by Johannes Miiller as occurring in three different
positions. When the organ is located at the lower end of the
trachea but above the bifurcation, he designated it ‘syrinx
trachealis.’ If found in the bronchi below the bifurcation,
‘syrinx bronchialis.’ But if the lower end of the trachea and
the upper portions of the bronchi both took part in its formation
he called it ‘syrinx tracheo-bronchialis’ (fig. 2). The syrinx of
the domestic chicken belongs to the last type.

In the domestic chicken, the upper larynx (fig. 1) is located
behind the tongue and on the floor of the pharynx. It is rudi-
mentary when compared with that of other animals and is ap-
parently incapable of producing voice. From the upper larynx
the trachea courses caudad, ventral to the oesophagus, passes
to the left of the ingluvies and pierces the pleura between the
limbs of the furcula to enter the so-called thoracic cavity. Shortly
after entering this cavity, the trachea bifurcates into the two
primary bronchi. In the region of the bifurcation a great modi-
fication of the cartilaginous and intercartilaginous elements
takes place. Here (fig. 2) a well developed bone, known as the
cross-piece, or pessulus, lies transversely in the dorso-ventral
plane between the two bronchi. Its dorsal and ventral extremi-
ties are greatly enlarged. The caudal end of the trachea is
compressed. It is composed of rings which are enlarged and
closely related to each other. The four most caudal rings are
imperfectly fused. Immediately caudad to this fusion are four

168 JAY ARTHUR MYERS

highly modified cartilages which have free ends dorsally, but
fuse with the pessulus ventrally.

The cartilages of the bronchi, unlike those of the trachea, are
present only as halves of rings. These half-rings form the
framework of the lateral bronchial walls. The first half-rings
are modified, and are attached to the pessulus both dorsally and
ventrally. The second are only slightly modified and are at-
tached ventrally to the first by a small piece of cartilage. Their
dorsal ends are free. Certain of these skeletal elements, so
briefly referred to, serve as attachments for vibrating mem-
branes. The external tympanic membranes (fig. 2) stretch be-
tween the first tracheal ring and the first half-ring. First, as
used here in reference to the tracheal rings, designates the most
caudal, as regards an enumeration of the total number of tra-
cheal rings in the caudo-cephalic direction. First, as used here
in reference to the bronchial half-rings, has a somewhat dif-
ferent meaning. It designates that bronchial half-ring which
of all the bronchial half-rings lies in the most cephalic position.
These designations are consistently adhered to throughout the
paper. The internal tympanic membranes form that part of the
medial wall of each primary bronchus which lies immediately
caudad to the pessulus. They stretch, therefore, from the
pessulus to the cephalic end of the medial membranous wall of
each primary bronchus. In fact, the internal tympanic mem-
branes may be regarded as specialized portions of the medial
membranous walls. Still more caudad to the pessulus and be-
tween the caudal extremities of the two internal tympanic
membranes, stretching transversely in the medio-lateral plane, is
another membrane, the bronchidesmus. From its _ position,
then, the bronchidesmus connects the medial walls of the two
bronchi.

a. Skeletal framework. In the study of the bony and carti-
laginous skeleton, three methods were pursued. First, numerous
gross dissections were made. Second, cartilage and bone stains
were used to stain the organ in toto. For staining bone 2 per
cent alizarine in 96 per cent alcohol was used, while } per cent
methylene blue in 67 per cent alcohol was employed as a cartilage

THE SYRINX OF GALLUS DOMESTICUS 169

stain. These organs were then washed and cleared, after which
the cartilaginous and the bony structures could be more easily
studied with the binocular microscope. Owing, however, to the
size and the shape of the organ as a whole, this method was not
entirely satisfactory. Third, wax reconstructions were made
according to the method described by Born.

The syringeal skeleton (fig. 4) consists of (1) the first four
tracheal rings which may be designated, the cephalic syringeal
skeletal elements; (2) the first three bronchial half-rings, or the
caudal syringeal skeletal elements; (3) four modified cartilages,
neither rings nor half-rings, which are found between the tra-
cheal rings and the first bronchial half-rings. These modified
structures will be designated the intermediate syringeal , car-
tilages; (4) a bony pessulus which lies at the summit of the
bronchial junction in the dorso-ventral plane and transverse
to the long axis of the trachea. Although the skeletal elements
are similar in most respects in both sexes, the following de-
scription applies, unless stated otherwise, only to the male.

The typical tracheal rings are broad flat bands of cartilage.
They differ from the type found in most of the higher animals
in that they are complete rings. In cross section the typical
rings have a cephalo-caudal diameter which is much greater
than the medio-lateral diameter, hence they appear very much
elongated (fig. 5). But as the caudal end of the trachea is ap-
proached, the cephalo-caudal diameter of the rings diminishes
while the medio-lateral diameter increases. The fifth, the sixth,
and the seventh rings appear almost square when seen in cross
section. ‘These, as well as all other rings cephalad of them,
are transverse to the long axis of the trachea and constitute the
framework of its walls. The medio-lateral diameter of the fourth
ring is greater than its cephalo-caudal diameter. The most
ventral portion of this cartilage dips caudad to a considerable
extent.

The first four tracheal rings (fig. 4) are very closely related to
each other. They are partially fused along their sides as well as
firmly bound together by dense fibrous tissue. Their ventral
and dorsal extremities are free, but the spaces between these

170 JAY ARTHUR MYERS

extremities are very narrow. This arrangement gives a very
strong wall to this portion of the trachea, and because of this
specialization this portion is known as the tympanum. The
most caudal, or first, tracheal ring. is smaller than the other
three and is transitional in size and shape between the tracheal
rings immediately above it and the intermediate syringeal car-
tilages immediately below it. As a whole, the tympanum arches
distinctly cephalad, its ventral and dorsal extremities projecting
caudad.

For the proper understanding of the arrangement of the
remaining cartilages a description of the pessulus (fig. 3) here
becomes necessary. In size, the pessulus far exceeds all other
skeletal parts. It is a well developed bar of bone located at the
junction of the bronchi, and lying dorso-ventrally in a plane
transverse to the long axis of the trachea. Its ventral and dorsal
extremities are large and serve for the attachment of some of the
cartilages referred to above.

The bone as a whole may be described as consisting of a shaft
and two large extremities (fig. 3). The shaft corresponds to a
little more than the middle third of the bone and in shape re-
sembles a three-sided prism with rounded borders. The cephalic
porder projects into the lumen of the trachea, and marks the
point of its bifureation. The lateral surfaces of the shaft form
the medial walls of the cephalic ends of the bronchi, between the
diverging courses of which the basal surface lies.

The ventral extremity is very large and may be considered as
being a pyramid whose apex points cephalad. On this pyramid
three distinct borders, a dorsal and two lateral; three surfaces, a
ventral and two dorso-lateral; and a base, may be described.
The dorsal border is continuous with the cephalic border of the
shaft and projects into the lumen of the trachea. The two
lateral borders give attachment to the intermediate syringeal
cartilages which will be described presently. The ventral or
anterior surface is broad and slightly convex and stands out so
prominently that when the syrinx is viewed as a whole, this sur-
face projects farther ventrad than any immediately neighboring
skeletal element. The caudal portions of the dorsolateral sur-

THE SYRINX OF GALLUS DOMESTICUS Pal

faces, like the lateral surfaces of the shaft of the pessulus with
which they are continuous, form the medial walls of the cephalic
ends of the bronchi, while the cephalic portions of these same
dorso-lateral surfaces form a part of the ventral wall of the
trachea. The base, or basal surface, lies in the same plane as
the corresponding surface of the shaft of the pessulus, and like
the latter surface can be plainly seen in a view of the caudal
aspect of the entire syrinx.

The dorsal extremity of the pessulus, like the ventral, is a three-
sided pyramid with its apex pointing cephalad. A ventral
border and two lateral borders, a dorsal surface and two ventro-
lateral surfaces, and a base, or basal surface, are to be noted.
With the exception of the dorsal surface, the surfaces and borders
of this extremity have the same corresponding relations as those
of the ventral extremity. The dorsal surface lies in close rela-
tion to the ventral wall of the oesophagus. To no part of this
extremity, however, do the intermediate syringeal cartilages find
attachment.

The first bronchial half-ring is attached at both ends to the
lateral borders of the extremities of the pessulus. At its dorsal
end this connection is composed of fibrous connective tissue.
At the ventral end the union is made by means of cartilage.
In old age, however, these attachments become ossified. In
females of one or two years the half-rings are united to the ven-
tral extremity of the pessulus by young cartilage which appears
much lighter than other cartilaginous portions, when stained
with hematoxylin.

The four cartilages which. occur between the tympanum
and the first bronchial half-rings (fig. 4), and which have been
designated above as the intermediate syringeal cartilages, appear
to differ structurally from all the other cartilages in the entire
respiratory tract. They are not complete rings nor are they half-
rings. Ventrally they are continuous with the pyramid of the
pessulus, while dorsally they are free. The most cephalic ones
are smallest and the most rudimentary. Ventrally they pro-
ceed from the very apex of the pyramid of the pessulus, extend
along the sides of the syrinx as thin flat bands, and end before

172 JAY ARTHUR MYERS

reaching its dorsal wall. The second, enumerated caudad from
the tympanum, are somewhat broader and extend farther dor-
sad. The first and the second cartilages are often fused for a
part of their course. The third intermediate syringeal cartilages
differ from the second only in being slightly broader. The
fourth and the last of this series present more striking differ-
ences. They are larger than any of the preceding ones. Their
free dorsal extremities lie laterad of the dorsal pyramid and
gradually become very broad, but their medio-lateral diameter
is not increased. These cartilages are arched slightly cephalad.

Caudad to the intermediate syringeal cartilages are the
bronchial half-rings (fig. 4). The first of these differ from the
typical half-rings in the following respects: first, they are longer
and have much greater diameters; second, both ends are attached
to the pessulus; third, well marked caudal prolongations extend
from their ventral extremities and connect them with the
second half-rings; fourth, their ventral extremities in old indi-
viduals become ossified; fifth, they are arched, with their con-
vexities pointing caudad. .

Between the first half-rings and the last intermediate car-
tilages are very large, somewhat oval-shaped spaces, the upper
thirds of which are directly opposite to the pessulus (fig. 4).

The second half-rings, which are somewhat smaller than
the first, have enlarged ventral extremities which are attached
to the cartilaginous prolongations of the first half-rings mentioned
above. Their dorsal extremities are free.

The third bronchial half-rings are quite similar to the typical
half-rings which lie caudad to. them. The only noticeable
modification is an enlargement of their ventral extremities.
They are somewhat flattened bands of cartilage which are free
at both ends. !

b. Vibrating membranes. Certain parts of the highly modified
skeleton, just described, serve as attachments for specialized
semitransparent membranes, which are the real voice producing
elements. Two pairs of these are present in the chicken. They
are known as the external and the internal tympanic membranes.
Another membrane, not strictly a vibrating membrane, will also
be discussed under this heading.

THE SYRINX OF GALLUS DOMESTICUS 173

It should be recalled that the first half-ring of each primary
bronchus and the last intermediate syringeal cartilage arch
caudad and cephalad respectively, thus forming two (one on
each side) oval spaces, occupied by the externa] tympanic mem-
branes (fig. 2). Caudally these membranes are attached along
the entire length of the cephalic borders of the first half-rings;
cephalically they are attached along the entire length of the
caudal borders of the last intermediate cartilages. Dorsally
and ventrally the membranes narrow and are attached to the
lateral borders of the corresponding pyramids of the pessulus.
The internal tympanic membranes are situated more caudad
(fig. 2), in the medial walls of the bronchi just below the tracheal
bifurcation and stretch between the dorsal and ventral free
ends of the half-rings. Cephalically they are attached to the
lateral borders of the shaft of the pessulus. Caudally they
extend to the level of the third half-rings where they are re-
placed by the heavy fibrous tissue of the medial bronchial
walls.

Stretching across the interbronchial interval, just caudad to
the internal tympanic membranes, is another membranous struc-
ture, the bronchidesmus (figs. | and 2) of Garrod. The middle
portion of this is somewhat narrower than its ends, and may
be said to lie between the level of the fifth and the level of the
eighth bronchial half-rings. Its ends, exceeding these levels and
extending for a variable distance above and below them, are
attached correspondingly to the dorsal third of the medial bron-
chial walls. The cephalic portions of these attachments show a
modification. As these portions of the ends of the bronchides-
mus extend to the attachment stated, they expand, dorso-
ventrally, and find further attachment as far ventral as the
ventral third of the membranous medial walls of the bronchi
and as far cephalad as the level of the third bronchial half-rings.
This last attachment may be said to mark the caudal limits of
the internal tympanic membranes. The caudal border of the
bronchidesmus is broader than its cephalic border and presents
two oval openings, one on each side of the median plane, which
lead into two smaller irregular pockets within the bronchidesmus.

7A JAY ARTHUR MYERS

In the interbronchial region, in immediate relation to the caudal
border of the bronchidesmus, numerous folds and pouches are
developed. In the mid-line, the dorsal surface of the bronchi-
desmus is attached, by means of a thin sheet of fibrous tissue,
to the ventral surface of the oesophagus and the dorsal portion |
of the cephalic part of the pericardium. From these attach-
ments this same sheet of tissue extends ventrally, and is further
attached to the caudal border of the bronchidesmus, which thus
receives additional anchorage by the sheet of tissue also being
attached to the ventral portion of the cephalic part of the peri-
cardium. From these last named attachments the sheet of
tissue extends cephalad in the median plane, and tapers to a
narrow cord. The cord, after a short course, again expands, this
time to gain attachment along the entire extent of the Junction
of the ventral surface and the base of the ventral pyramid of the
pessulus. Ventrally this cord and its expanded portions are
attached throughout the entire length to a reflection of the
fibrous pericardium surrounding the roots of the great vessels
of the heart.

c. Musculature. In general the musculature of the syrinx of
birds is composed of intrinsic and extrinsic muscles. Many
birds have from three to seven pairs of intrinsic syringeal
muscles. The frequent occurrence of these intrinsic muscles
has been recognized of value in the classification of birds.
Species possessing them are usually songsters. There are some
exceptions, however, such as the crow and the jay, which,
though possessing these intrinsic muscles, are no longer classified
as singing birds. From the syrinx of the domestic chicken the
intrinsic syringeal muscles are absent, and hence its voice organ
is of course correspondingly simpler. Because of their absence
from the syrinx of Gallus domesticus the intrinsic syringeal
muscles merit no further description here.

The principal extrinsic syringeal muscles are the tracheal
muscles known as the sterno-tracheales (fig. 2). In the chicken
they are well developed muscles which take origin, one on each
side, from the antero-lateral process of the sternum. Their
fibers are directed obliquely ventrally and cephalad, and reach

THE SYRINX OF GALLUS DOMESTICUS b75

the trachea at the level of the tenth ring (fig. 2). Here, as be-
yond, both muscles are firmly bound to the trachea by a strong
common fascial sheath. But despite their fascial attachment,
none of their fibers is inserted at this level. Springing from the
medial surface of both muscles are several small bundles of
fibers which, directed obliquely cephalad, are inserted on the
tracheal rings, from the thirteenth to the twenty-first. Ceph-
alad to these muscular bundles both muscles, now much dimin-
ished in size, proceed along the sides of the trachea to their final
insertion on the ventral cartilages of the upper larynx. The exact
extent and manner of insertion of the sterno-trachealis muscles
offers a field for further investigation. The action of these
muscles will be discussed in the section on function.

Two pairs of short bundles of muscle fibers are found on the
caudal end of the trachea. One pair (fig. 2) lies on the ventro-
lateral aspect of the trachea, the other on its dorso-lateral aspect.
Caudally these bundles end at the levels of the fifth to eighth
rings. Cephalically the majority of their fibers enter, and
apparently become a part of, the ventral and the dorsal margins
of the sterno-tracheales respectively. The fibers which do not
enter the sterno-trachealis muscles are inserted on the respec-
tive ventral and dorsal walls of the trachea. Some of the fibers
of the ventro-lateral bundles spread out cephalad to the level
of the twelfth ring, to cover the ventral surface of the trachea,
and certain fibers from the dorso-lateral bundles also spread out
to cover its dorsal surface.

d. Sexual differences. Sexual differences are very marked in
song birds, especially as regards the size of the labia and the
syringeal muscles. In male aquatic birds the tympanum is a
large bony swelling projecting from the left side of the trachea,
while in females the tympanum, though present, does not pro-
ject beyond the tracheal walls. The main sexual difference to
be noted in the syrinx of chickens is one of size (ef. figs. 5 and 6
for which males and females of the same varieties were chosen).
Male birds are usually larger than females, and so some dif-
ference would naturally be expected in the size of their voice
organs. But this difference in size of individuals is not sufficient

176 JAY ARTHUR MYERS

to account for all the differences observed. Quite naturally the
sterno-tracheal muscles are noticeably smaller in females; but
the bony rings above the tympanum, these, in the male (fig. 5)
are entirely different in size and shape from the corresponding
rings in the female (fig. 6). Again, in the male the tympanum
is composed of the first four tracheal rings, while in the female
only the first three form this structure. The tympanic mem-
branes, however, exhibit no marked difference.

It is not an uncommon thing to hear a female chicken try to
crow. ‘The sounds she produces are distinct, and cannot be
mistaken for anything other than an attempted crow. Judg-
ing from the structure of the syrinx, there is no apparent reason
why the female should not be able to crow perfectly, provided
the instinct for it were properly developed. Hacker (’00) calls
attention to the fact that the females of certain species of song
birds, when. kept in captivity, learn to sing as charmingly as the
males. Barrington (1773) gives numerous examples of one
species being trained to sing the song of another species.

2. Microscopic anatomy

For this phase of the investigation, cross, coronal, and longi-
tudinal sections were made through the syrinx of both male and
female adult chickens. The sections were cut five, ten, fifteen,
and twenty micra in thickness. The following stains were used:
iron hematoxylin, picrofuchsin, Malloru’s aniline-blue connec-
tive tissue stain, Weigert’s resorcin-fuchsin elastic tissue stain,
Unna’s orcein, and Mayer’s mucicarmine.

In figure 5 all of the rings, the half-rings, the cartilages, and
the pessulus are seen in cross section. It is to be noted that the
tracheal rings cephalad to the second are completely ossified.
Each consists of a thick peripheral layer of compact bone within
which is a central area of cancellous bone. A distinct periosteum
surrounds the whole. The cavities of the cancellous portions
contain bone-marrow not unlike that found in other bones of
birds.

As stated before, the first four tracheal rings are united to
form the tympanum. The first two rings are composed of hya-

THE SYRINX OF GALLUS DOMESTICUS EZ

line cartilage throughout; the third and the fourth are entirely of
bone.. The remaining rings of the trachea are also bone, but
each is separated from the next by a small space, which is bridged
by a heavy band of fibrous tissue which, on reaching the rings,
becomes continuous with their periosteum.

The first and the second intermediate syringeal cartilages are
small, thin, cartilaginous bars, each having a very thin and in-
dist'nct perichondrium. These cartilages are very rudimentary
in every respect. ‘The and the third fourthin termediate carti-
lages are much better developed and possess well marked
perichondria.

Each intercartilaginous space, from the caudal border of the
tympanum to the cephalic border of the fourth intermediate
cartilage, is occupied by a strong thick band of fibrous tissue.
As determined, after staining with Weigert’s elastic tissue stain,
these bands are composed almost entirely of elastic fibers.

As seen in figure 5, the first and the second bronchial half-
rings are cartilaginous, but as previously mentioned, the ventral
extremity of the first becomes ossified in old individuals.

The pessulus appears triangular in cross section, and is ossi-
fied throughout its entire extent. The marrow cavity is usually
quite extensive, and is surrounded by a comparatively thin layer
of compact bone. The lateral surfaces of the pessulus, as well
as its cephalic and lateral borders, are covered by the mucous
membrane of the respiratory tract. A distinct areolar tunic, or
submucosa, especially marked over the cephalic border, connects
the respiratory membrane to the periosteum of the pessulus. A
somewhat different arrangement is found on the caudal surface
of the pessulus. Here an areolar coat, continuous with the
bronchial submucosa, connects the periosteum of the pessulus
with the membranous reduplications in the interbronchial inter-
val immediately cephalad to the bronchidesmus.

Above the tympanum the epithelium of the tracheal mucous
membrane is of the stratified ciliated columnar variety, with a
distinct basement membrane. The tunica propria is well de-
veloped and contains many lymph cells as well as numerous dis-
tinct lymph nodules. These nodules, which are most numerous

178 JAY ARTHUR MYERS

in the region of the tracheal bifurcation, are quite near the sur-
face, since they lie just beneath the epithelium. Where »these
lymph nodules occur the epithelial cells are non-ciliated.

A distinct submucosa is present throughout practically the en-
tire extent of the mucous membrane of the trachea and the
bronchi, and connects this mucosa to the interannu!ar membranes
and the periosteum, or the perichondrium of the tracheal rings,
‘the intermediate syringeal cartilages, and the bronchial half-rings.
There is no sharp line of demarcation between the submucosa
and the tunica propria, but the former is easily distinguished
from the latter in that it is less dense and contains fewer |!ymph
cells. Over the tympanic membranes the tunica propria ‘s thin
and sparse and a submucosa is indistinguishable.

At the level of the caudal border of the third tracheal ring,
the epithelial cells loose their cilia and immediately become col-
umnar in shape. There is a gradual transition from stratified
ciliated columnar epithelium to stratified squamous. The lat-
ter is made up of several layers at the lower border of the tym-
panum, but becomes thinner and thinner, as far as a point slightly
caudad to the fourth intermediate syringeal cartilages, where it
consists of only a single layer of flat cells, covering the internal,
or medial, surfaces of the external tympanic membranes. The
lateral surfaces of the internal tympanic membranes, or those
surfaces of these membranes which face the lumen of each pri-
mary bronchus, are covered by a similar simple epithelium.
Below the limits of the external tympanic membranes the epi-
thelium gradually becomes thicker, and about midway between
the first and second bronchial half-rings it again assumes the
characteristics of a ciliated columnar epithelium. .

The disposition of the squamous epithelium suggests that the
portions of the syringeal walls covered by it are subject to con-
siderable movement. |

As stated above, the vibrating membranes are covered by a
thin epithe ium composed o a single layer of flattened cells;
beneath this is the tunica propria which is thin and ess distinct
than that found in other parts of the respiratory tract. Beneath
the tunica propria is a thin, dense layer of tissue which comprises

THE SYRINX OF GALLUS DOMESTICUS 179

the vibrating membranes proper. This layer is composed of
numerous white and elastic fibers. It is to be noted that there
is a tendency for all layers to become much thinner as the tym-
panic membranes are approached (fig. 5).

The external and the internal labia, which occur in song birds
in connection with the tympanic membranes, were not observed
in the chicken.

The semilunar membrane is poorly developed in the chicken.
It is nothing more than a modification of the mucosa over the
cephalic border of the shaft of the pessulus. The epithelium in
this position is thickened and belongs to the stratified ciliated
columnar type. The submucosa too, as already mentioned, is
especially thick. Thus it is evident that the semilunar membrane
in the chicken is but a poor representative of this structure as
found in many song birds.

II. DEVELOPMENT

For this division of the present investigation the following
selected stages were used.

Period of Incubation

68 hours 152 hours 272 hours
70 hours 164 hours 284 hours
72 hours 176 hours 296 hours
74 hours 188 hours 308 hours
78 hours 200 hours 320 hours
80 hours 212 hours 332 hours
92 hours 226 hours 356 hours
104 hours 236 hours 380 hours
128 hours 248 hours 404 hours
140 hours 260 hours 452 hours

Twenty-four hours after hatching.

Serial cross sections were made of nearly all the stages and
serial coronal sections were made of a large number of the stages.
In the early stages series were made of the entire embryo while
later only the syringeal region was sectioned. For the most
part the sections were cut ten micra in thickness. In the more
important stages a drawing of the embryo was made before sec-
tioning, which was utilized in obtaining the plane of sectioning

180 JAY ARTHUR MYERS

and in obtaining the curvature of the backline of the embryo for
reconstructions. Most series were stained with iron or alum
hematoxylin, with picrofuchsin or eosin as counter stains. Some
of the later stages, however, were stained with Mallory’s anilin-
blue connective tissue stain, Weigert’s resorcin-fuchsin elastic
tissue stain, and Mayer’s mucicarmine.

In transverse sections of a 68 hour embryo, the epithelial tube
of the foregut is surrounded by a condensed mass of mesenchyma.
This tube, which in its most cephalic part is cylindrical, when
followed caudad, enlarges and becomes triangular in shape. Ex-
tending ventrolaterally from this tube are two beginning diver-
ticula, the anlagen of the trachea and the bronchi. In length the
right is 0.05 mm. while the left is 0.03 mm.

Embryos of 74, 78, and 80 hours show a lengthening of the
trach@a and the bronchi, but the former is still relatively much
shorter than the latter. Wunderlich called attention to this con-
dition in Fringilla domestica and mentioned the fact that it rep-
resents a stage which is found throughout life in certain reptiles.
This might be regarded as a homology, but such homology is not
probable. It would seem that a logical explanation of this con-
dition might be found in a study of the position and the relations
of the organs of this region. Since the neck as such has not yet
developed it is obvious that the trachea springs from the diges-
tive tube and bifurcates at once at a point not far from the future
position of the lungs. As the neck lengthens, the oesophagus
and the trachea must keep pace. The trachea, therefore, becomes
drawn out. This elongation goes on to such an extent in the
chicken that the trachea eventually becomes much longer than
the bronchi.

A 128 hour embryo shows a marked increase in the length of
the trachea and the bronchi, and in a 140 hour stage these struc-
tures have nearly doubled in length. The right bronchus courses
laterally and gives off seven sac-like branches which later become
the so-called pipes of the lungs.

Since the tracheal bifurcation is the region of especial interest
in this paper, the general development of the trachea and the
bronchi will not be traced further.

THE SYRINX OF GALLUS DOMESTICUS 18t

1. Mucous membrane

In the early stages described above, the walls of the trachea and
the bronchi consist of an epithelial tube surrounded by a loose
mesenchyma. In the 68 hour stage the epithelium of this tube
may be said to belong to the stratified variety. The boundaries
between the cells are not well defined, but two or three layers of
nuclei can be observed. ‘The cells lining the lumen are mostly
columnar with their nuclei placed in the ends distal to the lumen.
The basal cells are much shorter and more irregular in shape.
Each bronchus presents a well defined lumen.

No noticeable differences occur in the structure of the tube
in embryos of 72, 74, and 78 hours. In an 80 hour embryo,
however, the beginning of the basement membrane is seen as a
small differentiated line which extends around the outside of the
epithelial tube. Immediately below its origin from the pharynx
the tracheal tube has a lumen of oval outline. More caudally
it elongates from side to side until immediately above the bifurca-
tion it is little more than a transverse slit. At this level the
dorsal epithelial wall becomes thicker, while the ventral wall ap- -
pears to fold inward and to come into contact with the dorsal
wall, thus dividing the one slit-like lumen intotwo. The lumina
of the two bronchi and the trachea have a smaller diameter at
80 hours than at any of the earlier stages. The epithelial walls
have not thickened at this stage, but the mass of mesenchyma
surrounding the digestive and respiratory tubes has condensed.

In 128 and 140 hour embryos, the lumen of the tracheal tube
is so small as to seem almost obliterated in some sections. The
thickness of the dorsal wall is nearly double that of the ventral.
About 0.1 mm. cephalad to the bifurcation, the tracheal tube
becomes compressed dorso-ventrally, thus a slit similar to that
described above is produced. It possesses, however, a somewhat
larger lumen.

The lumen of each bronchus possesses a greater transverse
diameter than that of the trachea, except in that region immedi-
ately above the bifurcation of the latter. The dorso-medial por-
tion of each bronchial wall is much thicker than any other part.

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 1

182 JAY ARTHUR MYERS

This seems to be due to a greater number of cell layers rather
than to the elongation of the cells, since four distinct layers of
nuclei appear in the thickened part, while only 2 or 3 layers are
present in the thinner portions of the wall. The same condition
explains the thickening of the dorsal wall of the trachea. A very
distinct basement membrane is present in these stages.

In 152 and 164 hour embryos the lumen of the trachea is still
very small. At a point 0.24 mm. above the bifurcation it begins
to enlarge, not only in the transverse diameter, but in the dorso-
ventral as well. A cross section of the lumen and walls of the
tube at this level presents a figure which is almost a perfect
Square, and is much larger than that described in previous
stages. Of the walls composing the square, the dorsal is thickest,
the ventral thinnest, while the lateral are intermediate in this
respect. The dorsal wall possesses four layers of nuclei, the lat-
eral walls three, and the ventral wall two layers.

Figure 12, from an embryo of 176 hours, shows the relative
thickness of the epithelium in the region of the tracheal bifurca-
tion. The epithelium is thickest Just cephalad to the bifurca-
tion, where not less than three or four distinct layers of nuclei
are visible. At the level of, and slightly caudad to the bifurca-
tion, the number of cells gradually diminishes, until only two
. layers of nuclei are present. The epithelium projecting into the
tracheal lumen at the point of the bifurcation appears slightly
thicker than that lining the medial bronchial walls with which
it is continuous. At this stage, too, slight irregularities or evagi-
nations become noticeable in the inner walls of the epithelial
tube. These are due to encroachments upon the tube, from
without, of growing mesenchymal condensations which lie im-
mediately beneath and in direct contact with the basement
membrane of the epithelium. Only two of these evaginations
have developed to a stage worthy of mention. They are some-
what caudad to the tracheal bifurcation, one projecting into the
lumen from the lateral wall of each primary bronchus. Caudad
to the site of these evaginations the epithelium again thickens
and for some distance three layers of nuclei can be distinguished.

THE SYRINX OF GALLUS DOMESTICUS 183

In a stage 24 hours later (200 hours), as wel as in a 212 hour
embryo, the epithelium shows a noteworthy characteristic. The
nuclei of the cells bordering upon the lumina have migrated from
the basal to the free ends of the cells, thus giving rise to a very
prominent superficial row of nuclei. Immediately beneath this
the other nuclei show an irregular arrangement. Although this
characteristic arrangement of nuclei is noticeable in the 176 hour
stage, it does not become very striking until the present stage is
reached. In this stage also a second evagination (fig. 13) ap-
pears in the lateral wall of each bronchus, just cephalad to the
one described as present in the preceding stage. At 248 hours
many of these evaginations may be observed in the walls of
both the trachea and the bronchi. In the latter they are con-
fined, however, to the lateral walls. _

A cross section of a 332 hour embryo shows two or three lay-
ers of nuclei in the epithelium, except in the region of the future
tympanic membranes, where a single layer occurs. The cells
‘in these regions are cuboidal. Throughout the region of the
bifurcation of the trachea, a considerable number of goblet cells,
as well as numerous cells exhibiting a somewhat differentiated
clear area in their free ends, occur in the epithelial layer nearest
the lumen. Numerous cilia are present on the free borders of
some cells.

In a 404 hour embryo a very distinct layer of nuclei appears
at the very base of the epithelium. These are much smaller
than those found nearer the lumen. As the regions of the future
tympanic membranes are approached, all cells between the layer
of small nuclei are left to cover the membranes. These cells
differ from those described in the 332 hour embryo in being much
less cuboidal, smaller and possessing much smaller nuclei.

The most noticeable differences between the last embryo and
one of 452 hours are (1) the nuclei of the cells covering the tym-
panic membranes have become much more flattened and in ap-
pearance suggest the nuclei of endothelial cells; (2) in addition
to individual goblet cells, small groups consisting of three or
more secreting cells are found in the epithelium. Each of these
groups is slightly invaginated, leaving a shallow pit connecting

184 JAY ARTHUR MYERS

with the lumen of the respiratory tract. Each cell appears light
and presents a pore-like opening which communicates with the
common pit. The nuclei of these secreting cells are situated
nearer the basement membrane than those of the typical epi-
thelial cells. These structures are not found in the epithelium,
covering the tympanic membranes. In a chick 24 hours after
hatching, such groups of secreting cells are much more numerous
and show a higher degree of development in having become more
invaginated. As determined by staining with mucicarmine it is
evident that these structures are the anlagen of the simple mu-
cous alveolar glands found in this region. Well developed cilia
project from the free borders of the typical columnar cells, but
they are not seen in the region of the tympanic membranes.

The vacuoles, which occur in such great abundance in the
mucous membrane of the digestive tube in human embryos (John-
son 710), were observed in the respiratory tube of chick embryos,
but they are neither constant or abundant. In a 280 hour em-
bryo, such vacuoles are quite numerous in the epithelium lining
the medial bronchial walls, but in all other stages they are prac-
tically absent.

2. Cartilaginous skeleton

Irn an 80 bour embryo the epithelial tubes constituting the
trachea, the bronchi, and the oesophagus are all closely sur-
rounded throughout their entire extent by a common area of
mesenchyma which, in immediate relation to them, is much denser
than it is a little beyond them. An inspection of figures 12, 13,
and 7 will make clear this arrangement of the mesenchyma.

In the 128 hour stage that portion of the condensed area of
mesenchyma surrounding the respiratory tract has become sepa-
rated from that surrounding the digestive tube. They now ap-
pear as two distinct areas, that surrounding the trachea being
the smaller. The condensed mesenchyma is, of course, sur-
rounded in turn by loose, unmodified mesenchymal tissue.

In a 152 hour embryo the mesenchymal condensation, common
to the entire respiratory tract, becomes more prominent in the
region of the tracheal bifurcation than in any other portion.

THE SYRINX OF GALLUS DOMESTICUS 185

Along the dorsal surface in this region the condensation is no
thicker than in the preceding stages, but it is much thicker lateral
and ventral to the bifurcation (fig. 7). It also extends between
the bronchi, just caudad to their union with the trachea. In a
164 hour embryo, at the points in the lateral bronchial walls
where the above mentioned evaginations of the epithelium occur,
the aggregated mesenchymal cells arrange themselves into very
compact areas. These areas appear quite round in cross section.
In the center of each area are several unmodified cells which are
immediately surrounded by others of the same type concen-
trically placed. This arrangement of mesenchymal cells is the
beginning of the anlagen of the first bronchial half-rings which,
of all the skeletal elements, are the first to appear. This anlage
extends from the ventro-lateral to the dorso-lateral parts ofeach
bronchus, but appears best developed in its middle portion.
These anlagen are more marked in a 176 hour embryo and are
represented in figure 7, as two rounded and elongated masses
projecting dorso-ventrally around the lateral walls of the epi-
thelial tubes of the bronchi a little below the tracheal bifurcation.
Twelve hours later the mesenchymal cells just cephalad to these
anlagen for the first bronchial half-rings become arranged so as
to form two other areas of aggregated cells similar to the ones just
described. These areas are the anlagen of the fourth intermedi-
ate syringeal cartilages, which at this stage lie very near those
of the first bronchial half-rings.

At 200 hours the first half-rings, and the fourth intermediate
cartilages stand out much more prominently, since the mese-
chyma immediately surrounding them is now less dense (fig.
13). The fourth intermediate syringeal cartilages differ from the
first half-rings only in extending farther ventrally. The anlage
of the pessulus appears very faintly in the mesenchyma between
the bronchi, and slightly caudad to the tracheal bifurcation. It
occupies the ventral three-fifths of the distance from the ventral
to the dorsal walls of the respiratory tube in the region of its
bifureation. In structure it does not appear different from the
above described anlagen, but it is much larger than either of
them. A V-shaped mass of condensed mesenchyma extends from

186 JAY ARTHUR MYERS

the cephalic border of the pessulus to the point of union of the
two bronchi.

In a 226 hour embryo, the cells in the center of the anlagen
have no definite arrangement, but are larger and more oval in
shape than those in the preceding stages. The central cells, in
enlarging, have crowded the outer cells together, thus causing
the individual outer cells to appear flattened and the whole periph-
eral area to appear narrower. ‘The first half-rings and the fourth
intermediate syringeal cartilages are now separated by a greater
space than in the stages previously described. The anlage of an
additional cartilage appear just cephalad to the developing fourth
intermediate syringeal cartilages. Though small, as yet, these
anlagen, the beginnings of the third intermediate syringeal car-
tilages, are fused with the cephalic extremity of the ventral pyra-
mid of the pesulus. Dorsally these anlagen extend only slightly
more than one-half of the distance to the dorsal extremity of the
pessulus where they end unattached. These structures appeared
in only one out of two embryos taken at this stage. These anla-
gen are shown in figures 8 and 9, which make clear the relation
and the extent of these and other developing skeletal elements.
The first bronchial half-rings extend around the lateral walls of
the bronchi but do not reach the pessulus at either extremity.
The fourth intermediate syringeal cartilages arch cephalad to
some extent and are fused with the ventral pyramidal extremity
of the pessulus. Their dorsal ends are unattached and lie some-
what lateral to the dorsal pyramid of the pessulus. The develop-
ing pessulus has gradually assumed the same form as in the
adult, except the shaft, which at this stage is round in cross sec-
tion, rather than triangular. At this stage, too, the mesenchyma
along the entire ventral surface of the trachea has become.more
condensed. This condensation represents the primordium of the
anlagen of the tracheal rings.

The 248 hour stage shows a marked advance in the develop-
ment of the skeletal parts (fig. 14). All the tracheal rings are
represented by circular (in cross section) condensations of mes-
enchyma which extend around the lumen, immediately external
and in contact with the epithelial tube. The first and the second

ee a a

THE SYRINX OF GALLUS DOMESTICUS 187

intermediate cartilages are here represented by extremely small
masses which lack the regular cell arrangement found in the
others. Ventrally they fuse with the ventral pyramid of the
pessulus. Immediately caudad to the first half-rings is a mesen-
chymal area, which is apparently condensing to form the anlage
for the second half-ring. None of the other bronchial cartilages
are represented at this stage.

At 260 hours the central cells of the anlagen for the first half-
rings, the fourth intermediate syringeal cartilages, and the pessu-
lus appear slightly more separated from each other. As would
be expected from the order of their first appearance this is most
marked in the anlagen for the first half-rings, where true embry-
onal cartilage is closely approached, and least marked in the
pessulus. The first seven half-rings are represented at this stage.

All the cartilaginous and the bony skeletal elements of the res-
piratory tract are represented in an embryo of 284 hours. The
pessulus, the first and the second half-rings, the tracheal rings
(except the first and the second) and the fourth intermediate
syringeal cartilages are composed of embryonal or primary car-
tilage. The perichondrium is represented by a thin layer of
cells which are very much elongated and rather sparsely distrib-
uted. All skeletal elements, other than those above mentioned,
are still in the mesenchymal stage. Figure 10, drawn from a
wax reconstruction of the syrinx of a 284 hour chick, shows the
extent, the size, the form, etc., of the cartilages, and their rela-
tion to the epithelial tube. All the intermediate syringeal car-
tilages are fused to the ventral pyramid of the pessulus. The
fourth are much the largest of these and closely approach the
first half-rings in size. They present a decided cephalic arching
in the middle portion of their course, and each shows a marked
enlargement, which ends freely, but in close relation to the middle
third of the dorsal pyramid of the pessulus. The third, with
a diameter about one-half as great as that of the fourth, and
placed slightly cephalad to the latter, pass around the epithelial
tube and present free dorsal extremities, which lie cephalad and
lateral to the apex of the dorsal pyramid of the pessulus. The
second are much smaller and take a course parallel to that of the

188 JAY ARTHUR MYERS

third. At this stage, the first are not fused with the ventral
pyramid, but are continuous with a mass of condensed mesen-
chyma which may be said to be a part of the apex of the pyra-
mid. They pass around the trachea and end freely on its dorso-
lateral aspect.

The first two tracheal rings are very small and, like the first
three intermediate cartilages, are composed entirely of con-
densed mesenchyma. At both their dorsal and their ventral
extremities they present a marked caudal dipping. The second
tracheal ring is, however, somewhat larger and more advanced
in its development than the first. It should be noted, also, that
the first four tracheal rings are not in direct contact with each
other as in the adult; but are separated by spaces which are occu-
pied by embryonal fibrous tissue. The remaining tracheal rings
call for no special description, since they differ from those of the
adult only in size, in being circular in cross section, and in being
composed entirely of cartilage. The ventral and dorsal extrami-
ties, or pyramids, of the pessulus, are cartilaginous throughout
and are similar in shape to these parts in the adult. The shaft,
however, as stated above, is round in cross section.

Second to the pessulus in size are the first bronchial half-rings.
These half-rings in their middle portions, arch markedly caudad.
Their ventral extremities are in close contact with the base of
the ventral pyramid of the pessulus, but fusion has not taken place.
Dorsally they end unattached, caudad and lateral to the pessulus.
The second half-rings, which are much smaller and immediately
caudad to the first, are connected with the latter at their ventral
extremities by means of a small mass of condensed mesenchyma.
A wax reconstruction of the syrinx at this stage (284 hours)
shows that the lower end of the trachea exhibits a slight compres-
sion (fig. 10). In the region of the intermediate syringeal carti-
lages this compression is well marked. |

In a 320 hour embryo, all the skeletal elements are represented
by primary cartilage. The first and the second intermediate
syringeal cartilages are the last to be transformed into true car-
tilages, and at this stage are the smallest of all the skeletal

THE SYRINX OF GALLUS DOMESTICUS 189

parts. These cartilages often appear fused into a single mass
for at least a part of their extent.

In a 452 hour embryo, the last of the series, most of the tra-
cheal rings cephalad to the tenth present two prolongations of
precartilage, one of which is directed cephalad, the other caudad.
The second to the tenth rings, inclusive, are now more or less
perfect squares when seen in. cross section. The third, the fourth,
and the fifth, however, are much larger than the others (fig.
16). The first is round and still quite small. The intermediate
cartilages also present a different appearance; being somewhat
compressed, they now appear oblong in cross section. All of
these cartilages are relatively much larger in all developmental
stages than in the adult.

In cross section, the shaft of the pessulus is becoming slightly
triangular, but it still does not possess the distinctly triangular
shape of that of the adult. The first bronchial half-rings are
only slightly compressed. At their dorsal extremities there are
indications of fusion with the pessulus, while at their ventral
extremities the two structures are separated only by their peri-
chondria.

Wunderlich found the syringeal skeleton of a 17 day chicken
embryo to be composed entirely of cartilage. He states that these
elements are cartilaginous in Fringilla domestica and Anas bos-
chas at the time of hatching. Rathke states that at hatching
ossification has begun in the syrinx of the domestic chicken. In
this investigation, however, no bone was observed in the syrinx
of Gallus domesticus at the time of hatching, nor in stages one day
later.

3. Submucosa

In the earlier stages, the anlagen of the skeletal elements, ex-
cept the pessulus, are in such close contact with the epithelial
tube that they produce actual evaginations of the epithelium (fig.
13). Ina284 hour embryo this is not true of the thirdand the fourth
intermediate syringeal cartilages, and of the first half-rings; here,
even typical mesenchymal cells occupy the considerable space be-
tween the above structures and the epithelial tube (fig. 15). The

190 JAY ARTHUR MYERS

mesenchyma referred to is continuous with, and seems to have mi-
erated inward from, that occupying the space between the carti- ~
lages. The same condition exists between the tube and all the
cartilaginous elements in the region of the tracheal bifurcation in a
296 hour embryo. Ina 332 hour embryo these intervening mesen-
chymal cells possess numerous protoplasmic processes which form a
loose network and which, at the 356 hour stage, become smaller and
resemble short connective tissue fibers. In these spaces between
the developing cartilages and the epithelial tube small, but dis-
tinct, fibers appear in a 404 hourembryo. These are true connec-
tive tissue fibers since they stand out very prominently when
treated with Mallory’s connective tissue stain. At this stage,
the tissue now forms a loose connection between the epithelium
on the one hand and the cartilage and intercartilaginous struc-
tures on the other. It contains blood vessels and nerves and con-
stitutes the submucosa. As in the adult, there is no sharp line -
of demarcation between the submucosa and the tunica propria.

4. Musculature

In the 164 hour embryo areas of differentiated cells may be
observed between the ribs. Similar aggregates of cells extend
_ from the antero-lateral process of the sternum to the trachea,
somewhat above its bifureation. The cells composing these ag-
gregates have large oval nuclei, each of which possesses a dis-
tinct nucleolus; and their cytoplasm, which has a strong affinity for
eosin, appears to be drawn out into short strands. These struc-
tures are more prominent in a 176 hour embryo. Wunderlich
states that the muscular system begins to differentiate on the
tenth day in Fringilla domestica and on the twelfth day in Anas
boschas.

In the 188 hour stage numerous cytoplasmic strands have
united to form long bundles which consist of minute fibrils.
These bundles are present throughout the entire extent of the
developing muscles, from the sternum to the cephalic end of
the trachea. The nuclei are oval and several seem to belong to
each bundle of fibrils. At the point where these bundles, or the

THE SYRINX OF GALLUS DOMESTICUS 19]

sterno-tracheal muscles, reach the trachea small additional masses
of developing muscular tissue extend caudad along the dorso-
lateral and ventro-lateral aspects of the trachea. These small
additional masses seem to arise from, and certainly do not differ
from, the tissue found in the developing sterno-tracheal muscles.

In the succeeding stages the muscles continue to develop by
the addition of more cytoplasmic bundles. The nuclei of the
muscle cells are easily distinguished from those of the developing
connective tissue cells, which are present between the muscular
bundles, for the former are more elongated and regular in shape.
No other structural changes call for special mention until the
296th hour is reached, when faint cross striations appear in cer-
tain fibers. These, however, are quite rare.

At 452 hours the fibers have arranged themselves into more
definite bundles. The fibers of these bundles show distinct cross
striations, and numerous elongated nuclei appear to le on or
between them. Certain of these fibers are attached directly to
the perichondrium of the lower tracheal rings.

5. Intercartilaginous membranes

When the aggregated mesenchymal cells arrange themselves
to form the anlagen of the skeletal elements, small spaces exist
between these anlagen. These spaces, also, are occupied by typi-
cal mesenchymal cells, but here they are fewer and farther apart
(fig. 13). This condition is particularly well marked in a 248
hour embryo, in which it occurs between all of the developing
cartilages except the first three intermediate syringeal cartilages.
The widest spaces are those between the first half-rings and the
fourth intermediate syringeal cartilages. In these spaces the
mesenchyma shows a slight condensation, suggesting the anJa-
gen of the external tympanic membranes. In a 260 hour embryo
the cells lying near the periphery of this developing membrane
have begun to elongate. Differentiation becomes more marked
in each of the succeeding stages (272, 284, 296, 308, and 320
hours), but it is not until the 332 hour stage that small connective
tissue fibers can be disclosed by the use of Mallory’s stain.

192 JAY ARTHUR MYERS

Extending caudad from the lateral borders of the shaft of the
pessulus in the 404 hour stage, and taking part in the formation
of the medial bronchial walls, a well marked strand of connective
tissue fibers is seen. A large number of these fibers become con-
tinuous with, and enter into the formation of, the bronchidesmus,
which now stretches between the medial walls of the two primary
bronchi.

On comparing figures 5 and 16 it will be seen that the tympanic
membranes have not as yet reached a very high stage of devel-
opment. From their structure and their siz2 one would expect
them to be quite inefficient as vibrating membranes, and capable
of producing only very simple sounds. The simple sounds actu-
ally produced by the young chick, seem to verify this deduction.

At the time of hatching the various structures described are
not essentially different, except for size, from those of the last
stage (404 hours) discussed. It thus appears evident that the
syrinx is very immature at the time of hatching. Between this
time and the adult stage, the four most caudal tracheal rings
unite, in the manner previously described, to form the tym-
panum; the pessulus and the tracheal rings cephalad to the sec-
ond become ossified; and finally, the tympanic membranes be-
come more like those of the adult. In addition to becoming
thinner, these membranes become more extensive and their cor-
responding fibers become more longitudinally arranged.

6. Summary of development

The first indication of the respiratory tract was observed in a
68 hour embryo in which the laryngeo-tracheal groove and the
developing bronchi were present. The trachea is at first very
short and, like the bronchi, is composed of an epithelial tube and
a loose surrounding mesenchyma. The bronchi are relatively
much longer than the trachea in the beginning. Owing, however,
to the rapid development of the neck, the trachea lengthens very
rapidly and is much longer than either of the bronchi in a 128
hour embryo. The epithelium is stratified and, at 80 hours,
rests upon a well defined basement membrane.

THE SYRINX OF GALLUS DOMESTICUS 193

Immediately above the bifurcation, the lumen of the tube is
at first slit-like in shape, but in later stages, 152 and 164 hours, it
is almost square in cross section. Its dorsal wall is about two
times as thick as its ventral wall.

The developing cartilages produce slight evaginations of the
epithelium of the respiratory tube. In a 248 hour embryo these
evaginations occur along the entire length of the trachea and the
bronchi.

At 332 hours only a single layer of cuboidal epithelial cells
covers the future tympanic membranes, while immediately ceph-
alad and caudad to these membranes two or three layers of
nuclei can be distinguished. A distinct layer of small nuclei
appears at the base of the epithelium. In the tympanic regions
this is the only layer of nuclei present. The cells possessing them
are slightly cuboidal, but at 452 hours they become very flat.

Certain cells resembling goblet cells, and other cells with clear
cytoplasm, are present in the 332 hour embryo in all portions
of the epithelium, except that covering the tympanic membranes.
They are quite numerous in the semilunar membrane. At 452
hours certain groups of secreting cells are found which, when
stained with mucicarmine, and when traced through succeeding
stages, were determined to be simple mucous alveolar glands.

Owing to the thickness of the sections it was difficult to detect
the first appearance of cilia, but one can be reasonably sure of
their presence in 248 and 260 hour embryos. They are very
abundant in and following the 332 hour stage.

Vacuoles in the epithelium appeared in the 284 hour stage,
but they were not very numerous in this embryo and are prac-
tically wanting in all other stages.

The skeletal elements are first represented by a condensation
of the mesenchyma, which in a 152 hour embryo is most marked
ventrally in the region of the bifurcation. The anlagen of the
first bronchial half-rings appear just caudad to the bifurcation
in the lateral walls of the bronchi, and are the only skeletal ele-
ments represented in the 164 hour stage. The next anlagen to
appear are those of the fourth intermediate syringeal cartilages
and of the pessulus which become detectable in 184 and 200 hour

194 JAY ARTHUR MYERS

embryos respectively. The third intermediate syringeal carti-
lages are represented at 226 hours. All of the tracheal rings, the
intermediate cartilages, and the first two half-rings are repre-
sented in the 248 hour embryo.

Cartilage cells were first observed in the 284 hour embryo, in
the first half-rings, in the fourth intermediate cartilages, and in
the pessulus. The first tracheal ring and the first and the sec-
ond intermediate syringeal cartilages are the last to differentiate.
Differentiation for these cartilages begins in the 320 hour embryo.
No bone has developed at the time of hatching, nor has the tym-
panum been fully formed.

The submucosa begins to develop ag 284 hours. At first it is
represented by mesenchymal cells, which later produce white and
elastic fibers. These fibers, however, do not take Mallory’s
connective tissue stain until the 404 hour stage. At this time
the submucosa contains numerous nerves and blood vessels.

The two sterno-tracheal muscles are quite well differentiated
at 176 hours. At 188 hours the long cytoplasmic strands or
processes of the developing cells are collected into bundle-like
masses. Faint cross striations were first observéd in a 296 hour
stage. At 452 hours the muscles are not essentially different in
structure from those of the adult.

The intercartilaginous membranes in early stages are not essen-
tially different in structure from the submucosa. In a 260 hour
embryo, the cells nearest their external surfaces elongate and
later develop strands of connective tissue fibers which extend be-
tween the cartilages and attach to these membranes. Promi-
nent bundles of such fibers extend caudally from the pessulus
and enter into the formation of the medial walls of the bronchi,
in a 404 hour embryo.

In early stages the external and the internal tympanic mem-
branes do not differ in structure from the smaller intercartilagi-
nous membranes of the trachea and the bronchi. At the time
of hatching the tympanic membranes are quite thick. It is not
until after this time that they become thinner and appeas as
true vibrating membranes.

THE SYRINX OF GALLUS DOMESTICUS 195
EXPERIMENTS ON FUNCTION

This division of the present paper may seem almost unneces-
sary since Duvernoy, Girardi, Cuvier, and others of the older
investigators conclusively demonstrated that voice is produced
in the lower larynx. Kitchner (’85), and other observers, how-
ever, have expressed their doubts concerning the correctness of
the conclusions arrived at by these early investigators. Because
of such doubts it was thought best to include these experiments.

Experiment I. The trachea of an adult cock was divided at its
middle, after which the bird was set free with others. After the
operation crowing occurred quite frequently, but the voice was
somewhat modified. In order to study these modifications more
carefully, phonographic records were made of the crowing before
and after cutting the trachea. These records were made in the
following manner. A normal adult cock was placed in a small
room. After becoming accustomed to the new environment he
had periods of crowing which were quite regular. An Edison
phonograph was arranged just outside, so that the horn projected
into the room through a small opening. This allowed the experi-
menter to operate the machine unseen. ‘The early morning hours
were found best for making records, as crowing was more fre-
quent and regular at that time.

It is interesting to note that such birds usually crow about five
or six times at intervals varying from ten to fifty seconds, then
after an interval of fifteen minutes to one hour, they again begin
to crow.

After a sufficient number of records had been made, the bird
was deeply anaesthetised and a small part of the trachea exposed
(fig. 17). This caused no noticeable difference in the voice.
After sufficient recovery the trachea was treated with a local
anaesthetic and cut entirely across. The cephalic end was tied
tightly so there was no possible chance for air to pass from it
through the upper larynx and the mouth. The caudal end was
left open and allowed to protrude through the skin of the neck
(fig. 18). The operation had no marked effect on the well-being
of the bird, for, not more than two hours later this same cock,

196 JAY ARTHUR MYERS

when placed with some other chickens, was eating and crowing
as though nothing had happened. Records of the crowing were
made on the following morning. These records were preserved
and carefully compared with those taken before the operation.
This comparison showed that after the trachea had been cut,
tones were produced as before but the pitch was noticeably higher.
It must be admitted, therefore, that the trachea and upper larynx
serve to modulate voice, just as the pharynx and cavities in the
mouth serve the same function in mammals.

Similar experiments were performed on the domestic duck with
precisely the same results.

Through the kindness of Dr. Max Meyer, professor in experi-
mental psychology, University of Missouri, the author is able
to give here the exact changes in pitch which result from divid-
ing the trachea. Dr. Meyer determined the pitch of the voice of
anormal adult male. In this particular individual he found the
- normal tone was one of about 375 double vibrations per second.
The pitch is constant from time to time. It is interesting to
note that there is also but little difference in the pitch from the
beginning to the end of crowing. It was observed, however,
that the pitch is slightly higher at the beginning, there being
a fall of not more than twelve double vibrations.

After the trachea was divided the number of double vibrations
was increased to about 500 per second.

The voice in crowing is not interrupted, but is produced by
one continuous flow of air causing vibrations of the tympanic
membranes. Ordinarily a single crow lasts for about three or
four seconds. But in one individual it was observed that after
the trachea was divided crowing extended over scarcely a single
second of time. As explained by Dr. Meyer, there are two pos-
sible reasons for the time of crowing being so much reduced.
First, when the neck is stretched pain may result from the wound.
Second, the tone produced is so unnatural that it is soon
discontinued.

Experiment II. Since the lungs of birds are not elastic struc-
tures as in mammals, but are more solid, it is obvious that other
organs with a large air capacity must be present, and further,

THE SYRINX OF GALLUS DOMESTICUS 197

that such organs must be capable of exhaling air in greater or
less amount at the will of the bird. Such structures are found in
the air sacs which are present throughout the thoracic and ab-
dominal regions and are continuous with the cavities of neigh-
boring bones.

A chicken was anaesthetized, the humerus sawed through at
its middle and a tightly fitting piece of rubber tubing placed
over the central stump. When air was forced through the tube
into the air sacs, by way of the humerus, sound was produced.
This varied in pitch with the amount of air pressure used, greater
pressure resulting in higher pitch. The trachea was then divided,
but this produced no noticeable result, since the bird was unable
to control the length of the trachea or the width of the glottis by
muscular contraction. Finally, the cervical air sacs were punc-
tured after which it was impossible to produce voice in this arti-
ficial manner, thus proving Herissaut’s statement that when
these sacs were ruptured birds are unable to sing. He explains
this inability to sing as follows: Since the air sacs form air cavi-
ties around the syrinx, it can be seen that there is a tendency to
equalize pressure on each side of the tympanic membranes, but
when sudden gusts of air are forced out through the bronchi the
equilibrium is disturbed. Thus the membranes are set into
vibration. It is evident that all structures through which the
voice passes from the syrinx to the exterior act as resonators.
So far as size and extent are concerned, the trachea forms a large
part of this resonating system.

Experiment IIT. In that part of this paper dealing with struc-
ture, it was noted that the sterno-trachealis muscles extend along
the sides of the trachea from the twelfth ring to the upper larynx.
When a pair of electrodes were applied to this muscle in an anaes-
thetized chicken, it was seen by its contraction to shorten the
trachea from one-fourth to one-third of its original length. It
should be recalled that the typical tracheal rings are so arranged
that they may overlap when the muscles contract. The trachea
may thus act as a pipe or horn capable of being lengthened and
shortened. This has a direct influence upon pitch as was shown
by the following experiment: The so-called thoracic cavity was

198 JAY ARTHUR MYERS

opened and one of the sterno-tracheal muscles was divided at A
(fig. 2). After this operation the tones produced by the chicken
were of a somewhat different quality. When both muscles were
cut the quality of voice was even more distinctly modified. Ob-
viously the division of these muscles was responsible for the
changes produced. Some weeks later this same chicken was
anaesthetized and electrodes applied both directly to the sterno-
tracheales and to the nerves supplying them. It was observed,
with some surprise, that the division of these muscles apparently
had but little effect upon the actual shortening of the trachea.
On stimulation the muscles immediately contracted and pro-
duced a marked shortening. By way of explanation, it should
be recalled that the tympanum is attached to the pessulus and
the first intermediate syringeal cartilages only by elastic mem-
branes; that, although the ventral ends of the intermediate car-
tilages are attached to the ventral pyramid of the pessulus, the
dorsal ends of these cartilages are unattached, and that all of
these cartilages are connected with each otber by the intercarti-
laginous membranes. Further, the external tympanic mem-
branes are attached to the caudal borders of the fourth intermedi-
ate cartilages. Now, if the tympanum be drawn cephalad it is
evident that the external tympanic membranes will, indirectly,
be made more tense. Under normal conditions stimulation of the
sterno-tracheales serves to shorten the trachea. They tend to
pull the caudal end of the trachea cephalad; especially is this the
case if there be a simultaneous contraction of the dorso-lateral
and ventro-lateral muscular bundles previously described. The
extent of this shortening of the trachea is prevented, however,
to some extent by the sternal attachments of the sterno-tracheales.
Hence, when these attachments are severed, the contraction of
the tracheal parts of these muscles tend to make the external
tympanic membranes more tense and a modification in the qual-
ity of the voice is the result. It is of course probable that other
factors, more physical than the above, also share in the produc-
tion of the modification observed.

From their structure it is evident that the external and the
internal tympanic membranes are vibrating structures. As in

THE SYRINX OF GALLUS DOMESTICUS 199

mammals the stratified ciliated columnar epithelium of the larynx
is transformed into the stratified squamous layer over the true
vocal cords, and submucous glands are absent, so in case of the
syrinx of the chicken the stratified ciliated columnar epithelium
is changed into a squamous epithelium over the tympanic mem-
branes. This squamous epithelium, however, is composed of but
a single layer. The prominent glands of the mucosa are also
absent from these membranes.

The semilunar membrane was believed by Savart, Wunder-
lich, and others, to play an important part as a vibrating struc-
ture. It is said to be more prominent in songsters than in other
birds, but Hacker (00) pointed out that in black birds its epithel-
ium is of the stratified ciliated columnar type, and that it proba-
bly is not of much importance in the production of voice, and
also that it is often as well developed in songless species as in the
best songsters. This structure certainly does not act as a vi-
brating membrane in the chicken for it is covered with stratified
ciliated columnar epithelium, and mucous glands are just as
abundant in it as in any unmodified part of the epithelium.

CONCLUSIONS
STRUCTURE

1. The syrinx of the domestic chicken belongs to the tracheo-
bronchialis type, and is quite simple when compared with the
voice organ of song birds.

2. No intrinsic muscles are present in the syrinx of Gallus
_ domesticus. The extrinsic paired sternotrachealis with its cau-
dal prolongations constitute the entire musculature of the syrinx.

3. The rigid skeleton is very highly modified. The first four
tracheal rings are imperfectly fused to form the tympanum. The
four intermediate syringeal cartilages are continuous ventrally
with the ventral pyramid of the pessulus, while dorsally they
end unattached. The first bronchial half-rings are large and in
adults are attached and fused at both ends to the pessulus. The
pessulus is the largest of all skeletal parts and lies dorso-ventrally
at the junction of the bronchi, in a plane transverse to the long

200 JAY ARTHUR MYERS

axis of the trachea. The tracheal rings, the pessulus, and the
ventral ends of the first half-rings become ossified, while all other
skeletal parts:remain cartilaginous.

4. The external tympanic membranes appear between the
fourth intermediate syringeal cartilages and the first half-rings,
while the internal tympanic membranes extend from the caudal
borders of the pessulus to the bronchidesmus and represent merely
a modified part of the medial bronchial walls.

5. The syrinx is lined with stratified ciliated columnar epithel-
lum containing numerous simple alveolar glands. Upon ap-
proaching the tympanic membranes this columnar epithelium
is transformed into a stratified squamous epithelium which be-
comes a single layer of flattened cells over the membranes proper.

6. The tympanum is attached to the remainder of the syrinx
only by elastic membranes.

DEVELOPMENT

1. The first indication of the respiratory system was observed
in a 68 hour embryo in which the laryngeotracheal groove and
the bronchi were represented. At first the trachea is much
shorter than the bronchi, but with the development of the neck,
it becomes, after the 140 hour stage, relatively much longer than
the bronchi. The walls of the trachea and the bronchi are at
first composed only of epithelium which contains two or three
rows of nuclei.

2. The mesenchymal condensation common to the entire epi-
thelial tube first becomes markedly prominent at the tracheal
bifurcation in an ambryo of 152 hours.

3. The anlagen of the first bronchial half-rings appear in a 176
hour embryo, those of the fourth intermediate syringeal ‘carti-
lages appear 12 hours later. The anlagen of the third intermedi-
ate syringeal cartilages and the anlage of the pessulus are pres-
ent at 200 hours. ;

4. Distinct cartilage cells were first observed in the first bron-
chial half-rings.

5. The first four tracheal rings have not united to form the
tympanum at hatching, nor have the other skeletal elements

THE SYRINX OF GALLUS DOMESTICUS 201

taken the shape of those found in the adult. No bone is present
~ at the time of hatching.

6. Ciliated cells are present in stages beyond 248 hours but
were not observed in the region of the future tympanic
membranes.

7. Mucous cells were first observed in 332 hour embryos and
only in later stages were they found arranged in the form of sim-
ple alveolar glands.

8. Muscular tissue is differentiated in the 176 hour stage.
Muscle fibers showing faint cross striations appear at 296 hours.
At 452 hours the muscles are well developed.

9. At the time of hatching the tympanic membranes are thick.
They are covered, however, as in the adult, with a single layer
of epithelial cells.

FUNCTION.

1. That the syrinx is the true voice organ of the chicken is
evident from the following deductions:

First, structurally it is the only part of the respiratory tract
capable of producing sound.

Second, when the trachea is divided and the cephalic portion
tightly tied, the chicken is still able to crow.

Third, after division of the trachea, voice can be reproduced
artificially by forcing air into the air sacs.

2. The upper larynx serves only to modulate the voice.

3. The sterno-tracheal muscles, by their contraction, shorten
the trachea and modify pitch. They also draw the tympanum
cephalad, thus indirectly varying the tenseness of the tympanic
membranes.

4. The air sacs are necessary in voice production, for voice
could not be produced artificially after puncturing the cervical
sacs.

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 1

PLATE 1

EXPLANATION OF FIGURES

1 Dissection of ventral portion of neck and cephalic portion of thorax to

show course of trachea, X 3.
2 Dissection of syringeal region.

Adult male.
The ventral body wall and the heart

have been removed to show the syrinx in position, X 3. Adult male.

3 Pessulus, X 163.

Young adult male.

ABBREVIATIONS

a, apices of pyramids

an,BI.BII., anlage of first and second
bronchial half-rings

an.i.s.c.T,ITJILJIV., anlagen of first,
second, third and fourth intermedi-
ate syringeal cartilages

an.pes., anlage of pessulus

ant.l.p., antero-lateral process of ster-
num

br., bronchidesmus

b.v., blood vessels

b.w., body wall

B., typical bronchial half-rings

b., ossified portion of shaft

b.sur., basal surface of shaft and pyr-
amids

BI,BII,BIII, first, second and third
bronchial half-rings

b.m., basement membrane

c., crop

cor., coracoid

c.d.m., ventro lateral muscle bundles

c.mes., condensed mesenchyma

d.sur., dorsal surface of pyramid

dor.p., dorsal pyramid of pessulus

e.t.m., external tympanic membrane

ep.t., epithelial tube

ep., epithelium

inf.l., lower larynx or syrinx

7.m., interannular membranes
i.t.m., internal tympanic membrane

7.s.c., intermediate syringeal carti-
lages
i.c.m., developing interannular and

intercartilaginous membranes
lat.b., lateral borders of pyramids
1.b., lateral border of shaft
m.c., Marrow cavity
m.b.w., medial bronchial wall
mes., mesenchyma
oe., oesophagus
pes., pessulus
per., developing perichondria
st.h.m., sterno hyoid muscle
sup.l., upper larynx
st.tr.m., sterno trachealis muscle
s., shaft of pessulus
sem.m., semilunar membrane
sm., submucosa
tr., tracheal rings
T., tympanum
v.c., vertebral column
ven,p., ventral pyramid
ven.s.p., ventral surface of pyramid

02

| THE SYRINX OF GALLUS DOMESTICUS PLATE 1
JAY ARTHUR MYERS

ven. s.p. one! aa. Sor: d.sur

PLATE 2 . Ae:
EXPLANATION OF FIGURES

4 Wax reconstruction of syringeal skeleton, X 8. Adult male. ‘5

204

THE SYRINX OF GALLUS DOMESTICUS PLATE 2
JAY ARTHUR MYERS

Sg area ree een

PLATE 3
EXPLANATION OF FIGURES

5 Mid-coronal section of syrinx, X 83. Adult male.

6 Mid-coronal section of syrinx, X 8}. Adult female.

7 Transparent drawing of wax reconstruction of epithelial tube and con-
densed mesenchyma in region of tracheal bifurcation. Ventral aspect, X 50.
176 hour chick embryo.

THE SYRINX OF GALLUS DOMESTICUS PLATE 3
JAY ARTHUR MYERS

207

PLATE 4
EXPLANATION OF FIGURES

8 Wax reconstruction of epithelial tube and related developing skeletal
structures in the region of the tracheal bifurcation. Ventral aspect, X 50. 226
hour chick embryo.

9 Same as 8. Dorsal aspect, 50.

10 Wax reconstruction of epithelial tube and related skeletal elements.
Ventral aspect, X 50. 284 hour chick embryo.
11 Same as 10. Dorsal aspect, x 50.

208

THE SYRINX OF GALLUS DOMESTICUS PLATE 4
JAY ARTHUR MYERS

209

PLATE 5
EXPLANATION OF FIGURES

12 Coronal section of the trachea in the region of its bifurcation, X 176.
176 hour chick embryo.

13 Coronal section of the trachea in the region of its bifurcation, x 100.
200 hour chick embryo.

14 Coronal section of the trachea in the region of its bifurcation, X 104.
248 hour chick embryo.

PLATE 5

THE SYRINX OF GALLUS DOMESTICUS

JAY ARTHUR MYERS

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211

PLATE 6
EXPLANATION OF FIGURES

15 Coronal section of the trachea in the region of its bifurcation, X 64.
284 hour chick embryo. —

16 Coronal section of the trachea in the region of its bifurcation, X 25.
452 hour chick embryo.

212

THE SYRINX OF GALLUS DOMESTICUS PLATE 6
JAY ARTHUR MYERS

Le Gt

PLATE 7
EXPLANATION OF FIGURES

17 Photograph, after exposure of the trachea.
18 Photograph after division of the trachea.

214

THE SYRINX OF GALLUS DOMESTICUS PLATE 7
JAY ARTHUR MYERS

STUDIES ON CILIATED CELLS

S. SAGUCHI

gs Medical Academy, Kanazawa, Japan
* ONE TEXT FIGURE AND FOUR PLATES
CONTENTS
Olea ROT CiMOTIGE eo a tnssierstae: Sioke ecrsas «Soni CORN os cP ORO Cee Tl LO
ie Materials and methods of investigation. ....%...<fe- 622. eans. +++ aes 219
MEE STEGhUre Or CWlintedsceliser 26s... Sy... 2. Dy. Sete cme gt eee oe 220
é AN, IDGSCiah NHIOING Siqucaa od SoG Oe Re Eee Dire 6 ole aac cae cals ieee eA
PG CUCTALCONSIGPEEADIONS 00% oss. 0. <5 ss nes eee ae Bn ae ae 228
. a. The manner of implantation of the cilia................... 228
b. The cytoplasm and rootlets of the cilia.................... 240
Mieevunetion of the ciliary apparatus... . 2... . vagy... doe neces «oe 248
V. Regressive metamorphosis of ciliated cells................-0--00000e 246
A. Transformation of ciliated cells into cells of different nature... 246
Gig BIT OLSEN) <6 cena ee cS aio i. | emer 246
Ido (QSSETRIGHINOINS. Baltes tis oa ee ere oo ens cia dno ada Cwieto Sas 247
(O5. SDUCTINTEN A CES, athe ee ae eR A ae, SLs 2 diag ee 249
eeALLOMiy Of CHIAVEG, COUS I. i. cu ai. x's. of OR. < ai. MARC aoe ee 249
€@, Bimination of evliated cells. ...:..... sk... eee ee ...oeA- 251
Wireivezenecrationvon ciliated cells i. yc on... «so Ae eee en ate os 251
. A. Transformation of other kinds of cells into ciliated cells........ 251
ERVIN LOSUSIOL CHIATC Ry CEES ci 5. oa sds. oo on eR A, gs 251
an the centrosome of the ciliated cell. .-22. fees.) sce. 202
(Sse SUELD ONCE ies aa) oe a erie 8. eee ak eee 257
MaPamnLOsis-Olicilinted GeHS.2h:¢0:..... .+ ss: /eeR eee ee ec 2k 258
D. Significance of mitosis and amitosis of ciliated cells............ 261
es Merclopment of ciliated cells. .:/......:.....s+.sugaeeaem eee os seo BOR
AMET SCORCH EA INe AO eR)... kk ee eee Sete. 262
B. Embryonic development of the ciliary apparatus............... 263
- C. Development of ciliated cells in the efferent tubule of testis of
DEE RIMG ICEMAN TG GEOG... 2.02 <2 0c EME eM tamie Rtas 2 265
D. Ciliogenesis in the daughter-cells produced by mitosis of the
Gite tee eee Meee nee ids. ss oe cas CE OT Ls ek, 266
Witt? Henneguy-Lenhossék’s hypothesis............ 0.0.0.5 e0e.e00-. O00 poset, On
(a, LBM SLIVS TIPS) CLONES 2 TE ge ct eet Se 268
217

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

218 S. SAGUCHI

I. INTRODUCTION

Since ciliary movement was first noticed by Anton de Heide,
in 1683, ciliated cells have been a problem for various investi-
gators. Their structures were studied by Friedreich (’58),
Marchi (’66), Eberth (66), Engelmann (’68, ’79, ’80), Eimer
(77), Frenzel (’86) and others; above all Engelmann and Frenzel
gave detailed accounts of the matter, so there has been left but
little to add as regards their gross structure. According to
these authors, ciliated cells are provided, on their distal borders,
with rod-like corpuscles, named basal knobs (Engelmann’s ‘Fuss-
stiickchen’) or basal rods (Frenzel’s ‘Fussstibchen’), with which
the cilia are connected. These corpuscles—later termed basal
corpuscles by Apathy (’97)—were frequently recognized by several
investigators and regarded as a constituent of great importance
of the ciliary apparatus, which consists of cilia, basal corpuscles
and rootlets.

The question also, whether the factor which produces the
ciliary movement is to be sought in either of these three struc-
tures or in any other structure; especially the question as to the
significance and development of basal corpuscles, were frequenily
discussed, and have not yet been decided definitely. Nearly
about the same time (98), but independently of each other,
Henneguy and Lenhossék announced their opinion as to these
questions. They regard basal corpuscles as derived from cen-
tral corpuscles and as representing a kinetic centre of the ciliary
movement, and point out, as evidence in support of this view,
the morphological, topographical and chemical resemblance be-
tween these two structures, and the behavior of central cor-
puscles or similar bodies to the tails of spermatids of certain
invertebrates and to those of antherozoids of certain plants.
Whether or not this hypothesis (Henneguy-Lenhossék’s hypoth-
esis) expresses the truth, can be solved, I think, only by studies
of the question of the existence or non-existence of centrosomes
and of mitosis in ciliated cells, and especially by ihat of cilio-
genesis. Benda (’00), Fuchs (’04), Ikeda (’06) and others believe
they have found that the basal corpuscles take origin from the

STUDIES ON CILIATED CELLS 219

dividing centrosome, whereas Gurwitsch (’01) and Wallengren
(05) assert, from cheir studies of the genesis of the cilia, both
embryologically and after mitosis of ciliated cells, that the basal
corpuscles are not derived from the centrosome, but differentiate
in the cuticle or superficial layer of the cell-plasm, and that,
accordingly, there is no reason to accept the Henneguy-Len-
hossék’s hypothesis.

In the present paper I intend to give an account of the
structure of ciliated cells, their de- and regeneration, and the
development of cilia, an account, which would throw some light
on the problem above mentioned.

II. MATERIALS AND METHODS OF INVESTIGATIONS

An extensive comparative study being necessary, I have fixed
epithelia from various regions of invertebrates and vertebrates,
which may be tabulated as follows:

Invertebrates

[Ameer

mR we Ode DE Aes OUI B CBD Ce eee Limax
lene

Gill \

Fapijh foe oa ee Anodonta

ESRD PUTS UGMI CRS ee ro CES 3 er Helix

Oviduct ;

{Rana temporaria
Pharynx

Rana esculenta
Pemroriicie Pee HB ees, 40 O84. s).. 2. Xe Bufo
Efferent tubule of testis Triton
Epididymis
Gall-duct ( Trigonocephalus
iferentevubuletot testis, s.tee2. tec. ss. <2. Eliaphis
Trachea Lizard
Efferent tubule of testis { Mouse
Epididymis r ii SMeHe fell tal eirahe! aiiey ewan ee lal op “ Rat

Embryonic materials

Ciliated infundibulum | ( Hyla, larvae
Tela chorioidea [ | Rhacophorus, larvae
Pharynx (SG lla lee ali | Hynobius, larvae

Epidermis J | Rana esculenta, larvae

220 S. SAGUCHI

Small pieces of the materials were preserved either in Meves’s
fluid or in sublimate-acetic mixture, the result of which was in
most cases favorable for the study of minute structures. With
the former fluid it was passed through grades of alcohol, after
washing thoroughly in running water, to 96 per cent alcohol;
with the latter it was brought immediately into 70 per cent
alcohol with iodine and then through grades of alcohol. Im-
bedded in paraffine through chloroform.

The sections were, for the most part, cut 4 « thick and stained
on the slide. For staining I have mainly employed Heidenhain’s
iron-haematoxylin method, with or without counterstaining with
plasma-dyes.

Ill. STRUCTURE OF CILIATED CELLS
A. DESCRIPTIONS OF MY OWN OBSERVATIONS

1. The foot of Anodonta. The epithelium consists of a row of
columnar ciliated cells (figs. 1, 2), the distal ends of which are
bordered with a well-defined, relatively broad cuticle which
stains faintly with iron-haematoxylin. In profile it is noticed
that the cuticle is striated longitudinally, each stria appearing
to be continuous with a ciltum, which is from six to seven times
as long as the height of the cuticle. Below the cuticle is a
narrow zone, consisting of a series of basal corpuscles, which
may be called ‘layer of basal corpuscles’ (fig. 2). These are
minute, oval bodies appearing, in surface view, as small granules
arranged in parallel rows, which are, in most cases, at right
angles to the larger side of the distal cell-end (fig. 3). Below
the layer of basal corpuscles is another zone of dense nature,
which stains more deeply with plasma-dyes. Through this zone,
which provisionally may be designated ‘transparent zone,” fine
fibers pass vertically from the basal corpuscles towards he cyto-
plasm proper, where they become lost to view. The cytoplasm
contains a large number of tortuous mitochondrial filaments,
stained black by iron-haematoxylin; they are mainly arranged
vertically and are accumulated especially in the upper portion
of the cell-body, under the transparent zone, without passing

STUDIES ON CILIATED CELLS ea k

into it. No centrosome and mitotic figure were seen in the
cells in question.

2. Gills of Anodonta. The epithelium consists of ciliated and
non-ciliated cells. Of the ciliated cells I have studied lateral-cells
and corner-cells. Both these cell-varieties are provided with a
cuticle carrying long cilia, which, in fixed preparations, are curved
towards the external surface of the gill-torus, as noticed by
Engelmann (’80); this is especially well marked in the lateral-
cells. The behavior of the layer of basal corpuscles, of the
transparent zone and of the chondriocontes is analogous to that
described above for the foot of the same species (fig. 4).

The layer of basal corpuscles, which seems to correspond to
the zone found by Wallengren (’05) below the cuticle, contains
basal corpuscles, in the shape and arrangement of which the
lateral- and corner-cells differ widely from each other. Viewed
from the surface (fig. 5a), the lateral cells, each of which has a
regular rectangular outline, are arranged in stone-wall-like rows
running along the gill-torus. The basal corpuscles are spheri-
cal granules, which form parallel rows arranged in the direction
of the short diameter of the cell-border, as is the case with the
foot-epithelium of the same species. Engelmann (’80) has also
described such a linear arrangement of basal corpuscles; he
states that the lines are inclined about 45° to the longer margin
of the cell-border, but I could not confirm this.

The corner-cells, separated from the series of lateral-cells by
two rows of non-ciliated cells, are closely apposed on their flat
faces, forming a series along the gill-torus (fig. 5b); m surface
view of this type of cell two parallel lines, stained black by iron-
haematoxylin, run along the longer axis of the cell-border. T ese
lines, named by Engelmann bandelets (‘Leistchen’) serve for
the attachment of the cilia, and might conceivably be formed,
as the author suggests, by the fusion of basal corpuscles.

3. The intestine of Anodonta (figs. 6-8, 16). The epithelium in
this region consists of ciliated, non-ciliated and glandular cells.
The first two of these are provided with striated cuticular borders;
the clear space between the striae in lateral view correspond
with pores seen in surface views; this suggests strongly that the

Paves S. SAGUCHI

cuticular substance is perforated by canaliculae, filled with fluid;
the striae are therefore nothing but the septa of these canalic-
ulae viewed in profile. The cilia pass through the striae and
come into connection with the basal corpuscles underneath the
cuticle. The basal corpuscles, spherical or oval in form, are
here also arranged in linear series running, in most cases, parallel
to the shorter diameter of the cell-border. Since it seems that
the larger diameter of most epithelial cells is oriented in a direc-
tion, perhaps parallel to the axis of the intestine, it is natural
that the rows of basal corpuscles all run in a direction, which
is at right angle to the axis of the intestine, a condition which,
I think, is of an important significance for the function of ciliated
cells in this situation. Under the layer of basal corpuscles fol-
lows a comparatively narrow, transparent zone, through which
fine fibers, arising from the basal corpuscles, pass downwards.

The chondriocontes in the cytoplasm are chiefly arranged in
a vertical direction and are largely accumulated beneath the
transparent zone (figs. 6, 8). They seem not to be floating in
the plasma-sap, but to be suspended on or imbedded in the beams
of the plasma-network. If a reagent which causes a shrinking
of the cell, such as sublimate-mixture, be employed (fig. 7)
there appears a sinuous or spiral fiber, stained deeply by iron-
haematoxylin, and splitting upwards into several filaments,
which end under the transparent zone. With Meves’s fluid,
on the contrary, no such feature appears (figs. 6, 8). From this
it is highly probable that this fiber, found by various investi-
gators and termed: ‘cone of rootlets,’ is produced by the act of
shrinking, which must result in the cohesion of beams of the
plasma-network with the suspended chondriocontes. Centro-
somes and mitosis are often met with in ciliated cells from
this location.

4. The middle-intestine of Helix. The constituent elements
of the intestinal epithelium of this species are the same as those of
Anodonta. The ciliated cells (figs. 9, 15) bear comparatively short
cilia, which pass through the cuticle and come into connection
with basal corpuscles; these latter are very small granules, so
closely applied to one another that they appear, at a certain’

STUDIES ON CILIATED CELLS 225

degree of differentiation of iron-haematoxylin, as a single dark
line beneath the cuticle. The transparent zone is about one
half the height of the cuticle and is marked off distinctly from
the cytoplasm proper. Chondriocontes are also visible; their
arrangement is similar to that described above for Anodonta.
Centrosomes and mitotic figures are easily recognizable; two-
or poly-nucleated cells also occur.

5. The hepatic duct of Helix. The epithelium in this region
is composed of ciliated cells with interspersed glandular- and
non-ciliated columnar cells; in approaching the gland proper
non-ciliated cells increase in number. The cilia pass, as usual,
through the cuticle in order to connect with basal corpuscles,
which appear as minute granules and form, viewed from the
surface, linear series running parallel with one another (figs. 10,
11). Sometimes the course of the chondriocontes is so regular,
that they form a sort of palisade (fig. 10). In order to follow
the fibrils which pass downwards from the basal corpuscles it
is necessary to remove the chondriocontes, which often prevent
close examination. This is realized practically in poorly pre-
served portions of the sublimate or Meves materials. Sections
from such portions show that the fibrils in question (fig. 11)
pass, in a slightly tortuous course, through the cytoplasm towards
the distal end of the nucleus. These fibrils (corresponding with
what are designated as rootlets of the cilia) appear not to be
free, but to be connected with protoplasmic networks and are
not to be confounded with the chondriocontes, which seem to
be suspended on or embedded in the beams of the network
and never pass into the transparent zone. Centrosomes and
mitosis of ciliated cells occur not infrequently; two-nucleated
cells also often are met with.

6. The intestine of Helix. There exist no noteworthy differ-
ences in structures of ciliated cells between the intestine of Limax
and that of Helix, so that its description can be omitted.

7. The epidermis of Amphibian larvae. The epidermis of
young Amphibian larvae is composed of two layers; in the upper
or cuticular layer, there are two kinds of cells: non-ciliated and
ciliated cells. The latter (figs. 27-32) are few in number and

224 S. SAGUCHI

are scattered over the epidermis. They are furnished, at the
distal border, with striated cuticle; each stria corresponding
with a cilium. With favorable staining the basal corpuscles
appear as diplosome- or dumb-bell-shaped granules (figs. 31, 32);
one of these granules is situated at the upper border, the other
at the lower, of the cuticle; the former is always smaller and
more easily decolorized than the latter, so that there often
appears a single row of basal corpuscles below the cuticle. The
axis of these diplosome-like basal bodies either corresponds with
the vertical axis of the cell in question (fig. 32) or is inclined in
a determinate direction (fig. 31). When studied in tangential
sections, the basal corpuscles form parallel rows and are inclined
towards one end of the row (fig. 33). Since the inclination of
basal corpuscles occurs only in a determinate direction, it is evi-
dent that, when the cell in question is cut parallel to the rows,
the feature as represented in figure 31 is produced, and, that,
on the other hand, the same holds true for the cell with vertical
basal corpuscles in the sections which are cut at right angles to
that direction (fig. 32).

The chondriocontes in the ciliated cells are more numerous
than in neighboring non-ciliated cells and are collected especially
beneath the cuticular border. In case the cilia are localized in
a certain circumscribed region, the main mass of the chondrio-
contes drifts to that portion, which indicates a close relation
between the two (fig. 27). In sublimate preparations, fibers
which, arising from the basal corpuscles, pass downwards, can
be readily seen (fig. 30); they are not to be identified with the
chondriocontes, but must be regarded, from their staining reac-
tion and the continuity with basal corpuscles, as rootlets of the
cilia.

8. Tela chorioidea of Amphibia-larvae. The ciliated epithe-
lium-cells from this structure (figs. 36-88) carry comparatively
thick cuticular borders, which are not homogeneous, but are
finely striated in the longitudinal direction. The cilia, which
may be located in a circumscribed portion, especially in the
middle of the cell-border, pass vertically through the cuticle
and are connected with basal corpuscles. ‘The latter are situ-

STUDIES ON CILIATED CELLS 225

ated in a layer corresponding to the transparent zone of the
Meves preparates, and appear as diplosome- or dumb-bell-shaped
granules; the distal granules are always small and readily decolor-
ized. The axis of the basal corpuscles is not vertical, but is
inclined to one side of the cell (fig. 38). Since, in other cases
there are vertical basal corpuscles, it appears probable that here
also there may be the same condition as in the ciliated epidermis
cells of the same species. The corpuscles are, however, irregu-
larly disseminated, without forming rows (fig. 39). In the cyto-
plasm there are numerous chondriocontes, which are often ori-
ented towards the cilia, a condition which is especially striking
in cases when the cilia are localized in a certain portion of the
cell-border (fig. 36).

9. The ciliated infundibulum of Amphibia-larvae. The ciliated
cells (fig. 41) are short, cylindrical in shape and covered with
thin structureless cuticular borders. The cilia are very long and
often adherent into a thick curved bundle, the free end of which
is always directed towards the peritoneal canal. The cilia pene-
trate the cuticle and come into connection with the basal cor-
puscles, which appear, in tangential sections of sublimate-mate-
rials, as very small granules scattered irregularly over the cell-
surface, with the exception of a narrow peripheral zone. The
chondriocontes are mainly accumulated in the distal portion of
the cell-body, separated, however, from the layer of basal cor-
puscles by the transparent zone.

10. The pharynx and oesophagus of Amphibia (figs. 42-55).
The cuticular border of the ciliated cells is longitudinally striated,
each stria corresponding to a ciliary fiber. Since the basal cor-
puscles are very small and set closely side by side, it is difficult,
in side view, to distinguish between them (fig. 46). In tangential
sections they form linear series, parallel to one another, the cor-
puscles in the same row being united by a slightly staining
fiber (figs. 47, 50); the lines lie, in most cases, in a direction at
right angles to the longer side of the cell-border. In the trans-
parent zone there are fibrils which run from the basal corpuscles
downwards and are to be identified with the rootlets of the
cilia. The chondriocontes are mainly arranged vertically and

226 S. SAGUCHI

are accumulated especially underneath the transparent zone.
Ciliated cells with a centrosome and those with two or more
nuclei often oecur.

11. The gall-duct of Amphibia. The epithelium of the gall-
duct of Amphibia consists of ciliated and non-ciliated columnar
and basal cells. The ciliated cells (fig. 57) are columnar in shape
and bordered with a cuticle, through which the cilia pass to con-
nect with the basal corpuscles. These are small granules, situ-
ated underneath the cuticle. If, as in a certain degree of differ-
entiation is the case, the poimts where the cilia are connected
with the upper border of the cuticle appear as black granules,
then the feature of diplosome- or dumb-bell-shaped corpuscles
would be brought about. The behavior of the transparent zone
and of the rootlets of the cilia is about the same as described
in the pharynx of Amphibia. Ciliated cells with two nuclei
and those with centrosomes are not infrequent here.

12. The oviduct of Amphibia. The oviducal epithelium is com-
posed of ciliated and glandular cells. The former (figs. 63, 66)
have thin cuticular borders; the basal corpuscles appear either
as short rods in the cuticle, or as small granules underneath it.
This difference of shape may perhaps be correlated partly with
the degree of staining, partly with different animals. Thus I
have found short, rod-like basal corpuscles in the oviduct of
Triton, whereas they appear in that of the frog as of minute
granules underneath the cuticle. In tangential sections they
are arranged in parallel rows, all of the granules of one row being
united by a fine slightly-staining thread. The direction of the
rows corresponds to that of the short side of the distal cell-border
(fig. 67). The chondriocontes are mainly gathered under the
cuticle, the transparent zone is illy defined; binucleate ciliated
cells often occur.

13. Ciliated cells in the peritoneum of Rana temporaria. The
occurrence of ciliated cells in the peritoneum of female frogs was
first described by Thiry (’62), and then confirmed by Schweiger-
Seidel and Dogiel, Neumann, Nussbaum and others. According
to these authors the ciliated cells.in question are flattened and
are smaller than neighboring endothelial cells; they are either

STUDIES ON CILIATED CELLS pats

scattered or form rows. The type of cell which I have found
among the peritoneal cells near the oviduct is represented in
figure 68. The cilia are comparatively thick and are connected
with spherical basal bodies; a special cuticular border seems
to be wanting in this cell.

14. The trachea of Trigonocephalus. The ciliated cells in this
part (fig. 69) have on their free surface, cuticular borders and
relatively long cilia. The basal corpuscles are differentiated
with difficulty, and therefore appear in most cases as a dark line
underneath the cuticle. In tangential sections they appear as
minute granules, closely applied to one another, the whole, at
first sight, resembling a fine network. On close inspection, how-
ever, I had no difficulty in making out linear series of granules,
arranged in a determinate direction. The transparent zone and
the chondriocontes behave in the same manner as described in
other species. Ciliated cells with two nuclei are not infrequent.

15. Efferent tubules of the testis of Reptilia. Of the reptiles,
have studied snakes, adders and lizards. The epithelium con-
sists of ciliated cells and cells with brush borders. ‘The former
are small in number in proportion to the latter. At the free
extremity of the ciliated cells (figs. 72, 73, 76) there is a narrow
zone, darkly stained by iron-haematoxylin and presenting the
appearance of a cuticular border. The basal corpuscles are
either imbedded in this zone or situated beneath it. The chon-
driocontes are collected below the cuticle, being separated from
it by a narrow transparent zone. Binucleate ciliated cells often
occur in the efferent duct of these forms.

16. The oviduct of the lizard. The oviducal: epithelium con-
sists of ciliated and glandular cells. The former are few in
number as compared with the latter and bear on their free sur-
face thin cuticular borders. The basal corpuscles are in most
cases rod-like granules imbedded in the cuticle; in other cases
they appear as small spherical bodies beneath the cuticle. This
difference may perhaps be connected with the degree of stain-
ing. The transparent zone is illy defined; binucleate ciliated
cells are not rare. |

228 S. SAGUCHI

17. Efferent ducts of the rat and mouse. The epithelium con-
sists of ciliated cells and cells with brush borders. The ciliated
cells (figs. 84-88) taper gradually to their proximal extremity.
Their nuclei are large and take a higher position than those of
neighboring cells, as already noticed by Lenhossék (1898). The
uppermost portion of the cell-body generally is of a dense char-
acter, and basal corpuscles, rod-like, diplosome- or dumb-bell-
shaped, are arranged here in parallel rows. Any well-defined
cuticular border, such as seen in other places, is not discernible
here. There are centrosomes in the transparent zone. ‘The
chondriocontes are mainly collected below the transparent zone,
without entering into it. The basal corpuscles, viewed in tan-
gential sections, are not scattered irregularly, but are arranged
in linear series, parallel to one another and at right angles to the
larger diameter of the cell-border. There is always a single
nucleus.

18. The trachea of the rat and mouse. The ciliated cells of the
trachea of these forms (figs. 91-95) are bordered with a distinct
cuticle through which the cilia pass downwards to connect with
basal corpuscles. These are small spherical granules situated
under the cuticle; in a surface view their linear arrangement is
conspicuous (fig. 95). The chondriocontes never enter into the
transparent zone. The cells are often provided with two nuclei,
the centrosome is readily discernible.

B. GENERAL CONSIDERATIONS

a. The manner of implantation of the cilia

Ciliated cells are either columnar, or cubical, or, in rare cases,
flattened in shape, and, although they participate in the forma-
tion of the simple or stratified epithelium, it can hardly be said
that there is any epithelium which consists of ciliated cells only,
other kinds of cells, such as non-ciliated columnar or glandular
cells almost invariably entering into its composition. And while
the ciliated cells, on the one hand, are partly eliminated after
degeneration, partly converted into columnar or glandular cells,
the columnar epithelial cells, on the other hand, become trans-

STUDIES ON CILIATED CELLS 229

formed into ciliated cells. This is a physiological change which
is going on, not only in embryonic or young tissues, but also in
those which are fully developed. Under these conditions, the
differentiation of the superficial plasma-portion of a ciliated cell
might be considered from two morphological points of view:
first, from the structures derived from the normal columnar
cell, and then from what are newly formed with the develop-
ment of the ciliary apparatus; and it is natural that these differ-
entiations vary according to the forms of epithelial tissues in
which the ciliated cells are involved.

It is extremely rare that the ciliated cell exhibits no special
differentiation in its distal border. Even in such cases as where
a distinct cuticle seems to be lacking, as Lenhossék (’98) and
Studni¢ka (99, ’00) state, the distal border of the ciliated cell
where the basal corpuscles lie, is somewhat dense in character
and stains more heavily with plasma-dyes. This fact might
have, as Lenhossék remarks, a certain amount of importance for
the physiological function of the cilia.

1. Relation between the cilia and the cuticle. Friedreich (’58)
was the first to describe the cuticular border of the ciliated cell;
he found a striated cuticle in the ciliated cells of the trachea
of man and bull, and of the ventricular wall of the human
brain; and believed that the cilia pass into the cytoplasm along
the striae. The structure in question has since been noticed by
Eberth (’66), Marchi (’66), Engelmann (’68) and others.

I find in the literature of the subject five different opinions
with regard to the structure of the cuticular border and the
manner of implantation of the cilia:

1) Rabl-Riickhard (’68) asserts that, although he found a
cuticle in the ciliated cells of gills of Annelida, the cilia never
pass through it, but are attached to its upper surface by some-
what dilated bases.

2) Friedreich (58), Stuart (67), Apathy (97) and Gurwitsch
(01, ’04) believe that the ciliated cell has a homogeneous cuticle,
through which the cilia pass into the cytoplasm, and, in addi-
tion, it was shown by Gurwitsch that the cuticle must be soft,
since the cilia pass through it irregularly.

230 S. SAGUCHI

3) According to Engelmann (’80), Gaule (’81), Carriére (82),
Heidenhain (’99) and others, the cuticle is provided with rod-
like corpuscles, which appear, in profile, as longitudinal parallel
striae, with the upper ends of which the cilia are connected; a
view which is not markedly different from that described under
2).

4) Marchi (66) and Studni¢ka (00) admit sieve-like perfora-
tions of the cuticle, through which the cilia pass downwards
into the cytoplasm.

5) This view admits an alveolar structure of the cuticular
border. Gurwitsch (’01) finds that the cuticle, in surface views
of the ciliated cells from the rabbit’s oviduct, is made up of
regularly arranged alveoli; at the nodes of the alveolar net-
works there are basal corpuscles, with which the cilia are con-
nected. Studniéka (’00) also found an alveolar structure of the
cuticle in the ependyma cells of Spinax niger.

I have, in turn, found, in all forms studied, th the super-
ficial portion of protoplasm of the ciliated cell, that is to say,
the part where the cilia are implanted in the cell, is always. of
a denser character, appearing either as a crust or as a well-
defined cuticle, which varies greatly in thickness.

Whether the longitudinal striation of the cuticular border,
seen in profile, is a feature brought about by the passage of the
cilia, or is owing to rod-like structures in the cuticle, or is an
appearance due to canaliculi, or is produced by an alveolar struc-
ture.of the cuticular border, is a question which is very diffi-
cult to solve; at least when one attempts to draw any conclu-
sion from the study of ciliated cells themselves, since the feature
is more complicated by the implantation of the cilia. I believe
that the clue to the solution of the problem is furnished by the
study, either of those cases in which the cilia are limited in a
certain circumscribed portion of the cuticle (e.g., in the epi-
dermis and tela of Amphibia-larvae), or in the transformation
of non-ciliated into ciliated cells, or in the redifferentiation of
ciliated cells into non-ciliated. From such studies I have been
able to find three types of differentiation of the superficial por-
tion in the ciliated cells studied:

STUDIES ON CILIATED CELLS Zo

1) In the first type, such as in efferent tubules of the testis
of Reptilia and mammals, I have never been able to recognize
any well-defined cuticle; what can be seen is an ill-defined crust,
in which the basal corpuscles le, thus giving rise to the appear-
ance of a longitudinal striated cuticular border. That this ap-
pearance is owing to the existence of basal bodies in the crust, is
readily explained by the study of ciliogenesis in epididymis cells
of mammals. In efferent tubules of the mouse, as will be after-
wards described, it is evident that cells with brush borders, which
are provided with a crust on their distal margin (fig. 89), become
converted into ciliated cells, and that from the way that the
newly-formed basal corpuscles arrange themselves in the crust.
In one word, the striated cuticle in this case is nothing but a
portion of the crust defined by the arrangement of basal bodies.

2) To the second type belong the ciliated cells of the epi-
thelium of the pharynx and tela of Amphibian larvae. As the
representative of this group I take the ciliated cells of the epi-
dermis, the most closely examined. As will be afterwards de-
seribed, these ciliated cells are developed from non-ciliated, the
cuticle of the latter becoming directly converted into that of the
former. ‘The cuticle, in profile longitudinally striated, exhibits,
in surface view, a well-marked reticular appearance. If these
two features are considered associated with each other, it becomes
evident that the cuticle is composed of closely apposed aloeoli,
the junction of the alveolar walls appearing, in side view, as
striae (compare: F. E. Schulze ’69, ’88; O. Schutze ’07;5. Saguchi
15), through which the cilia pass into the cytoplasm.

The structure of the cuticle of ciliated ependyma cells is the
same as that above described, except that the longitudinal striae
are very closely applied, rendering close examination extremely
difficult (figs. 36, 38). Studnicka (’99) describes the cuticle of
ciliated cells in the tela epithelium of Petromyzon as provided
with small canals through which the cilia pass into the interior
of the cell. This seems, however to me to be an artificial result
brought about by the fixation; for but one of the seven cells
in his figure 5 has such canaliculi, and he says in his text. that
“‘sie (canaliculi) sind, wie es scheint, viel grésser als es zu diesem
Zweck (passing through of the cilia) nétig ware.

232 S. SAGUCHI

His figure 5 to 7 and 8, rather, appear to me evidently to show
an alveolar structure of the cuticular border.

3) The intestines of Helix, Anodonta, Lumbricus and Limax, and
the hepatic duct of Helix belong to this group. Before proceeding
to describe the ciliated cells it will be necessary to say a few
words with regard to the structure of the cuticle of non-ciliated
intestinal cells. There are three opinions with regard to this
question: (1) the cuticle is perforated by small vertical canals
(K6olliker, Funke); (2) it is provided with rods (R. Heidenhain) ;
(3) it is composed either of coarser or of slender, finger-shaped
rods (Studniéka). In intestinal cells of the invertebrates studied,
I have found that the cuticle has, viewed ‘in profile, an appear-
ance of longitudinal striation, seemingly caused by a parallel
arrangement of rods; the clear vertical narrow lines correspond
to the spaces between them. In surface view, minute, round,
clear pores appear scattered over the cuticle. These facts point
to the canalization of the latter, as Kélliker and Funke maintain.

The structure of the cuticle of ciliated cells is the same as that
of the non-ciliated and can readily be observed in the functional
change of the former, that is to say, in their transformation into
non-ciliated or glandular cells (figs. 8, 11). In these figures it
can well be seen that the cilia never pass through the canaliculi,
but through the axis of the rods themselves.

The intestinal cell has been considered by some to have a
brush border, and there is much diversity of opinion in regard
to the relation between the cilia and the hairs of the supposed
brush border. Vignon (’00) found, in the intestine of Chirono-
mus larvae, that the cilia are attached to the free extremities
of the hairs of the brush border, and believes that there is no
genetic connection between these two structures, whereas Pre-
nant (’97—’99) and Holmgren (’03) assert that the hairs of the
brush border are nothing but atrophied cilia. According to
Gurwitsch (’01), there exists no relation, either genetic or ana-
tomic, between the cilia and the hairs, the former passing inde-
pendently through the spaces between the latter.

2. Relation between the cilia and the brush border. Ot the cili-
ated epithelia studied, I have found cells with brush borders in

STUDIES ON CILIATED CELLS 233

only the efferent tubules of the reptilian and mammalian testis.
The cells with brush borders in these places, as will be afterwards
more particularly described, become converted into ciliated.
In this transformation the cilia are produced, not by the lengthen-
ing of the hairs, but from an intracellular constituent, which
passes out through the axis of the hairs, so that there exists no
genetic relation between the two. I will return to this question
further on.

3. The basal corpuscles. Historical. By the basal corpuscle
is meant a minute granular or rod-like body, situated at the
proximal end of each cilitum and stained black by iron-haema-
toxylin. It would seem never to be lacking in the ciliated cell
proper; there is, however, no uniformity as to its shape and
position; it also varies considerably according to the degree of
coloration.

A review of the literature shows that there is a considerable
difference of opinion as regards the shape, position and arrange-
ment of basal corpuscles, which is briefly summarized as follows:

Shape: (a) spherical or elliptical granules (Lenhossék ’98,
Studni¢ka ’99, Wallengren ’05, Erhard ’10); (6) short rod-like
corpuscles (Studnicka ’99, Ikeda ’06); (c) dumb-bell-shaped or
diplosome-like granules (Gurwitsch ’00, ’01; Henry ’00; Fuchs
04; Kolacév 710; Tschassownikow ’13).

Position: the basal corpuscles are situated (a) in the distal
border of the ciliated cell destitute of the cuticle (Lenhossék ’98) ;
(b) in the cuticle itself (Heidenhain ’99, Gurwitsch ’01;) (c)
underneath the cuticle (Apathy ’97, Studnicka ’99, Wallengren
’05, Erhard ’10); (d) more or less deeply in the cytoplasm below
the cuticle, as in the ciliated cells in the tela of Petromyzon and

Salamandra (Studni¢ka 799).

' Arrangement of basal corpuscles; viewed from the surface:
they are either (a) irregularly scattered (Lenhossék ’98); or (6)
gathered in the central part (Studnicka ’00); or (c) arranged in
linear series (Engelmann ’80, Gurwitsch ’01); or (d) fused into
lines (Engelmann ’80).

Summary and discussion. It is worthy of remark, that the
result of staining with iron-haematoxylin, which is usually applied

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

234 S. SAGUCHI

in order to exhibit the basal corpuscle, varies according to the
grade of differentiation. This is an advantage, and, at the same
time, a difficulty, of that technic. ‘To speak more correctly:
while, on the one hand, it enables one to judge the intensity of
its affinity for cell-constituents, the same constituent of the cell,
on the other hand, often presents a good deal of variety accord-
ing to the degree of staining, which may give rise to misinter-
pretation. Not only the manipulation of staining, but also the
degree of maturation of haematoxylin-solution used has a marked
effect upon the result. An especially important factor in this
staining is the method of fixing and the quality of fixative.
For example, in preparations from materials perfectly fixed in
Flemming’s fluid the mitochondrial filaments stain deeply, where-
as the basal corpuscles remain unstained ; in poorly-fixed Flemming
and in the sublimate-material, on the other hand, it shows an
inverse staining capacity.

So far as can be seen from my preparations, the basal cor-
puscles may be classified according to their shape and position
as follows:

1) Spherical or elliptical basal corpuscles which are situated
beneath the cuticle; these forms are met with in the gill (fig. 5,
lateral cells), foot (figs. 1-3) and intestine (figs. 6-8) of Anodonta,
in the intestine (fig. 9) and hepatic duct (figs. 10, 11) of Helix,
in the intestine of Limax and Lumbricus, in the pharynx of
Rana, Bufo and Triton (figs. 46, 49), in the gall-duct of Rana
(fig. 57), and in the trachea of Trigonocephalus, of the mouse and
rat (fig. 92). Such cases as this are found in the description
and figures of the following authors who studied the intestines
of invertebrates: Apathy (’97, typhlosole of Anodonta, Lenhossék
(’98, middle intestine of Anodonta), Heidenhain (’99, intestine of
Helix), Gurwitsch (’01, intestine and mouth of Lumbricus),
Holmgren (’03, pharyngeal pouch of Lumbricus), Erhard ’10,
typhlosole and hepatic duct of Anodonta), and Kolacév (10, in-
testine of Anodonta).

The corpuscles found by Engelmann (’80) in the intestine of
Cyclas and Unio, and named by him ‘Fussstiicke’ may, as al-
ready stated by Studniéka (99), be identified with the basal
corpuscles. Heidenhain (’99) describes and figures lozenge-

STUDIES ON CILIATED CELLS 235

shaped basal bodies at the distal margin of the cell; Brasil (’04)
has found in ciliated cells of the middle intestine of Lagis coreni,
rod-like corpuscles, termed ‘La batonnet cilifére,’ which, to my
mind, are not special rods, but correspond with the intracuticular
portions of the cilia.

As to the ciliated cells of the gills of Anodonta, my observa-
tions are in accord with those of Wallengren (’05) and Erhard
(i10):

The basal corpuscles in the ciliated cells of the Amphibian
- pharynx are, so far as can be seen from my materials, extremely
small, often appearing in profile as a dark line beneath the
cuticle, a feature which has been already noticed by Lenhossék
(98). In all of my preparations which are stained to varying
extents, I have not been able to make out rod-like or dumb-bell-
shaped basal corpuscles in the cuticle, as described by Eimer
(77) and Studnitka (99) in the pharynx of Salamandra, by
. Gurwitsch (’01) in the oesophagus of Bufo, and by Tschassowni-
kow (13) in the oesophagus of the axolotl. I am not quite sure
whether this difference is due to the materials used or to other
factors.

2) Dumb-bell-shaped or diplosome-like basal corpuscles.
These are situated (a) in the crust, as in the ciliated cells of
efferent tubules of the mouse and rat (figs. 84-88); (b) in the
cuticle, as those of the Amphibian epidermis (figs. 31-33); (c)
beneath the striated cuticle, as in those of tela of Amphibia
(figs. 37-38).

In the eases (a) and (b) the upper granules are easily decolor-
ized, thus giving rise to the appearance similar to that described
under 1).

Regarding the basal corpuscles in the ciliated cells of the
efferent tubule, I refer to the papers of Lenhossék (’98), Henry
(00), Ach (02), Fuchs (02, ’04), and Ikeda (’06). Of these
authors, Lenhossék, Henry and Ikeda have found oval or short
rod-like basal corpuscles, while Fuchs noticed, in addition to
these, diplosome-like bodies.

My observations on the tela epithelium are entirely in accord-
ance with those of Studniéka (’99, ’00) on the ciliated ependyma
cells of Cyclostoma, fishes, Rana, Salanandra, and of man, and

236 S. SAGUCHI

with those of Gurwitsch (01) on the ciliated cells of the tela
epithelium of Salamandra.

3) Short rod-like basal corpuscles, which are imbedded in
the thin cuticular or crust-like, distal border of the cell. The
ciliated epithelial cells of the oviduct of Rana temporaria, Tri-
ton, and the lizard, and those of efferent tubules of. the lizard,
snake, and Trigonocephalus belong to this type (figs. 66, 73, 76).

As regards the arrangement of basal corpuscles in surface
view, I can distinguish the following three types:

1) The basal corpuscles are gathered, without special dis- ©
position, in the middle of the cell; such a form is found in the
ciliated cells of tela chorioidea of Amphibian larvae (fig. 39)
and corresponds with what Studnicka (’00) noticed in the ciliated
ependyma cells of Cyclostomata, Rana, and especially of man.

2) They are arranged in linear series, parallel to each other,
and in most cases at right angles to the longer side of the cell-
border. I have found such a type in the following situations:
in the gill (fig. 5 a), intestine (fig. 16,) and foot (fig.3) of Anodonta,
in the hepatic duct of Helix, in the epidermis (fig. 33), pharnyx
(figs. 47, 50), and oviduct (fig. 67) of Amphibia, in the trachea
(fig. 95) and the efferent tubule (figs. 83, 90) of the mouse and
rat.

That the view of Engelmann (’80) as to the arrangement of
the basal corpuscles in ciliated cells of gills of Anodonta is at vari-
ance with that of my own, has been already mentioned in the
foregoing chapter.

For the surface view of ciliated intestinal cells of invertebrates
I refer to the figures of Heidenhain (’99) from the hepatic duct
of Helix, of Gurwitsch (’01) from typhlosoles of Lumbricus and
Anodonta, and of Kolacév (’10) from the intestine of Anodonta.
According to the figure of Heidenhain, the rows of basal corpuscles ~
are nearly at right angles to the longer side of the cell; while Gur-
witsch figures rows parallel to the latter. This latter type I
have seen very rarely, but never such a type as Kolacév figures
in which the basal corpuscles are irregularly scattered over the
cell-surface.

STUDIES ON CILIATED CELLS 230

The figures of Henry (’00) of the ciliated cell of the epidermis,
coincide in many points with mine, whereas in Lenhossék’s
(98), Fuch’s (04) and Ikeda’s (’06) figures we find no definite
arrangement of the basal corpuscles.

3) It will be seen from the foregoing that the basal corpuscles
show a marked tendency to form parallel rows and to undergo
fusion with each other; and in fact, my attention was repeatedly
attracted, in some places (in the oviduct of Triton, in the pharnyx
of Amphibia, in the foot of Anodonta) by the presence of a faintly
staining fibril, uniting the basal corpuscles of the same row, as
Heidenhain (’99) shows in his figure from the hepatic duct of
Helix. The case which may be regarded as the extreme of this
process is found in the corner-cells of gills of Anodonta (fig. 5 b).
In flat view of this cell as mentioned above, there can be easily
found two parallel stripes, which are stained black by iron-haem-
atoxylin, and from which the cilia arise. Regarding the sig-
nificance of these stripes Engelmann (’80) expresses himself as
follows: ‘‘Die Cilien entspringen oben auf jeder Zelle von zwei,
den langen Rindern parallelen Leistchen, die nichts anders als
die verschmolzenen, oder richtiger reihenweise anelnander ge-
fiigten Fussstiicke der elementalen Cilien,” a view with which
I agree entirely. The stripes, for which it will be better to re-
serve the name ‘basal stripes,’ are not to be identified with
‘Basalkorperfasern,’ found by Kuperweiser (’06) in the ciliated
cells of the corona of Cyphonautes-larvae; for the cilia never
arise from these fibers.

4. The so-called basal rods (Frenzel’s Fussstébchen). As early
as 1877 Eimer noticed, on the upper border of the ciliated cells
from the pharnyx of Salamandra and from the gills of Siredon
pisciformis, the existence of rod-like corpuscles, the juxtaposi-
tion of which gives rise to the appearance of a cuticle. Three
years later Engelmann described strongly refracting rods on or
in the distal border of the ciliated cells from intestine of Cyclas
and from the nasal mucous membrane of the frog, and termed
them ‘Fussstiicke.’ These rods are, according to his descrip-
tion, attached by means of the intermediate segments (Zwisch-
englieder) to the hair-bulbs. From these observations, the

238 S. SAGUCHI

author claims, with Eimer, that the cuticular border of the
ciliated cell, as seen by Eberth, Marchi and many others, is
nothing but the juxtaposition of the ‘Fussstiicke.’ Similar
bodies were afterwards found by Gaule (’81) and Frenzel (’86).
Especially the latter author recognized the presence of Engel-
mann’s ‘Fussstiicke’ in ciliated cells from various classes of in-
vertebrates and gave the name of ‘Fussstaébchen’ to them. Ac-
cording to him, the length and the structure of these corpuscles
vary in various animals and situations. In the simplest case it
consists of a rod with a small knob at one or both ends, but the
most complex one he found in the intestine of Littorina and Ris-
soa, which is composed of the following five segments: (1) the
lower knob, (2) the basal block, (3) the side-knob, (4) the rod,
and (5) the upper knob.

It is difficult at the present time to harmonize the ‘rod theory,’
urged by Engelmann, Frenzel and others, with the so-called
‘cuticular theory’ of Eberth and Marchi; for the same structure
is materially influenced by the technique and by the character
of the optical instruments used. Most of the recent investi-
gators (Schiefferdecker 91, Apathy ’97, Lenhossék ’98, Heiden-
hain ’99, Studni¢ka 799, ’00, Gurwitsch ’01, Wallengren ’05, Kuper-
wieser 706, Erhard ’10, Tschassownikow 713) have found a well-
defined cuticle in the ciliated cell, through which the cilia pass.
Lenhossék especially expresses himself as follows:

Der Versuch von Engelmann und Frenzel, die Existenz einer eigent-
lichen Cuticula in Frage zu stellen und das, was man als soleche be-
schrieben hat, bloss als das Ergebniss der mosaikartigen Zusammen-
lagerung der vertikalen basalen Teile der Flimmerhaare zu erkliren,
muss als verfehlt bezeichnet werden. Die ‘altere Cuticulartheorie,’
wie sie Frenzel nennt, ist noch immer richtige.

Brasil (’04) still maintains, in the ciliated intestinal cells of
Pectinaria, the existence of rod-like basal differentiations of the
cilia, which correspond, according to him, to the basal rods of
Frenzel. Studni¢ka (’99), on the other hand, finds the cuticle
in some cases, in others not, but an arrangement of rod-like cor-
puscles.

STUDIES ON CILIATED CELLS 239

_ 1 have, in my turn, noticed in all ciliated cells studied, as the
product of differentiation at the distal cell-border, a crust or
striated cuticle provided with basal corpuscles or penetrated
by the cilia, but I have never seen rod-like corpuscles situated
on the outside of the cell-border. The cilia, from the basal cor-
puscles to their distal extremities, whether they are within or
outside of the cuticle, show no trace of structure, but appear
completely homogeneous. In the following I discuss the value
of the ‘rod theory,’ comparing my results with those of Engel-
mann and Frenzel.

Engelmann (’80), (1) in his figures 11 a and b, 12, 15, shows a
well-defined, homogeneous border on the row of his basal knobs;
(2) in his figures 5, 9, 18, and 19, a row of basal knobs, the upper
and the lower ends of which are defined by straight lines, so that
the appearance of a striated cuticle occurs; (8) in figure 20,
_ basal knobs arranged on the surface of a cell from the olfactory
pit of Rana temporaria; the upper ends of these bodies are con-
nected, by means of intermediate segments, with the hair-bulbs
of the cilia. Thus Engelmann admits three types of implanta-
tion of the cilia. Is it rational to believe such a variety of
structure in cells which fulfill the same function? I will try to
account for this variety of structure in the following manner:
In the first case Engelmann’s conclusions are nearly in agreement
with mine; for, in his figures, it is clearly seen that the cilia pass
through the cuticle superposed upon the row of basal knobs
which seem to correspond to my basal corpuscles. In the sec-
ond case the author, in all probability, saw a striated cuticle
with or without basal corpuscles. In the third case the cutic-
ular substance, for some reason or other, escaped his observa-
tion, while the striae or the rod-like basal corpuscles, which
stand out sharply, he takes to be independent rods upon the
cell-border. The basal rods of Frenzel, on the other hand, seem
to be distinct from the basal knobs of Engelmann in shape and
refrangibility, as Frenzel says. I am rather, with Studni¢ka
(99), of the opinion that the basal knobs of Engelmann corre-
spond to the lower knobs of Frenzel. The hair-bulb of the
above authors might be identified with the node produced by

240 S. SAGUCHI

the accumulation of plasma at the point of union of thecilium
with the upper border of the cuticle, a view which has been held
by Lenhossék (’98), Wallengren (05) and Erhard (10). These
nodes are not only characteristic of cliated cells, but also seen
in ordinary epithelial cells; their existence in the epidermis
cells of Amphibia-larvae has been shown by Leidig (’85) and
Studnicka (98).

From the above the inference would appear justifiable that
the adherents of the ‘rod theory’ failed to notice any structural
difference between the substance of the cuticle and that of the
ciliary apparatus, but considered the more readily recognizable
parts as a continuous structure, and overlooked the rest, a re-
sult either of poor fixation or of studying fresh tissues.

b. The cytoplasm and rootlets of the cilia

In the literature there are three types of special structure of
the interior of the ciliated cell:

1) Valentin and Buhlmann first A aside the longitudinal
striation of the cytoplasm, which has since been recognized by
Friedreich (’58), Eberth (’66), Marchi (’66), Eimer (’77), and
especially by Engelmann (’80), and named by the last author
‘rootlets of the cilia.’ And besides these, Lenhossék (’98),
Fischer (’99), Peter (’99), Heidenhain (’99), Gurwitsch (701),
Joseph (’08), Kuperwieser (’06) and many others have found
that the rootlets of the cilia are connected, above, with the basal
corpuscles; below, they either lose themselves in the neighbor-
hood of the nucleus or descend, forming a conical bundle, to
the base of the cell. Apathy (97) and Metalnikoff (00), on the
contrary, look upon this conical bundle as the termination: of
nerves which are not connected with the basal corpuscles, but
which end freely between them. |

2) According to Lenhossék (’98) and Fuchs (’02), the ciliated
cells of the epididymis are devoid of rootlets of the cilia, but
they contain, in the upper portion, Hagler substance which
Fuchs takes to be mitrochondria.

STUDIES ON CILIATED CELLS 241

3) Neither rootlets nor granules are visible (Lenhossék, ’98)
in the trachea of the rabbit; (Gurwitsch, ’01), in the oviduct of
the rabbit; (Tschassownikow, 713), in the oesophagus of the
axolotl.

I have been able to distinguish the following two plasma divi-
sions in all the ciliated cells studied:

a) Under the cuticle there is a dense, transparent zone (figs.
6-9, 42-45), which is marked off below from the cytoplasm
proper by a relatively distinct boundary-line. Apparently
it never is lacking in ciliated cells, though it varies greatly in
thickness. The rootlets of the cilia, arising from the basal cor-
puscles, pass through this zone (figs. 6, 54). Its existence was
noticed by Gurwitsch (’01) in the ciliated cells of the pharnyx of
Bufo, of the intestine of Lumbricus and of the tela chorioidea of
Salamandra, and we also find the same in the figures of Heiden-
hain (99), and Erhard (10). As stated above, the basal bodies
are usually situated, either within the cuticle, or between this
and the transparent zone; they may occur occasionally within
the latter, as in the ciliated cells of the tela of Amphibian larvae
(figs. 37, 38).

b) The cytoplasm proper occupies by far the largest part of
the cell-body; it exhibits a reticular or alveolar structure and
contains a goodly number of mitochondria.

The size and arrangement of the meshes of the protoplasmic
reticulum are not the same in different cells. We find a most
striking instance of the longitudinal elongation of these proto-
plasmic meshes in the ciliated cells of the intestine of Anodonta and
of the hepatic duct of Helix (figs. 6-11). In these cases the main
beams run vertically and pass through the transparent zone to
come into connection with the basal corpuscles. It is natural
that these longitudinal striae, which correspond to what is
described by various investigators as rootlets of the cilia, do not
run independently, but are connected with each other by minute
lateral fibrils. In this respect I agree entirely with Kolaév
(10), who says:

Auf diese Weise entsteht das typische Bild eines etwas in die Linge
gezogenen Netzes mit Verdickungen an den Knotenpunkten, wobei die

242 S. SAGUCHI

Langsseiten der Schlingen dieses Netzes, die sich durch ihre Massivitat
und ihre intensive Farbung auszeichnen, die Wurzeln der Flimmer-
haare darstellen, wihrend die Querbalken schwacher ausgebildet sind,
infolge dessen sie nicht immer wahrnehmbar ist.

I have found the so-called cone of fibrils, which is regarded as
a bundle of rootlets of the cilia in sublimate-preparations only,
but never in Meves-preparations. From this it may be in-
ferred that the cone is not a real condition, but an artificial
product due to the shrinking effect of sublimate-solution, by
virtue of which the rootlets of the cilia adhere into a bundle.

The mitochondria in the ciliated cells were first noticed by
Benda (’99) in the mid-intestine of Anodonta, in the hepatic duct
of Helix, ete. He thinks that the rootlets of the cilia are formed
of mitochondria or chondriocontes. Fuchs (’02) says that, in
the ciliated cells of the epididymis of the mouse, the region be-
tween the row of basal corpuscles and the nucleus stains darkly
and contains, in Benda preparations, a large number of mito-
chondria. Perhaps a dark granular zone found by Lenhossék
(98) in the upper portion of the ciliated epididymis cell is a
similar structure. Recently, Meves and Tsukaguchi (14)
have found that, in the ciliated cells of the small bronchi, the
chondriocontes are accumulated for the mosi part in the super-
ficial portion of the cell, some descending beside the nucleus.

This description of Meves and Tsukaguchi holds good for all
the ciliated cells I have studied. The chondriocontes course
chiefly in the direction of the cell-axis and are especially abun-
dant beneath the transparent zone, without entering into it.

As regards the mutual dependence between the protoplasmic
networks and the chondriocontes, I am fully justified in believ-
ing that the latter are not free, but are either imbedded in the
trabeculae of the former or suspended on it; and, as the chon-
driocontes run mainly vertically and are suspended on the lke-
wise vertical protoplasmic beams, that is to say, on the rootlets
of the cilia, it often occurs that the latter are in a great measure
hidden by the mitochondria; in fact, it would seem that these
structures have not till now been distinguished from each other
with certainty. Perhaps such granular or knotty appearance

STUDIES ON CILIATED CELLS . 243

of rootlets of the cilia, as are described by Eberth (’66), Gaule
(81), Lenhossék (’98), Benda (’99), Kolacév (10) and others
are produced by a linear arrangement of mitochondria; on the
other hand, however, there is no reason for believing the exist-
ence of such straight rootlets free from nodes, as are figured by
Apathy (’97), Heidenhain (’99), and Erhard (710).

IV. FUNCTION OF THE CILIARY APPARATUS

Although this complex and difficult problem has received
much attention, it is still far from a satisfactory solution. The
review of the literature concerning this is given by Pitter (03),
Erhard (710) and Prenant (’14) to which the reader is referred
for details. It may be briefly summarized as follows:

1) Some authors (Pitter, 03; Gurwitsch, ’04; Erhard, 710;
Kolacév, 710) admit an active mobility of the cilia, others (Peter
99) a passive.

2) As to the function of the basal corpuscles, some look upon
them as a.kinetie center of the ciliary movement (Henneguy,
98; Lenhossék, ’98; Peter, ’99; Joseph, ’03), others as an end-
organ of the nerve (Apathy, ’97), and still others as a support-
ing organ (Hismond, ’00); Maier, 03; Kuperwieser, 06; Erhard,
10; Kolacév, 710).

3) The rootlets of the cilia are regarded (a) as exhibiting
contractibility and mobility (Stuart, ’67; Simroth, ’76; Benda,
99); (b) as primitive fibrillae of the nerve (Eimer, 77; Apathy,
97; Metalnikoff, ’00); (c) as a nutritive organ (Engelmann, ’80;
Kolacév, 710); (d) as a supporting organ (Peter, ’99; Eismond,
700; Maier, ’03).

It is necessary to say here a few- words as to whether proto-
plasm or nucleus takes part directly in the ciliary movement.
Of course, all protoplasm may be endowed with contractility,
but there is no reason for supposing that it causes directly the
ciliary movement, except that it may furnish a fresh supply to
the ciliary apparatus; otherwise such special cell-organs, as the
basal corpuscles and the rootlets of the cilia, would lose their
significance. This is sufficiently demonstrated in the experi-
ments of Peter (99) which show that even where the ciliated

244 ; S. SAGUCHI

cell has lost its nucleus and the greater part of the cytoplasm,
the cilia still continue to move, provided the ciliary apparatus
be left intact.

The basal corpuscles, on the contrary, seem to play an im-
portant part in the ciliary movement and are never lacking in
all true ciliated cells. Even when they have not been detected,
it would be going too far to conclude that they are not essential
to the movement of the cilia; for it often occurs that they are not
brought out by staining. Moreover I cannot so disregard the
basal corpuscles which Kolacév (’10) describes: ‘“‘Fiir die Me-
chanik der Flimmerbewegung . . . . ist das Vorhanden-
sein eines fest fixierten K6rperchens durchaus zweckentsprech-
end, wenn nicht gar physiologisch notwendig.” ‘The view of
Apathy (’97), postulating the nervous nature of the basal cor-
puscles and the rootlets of the cilia, is very curious and seems
to have obtained few adherents amongst histologists.

Those investigators who accept an active mobility of the
cilia themselves, claim to have observed, either the. movement
of broken cilia or of certain structures in them. Although I
have studied sections from different places and with varying
degrees of staining with iron-haematoxylin, I have never been
able to detect either axis-fibrils, as seen by Koltzoff (06) and
Erhard (10), or the transverse striation described by Kolacév
(10). In the following I, first, summarize my observations and
then express my opinion concerning the ciliary movement: (a)
There can be seen no trace of structure in the cilium; (0) at the
basis of each cilium there is always a basal corpuscle, (c) beneath
the row of basal corpuscles in most cases there can be seen a
transparent zone, through which the rootlets of the cilia pass
downwards from the basal corpuscles; (d) the rootlets of the
cilia are only a part of the trabeculae of the protoplasmic reticu-
lum; (e) the cilium, basal corpuscle and rootlet are a continuous
structure; (f) viewed in tangential sections, the basal corpuscles
are arranged in linear series, parallel to each other; the cor-
puscles in the same row show a marked tendency to undergo
fusion with each other; (g) the dumb-bell-shaped or diplosome-
lke basal corpusc es form, in like manner, parallel rows. It
often occurs that the upper extremity of every basal corpuscle

STUDIES ON CILIATED CELLS 245

is inclined towards any one end of the row, and, at the same
time, towards any one side of the cell; (h) in most cases these
rows are at right angles to the longer side of the distal cell-border;
(7) it seems that the direction of the rows agrees with that of
the ciliary movement. These data lead us to the following con-
clusions:

1) The cilium itself hee no active mobility.

2) The upper extremities of the rootlets are fixed in the com-
pact, transparent zone, affording support to the cla | have

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no reason for supposing that the rootlets may cause the ciliary
movement.

3) I am inclined to believe that the kinetic center of the ciliary
movement is to be sought in the basal corpuscles, as Henneguy
and Lenhossék maintain, and in the following manner: it
might be conceived that the basal end of the cilium and the dis-
tal end of the rootlet are connected either directly or by means
of a joint, around which is the basal corpuscle (s. text-figure).
The latter, like muscle-substance, is endowed with contrac-

246 S. SAGUCHI

tility, by virtue of which the cilium is bent at that point; hence
the rootlet acts as a support of the cilium, while the transparent
zone holds the rootlet in its position; the restoration of the bent
cilium may be effected either by the elasticity of the ciltum it-
self, or by the antagonistic action of the contractile substance.
It must be remembered, in this connection, that Eismond (’00)
compared the ciliary apparatus to the skeleton of the fin of a
bony fish, but I am far from agreeing with him in regarding
both the basal corpuscle and the rootlet as supporting organs
of the cilium. And, as the ciliary movement usually proceeds
in a determinate direction, it is natural that there should be
linear arrangement of the basal corpuscles in that direction.
With these conditions, a stimulation which causes the movement
of the cilia, is transmitted in a waving manner from one end to
the other of the same row, and thus the regular succession of the
ciliary movement is attained; this must be looked upon as being
most completely effected when all of the basal corpuscles of the
same row are fused, as in the corner-cells of gills of Anodonta;
the movements in different rows, on the contrary, are conceiv-
ably independent of each other.

V. REGRESSIVE METAMORPHOSIS OF CILIATED CELLS

A. TRANSFORMATION OF CILIATED CELLS INTO CELLS OF
DIFFERENT NATURE

Historical.

That ciliated cells become converted into glandular cells has
been observed by Knauff (’67), Flemming (’85), Osawa (97),
and others in the trachea, and by Lenhossék (’98) and Tschas-
sownikow (713) in the pharnyx of Amphibia. All of these au-
thors state that droplets of secretion first appear above the
nucleus, which becomes pressed downwards with the increasing
accumulation of the former, so that at last there is formed a gob-
let or chalice cell. According to Lenhossék (’98) and Frenzel
(86), even in such glandular cells, the cilia can still be preserved
and move actively. Next, the cilia are cast off and the secretion
is discharged. The casting off of the cilia, according to Brasil

STUDIES ON CILIATED CELLS 247

(04), results from the disappearance of the rootlets of the cilia
on account of the accumulation of secreted material; concerning
this he writes as follows: ‘“‘La destruction du cdne radiculaire
détruit les communication, quelle qu’en soit la nature, du cyto-
plasme et des cils. Isolés, ceux-ci ne peuvent plus que dégénérer
et disparaitre.”’

The transformation of ciliated cells into columnar has been
observed by Henry (00) in the epididymis, and by Gurwitsch
(00) in the intestine and the mouth of Lumbricus.

Observations

1. The hepatic duct of Helix. The epithelium from this struc-
ture consists of ciliated, non-ciliated columnar, and glandular
cells. The ciliated cells become converted into non-ciliated
columnar and the latter into glandular. This process can eas-
ily be followed in one and the same section. First, minute
granules, stained yellowish by iron-haematoxylin, make their
appearance above the nucleus (fig. 11, the cell to the left); they
then increase in size and number and pass gradually upwards.
Next, the cilia and the basal corpuscles disappear (fig. 11, the
cell to the right); it seems that the cilia are not withdrawn, but
are cast off in one of two ways: (a) they are broken off at the
junction with the cell; the broken fragments are, in fact, met
with in large number in the lumen; (b) they curl up and become
converted into small drops, which at first are applied to the
surface of the cell, but afterwards are separated from it. Thus
the ciliated cells are turned into non-ciliated columnar, and
after the discharge of secreting mass into goblet cells.

2. The intestines of Anodonta and Lumbricus. The epithelium
from these organs is composed of the same kinds of cells as
these found in the hepatic duct of Helix. In many of the non-
ciliated columnar cells there can be seen a row of ‘basal corpuscles
and a transparent zone, just as in the ciliated cells. On ob-
serving closely the cuticle of such cells, we often find some cilia
(fig. 8) which are, as usual, connected with the basal corpuscles.
Such cells might be interpreted as a form of transition between

248 S. SAGUCHI

the ciliated and non-ciliated cell, and as being on the road partly
to the development, partly to the metamorphosis, of the ciliated
cell.

3. The pharnyx of Amphibia. Here some ciliated epithelial
cells transform themselves into goblet cells; first, the cilia dis-
appear and then the upper portion of the cell becomes narrower,
in consequence of the pressure of neighboring cells, which may
cause a bulging of the cuticular border (fig. 53); on the surface
of the latter there can often be seen degenerated remains of the
cilia. As the process proceeds, the lower half of the cell en-
larges, and elongates downwards; the chondrioncotes gather
into a conical heap, above the nucleus, secretion granules first
being formed at the top of the cone. Such cases as this are,
however, not frequently seen; most of the goblet cells, rather,
seem to be formed by the proliferation of basal cells.

Lenhossék (’98) and Tschassownikow (’13) report that ciliated
cells in the pharnyx of Amphibia transform into goblet cells,
and, that the cells may retain their cilia for a long time in spite
of the accumulation of mucous droplets. Though I studied this
point in considerable detail, I have not been able to confirm the
latter opinion of these authors. I have frequently found some
features which looked as if they might be due to the accumula-
tion of mucous droplets in the upper portion of the ciliated cell,
but, on closer inspection with higher power it became at once
apparent that it was an appearance produced by the superposi-
tion- of a tangential section of a goblet cell upon a neighboring
ciliated cell, which may easily be understood when one recalls
that the bulging goblet cell undermines neighboring ciliated cells.

4. The oviduct of Amphibia. The oviducal epithelium is com-
posed of ciliated and glandular cells. The former become con-
verted into the latter by the accumulation of secreted material;
they retain their cilia for some time (fig. 65, a and b) before the
discharge of the contents sets in, as stated by Lenhossék and
Tschassownikow.

5. The oviduct of the lizard. The above statement for Am-
phibia holds good for this form (fig. 78).

STUDIES ON CILIATED CELLS 249

Summary

1. Ciliated cells are transformed into non-ciliated columnar
and glandular cells.

2. In the transformation of the ciliated into the glandular
cell, the cilia disappear, either before or after the accumulation
of secreted material.

3. The disappearance of the cilia is not by withdrawal but by
ther being cast off.

B. ATROPHY OF CILIATED CELLS

That ciliated cells undergo atrophy, without being cast off, I
have noticed in the gall-duct of Rana temporaria. The first
change which occurs in the cell is nuclear hyperchromasy
(compare my previous paper, 1915): there appear in the nucleus
numerous nucleolar granules, stained black by iron-haematoxy-
lin, just as the nucleolus. With the increase of these corpuscles
in number, the nuclear sap comes to stain more and more darkly,
so that at last the nucleus becomes entirely a black mass. The
cytoplasm also sooner or later grows black, especially in its
upper portion (fig. 58, 59). In the course of time the black mass
grows more and more pale (fig. 60) and then there can be seen
in the cytoplasm numerous, larger or smaller round or oval
black corpuscles, which often are so numerous as to hide the
nucleus entirely from view; the chondriocontes which were
found before, have now disappeared. I think that the cor-
puscles in question are derived partly from degenerated chon-
driocontes, partly from the nucleolar granules passed out of the
nucleus. While the cytoplasm still is in the state of heavy nu-
cleolar hyperchromasy, the cell in question becomes constricted
at the upper part, below the cuticle, two pieces, the upper
smaller and the lower larger one, being thus produced (figs. 59,
60). Then the connection between the two becomes lost; the
upper ciliated one is, in all probability, cast off into the lumen.

The ciliated corpuscles, first found by Neumann and then
recognized by Schmidt (’82) must be remembered in this con-
nection. ‘These corpuscles, according to Neumann, bear cilia,

JOURNAL OF MORPHOLOGY, VOL. 29, No. 1

250 S. SAGUCHI

either in a circumscribed portion, or over the whole of the sur-
face. Schmidt says that, though occurring numerously in the
epithelium affected by catarrh, they are by no means infrequent
in the normal epithelium; the author surmises their mode of
development from the experiment, that, when ciliated cells are
isolated, they undergo change in shape and constrict off spheri-
cal ciliated corpuscles. Since these bodies, according to his
description, have no cuticular border, it must be fegarded as a
portion of the cytoplasm which has taken cilia with it. From
this description and his figures, it would seem that the ciliated
corpuscle of Neumann corresponds with the upper piece which
is produced by the constriction of the atrophying ciliated cell.
In contradistinction to the view of Schmidt, however, I cannot
regard the corpuscle in question as derived from the cytoplasm
only, but as composed mainly of the cuticular border. Similar
corpuscles, but without cilia, were found by R. Heidenhain (’88)
in the intestine of the rabbit, into which sulphate of magnesium
was injected. From these. facts it is evident that the constric-
tion of the cell-body is a phenomenon which occurs in the degen-
eration, either of the non-ciliated columnar, or of the ciliated
epithelial cell.

The lower piece which is left behind in the epithelium rounds
itself off towards the basement membrane (figs. 61, 62), mean-
while the cytoplasm and nucleus become more and more clear
and the black corpuscles are absorbed. The chondriocontes ap-
pear afresh in the cytoplasm (fig. 62), which indicates that the
cell in question has not yet lost its vital activities. Thus the
atrophied ciliated cell is transformed into a replacement cell;
whether the latter returns to the ciliated cell, it is difficult to
determine with certainty. Now the question arises, why are
the cilia and the cuticular border cast off in the atrophy of the
ciliated cell? I am inclined to believe that this phenomenon is
owing to their intense functional specialization which incapaci-
tates the structures from undergoing redifferentiation.

i)
oO
—

STUDIES ON CILIATED CELLS

C. ELIMINATION OF CILIATED CELLS

In the epithelium of the intestine of Anodonta it is often seen
that some ciliated cells are being shed into the lumen. In the
nuclei of such cells there appear numerous nucleolar corpuscles,
while the nuclear sap becomes increasingly darker; that is to say,
the nucleus is in the state of nucleolar hyperchromasy; in the
cytoplasm, in addition, numerous larger or smaller vacuoles make
their appearance, so that the whole exhibits a phenomenon of
degeneration.

VI. REGENERATION OF .CILIATED CELLS

As the ciliated cells are reduced in number inthe manner
above mentioned, it is natural that they must be replaced by
new ones. This is carried out either by the transformation of
different kinds of cells into ciliated, or by the division of ciliated
cells themselves.

A. TRANSFORMATION OF OTHER KINDS OF CELLS INTO CILIATED
CELLS

That ciliated cells are derived from rep'acement cells, was
noticed by Drasch (’81), Flemming (’85), Bockendahl (’85),
Joseph (’05), Tschassownikow (’13) and others. According to
these authors, the mitotic figures which often occur in the cil-
iated epithelium, do not belong to ciliated cells themselves, but
to cells of different nature, especially to replacement cells, which
form a source of ciliated cells. Schnitzler (93), on the con-
trary, admits the transformation of goblet cells into ciliated.

I have observed, in the efferent tubule of testis of the adult
mouse and rat, that ciliated cells are derived from neighboring
non-ciliated, with which process I shall deal later in the chapter
on the development of the cilia.

B. MITOSIS OF CILIATED CELLS

Although the question as to whether the ciliated cell mul-
tiplies by mitosis or not, has received much attention, it is still

252 S. SAGUCHI

far from a satisfactory solution. From the well-known fact
that the centrosome directs mitosis in general, it must be ad-
mitted that the mitosis of a ciliated cell is also in close relation
to the existence of the centrosome.

The centrosome of the ciliated cell

Upon this question, two distinct and opposed views are held
by histologists. Henneguy (’98), Lenhossék (’98), Zimmerman
(98, in the uterus), Heidenhain (’99), Fuchs (02, ’04), Joseph
(03, ’04) and others say that ciliated cells lack centrosomes;
many investigators (Studnicka ’99, Fischel ’00, Eismond ’00,
Henry ’00, Benda ’00-’01, Gurwitsch ’00, ’01, Ach ’02, Wallen-
gren ’05, Ikeda ’06, Erhard ’10, and Tschassownikow 713), on
the contrary, believe that they have found centrosomes in
ciliated cells.

It is a difhcult matter to find centrosomes with certainty; for
they are minute corpuscles and often are apt to escape observa-
tion. Hence, it can hardly be said that they are absent when
they cannot be detected; on the other hand, there are many
other corpuscles which are similar to the centrosome in shape,
position, and staining reaction, but of a different nature. Wal-
lengren (’05) noticed such granules in ciliated cells, and said
that they must be passed out of the nucleus, and to be closely
related to the secreting process. We can only speak of centro-
somes where the corpuscles show constant shape position and,
staining powers and directly conduct mitotic division of the
cell. It is very difficult, though not impossible, to follow such
processes. Wallengren (’05) has already noticed that diplosome-
like granules which are present between the basal corpuscles
become centrosomes directing the karyokinetic cell-division.

I have noticed what are to be regarded as centrosomes in the
following situations. Before describing my observations, it
must be remarked that the centrosomes, in my conception, are
to be recognized from the constancy of their shape, position and
staining reactions, and, that whether or not these corpuscles, in
reality, conduct the mitotic division, in other words, whether all

STUDIES ON CILIATED CELLS 253

the ciliated cells which fossess centrosomes always multiply by
means of mitotic decision, is another matter, which will be dealt
with separately in the next section.

1. The intestines of Helix and Anodonta. The ciliated cell from
these organs contains a well-marked centrosome (figs. 6, 14, 15)
which is commonly situated between the nucleus and the cuticu-
lar border, either near the cell-axis or at the periphery of the
cell (fig. 6). It generally consists of two granules; the line of
connection between them being in most cases parallel to the
cell axis. They are surrounded with a clear halo, into which
chondriocontes never enter. In the ciliated cells of the typhlo-
sole of Anodonta, Erhard (’10) claimed to have found a centro-
some in the form of double granules immediately below the cuticle,
but the corpuscles in his figures 1, 11, and 12 are too indistinct
to be distinguished from the basal corpuscles in this region.

2. The pharnyx of Hynobius larvae. Here the centrosome of
the ciliated cell is a double granule (fig. 55) between the nucleus
and the cuticle, especially near the latter and often near the
periphery of the cell. The granules are either equal or unequal
in size, and are surrounded by a halo. The line of connection
between them is usually vertical, but an oblique or even a hori-
zontal direction is not infrequent. I have also noted occasion-
ally a centrosome containing one, three or four granules. There
are descriptions of the central corpuscle of the ciliated cell in
the pharnyx of Urodela, by Studni¢ka (’99), Eismond (’00),
Fischel (’00), Gurwitseh (01) and Tschassownikow (713). The
first three authors state that the centrosome occurs in the form
of a diplosome between the nucleus and the cuticular border,
just as I have found it. Studni¢ka, in addition, noticed, in
the pharnyx of Salamandra, a centrosome consisting of three
granules. On the other hand, Gurwitsch figures a centrosome
in the superficial layer of a ciliated cell from the region interme-
diate between the pharnyx and the oesophagus of Salamandra}
an observation with which those of the above authors and of
mine are not in accord.

3. The pharnyx of Bufo. The centrosome is situated above
and near the nucleus (fig. 49, the cell to the left), and consists of

254 S. SAGUCHI

two granules, which are usually arranged in a horizontal plane.
Cases in which they are separated from each other or in which
they seem to consist of a single granule are not rare.

4. The gall-duct of Rana esculenta. The centrosome (fig. 57)
surrounded by a clear halo is situated above the nucleus and con-
sists of two granules, the axis of which either ono to the
cell-axis or is more or less oblique to it.

5. The trachea of Trigonocephalus and the rat. The centrosome
in both these forms, is situated between the nucleus and the
cuticle, surrounded by a halo, just as described under 4. (fig. 69).

6. The efferent tubule of testis of the mouse and rat. The
existence of centrosomes in ciliated cells in the vas efferens was
noted by Zimmerman (’98), Henry (’00), Ach (02), Ikeda (06)
and Erhard (’10). According to Zimmerman, who has inves-
tigated ciliated cells of the human epididymis, the centrosome,
surrounded by a clear halo, is situated immediately below the
surface, and consists of two granules, the line of connection be-
tween them being either vertical or more or less oblique to the
cell-axis. The observations of Ikeda and Erhard are in accord
with those of Zimmerman. On the other hand, there is some
difference of opinion as to the shape and position of the centro-
some. In the epididymis of man, Henry found it above and near
the nucleus, while Ach says that it consists of one, two or three
granules, surrounded by a clear halo and that it lies either above
or by the side of the nucleus or near the cell-basis.

In ciliated cells of the efferent tubule of the mouse and rat,
I have also frequently seen centrosomes, which differ consider-
ably in shape in the two species.

In the mouse, the centrosome of the ciliated cell (figs. 82,
86) is situated immediately below the row of basal corpuscles,
either in the middle or near the periphery of the cell, and con-
sists of two granules which are always arranged in the horizontal
plane. In order to distinguish them from the adjacent basal
corpuscles with certainty, it is necessary to examine sections
carried through the ciliated cell in an exactly vertical direction.
Furthermore, I have often noticed, at the surface of neighboring
cells with brush borders, a two-granulated centrosome, arranged

STUDIES ON CILIATED CELLS 255

in the vertical direction; the upper granule often bears a cilium,
thus forming the so-called ‘Zentralgeisselzelle’ of Zimmerman.
This is found not only in the efferent tubule of the mouse, but
also in that of the rat (fig. 89).

In the efferent tubule of the rat, on the contrary, there are
no such typical centrosomes as above described, but instead
curious ring-shaped corpuscles in the transparent zone below
the cuticle (figs. 87, 88). Most of these rings have a smooth
internal and an uneven outer edge; in a certain sense they can
be spoken of as being formed by the apposition of granules.
Such rings are not always single, but there are many cells with
two, either of equal or of unequal size (fig. 87); in either case they
are arranged in a horizontal direction and connected with each
other by a fiber.

I am inclined to believe, from the position and staining of
these rings, that they are derived from the centrosomes; a cen-
trosome divides repeatedly and forms a ring by secondary
fusion of separated particles; the connecting fiber representing
the so-called ‘centrodesmosis.’ And, as a form of transition I
have found a cell with a ring and a granule, of which the latter
can be regarded as a component, still not divided, of the centro-
some. Whether the ‘Zentralkorperballen’ found by Benda
(00) and Ikeda (’06) in the efferent tubule of the human testis
and my ring are of the same character or not remains uncertain,
but there are some differences between the two concerning the
shape and position. Moreover, these authors admit that the
‘Zentralk6rperballen’ take part in the formation of the cilia, a
view with which I do not agree, for, on the one hand, the ciliated
cell with such rings is always in the fully developed state and,
on the other hand, it seems conclusive that the ciliary apparatus
never originates from the centrosome, but from a certain other
constituent of the cell, as will be afterwards described.

As above described, Henneguy (’98), Lenhossék (’98), Joseph
(03) and Fuchs (02, ’04) believe that, in consequence of the
absence of the centrosome, mitotic division does not occur in
the ciliated cell. Ach (’02) and Tschassnowikow (’13) say that
no mitotic figure occurs in ciliated cells in spite of the existence

256 S. SAGUCHI

of the centrosome; Tschassownikow especially points out that
the ciliated cell, though it shows no karyokinetic figure, can
scarcely be said to be incapable of undergoing division, for it
is provided with organs of cell-division, i.e., the nucleus and the
centrosome. On the other hand, many of the investigators
(Hammer ’97, Gurwitsch 701, Maier ’03, Wallengren ’05, Er-
hard 710, ’11, Gutheil ’11) believe they have found mitotic fig-
ures in ciliated cells. Gurwitsch represents in his figure 19, a
cell with a nucleus at the spireme-stage, which he takes as a cil-
lated cell; judging from his figure, however, it seems to me that
the cell has no cilia and basal corpuscles, but a relatively high
cuticular border: Just as little is certain whether the mitotic
figures found by Maier in the epithelium of the gills of Triton
and by Erhard in ependyma cells of an Acanthias embryo belong
to ciliated or non-ciliated cells. On the contrary, the observa-
tion of Erhard in the typhlosoles, and especially that of Wallen-
gren on gills of Anodonta appears to me to admit of very little
doubt.

In the intestines of Anodonta and Helix and in the gall duct of
Helix I have been able to follow the karyokinetic process of the
ciliated cell, from the prophase to the anaphase. In the follow-
ing I deal with the intestine of Anodonta as a representative of
such cells.

Prophase (figs. 17, 18). The first change of the nucleus con-
sists, as usual, in the formation of the spireme; the cytoplasm
becomes clear and the chondriocontes, which gradually grow
pale, are scattered over the whole of the cytoplasm. At first
the basal corpuscles still stain deeply, but afterwards they dis-
appear. Contrary to the view of Wallengren (’05) I have found
that the cilium and the basal corpuscle become lost simultane-
ously. All of the cilia and the basal corpuscles, however, do not
disappear suddenly, but by degrees, so that it often occurs that
a few basal corpuscles with cilia are left behind for some time
(fig. 19); moreover I have noticed, in the intestine of Helix, cells
with distinct cilia, even in the metaphase. The ciliated cell in
the resting condition is long and narrow in shape; but on enter-
ing upon the karyokinetic process it becomes swollen where the

STUDIES ON CILIATED CELLS 257

nucleus is situated, so that it takes the form of a pear. AI-
though the distal border of the cell in question becomes dimin-
ished in extent, I have never been able to find that it becomes
rounded off, after separating from the surface of the epithelium,
as described by Wallengren. In some cases the distal border
is either bulged (fig. 19) or indented, in consequence of the
pressure of neighboring cells. The cuticular border, so far as
can be seen from our materials, is left intact throughout the proc-
ess of cell-division. Since the basal corpuscles are lost to
view, the limits between the cytoplasm and the cuticle become
indistinct, so that it looks as if the cuticle had disappeared, as
Wallengren asserts.

Metaphase (fig. 19). The plane of division, so far as could be
observed, is at right angles to the surface of the epithelium, so
that the two resulting daughter-cells lie side by side.

Anaphase (fig. 20). The chromosomes send off lateral
branches which join or anastomose together in a reticular man-
ner while the nuclear membrane and nucleolus reappear. The
cytoplasmic fission sets in at the inferior end of the cell and grad-
ually proceeds upwards. Near and below the cuticle there ap-
pear the so-called intermediate corpuscle, from which proto-
plasmic filaments run towards the centrosomes. The chondrio-
contes, again becoming deeply stained, are arranged in the ver-
tical direction, and are chiefly accumulated below the cuticle;
the cell becomes in the meanwhile lengthened out downwards.
Next, basal corpuscles and cilia make their appearance, which
process will be referred to later on.

Although I have subjected various epithelial tissues of verte-
brates to a careful examination, I have never been able to find
karyokinetic division of the ciliated cell; the mitotic figures which
are often seen in the ciliated epithelium, do not belong to ciliated
cells, but either to non-ciliated columnar, or to basal cells or to
glandular cells.

Summary

1. The centrosome can be detected in ciliated cells of both
invertebrates and vertebrates.

258 S. SAGUCHI

2. It can not be said that the centrosome is always lacking in
ease it can not be detected in the ciliated cell.

3. The centrosome may be situated in every level between the
nucleus and the cuticle.

4. I have been able to find mitosis of the ciliated cells in in-
vertebrates only.

C. AMITOSIS OF CILIATED CELLS

Henry (99, 700), Ach (’02), Wallengren (’05), Jordan (713)
and others have noticed ciliated cells with two nuclei, which,
according to these authors must be a result of direct nuclear
division. I also found what appears to be amitosis of the cili-
ated cell in the following places.

1. The intestine and hepatic.duct of Helix. Here often occur
ciliated cells with two nuclei (figs. 13, 14) which are oval in
shape; these cells also may contain, as usual, a centrosome con-
sisting of two granules, situated about midway between the
cuticle and the nucleus (fig. 14). On close examination of prepa-
rations it would appear that these two nuclei are produced by
direct nuclear division. In the middle of the nucleus there first
appears a transverse furrow (fig. 12); by the deepening of which
it becomes separated into two nearly equal parts. I have never
observed cases in which the division was effected by the stretch-
ing of the nucleus. Cell-division follows nuclear division; the
cell-boundary appears between the two nuclei; thus two super-
posed daughter-cells are produced, of which the upper alone
bears cilia, while the lower one becomes transformed into a basal
cell and then, by the. accumulation of secreting granules in its
interior, into a glandular cell, which elongates upwards between
the ciliated cells until it reaches the surface of the epithelium.

Besides cells with two nuclei, there are occasionally seen those
with three, four or five nuclei; even in these cases the internal
structure at first shows no noticeable change. Whether these mul-
tinucleated cells are capable of division is doubtful; in all like-
lihood one or several of the nuclei undergo degeneration later on.

2. The pharnyx of Amphibia (Rana temporaria and esculenta,
Bufo, Triton). In the normal condition, the surface of the

STUDIES ON CILIATED CELLS 259

nuclei of the ciliated pharyngeal cells is smooth or shows at the
most some irregularities. At the beginning of the nuclear con-
striction the nuclear membrane is characteristically thrown into
folds, this is most marked in Rana temporaria. The cleavage-
plane of the nucleus is either vertical (figs. 42, 49) or oblique, or
even horizontal (fig. 44). The furrow formed by a pushing in
_ of the nuclear membrane appears, in Rana esculenta, as two par-
allel straight lines (fig. 42), but in Rana temporaria as zigzag
lines which can be made out only by careful focussing (fig. 51).
Between the structure of the amitotic dividing nucleus and that
of the norma! one there are no noteworthy differences, as will
be seen in my figures. The daughter nuclei are at first closely
apposed by their divided faces; later on. they are gradually
separated from each other (figs. 43, 52). I have observed in
Bufo a curious phenomenon in the behavior of the centrosome in
the amitotic process: the ciliated cell in the pharyngeal epithelium
of this animal, as already mentioned, contains a bigranulated
centrosome lying above the nucleus (fig. 49, the cell to the left).
With the separation of the dividing nuclei from each other, each
of the granules accompanies each daughter-nucleus (fig. 49, the
cell to the right), a fact which indicates that the centrosome is
not entirely independent of amitotic nuclear division.

Cell-division follows nuclear division. Since the cytoplasmic
fission always takes place along its longer axis of the cell, being
inaugurated either at the upper end (fig. 45) or at the lower
(fig. 48), it must be thought that the superposed nuclei, as it
often occurs, undergo locomotion before the cell-division sets
in. In the amitotic process there are no visible structural
changes of the cytoplasm, the nucleus, or of the ciliary appara-
tus, except that the two former increase more or less in volume.

3. The gall-duct of Rana temporaria. Ciliated cells with two
closely applied nuclei occur, though not frequently, in the bile-
duct epithelium. The process of cell-cleavage, however, was
not observed.

4. The oviduct of Rana temporaria and esculenta. In the ovi-
ducal epithelium are large ciliated cells with two nuclei (fig.
64), which cannot be interpreted except as having been pro-

260 S. SAGUCHI

duced by amitosis, for mitosis of ciliated cells has never been
observed here. Next, cytoplasmic division follows, the plane of
which is always vertical. Sometimes the amitotic process seems
to occur repeatedly; in figure 63 is a ciliated cell with six nuclei
which are closely apposed on their flat side-faces; I am of opin-
ion that the nucleus, in this case, has repeatedly undergone
amitotic division, while cytoplasmic fission has not begun.

5. Efferent tubules of Reptilia. Ciliated cells with two nuclei
often occur in the efferent tubules of Trigonocephalus and Ela-
phis (figs. 72-74), but rarely in the lizard. The direction of
constriction of the nuclear membrane is not a constant; the plane
of cytoplasmic division, however, is always perpendicular.

6. The oviduct of the lizard. Binucleated ciliated cells are
rarely seen here (fig. 77); the two nuclei which are evident must
have been produced by amitosis, for mitosis has not been de-
tected.

7. The trachea of Trigonocephalus. The two nuclei, either
superposed or juxtaposed, are closely apposed by their flat faces;
between these extremes there occur intermediate conditions.

&. The trachea of the rat. The arrangement of the two nuclei
is the same as described under 7 (fig. 93). The cell-body grad-
ually enlarges, especially increases in width. The cleavage of
the cytoplasm begins either at the upper or at the lower end of
the cell (fig. 94), and passes perpendiculraly between the nuclei.
I have also often noticed that a granule accompanies each of the
divided nuclei; from their position, shape and staining it is prob-
able that these granules are derived from the pre-existing centro-
some.

Summary

1. The ciliated cell may divide by amitosis.

2. This cell multiplication by amitosis occurs only in verte-
brates. .

3. The nucleus and the cell-body are constricted by pushing
in of the nuclear membrane.

4. Cell-division follows nuclear division. —

5. The ciliary apparatus remains unaltered in the amitotic
process.

STUDIES ON CILIATED CELLS 261

6. It seems probable that there exists some connection be-
tween the centrosome and the amitosis.

D. SIGNIFICANCE OF MITOSIS AND AMITOSIS OF CILIATED CELLS

As mentioned above, there are two methods of division of the
ciliated cell, mitotic and amitotic. Mitosis occurs only in in-
vertebrates; in vertebrates I have never been able to find it.
Those who accept the hypothesis of Henneguy and Lenhossék,
assert that the absence of mitosis in ciliated cells is a consequence
of the lack of the centrosome. I do not agree with this, for the
centrosome can easily be detected in ciliated cells in which mi-
tosis does not occur. On the contrary, amitosis is the sole
method of division of ciliated cells of vertebrates, in spite of the
presence of the centrosome.

As to the significance of amitosis, two distinct and opposed
views are held by histologists. According to one view, urged
strongly by Flemming, Ziegler, and vom Rath, amitosis is not
accompanied by the cytoplasmic division, but such a cell degen-
erates sooner or later. That the nuclei of degenerating cells
may multiply by amitosis has received much attention (Nissen
’86, Heidenhain ’90, Plate ’98, Dobell ’07, Reichenow’ 08) ; and,
in fact, I have also noticed that the nucleus multiplies by direct
division, in the degeneration of certain glandular cells in the
larval epidermis of some Amphibia (Saguchi ’15).

On the other hand, Child (’07), Patterson (08), Maximow
(08), Des Cilleules (14) and others affirm that amitosis is not
always degenerative, but can be accompanied by the actual cell-
multiplication; and, that mitosis follows amitosis and vice versa.
According to Child and Patterson, amitosis is in close relation
to the rapid nuclear multiplication and accordingly to the growth
of tissues. Child, in addition, remarks as to the occurrence of
amitosis as follows: ‘‘Moreover, in several cases I have noted
that in growing tissues where nuclei of different size are present,
mitosis seems to occur more frequently in larger nuclei sur-
rounded by considerable undifferentiated cytoplasm, while ami-
tosis is more characteristic of the smaller nuclei with scanty
cytoplasm.” Recently, Jordan (’13) described ciliated cells

262 S. SAGUCHI

with two nuclei in the epididymis of various vertebrate animals,
in the trachea of the cat, in gills of Unio, and he believes that
these nuclei are produced by amitosis which is connected with
the following cytoplasmic division. He expresses himself re-
garding the cause of amitosis in ciliated cells as follows: ‘The
fundamental cause of amitotic cell division in ciliated cells is
the destruction of the centrosome in the formation of the basal
bodies from which the cilia develop.”’ Contrary tothe view
of this author, Henry (’00), Ach (02), Ikeda (06), and I have
noted the existence of centrosomes in ciliated cells; and, on the
other hand, there are many cases in which they may be detected
in cells with two nuclei resulting from amitosis (Flemm ng,
Maximow).

My conclusions concerning the significance of mitosis and
amitosis in ciliated cells may be summarized as follows:

1. The occurrence of amitosis in ciliated cells is not owing to
the lack of the centrosome; for the latter can be detected in many
cases in such cells.

2. The sole method of multiplication of ciliated cells in inver-
tebrates is by mitosis, in vertebrates by amitosis; the cause
bringing about this difference between these subkingdoms,
must be due essentially to the degree of differentiation of the
cell-plasm.

VII. DEVELOPMENT OF CILIATED CELLS
A. HISTORICAL

As early as 1875 Eichhorst described the development of cilia
in the ependyma cells of the spinal cord of man; a transparent
cuticle first appears at the distal border of the columnar cell;
this afterwards becomes striated longitudinally, the cilia passing
through this striated cuticle. According to Engelmann (’80),
cilia regenerate by the elongation of their rootlets, while Fol
(796) described the formation of cilia by the prolongation of the
distal cell-border. Gurwitsch (01) distinguishes two types of
ciliogenesis: (1) first, the basal corpuscles appear at the nodes
of the alveolar meshes of the cuticle and afterwards the cilia
become developed from them (in the oviduct of the rabbit and

STUDIES ON CILIATED CELLS 263

in the pharnyx of Bufo); (2) first, the alveolar septa themselves
become transformed into the cilia, while the basal corpuscles
secondarily make their appearance at their basis (in the pharnyx
of Salamandra larvae). On the other hand, the observations of
Benda (’00), Fuchs (04) and Ikeda (’06) on the efferent tubules
of the human testis, had a marked influence upon the develop-
ment of the so-called Henneguy-Lenhossék’s hypothesis. Ac-
cording to these authors the centrosome, after multiplying by
repeated divisions, gives rise to the basal corpuscles, from which
the cilia develop. Wallengren (’05) studied ciliogenesis in the
daughter cells produced by the mitotic division of the ciliated
cell and found that, contrary to this view, the basal corpuscles
are developed, independently of the centrosome, within the
superficial portion of the cell-protoplasm, a view with which
those of Heidenhain (’99) and Erhard (’10) are in accord. Ach
(02) asserts that the basal corpuscles are derived from granules
situated above the nucleus, from which they are cast off, while
Gutheil (’11) maintains that the ciliary apparatus is developed
from the microsomes suspended on protoplasmic networks.

B. EMBRYONIC DEVELOPMENT OF THE CILIARY APPARATUS

1. The epidermis of Amphibian larvae (Rhacophorus, Hynobius.
and Hyla). The development of the ciliated cell in the epider-
mis of these larvae begins at an early embryonic period in which
the larvae are still enclosed within the gelatinous coat. The
epithelial cell which is preparing to transform into ciliated (fig.
23, the cell to the left) is always provided with a well-marked
cuticular border, the actual structure of which has been already
referred to above in the section ‘‘ Relations between the cilia and
the crust or cuticle.” The cells in question are most commonly
large, so that the lower ends often reach the basement mem-
brane; most of these cells are laden with yolk spherules of various
size (figs. 24, 26), in the intervals between which mitochondrial
filaments (chondriocontes) course in different directions; they
are also gathered in considerable numbers below the cuticle.
At successive periods, these chondriocontes, after or without
becoming vertically arranged, pass into the cuticle (fig. 24).

264 S. SAGUCHI

In this they do not pass into the alveoli, but ascend along the
striae, which are nothing but nodes of the alveolar walls in the
cuticle. Soon all the striae are occupied by the immigrant
chondriocontes, so that deeply staining parallel striae occupy the
same place as the alveolar ones (fig. 25). These, however, are
not always parallel to the radii, sometimes they are more or less
inclined in one direction, as seen in figure 25. ‘This is, in all
probability, due to the previous inclination of the alveolar walls.
At successive periods the mitochondrial striae gradually grow
pale; there are, however, cases in which it occurs only after com-
pletion of the development of the cilia. Next, they emit from
their distal ends minute faintly stained prolongations (fig. 26),
which are the young cilia. -At the beginning they are relatively
thick and short; later, they lengthen out (fig. 27). The chon-
driocontes are not used up in the formation of the cilia, but a
number of them remain behind in the cell, especially gathered
below the cuticle. From this manner of development it is pos-
sible that some of these chondriocontes are in continuity with
the cilia, and give rise to the so-called rootlets.

2. The pharnyx of Rhacophorus larvae. The ciliogenesis begins
in a larva about 15mm. inlength. The chondriocontes, growing
more and more pale, ascend along the cuticular striae and project
beyond the limits of the cuticle (fig. 56). At first they are short,
and often curved in the shape of hooks, but afterwards they
lengthen out.

3.. Tela chorioidea of Amphibian larvae (Hyla, Rhacophorus
and Hynobius). In the early embryonic stage, the tela epi-
thelium of Hyla consists of flattened cells, which contain numer-
ous yolk-spherules and chondriocontes; the latter are accumu-
lated near the upper border of the cell (fig. 34). In the next
stage the cilia make their appearance (fig. 35). From the fact
that the cilia are produced in that part which coincides with the
accumulation of chondriocontes, the inference is warranted that
there may be a genetic connection between the two.

4. The ciliated infundibulum of Hyla larvae. The chondrio-
contes are collected below the cuticle through which they pass
out of the cell in order to form the cilia; the continuity between
the two is readily discernible in favorable conditions (fig. 40).

STUDIES ON CILIATED CELLS 265

Although, from these observations no definite conclusion as
regards the development ofthe basal corpuscles and the root-
lets, can be reached there is no indication of the formation of
cilia from pre-existing basal corpuscles. The chondriocontes
give rise to the cilia. The basal corpuscles and the rootlets
are, in all probability, formed by the special differentiation of
the chondriocontes remaining behind in the cell.

C. DEVELOPMENT OF CILIATED CELLS IN THE EFFERENT TUBULE
OF TESTIS OF THE MOUSE AND RAT

Contrary to the view of Hammer (’97), Henry- (99), Ach (02)
and Jordan (713), I could not find any division figure, either
mitotic or amitotic, in ciliated cells of the efferent tubules; the
regeneration of these cells is, rather, effected, as mentioned be-
fore, by the transformation of cells with brush borders; the
ciliogenesis which occurs in this corresponds in all respects with
that of the embryonal stage; first, the chondriocontes increase
largely in number and are chiefly accumulated between the nu-
cleus and the distal cell-border (fig. 79). It is certain that they
are not derived from the centrosome, though nothing is known
of the manner of their increase. They then proceed towards
the distal cell-border and transform into rod-like corpuscles
arranged in linear rows (fig. 80). These rods can scarcely be
said to be basal corpuscles, for they stain in the same way as the
chondriocontes. They emit, at successive periods, short initial
cilia (fig. 81), which gradually lengthen (fig. 82). In figure 82
there is, as usual, a centrosome consisting of two granules, the ex-
istence of which indicates that the latter takes no part in the for-
mation of the cilia. That the process of ciliogenesis takes place
in cells with brush borders has been already referred to; the
developing cilia are seen to pass, not through the interspace
between the hairs of the brush border, but through their axes, as
represented in figure 84 (the cell to the right). Since the cilia
are longer than the hairs, it is evident that the former project
beyond the distal extremity of the latter, which can no longer
be detected in fully developed ciliated cells.

JOURNAL OF MORPHOLOGY, VOL. 29, No 1

266 S. SAGUCHI

Whether or not the ring-shaped corpuscles which I found in
ciliated cells of the efferent tubule of the rat, are the same as the
‘Zentralkorperballen’ of Benda and Ikeda, I am not certain; I
have not, however, sufficient evidence to show that they have
any connection with ciliogenesis. It seems probable that these
structures, as well as the granules or threads described by Fuchs,
are similar to the chondriocontes.

D. CILIOGENESIS IN THE DAUGHTER-CELLS PRODUCED BY MITOSIS
OF THE CILIATED CELL

As already mentioned, the ciliated cells in the intestine of Ano-
donta multiply by mitosis; at the beginning of the metaphase
the basal corpuscles and the cilia disappear, and in the anaphase
the ciliogenesis sets in; the process is, in the main features, sim-
ilar to that of embryonic development of the cilia. The chon-
driocontes now give the previous staining reaction and are col-
lected above the nucleus (fig. 21). At successive periods, some
of these filaments proceed towards the cuticle, their upper ends
often swelling out into bulbous enlargements, from which the
cilia pass out through the cuticle (fig. 22). These granules are,
in all probability, not identical with basal corpuscles, but mere
local accumulations, of the mitochondrial substance.

Summary

1. The ciliary apparatus is produced by the differentiation of
mitochondria or chondriocontes, whether the process occurs in
embryonic or in adult cells.

2. The centrosome takes no part in the formation of the cilia.

VIII. HENNEGUY-LENHOSSEK’S HYPOTHESIS

Henneguy and Lenhossék, at nearly the same time (98), but
independently, formulated an hypothesis that the cilary appa-
ratus, especially the basal corpuscles are derived from the cen-
trosome; an hypothesis which has since obtained some adherence
among histologists (Benda ’00, Fist ’00, Holmgren ’03, Fuchs
04, Joseph ’05, Ikeda ’06). The arguments in favor of this

STUDIES ON CILIATED CELLS 267

hypothesis are: (a) the shape and position of basal corpuscles in
the ciliated cell correspond with those of the centrosome in
neighboring non-ciliated cells (Lenhossék, Holmgren); (b) viewed
in unstained preparations, the basal corpuscle refracts light as
strongly as does the centrosome (Lenhossék); (¢) both the above
structures show stain in the same way (Lenhossék); (d) the cili-
ated cell lacks centrosomes (Lenhossék, Fiisst, Fuchs, Jordan);
(e) the ciliated cell bears resemblance either to a spermatid
(Henneguy, Lenhossék) or to a ‘Zentralgeisselzelle’ (Joseph) ; (f)
no mitotic figure is seen in the ciliated cell, because the latter
lacks centrosomes (Henneguy, Lenhossék, Fuchs, Joseph) ; (g) the
basal corpuscles arise from the centrosome.

There are many other investigators whose opinions are ad-
verse to the above hypothesis; they bring forward the following
facts in support of their view; (a) the granules which stain black
with iron-haematoxylin cannot always be said to be centro-
somes, for there are many other cell-constituents which give the
same reaction (Studnicka ’99, Fischer 99); (6) contrary to the
view of Lenhossék, the centrosome is often situated deeply; (c) it
can scarcely be said that the ciliated cell lacks centrosomes when
it is not met with (Merkel ’08); (d) the ciliated cell has a centro-
some (Studni¢ka 99, Kismond ’00, Fischel ’00, Henry ’00, Gur-
witsch ’00, Wallengren ’05, Erhard 710, Tschassownikow ’13);
(e) sometimes mitosis is observed in ciliated cells (Gurwitsch
00, 01, Maier ’03, Wallengren ’05, Erhard ’10, Gutheil ’11);
(f) the basal corpuscles are not derived from the centrosome, but
from other cell-constituents (Gurwitsch ’00, ’01, Wallengren
05, Erhard ’10, Gutheil ’11).

My observations also are not in accordance with the hypothe-
sis of Henneguy and Lenhossék; they are summarized as follows:

1. The basal corpuscle refracts light strongly and_ stains
deeply with iron-haematoxylin, but these properties are not
characteristic of these bodies.

2. I have found centrosomes in many ciliated cells.

3. The existence of the centrosome does not always signify
the occurrence of mitosis, for the ciliated cells of vertebrates do
not multiply by mitosis, though they contain distinct centro-
somes.

268 S. SAGUCHI

4. The resemblance of ciliated cells to spermatids or to “Zentral-
geisselzellen’ must be regarded as accidental.

5. The ciliary apparatus, especially the cilia, are not derived
from the centrosome, but from the chondriocontes.

Kanazawa, Japan, April 14, 1916.

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EXPLANATION OF PLATES

All figures are drawn with the Zeiss camera under Zeiss ;z oil-immersion
objective and Zeiss compensating ocular 18, at the distance of 250mm. tube
length 160 mm. By reproduction they were reduced to three-fourths of the origi-
nal. Figures 2, 3, 5, 7, 10, 14, 15, 30-33, 37-39, 46, 47, 49, 50, 55, 57, 69, 67, 73,
79-83, 86, 90, 92, 95 are from preparations stained by iron-haematoxylin, after
fixation with sublimate; the others from Meves preparations.

PLATE 1
EXPLANATION OF FIGURES

1 to 3 Ciliated cells from the foot of Anodonta, figure 3 surface view.

-4,5 From gills of Andonta, figure 4 lateral cell, figure 5 surface view of the
lateral surface of the gill-torus, a, lateral cell; b, corner-cell.

6 to 8, 16 to 20 From the intestine of Anodonta, figure 16 surface view.

9,13 to15 From the intestine of Helix.

10 to 12 From the hepatic duct of Helix.

272

STUDIES ON CILIATED CELLS PLATE 1
S. SAGUCHI

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Be ee i

a

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273

PLATE 2
EXPLANATION OF FIGURES

21, 22 From the intestine of Anodonta.

23 From the epidermis of the tail of 6 mm. Hyla larva.

24 to 27 From the epidermis of the tails of 12 mm. Rhacophorus larvae.

29 From the epidermis near the olfactory pit of 11 mm. Hyla larva.

30 to 32. From the epidermis near the olfactory pit of Hynobius larvae.

33 Surface view of a ciliated cell from the abdominal epidermis of 6 mm.
Hyla larva.

34 to 36, 38 From the tela epithelium of Hyla larvae.

37. From the tela-epithelium of 10 mm. Rhacophorus larva.

39 Flat view of a ciliated cell from the tela of Hynobius larva (13 mm.).

40, 41 From the ciliated infundibulum of Hyla larvae.

STUDIES ON CILIATED CELLS
S. SAGUCHI

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PLATE 3
EXPLANATION OF FIGURES

42 to 47 From the pharynx of Rana esculenta, figure 47, surface view.
48 to 50 From the pharynx of Bufo, figure 50, surface view.

51 to 53 From the pharynx of Rana temporaria.

54 to 55 From the pharynx of 20 mm. Hynobius larva.

56 From the pharynx of 15 mm. Rhacophorus larva.

57 From the gall-duct of Rana esculenta.

58 to 62. From the gall-duct of Rana temporaria.

STUDIES ON CILIATED CELLS PLATE 3
S. SAGUCHI

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Ft ips rae peecger Wt vane o rl)

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PLATE 4
EXPLANATION OF FIGURES

63 From the oviduct of Rana esculenta.

64 and 65 From the oviduct of Rana temporaria.

66 to 67. From the oviduct of the triton, figure 67, surface view.

68 <A ciliated cell from the abdominal endothelium of Rana temporaria.

69 to 71. From the trachea of Trigonocephalus.

72, 73 From the efferent tubule of testis of Elaphis.

74,75 From the efferent tubule of testis of Trigonocephalus.

76 From the efferent tubule of testis of a lizard.

77, 78 From the oviduct of a lizard.

79 to 83, 85, 86 From the efferent tubule of testis of the mouse, figure 83 sur-
face view.

84, 87 to 90 From the efferent tubule of testis of the rat, figure 90 surface
view.

91 to 95 From the trachea of the rat, figure 95 surface view.

STUDIES ON CILIATED CELLS PLATE 4

S. SAGUCHI

[NN

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a . 7

THE PRIMORDIAL CRANIUM OF THE CAT

ROBERT J. TERRY
Department of Anatomy, Washington University Medical School

THIRTY FIGURES (TWELVE PLATES)

CONTENTS
(CRUE ERO aT Sis ee ee A ee Se 282
| lps Pere Land e7eT trot Fe epee Rone ee ae i ec | he 285
PAPER OBS Gy AULOHS arte cet ce te seat cs... 5... . ss Se ee ne cect 287
Basal aplate: | aabryos ofe2s1 mm .:.:.. . . . «2/0: CG ee oss de ee 287
(OCCU CIN TRSfUnG Gs i). et ee ee 289
PAIS EE CIES ECOP HENS AR 4c ccyce ios da 5 os. oo pe been a 58 a 293
Basal plate and occipital region in smaller embryos.................... 294
Giic rerione Em tyOS Om esol RIM: S600... . ... 5S ae ey «Ss Sk ose 298
Pataca icilariseMOUbCE TOEMs 95202... . . - - =e geen otal. ese ais 299
Parsicochleatsis 8.02. -ns so): tat Se oes 3 > 3 clots Sob NO er 302
Paine Ol ineiotte-CApAIle. 2. cose Mes. os... ee eee Eerore. 305
Dinemreriont alsmaller embtyoss2-2 iia... .. . -.. . eae ee 2. oo 311
INGEV Ce piaE Ne One NEC COI. Aaae aoa. . ...« » «0 Geer el eee 314
loo ecse IsuimrtRerOtiCy TC PION. sis. f cc. c:. -.- . « += 4 Seem = mentee eats 316
Orbito-temporal region in embryos of 23.1 mm......................... 317
Orbito-temporal region in smaller embryos...................2......--- 325
Bihmerdalregionin embryos of 23...mm.... .. .s,.c:e0seeee ee oe. 2s 2! - 329
Ethmoidal region of smaller embryos..... oe... ee 340
1255 59 be BF SROTERS STO CU atcha Oa Do a A 342
OC CI Ki ane CER IRIANee See eC cena. be oe ss Re ee te AS 342
Braised jel Nea Peas tig See Be ene te ete. 342
LMS SBS aa Ge Re a ee OE Si. oS 351
Oecinia-ailaniaanticulatouee: co... .....,. + .: caeeeeee ie on.) -Aln soe 353
Ee Om FHC OrATICH WAAR RUM sc... .... . «++ cee ook oc eee 354
BUTCH RGU 2S eet ews ee ee. 2 a aie 355
Pl orarieny His PRU} hae ae er icc: « : + 22. . sp a ish id a es 356
(SUG PSC 2 er ee ee, oe 300
POsiiOH Gltne GliG CADSULESe 0.4... ... --. 2 ae eens wa ees 357
Origin of the cartilaginous*otie. capsule...../2238ee.4--.. ). 5... ss 359
Foramina acustica and meatus acusticus internus......:........... 363
HOraMmen VaetvEnUAtICUMIS ye ....5... <<». 02 fa Rhona - 364
CRmabarigyes/ longhair ee. rT 365
Lamina) partetalisiand tectum’ postérius: ..<.2.4¢-c0+22+:-. +e sss + 366
Ha ClolgepiiGea USMC MEN VER cass. 2 2) ss «.- aeeeeeRe es «nk Pls oe 369

281

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2
SEPTEMBER, 1917

282 ROBERT J. TERRY

Orbito-temporal region. 3. wae. Ree es te komt Oe eee 370
iELypophyséal cartilagey.20 aoomes.:. sca se an ae 370
Fenestra-basieramialis postemon..<.:!) ices si eo ie ae 371
Crista transversa and dorsumvsellae. . tien... sae 48 eee ee 371
Poramen hy pophyseossn.c eee is ts ok Se ee) eee 374
Ala-témporalige? J40502 50 A eects soe ae nk a bet eo eee 374
Peery goad s 225 oho og ee MO ane, os be ae eo 380
Carotid Soramen:.sc 8p. ere «echoes See Ree ee 381
Ala: orbitals fos cic ocho ees G2 sso cae ae ene eee 384

Ethmoidalsregione. 2 eh fc. ee ee a Ee ee 385
Regionof ‘the. olfactory, femestray.,.<-5. seene ein ni oe a ee 385
Floor of the nose and Jacobson’s cartilage......2.¢5:.2:-.--.45aehe 387
Tectuit Wastin 550.20 Cees I ORR On ee eee 390
Paranasal:cantilaces.n.c see. . on ee ee eee 391
Lamina antorbitaligs 0 oie poe ose eee ee Oe eee 394

SUMMALY . 2. ead eicg ceed eo 6 ao OE osc os oe ee oe 396

WiterAture sss he hea Noe ocean CIES © fee nC CO er eee 401

ix planation oftiveurestss. 42 eee... . ol nt ee eee eee 405

EMD DTC VIATLONS aye; sas 2550ek eee os = iala Smo eg eee aie 406

IPUPUTOS.. ys 08 shies oe see Doles RS ee cee eee 409
INTRODUCTION

Studies of the primordial cranium of mammals have in most
instances dealt with but a single stage, and offer, therefore,
almost no data, on developmental processes. Moreover, there .
seems to be a tendency, unfortunately, to pursue the study after
this manner and so to continue limiting inquiry to the methods
of comparative, descriptive anatomy. This criticism cannot
be made of investigation of the crania of the ichthyopsida. It
has been rather the rule than the exception for research in this
group to include as complete a survey of developmental processes
as the technique of the time permitted; that is, the studies pro-
ceeded toward the solution of cranial problems by comparative
embryological methods. No doubt, certain physical conditions
have in the one case been an obstacle to embryological work.
The difficulty of securing material in control and of sufficient
amount, and the great extent to which the investigation of even
a few stages leads one, are factors which have determined in
no small degree the methods and results of research on the
crania of higher forms. However, these difficulties are not
serious and should not stand in the way of gaining for the mam-

PRIMORDIAL CRANIUM OF THE CAT 283

malian cranium that knowledge of its development which is so
much desired.

For the study of problems of the mammalian primordial
cranium, the domestic cat offers material possessing certain
advantages. In general, the processes of chondrification pro-
ceed sufficiently slowly to permit of easy determination of the
origin of parts and of subsequent study of their individual his-
tories. Also, the cat among the domestic mammals has re-
mained standardized to a degree not exceeded, if equalled, by
any other, and is on this account of value for anatomical study.
Yet, notwithstanding these points in its favor, the house cat
has not been utilized for cranial study to the extent that might
be anticipated. There is at the present time no paper on the
development of the cranium as a whole and no extensive de-
scription of a single stage in the course of its development. Not
even Parker described the primordial cranium of the domestic
cat. The only investigation which attempts to deal with the
whole chondrocranium is that by Decker in which brief accounts
of two rather advanced stages are presented. Wincza’s com-
munication discusses a- number of questions, for the solution of
which cat material has been employed, but it does not include
all regions of the cranium. This valuable paper is available to a
relatively small number of investigators since it was published
in the Polish language. ~

What has been said in regard to cat for the study of the
whole chondrocranium does not apply in the case of investiga-
tions of special problems, although even in the latter case this
material has been used to a more limited extent than might be
expected. Of the cranial regions usually recognized, the occipi-
tal in cat has received less attention than have the others.
The otic region is represented by a number of papers concerned
for the most part with late embryonic stages and adult condi-
tions. Among these, the publications of Spence, Bondy, van
Kampen, and Denker have been consulted in the present work.
Wincza’s paper deals especially with the ala temporalis and
carotid foramen; an article by Arai includes the cat in a study
of the craniopharyngeal canal, and a paper by Williams deals

284 ROBERT J. TERRY

with the notochord in its later history. In the ethmoidal region
interest has been centered upon the skeletal structure of the -
floor of the nose. Harvey, Broom, and Zuckerkandl have each
contributed valuable descriptions of the cartilaginous frame-
work about Jacobson’s organ and the incisive ducts in cat.

In the present paper the monographs on the anatomy of cat
by Strauss-Durckheim, Wilder and Gage, Jayne, and Reighard
have been very helpful, as have those works of a more general
scope, but including the cat, by Chauveau, Paul Martin, and
Weber. Finally should be mentioned those studies, in which
‘ eat has offered the material, of head structures other than the
cranium which are inseparably connected with the problems of
the skeleton, many of which have aided the present investiga-
tion. Among these are, specially, Retzius’ researches on the
ear; G6ppert and Corning on the ocular muscles; Peter, Born
and Seydel on the nose; Froriep and van Wijhe on the occipito-
spinal nerves.

This paper is concerned with some of the problems of cranial
development in mammals, the chondrocranium (exclusive of the
visceral skeleton) in cat serving as the material for study. It
was the intention to give the descriptive portions of the several
cranial regions, as far as possible equal treatment, but to limit
the discussion to a few problems upon which some light was
thrown by the structure and development of the cranium in
the particular form under consideration. The occipital region
was looked to with keen interest as an unworked field for obser-
vation, and for any evidence of those processes revealed by
Weiss, Gaupp, and Weigner in mammals which indicate a close
resemblance to, if not an actual repetition of the steps in the
development of the atlas. As stated above, the work on the
otic region, hitherto, treats of late embryonic and adult condi-
tions. In the present paper, attention has been directed mainly
to conditions of early development, such as the origin of the
cartilaginous otic capsule, the comparison of the embryonic
vestibule with that of reptiles and the theoretical questions
concerned with the development of the cochlear skeleton. Con-
sideration of questions relating to the development and signifi-

PRIMORDIAL CRANIUM OF THE CAT 285

cance of the ala temporalis and to the formation of the hypo-
physeal skeleton forms the main part of the study of orbito-
temporal region. Concerning the origin and early history of
the ethmoidal skeleton of mammals comparatively little is
known, whereas, on the contrary, a great literature exists on
the development of the nasal conchae, floor of the nose and
nasal sinuses. Cat material was found favorable for the inves-
tigation of many early processes of ethmoidal development, and
to a discussion of these, practically the whole of the section on
the ethmoidal region has been devoted.

MATERIAL AND METHODS

The present study starts with a cat embryo of 23.1 mm.,
series no. 466 of the Harvard Embryological Collection. From
this, a model of the chondrocranium was reconstructed by stu-
dents of the Harvard Medical School under the direction of the
author while a teaching fellow in histology in that institution.!
The model, enlarged thirty-three times, includes, in addition
to the chondrocranium, the ossifications, main bloodvessels and
nerves. It is an example of care and industry and as such has
been on the one hand invaluable as material for study and on
the other a reminder of the enthusiasm and earnest effort of those
students, then in their first year of medical study, Messrs. G.
D. Cutler, I. Gerber and R. D. Leonard, who responded to the
suggestion to undertake the labors of cranial reconstruction.

Through the kindness of the late Professor Minot and Professor
F. T. Lewis, the model, together with the following series of cat
embryos from the collection at the Harvard Medical School,
was placed at my disposal in St. Louis.

1 The model was reconstructed in 1907. The present investigation was un-
dertaken in St. Louis several years later but on account of interruptions its
progress was delayed. I take this opportunity to acknowledge the many cour-
tesies of Prof. J. S. Kingsley and the staff of the Marine Biological Laboratory
at South Harpswell, Maine, where during the summer of 1915 it was my privilege
to work.

286 ROBERT J. TERRY

Cat 9.7 mm., frontal, Series 448
Cat 10.6 mm., frontal, Series 476
Cat 12.0 mm., frontal, Series 404
Cat 12.0 mm., horizontal of head, Series 403
Cat 12.0 mm., sagittal, Series 400
Cat 17.0 mm., sagittal, Series 492

I am indebted also to Professor Huntington for the use of
series of cat embryos of the following stages, from the collec-
tion at the College of Physicians and Surgeons, Columbia
University.

Cat 10 mm., Series 500
Cat 11 mm., Series 473
Cat 12 mm., Series 263
Cat 13 mm., Series 262

From the collection in the Department of Anatomy of Wash-
ington University the following were studied:

Cat 12 mm., frontal, Series 50
Cat 12 mm., transverse, Series 52
Cat 15 mm., transverse, Series 56
Cat 17 mm., Series 80
Cat 17 mm., sagittal, Series 81
Cat 17 mm., transverse, Series 82

Several special reconstructions were made of complex regions.
One is of the left otic capsule of the 23.1 mm. embryo; a second
represents the course and relations of the facial nerve in the
same specimen; a third, the eye-ball and its muscles in relation
to the chondrocranium; a fourth the cranial relations of the noto-
chord. The atlas and epistropheus were included in the main
model. The base of the cranium in the region of the carotid
artery was reconstructed from a 12 mm. embryo; from the same
a reconstruction of the hypophyseal cartilage was made. The
nasal capsule and nasal sac have been modeled from an embryo
of 17 mm.

The study of all stages of the chondrocranium was facilitated
by a collection of preparations made by the van Wijhe (’02)

PRIMORDIAL CRANIUM OF THE CAT 287

method. These are of great value for studies of the cartilaginous
skeleton, especially when used in comparison with the sections.
Cat embryos were fixed in formalin, stained with methylene
blue, decolorized, cleared and preserved in liquid Canada bal-
sam. The last procedure, which departs slightly from van
Wijhe’s final treatment, is of much advantage in permitting the
free handling and turning of the specimen so that it may be
easily observed from every aspect. The following stages were
prepared and studied: Cat embryos of 10 mm., 12 mm., 15 mm.,
17 mm., 20 mm., 24 mm., 30 mm., and 35 mm.

As stated above, the present paper centers upon a particular
stage, with which earlier and later stages have been compared.
In accordance with this method the structures of each region
of the chondrocranium as found in the stage of 23.1 mm., that
is, the stage of the model, are first described, then younger stages
are considered.

PART I. OBSERVATIONS
Basal plate.—Embryos of 23.1 mm.

The term basal plate is used here to designate that portion
of the floor of the chondrocranium corresponding in cephalo-
caudal extent with the cranial part of the notochord, and in
lateral extent to the level of the basal foramina and cochlear
capsule.

The basal plate in the embryo of 23.1 mm. is represented in
figures 1, 2 and 3. In the otic region it is very narrow; in the
occipital region, on the contrary, very broad. Foramina are
present at the margin of the basal plate, between it and the
cranial side walls, but no openings exist in the plate itself.
These marginal foramina are the fissura basi-cochlearis posterior,
the jugular and hypoglossal foramina.

The anterior, or otic portion of the basal plate, subcylindrical
in shape, lies between the cochlear prominences, and, within

288 ROBERT J. TERRY

the cranium, forms the bottom of a deep sulcus whose sides are
constituted by the median walls of the cochleae. This sulcus is
occupied by no part of the brain, but is filled with a loose web of
mesenchymal tissue, in which the basilar artery and abducent
nerves run (fig. 22). Continuity between the cochlear promi-
nence and basal plate is brought about by means of a thin strip
of cartilage interrupted by the marginal foramina above men-
tioned. This strip is merely a septum between two oppositely
placed grooves, one outside, the other within the cranium, which,
in their semicircular courses, demarcate the limits between the
ear capsule and cranial floor (figs. 1, 2). These grooves ex-
tend anteriorly on the outside of the cranium beyond the con-
fines of the basal plate and include the carotid foramina; pos-
teriorly, both within and without the cranium, they have a some-
what lateral direction between the occipital division of the
floor and the otic capsule. Here are two large openings, the
jugular foramen, to be presently described, and the fissura
basicochlearis posterior (figs. 2, 12). The latter is sickle-shaped,
broad laterally where it approaches the jugular foramen, from
which it is separated by the commissura basivestibularis. It
gives passage to no nerve or large vessel.

The occipital portion of the basal plate forms the floor of the
occipital region of the cranium. It presents a slightly concave
intracranial surface and a convex face directed toward the naso-
pharyngeal duct; at the sides it is continuous, at the level of the
hypoglossal canals and jugular foramina, with the lateral occipi-
tal walls. The caudal free margin is concave from side to side,
forming the ventral margin of the foramen occipitale magnum,
where on each side is the basal, smaller part of the occipital
condyle (fig. 19); between these is a shallow incisura occipitalis
anterior.

The following observations were made on the position, rela-
tions and termination of the cranial portion of the notochord.
As shown in figures 14 and 19, this structure passes through the
middle of the body of the epistropheus, inclines ventrally on
entering the dens, and holds a position ventral of the middle of
the dens throughout the rest of its vertebral course. It leaves

PRIMORDIAL CRANIUM OF THE CAT 289

the dens from the ventral surface, not at its extremity, and
enters the ligamentum apicis dentis. It then passes over into
‘the cranium, lying at first Just beneath the perichondrium of the
dorsal surface of the cranial floor, with the great thickness of
the caudal edge of the basal plate beneath it. From this point
the chorda dips into the cartilage of the floor as it extends for-
ward, lying midway between the cranial and pharyngeal sur-
faces in the middle third of the plate. At no point does it sink
nearer the pharyngeal surface nor was there observed any trace
of a connection with the pharyngeal wall. Proceeding toward
the sella turcica, the notochord gradually approaches the intra-
cranial surface of the basal plate, until it attains the level of the
dorsum sellae where it makes a rather abrupt bend so as to
come to lie beneath the perichondrium of the caudal surface of
the back of the saddle. Its terminal piece is marked by distor-
tion to some extent and by a few irregular turns. Although
shrunken in many places, and showing other evidences of de-
generation, the head notochord is, nevertheless, continuous
throughout. Within the apical ligament it is considerably
expanded.

Occipital region

From the basal plate, the side walls of the occipital region,
the lateral occipital arches, continue laterally and dorsally, be-
coming confluent with the otic capsule, parietal plate and tectum
posterius (figs. 1, 2, 3, 4). They lie in a plane transverse
to the longitudinal axis of the posterior half of the cranium,
but, owing to the flexure of the long axis of the whole cranium,
this is at the same time, parallel with the plane of the floor of
the nose.

The lateral occipital arches are connected with the pars
canalicularis of the otic capsule by synchondrosis, marked in
the sections by a narrow plane of young cartilage extending a
considerable distance from the jugular foramen toward the
parietal plate. Within the cranium a deep, wide groove, the
sulcus sigmoideus, lodging the transverse sinus, lies opposite the
ventral portion of the synchondrosis and leads to the jugular

290 ROBERT J. TERRY

foramen. Outside the wall a corresponding groove separates
the paracondyloid process (figs. 2, 3) from the pars canalicularis
of the otic capsule. The caudal free margin of the lateral occipi-
tal arch enters into the boundaries of the foramen magnum
(figs. 1, 2, 3). Its ventral portion forms the larger part of
the occipital condyle; its dorsal portion, a rough angular process
directed medially. The processes of opposite sides mark the
dorsal limit of the foramen magnum at this stage and afford at-
tachment to the spino-occipital membrane. Dorsad of the
level of these processes the lateral occipital arches are continued
into the broad, curved posterior portions of the parietal plates,
between which the tectum posterius extends in an arch from
side to side.

Within the cranium, at the junction of basal plate and lateral
occipital arch, is a rounded prominence, the cartilaginous pre-
cursor of the tuberculum jugulare, separating the entrance
to the hypoglossal canal from the fossa occipito-canalicularis
(fig. 1). At its cephalic end, this elevation, broadening con-
siderably, becomes continuous with the basi-vestibular commis-
sure (figs. 9, 10, 19). This commissure is united with the otic
capsule at the boundary between the medial wall of the promi-
nentia utriculo-ampullaris inferior and the cochlear capsule,
and forms here a prominence making the posterior wall of the
internal acustic meatus. The jugular tubercle, which presents
much more the form of a ridge than of a tubercle, stands within
the cranium opposite the paracondyloid process. Both pro-
cesses contribute to the formation of the deep caudal wall of the
jugular foramen, a relation observed by von Noorden in the
human embryo. The occipito-canalicular fossa lies between the
inferior ampullary eminence and the basivestibular commissure
and connects the sigmoid sulcus with the jugular foramen.

The jugular foramen (figs. 1, 2, 12) when viewed from within
the cranium is crescentic, the convex side being formed caudally
by the tuberculum jugulare and medially by the commissura
basivestibularis; the concave margin, directed laterad, is consti-
tuted by the medial wall of the prominentia utriculo-ampullaris
inferior. The vena jugularis interna and the accessorius, vagus

PRIMORDIAL CRANIUM OF THE CAT 291

and glossopharyngeus nerves pass straight through the foramen.
Although the paracondyloid process forms a deep wall for the
foramen posteriorly, there is no inclination forward of this pro-
cess nor a lamina alaris with attendant horizontal course of the
nerves. On the extracranial surface, the foramen is divided into
cephalic and caudal parts by an angular process of the cochlear
wall (figs. 12, 19). The compartment posterior to the process
is occupied by the jugular vein and the group of nerves; the
anterior compartment, filled with connective tissue, lies within
the fenestra perilymphaticum and forms a communication be-
tween the cavum cochleae and fossa occipito-canalicularis; it is
the beginning of the aquaeductus cochleae.

The hypoglossal canal (figs. 1, 2, 12) transmits the three pre-
viously united ventral roots of the hypoglossal nerve. It runs
in a ventro-lateral direction, beginning caudad and medialward
of the jugular foramen and terminating on the external surface
at the level of the medial edge of the paracondyloid process.

The broad, square paracondyloid process (figs. 2, 3, 12, 19)
projects widely from the ventral part of the pars lateralis of the
occipital region, with ventral and lateral free edges, cephalic
and caudal surfaces. The narrow cephalic surface enters into
the wall of the jugular foramen; the ventral broad free edge is
continuous medially with that part of the extracranial surface
lying between the jugular foramen and the hypoglossal canal.

The foramen magnum (figs. 1, 2) is hexagonal with
rounded angles, the sides consisting of the free caudal margins
of the basal plate and lateral occipital arches and, dorsally,
the edge of the spino-occipital membrane. The foramen is
divisible into a large ventral part included between the condy-
lar portions of the occipital arches, and a smaller dorsal region
extending thence to the spino-occipital membrane. ‘The lateral
boundaries of these two divisions come together in a notch of the
lateral occipital wall just dorsad of each condyle (figs. 1, 2,
3, 4). A number of small veins in the connective tissue of
these notches, were connected with the sinus transversus. The
plane of the whole foramen magnum is nearly transverse to the
longitudinal axis of the posterior half of the cranium; however,

292 ROBERT J. TERRY

the positions of the planes of the dorsal and ventral divisions
differ from one another, that of the ventral, condylar part is
transverse, whereas that of the dorsal division is very oblique.
The latter faces ventro-caudad and forms an angle, open cau-
dally, of approximately 145 degrees with the plane of the ventral
part of the foramen (fig. 3).

The occipital condyles (figs. 2, 3, 19) are a pair of oval emi-
nences only slightly raised above the level of the ventro-lateral
margins of the foramen magnum. Each condyle extends at
first laterally from the incisura occipitalis anterior along the
caudal margin of the basal plate to the level of the hypoglossal
canal, then dorso-laterally upon the lateral occipital arch. The
basilar portion is broader but shorter than the lateral which
stretches out upon the occipital arch as far as the deep notch
mentioned above (p. 291). The lateral and basal parts of the
condyle are connected with the lateral mass and ventral arch of
the atlas by imtervening mesenchyma; an articular cavity is
not present.

The tectum posterius (figs. 1 and 2) is a slender transverse
bridge of cartilage arching over the brain and connecting the
parietal plates from side to side. It is far from the auditory
capsules caudally and dorsally, standing closer to the occipital
side walls. The tectum expands laterally in joining the parietal
plates, becomes narrow in its middle opposite the medulla ob-
longata. The caudo-ventral margin of the tectum is con-
cave from side to side, bounds the incisura occipitalis posterior
and affords attachment to the spino-occipital membrane; the
cephalic, and at the same time dorsal, margin is straight, pre-
senting no indication of a processus ascendens.

The term incisura occipitalis posterior (fig. 1) is given ten-
tatively to the bay extending from the foramen magnum to
the tectum posterius. Its lateral boundaries are the caudal
margins of a pair of cartilaginous plates continuous with the
occipital walls ventrally, and with the laminae parietales an-
teriorly. This notch is filled by the spino-occipital membrane.

Hypoglossal nerve. Three ventral roots unite to form a single
nerve in the embryo of 23.1 mm. A dorsal root opposite to,

PRIMORDIAL CRANIUM OF THE CAT 293

but not united with, the third ventral root, arises from the
spinal cord between the atlas and occipital arch. In smaller
specimens further evidences of a dorsal root and ganglion were
observed. This component was best developed in an embryo of
15 mm. (W. U. C. ser. 52, sl. 22-24) in which the dorsal root
joined the third ventral root before reaching the hypoglossal
foramen.

Atlas and epistropheus

In connection with the occipital region some observations on
the epistropheus and atlas should be mentioned. These verte-
brae have not reached their full chondrogenous development,
the neural arches specially being very incomplete (fig. 9). The
dens epistrophei is relatively very much*longer in the embryo
of the present stage than in the adult. Its relations are also
different in that it projects beyond the anterior arch of the
atlas so far craniad as to enter a little way into the cranial
cavity through the occipital foramen (figs. 9, 14, 19). The
atlas is remarkably massive. Just cephalad of the neural arches
is a pair of processes of special interest. These project dorsad
from the spot where the neural and anterior arches meet (the
future lateral mass), inclining a little toward the median plane,
and end in blunt extremities. These atlantal processes, which
are the cartilaginous precoursors of the little bridges of bone
of the adult atlas, completing the circumferences of the foramina
atlantalia, form, with the neural arches, a notch on each side
lodging the ganglion of the first spinal nerve and the vertebral
artery. The articular surfaces of the atlas for the occipital
condyles are formed at the meeting place of the neural and ante-
rior arches. Two parts enter into the formation of the articular ~
surfaces: (1) a thickening at the junction of the neural and
anterior arches, which meets the basal portion of the occipital
condyle; (2) the atlantal process which articulates with the
lateral part of the condyle.

294 ROBERT J. TERRY

Basal plate and occipital region in smaller embryos

In van Wijhe preparations of embryos of 10 mm. (fig. 5)
there appears in the floor of the occipital region a pair of faintly
stained, elongate parachordal plates. These are united anteriorly
by a commissure beneath the notochord, but are separated across
the midline in the rest of their extent. Each plate is thickened
at its caudal end, and is then continued laterally intc the occipi-
tal arch. The lateral margin of the parachordal plate presents a
prominent angle subdividing it into an anterior oblique part oppo-
site the mesenchymal cochlear capsule, and a posterior straight
part opposite the jugular vein. In the angle between the straight
part of the margin and the lateral occipital arch are the three
roots of the hypoglossal nerve. Between the parachordal plates
and behind their commissure is a vacuity traversed by the
notochord. This space is constricted at its middle by opposite
projections from the medial edges of the parachordals. The
notochord extends forward as far as the hypophysis and appears
to lie in a ‘tract of blue-stained tissue which terminates just
behind the hypophyseal cartilage. Each lateral occipital arch
is slender and cylindrical medially where it joins the parachordal
plate, expanded and flat laterally at its free extremity. Where
these two parts come together the cartilage is only slightly
stained. The lateral arches at this stage lie far removed in a
caudal direction from the otic capsules which are represented
by parts of the anterior and posterior semicircular canals.

The atlas has the form of a transverse arch open dorsally.
Each lateral extremity of the arch, deeply stained, is in the
form of a broad plate presenting two processes, the neural and
atlantal. The middle, slender hypochordal part of the arch is
only slightly stained. The epistropheus likewise forms an arch,
the ventral medial part of which includes the notochord. Here
a darkly stained tract on each side is separated from the noto-
chord medially and the deeply stained neural arch laterally
by very lightly stained zones. The two tracts’ near the noto-
chord are the beginnings of the centrum of the epistropheus.
Just cephalad of the epistropheal centrum and separated from

PRIMORDIAL CRANIUM OF THE CAT 295

it by a transverse plane of unstained tissue is the broad conical
mass of young cartilage surrounding the notochord, the begin-
ning of the atlantal centrum. Between the apex of the latter
and the commissure of the parachordals the notochord stands -
free of any chondrified tissue as evidenced by the absence of the
blue stain about it.

Transverse sections of an embryo of 10.6 mm. (fig. 15) make
clear the relations of the notochord, dens epistrophei and para-
chordal plates at the stage of cartilaginous structure of the
latter. The parachordals are connected across the median plane,
ventrad of the notochord by loose tissue. This tissue presents
more and more the characters of mesenchyma when traced
toward the median plane, and more and more the condition of
‘cartilage when followed toward the parachordals into which it
passes. An imperfect basal plate is thus formed in the occipital
region which extends from side to side ventrad of the notochord
and which passes laterally into the lateral occipital arches.
Figure 15 shows the notochord covered dorsally and laterally
by a layer of cellular tissue lying upon the dorsal surface of the
stretch of mesenchyma connecting the parachordal plates.
When followed caudad this layer increases in thickness, especially
on the dorsal side of the notochord, and passes over into the
mesenchyma of the centrum of the atlas.

In van Wijhe preparations of 12 mm. (fig. 6) the most impor-
tant differences from the preceding stage in the posterior part
of the cranium are the presence of a hypoglossal foramen, the
beginning of the parietal plate and the slender cartilaginous basal
plate of the otic region. The hypoglossal foramen has resulted
from the development of a bar of cartilage uniting the lateral
angle of the parachordal plate and lateral occipital arch outside
the roots of the twelfth nerve. The beginning of the parietal
plate appears standing free, dorsad of the posterior semicircular
canal of the otic capsule. The basal plate of the otic region is
continuous behind with the primary commissure of the para-
chordals, terminates in front in an expansion which extends
nearly as far as the cochlear wall, and anteriorly projects some-
what dorsad of the hypophyseal cartilage.

296 ROBERT J. TERRY

In sections of 12 mm. embryos (fig. 17) the notochord, as it
enters upon its cranial course, lies at first dorsad of the still
imperfect basal plate, then sinks into the otic portion of the
plate; it is now. surrounded on all sides by cartilage at the level
of the primary parachordal commissure. The notochord emerges
from the basal plate at its free anterior end, which is inclined
dorso-cephalad, and terminates in the mass of mesenchyma
which fills the interval (fenestra basicranialis posterior) between
the expanded end of the basal plate and the hypophyseal car-
tilage. Where the notochord enters the cranium it is surrounded,
as in the preceding stage, by a layer of mesenchyma which ex-
tends caudally to join with the chondrifying tissue forming the
centrum of the atlas. The centrum stands in the same trans-
verse plane as the arches of the atlas, from which it is separated’
by a stratum of less compact mesenchyma. Sagittal sections
show a plane of densely packed nuclei separating the centrum
of the atlas from the centrum of the epistropheus already laid
down in young cartilage. _Chondrification of the hypochordal
arch of the atlas is less advanced than that of the tissue be-
neath the notochord between the caudal margins of the para-
chordal plates; in the latter young cartilage is present, while
in the hypochordal arch of the atlas mesenchyma alone is to be
found.

Between the caudal margin of the parachordal plates and the
lateral mass of the atlas is a transverse stretch of deeply staining
tissue, dense laterally and thin medially where it meets the
mesenchyma about the notochord. Its later history is not clear.

Two marked advances in development of the floor of the cra-
nium appear in a van Wijhe preparation of 15 mm. (fig. 7).
First, the basal plate is nearly perfected, the unchondrified part
in the occipital region being now considerably reduced. The
bar completing the boundaries of the hypoglossal foramen stands
opposite the primary commissure of the parachordals and is
thickened at its origin, just where the jugular tubercle and
paracondyloid processes later are developed. At the same spot a
slight projection forward toward the cochlear capsules, medial
to the vena jugularis, is probably the beginning of the basi-

PRIMORDIAL CRANIUM OF TdEK CAT 297

vestibular commissure. Second, the anterior expanded ex-
tremity of the basal plate is united with the hypophyseal car-
tilage forming the crista transversa. The carotid artery as it
enters the cranium is pressed against the side of the expanded
end.

The dorsal extremity of the lateral occipital arch is not.
united anteriorly with the pars canalicularis of the otic capsule;
it is, however, joined with the parietal plate which now pre-
sents a prominent dorso-medial angle, the beginning of the
tectum posterius.

In the atlas the hypochordal arch is partly chondrified. It is
composed of two bars, right and left, which are continuous at
each side with the lateral masses and approach each other
medially. The lateral mass has been formed from the expanded
end of the hypochordal arch of the preceding stage. The
centrum of the atlas has united with that of the epistropheus so
that a dens epistrophei can be described. The anterior ex-
tremity of the latter projects cephalad beyond the transverse
plane of the atlantal hypochordal arch. The lateral arches of
the epistropheus are connected with the centrum by a lightly
stained zone.

Sagittal sections of the embryos of 15 mm. show that the
basal plate is chondrified and is continuous with the floor of the
cranium in the hypophyseal region (fig. 18). Here, the anterior
end of the plate is still recognizable as an elevation, the crista
transversa, behind the hypophysis. The bent extremity of the
notochord lies upon the transverse crest imbedded in a hill of
mesenchyma. In the caudal region of the basal plate the noto-
chord still occupies a position near the intracranial surface,
covered by connective tissue continuous with the dens epis-
trophei. A superficial constriction marks the original plane of
fusion of the centra of the first and second vertebrae. Chon-.
drification of the dens is less advanced toward its extremity than
at its base. Since the last stage described chondrification has
extended forward in the mesenchyma about the notochord, in
consequence of which the extremity of the dens has been length-
ened and now lies upon the caudal margin of the basal plate.

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

298 ROBERT J. TERRY

The hypochordal arch of the atlas is composed of young carti-
lage, least developed toward the midplane and continuous, right
and left, with the lateral masses.

In embryos of 17 to 20 mm. (fig. 8) the basal plate is chondri-
fied from side to side. Boundaries of the jugular foramina are
established by the presence of the basicochlear commissures
and the more complete union of the lateral occipital arches and
the otic capsules. In relation to the hypoglossal foramen, the
jugular tubercle appears anterior, the paracondyloid process
lateral; the one within the cranium, the other outside. The basal
foramina are all relatively large. A long, wide basi-cochlear
fissure is limited anteriorly by the basi-cochlear commissure
which separates it from the carotid foramen. The tectum pos-
terius is represented in cartilage by a spur springing on either
side from the parietal plate. The hypochordal arch of the
atlas is complete from side to side. The dens epistrophei is
further chondrified cranially.

Otic region. Embryo of 23.1 mm.

The otic capsule, externally, presents two well defined sub-
divisions, one serving as the framework of the semicircular
canals, the other enclosing the cochlear canal (figs. 1, 2, 3).
The vestibule, on account of its intimate relation both with the
pars canalicularis and the pars cochlearis, will be included in
the description of these subdivisions.

Regarding the position of the otic capsule at the stage repre-
sented by the model, a departure from the mammalian type is to
be noted. The long axis of the whole auditory capsule of mam-
mals is, as Gaupp has indicated, directed from behind and
laterally, forward and medially; just the opposite of what
occurs in lower vertebrates. The long axis of the otic capsule
of the cat embryo of 23.1 mm. is inclined somewhat trans-
versely (figs. 1, 2). It is true that the broader canalicular part
reaches caudally a little way beyond the cochlear division, but
in the cephalic direction both attain almost to the same level.

Regarding the relation of the otic capsule to the walls of the
cranium, the pars cochlearis lies wholly in the floor and the pars

PRIMORDIAL CRANIUM OF THE CAT 299

canalicularis stands nearly upright in the lateral wall. The
external surface of this part rises straight toward the lamina
parietalis; the internal surface inclines from above, ventrad
and a little medialward. The cochlear capsule, very large and
rounded, lies beneath the brain in the base of the skull, ap-
proaching closely its fellow opposite, the two making up almost,
the entire cranial floor in the otic region.

At its circumference the otic capsule is connected with neigh-
boring parts of the side wall and base of the cranium by broader
or narrower stretches of cartilage with intervening vacuities.
The several connections between the otic capsule and the occipi-
tal wall and basal plate as well as the related openings have
already been described (p. 289). There remain to be noted the
bonds between the capsule and parietal plate, and certain
parts in the orbito-temporal region.

The dorsal, narrow margin of the pars canalicularis is, in
large part, free, forming the ventral boundary of the foramen
jugulare spurium (figs. 3 and 4). Cephalad and caudad of this
narrow fissure it is connected with the lamina parietalis; in the
former situation, by the commissura parieto-capsularis, in the
latter place with that part of the parietal plate which is con-
tinuous ventrally with the occipital wall. Between the cephalic
pole of the pars cochlearis and the ala temporalis is the commis-
sura alicochlearis which limits the carotid foramen laterally.
Between this opening and the fissura basicochlearis posterior
the cochlear capsule is united continuously with the basa.
plate (p. 288). ;

The pars canalicularits. Outer form

Oval and laterally compressed, the massive pars canalicularis
stands in the side of the skull, contributing a large part of its
lateral wall. It presents an extracranial lateral surface, an-
terior and posterior surfaces mainly within the cranium, and a
narrow arched dorsal margin. A vestibular region unites this
subdivision of the otic capsule with the pars cochlearis.

The lateral surface (figs. 38, 4) convex and smooth, shows only
slight elevations corresponding to the semicircular canals.

300 ROBERT J. TERRY

Rounded prominences at the cephalic and caudal poles, which
appear on both the medial and lateral aspects of the otic capsule,
are identified as the prominentia utriculo-ampullaris superior
and the prominentia utriculo-ampullaris inferior, respectively
(fig. 10). The lateral surface of the pars canalicularis terminates
ventrally in a broad irregular ridge, the crista parotica, which,
projecting basally, extends from the superior utricular promi-
nence the full length of this surface. In its caudal half the
crista parotica (figs. 2, 20) gives rise to an oval elevation con-
nected medially with the base of Reichert’s cartilage. The ele-
vation bears a close relation to the future processus mastoideus,
which in the cat belongs exclusively to the-otic region; but that
it gives rise to it I am unable to say. The parotic crest, es-
pecially in its caudal two thirds, projects from that part of the
ear capsule lodging the lateral semicircular canal. In its cephalic
part is a slight depression of its lateral surface, the fossa incudis
(fig. 3) where the cartilaginous incus is connected by a liga-
ment. A tegmen tympani at the stage represented by the
model is not present. Further relations of the crista parotica
with Reichert’s cartilage, and the facial canal will be discussed
under these subjects. A deep groove separates the crista parot-
ica from the pars cochlearis. This can be traced anteriorly
beyond the limits of the crest upon the inferior cochlear promi-
nence toward the foramen faciale; posteriorly as far as the
jugular foramen. The facial foramen (fig. 1) transmitting the
N. facialis, is directed antero-laterally and les without the plane
of the membrana limitans (vide infra). Here is formed the
geniculate ganglion and the origin of the great superficial petrosal
nerve. In its anterior part the groove lodges the facial nerve
and is identified as the sulcus facialis. At the base of Reichert’s
cartilage it becomes narrow through the approximation of this
cartilage toward the crista parotica and the wall of the coch-
lea, here forming the promontory (fig. 12). Since, at this spot
the nerve makes its exit from the groove, it is to be regarded as
the foramen stylomastoideum primitivum. Caudad of this
foramen, the groove is broad and deep, filled with connective
tissue and occupied to a small extent by the hinder part of the

PRIMORDIAL CRANIUM OF THE CAT 301

cavum tympani. In it lies also the vena capitis lateralis. In
the model the expanded posterior part of the groove com-
municates freely with the great foramen cochleae, opening at
its medial side.

The intracranial surface of the pars canalicularis is depressed
below the general surface of the cranium and presents an uneven
contour (fig. 1). Ventrally it passes into the pars cochlearis.
At the place of transition a great quadrilateral fenestra acustica
transmits the divisions of the N. acusticus. <A ridge, eminentia
cruris communis, produced by the crus commune of the anterior
and posterior semicircular canals, subdivides the intracranial
surface into anterior and posterior faces. The eminence pre-
sents the foramen endolymphaticum and inferiorly passes into
the prominentia utricularis. The latter, corresponding to the
utricle and saccule, reaches below to the acustic window. The
posterior surface of the pars canalicularis looks caudad, mesad
and slightly ventrad, contrasting in its position therefore with
the caudally and ventrally directed corresponding surface in
mammals generally. It passes caudally into the medial surface
of the lateral occipital arch and ventrally into the prominentia
utriculo-ampullaris inferior. The posterior surface is hollowed
to form the sigmoid sulcus, occupied by the sinus transversus.
The anterior surface of the pars canalicularis presents the fossa
subarcuata anterior limited anteriorly and dorsally by the
prominentia semicircularis anterior. This prominence begins
at the dorsal pole of the pars canalicularis and curves anteriorly
and ventrally to the prominentia ampullaris superior. On this
surface, also, the stout commissura suprafacialis? is found, con-
necting the medial wall of the prominentia utriculo-ampullaris
superior with the anterior part of the roof of the pars coch-
learis, and participating in the ventro-caudal circumference of
the spheno-parietal fenestra. It is continued dorsally into a

In van Wijhe preparations of embryos 17 to 30 mm. long, the suprafacial
commissure appears deeply stained and separated from the pars canalicularis
by a zone of lightly stained cartilage. It continues directly into the com-
missura orbito-parietalis where this is united with the otic capsule (commissura
parieto-capsularis) (fig. 9).

302 ROBERT J. TERRY

prominent ridge which joins the orbito-parietal commissure
(figs. 1, 3). The suprafacial commissure constitutes the roof of
the short first portion of the facial canal, the floor of which is
made by a cartilaginous septum between it and the cavum
cochleae. The canal leads from the meatus acusticus internus
to the foramen faciale. The dorsal circumference of the pars
canalicularis is partly free, partly continuous with the cranial
wall. Posteriorly it passes into the occipital wall; anteriorly it
is connected with the commissura parieto-capsularis. Between
these connections the dorsal margin is free, forming the ventral
boundary of the foramen jugulare spurium. Upon the medial
side of the dorsal circumference is a groove occupied by the
transverse sinus and its main anterior tributary.

Pars cochlearis

The most conspicuous object of the cranial floor as presented
by the model is the huge, rounded bulging of the pars cochlearis
of the auditory capsule (figs. 1, 2). The strong walls of this
shell enclose the cochlear canal and the saccule. The form of the
cochlear capsule is not quite round, but longer in a direction
from behind, forward and medialward. Upon the ventral,
extracranial surface a shallow groove, sulcus septalis, extends
from behind and laterally, medially and anteriorly. Upon the
caudal aspect is the large foramen cochleae. Where the cochlear
and canalicular parts come together are three openings: the
fenestra vestibuli, appearing outside the cranium, the fenestra
acustica, within the cranium and the foramen perilymphaticum,
appearing partly inside and partly outside the skull. The pars
cochlearis shows no sharp boundary toward the pars canalicu-
laris; as stated above, the two are continuous in the region of
the vestibule. On the surface, this common vestibular zone
corresponds to the intermediate stretch which includes the sulcus
facialis laterally, and the region of the fenestra acustica, medially.
The connections between the cochlear capsule and the floor of
the cranium have already been described (p. 288).

Foramina acustica (figs. 10, 11). A large quadrilateral
opening, fenestra acustica, the future porus acusticus internus,

PRIMORDIAL CRANIUM OF THE CAT 303

is situated upon the medial aspect of the ear capsule, partly in
the wall of the cochlea, partly in that of the vestibule. Its
plane faces dorsad and mesad, the lateral margin made by the
prominentia utricularis being considerably higher than the
medial cochlear edge. The fenestra leads into a short, imper-
fectly formed meatus acusticus internus; within is an incomplete
floor presenting two openings, one transmitting the facial nerve,
the other the branches of the acustic nerve. The former, which
lies anteriorly, is the beginning of the primary facial canal. It
will be recalled that this short canal passes beneath the supra-
facial commissure and ends in the facial foramen outside the
chondrocranium. The opening for the acustic nerve is an irregu-
lar gap; for convenience of description it will be referred to as the
acustic fissure. It is shaped like a V with apex caudad, one
limb lying almost wholly in the cochlear, the other in the ves-
tibular region. The latter division, widened in the form of an
oval notch, lies anterior and slightly dorsal to the cochlear di-
vision. It transmits the nerves to the utricle, and to the
ampullae of the anterior and lateral semicircular canals. Its
position and relations to the structures just named identify it
with the superior acustic foramen of other mammalian embryos.
The larger cochlear portion of the acustic fissure lies caudad,
medialward and somewhat ventrad to the superior acustic
foramen. It gives passage to the nerve of the cochlea and the
nerve to the saecule, and is identified with the inferior acustic
foramen. In the dorsal caudal corner of the meatus acusticus
internus is a notch opening into the cochlear part of the fissure
and leading to a groove, lodging the nerve to the ampulla pos-
terior. The notch is the forerunner of the foramen singulare
and will be designated the incisura singularis.

The position and relations of the facial and acustic foramina
having been noted, it now remains to describe the walls of the
internal acustic meatus. Figures 13 and 14 show the meatus
from the medial aspect. Of the stretches of cartilage inter-
vening between the facial and acustic foramina two are of special
interest: one, constituting the primary floor of the meatus, sepa-
rating the two named foramina; the other forming the incom-

304. | ROBERT J. TERRY

plete lateral wall of the meatus. The primary floor of the
meatus appears in the model as an extension from the roof of the
anterior part of the cochlear cavity. It can be followed laterally
from the dorsal part of the cochlear capsule at the medial mar-
gin of the fenestra acustica to pass into the first turn of the sep-
tum spirale.. This part is the forerunner of the longitudinal
bony ridge in the floor of the meatus of the adult, the crista
transversa of human anatomy, which separates the superior
cribriform area and entrance to the facial canal above from the
middle cribriform area and the spiral tract of foramina below
(Jayne 798, p. 200). Anteriorly it continues as the floor of the
primary facia! canal and at the same time the roof of the fore
part of the cochlear cavity. Lateral to the facial foramen the
primary ficer cf the meatus passes into the floor of the promi-
nentia uiriculo-empullaris superior and forms the ventral bound-
ary of the superior acustic foramen. The posterior free edge
of the floor constitutes the cephalic margin of the inferior acustic
foramen. The lateral wall of the meatus is formed mostly of
precartilage. Its free ventral margin bounds the acustic fissure
dorsally. The wall itself covers the medial aspect of the sac-
cule. The medial edge of the meatus, derived from the roof of
the cochlear capsule, stretches from the suprafacial commis-
sure to the posterior wall and is very low. The anterior and
posterior walls, on the contrary, tend to become very high
toward the vestibular part of the capsule, and are formed re-
spectively by the suprafacial commissure and an elevation made
at the junction of the basivestibular commissure with the promi-
nentia ampullaris inferior and cochlear capsule.

Within the meatus acusticus internus are found, anteriorly,
the nerve of the vestibule and its ganglion, together with the
facial nerve, and, posteriorly, the nerve of the cochlea.

In the model of the chondrocranium, there is a small flat-
tened surface of the cochlear capsule, lateral to the suprafacial
commissure (figs. 3, 20). This, the planum supracochleare of
Voit, supports the seventh nerve as it passes out of the foramen
faciale, the geniculate ganglion and the beginning of the great
superficial petrosal nerve. Upon it rest also the caudal part

PRIMORDIAL CRANIUM OF THE CAT 305
of the semilunar ganglion and the roots of the fifth nerve. As
shown by the sections, these structures are embedded in mesen-
chyma which extends laterally to Meckel’s cartilage and medially
as far as the plane of the chondrocranial wall; here, in the form
of a membrane, it becomes fixed to the margins of the fenestra
sphenoparietalis. For this region the name cavum supra-
cochleare has been proposed by Voit. The cavum supracoch-
leare and the several structures therein are excluded from the
cavity of the chondrocranium by the membrane of the spheno-
parietal window.

Cavities of the otic capsule

A frontal section through the vestibular region shows a large
irregular space containing parts of the membranous labyrinth
(fig. 10). This space extends anteriorly into the pars cochlearis
as the cavum cochleae, lodging the cochlear duct; posteriorly
into the pars canalicularis in the form of the canales semi-
circulares. The main room opened by the section, vestibulum,
contains the utricle and saccule.

Cavum cochleae (figs. 19, 20, 21, 22). The great oval cavity
of the pars cochlearis, traversed by a low septum spirale, has
already begun’ to asssume the form of a winding canal. This
may be followed from the vestibule, with which it is in wide
communication, ventrally, then in a spiral course into the ante-
rior part of the cochlear. capsule. At its commencement the
canal is quite wide, and its limiting cartilaginous walls incom-
plete through the presence of large openings; caudally, the
perilymphatic foramen; laterally, the fenestra vestibuli; dorsally,
the inferior acustic foramen. The cochlear duct makes a little
more than one complete turn and occupies but a small part of
the cavity which is elsewhere filled by young connective tissue
(fig. 9). This tissue extends into the perilymphatic foramen and
to the edge of the spiral septum where, by condensation of its
elements, it presents the form of a spiral membrane (fig. 22).
No indication of cartilage formation was observed in this mem-
brane in the present or in a later stage. The cartilaginous sep-
tum, spirale takes origin in the primary floor of. the internal

306 ROBERT J. TERRY

acustic meatus (figs. 10, 11, 19), makes a steep descent toward
the floor of the cochlear cavity, and continues as a low ridge
to the extent of somewhat more than half a turn from the be-
ginning of the septum. Its position externally, is indicated on
the ventral surface of the cochlear capsule by the sulcus septalis
(p. 302).

The oval fenestra vestibuli (figs. 3, 20, 21) appears externally
at the bottom of a deep depression of the surface of the capsular
wall, standing in a coronal plane, above and lateral to the peri-
lymphatic foramen. Its superior and medial boundaries are very
prominent; its inferior limit obscure. Within this depression
is the foot-plate of the cartilaginous stapes, embedded in mesen-
chyma which completely fills the window. Within the cavum
cochleae, the fenestra appears on an eminence of the lateral
wall which projects posteriorly toward the vestibule.

The large foramen perilymphaticum (figs. 2, 12, 20) extends
upon both the caudal and dorsal surfaces of the pars cochlearis
and is incompletely divided by a process of the cochlear capsule
into two parts, the fenestra cochleae and the aquaeductus
cochleae. The former is located at the caudal pole of the coch-
lear prominence, stands in a transverse plane and is occupied by
mesenchyma. In figure 11 it appears completely separated
from the aquaeductus cochleae, but the septum between these
openings is chondrified only in its medial part; laterally it is
composed of precartilage. The aquaeductus cochleae, lying in a
frontal plane, opens into the fossa occipito-canalicularis above
(p.291),and communicates with the cavum cochleae below. It is
filled with mesenchyma, through which small veins pass to the
vena jugularis interna. The aqueduct of the cochlea at the
present stage is an extension of the jugular foramen forward in
the form of a deep notch between the commissura basivestibu-
laris and the prominentia utriculo-ampullaris inferior. -It con-
stitutes a vacuity in the roof of the cochlear capsule. The
aquaeductus cochleae is separated from the jugular foramen
proper (i.e. the posterior part transmitting the vein and nerves)
by the free angular projection of the cochlear wall above men-
tioned (indicated by * in figs. 2, 12, 19).

PRIMORDIAL CRANIUM OF THE CAT 307

Vestibulum. A frontal section through the middle of the
vestibular region reveals a space within the cartilage stretching
antero-posteriorly and lying nearer the medial than the lateral

margin of the section (fig. 10). This space, a part of the future
“vestibule, is narrowed in its middle by the encroachment of a
massive projection of the lateral wall and is expanded rather
widely in front and behind this. The anterior wide room, con-
taining in the section the utricle and recessus utriculi and the
ampullae of the anterior and lateral semicircular ducts, will be
described under the name of the cavum vestibulare anterius.
The posterior room includes, in the section, the posterior part of
the utricle, the ventral part of the ductus endolymphaticus, the
beginning of the canalis utriculi-saccularis, the sinus inferior,
ampulla posterior and the crus simplex of the ductus semicircu-
laris lateralis. This room will be further considered under the
name of the cavum vestibulare posterior. The parts of the mem-
branous labyrinth mentioned do not fill completely the space
limited by the cartilaginous walls of the pars vestibularis, but
leave an interval filled by mesenchyma representing the future
perilymphatic space.

Cavum vestibulare anterius (figs. 10, 11). This large, irregu-
larly shaped cavity occupies the dorsal part of the vestibular
region. Its contents have been noted. Its anterior wall swells
out as the prominentia utriculo-ampullaris superior. This cor-
responds to an anterior extension of the cavity called recessus
ampullaris anterior containing the ampulla anterior. The floor
is broad, slopes ventrad in a medial direction, then drops abruptly
to continue into the lateral cochlear wall. At this spot is located
the fenestra vestibuli (figs. 19, 20). The medial wall bulges
slightly into the cranial cavity forming the prominentia utricu-
laris, in conformity with the subjacent surface of the utricle and
saccule. The ventral free edge of this wall forms the dorsal
boundary of the superior acustic foramen as already described
(p. 304). The lateral wall presents a dorso-ventral ridge which
projects into the cavity, fitting into the angle between the am-
pulla lateralis and ampulla anterior. The considerable space
behind the ridge, containing the greater part of the lateral am-

308 ROBERT J. TERRY

pulla opens posteriorly into the canalis semicircularis lateralis.
The posterior wall is formed by the mass of cartilage already re-
ferred to which projects medialward from the lateral wall of the
otic capsule (fig. 11). This crista intervestibularis, as it may be
termed, intervenes between the anterior and posterior vestibular ”
caves, but fails to meet the medial vestibular wall; there is left a
communicating space between the two divisions occupied by a
part of the utricle. Ventrally, the crista intervestibularis enters
into the roof of the lateral semicircular canal; dorsally it becomes
continuous with the massa angularis, the great body of cartilage
encompassed by the semicircular canals. The dorsal wall of the
cavum vestibulare anterius is made by that portion of the angu-
lar mass which fills the concavity of the canalis semicircularis
anterior.

Cavum vestibulare posterius. In form, the posterior division of
the vestibule is oval dorsally, narrow and tunnel-shaped ven-
trally, expanding into a roomy space in the region of the fenestra
cochleae. The posterior wall bulges in adaptation to the adja-
cent recessus ampullaris posterior, forming on the surface of the
ear capsule the prominentia utriculo-ampullaris inferior. The
ventral part of the posterior wall presents the posterior orifice
of the lateral semicircular canal. The dorsal part, at its junc-
tion with the roof of the cavum vestibuli posterius, shows the

' orifice of the posterior semicircular canal. The medial wall, con-

tinuous with the medial wall of the anterior cave, corresponds
to that part of the otic capsule marked on the surface by the
beginning of the prominentia cruris communis and the incisura
singularis. It presents a ventral free edge looking into the in-
ferior acustic foramen. The dorsal wall consists of that part of
the massa angularis intervening between the canalis semicircu-
laris posterior and the vestibule. In the highest part of the
roof are two openings:—the great circular orifice of the cavum
cruris communis, containing the crus commune of the anterior
and posterior canals; the small irregular hole, foramen endolym-
phaticum, looking medialwards and transmitting the ductus en-
dolymphaticus. A floor is present in the caudal half only, be-
neath the ampullary end of the posterior semicircular duct;

PRIMORDIAL CRANIUM OF THE CAT 309

where the floor is wanting anteriorly there is a wide communi-
cation with the cavum cochleae.

The semicircular canals (figs. 2, 9, 10, 11, 19) are cylindrical
tunnels of a diameter from two to two and one-half times that
of the contained membranous ducts. The future perilymphatic
space between the ducts and walls of the canals, is filled with
mesenchyma. Within the compass of the canals is the body of
cartilage to which Gaupp has given the name massa angularis.
The lateral semicircular canal lies in a frontal plane; its floor,
lateral and medial walls go into the cartilage of the crista parotica;
its roof is formed by the crista intervestibularis. The plane of
the anterior semicircular canal is dorso-ventrad inclining latero-
mesad from before backward. Within its concavity is that part
of the massa angularis which forms the roof of the cavum vestib-
ulare anterius and which corresponds to the fossa subarcuata of
the intracranial surface of the pars canalicularis. The posterior
semicircular canal also runs in a dorso-ventral plane, which,
however, is inclined from behind and laterally, forward and medi-
ally. It includes within its concavity that part of the massa
angularis forming the roof of the cavum vestibulare posterius
and which corresponds on the intracranial surface of the pars
canalicularis to a fossa. From the bottom of this fossa, which
is situated behind the prominentia cruris communis, a canal,
transmitting some blood vessels, leads to a great vacuity within
the angular mass.

The crista intervestibularis (fig. 11) is a projection of the base
of the massa angularis. It begins just dorsad of the fenestra
vestibuli as a ridge lying between the ampulla lateralis and the
saccule; it reaches its maximum height opposite the ductus utric-
ulo-saccularis.

The massa angularis (figs. 2, 10, 11), filling the space between
the three semicircular canals and the vestibule, is composed of
hyaline cartilage, fully formed. Its relation to the walls of the
canals and vestibule have already been described. Ventrally
the mass becomes continuous with the crista intervestibularis.
The angular mass is not continuous throughout, being broken
in its central portion by a space occupied by connective tissue

310 ROBERT J. TERRY

and blood vessels (indicated by ** fig. 2). The latter find a pas-
sage to the cranial cavity by the opening in the fossa behind the
eminentia cruris communis (vide supra); veins passing out of
this opening join the sigmoid sinus. The space extends cephalo-
caudad and dorsad; approaching the anterior and posterior
semicircular canals and the crus commune, and reaching ventrad
as far as the level of the roof of the vestibular cavities and the
crista intervestibularis. It does not at any point communicate
with the vestibule.

Lamina parietalis (figs. 1, 2, 3,4). This plateof cartilage stands
in a sagittal plane dorsad of the pars canalicularis. The concave
extracranial surface gives origin to part of the temporal muscle;
the convex intracranial surface is smooth. The parietal plate is
broad anteriorly and posteriorly and narrow between where it
lies dorsad of the pars canalicularis of the otic capsule. It goes
over anteriorly into the commissura orbito-parietalis posteriorly
into the lateral occipital wall, and, in connection with these two
parts, is fixed to the pars canalicularis. Between the four ele-
ments named is the foramen jugulare spurium, narrow and
curved around the dorsal circumference of the otic capsule.
Some minute veins traversing the foramen connect the transverse
sinus with extracranial veins. The foramen of the right side is
subdivided by a cartilaginous connection of the parietal plate
and pars canalicularis. The hinder of the two resulting foramina
is located opposite the summit of the posterior semicircular
canal. In van Wijhe preparations of embryos 24 to 30 mm. in
length, union of the parietal plate and pars canalicularis was ob-
served dividing the spurius jugular foramen into two parts.
This connection was found on one side or the other, rarely on
both, occurring, as in the stage modeled, at the summit of the
anterior semicircular canal. The parietal plate at this level is
very narrow, is notched in its dorsal margin and, compared with
the regions anterior and posterior, is less chondrified.

PRIMORDIAL CRANIUM OF THE CAT ald

Otic region in smaller embryos

In cat embryos of 17 mm. (H. E. C. ser. 492 and van Wijhe
preparations, fig. 8) both pars canalicularis and pars cochlearis
are largely chondrified and stand in connection with each other.
At their margins they are united with the floor and walls of the
cranium by commissures between which openings are found.
The basal plate, sella turcica, parietal plate, orbito-parietal com-
missure and occipital wall, parts adjacent to the auditory cap-
sule, are all formed of cartilage. The cartilaginous structure of
the ventral portion of the occipital wall and that of the floor of
the cranium are further advanced in development than the car-
tilage in the remaining parts.

In the pars canalicularis, cartilage has formed upon its lateral
surface, anterior, posterior and dorsal margins, around and be-
tween the semicircular ducts; its medial surface is chondrified
about the circumference and crus commune. The prominentiae
utriculo-ampullaris superior and inferior present cartilaginous
walls, that of the last named being continuous ventrally with
the cochlear wall. A chondrified medial wall of the vestibule
forms the dorsal boundary of the future internal acustic meatus.
At the margins of the pars canalicularis the sections show that
planes of prochondral tissue separate it from the parieto-capsular
commissure in front and lateral occipital arch posteriorly.

As shown by the sections through the cochlear capsule, pre-
cartilage is everywhere present excepting at the anterior and
posterior poles. At these two spots the cochlea is united with
the cartilage of the cranial base by commissures, but between
the commissures it is separated from the basal cartilage by an
extensive basicochlear fissure filled with mesenchyma. The roof
of the cochlear capsule is considerably further developed than
the floor and is nearer the cartilaginous state toward the pars
canalicularis than in the direction of the median plane. At the
posterior pole young cartilage can be followed from the promi-
nentia utriculo-ampullaris inferior medially and caudally into the
cochlea. This area lies between the fenestra acustica and the
foramen perilymphaticum; from it the basivestibular commis-

312 ROBERT J. TERRY

sure, just caudad, can be differentiated by its more advanced
state of development. At the anterior pole, cartilage formation
is found in connection with the suprafacial commissure. Where
this bar joins the cochlear capsule two regions of the capsule,
distinguished by their different states of development, can be
seen in the sections. One region, that next to the epithelial coch-
lear duct is composed of mesenchyma which passes peripherally
into precartilage. The other is a circumscribed area superim-
posed upon the part just mentioned. Its form is somewhat
circular in sagittal sections; it is composed of young cartilage.
This area occupies the most cephalic part of the cochlear cap-
sule. It can be followed medially through sections 198-192 (H.
E. C. ser. 492) of the anterior portion of the pars cochlearis as a
more or less distinct tract; further on it becomes completely fused
with the deeper stratum of the wall of the cavum cochleae. In
sections 191-186 the anterior pole of the cochlear capsule appears
as a simple curved plate of young cartilage. In section 185 this
is joined with the alicochlear commissure. The relations of the
cochlear capsule to the latter and to the suprafacial commissure
will be understood by reference to figure 8. - When traced in the
lateral direction, the curved plate in question goes over into the —
suprafacial commissure, with which it conforms in the degree
of cartilaginous differentiation, outward size and shape. A sec-
ond connection between the anterior pole of the cochlear capsule
and basal cartilage is presented at this stage by the cartilaginous
basicochlear commissure, or synchondrosis, which forms the pos-
terior boundary of the carotid foramen. The parietal plate is
partly separated from the canalicular division by the foramen
jugulare spurium. It is continuous through young cartilage or
precartilage with the occipital arch and pars canalicularis posteri-
orly and with the commissura orbito-parietalis anteriorly. The
tectum posterius is represented by a short process of the lamina
parietalis.

Cartilage is found in the otic capsules of a cat embryo of 15
mm. (fig. 7) about the walls of the semicircular ducts and the
vesibule, as indicated by the deep blue stain in van Wijhe prepa-
rations; the cochlear capsule is unstained. The basivestibular

PRIMORDIAL CRANIUM OF THE CAT 313

commissure, the alicochlear commissure and the basicochlear
commissure behind the carotid artery are likewise unstained;
the commissura orbito-parietalis is represented by a faintly
stained strip of cartilage independent of both the orbital plate
and otic capsule. The parietal plate is a triangular cartilage
surmounting the extremity of the occipital arch and joined to
it; it is unconnected with, though close to, the pars canalicularis.
Its medial and dorsal angle is the beginning of the tectum pos-
terius. Sections (H. E. C. ser. 400) show -the material of the
basal plate and floor of the sella turcica to be young cartilage.
The basivestibular, alicochlear and basicochlear commissures
are composed of mesenchyma. The suprafacial commissure ap-
pears as a bar extending from the anterior pole of the pars canal-
icularis over the nervus facialis to the anterior part of the coch-
lear capsule. It is composed of precartilage, easily distinguished
from that of the otic capsule by the more abundant, clear ground
substance between the nuclei. The relations of this commissure
are of high interest. Followed laterally across the facial nerve
it meets the pars canalicularis over the prominentia utriculo-
ampullaris superior. It then passes without the smallest differ-
ence in degree of chondrification, without boundary of any sort,
into the commissura orbito-parietalis. Chondrification of these
commissures is quite uniform, and represents a state of histogene-
sis different from that of the otie capsule. Between the orbito-
parietal commissure and the otic capsule is a plane of mesen-
chymal tissue. The separation of the suprafacial commissure
and otic capsule is not so sharp.

When now sections are followed in series from the spot where
the suprafacial commissure joins the pars cochlearis, toward the
median plane, an equally interesting connection becomes mani-
fest. It was shown above that in embryos of 17 mm. the coch-
lear end of the commissure became continuous with a stretch of
precartilage in the anterior part of the cochlear capsule, corre-
sponding in shape and state of development exactly with that of
the commissure itself. In the present stage this stretch again -
appears and can be followed medialward and cephalad almost as
far as the point of union of the commissura alicochlearis with the
cochlear capsule.

THE JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

314 ROBERT J. TERRY

Figure 6 made from a van Wijhe preparation of 12 mm. shows
the otic capsule from its medial side. Only those parts appear
which are chondrified. The three semicircular ducts are in large
part walled by cartilage. The blue stain is most intense upon the
lateral aspect, faint on the medial side of the ducts. The parietal
plate is a small triangular cartilage, lying dorsad of the interval
between the posterior semicircular canal and the lateral occipi-
tal arch. It is entirely independent of other cartilages of the
cranium.

The first trace of chondrification of the otic capsule was found
in embryos of about 10 mm. (fig. 5). In van Wijhe specimens of
this stage a narrow streak of blue follows the dorsal and lateral
circumferences of the anterior and posterior semicircular canals.

Nerves in the otic region

A brief description of the nerves and blood vessels which have
been referred to in the description of the otic region will serve to
correlate the many structures which have just been described.
The roots of the trigeminal nerve pass forward over the supra-
faciat commissure and through the septum transversum (vide
infra), to the semilunar ganglion, the caudal half of which rests
upon the planum supracochleare. The abducent nerve runs
along the medial side of the cochlear capsule, leaving the otic
region by passing forward between this structure and the dor-
sum sellae. The seventh nerve, together with the vestibular
and cochlear divisions of the acustic, enter the internal acustic
meatus from before backward in the order named. The glosso-
pharyngeal, vagus and accessory traverse the jugular foramen,
behind the otic capsule.

The facial nerve, including the pars intermedia (figs. 2, 4, 20,
21), is close to the ganglion of the vestibular nerve as it lies in
the internal acustic meatus. It passes through the primary
facial canal and the facial foramen to enter the cavum supra-
cochleare and there, outside of the cavity of the chondrocra-
nium, presents upon its dorsal side the geniculate ganglion (fig.
20). Connected with the ventral surface of the latter is the great
superficial petrosal nerve. Its position is entirely extracranial.

PRIMORDIAL CRANIUM OF THE CAT S15

It stretches across the lateral wall of the cochlear capsule, beween
the geniculate ganglion and a plexus of nerves about the internal
carotid artery. In the plexus it joins the N. pterygoideus Vidi-
ani (fig. 3). Leaving the region of the geniculate ganglion the
facial nerve enters upon the second part of its cranial course. It
undergoes first its characteristic bend and then passes nearly
straight caudad, lying for a short distance upon the prominen-
tia utriculoampullaris superior, then enters the sulcus facialis.
Above the nerve is the lateral semicircular canal, separated by a
floor of thick cartilage from the sulcus facialis. Continuing its
course, backward through the groove, the nerve crosses dorsad.
of the incudo-stapedial articulation, separated from the vestib-
ular window and basis stapedis which lie ventrad. Passing be-
neath and laterad of the origin of the stapedius muscle (origi-
nates from the roof and lateral wall of the sulcus facialis) to
which it supplies a twig, the facial reaches the base of Reichert’s
cartilage, where, bending sharply ventrad it leaves the groove.
The term foramen stylo-mastoideum primitivum has been given
by Broman (’99) to the exit from the sulcus facialis bounded by
the upper, proximal division of Reichert’s cartilage and the ear
capsule. After passing the confines of this ill defined foramen
(fig. 19) the facial nerve descends upon the caudal side of Reich-
ert’s cartilage and leaves the otic region.

At the side of Reichert’s cartilage the facial nerve gives off
its chorda tympani branch (figs. 2, 22). This stout nerve winds
about the lateral side of Reichert’s cartilage, ascends somewhat
and, turning mesad and cephalad, enters the region of the first
pharyngeal pouch. Here it lies at first upon the medial surface
of the manubrium of the cartilaginous malleus, ventrad of the
insertion of the M. tensor tympani and of the incudo-stapedial
articulation. Proceeding forward it passes out of the tympanic
region, following closely the medial and ventral surface of
Meckel’s cartilage.

Acustic nerve. Two chief branches were present, an anterior
and posterior. The anterior ramus gives.a twig to the recessus
utriculi, one to the ampulla anterior, another to the ampulla
externa. The posterior ramus gives rise to a ramulus sacculi, a

316 ROBERT J. TERRY

twig to the posterior ampulla (the two together may be regarded
as a ramus medius), and continues as the ramulus basilaris. In
addition to the ramulus sacculi, described by Retzius (’84), a
small twig to the sacculus coming from the anterior ramus was
observed.

The vagus, together with the glossopharyngeus and acces-
sorius, form a bundle which occupies a position in the fossa occi-
pito-canalicularis close to the lateral occipital arch and consid-
erably posterior to the pars canalicularis of the otic capsule (figs.
1, 2, 19). The vagus lies medialward of the vena jugularis with
the glossopharyngeus anterior and the accessorius posterior to
it. These relations are maintained in passing through the jugu-
lar foramen, excepting that the accessorius becomes incorpor-
ated with the vagus. The jugular ganglion is found upon the
roots of the vagus as it lies in the fossa occipito-canalicularis
and therefore above the jugular foramen. Some distance out-
side the cranium the ganglion nodosum appears.

The ganglion superius of the N. glossopharyngeus (figs. 1, 2,
19 to 23) is situated partly in the recessus occipito-canalicularis,
and partly upon the roots of the nerve as they lie in the cranial
cavity above the recess. The ganglion petrosum, much larger,
is located on the nerve below the jugular foramen and above the
level of the ganglion nodosum of the vagus. The tympanic
nerve arises from the upper end of the ganglion petrosum and
proceeds in the direction of the foramen cochleae. This nerve
runs in the thick mesenchyma between the medial epithelial wall
of the first pharyngeal pouch and the foramen cochleae. After
much branching, it reaches the ventrolateral surface of the pos-
terior cochlear prominence where it enters a plexus of nerves,
derived in part from the sympathetic around the internal carotid
artery.

Blood vessels in the otic region

A great blood sinus runs upon the inner surface of the cranial
wall in the suleus which circumscribes the pars canalicularis.
This, a forerunner of the sinus transversus system, becomes con-
tinuous at the fossa occipito-canalicularis with the vena jugularis

PRIMORDIAL CRANIUM OF THE CAT BLT

interna. Small tributaries enter from the connective tissue fill-
ing the foramen jugulare spurium; some of these are emissary
veins. Behind the pars canalicularis the sinus is joined by a
small vein formed by tributary systems, one being the plexus of
veins in the mesenchyma which fills the vacuity of the massa
angularis (p. 309). A plexus of veins in the facial sulcus empties
into a large vein which, running backward in company with the
facial nerve, joins the internal jugular. An extensive network
of veins within the mesenchyma of the cavum cochleae is drained
in part by two veins which pass to the vena jugularis interna by -
way of the aquaeductus cochleae.

Vestiges of a stapedial artery are present in the embryo of 23.1
mm., perforating the stapes (fig. 21): These can be followed an-
teriorly toward the terminal branch of the internal maxillary ar-
tery and posteriorly toward a plexus of small vessels on the ven-
tral surface of the cochlear capsule, which is connected with an
offset from the internal carotid artery. In an embryo of 15 mm.
the stapedial artery is a relatively large branch of the A. carotis
interna, extending forward through the mesenchymal beginning
of the stapes to the semilunar ganglion whence it continues as the
mandibular artery.

The internal acustic artery arises from the basilar and enters
the internal acustic foramen together with the acustic and sev-
enth nerves, giving off several branches to the membranous
labyrinth.

Orbito-temporal region. Embryo of 23.1 mm.

The basis cranii (figs. 1, 2, 3) of the orbito-temporal region is
an unbroken bar of cartilage continuous with the basal plate of
the otic region posteriorly, and with the nasal septum of the eth-
moidal skeleton. anteriorly. The extracranial surface, strongly
convex from side to side looks toward the pharynx, from which it
is separated by an interval filled by wide-meshed mesenchyma.
The intracranial surface presents in its posterior one-third the sella
turcica with the root of the ala temporalis on.each side, and in
front of this, in successively higher planes, the two roots of the
- ala orbitalis, the optic foramen intervening. At the level of the

318 ROBERT J. TERRY

sella turcica the basis cranii is bent in a sagittal plane so that the
otic and orbital portions form an angle, open ventrally. Also,
where the orbito-temporal portion of the base goes over into
the septum nasi, a similar angle is formed.

At the level of the sella turcica the base is flattened dorso-ven-
trally, becomes thicker opposite the optic foramina and finally
triangular in its most anterior part. Here, the two extracranial
surfaces incline medially and ventrally to meet in a keel, forming
a short interorbital septum which passes forward into the sep-
tum nasi.

Sella turcica (figs. 1,23). The elongate, shallow pitiutary fossa
is limited anteriorly by a low tuberculum sellae and posteriorly
by a well defined wall. The base of the latter is made by the
crista transversa extending nearly to the cochlear capsules, a
slight interval remaining between these parts transmitting the
abducent nerve. The dorsum sellae is represented by a conical
elevation of the middle of the crista transversa. Remains of a
hypophyseal canal are present and are occupied by epithelial
vestiges of the stalk of the anterior lobe of the pituitary body.

Ala temporalis (figs. 1, 2, 3, 4, 23). The ala temporalis of the
23.1 mm. embryo extends from the processus alaris of the basis
cranil, opposite the sella turcica, outward beneath the semilunar
ganglion; it is limited by free margins in front and behind. Its
structure is of young cartilage separate from that of the proces-
sus alaris, a stratum of mesenchyma standing between them.
The temporal wing consists of a larger blade-formed lateral por-
tion, the lamina ascendens, and a small, medial pterygoid proc-
ess. A separate pterygoid cartilage is present, lying mesad of
the pterygoid process below the basis cranii. In connection with
the description of the ala temporalis the cavum epiptericum will
be considered.

Processus alaris (figs. 2, 23). The alar process lies in front of
the carotid foramen, supports the internal carotid artery in its
forward course and forms the ventral boundary of the innermost
part of the spheno-orbital fissure. Laterally it extends to the
temporal wing, the layer of mesenchyma above mentioned limit-
ing the two parts (fig. 23). This layer takes an oblique direc-

PRIMORDIAL CRANIUM OF THE CAT 319

tion from before backward and laterally, on account of which
the ala temporalis stands in front, as well as to the side of the
processus alaris. Between the latter and the anterior pole of the
cochlear capsule extends a cartilaginous bridge, the commissura
alicochlearis, forming the lateral boundary of the carotid fora-
men. It is quite distinct from the temporal wing, the two being
separated by the continuation of the zone of mesenchyma just
described. The processus alaris and commissura alicochlearis
are, however, continuous, and together form an arch around the
front and side of the carotid foramen.

The lamina ascendens (figs. 1, 2, 3, 23) of the ala temporalis
is a cartilaginous plate which extends laterally and dorsally to-
ward the commissura orbito-parietalis, but remains widely sepa-
rated from it. It is somewhat triangular in form, presenting
free margins, anterior and posterior, which meet laterally in a
rounded free point, and a base directed toward the oblique line
of junction with the alar process and alicochlear commissure.
The dorsal surface slopes from an intermediate longitudinal
ridge, forward and backward, thus presenting two subdivisions:
an anterior face entering into the floor of the spheno-orbital fis-
sure; and a posterior, supporting the cephalic end of the semilunar
ganglion and forming the floor of the epipteric cave. The longi-
tudinal ridge itself lies opposite the lower margin of the ala or-
bitalis and enters into the ventral boundary of the spheno-orbital
fissure. The ventral surface of the lamina ascendens overhangs
the mandible and gives origin to part of the pterygoid muscle.
A short canal, the forerunner of the foramen rotundum, traverses
the lamina ascendens from behind forward, giving passage to
the maxillary nerve. The posterior margin of the ala is free and
limits anteriorly a broad, deep fissure whose posterior boundary
is the cochlear capsule. The fissure ends medially at the ali-
cochlear commissure and, like the spheno-orbital fissure, is open
laterally. To this gap, which has long been known, the name
fissura alicochlearis may be given. Through it pass the mandib-
ular and the great superficial petrosal nerves, the former through
the incisura ovalis in the posterior margin of the lamina ascen-
dens, the latter traversing another notch, incisura lacera, and

320 ROBERT J. TERRY

joining beneath the lamina the great; deep petrosal nerve to form
the N. pterygoideus. Incisura lacera is the name proposed for
the deepest part of the fissura alicochlearis, a part distinguished
by certain important relations. It reaches medially toward the
carotid foramen, from which it is separated by the commissura
alicochlearis, and here adjoins the posterior end of the mesen-
chymal zone dividing the commissure from the lamina ascendens.
A prominent spine of the caudal margin of the ascending plate
forms its antero-lateral boundary and stands between it and the
incisura ovalis. On the anterior margin of the ala temporalis,
adjacent to the processus alaris, is the broad processus pterygoid-
eus (fig. 1), in connection with which is later formed the insignifi-
cant bony lamina lateralis processus pterygoidei of the adult.
The pterygoid process projects forward and toward the mid-
plane, lying medial of the foramen rotundum. Its medial end
is separated from the adjacent pterygoid cartilage by a layer of
mesenchyma. At this spot the Vidian nerve begins to turn from
beneath the lamina ascendens to gain, eventually, a position dor-
sad of the pterygoid cartilage and within the spheno-orbital
fissure.

The base of the ala temporalis is directed obliquely from be-
hind, forward and medialward and for the most part corresponds
to the synchondrosis between the ascending plate, alar process
and alicochlear commissure. ‘Two other regions, however, must
be included in the base: posteriorly, the medial free margin of
the spine separating the incisura lacera from the incisura ovalis,
and anteriorly, the medial free margin of the processus pterygoid-
eus. The relations into which the base of the ala enters with
the rest of the chondrocranium are, therefore, the medial corner
of the spheno-orbital fissure, processus alaris, commissura ali
cochlearis and incisura lacera.

Ala orbitalis (figs. 1, 2, 3, 4). This great sickle-shaped carti-
lage forms, on each side, the larger part of the medial wall of the
orbit and the lateral wall of the fore part of the cranial cavity.
Its lateral and medial surfaces are respectively concave and con-
vex, apparently in adaptation to the eye-ball and its adnexa.
The anterior extremity is joined to the nasal capsule by the com-

PRIMORDIAL CRANIUM OF THE CAT 321

missura spheno-ethmoidalis; the posterior extremity is connected
with the fore part of the basis cranii by two roots, named preoptic
and metoptic, relative to the optic nerve which they embrace.
The preoptic root is broad and straight whereas the metoptic
root is narrow and bent so as to present a prominent angle of its
caudal margin directed backward. The optic foramen, large and
irregulary oval, is bounded medially by the basis cranii, on its
other sides by the orbital wing and its two roots. Through the
optic foramen a short, blunt process, processus orbitalis, extends
into the orbit from the cephalic edge of the metoptic root. On
the right side this process lies close to the basis cranii. From.the
roots of the orbital wing some of the ocular muscles take origin
(vide infra). The short concave, anterior margin of the wing is
free and separated from the nasal capsule by the fissura orbito-
ethmoidalis. This is filled by membrane and transmits the lat-
eral branch of the nasal nerve. The extensive, convex, posterior
margin, dorsally, passes into the commissura orbito-parietalis con-
necting the orbital wing with the parietal plate, and ventrally
is free in the anterior boundary of the fenestra spheno-parietalis.

The spheno-orbital fissure (Wincza, ’98) (figs. 1, 2, 3, 4, 23)
in the present stage stands in marked contrast to the circular,
completely walled opening of the adult cranium. It is a narrow, »
deep gap running in a frontal plane between the ala orbitalis
above and the ala temporalis and pterygoid cartilage below. It
is open laterally, but closed medially by that part of the basis
cranii lying between the metoptic root of the ala orbitalis and
the processus alaris. It gives passage to the oculomotor, pathetic,
ophthalmic and abducent nerves, together with a number of
veins which go to join the plexus about the semilunar ganglion
and carotid artery.

The carotid foramen (figs. 1, 2) is completely walled, as de-
scribed by Decker and later by Wincza. It is circular, not large
as compared with that in Lepus, stands opposite the middle of
the sella turcica and traverses the floor of the skull straight ven-
tro-dorsad. In front is the processus alaris; behind, the coch-
lear capsule; laterally, the alicochlear commissure. Upon its
medial side is the sella turcica.

aoe ROBERT J. TERRY

Pterygoid cartilage (figs. 1, 3, 24). In the model of the cranium
of the 23.1 mm. embryo the pterygoid cartilages appear as a pair
of irregular but symmetrically formed bodies lying one on either
side of the naso-pharyngeal duct and adjacent to the alae tem-
porales. Each cartilage presents a short cylindrical, transversely
placed pedicle and, continuous with it and in a dorso-ventral
plane, an elongate, bent plate. The pedicle consists of dense
mesenchyma continuous with the perichondrium of the margin
of the pterygoid process of the lamina ascendens; in the center
bone has begun to form. The N. pterygoideus (Vidiani) turns
dorsad upon the posterior aspect of the joint between the pedicle
and pterygoid process to enter the spheno-orbital fissure. The
plate-shaped part of the pterygoid cartilage presents a flat free
surface directed forward, a medial concave margin turned toward
the naso-pharyngeal duct and a lateral convex margin giving
attachment to the M. pterygoideus. In structure the lamina
consists of mesenchymal syncytium, within which bone has
formed in two regions. One center lies in the dorsal half of the
plate and is continuous with the ossific center of the pedicle;
the second is found in the ventral half and seems to be separated
from the first by a stratum of unossified tissue, broad at the mar-
gin and surfaces of the plate, but becoming narrower toward
the center. I find it impossible to state whether the two bony
centers so clearly separated one from the other at the margins
of the lamina are entirely distinct throughout. A mesenchymal
condensation surrounds the pterygoid cartilage, extending for-
ward, becoming somewhat: less compact, and finally joining the
mass of mesenchyma in which the palate bone is forming. This
mesenchymal mantle extends dorsally toward the cranial base
without, however, quite reaching it.

The region named cavum epiptericum by Gaupp (05) and
interpreted in its relation to the cranial cavity of mammals by
this investigator (’02) as an acquisition of a space which, in rep-
tiles, is extracranial, presents some interesting peculiarities in
the embryos of cat. First, the epipteric cave with its contained
structures is, in the absence of those bones which in the adult
form the lateral wall of the skull in this region, wholly outside’

PRIMORDIAL CRANIUM OF THE CAT azo

the confines of the brain case of the 23.1 mm, embryo. The ex-
clusion of the space from the cavum crani is brought about by a
strong membrane, conspicuous in the sections, which arises from
the base of the cranium and is applied to the medial surface of
the semilunar ganglion, excluding this structure, as it rests on
the ala temporalis, from the cranial space occupied by the brain.
Less dense mesenchyma surrounds the ganglion and extends lat-
erally as far as the temporal muscle; forward through the spheno-
orbital fissure and about the ala temporalis; backward, into the
cavum supracochleare. The medial limiting membrane calls for
special description. We may tentatively refer to it as the mem-
brana limitans (figs. 19 to 23). It fills the foramen spheno-
parietale attaching itself to its margins, i.e., to the commissura
orbito-parietalis, commissura suprafacialis, where it is perfor-
ated by the roots of the trigeminus, and to the metoptic root of
the ala orbitalis; then upon the base of the cranium, from the
anterior pole of the cochlear capsule along the commissura. ali-
cochlearis, crista transversa and dorsum sellae, the lateral ele-
vated margins of the hypophyseal fossa, and on to the tubercu-
lum ephippi. In the bottom of the sella turcica and upon the
dorsum sellae the membrane is continuous from side to side.
At the saddle-back it is continuous with a stout meningeal mem-
brane which ascends into the narrow space in the flexure of the
mid-brain and diencephalon; this may be refered to as the sep-
tum transversum (see p. 327). The thickness of the limiting
membrane is not the same throughout. It is densest at its
broad attachment to the cranial base where it covers the carotid
foramen. Also a definite band of condensed tissue extends
through the septum transversum from the crista transversa,
crossing the N. abducens and the roots of the N. trigeminus run-
ning parallel with the commissura suprafacialis and reaching
laterally the parietal plate. It is along this stretch that a small
cartilaginous bar is later developed (embryo of 7 em.) over the
dorso-medial surface of the semilunar ganglion and roots of the
trigeminus where the latter cross the suprafacial commissure.
The floor of the epipteric cave is formed by the lamina ascen-
dens of the ala temporalis. The following structures are found

>

324 ROBERT J. TERRY

within the cave: the ganglion semilunare and the three divisions
of the N. V., the NN. IJJ, IV and VI. The caudal half of the
semilunar ganglion rests upon the supracochlear plane, in its
cephalic half upon the alicochlear commissure and the posterior
subdivision of the dorsal surface of the lamina ascendens. Be-
neath it, the mandibular nerve passes to leave the cave through
the incisura ovalis. The ophthalmic and maxillary nerves leave
the region immediately in front of the ganglion, the one by way
of the spheno-orbital fissure, the other by the foramen rotundum.
Both the oculomotor and trochlear nerves run a long course in
the loose tissue immediately surrounding the brain, proceeding
from their origins ventrad and cephalad toward the spheno-
orbital fissure, where they lie above the ophthalmic nerve. They
pierce the membrana limitans just before entering the fissure,
and their course in the epipteric cave is therefore very short
(fig. 23). On the contrary, the course of the abducent nerve
through the cavum epiptericum is very long; it enters the space
from behind, passing between the dorsum sellae and cochlear
capsule, over the crista transversa and beneath that strand of
condensed mesenchyma in the septum transversum which is the
forerunner of the cartilage referred to above. Running cephalo-
laterad, it crosses laterally the carotid artery and gains the medial
side of the semilunar ganglion and ophthalmic nerve; in the spheno-
orbital fissure it crosses dorsally the N. maxillaris. The internal
carotid artery enters the membrana limitans at the carotid fora-
men, turns forward in this tissue, crosses the processus alaris at
the side of the hypophysis, then pierces the membrane in a dor-
sal and medial direction to enter the cavum cranii. At its en-
trance into the basal portion of the membrana, limitans the artery
is ventrad of the sixth nerve, but it turns immediately mesad
beneath it. Several veins accompany the nerves through the
spheno-orbital fissure and go to form, by anastomoses, a plexus
in the membrana limitans which surrounds the carotid artery.
The vessels of this plexus are separated by mesenchymal tissue,
altogether constituting the beginnings of the channels and walls
of the later cavernous sinus.

PRIMORDIAL CRANIUM OF THE CAT a0

The orbit (figs. 3, 4, 24, 25, 26) is relatively shallow and is ill-
defined in extent and boundaries. The planum antorbitale and
prominentia lateralis of the ethmoidal skeleton form its anterior
wall; the ala orbitalis and its two commissures enter into the
posterior wall. The dorsal limit is given by the frontal bone
which extends along the spheno-ethmoidal commissure. The
ventral limits are found in the zygomatic and maxillary bones.
The ocular muscles arise in the following way. From the pre-
optic root springs the superior oblique; from the orbital process
of the metoptic root arise the rectus superior, internus and exter-
nus. The origin of the inferior rectus is conjoined with that of
the retractor oculi on the lateral surface of the cranial base, ven-
trad of the metoptic root and adjacent processus alaris; these
muscles arise within the spheno-orbital fissure. The inferior
oblique springs from the ventral margin of the planum antor-
bitale well forward of the origins of the other ocular. muscles.

Orbito-temporal region in smaller embryos

Van Wijhe preparations of 10 mm. (fig. 5) present the first
trace of chondrification in the orbito-temporal region as a small
erescentic cartilage ventrad of the anterior hypophyseal lobe. ,
The concavity of the crescent embraces the hypophyseal stalk.
Behind this hypophyseal cartilage and occupying a dorsal plane
is the termination of the notochord.

Sections of an embryo of 12 mm. (figs. 16, 17) show that the
cranial floor beneath the hypophysis consists of a horseshoe-
shaped cartilage independent of other parts of the chondrocra-
nium. The legs of the horseshoe lie on either side of the mid-
line beneath the anterior pituitary lobe, reaching as far forward
as the trabecular plate, but not united with it; the commissure
of the horseshoe crosses behind the stalk of Rathke’s pouch.
Between the commissure and the terminal expansion of the basal
plate is a small space, fenestra basicranialis posterior, occupied
by mesenchyma in which the cephalic end of the notochord lies.
In median sagittal sections of embryos of 12 mm. (fig. 17) the
anterior expanded extremity of the basal plate is turned some-
what in the dorsal direction above the line of the posterior parts

326 ROBERT J. TERRY

of the hypophyseal cartilage. The trabecular plate makes its
appearance in embryos of the present stage (fig. 17), consisting
of a single thick mass of young cartilage continuous anteriorly
with the beginnings of the septum nasi. Caudally it reaches
almost to the hypophyseal cartilage. In the van Wijhe prepara-
tions the limits of the trabecular plate are clearer than in the sec-
tions (fig. 6). On its dorsal surface the sulcus chiasmaticus
appears; on its sides, the beginnings of the pre- and metoptic
processes.

In a frontal section passing through the hypophysis and coch-
lear canal of an embryo of 12 mm. (fig. 16) the carotid artery ap-
pears in its course through the cranial wall. It lies in an oval
area of less dense mesenchyma than that a little way behind its -
position. The denser tissue anterior to the area forms a curved
bar, continuous with the side of the hypophyseal cartilage medi-
ally, thence extending in a curve outside the artery toward the
cochlear capsule. This will be referred to as the commissural
element; it is the beginning of the processus alaris and commis-
sura alicochlearis. The oval, light area about the carotid is lim-
ited caudally and medially by the cochlear capsule and a bridge
of mesenchyma (future basicochlear commissure) stretching from
the latter to the hypophyseal cartilage. .

In the mesenchyma laterad of the commissural element is a
small condensation beneath the Gasserian ganglion, which proves
to be part of the medial extremity of the future ala temporalis.
This condensation will be refered to as the alar element. The
less dense mesenchyma between the latter and the commissural
element extends obliquely from before, backward and outward.
The mesenchyma of the alar element becomes broader and denser
as it extends laterally; its caudal concave margin, pressed against
the mandibular nerve, forms the primitive incisura ovalis; within
its anterior part appears the maxillary nerve. The ophthalmic
nerve (whose ganglionic cells are in part separate from the semi-
lunar ganglion) passes over the alar element toward the eye.
The van Wijhe specimens of 12 mm. (fig. 6) show a small darkly
stained nodule far removed from the hypophyseal cartilages and
lying immediately ventrad of the anterior end of the semilunar

PRIMORDIAL CRANIUM OF THE CAT yall

ganglion. This center is located at the site of the anterior part
of the alar element.

In sections the ala orbitalis is a plate of condensed mesenchyma
limited sharply in front, above and behind, but connected with
the trabecular plate by two roots. The preoptic root extends
from the trabecular plate anterior to the sulcus chiasmaticus and
passes laterally without interruption into the main body of the
ala. The metoptic root is joined to the side of the caudal por-
tion of the trabecular plate. This root terminates laterally in a
pointed extremity connected by less dense mesenchyma with the
ala orbitalis. The extremity lies beyond the optic foramen, im-
mediately dorsad of the third nerve where this enters the orbit.

The cavum epiptericum in the 12 mm. embryo, is clearly de-
fined toward the base of the neuro-cranium. The membrana
limitans (figs. 16, 17) can be followed over the medial aspect of
the semilunar ganglion to the anterior end of the basal plate, to
the commissural element and over the carotid artery. Upon
the lateral side of the membrane, opposite the vessel runs the
abducent nerve. At its insertion into the anterior margin of the
basal plate (the future crista transversa) the limiting membrane
becomes continuous with the septum transversum. Within the
latter immediately caudad of the hypophysis is a small, trans-
versely placed precartilaginous rod (indicated by an * in fig. 17).

The pterygoid cartilage is represented by a condensation of
mesenchyma lying anterior and ventral of the alar element and
close to the epithelium of the pharynx. A constriction incom-
pletely subdivides it into dorsal and ventral parts. Behind this
mass is the first pharyngeal pouch; through its dorsal extremity
runs the pterygoid nerve.

-_ In embryos of 15 mm. the hypophyseal cartilage has united
anteriorly with the trabecular plate, forming the floor of the sella
turcica, perforated by a foramen hypophyseos (figs. 7, 18).
Union of the basal plate and hypophyseal cartilage has also oc-
curred, but the confines of the originally separate cartilages are
still evident (fig. 18). Asaresult of the incongruity in the meet-
ing of these parts (indicated in the 12 mm. stage) there remains
a transverse ridge in the basis cranii behind the pituitary fossa,

328 ROBERT J. TERRY

the beginning of the crista transversa. This is the stage of
precartilaginous structure of the alar and commissural elements.
The latter is continuous with the side of the sella turcica and sep-
arated from the alar element by an oblique layer of mesenchyma.
The boundaries of the carotid foramen are well defined, the me-
‘ dial boundary being formed by the posterior part of the side of
the sella turcica; the caudal limit by the prochondral union of the
basal plate and cochlear capsule, the commissura basicochlearis;
the anterior and lateral by the prochondral commissural element.
The alar element has a homogeneous structure of young cartilage
and is now recognizable as the ala temporalis; both the mandibu-
lar and maxillary nerves pass through notches in its margins.

In van Wijhe preparations of 15 mm. (fig. 7) a continuous
stretch of cartilage occurs in the floor of the cranium in the otic,
hypophyseal, trabecular and nasal septal regions. The tubercu-
lum sellae is apparently developed from the caudal and dorsal
edge of the trabecular plate. The junction of the basal plate
and floor, in the hypophyseal region, is marked by a broad ex-
pansion of lightly stained tissue (young cartilage). In a median
section (fig. 18) the cartilage in the septum transversum behind
the hypophysis, present in the preceding stage, appears as a
small nodule. The ala temporalis is represented by a slender
sickle-shaped cartilage standing ventrad of the anterior pole of
the semilunar ganglion. It is laterally removed from the sella
turcica and from the commissural element (the interval is ex-
aggerated in figure 7). In the epipteric region the membrana
limitans is clearly defined throughout. The origin of the trans-
verse septum is*marked by a band-like thickening, extending from
the crista transversa laterad over the semilunar ganglion and roots
of the trigeminus, and terminating on the ‘suprafacial commis-
sure and parietal plate.

The pterygoid presents no important change from the preced-
ing stage. Chondrification of the ala orbitalis has begun over
the eye-ball in the form of a triangular plate, separate from all
neighboring cartilages (fig. 7). Posterior to the orbital ala is
the independently chondrifying commissura orbito-parietalis; far
removed anteriorly are the cartilages of the nasal, capsule. One

PRIMORDIAL CRANIUM OF THE CAT 329

angle of the ala orbitalis is directed medially toward the trabecu-
lar plate and its two processes, preoptic and metoptic. The ex-
tremity of the latter presents the relation with the oculomotor
nerve observed in the earlier stage. From the metoptic process
a thick projection extends a short distance laterally, Just behind
the optic nerve, to end in the muscle mass about the nerve; this
is the beginning of the orbital process of later stages.

Van Wijhe preparations of embryos of 17 mm. (fig. 8) show a
lightly stained curved bar, the combined processus alaris and ali-
cochlear commissure, extending around the carotid artery, from
the side of the sella turcica to the anterior pole of the cochlear
capsule. Just in front and laterad of the commissure, and sepa-
rated by an interval of unstained tissue, is the triangular ala tem-
poralis, with the maxillary nerve against its anterior, concave
margin, and the mandibular nerve at its posterior side. The
separate cartilage behind the infundibulum in the preceding stage
is no longer apparent in the sections, but there is now at this
spot a Corsal, median process, partly cartilaginous, largely mesen-
- chymal, of the crista transversa. Union of the orbital plate
with neighboring skeletal parts has occurred (fig. 8): the medial
angle, presenting a notch for the optic nerve, is connected with the
pre- and metoptic processes of the trabecular plate; the anterior
angle is prolonged to the paranasal cartilage as the commissura
spheno-ethmoidalis, thereby completing the boundaries of the
fissura orbito-nasalis; the posterior angle is fused with the com-
missura orbito-parietalis. This commissure, which has united
also with the parietal plate, has extended ventrally to the pars
canalicularis (commissura parieto-capsularis), but, as sections
show, is separated from the otic capsule by a thin layer of mesen-
chyma (p. 313). Continuity of the cartilage of the orbito-parie-
tal commissure and suprafacial commissure has been described
above (p. 301).

Ethmoidal region. Embryo of 23.1 mm..

The parts of the chondrocranium included in this most clearly
defined region of the skull are the paired nasal capsules (figs. 1,
2, 3, 4). These conform closely with the membranous walls of

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

330 ROBERT J. TERRY

the cavum nasi within, and are shaped externally somewhat
like a pair of spindles pressed together, making a single strong
framework, the cartilaginous ethmoidal skeleton, at the anterior
end of the skull.

The length of the cartilaginous ethmoidal skeleton is equal to
about one-third that of the entire cranium. Its anterior half
projects free beyond the brain case; its posterior half, terminat-
ing on each side in the posterior cupola, is subcerebral in posi-
tion. Here it is continuous with parts in the orbito-temporal
region: the trabecular plate passing into the septum nasi and
roof of the posterior cupola, the commissura spheno-ethmoidalis
joining the lateral nasal wall. An extensive roof, tectum nasi,
is in the anterior half of the ethmoidal skeleton; an incomplete
one, lamina infracribrosa, in the posterior. The roof goes over on
either side into the paries nasi. The interior room of the nasal
skeleton opens into the cranial cavity by the fenestrae olfactoriae,
and upon the face through the fenestrae narinae. The floor of the
capsule, solum nasi, is very incomplete, presenting a great fenestra
basalis, within the compass of which are the paraseptal cartilages
standing next to the nasal septum. The side walls within, present
the beginnings of the complex of turbinals in the form of simple
inrollings and elevations.

The tectum nasi (figs. 1, 3, 27 to 30) is furrowed in the mid-
line of its dorsal surface by the sulcus supraseptalis, deepest an-
teriorly, extending from the fenestra olfactoria to the level of the
fenestra narina. On either side the roof is highly arched and
passes laterally into the anterior region of the paries nasi.

The side wall (figs. 3, 4) presents three regions: an anterior,
continuous with the tectum nasi, a middle region occupied by the
rounded prominentia lateralis, and a posterior area, the planum
antorbitale. wo grooves demarcate the prominentia lateralis
from the anterior and posterior regions. One of them, the sul-
cus lateralis anterior, at first pursues a curved course from the
olfactory window near the mid-line, cephalo-ventrad between
the tectum nasi and prominentia lateralis. This part of the sul-
cus stands opposite the crista semicircularis within the nasal
capsule and is interrupted by the epiphanial foramina of which

PRIMORDIAL CRANIUM OF THE CAT 331

there are {wo on each side. In its ventral one-third the groove
is broad and shallow and adjoins the anterior region of the paries
nasi and the lateral prominence. It occupies an area which
passes ventrally into the maxilloturbinal and stands at a level an-
terior to the crista semicircularis. This part of the paries nasi
corresponds to the lamina supraconchalis of Voit. The second
groove, sulcus lateralis posterior, limits the lateral prominence
posteriorly; it is broad and shallow and stands opposite ethmo-
turbinal I within the capsule. The anterior region of the par-
ies nasi extends from the antero-lateral sulcus to the lateral mar-
gin of the fenestra narina. It is co-extensive with the roof dor-
sally, but becomes narrow ventrally where it joins the lamina
transversalis anterior. The surface in this region is convex,
corresponding to the internal concavity of this part of the lateral
wall. The middle region, the prominentia lateralis, is narrow
from before backward. Dorsally it is united with the commis-
sura spheno-ethmoidalis and forms the lateral boundary of the
olfactory window, between the posterior extremities of the crista
semicircularis and ethmoturbinal I (vide infra). Ventrally it
passes into the maxillo-turbinal. The posterior area, antorbital
plane, corresponds to the region within occupied by the ethmo-
turbinals, and forms the antero-medial wall of the orbit. Where
it adjoins the middle region of the paries nasi (sulcus lateralis
posterior) there is present ventrally a rounded prominence, giv-
ing origin to the inferior oblique muscle of the eye. The dorsal
margin of the antorbital plane at the orbito-nasal fissure, partici-
pates, anteriorly in the lateral boundary of the olfactory window,
and posteriorly passes into the lamina infracribrosa. The ven-
tral margin is straight and free in the lateral boundary of the
fenestra basalis. Caudally, this division of the nasal capsular
wall continues into the posterior cupola. This conical shell ex-
tends backward at the side of the nasal septum and trabecular
plate beneath the preoptic root of the ala orbitalis. It is closed
ventrally by the lamina transversalis posterior, which reaches to
the septum nasi. The roof of the posterior cupola is formed by
the unpaired lamina infracribrosa (figs. 1, 25). This plate pre-
sents a free edge anteriorly toward the fenestra olfactoria, con-

oan ROBERT J. TERRY

tinues caudally into the dorsal surface of the trabeqular plate
and laterally goes into the planum antorbitale. A slight median
ridge, crista interorbitalis, separates two shallow fossae lodging
the olfactory tracts.

Ventrally, the nasal capsule presents the great fenestra basalis
(figs. 1, 2), the relations of which to the cavum nasi are somewhat
complicated. It is limited laterally by the ventral margin of
the planum antorbitale and by the maxillo-turbinal. In the
region of the latter it is very narrow from side to side, and is
partly covered ventrally by the paraseptal cartilage hanging
down from the septum. Anteriorly the basal window reaches to
the lamina transversalis anterior which stands between it and
the fenestra narina. The caudal limit is formed by the lamina
transversalis posterior. Further relations of the basal window
will be better understood when considered in connection with
the description of the nasal cavity.

The solum nasi is represented by the two transverse laminae
and the horizontal portion of the paraseptal cartilage (figs. 2, 3,
13, 25, 26). The lamina transversalis posterior (figs. 2, 18, 25)
forms the floor of the posterior cupola and appears in the sec-
tions and in the model as an inrolling of the caudo-ventral part
of the planum antorbitale. Its medial margin is turned dorsad;
in its caudal half it is applied closely to, but not actually joined
with, the keeled trabecular plate behind the level of the vomer;
in its cephalic half it is free, being separated from the nasal sep-
tum by a narrow stretch of the fenestra basalis. Here the lam-
ina is overlapped by the caudal end of the vomer. The band-
like lamina transversalis anterior (figs. 2. 3, 13), incompletely
chondrified, bounds the fenestra narina ventro-laterally, connect-
ing the septum nasi with the paries nasi. It is continuous with
both parts, that is to say, a zona annularis is present. Its hori-
zontal, broader, septal end stands opposite the anterior half of
the os incisivum. Followed laterally, the lamina undergoes a
curve in the dorsal direction, and comes to lie in a sagittal plane.’

3 In cat embryos of about 70 mm. the lamina transversalis anterior presents

two backwardly directed processes which embrace the funnel-shaped depression
of the floor leading into the incisive duct. These have been called by Zucker-

PRIMORDIAL CRANIUM OF THE CAT S30.

Just ventrad of its Junction with the anterior part of the paries
nasi it is crossed by the naso-lacrimal duct. The caudal margin
of the lamina is free and is separated by a wide interval from
the paraseptal cartilage.

Behind the anterior transverse lamina, the tear duct lies upon
the most ventral part of the paries nasi and is further supported
by a cylindrical processus maxillaris anterior of the latter (figs.
3, 13, 30) directed forward. At this place the os maxillare over-
laps the nasal capsule and, in the model, hides from view the
maxillary process and tear duct.

The cartilago paraseptalis (figs. 2, 3, 13, 28, 29), scroll-formed
in adaptation to Jacobson’s organ, hangs from the septum nasi
below the level of the plane of the fenestra basalis. It is uncon-
nected with other parts of the nasal skeleton. The medial half
of each cartilage lies in a sagittal plane applied against the ven-
tral part of the septum. The lateral half is rolled dorsally to
form a gutter lodging the vomero-nasal organ. The cephalic
margin is free and straight; the caudal pointed. The long axis
of Jacobson’s cartilage extends from behind cephalo-ventrad,
the caudal extremity lying at the level of the basal window, the
cephalic end reaching a position ventrad of the plane of the an-
terior transverse lamina. At this stage the paired naso-palatine
cartilage is represented by a stretch of prochondral. tissue upon
the lateral side of each incisive duct. The U-shaped beginning

kand! the medial and lateral limbs of the ventro-lateral process of the septal
cartilage. The incisive duct is partly enveloped on its lateral’side by a trough-
shaped nasopalatine cartilage, which reaches from a spot near the oral end of the
duct, to the level of the entrance of the duct of Jacobson’s organ. ‘The last named
canal is surrounded completely by a cartilaginous tube which, as it ascends
toward the cavum nasi, gradually loses its dorsal wall and becomes continuous
with the anterior extremity of the paraseptal (Jacobson’s) cartilage. The car-
tilage of Jacobson’s duct lies medial of the process of the lamina transversalis
anterior; neither it nor the nasopalatine cartilage is joined with the processes of
the anterior transverse lamina.

4 The paraseptal cartilage in embryos of 70 mm. presents an anterior process,
continuous with the cartilage of the duct of Jacobson’s organ, and continues
posteriorly into a slender cartilaginous paraseptal rod. The latter lies against
the side of the ventral edge of the vomer and extends to the floor of the posterior
cupola, the lamina transversalis posterior with which it is directly continuous.

334 ROBERT J. TERRY

of the vomer (figs. 2, 26, 27) embracing the ventral edge of the
septum nasi, lies at some distance behind the paraseptal.

The fenestra narina (figs. 2, 3, 4, 13), oval with its long axis
dorso-ventral, faces rostro-laterad. Its medial boundary is
formed by the septum, the lateral and ventral by the lamina
‘transversalis anterior, the dorsal, by the paries nasi. The lat-
eral margin presents a deep notch, the incisura lacrimalis, where
the naso-lacrimal duct turns medialward toward its termination.
The ventral margin of this notch is formed by the sagittal por-
tion of the anterior transverse lamina; the dorsal margin by the
rostral extremity of the atrioturbinale, or inrolled ventral margin
of the paries nasi. The lacrimal notch is the meeting place of
two divisions of the fenestra narina, a dorsal and a ventral.
The former leads to the atrial region of the cavum nasi; the
latter division receives the naso-lacrimal duct and opens into
the inferor meatus. The names pars atrialis and pars lacri-
malis, respectively will be used in further reference to these divi-
sions of the fenestra narina. In the present stage the superior
alar process is represented in dense mesenchyma. It is chon-
drified in the 7 cm. embryo.

Fenestra olfactoria (figs. 1, 13, 26). The paired, quadrilateral
olfactory fenestrae offer wide communications, in the present
stage, between the nasal and cranial cavities. Their position is
in the caudal half of the nasal capsules, that is, in the subcere-
bral division, between the tectum nasi, anteriorly, and the roof
(lamina infracribrosa) of the posterior cupola, posteriorly. The
plane of each opening looks dorso-caudad and also somewhat
mesad. The anterior boundary, formed by the caudal free mar-
gins of the tectum nasi and prominentia lateralis, is considerably
wider than the posterior limit, made by the infracribrous plate.
The medial side is formed by the dorsal concave margin of the
septum nasi. The oblique lateral boundaries of the olfactory
fenestrae are formed by the dorsal margins of the prominentiae
laterales and the antorbital plates. On the anterior and lateral
sides of the fenestra olfactoria of the model are three processes,
the caudal extremities of the crista semicircularis, ethmotur-
binal I and ethmoturbinal II. Between these processes, the

PRIMORDIAL CRANIUM OF THE CAT 335

olfactory fenestra extends in the form of three bays or sinuses.
In the present stage there is no cartilaginous cribriform plate;
its place is occupied by mesenchyma perforated by the olfactory
nerves. These are in two groups, one near the septum, the
second represented by bundles passing through the sinuses at the
side of the window. The sheet of mesenchyma perforated by
the olfactory nerves does not quite fill the fenestra olfactoria.
It is closely applied to the septum nasi, then crosses the mid-
line to be continuous with the membrane of the opposite side;
it is fixed at the anterior boundary of the window (tectum nasi).
Posteriorly the membrane passes over the lamina infracribrosa
against which it is closely applied. In the lateral direction it
becomes continuous with the membrane filling the spheno-
ethmoidal fissure. This is fixed to the dorsal but not to the
ventral boundary of the fenestra, which, it will be recalled, is
formed by the antorbital plate. In relation to this membrane
is the lateral branch of the nasal nerve (fig. 26). The latter
appears in the sections through the anterior part of the orbit,
running toward the spheno-ethmoidal fissure. This it enters,
passing ventrad of the membrane, a position it retains in its
course forward to the olfactory fenestra. Here it enters the
nasal capsule, pursues a short course through the crista semi-
circularis and then passes to the exterior by one of the epiphanial
foramina.

Septum nasi (figs. 1, 2, 25 to 30). This median partition is
the direct continuation of the trabecular plate forward into the
ethmoidal region. It is low and broad caudally where it lies
between, and enters into the median walls of the posterior
cupolae. As it extends forward the dorsal margin ascends, the
height of the septum increasing gradually toward the fenestrae
olfactoriae; between the olfactory fenestrae it increases rapidly
and reaches its maximum height at the tectum nasi; then de-
creases gradually in approaching the level of the fenestrae
narinae. The ventral margin of the septum presents a longitu-
dinal concavity, and is thickened between the paraseptal car-
_ tilages and again opposite the vomer. Anterior to the para-
septals it is united on each side to the anterior transverse lam-

336 ROBERT J. TERRY

ina, the line of junction being marked ventrally by a longi-
rudinal groove. The anterior free margin is straight and
reaches further rostrad than the lateral wall of the nose. Dor-
sally, the septum presents between the olfactory fenestrae a
free concave edge (there is no evidence of a crista galli) and, in
its precerebral portion, continues into the tectum nasi. The
latter relation appears in the sections of the anterior third of the
nose as a bifurcation of the septum into two laminae, which
extend on either side into the roof of the nose (fig. 28). In
this way the sulcus supraseptalis is formed.

Interior of the nasal capsule (figs. 18, 25 to 30). The confor-
mation of the nasal capsular walls from within is extremely
simple at the present stage as compared with that of the adult.
Turbinal processes are in evidence in the form of ridges, the
maxilloturbinal alone showing any degree of scroll form. The
bones in relation to the nasal cavity are the vomer, incisivum
and maxilla. |

Lateral wall of the cavum nasi. In figure 13, which repre-
sents the left lateral wall of the nasal capsule from within, the
following parts, already referred to, will be recognized: the
tectum nasi extending from the fenestra narina to the fenestra
olfactoria, the posterior cupola and lamina transversalis anterior,
parts showing cut surfaces at their junction with the septum
nasi; ethmoturbinale I and II presenting at the olfactory fenes-
tra; the crista semicircularis and the nasoturbinal; the inrolled
ventral margin of the paries nasi forming the maxilloturbinal
and atrioturbinal. The lateral wall of the cavum nasi presents
two unequal divisions: a small region ventrad of the level of the
maxillo- and atrioturbinals, and an extensive region dorsad of
this level. The former includes the sagittal portion of the
lamina transversalis anterior and the incisura posttransversalis;
the latter corresponds to the rest of the lateral nasal wall.

Ventral region of lateral wall of the cavum nasi. The sagittal
portion of the lamina transversalis anterior presents a smooth,
concave surface toward the cavum nasi, becoming broad ven-
trally where it passes into the floor of the nose (frontal portion
of the lamina transversalis anterior). Caudad of the lamina

PRIMORDIAL CRANIUM OF THE CAT 337

the cartilaginous lateral wall of this region is deficient; here the
great notch, the incisura posttransversalis is found (figs. 2, 3, 4,
13, 29). This space is entered from behind and ventrally by the
-eartilaginous anterior maxillary process. The post-transverse
notch is closed toward the nasal mucosa, by a layer of mesen-
chyma and by the incisive and maxillary bones which lie just
outside the plane of the cartilaginous nasal wall (figs. 29, 30).

The dorsal region of the lateral wall of the cavum nasi corre-
‘sponds on the exterior to the paries nasi as described on p. 380
and may, like it, be considered as presenting three divisions,
anterior, middle and posterior.

In the anterior division (pars maxil!lo-nasoturbinalis) will be
included, for convenicnen, the inner surface of the lamina supra-
conchalis, although, as will be seen later, its primary relation to the
components of the nasal side wall was not established. This
division, then, extends from the level of the fenestra narina to
the crista semicirculars, and is limited ventrally by the maxillo-
and atrioturbinals. The most cephalic portion reaches the
atrioturbinal ventrally, and forms the lateral boundary of that
part of the nasal cavity here designated the atrium. The atrio-
turbinal is in line with the maxilloturbinal but is separated from
that process by a notch, the incisura maxillo-atrioturbinalis.
The succeeding part of the anterior division stands opposite the
area of the lamina supraconchalis and sulcus lateralis of the ex-
ternal surface of the nasal capsule, and further includes the
maxillo-turbinal and crista semicircularis in its ventral and
caudal limits respectively. The maxilloturbinal, triangular in
general form, is continuous laterally by its base, with the paries
nasi at the eminentia lateralis. It stands mainly in a frontal
plane; its medial margin, opposite the septum, inclines ventro-
caudad to meet the caudal margin at an angle opposite the
paraseptal cartilage. Anterior to the level of the paraseptal it
participates with the paries nasi in the caudal boundary of the
‘post-transverse notch; posteriorly to the paraseptal it forms,
by its free margin, a wide notch or sinus with the ventral free
border of the antorbital part of the paries nasi, both entering into
the boundary of the fenestra basalis. The maxilloturbinal

338 ROBERT J. TERRY

reaches its greatest breadth opposite the base of the crista semi-
circularis; from this point caudad it rapidly diminishes in width.
On the lateral wall, dorsad of the maxilloturbinal, is a low
antero-posterior eminence produced by a slight inward bulging.
of the paries nasi in the region of the lamina supraconchalis.
This elevation is at the base of the great naso-turbinal body com-
posed of mesenchyma in the present stage (figs. 13, 29). Pos-
teriorly, the elevation in question and the nasoturbinal con-
tinue into the crista semicircularis (figs. 13, 27, 28, 29). The
latter, at present, forms the anterior boundary of the entrance
into the recessus lateralis (figs. 23, 27, 28, 29); it extends ventro-
dorsad to the tectum nasi, sweeping in a fine curve caudally,
alongside the septum, and terminating at the olfactory fenestra
as already described (p. 334, fig. 1). Where the crest ap-
proaches the tectum nasi, more or less complete discontinuity
of the cartilage occurs in the line of the sulcus lateralis. A
small fissure here, made by the foramina epiphanialia (figs. 28,
29), separates, for a short distance, the wall of the recessus
lateralis from the tectum nasi. A wide meatus of the lateral
nasal wall (here termed meatus supraconchalis) runs between
the naso- and maxilloturbinal bodies, continuing anteriorly into.
the atrium. Posteriorly this meatus extends ventrad of the
crista semicircularis (here it is very narrow) and enters into a
wide space which opens into the fenestra basalis (fig. 13). Just
where the meatus passes into this space, and at.a spot anterior
to the ventral end of the crista semicircularis, the lateral nasal
glands lie under cover of the mucosa (fig. 27). In its posterior
half the meatus supraconchalis is extended into a groove be-
tween the maxilloturbinal ventrally, and paries nasi (lamina
supraconchalis) laterally, the sulcus supraconchalis of Voit.
The middle division corresponds to the prominentia lateralis
of the exterior and presents the recessus lateralis to which refer-
ence has been made. This large cavity communicates with
the general room of the nasal capsule by a wide opening behind
the crista semicircularis. Anteriorly it undermines the crest
for a short distance in the form of a blind pocket; caudally it
reaches the first ethmoturbinal, and dorso-caudally opens into

PRIMORDIAL CRANIUM OF THE CAT 339

the olfactory fenestra through the sinus between the crista
semicircularis and ethmoturbinal I (p. 335). Although at this
stage the cartilaginous parts fail to meet in forming a medial
wall for the inferior portion of the lateral recess, the soft parts
which stretch between ethmoidal I, the crista semicircularis and
the floor shut off this part of the recess from the common meatus
of the nose and convert this part of the cavity into a blind pocket.
Similarly, the entrance from the common meatus into the re-
cessus lateralis between ethmoidal I and crista semicircularis
is very broad, as shown in the models, but by the presence of the
soft parts over these elevations, it is reduced to a narrow fis-
sure, the hiatus semilunaris of later stages. The lateral recess
is incompletely subdivided into dorsal and ventral rooms, re-
cessus lateralis superior and recessus lateralis inferior, by a
slight frontal ridge springing from the lateral surface of ethmo-
turbinal I, and by an oppositely placed ridge of the lateral wall
of the recess (fig. 27). The superior lateral recess opens into the
common meatus of the nose through the dorsal part of the hiatus
semilunaris. Within it are two antero-posterior, curving ridges
of the mucosa, one upon the roof, the other on the lateral wall.
Each includes a condensation of the mesenchyma which is in
contact, but apparently not continuous by any transitional zone,
with the cartilaginous wall. These ridges separate three out-
pocketings of the recessus lateralis superior, a lateral, a superior
and an inferior groove (fig. 27). The recessus lateralis inferior
is incompletely walled medially, as already explained. It
lodges a blind sac of mucosa which communicates with the
common meatus through the ventral part of the hiatus
semilunaris.

Posterior division. (Pars ethmoturbinalis). This region of
the dorsal part of the lateral nasal wall corresponds to the
antorbital plane of the exterior. It is characterized by the
presence of the bases of the ethmoturbinals. Ethmoturbinal I
appears in the model as a massive irregular ridge, extending
dorso-ventrally on the lateral nasal wall at the caudal margin
of the entrance into the recessus lateralis (fig. 13). Anteriorly,
the process goes over into precartilage in the form of a broad,

340 ROBERT J. TERRY

thick piece, triangular in section, extending cephalad toward the
crista semicircularis (fig. 27). Its medial surface bounds the
common meatus; a dorso-lateral surface enters into the floor of
the recessis lateralis superior; the ventro-lateral face is turned
toward the recessus lateralis inferior. Ethmoturbinal I reaches
the olfactory fenestra in the thick layer of mesenchyma filling
this space (fig. 1); ventrally it is separated by a wide stretch
from the level of the solum nasi; anteriorly it enters into the
caudal boundary of the hiatus semilunaris. Ethmoturbinal II
(figs. 1, 18, 26) is represented by a small cartilaginous plate,
_ with precartilaginous margins, jutting mesad from the lateral
nasal wall between ethmoturbinal I and the posterior cupola.
From the level of the olfactory fenestra its long axis extends
ventro-rostrad. It terminates a considerable distance above
the plane of the fenestra basalis.

The cavity of the posterior cupola les behind ethmoturbinal
I, occupying the caudal extremity of the nasal capsule. The
walls formed by the septum nasi, lamina infracribrosa, lamina
transversalis posterior and antorbital plane, are smooth. The
cavity opens anteriorly and ventrally into the common meatus
of the nose and the fenestra basalis.

Ethmoidal region in smaller embryos

The first evidences of chondrification in the ethmoidal region
were found in embryos of 12 mm. in which the process was mani-
fested in the septum nasi (fig. 17). In van Wijhe preparations
the ventral part of the septum was stained. blue (fig. 6), appear-
ing in the form of two streaks extending from the trabecular
plate forward, side by side and separated by a less deeply stained —
tract. In embryos of 15 mm. chondrification of the septum has
extended dorsally, reaching its greatest height in front. It is
now a single median cartilage (fig. 18). The septum is contin-
uous with the trabecular plate caudally, and in front gives off a
pair of arching processes from its dorsal margin (fig. 7). The
latter, which may be called the parieto-tectal cartilages, are at
this stage in relation to the roof and lateral wall of the anterior
one-third of the nasal cavity. Whether these processes are pri-

PRIMORDIAL CRANIUM OF THE CAT 341

marily outgrowths of the septum is brought into question by the
fact that they are most deeply stained in the van Wijhe prepa-
rations in their lateral parts and less so next to the septum.
In the midline dorsally a deep groove, the beginning of the sulcus
supraseptalis, lies between them. Besides the paired parieto-
tectal cartilages, there is, in the nasal region of van Wijhe prepa-
rations of 15 mm., a mass of cartilage quite independent of
other chondrifying tracts. This is a curved plate, overlying, on
each side, the diverticulum of the cavum nasi, which later is
included in the recessus lateralis of the cartilaginous wall. This
cartilage may be referred to, tentatively, as the paranasal car-
tilage. The parietotectal and paranasal cartilages stand close
together, the one in front of the other. It is of importance to
note that the dorso-cephalic margin of the latter overlaps the
dorso-caudal edge of the former. Van Wijhe preparations of
17 mm. exhibit still a third chondrifying tract in relation to the
nasal wall (fig. 8). This is a small plate of cartilage at the
very back of the cavum nasi, on either side of the nasal septum.
It appears to be entirely free from the septum and paranasal
cartilage. This lamina antorbitalis, as it may be called, les in
a plane anterior to that of the origin of the preoptic root from
the trabecular plate, and behind the paranasal cartilage. It is
curved about the caudal end of the nasal sac, thus indicating
the beginning of the posterior cupola. The anterior margin of
the antorbital lamina projects into the fold of ethmoturbinal I
behind the diverticulum of the lateral recess, and is overlapped
by the caudal edge of the paranasal cartilage. The latter is
larger than in the preceding stage and presents anterior and
ventral incurved margins, continuous with each other. The
ventral edge projects into the fold of the maxilloturbinal and
represents the base of the cartilaginous process of that name.
The anterior incurved margin overlaps the lateral and, at the
same time, caudal margin of the parieto-tectal, and fusion has
occurred to some extent between them. A double layered curved
ridge is thus formed, projecting into that fold of the nasal wall
which bounds the lateral recess anteriorly; this is the beginning
of the crista semicircularis. Where fusion has not occurred be-

342 ROBERT J. TERRY

tween the paranasal and parieto-tectal cartilage, spaces remain,
one of which is traversed by the lateral branch of the nasal
nerve; this is the beginning of the foramen epiphaniale. The
overlapping and fusion in the ventral region occurs between the
inrolled anterior and ventral margins, where, in later stages, the
lamina supraconchalis and nasoturbinal are found. The forma-
tion of these parts, however, was not observed. The dorsal
margin of the parieto-tectal cartilage hes next the olfactory
bulb and is jomed with the commissura spheno-ethmoidalis. -
The triangular parieto-tectal cartilage has grown backward
along the septum nasi nearly its full length, thus forming the
roof of the nose. Its caudal and lateral oblique margin enters
into the formation of the crista semicircularis. In its anterior
part it reaches, in a ventral direction, as far as the naso-lacrimal
duct. The lamina transversalis anterior is unchondrified. The
paraseptal cartilages are represented by incompletely chondrified
tracts, independent of other skeletal parts.

PART II. DISCUSSION
Occipital region

Basal plate. As we have seen, the first evidence of a basal
plate was in the form of a pair of small cartilages on either side
of the notochord of the occipital region, united anteriorly by a
hypochordal commissure. Wineza has already observed this
early form of the base of the cranium and called the two com-
ponent laminae the parachordal plates.

Regarding the chondrification of the basal plate in mammals,
several authors have shown that the initial stage is character-
ized by the presence of a pair of cartilaginous centers or tracts,
one on either side of the notochord in the occipital region.
Parker refers to the basal chondrification in the embryo pig,
first (75), as the ‘investing mass,’ later (’77) as the parachordal

PRIMORDIAL CRANIUM OF THE CAT 343

cartilages. It is not clear from the description that there are
two separate elements present. The term “investing mass” is
misleading with respect to the notochord; Parker expressly states
that the former lies beneath the notochord and so represents
the relations of these two parts in the figures. Froriep (’86)
recognized a tendency to the formation of bilateral symmetrical
anlagen of the caudal part of the occipital floor in the calf (p..
91, woodcut to fig. IV, fig. IV, 2). This author remarks on the
striking difference between cervical vertebrae and the occipital
vertebra presented by the bilaterality of the anlagen of the
bodies. In the former it becomes more pronounced in the
cranial direction, whereas in the occipital vertebra this con-
dition is presented in a lesser degree. In reference to the anlage
in the occipital floor, Froriep says: ‘‘ In einem Querschnitt dagegen
wie Fig. IV, 2, ist eine bilaterale Sonderung des Knorpelgewebes
nicht zu bemerken, die Knorpellage ist hier ventralwarts der
Chorda fast ebenso michtig wie zu beiden Seiten” (p. 91).

In the light of recent studies the condition represented in the
figure might justly receive a different interpretation with respect
to bilaterality of the anlage; the figure shows two cartilages in
the occipital floor, one on each side of the notochord and some
distance removed from it, united by continuous cartilage across
the midline ventrad of the notochord. Levi (’00) described a
pair of precartilaginous and cartilaginous anlagen for the middle
piece (basilar portion) of the occipital region in a human embryo
of about 13 mm. These were united across the midplane by
connective tissue in which ran the notochord, and which was
continuous in a caudal direction with the connective tissue of the
first cervical vertebral arch (p. 355). Bardeen (’08) also ob-
served the beginning chondrification of the base of the occipital
in man in two bilateral centers. Other investigators have
recorded an unpaired chondrogenous beginning of the occipital
basal plate, or, again, its development in connection with the
lateral occipital arch. Weiss (201) found, in the white rat, that
chondrification of the floor of the occipital region was mani-
fested, first, by centers in the hypochordal region, one of them
in Froriep’s apparently unsegmented portion, the other in the

344. ROBERT J. TERRY

region of Froriep’s occipital vertebra. Noordenbos (’05) found
the occipital basal anlage to be single in the mole, calf and
pig and also in the rabbit. Regarding the parachordal plate
in the latter, this author found that it was formed by the fusion
of the opposed ends of the two free occipital arches which were
first to develop and from this starting point, grew forward (p.
.375). Here are then, apparently, three different conditions pre-
sented in the origin of the cartilaginous basal part of the
occipital in mammals: the appearance of a hypochordal center; a
pair of bilaterally placed masses; origin by growth and fusion
of the apposed ends of the lateral occipital arches.

Regarding the relation of the notochord to basal plate, it was
found that in cat embryos of about 10 mm. the former entérs
the occipital region between the parachordal cartilages and lies
in the dorsal part of the mesenchymal sheet which unites these
cartilages across the midplane. This mesenchymal sheet later
becomes chondrified in connection with the parachordals, form-
ing thus a hypochordal bridge closing the space which originally
separated these cartilages (Terry, 713). Where the notochord
lies between the parachordals it is surrounded by a layer of
denser mesenchyma than that concerned in hypochordal arch
formation; this specialized sheath is continuous with the mesen-
chyma about the notochord in the region of the atlas—that in
which the atlantal centrum is later formed. In regard to a
cartilaginous hypochordal layer in the occipital region of mam-
mals generally, there seems to be no doubt of its constant oc-
currence. My own observation of the position of the noto-
chord with reference to the basi-occipital region in cat is in agree-
ment with that of Williams (’08), namely, that after chondrifi-
cation is well established, the caudal portion of the basal plate
is hypochordal. Recently Kernan (’15) has observed the hypo-
chordal position of the basal plate in cat embryos. Parker,
Froriep, Levi, Noordenbos, and Weiss have observed, in various
mammals, that the caudal part of the occipital basal cartilage is
ventrad of the notochord.

The parachordals in cat are united at their anterior ends
across the midplane (embryos of about 10 mm.) by a hypo-

PRIMORDIAL CRANIUM OF THE CAT 345

chordal commissure of young cartilage. This lies at a level
cephalad of that of the anterior root bundle of the hypoglossal
nerve. Cartilage afterwards forms dorsad of the notochord in
the region of the primary commissure, so that the former comes
secondarily to lie within the basal plate. I am aware of the
fact that some observers have described this anterior commis-
sure of the parachordal in other forms as lying dorsad of the
notochord, but’in cat I have found it primarily hypochordal.
Weiss, however, found the primary process of cartilage forma-
tion hypochordal in the apparently unsegmented division of the
basal plate. The next cartilaginous union to be established be-
tween the parachordal cartilages in cat is the hypochordal arch
uniting their caudal extremities. This has formed somewhat
earlier than the anterior arch of the atlas, next to which it stands.
The posterior hypochordal commissure is in the same transverse
plane as the primitive lateral occipital arch. Between the two
hypochordal arches, anterior (primary) and posterior, there
remains a sheet of mesenchyma, stretching from side to side
beneath the notochord, and continuing into the medial edges
of the parachordals. The direction in which chondrification
proceeds in this tissue is lateromesad. In the middle of this
tissue a third commissural process is indicated where the medial
edge of each parachordal sends a projection toward the mid-
plane, producing a constriction in the vacuity between the
parachordals. These two symmetrical processes are directed
ventro-mesad to a hypochordal plane and lhe at a level corre-
sponding to the middle of the future hypoglossal foramen. In
the smaller embryos (9 mm.) four membranous arches in the
occipital region were noted by Kernan, who states that the two
cranial have a tendency to fuse.

When, in the cat, the parachordal plates have formed, the
three root bundles of the hypoglossal lie against their lateral
margins, in the angle formed by the lateral occipital arch. The
foramen is later completed by the formation of a cartilaginous
bar in front of the nerve roots, which extends laterally and
dorsally from the anterolateral corner of the parachordal,
to unite with the primary lateral occipital arch beyond the

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

346 : ROBERT J. TERRY

nerve roots. The three roots are united in passing through
the hypoglossal notch of the primitive cartilaginous occipital
element, and there is no indication of a subdivision of the mar-
gin into smaller notches for each root, as appears to be the case
in an earlier stage and before cartilage has formed. This con-
dition varies in mammals; in rabbits for example, (Noordenbos,
Voit) two canals are present on each side. That two canals
occur occasionally in the human skull as an anomaly is well
known. It will be recalled that the hypoglossal nerve in cat
embryos shows a tendency to conform with a spinal nerve in
presenting a posterior root and ganglion in relation to the third
motor root. The presence of this ganglion was discovered by
Vulpian (62) and I can confirm this observation here.

The presence of more than two cartilaginous hypochordal
commissures in the development of the occipital basal plate has,
I believe, not been recognized. Also, the recognition of the
primary hypochordal nature of the anterior commissure appar-
ently rests on only one other observation, that of Weiss, in the
rat. Until further distribution of these phenomena be dis-
covered, or the present observation confirmed, it would seem of
little profit to attempt an interpretation of their significance.
The antero-posterior succession of a series of transversely placed
bar-like structures in the base of the skull at once suggests the
idea of segmentation. A relation of these bars laterally with the
hypoglossal nerve roots may or may not be a primary one. But
in utilizing the results of chondrocranial study in any discussion
of the segmentation of the cranium, it must be borne in mind
that such evidence can be of high value only when the relation
of chondral to blastemal developmental processes is known. It
seems highly probable that the cartilaginous commissures here
described and the membranous bars observed by Kernan (’15)
are two developmental phases of one and the same process,
which subsequent investigation will elucidate.

In regard to the condensed tissue sheath about the occipital
notochord found in cat, it may be said that a number of obser-
vations made on different animals point to the presence of such
a layer as probably of general occurrence. Froriep (’86, p. 92)

PRIMORDIAL CRANIUM OF THE CAT 347

records the presence in the calf of a connective tissue layer
dorsad of the chorda. Weiss (01) found, in embryos of the
white rat, an exceptional development of the perichordal sheath
in the occipital region, not separated from the horizontal plate
of the primitive arch of the atlas (p. 511). The work of Gaupp
(06) on Echidna, and Weigner (’12) on man, support the view,
first brought forward by Weiss, of a special development of
perichordal tissue about the occipital notochord in mammalian
embryos. Weiss described the notochord as occupying, in the
blastemal stage, a position at the dorsal surface of the segmented
portion of the floor of the occipital region; he found that the
cranial end of the perichordal sheath grew to assume a globular
form; in the chondral stage, cartilage appeared in the perinoto-
chordal sheath, quite independently of the process of chondrifica-
tion which takes place lateral to and beneath the notochord in
the formation of the lateral occipital arches and the basal plate.
The more or less spherical cartilage so formed about the noto-
chord is fused, in later stages of development, with the carti-
laginous centrum of the atlas, and becomes eventually the ex-
tremity of the dens epistrophei. Weiss saw in the cartilage
forming the end of the dens epistrophei, which is marked off
from the cartilaginous centrum of the atlas by grooves, an ele-
ment comparable with a vertebral centrum, and concluded that
it represented the body of an occipital vertebra, or of a proatlas.
Gaupp (06) found the dens epistrophei in Echidna embryos to
be composed of the centrum of the atlas and, in addition, of
material lying cephalad (and perhaps derived from the basis
eranii). This author is of the opinion that the dens epistrophei
and the ligamentum apicis dentis represent the anterior reduced
end of the vertebral column in which a number of vertebral
centra lie imbedded. Weigner (’11) found in a human embryo of
13.5 mm. paired anlagen in the floor of the occipital region, pre-
senting a notch laterally for the hypoglossal nerve, with a deep
groove between their caudal extremities occupied by mesen-
chyma, in which the notochord lies. In the ventral part of this
sheet, the hypochordal arch of the occipital region was observed.
In the atlantal region, in the tissue dorsad of the notochord, the

348 ROBERT J. TERRY

paired anlagen of the atlantal centrum were noted. Evidence
of the beginning of the occipital centrum was presented in an
embryo of 14.5 mm.; the anlage was clearly defined in a later
stage (15.3 mm.) as a pair of centers behind the notochord, which
pass in a caudal direction gradually into the older centers of the
body of the atlas. In man, according to Weigner, the body of
the definitive epistropheus with its tooth-process, is developed
from three vertebral bodies; those of the occipital vertebra, atlas
and epistropheus. The dens itself is formed from the centrum
of the occipital vertebra and of the atlas. In the present work
no separate centers, in advance of that for the atlantal cen-
trum, were seen, but the tissue about the occipital notochord
became condensed next to the chondrifying center of the atlas,
and eventually became the cartilaginous apex of the dens
epistrophei. In the ossification of the dens epistrophei of cat
(as in several mammals) there is, in addition to the bilateral
atlantal centers, a single center for the apex of this process
(Jayne ’98).:

Since Froriep’s work on the development of the occipital
region (’83, ’86, ’02), the interpretation which that investigator
drew from his own results of the relation between cranial and
vertebral development and structure has been, in general, sus-
tained; some of the conclusions have, however, been modified
by new evidence brought out by recent research. Noordenbos,
in 1905, attacked the evidence which has been used in support
of the vertebral theory of the skull, claiming in effect that it
does not support the homology of parachordal plate and occipital
arches with vertebral centra and vertebral arches. Noordenbos
rightly objects to the comparison of vertebral bodies, arising as
separate, rounded cartilaginous masses, with the parachordal
plates, continuous unsegmented masses presenting no trace of
special chondral centers. He states that vertebrae arise around
the body notochord while the parachordal plate does not. This
plate takes origin in one of the three ways mentioned above:
as an independent center at the side of the notochord; in con-
nection with the lateral occipital arch; in connection with a
hypochordal plate. By the van Wijhe method the vertebral

PRIMORDIAL CRANIUM OF THE CAT 349

centra in the mole were found to arise in connection with intra-
vertebral capsules, outside the sheath of the notochord. Further-
more, the relation of the neural arch of a vertebra to its centrum
differs from that between the lateral occipital arch and para-
chordal; in the former the parts are primarily independent, in
the latter continuous. On account of these discrepancies be-
tween vertebral and occipital chondrogenous development,
Noordenbos finds weak support for the vertebral theory in the
chondrocranium. He says (p. 373): ‘“‘Ich méchte aus diesen
Erscheinungen, im Gegensatz zur allgemein giltigen Auffassung,
schliessen, dass fiir das Chondrocranium die Wirbeltheorie nicht
aufrecht zu halten sei.” But the vertebral theory, notwith-
standing the blows dealt it from the time of Huxley’s attack to
the present, has shown itself tenacious of life, and the thought
uttered by Oken more than one hundred years ago demands
deference of the worker of today.

Recent investigations into vertebral development, (Bardeen,
Weiss, Weigner) demonstrate the presence of a pair of chondro-
genous centers, lying close to the midline and reaching a some-
what higher level dorsally than the notochord, which grow to
surround the latter, and so form the cartilaginous vertebral
body. There is, in general, apparently a fundamental difference
in the original relation to the notochord of the parachordal plate
and vertebral centrum. At one spot, only, does the relation of
the parachordal to the notochord approach that of a vertebral
centrum, namely at the level of the anterior commissure; car-
tilage is here developed around the notochord. The discovery
of processes of chondrification in the perichordal sheath of the
occipital region, related eventually to the dens epistrophei and
which fulfill the conditions of vertebral central development in
‘general, have been mentioned. It would seem that the evidence
presented by these investigators (Weiss, Gaupp, Weigner) jus-
tifies the interpretation which has been put forward of rudi-
mentary centra in the occipital region. To this evidence must
be added that given by cat. By the interpretation of Weiss of
the hypochordal nature of the caudal part of the basal plate,
the objection to comparing the lateral occipital arch with the

350 ROBERT J. TERRY

neural arch of an ordinary vertebra is largely overcome. The
lateral occipital arch presents the same relations to a centrum
as does the atlantal neural arch, and also the same relations to
a hypochordal arch as obtains between the neural and ventral
arches of the atlas. That the order of formation of the hypo-
chordal and lateral occipital arches varies somewhat in different
species is no obstacle to the interpretation of their equivalency
to vertebral structures; the work of Weiss (01) and Levi (’08)
has shown that there is also great variability in the develop-
ment of the ventral arch of the atlas among mammals.

The fundamental differences between occipital and vertebral
development, which have been so clearly indicated by Noor-
denbos, must, I think, be recognized; but if the interpretation of
Weiss be correct, that the occipital develops not as a typical
vertebra, but like a specialized vertebra, namely, the atlas, we
must admit that there is still evidence of vertebral structure
in the skull. This interpretation is in accord with the physio-
logical environment of the region: a transitional zone between a
rigid (cranial) and a movable (spinal) division of the axial skele-
ton. Regarded from this aspect, the structural conditions are
seen to change as we pass along the vertebral column toward the
head, the form of the vertebrae becoming less typical, due to
tendencies along certain definite lines (regression of centrum,
development of hypochordal parts). The occipital region shows
by its structures the culmination of these tendencies; extremely
rudimentary centrum separated from all connection with highly
perfected arches, lateral and hypochordal; characters which, to a
lesser extent, mark the atlas from a typical vertebra.

There is probably more than a superficial resemblance be-
tween the lateral occipital arch and neural atlantal arch in re-
spect to the relations of these parts to nerves. The primary —
notch formed for the hypoglossal nerve bundles at the side of the
parachordal plate, in front of the base of the lateral occipital arch
(Noordenbos describes it in the occipital arch), and its subse-
quent conversion into a foramen, are phenomena which seem to
parallel the development of the atlas in the region of the first
spinal nerve. In cat embryos of 15 and 23 mm. the first spinal

PRIMORDIAL CRANIUM OF THE CAT 351

nerve makes its exit through a notch at the side of the lateral
mass of the atlas, between the base of the neural process poster-
iorly and a short but prominent atlantal process directed dorsad
from the lateral mass. The articular regions of the atlas and
occipital are comparable, in respect to their relations, to the com-
ponents of these two skeletal elements. In cat the occipital
condyles are formed at the spot where the lateral and hypochor-
dal arches come together, that is on the parachordal plate. This
is In agreement with Levi’s and Weigner’s observation of the
relation of condyle and parachordal in man. Likewise, the cor-
responding articular surfaces of the atlas are formed where ven-
tral arch and neural arch come together, namely at the massa
lateralis. The early establishment of similar relations to nerve
and articular surface offers a basis for a comparison of para-
chordal plate and lateral mass of atlas. Apparently these parts
are not distinct elements in their relation to the occipital and
atlantal arches, but mark a definite locus between the hypo-
chordal arches on the one hand, and neural or lateral occipital
arch on the other, constitute the region of articulation, and mark
the ventral limit of the exit of the nerves. In this sense the para-
chordal plate could not include the cartilage ventrad of the
notochord; this would fall into the category of the hypochordal
arches. The term occipital basal plate would include the orig-
inally paired parachordals and the hypochordal cartilage. Com-
parison of parachordal plate and lateral mass which is here pro-
posed, while attempting to bring out the relations of the occipi-
tal and atlas in further detail does not at the same time close the
way to a better understanding of a possible relation of atlantal
centrum and lateral mass which has been advanced by authors
(Hagen, ’00).

Atlas. Reference has been made to a peculiar character of the
atlas, namely the foramen in the neural arch of the adult bone
and its relation to the notch in the arch of its cartilaginous prede-
cessor. This atlantal foramen transmits the vertebral artery
and the first spinal nerve in cat. It is present normally in most,
if not all mammalian orders, holding a position nearer or farther
from the cephalic margin of the neural arch, through which varia-

352 ROBERT J. TERRY

tion of its position the bar of bone forming its cephalic limit is
narrow or broad. In man the first spinal nerve and vertebral
artery normally traverse a notch in the superior margin of the
neural arch; in some instances, however, they pass through a
foramen produced by osseous bridging of the notch. Bolk (’99)
has pointed out that the usual conditions are indicative of re-
gressive processes in the formation of the human atlas, that in
man this bone is reduced in mass as compared with the atlas
of those animals in which an atlantal foramen obtains. The
bony reduction goes hand in hand with the imperfect develop-
ment, and probable loss to some extent, of muscle and nerve in
the dorsal part of the neck at the level between epistropheus and -
occiput. The recognition of the human atlas as an atypical
example of the form which generally prevails in mammalia is
helpful in approaching problems of structure in the head-neck
region. Out of the recently much discussed phenomenon of
manifestation of an occipital vertebra or assimilation into the
occiput of the atlas (Swjetschnikow ’06, Kollmann ’07, v. Schu-
macher ’07, Smith ’09, Glaesmer ’10), the question has presented
itself to me as to the development of parts in relation to the
atlantal foramen. A number of observations on the develop-
ment and comparative anatomy of the atlas have been made and
will be reported in another place. At present I wish to discuss
only those which have some bearing upon the occipital region.
The atlas of the smallest cat embryo studied (10 mm.) was
represented in cartilage by a pair of neural arches, a small cen-
trum about the notochord, and the beginnings of the hypochordal
arch. The expanded base of the neural arch (lateral mass)
sends dorsad in front of the latter a small, blunt atlantal
process. The notch between the process and arch Jodging the
first spinal nerve and vertebral artery, is the first step toward the
formation of the atlantal foramen. In the stage represented
by the model, the notch is relatively deeper, owing to the in-
crease in length of the atlantal process, which is now in the
form of a short bar. The base of this bar, anteriorly, partici-
pates in the articulation with the occipital condylar surface; its
dorsal extremity is free. The boundaries of the foramen are

PRIMORDIAL CRANIUM OF THE CAT 303

completed, in the full term fetus, by connective tissue stretching
between the free extremity of the anterior bar and the neural
arch, anterior to the first spinal nerve.

Observations on the sulcus in the atlantal neural arch for the
first spinal nerve in man have been made by Macalister (’93),
who gave the name post-glenoid tubercle to the process which
rises from the lateral mass and limits the sulcus anteriorly. This
process was found to vary considerably in its extent, an ob-
servation easily verified in even a small series of specimens.
Macalister also noted the presence of an independent bony center
in the ligament completing the atlantal foramen in the atlases of
young skeletons. The question, whether this represents the
typical mode of origin of the bony rod which, in man, completes
the atlantal foramen, remains for future enquiry. Separate
ossifications in the region of the neural arch of the atlas, be-
tween it and occipital, have several times been observed in man.
Trolard (92) found, in two instances, in the posterior ligament
of the atlanto-occipital joint an osseous bar placed horizontally,
in one case nearly reaching the midplane. The possibility of
relation of these independent ossicles in man to the arch of the
atlas has, I believe, not been considered. It is well known that
an osseous element in the posterior occipito-atlantal ligament,
compared with the proatlas of reptiles and extinct amphibia,
has been described for Erinaceus (see Baur, 94). The possi-
bility of the proatlas being a component of the atlas in a per-
sistent type was many years ago suggested by Osborn (’00).
The question of special interest which I wish to mention here
in regard to the post-glenoid tubercle, the bar of bone complet-
ing the atlantal foramen and the ossicles in the posterior occipito-
-atlantal ligament, is whether these structures may not possibly
represent parts of one element which, in a primitive state, was
separate from, but closely related to the atlas.

Occipito-atlantal articulation. The discovery by Fischer (’01)
of a single, horseshoe-shaped surface at the ventral margin of the
foramen magnum in embryos of Talpa, articulating with the ven-
tral arch of the atlas would seem to lessen the gap between
reptilian monoconydlic and mammalian dicondylic articulation.

354 ROBERT J. TERRY

That the condition in Talpa is primitive, and not secondarily
acquired, is supported by Gaupp’s (08) observation of a simi-
lar atlanto-occipital articulation in Echidna. Whereas, in cat,
the occipito-atlantal articulation is apparently dicondylic pri-
marily, the joint surfaces are located to a considerable extent
upon the basal plate, as well as on the lateral arch, and meet
corresponding surfaces of the ventral arch of the atlas and its
lateral mass, including the atlantal process. The participation
of the basal plate in the articular surface is evidence of greater
proximity of the two condylar surfaces toward the median plane
than in those mammals (Lepus) where the surfaces are restricted
to the region lateral to the foramen magnum. This embryonic
state of the condyles is, therefore, apparently intermediate be-
tween typical dicondylism and the condition observed by Fischer
in Talpa. In the later development of cat embryos the condy-
lar surface grows further dorsad by the side of the foramen
magnum.

If we accept the comparison of occipital and atlas, we must
throw aside the idea of that form of articulation between them,
such as exists between the centra of typical vertebrae.

The basal plate in the cat is a derivative of the parachordal
cartilages and hypochordal arches and therefore the develop-
ment of an articular surface upon its caudal margin must in-
volve either one or both of its constituent elements. The point
to be emphasized now is the fact that a part of the occipital
element, which apparently is as distinct from the centrum as the
lateral mass is distinct from the body of the atlas, enters into the
constitution of the condyle; that is to say, the condyle belongs.
to an arch structure.

Further study of that region dorsad of the condyle which
is characterized by a notch traversed by veins is necessary
before any conclusion can be drawn regarding its significance; it
seems not improbable that it may have to do with the foramen
condyloideum.

Plane of the foramen magnum. Although a marked flexure
exists between the head and trunk of cat embryos, this does not
explain the basal position of the plane of the foramen magnum

PRIMORDIAL CRANIUM OF THE CAT 355

and the occipital condyles referred to on p. 292, which is in
contrast with their caudal position in the adult. The immediate
cause of this basal position is not difficult to find. Since the
lateral occipital arches are quite narrow antero-posteriorly and
are joined directly with the otic capsules, it is evident that their
basal inclination cannot be attributed either to growth, as in
man, or to the presence of wide fissures between them and the
ear capsules. The explanation is to be found in the flexures
to which the whole chondrocranium is subjected. One result of
these flexures upon the longitudinal axis of the cranium is to
put its anterior and posterior halves nearly at right angles
with each other. It follows that the plane of the foramen mag-
num stands parallel with that of the floor of the nose. It is of
interest to find that, with the formation of the bony cranium, a
nearly straight longitudinal axis is substituted for the primary
angular axis and, with it, the plane of the foramen magnum
becomes less oblique.

A primitive condition, and an exceptional one in the primor-
dial skull of mammals, it seen at the stage represented by the
model in the abrupt ascent of the lateral occipital walls from the
basal plate. The mammalian chondrocranium, as contrasted
with that of lower animals, shows a tendency toward lateral ex-
trusion of these walls; as Gaupp (’06) says: ‘‘ Die Seitenteile der
Occipitalregion sind bei Saéugern nicht mehr steil aufgerichtet,
sondern nach hinten hin basalwirts niedergelegt am stirksten
und vollkommensten beim Menschen.”

Basal fissures. The fissura basicochlearis posterior of cat is
apparently comparable with the opening of the same name in
the chondrocranium of Talpa, first described and named by
Noordenbos (05). Mead has noted a probable homologue of
the posterior basicochlear fissure in Sus. In Lepus this opening
is not present in the stages of development studied by Voit,
but an anterior basicochlear fissure was observed by that in-
vestigator. These fissures are filled with mesenchyma, which,
in the cat embryo, passes into a zone of precartilage at the edges
of the opening. The posterior basicochlear fissure, present in
Talpa embryos of 14 mm., disappears in embryos of 19 to 20

356 ROBERT J. TERRY

mm. and older, being replaced by cartilage (Noordenbos).
‘Parker (’85) and Fischer (’01) had already shown continuous
cartilage in the region between basal plate and cochlear promi-
nence in Talpa embryos of later stages. Tarsius exhibits still
another phase of vacuity at the basicochlear junction, present-
ing an extensive slit separating the ear capsule and cranial floor
(Fischer, 05). In the adult cat, a fissure separates the pars
petrosa from the basi-occipital and it appears that in the adult
pig the foramen lacerum anterius and the foramen jugulare are
connected by a fissure median to the auditory bulla (Mead,
08). The persistence of an original fissure, growing larger as
the cranium enlarges, is an interesting phenomenon calling for
further study. The posterior basicochlear fissure of Talpa is
one of several spaces which, as Noordenbos has shown, are de-
rived from the original space separating the independently arising
otic capsule from the basal and lateral parts of the chondro-
cranium. That part of the original space between the base of
the skull and the ear capsule is broken up by the later formation
of synchondroses, uniting the auditory capsule with the para-
chordal plate and with the basal region which later enters into
the sphenoid; and so there arise a canalis caroticus, an anterior
basicochlear fissure and a posterior basicochlear fissure. The
observations on cat embryos, presented here, show that the
origin of the cartilaginous basal plate and otic capsule are in-
dependent and that the fissura basicochlearis posterior is derived
from the original space separating the parts.

Foramen magnum. In Lacerta the dorsal boundary of the -
foramen magnum is the tectum synoticum. Fischer (’03) found
the apparent foramen occipitale magnum of the Semnopithecus
embryo larger than the future real foramen magnum, the hinder
part of the former being closed by membrane. This author re-
marks on the probability of the membrana atlanto-occipitalis in
part undergoing ossification. Bolk (’03) described this region
in human embryos, and applies the name incisura occipitalis
posterior to a little space filled with membrane made secondarily
by the approximation of the dorsal extremities of the occipital
side walls in the formation of the foramen magnum. Between

PRIMORDIAL CRANIUM OF THE CAT 357

this notch and the tectum posterius is a broad space filled by
membrane continuous with that of the incisura posterior. A
pair of chondral centers lies in this membrane and a third center
stretches through the cranial roof anterior to the tectum pos-
terius. The latter disappears in further development; the pair
of centers remaining help to complete the boundary of the in-
_ eisura posterior, while the membrane between the latter and the
tectum posterius undergoes ossification. Voit (’09) also found
a space (incisura occipitalis posterior) in Lepus between the
dorsally open foramen magnum and the tectum posterius, and
‘since, as is explained, the latter belongs to the otic region, the
side boundaries of the incisura occipitalis posterior are regarded
as the dorsal portions of the occipital pillars. If we compare
now the extent of the region between the dorsal confines of the
foramen magnum and the tectum posterius in lizard, rabbit,
cat, ape and man, it at once appears that there is a progressively
increasing area exhibited. This begins with Lacerta, where, as
Gaupp observed, the tectum is so shaped as to give to the fora-
men magnum an angle in the dorsal median line, and reaches
the great expanse described by Bolk in the human embryo, in
which the tectum is far removed from the foramen magnum.
It is evident, also, that the term incisura occipitalis posterior
has not the same value throughout its application; in the rabbit
Voit apparently regards the space limited laterally by the dorsal
portions of the occipital pillars as the incisura occipitalis posterior,
while Bolk limits the term to only a small part of the region
encompassed by the dorsal limits of the occipital walls.

Otic region

Position of the otic capsules. It has been noted (p. 298) that
the approximately transverse position of the plane of the otic
capsules in the stage represented by the model forms an ex-
ception to the general rule in mammals of obliquity of the prin-
cipal otic axis toward the longitudinal axis of the skull. It
will be recalled that the degree of differentiation exhibited by
the stage of the model is one, expressed in terms of the skeleton,
wherein bone formation has advanced but little; of the mem-

358 ROBERT J. TERRY

brane bones several have still to make their appearance and
none of the purely endochondral ossifications is present. Talpa
of 27.3 mm., Semnopithecus of 53 mm., Homo of 8 em., in which
the obliquity of the principal otic axis has been recorded, are
all at stages of development in which bone formation is well
established and therefore can hardly be compared with cat
embryos in the stages under consideration. On the other
hand, obliquity of the otic axis is present in the mole of much
younger stages, if one can judge by the photographs of Noorden-
bos, and the same is true for the Sus cranium described by Mead,
which is at approximately the same stage as the Felis cranium
modeled. Again, Voit states that in Lepus the two canalicular
parts stand parallel, and only a slight convergence of the coch-
lear parts is present; the stage is one in which osseous develop-
ment is advanced (45 mm. gr. L.). Therefore, it appears that
the definitive oblique direction of the long axis of the auditory
capsule, typical of mammals, is attained at different periods in
the species considered, the tendency being toward its early
establishment. As in the case of the occipital region, so also
with the otic capsule, the position changes with the development
of the bony cranium. The shifting of the otic axis from a posi-
tion at right angles to the cranial base in the chondral stage
to one of marked obliquity (cephalo-ventro-mesad) in the
osseous stage, can hardly be a result of the straightening of the
cranial axis. The factors involved in influencing the change
must remain for future inquiry.

Another characteristic of the position of the mammalian otic
capsule is its location in the base of the skull rather than i2 the
lateral wall as is the case in increasing degree from this class
back to lower vertebrates. In mammals, not only does the coch-
lear capsule hold a basal position, but the phylogenetically
older canalicular part is rotated ventralward as well as caudal-
ward. Toward the attainment of this mammalian peculiarity
the cat cranium, in the stages under discussion, presents what
seems to be the initial steps. Though the cochlea, a phylo-
genetically later acquisition to the ear, asserts itself early in
claims for space, the relations established in the chondocranium

PRIMORDIAL CRANIUM OF THE CAT 359

are readjusted in the bony cranium, the cochlear capsules being
widely separated by a broad processus basilaris, and are them-
selves relatively smaller in the adult skull.

Origin of the cartilaginous otic capsule. In discussing the ob-
servations which were made on the chondrification of the otic
capsule two questions of special interest present themselves: the
relation which the origin of the cartilaginous capsule as a whole
bears to the rest of the cranium; the original relation between
the pars cochlearis and the cartilaginous basis cranii. The first
question was raised by Huxley and there was sufficient evidence,
notwithstanding the crude methods of his time, for the ad-
vancement of the theory of intrinsic skeletal capsules for each
of the sense organs, ear, eye, and nose. Subsequent discovery
has tended to confirm the truth of this theory, the evidence
coming, as might be expected, chiefly from the lower vertebrates.
What mammalian crania will show must wait until the study of
successive developmental stages of species has been repeated by
modern methods. By the van Wijhe method, Noordenbos has
presented, recently, very strong evidence of the independent
origin of the cartilaginous otic capsule in Talpa; similar results
were obtained for rabbit, ox and pig.

The second question has arisen in connection with Gaupp’s
theory of the reformation of the cranial base to contribute a
supporting wall for the cochlear duct. There appears to be in
the reptiles a beginning development of the cochlear capsule
at the expense of the basal plate. Is the theory supported by
evidence from the mammalian chondrocranium and, what con-
cerns us here, does the development of the cochlear capsule in
cat throw any light on the problem? So far as mammals are
concerned, it is convenient to consider these two questions to-
gether. First, it should be borne in mind that only the cireum-
stances of chondrogenous development will be reviewed; the
conditions of blastemal structure are here excluded.

In regard to the pars canalicularis the evidence afforded
both by sections and van Wijhe preparations indicates that this
component of the ear capsule arises independently of other parts
of the cranium. There is some difference as to the form of the

360 ROBERT J. TERRY

cartilage first appearing in the pars canalicularis from what has
been observed in other animals. I refer to the observation of a
plate of cartilage upon the lateral side of the semicircular canals;
in the cat, cartilage forms upon the lateral surfaces of the canals
in more or less separate stretches for each canal. The canals
are subsequently completely walled and the intervals between
them filled through the development of cartilage, but whether
this is by extension of cartilage formation from the canalicular
walls already established or from independent chondrifying
centers was not observed. The more or less compact mass con-
stituting the pars canalicularis is secondarily connected with
the lateral occipital arch and parietal plate, although its dorsal
margin remains free in the fissura jugulare spurium, and the
posterior margin is clearly indicated, even at the 23.1 mm.
stage, in the stretch of young cartilage between it and the lateral
occipital arch directed toward the jugular foramen. The pars
canalicularis is also apparently formed independently of the
suprafacial commissure, if one may judge this by the difference
in degree of development of these two closely associated parts.

In the pars cochlearis, cartilage was first observed in the
region next the pars canalicularis and in the anterior and pos-
terior poles, i.e. in the neighborhood of the suprafacial and basi-
vestibular commissures. There was no actual separation of these
chondrifying tracts from one another, no independent centers of
cartilage formation. At the stage when the medial wall of the
cochlear capsule is in precartilage, the capsule is separated
from the chondrified basal plate by a fissure filled with mesen-
chyma. Union of the capsule by cartilage with the basal plate
behind the carotid foramen, with the alicochlear commissure and
basivestibular commissure, is brought about secondarily. Be-
tween the commissura suprafacialis and anterior pole of the
cochlear capsule a smaller degree of difference in development
obtains than is the case between this commissure and the pars
canalicularis; the ventral end of the commissure, however,
appears to be blended, if not actually continuous, with the coch-
lear capsule. In this discussion, the fact of the continuity of
these two parts is important because of the possibility of pa-

PRIMORDIAL CRANIUM OF THE CAT 361

rietal if not actual basal relationship and significance of the
commissure. The evidence of the parietal nature of the supra-
facial commissure may be considered at once, since upon its
interpretation depends to a large extent the questiqn of the
cochlear relations to the basal plate.

The relations of the suprafacial commissure in cat appear to
differ somewhat from those described in other mammals. In
Talpa, according to Fischer (’01), the roof of the facial canal is
made by a thin lamella of cartilage stretching from the pars
canalium semicircularium to the highest elevation of the coch-
lear capsule. Fischer regards the walls of the facial canal as
made entirely by the ear capsule, and contrasts this condition
with the formation of the canal in Lacerta, in which, as Gaupp
(00) has found, the foramen for the seventh cerebral nerve lies
in the boundary zone between the basal plate and ear capsule.
Noordenbos (05) named the roof of the facial canal the tectum
nervi fascialis, and found it connected with the medial wall of
the anterior ampullary swelling of the pars canalicularis. Voit
(09) found, in the rabbit, that the suprafacial commissure
stretched from the anterior end of the pars posterior of the otic
capsule, beneath the prominentia utriculo-ampullaris posterior
and right above the superior acustic foramen, to the roof of
the anterior part of the pars cochlearis. In comparing the
facial foramen in rabbit and lizard, Voit evidently agrees with
Gaupp that, in mammals, the walls of the foramen are in part
contributed to by the cochlear capsule. In the dog, the supra-
facial commissure bridges over the facial foramen, from the
borders of the pars utriculo-canalicularis and the pars sacculo-
cochlearis, according to Olmstead (’11). De Burlet (14) de-
scribed the commissura praefacialis of Balaenoptera rostrata
as a cartilaginous bridge between the pars cochlearis and pars
canalicularis. In De Burlet’s plates VI and VII, however,
there is shown what appears to be a connection between the
praefacial commissure and lamina parietalis. The relations of
the lateral end of the suprafacial commissure in the cat differ
from those in the mammals mentioned, with the exception pos-
sibly of Balaenoptera. Connection between the commissure

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

362 ROBERT J. TERRY

and pars canalicularis is likewise seen in cat, but the relation is
apparently not the primary one. The primary lateral termina-
tion of the suprafacial commissure in the cat is not in the otic
capsule, but in the commissura orbito-parietalis, where the
latter meets the prominentia ampullaris superior. Continuity
with the orbito-parietal commissure (a part of the lateral cranial
wall) and, at the same time, partial separation from the otic
capsule, is to be regarded as evidence pointing toward the
parietal nature of the suprafacial commissure. While I find no
reference to a relation between the suprafacial commissure and
cranial side wall in descriptions of mammalian chondrocrania,
the constant proximity of these parts strongly suggests that the
continuity seen in cat may obtain in other mammals. De
Burlet’s figures of the Balaenoptera chondrocranium are of
great interest in this connection. Further support of the view
of the parietal nature of the suprafacial commissure is offered
by the relation of this structure to the exit of the trigeminus.
As stated in the description of the orbito-temporal region, the
roots of this nerve and the semilunar ganglion lie between the
suprafacial commissure and a thickened band of the transverse
septum in which is developed an accessory cartilaginous rod
resting upon the dorso-medial surface of the ganglion. A simi-
lar structure was observed in the rabbit by Voit who inter-
preted the ‘Restknorpel b’ as possibly representing the pila
prootica of Lacerta, a structure of the primary cranial wall. In
Lacerta the trigeminus makes its exit by way of the prootic
fenestra whose boundaries are the prootic pillar and prefacial
commissure. In the cat the fifth nerve leaves the cranial cavity
between the accessory cartilaginous rod and the suprafacial
commissure. Continuity of the anterior part of the otic cap-
sule with a portion of the lateral wall of the cranium in the
cat should make us hesitate in assigning entirely otic boundaries
for the facial canal. The evidence so far indicates possibly that
the foramen faciale in the cat stands in the boundary zone
between the pars cochlearis of the otic capsule and the cranial
wall, represented by the suprafacial commissure. Such a rela-
tion is in harmony with that which obtains in reptiles, to the

PRIMORDIAL CRANIUM OF THE CAT 363

extent that the foramen for the facial nerve stands between a
sense capsule (otic) and cranial wall (basal plate).

In accordance with our observations, the cochlear capsule in
the cat is developed in connection with the pars canalicularis
and with the suprafacial commissure which gives evidence of
being, in part at least, a parietal structure. The cochlear cap-
sule chondrifies independently of the basal plate, with which it is
secondarily united by commissures. Its precocious growth and
great bulk encroach upon the broad region occupied in lower
vertebrates by the basal plate. If we can, on the evidence given,
interpret the suprafacial commissure as a parietal structure in
the cat, it would appear that its relation to the cochlear capsule
(continuity) affords support to the theory (Gaupp) of the latter
having preempted the territory of the basal plate and developed
at its expense.

Foramina acustica and meatus acusticus internus. The acustic
foramen or fissure and the entrance to the facial canal are estab-
lished early in the development of the otic capsule. These
openings lie between the suprafacial commissure behind and,
in the 23.1 mm. stage, are found at the bottom of a shallow in-
ternal acustic meatus. The single acustic fissure is constricted
in its middle so as partly to separate two wide divisions accommo-
dating the vestibular and cochlear nerves. Completely sepa-
rated foramina were not observed in any of the stages studied.
Comparable with this form of acustic nerve entrance is the
single dumb-bell shaped foramen which Mead has described in
Sus. In the rabbit (Voit) and the dog (Olmstead) there are
separate foramina for the vestibular and cochlear nerves. In
the cranium of Talpa of the stage described by Fischer there are
also two separate acustic foramina; but in younger embryos
Noordenbos found a round porus acusticus internus, in the
bottom of which openings for the cochlear and vestibular nerves
were not clearly separated on account of lack of chondrification.
The persistence of a single opening in the cat speaks for tardy
development of the medial wall of the ear capsule, a tendency
characteristic of the lower vertebrates. The relative positions
of the foramina, one to the other, or of the nerves, where a single

364 ROBERT J. TERRY

opening exists, while in general constant for mammals, shows an
interesting variation in the cat. In mammals these openings lie
approximately one above the other, so that a superior and an
inferior acustic foramen, for the vestibular and cochlear nerves
respectively can be spoken of. In the cat, at the stage of 23.1
mm. the vestibular nerve occupies the antero-lateral part of the
fissure; the cochlear nerve the medio-caudal end. The antero-
posterior order of the acustic rami recalls the condition in rep-
tiles. Although a common meatus for the two divisions of the
acustic nerve occurs in birds (Tonkoff, ’00) this is separate
from the exit of the facial nerve, and therefore is not compar-
able with the internal acustic meatus of mammals, which in-
cludes separate passages for the vestibular and cochlear rami
and for the nervus facialis. The development of the internal
acustic meatus begins very early and seems to be a result, not
of a depression of the medial otic wall, but, as Voit remarks,
of the elevation of the surrounding cartilaginous parts. In the
cat, the elevations are made by the suprafacial commissure
anteriorly, the otic extremity of the basivestibular commissure
posteriorly and the prominentia utricularis dorsally and later-
ally. These three parts rise above the level of the cochlear
roof and form three sides of the meatus acusticus internus and
porus acusticus. The low, medial and ventral side is the roof
of the cochlea. Of these three elevations, that of the supra-
facial commissure is most prominent and is probably the chief
factor in determining the presence of the meatus.

Foramen perilymphaticum. Since Fischer’s (’03) description
of the derivation of the aquaeductus cochleae and fenestra
cochleae from the perilymphatic foramen, several observations
have been made by other investigators concerning this interest-
ing phenomenon. Fischer found in an embryo Semnopithecus
that the downward directed opening at the basal side of the ear
capsule was divided into two parts by a process which sprang
from the anterior margin of the opening and extended backward.
The larger lateral part looked out from the free outer surface
of the skull and was closed by thick membrane; it was identified
as the fenestra cochleae. The medial smaller opening, on a

PRIMORDIAL CRANIUM OF THE CAT 365

higher plane, looked inward, was traversed by the perilymphatic
duct and was recognized as the aquaeductus cochleae. Follow-
ing his observation, Fischer states that Hertwig’s enlarged
model of the otic region of man shows obscurely the process in
question. I find in this model a free corner of the cochlear wall
projecting forward from the posterior margin of the large fora-
men so as to divide the opening into a large lateral and a very
small medial part. In the rabbit, Voit found the conditions
exactly as Fischer saw them in Semnopithecus and named the
dividing process the processus intraperilymphaticus. Macklin
(14) described the intraperilymphatic process in the human
embryo as a “short conical projection directed forward from the
inferior utriculoampullary prominence.” In the cat, a process
of the caudal wall of the cochlear capsule, adjacent to the
basivestibular commissure, projects laterally, and tends to sepa-
rate the perilymphatic foramen into two parts. We find, there-
fore, that the perilymphatic process in the ape and the rabbit
is directed backward, and in man forward, while in the cat the
process which separates the perilymphatic foramen into intra-
and extracranial openings is directed laterally. If these be
comparable processes they probably indicate, merely, differences
in the place where chondrification begins in the septum dividing
the perilymphatic foramen.

Cavum vestibulare. It is apparent from the foregoing de-
scription of the vestibular cavity that the conditions present in
the embryo of 23.1 mm. are far from what obtains in the adult
mammalan temporal bone. Only on the most general lines
are the form and relations seen in-the bony walled vestibular
spaces of adult cat referable to the conditions of the cartilaginous
otic capsule. Such characteristics of adult structure as the sharp
delimitation of special recesses for the utricle and saccule, ap-
parently are not even indicated in embryos considerably further
developed than those of the stage modeled. Between these
early stages and adult conditions many processes of formation
are involved, about which almost nothing is known.

If the vestibular cavities of the cat embryo of the stages de-
scribed present but few indications of their adult form, they

366 ROBERT J. TERRY

do show a certain agreement with conditions observed in the
lower groups. The tendency to subdivision of the vestibule
into anterior and posterior rooms is strongly suggestive of
the conformation of the cavum vestibulare in Lacerta, as de-
scribed by Gaupp. The contents of the anterior and posterior
vestibular cavities in the cat appear to be comparable with the
parts contained in the cavum vestibulare anterius and cavum .
vestibulare posterius of lizard. The anterior and posterior
acustic foramina in lizard and cat are similarly related to the
vestibular cavities. Furthermore the relative positions of the
two spaces, one to the other, and to the otic capsule as a whole,
are strikingly similar in the two forms. Such a comparison must
accept of necessity the homology of the boundary structure be-
tween the vestibular cavities. In the cat this is the medialward
projecting ventral part of the massa angularis, the part desig-
nated crista intervestibularis. In the lizard it is the septum
intervestibulare. Gaupp describes the latter as a transverse
vertical partition between the two vestibular cavities, presenting
a lateral opening filled with membrane and a medial foramen for
the utriculus. The crista intervestibularis is likewise transverse
in position, but it cannot be called a partition since it fails to
extend entirely across, between the anterior and posterior cavi-
ties. While it possesses no opening, yet, by its failure to reach
the medial vestibular wall, a space is left between the latter
and the free medial edge of the crista, by which the anterior
and posterior cavities are put into communication and which is
occupied by the utriculus.

Lamina parietalis and tectum posterius. Decker (83) found the
parietal plates in cat embryos of 5.5 to 6.1 cm. bent inward, which
is not the case in the younger embryos of the present study;
rather, the dorsal, irregular margins are turned a little laterally.
Decker’s observation is interesting in proving that the parietal
plate participates in the cranial roof, to only a slight extent, as
his figure shows, but, nevertheless, marking an unusual develop-
ment of this part of the cranial wall for mammals. The lamina
supracapsularis of Echidna, remarkable for its great breadthand
its continuity with the ear capsule, is, in its anterior part, com-

PRIMORDIAL CRANIUM OF THE CAT 367

parable with the lamina parietalis of placental mammals, also
to the hinder portion of the taenia marginalis of Lacerta (Gaupp,
’08, b).

Chondrification of the parietal plate independently of the ear
capsule was not observed in the series of Echidna studied by
Gaupp, but it was noted that the plate was separated from the
occipital pillar caudally and from the ala orbitalis rostrally by
stretches of unchondrified tissue. _Noordenbos is apparently the
first to have observed the independent origin of the parietal plate
and its secondary union with other parts of the skull. In Talpa
of 11 mm. this cartilage was dorsad of the ear capsule and im-
mediately in front of the tectum interoccipitale; its union with
the otic capsule occurred very soon after its appearance. Evi-
dently the parietal plate in Talpa does not unite posteriorly with
the occipital arch, but with the tectum interoccipitale. The
latter appears in the mole at the same stage as does the parietal
plate, in the form of an independent piece arched over the cere-
bellar region. Noordenbos observed its union, first with the oc-
cipital arch, then considerably later with the parietal plate. On
account of the primary union with the occipital arch Noordenbos
is inclined to adopt the term ‘tectum interoccipitale’ as more cor-
rectly expressing its relations than the terms ‘tectum synoticum’
and ‘tectum posterius.’ Whether the tectum arises by paired
anlagen in the mole could not be stated; its origin in the rabbit
was observed by Noordenbos to be paired.

In regard to the origin of the parietal plate in cat, I am unable
to present a conclusion, owing to lack of material at a critical
stage in the development of this part. Apparently primary con-
ditions similar to those described for Talpa obtain in Felis. A
cartilage, which I have called lamina parietalis, arises by. paired
beginnings in the form of triangular plates, above the interval
between the occipital arch and pars canalicularis. At a later
stage the parietal plate has united with the lateral occipital arch
and presents a prominent angle toward the mid-dorsal line, which
is the beginning of the tectum posterius. At this stage (15 mm.)
there is a faintly stained tract of cartilage in the region of the
future commissura orbito-parietalis, but extending caudad into

368 ROBERT J. TERRY

the otic region. There remains, however, a wide gap, equal in
extent to the dorsal margin of the ear capsule, between this
tract of cartilage, which I have referred to as the beginning of
the commissura orbitoparietalis, and the parietal plate. Now in
_ the mole, Noordenbos found a cartilaginous plate immediately
anterior to the tectum interoccipitale and identified it as the
parietal plate. It united subsequently with the otic capsule,
opposite the junction of the anterior and middle thirds of the
anterior semicircular canal (synchondrosis parieto-canalicularis),
with the anterior margin and ventral end of the tectum interoc-
cipitale, and also with the ala orbitalis. The last connection
-eame about through the synchondrosis orbito-parietalis, by ex-
tension of the lateral hinder angle of the ala orbitalis.

In sections of cat embryos of 17 mm. a parietal plate of young
cartilage extends from the occipital arch to the commissura or-
bito-parietalis. The arch of the tectum posterius is represented
merely by a prong, springing on either side from the broad plate
of cartilage. forming the caudal end of the parietal plate, and
which is united by stretches of young cartilage with the pars
canalicularis and lateral occipital arch. The anterior end of the
parietal plate, while approaching the otic capsule at the level of
the middle of the anterior semicircular canal, is still not united
with it, but is separated by a plane of mesenchyma. In later
stages (24 to 30 mm.) van Wijhe preparations show that chon-
drification is less advanced, in the narrow part of the parietal
plate, where the inconstant union with the pars canalicularis
occurs (p. 310), and where union has occurred with the occipital
arch and otic capsule. There seems to be no doubt of the car-
tilaginous plates, identified as the beginnings of the parietal plate,
going to form also the tectum posterius (the arch is complete in
the 23.1 mm. stage) and also the posterior part of the parietal
plate. The relation of the commissura orbito-parietalis to the
otic capsule anteriorly (the so-called parieto-capsular commissure)
is evidence of the probable homology of this cartilage with the
parietal plate of Talpa, as described by Noordenbos. There is
no evidence of another center of chondrification between the ter-
mination of the orbito-parietal commissure and the tectum pos-

PRIMORDIAL CRANIUM OF THE CAT 369

terius, and it is doubtful, notwithstanding the great space be-
tween these parts, if another center does develop and enter into
the formation of the parietal plate. In favor of this assumption
is the brief period between the stage when the orbito-parietal
commissure and tectum posterius are separate (15 mm.) and the
stage when they are joined (17 mm.). Apparently, in the cat,
the parietal plate is formed by the coalescence of two cartilages
arising independently, one, mostly anterior to the otic region,
which gives rise also to the larger part of the orbito-parietal com-
missure and to the parieto-capsular commissure; the other dorsad
of the interval between the lateral occipital arch and pars cana-
licularis which unites with these parts, forms the broad caudal
portion of the parietal plate and also gives rise to the tectum
posterius.

Facial and acustic nerves. The suprafacial commissure, form-
ing the roof of the primary facial canal, separates the facial nerve
from the ganglion semilunare. As the seventh nerve (including
the pars intermedia Wrisbergil) leaves the canal, the geniculate
ganglion is formed on its dorsal side. This is in contact with
the ganglion of the trigeminus, both structures lying outside the
plane of the fenestra sphenoparietalis. The lateral opening of this
primary facial canal should be compared with the foramen faciale
of reptiles. A foramen or canal, traversed by the facial nerve
beyond the ganglion geniculi, is a new acquisition for mammals
and not to be found in the reptilian cranium. Such is the stretch
which Fischer (’01) has described in Talpa, roofed over by the
‘‘oanz dimne Knorpelspange”’ (p. 504), separating the proper
facial opening from the hiatus spurius. Also the foramen faciale
externum of the tegmen tympani of the rabbit forms an acquisi-
tion to the primary facial canal, whose lateral opening in the tym-
panum is the apertura tympanica. ‘This conception of the facial
canal is partly in accord with that of Vrolik (73). In the cat,
at the stage modeled, the exit of the primary facial canal is at the
level of the ganglion geniculi (position of the future bony hiatus
canalis facialis) and outside the cavity of the chondrocranium.
In the bony cranium of cat, and probably in later stages of the
chondrocranium, the exit from the cranial cavity is by the aper-
tura tympanica.

370 ROBERT J. TERRY

Regarding the course of the seventh nerve in the sulcus fa-
cialis, it is to be remembered that in adult Felis domestica the
second part of the facial nerve traverses an open groove in the
medial tympanic wall (the rule in mammals), whose lateral bound-
ary is the ossified processus paroticus (crista parotica of van Kam-
pen, ’04). Neither in the embryo nor in the adult does the free
margin of the parotic crest incline toward the vestibular wall in
the formation of a canal. In Felis pardus, however, the nerve
does run in a closed canal (Denker,’99). The groove in the adult
domestic cat begins anteriorly at the apertura tympanica and
terminates posteriorly opposite the level of the tympanohyale.

Finally, reference should be made to the discovery by Spence
(90) in the adult and new born cat of a bony or cartilaginous
support of the chorda tympani, projecting from the tympanic
bone. Bondy (’07) has confirmed this observation, finding the
process not only in cat but in anumber of other mammals. No
evidence of the support was found in the stages described here;
its formation takes place according to Bondy, late in fetal life.

Acustic nerve. Retzius (’84) deseribed the nervus acusticus of
the cat as dividing into two or three chief branches, preferring
two in his account. I found this mode of branching in the cat
embryo of 23.1 mm., and it may be remarked that, in our pres-
ent state of knowledge of the distribution of the acustic nerve in
the cat, the nomenclature of Retzius seems preferable to one
which attempts to represent the origins of the nerve fibers. For,
in the case of the ramus posterior, cells of the vestibular and
spiral ganglia are intimately associated, and no safe conclusion
on the origin of fibers of this ramus can be reached without fur-
ther neurological investigation. The small twig from the an-
terior ramus to the sacculus appears to correspond with the
ramulus maculae sacculi pars superior found by Voit (07) in
Lepus.

Orbito-temporal region
Hypophyseal cartilage. Chondrification of the base of the

cranium in the hypophyseal region has been observed in several
mammals to take place independently of the rest of the chondro-

PRIMORDIAL CRANIUM OF THE CAT 371

cranium. Parker (’75) observed ‘‘a secondary growth of carti-
lage beneath the pituitary body” in Sus. A sphenoidal cartilage,
independent of the occipital skeleton of the ox, is described by
Froriep (’86) as lying beneath the hypophysis. ‘This observation
is confirmed by Noordenbos (’05) who found, moreover, that the
cartilage was paired. Noordenbos has discovered, by van
Wijhe’s method, the origin of the middle piece of the cranial
base by the fusion of several small islands of cartilage in the cra-
nia of mole, rabbit and pig. For these pieces, which surround the
stalk of the hypophysis, Noordenbos has proposed the name
‘msulae polares.’ Wineza (’96) noted the independence of the
cartilaginous basi-sphenoid and alisphenoid (ala temporalis) in
cat. As we have seen, the cranial floor, beneath the hypophysis,
is first represented by a crescentic cartilage, which soon grows
around the stalk of the hypophysis, probably completely sur- °
rounding it, although this was not actually observed. ‘The for-
mation of the sella turcica is brought about by the union of the
hypophyseal cartilage anteriorly with the trabecular plate and
posteriorly with the basal plate, the former contributing the
tuberculum sellae, the latter the crista transversa which is the
beginning of the dorsum sellae.

Fenestra basi-cranialis posterior. The existence of an opening
in the basis cranii between the anterior end of the basal plate
and the hypophyseal cartilage is merely temporary in the cat.
In embryos of 12 mm. the fenestra basi-cranialis posterior has
no lateral limits, since the cochlear capsule is not yet jomed with
the basal plate. The anterior boundary is made by the hypo-
physeal cartilage, so that the fenestra lies, not within the basal
(parachordal) plate, but anterior to it, as Noordenbos insists.

_Crista transversa and dorsum sellae. The crista transversa rep-
resents the anterior, dorsally turned, free edge of the basal plate.
The upward bend of this margin just prior to the fusion of the
basal plate and hypophyseal cartilage, can be seen in sagittal
sections of embryos of 12 mm. and its identity with the crista
transversa proved by sections of 15 mm. specimens in which the
line of fusion of the two plates is still distinct. Noordenbos found
that the dorsum sellae of Talpa is formed from the anterior mar-

372 ROBERT J. TERRY —

gin of the parachordal plate. In the cat, the dorsum sellae is
also in part at least, derived from it, but probably the greater
part is derived from the mesenchyma above the crista transversa
and in front of the end of the notochord, in which the small
cartilaginous nodule was found in the smaller embryos.

Let us consider briefly some observations regarding the dor-
sum sellae. I believe no comparative study of its formation
has been made. This structure reaches a high development in
man and apes. Fischer (’03) found in a Macacus embryo the
upper border isolated from the rest of the dorsum sellae, lying as
a transverse bar, and terminating laterally in the posterior cli-
noid processes. This author also points out that in the adult
human cranium a groove or ridge stands between the dorsal
border and the clivus and puts forth the suggestion that this
‘ structure, isolated in Macacus, is probably genetically foreign
to the basal plate. Voit (09) supports this view by the discov-
ery in Lepus of a partial separation of the dorsal part of the sad-
dle-back by a wide foramen from the rest of that structure. Faw-
cett (10) found in human embryos of 19 and 21 mm. a rounded
mass of cartilage, behind the pituitary body, connected with the
clivus region by a fibrous bridge; he concluded that the dorsum
sellae arises independently inman. In his study of the primordial
cranium of Talpa, Fischer (01) found the hypophyseal fessa to be
a slight depression and noted the absence of a dorsum ephippii.
Noordenbos (05) speaks of a weakly developed dorsum sellae
turcicae in mole embryos and states that it is a structure of the
parachordal plate. This investigator observed that in embryos
of 11 mm. the caudal end of the polar plate, lay somewhat be-
neath the cranial end of the parachordal plate. With the union
of these parts the hypophyseal fossa is formed, limited posteri-
orly by the projecting anterior end of the parachordal plate.

Fischer’s and Voit’s observations point to the origin of the up-
per part of the dorsum sellae as possibly distinct from the basal
plate in Macacus and Lepus, and, according to Fawcett, the ori-
gin of the dorsum sellae in man is from an independent center of
chondrification. Noordenbos found the dorsum sellae of Talpa
as a product of the parachordal (basal) plate. These, observa-

PRIMORDIAL CRANIUM OF THE CAT 373

tions suggest the possibility of the dorsum sellae of different spe-
cies not being strictly homologous. Gaupp says (’00, p. 538)
“Dass die hinten begrenzende Crista sellaris, wie sie bei dem
Chondrocranium der Saurier (und auch bei dem der Vogel)
vorkommt, der Sattelsehne des Saiugercranium entspricht, ist
allgemein anerkannt.’”’ But does the crista sellaris of reptiles
compare with the dorsum sellae of mammals? And are the latter
strictly homologous in the different orders of mammals?

This is not the time for a full discussion of these questions
which requires a larger basis of observations, but a few comments
may be offered. Regarding the homology of the dorsum sellae
among the mammals the following may be noted. The saddle- -
back of the chondrocranium of Echidna (Gaupp ’08), Talpa (Noor-
denbos, ’05), Caluromys and Didelphis (my own observation) is
very low. As already stated, Fischer denies its presence alto-
gether in the Talpa embryo he studied. In contrast with the
insignificant low ridge-like dorsum ephippii of these species is
the high saddle-back of the chondrocrania of man, apes, rabbit
and cat. In all these species evidence is at hand indicating the
presence of an element in the dorsal part of the saddle-back, more
or less independent of the base of that structure. In embryos
of cat smaller than the stage modeled, the notochord terminates
in a mass of mesenchyma which surmounts the crista transversa,
whereas in the latter stage it ends in the perichondrium of a car-
tilaginous tubercle which rises from the middle of the transverse
crest. This tubercle is developed from the mesenchymal mass,
and may possibly have its beginning in the prochondral nucleus
observed in the embryos of earlier stages (p. 327). In the cat
embryo of. the stage modeled, the dorsum sellae is formed to
some extent also from the up-turned edge of the parachordal
plate (crista transversa). It would seem, in respect to the con-
trast between the caudal limits of the hypophyseal fossa in the
two groups here presented, that there is an element present in
the one which is not found in the other, or that in one group a
simple crista transversa forms the back of the pituitary fossa,
whereas in the other a crista transversa plus an additional ele-
ment enters into the construction of a dorsum sellae.

374 ROBERT J. TERRY

There is nothing in the model of the cat embryo to indicate
the presence of post-clinoid processes, which are found in the
bony cranium and are therefore formed later. These processes.
in connection with the processus interclinoideae, Voit regards as
vestiges of the primitive cranial wall in this region. Interclinoid
processes have often been observed in the adult cranium of man,
and Fischer has noted them in the chondrocranium of Macacus.

Foramen hypophyseos. The foramen hypophyseos is converted
into a canal by the growth in thickness of the floor of the sella
turcica. In embryos of 17 mm. the stalk of Rathke’s pouch is
still intact as it lies in the canal. In the floor of the sella turcica
. of the stage modeled, the hypophyseal canal is present, but only
vestiges of the stalk are apparent in it. Arai (’07) has described
a bony walled canalis cranio-pharyngeus in the cat, containing
a vein and a hypophysis accessoria cranio-pharyngei; also an
epithelial-lined blind canal interpreted as a possible vestige of
the stalk of Rathke’s pouch. Voit has criticised Arai’s homology
of the cranio-pharnygeal canal and the hypophyseal foramen in
the rabbit, asserting that the former is a secondary development,
occurring in a position caudad of the location of the hypophyseal
foramen. This criticism is not pertinent in the cat; the foramen
and the canal have the same location.

Ala temporalis. Wineza (’96) described the boundary line be-
tween the alisphenoid and basisphenoid (properly lingula) in
embryos of the cat. My observations are in accord with this
description; a zone of perichondral tissue standing between a
chondrified processus alaris of the basis cranii and a broad car-
tilaginous plate, ala temporalis, in relation to the Gasserian gan-
glion. The complete independence of the alisphenoid in the cat
led Wincza to investigate its relation to the cranium in other
mammals with the following results: In the dog embryo, a sepa-
rating zone was found between the cartilaginous alisphenoid and
basisphenoid; in embryos of the polar bear complete separation
of the two parts, with a small wedge-shaped cartilage in the
cleft; in man, a joint between alisphenoid and basisphenoid, re-
calling the relation between the head of the femur and the ace-
tabulum; in hedgehog embryos a boundary between the basi-

PRIMORDIAL CRANIUM OF THE CAT 375

and alisphenoid behind, both parts united in front in three of
the stages studied. Wincza’s observations have since been con-
firmed for man by Levi (00), Gaupp (02) and Fawcett (’10);
for the dog by Olmstead (11). Noordenbos (05), Voit (09) and
Fuchs (’10) have seen the separating zone in Lepus. Noorden-
bos also found the ala temporalis a free process in the pig and
horse. A characteristic of the synchondrosis between alisphe-
noid and basisphenoid of the cat described by Wincza, is its
oblique course from behind, forward and medialward. Whether |
the obliquity is a constant feature of the separating zone of the
ala temporalis in other forms studied by Wineza is not specfi-
cally stated. Figure 8 of Wincza’s paper shows a cleft separating
the two parts in the polar bear, having the same direction as
the boundary zone in the cat. Macklin (714) found in a 40 mm.
human embryo that the connection between the lateral portion
of the ala and the processus alaris took place between the ven-
tral surface of the latter and the subjacent ala.

In contrast to the type of independent ala temporalis there has
been observed another type, characterized by its continuity with
the basis cranil. Wincza saw no trace of a boundary between
basisphenoid and alisphenoid in the chondrocranium of embryos
of the horse, pig, sheep and calf. Noordenbos, however, as just
stated, disagrees with the observation on the horse and pig;
he finds the ala temporalis in mole to be a process of the side
of the sella turcica. In Echidna, Gaupp identified the ala tem-
poralis in the small continuous process which springs from the
side of the sella turcica, laterad of the carotid foramen.

From these records we learn that, in a variety of mammals,
the ala temporalis is more or less distinct from the rest of the
cranium, being separated from a basal process by a stratum of
some tissue other than cartilage, or even by a cleft of greater or
less extent; whereas in others the ala is a simple process continu-
ous with the cranial base. Furthermore, Noordenbos, from his
own observations, recognizes two types of embryonic origin of
the ala temporalis in mammals; one type. represented by the
mole, in which the ala arises as a lateral process of the pole-plate;
the ‘other type, represented by the rabbit, wherein the ala arises

376 ROBERT J. TERRY

independently and unites secondarily with a process (processus
alaris) of the margin of the sella turcica.

Of the many questions yet unanswered regarding the signifi-
cance and relations of the ala temporalis, one only will be dis-
cussed here. The cat belongs to the type in which the temporal
wing is more or less separate from the rest of the cranium, and
in which the connection is an indirect one through a processus
alaris. The successive stages of development of the ala tempor-
alis in the cat seem to throw some light on the nature of the
differences between the temporal wing of the continuous type
and that of the separate type. The following discussion deals
with this question.

We may first compare the development of the ala temporalis
in the two types, i.e., the one in which the temporal wing is con-
tinuous with the rest of the cranium and that in which it is more
or less separate. For the first, Talpa may be chosen as an ex-
ample; for the second, the cat. The following results have been
brought out. by Noordenbos in his study of the mole. In embryos
of 12-13 mm. three lateral processes at the side of the pole-plate
(basisphenoid) are described. With the posterior one of these
processes (basicochlear synchondrosis) we are not here concerned.
The intermediate process, knee-formed, extends from the pole-
plate in front of, and then bends laterally around, the carotid
artery passing backward to join the cochlear capsule. The an-
terior process ends free. In embryos of 14 to 17 mm. the latter
has grown so as to come into relation with the Gasserian gan-
glion. In still older embryos (17-19 mm.) the anterior imb and
knee of the middle process grow out in connection with the an-
terior process to reach the under surface of the semilunar ganglion
and thus is formed the ala temporalis. ‘‘This little plate is
connected with the lateral margin of the basisphenoid through
the processus anterior and the anterior limb of the processus in-
termedius.”’ Noordenbos states that the largest part of the ala
temporalis is contributed by the anterior lateral process of the
pole-plate; a small part arises from the knee of the middle lateral
process. Union of the two elements of the ala occurs in embry-
os of 20 to 25 mm., but there remains for a long time, a small

PRIMORDIAL CRANIUM OF THE CAT 377

fissure-like opening in the root of the ala as the last vestige of the
original gap between the anterior and middle lateral processes of
the pole-plate. The middle process, the synchondrosis spheno-
cochlearis lateralis, is, in its caudal half, the part named by
Fischer in a later stage the ‘trabecula alacochlearis.’ Noorden-
bos has shown, however, that the trabecula alacochlearis geneti-
cally has its anterior connection, not with the ala, but with the
basisphenoid, and only secondarily unites with the hinder mar-
gin of the root of the ala temporalis. |
Let us consider now, the development of the ala temporalis in
the cat and compare it with that of the mole, taking as a point
of departure the stage of 17 mm. In the cat there arises from the
side of the sella turcica, a precartilaginous bar, which bends about
the carotid artery, its anterior limb (processus alaris) crossing
transversely in front of the vessel, its posterior limb (commissura
alicochlearis) extending backward upon the side of the artery
and joining the cochlear capsule. Here, then, are elements
present in both mole and cat which are in agreement in several
important relations. In order further to identify this combined
alar process and alicochlear commissure of cat with the middle
process of mole, it should be recalled that it is derived from the
commissural element of the earliest stage (12 mm.) the relations
of which to the base of the cranium, to the cochlear capsule and
to the carotid artery are equivalent to the relations of the middle
process of mole at its first appearance (12 to 13mm.). Compar-
ing, next, the relations of the middle process of mole and the
precartilaginous derivative of the commissural element in cat,
with parts lying laterally, there is present in each case an ele-
ment, separate from the process under consideration, related to
the semilunar ganglion. In Talpa this element, derived from
the anterior process, grows out alongside the anterior limb of the
middle process, from which, however, it is at first separate. It
is noteworthy that the -former extends somewhat caudally as
well as laterally, and, in conformity therewith, the space inter-
vening between it and the middle process extends from behind,
forward and medialward. In embryos of 20 to 25 mm. these
two, pieces of the ala temporalis unite, the anterior limb of the

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

378 ROBERT J. TERRY

middle process being thereby taken into the root of the ala. In
cat embryos of 17 mm., the ala temporalis, the derivative of the
mesenchymal alar element in relation to the Gasserian ganglion,
stands lateral to and in front of the anterior limb of the com-
missural element from which, however, it is separated by a layer
of mesenchyma (p. 329). Caudally the ala temporalis is sepa-
rated from the posterior limb of the commissural element by the
space which later results in the incisura lacera. The lamina
presents then an oblique line of junction with the anterior limb
of the commissural element, extending from behind, forward and
medially. Later stages (23.1 mm.) as already described, show
along this line a persistent sign of the separation of ala tempor-
alis and the arch made by the processus alaris and alicochlear
commissure, in the perichondral boundary zone first described
by Wincza. The anterior process, which in mole forms the
greater part of the ala temporalis, is entirely separated by an
interval from the anterior imb and knee of the middle process
for a time; the alar element, which in the cat forms the entire
ala temporalis, is separated from the commissural element by an
interval (incisura lacera) only in its caudal part. It will be re-
called that Wincza found in the polar-bear the alisphenoid sepa-
rated from the basi-sphenoid by a cleft which, as the figure shows,
runs from behind forward and medialward. Also the same au-
thor found in the hedgehog a limiting zone in the posterior part
only of the ala temporalis. :

Apparently the alar element of the cat and the anterior lat-
eral process of the pole-plate of the mole are, in several respects,
comparable. The one real difference between the alar element
of the cat and the anterior process of the mole lies in the relation
of these parts to the side of the sella turcica: in the mole the ele-
ment in question is connected medially with the sella; in the cat
it passes medially into the commissural element, without inde-
pendent connection, if any at all, with-the side of the sella tur-
cica. There is a reduction, if not entire absence, of a medial
part of the alar element, next to the hypophyseal cartilage com-
parable with the root of the anterior process of mole.

PRIMORDIAL CRANIUM OF THE CAT 379

The differences between the independent ala temporalis of the
cat and thé continuous ala of the mole are apparent rather than
real. A very simple explanation removes these apparent differ-
ences. 1) The alar element of the cat is wanting in a medial
part, comparable with the origin of the anterior process from
the pole-plate in the mole. Excepting in the undifferentiated
mesenchymal continuity of the alar element and anterior limb
of the commissural element, there is no indication of a connection
between it or its derivative, the ala temporalis, and the side of
the sella turcica. 2) The processus alaris is compound in the
mole, being derived from the root of the anterior process plus
the anterior limb of the middle process; it is simple in the cat,
being composed of the anterior limb of the commissural element
only. The processus alaris of the cat is therefore comparable
with only the caudal part of the ala temporalis of the mole, i.e.,
with that part derived from the anterior limb of the middle
process. 3) The alar element of the cat and its derivative fails
to unite with the commissural element and its derivatives, and
there remains throughout the cartilaginous stage of the ala tem-
poralis, a synchondrosis representing the limiting margins of the
two elements. In the mole, partial fusion takes place between
the comparable elements, but a cleft-like vestige remains locat-
ing the original separating space. Perhaps the conditions in
the hedge-hog and bear described by Wincza may be similarly
explained.

The conclusions reached therefore are: 1) the reduction or the
absence of a medial part of the alar element of the cat, compara-
ble with the origin of the anterior process from the sella turcica
of mole; 2) the presence of a simple processus alaris in the cat,
of a compound one in the mole; 3) the persistence of the original
boundary between the lateral and commissural elements in the
cat and the obliteration of the limits between the comparable
anterior and middle processes in the mole. It follows that the
ala temporalis of mole and cat are in the main comparable. It is
probable that other examples of the types of continuous and inde-
pendent temporal wings may be similarly explained.

380 ROBERT J. TERRY

Whether the lamina ascendens of the cat should be regarded
as an independent element in origin, or continuous with the basis
cranii, is a question which could be answered either way from the
evidence here presented, and would be purely a choice of inter-
pretations. The whole ala temporalis is shadowed in mesen-
chyma, continuous with the basis cranii; in this adumbration
condensations appear which are distinct from one another or
confluent at the edges, as you choose to describe the conditions.
Comparison of the lateral element of the cat with the anterior
process of the mole inclines me to regard this element and its
derivative, the ala temporalis, as not an independent element
genetically. There appear to be two parts under consideration
in comparisons of the ala temporalis of different mammals, (1)
a part which is related chiefly to the carotid artery, represented
by the middle process of the mole and the commissural process
of the cat; (2) a part which is related to the semilunar ganglion
and the three divisions of the fifth nerve. These two parts
are typically both connected with the cranial base, the one arch-
like, the other process-like. Both are typically originally sepa-
rate from one another, the process standing in front and at the
side of the arch. In some forms the process unites with the arch
completely (mole), in others partially (hedge-hog), in still others
not at all (polar-bear, cat). Finally, this conception of the com-
parison of the anterior process of mole and the ala temporalis of
cat, supports the homology of the ala temporalis of placental
mammals with the ala temporalis of Echidna.

Pterygoid. The pterygoid cartilage is developed relatively late,
not until after bone has begun to be formed in its dorsal part. It
is represented by a rather ill-defined mesenchymal condensation,
even at the time when the ala temporalis is well chondrified.
Only its caudal part is cylindrical and thus bears some resem-
blance to the cartilage of the medial lamella of the pterygoid proc-
ess in Talpa. It is unlike this process in not reaching forward to
the ethmoidal region. However, as pointed out, it develops in
the same morphological plane as the palate bone, lies next the
ductus nasopharyngeus, in front of the first peaeyees pouch
and is crossed dorsad by the Vidian nerve.

PRIMORDIAL CRANIUM OF THE CAT 381

Jayne (’98) has described, in the skull of the adult cat, a ptery-
goid process presenting a well defined internal pterygoid plate or
process and a variable external plate or process. Union of the
originally separate pterygoid bones with the alisphenoid takes
place very early, and sutures or lines indicating their boundaries
cannot be found in the adult. The pterygoid elements are rep-
resented therefore, as processes of the alisphenoids. Reighard
(02) describes an external pterygoid muscle, taking origin from
the external pterygoid fossa whose surface includes the lateral
aspect of the external pterygoid plate of Jayne, and an internal
pterygoid muscle springing from the internal pterygoid fossa; the
latter is bounded in part by the medial surface of the external
plate. The internal pterygoid plate terminates in a hamular
process, related, in the usual manner, to the tendon of the ten-
sor palati. The origin of these two bony processes was found in
the present study in cat embryos of 7 em., and 23.1 mm., the
external process being an extension of the endochondral ossifica-
tion of the pterygoid process of the ala temporalis, the internal
process consisting of an ossification, at first in membrane and
subsequently in cartilage, in connection with the separate ptery-
goid cartilage. The latter accords with an early stage of the
human internal pterygoid plate as described by Fawcett (’10),
both in its early ossification (it is the first part of the sphenoid to
ossify in the cat) and in the ossific process, proceeding primarily
in membrane and later in cartilage. The external plate is feebly
developed in the cat, but its ossification in relation to that of the
ala temporalis is nevertheless, in principle, the same as in man.
It will be remembered that the Vidian nerve runs along the mes-
enchymal junction of the pterygoid cartilage and pterygoid proc-
ess of the ala temporalis; now, although no suture or line can
be found in the adult skull indicative of the original limit of the
pterygoid bone toward the alisphenoid, as Jayne has stated, yet
the course of the bony walled Vidian canal of the adult can be
taken as marking this boundary.

Carotid foramen. The epipteric cavity in the cat embryos is
limited, toward the primary cranial cavity, by a membrane whose
relations to the base of the skull are of considerable interest as

382 ROBERT J. TERRY

affecting the question of the nature of the region about the ca-
rotid artery. In Echidna the carotid enters directly the primary
cranial cavity, but the position of the foramen through which it
passes lies within the lateral confines (trabecula basis cranii) of
the hypophyseal fossa and therefore may be compared with the
entrance into the cranium of this vessel in Lacerta. In placental
mammals the carotid foramen lies laterad of the sella turcica, a
position which has been explained by two assumptions: (a) lat-
eral migration of the vessel, (b) non-equivalency of the mammal-
jan and reptilian carotid. In accordance with the theory of lat-
eral migration, the carotid foramen is supposed to have moved
outward across that part of the cranial floor equivalent to the tra-
becula; or both the trabecula and artery have moved lateral
while still retaining their primitive relations to each other. The
trabecula cranii of Lacerta is represented in mammals, accord-
ing to Gaupp (’02), by the alicochlear commissure. The unity
of this commissure, including both the processus alaris and com-
missura alicochlearis, its distinction from the ala temporalis, and
its relation to the base of the cranium were recognized by Gaupp.
In one place (’06), he says: ‘‘The processus alaris of man appears
as a process only through the decadence of the cartilaginous
bridge which closes laterally the carotid foramen. It belongs to
the median cartilaginous mass in the base of the orbito-temporal
region.”’ Voit, who has advocated the view of non-equivalency
of the internal carotid in mammal and reptile, locates the carotid
foramen in Lepus laterad of the trabecular region. He concludes
that the commissura alicochlearis plus the processus alaris alae
temporalis should not be compared with some part of the tra-
becula, but rather the processus alaris should be referred to the
processus basipterigoideus of Lacerta and ala temporalis of
Echidna. The commissura alicochlearis is regarded by Voit as a
new structure, in mammals, in the floor of the epipteric cavity, a
continuation of the floor of the cavum supracochleare. Fuchs
(10) also, compares the medial part (root) of the ala temporalis
with the processus basipterigoideus of reptiles. In accordance
with Voit’s interpretation, the carotid artery first enters the epi-
pteric cave, then, after traversing the medial limiting membrane

PRIMORDIAL CRANIUM OF THE CAT 383

of the cave, comes into the primary cranial cavity. Recently, De
Burlet (713) has brought forward evidence of the carotid in Pho-
caena traversing the trabecula or its equivalent. In the por-
poise the carotid passes directly into the primary cranial cavity.
As we have seen, the limiting membrane in the cat is fixed to the
basis cranii, neither to one or the other side of the carotid fora-
men, but broadly over the region where the vessel enters. It is
attached both to the alicochlear commissure and to the lateral
margin of the sella turcica. The former does not, in the cat,
enter into the floor of the cavum epiptericum, nor does the ca-
rotid artery pass directly into the primary cranial cavity. The
vessel first traverses that part of the membrana limitans which
is fixed to the cranial floor, before passing into the original cavity
of the skull. As to the homology of the commissura alicochlearis,
it is evident that if the processus alaris is not included as a part
of it, the difficulty of comparing the commissure with the tra-
becula cranii is much increased; if the alar process be recognized
as the continuation of the alicochlear commissure forward, in
continuity with the median basal cartilage of the orbito-temporal
region, the comparison is far less difficult. Reviewing the con-
clusions stated above, we may note, first, that the name commis-
sura alicochlearis is a misnomer, since it does not express the true
relation of the commissura, but implies a connection with the
ala temporalis which does not exist in the mammals so far studied.
Secondly the studies of Noordenbos on the mole and my own on the
cat show that the so-called processus alaris may be simple or com-
pound in different animals, but that it is primarily a part of the
commissura alicochlearis (its anterior end in fact), continuing into
the median basal cartilage; relation of the processus alaris to
the ala temporalis is secondary and obtains in those types (mole)
where the ala springs from the basal cartilage; its root, at first
separate from, later becomes fused with the processus alaris to
produce the compound form of alar process. When the ala
temporalis is independent of the basal cartilage (cat) the former
has nothing to do with the processus alaris, which then is the
simple extension forward of the commissura alicochlearis into
the sella turcica.

384 ROBERT J. TERRY

A word may be said regarding the membranous structure here
called septum transversum. The development, in its basal part,
of a marked thickening which extends from the crista transversa
to the parietal plate, together with the presence in it of a carti-
laginous bar over the semilunar ganglion are suggestive of struc-
tures in the reptilia, such as Shino (14) has described in the
crocodile and compared with the pila prootica of Lacerta. A
cartilage over the semilunar ganglion in Lepus recorded by Voit
was interpreted as a vestige of the primary cranial wall; in the
cat, a cartilaginous mass, having the same position and relations,
was found within the septum transversum.

Ala orbitalis. The occurrence generally, in a wide range of
types, of the independent origin of the ala orbitalis has been em-
phasized by Noordenbos. This phenomenon; as shown above, is
also characteristic of the cranial development of the cat. The idea
of the association of the ala orbitalis, primarily with the optic
nerve and eye-ball, seems to be well founded and receives further
support from the early form and relations of this cartilage in the
cat. The relations of the origins of the ocular muscles may be
interpreted as further indicating a close connection between the
orbital wing and the organ of sight. The definitive origins of
these muscles are in the main related to the optic foramen, about
as they are in the chondrocranium, but some shifting has evi-
dently taken place as comparison of the two states shows (Wilder
and Gage ’86; Corning ’02). Four definite separate spots in the
chondrocranium, are occupied by, and one of them apparently
specially adapted to, the attachment of the muscles of the orbit.
How these attachments compare with those in the mammalian
types represented in the literature of the chondrocranium I can-
not say, since this question does not seem to have received atten-
tion. Does the superior oblique constantly spring from the
preoptic root; does the orbital process of the metoptic root
function generally as a point of attachment of a definite group of
eye-muscles; is the side of the basis cranii in the orbital fissure
a special locus of origin of another group, and is the origin of
the inferior oblique constantly the planum antorbitale? Regard-
ing the metoptic root, it has been noted that, in contrast to the

PRIMORDIAL CRANIUM OF THE CAT 385

straight direction of the preoptic, it presents a marked bend, convex
caudally. This curveis apparent to a slight extent in the bony
cranium. Judging from figures of the chondrocranium of several
mammals, the bend in question seems to be a characteristic of this
cartilaginous rod. In cat the knuckle of the curve apparently mark
the place of union of the metoptic process of the trabecular plate
and the corresponding process of the ala orbitalis. Opposite this
spot the oculo-motor nerve leaves the cranium by the orbital fissure.
What significance there is in the form and relations of the metop-
tic root, which are early established and permanently retained,
must await future inquiry.

Ethmoidal region

Region of the olfactory fenestra. The floor of the condrocranium
of mammals, between the levels of the preoptic root of the ala
orbitalis and the fenestra olfactoria, is made by the lamina infra-
cribosa, which is the roof of the posterior cupola of the nasal cap-
sule and an extension of the planum antorbitale.. The lateral
branch of the naso-ciliary nerve runs upon this lamina on its way
toward the interior of the nasal capsule, having come through
the spheno-ethmoidal fenestra from the orbit. The lamina cri-
brosa, a structure peculiar to mammals, develops over the fenes-
tra olfactoria. Now, in reptiles the ethmoidal nerve and the .
whole of the posterior cupola, with the olfactory fenestra, are
extracranial. <A study of these contrasting conditions of the mam-
malian and reptilian ethmoidal skeletons has led Gaupp to the
conclusion that a new region, named by him recessus supracri-
brosus, has been added to the mammalian brain case, and that
this region is comparable, in reptiles, with the extracranial parts
about the olfactory fenestra. In the cat, the form and relations
of the posterior cupola and olfactory fenestra are essentially as
in other mammals. The fenestra olfactoria opens directly into,
the chondrocranial cavity. As already stated, the lamina cri-
brosa was not present in the stages of the cat studied, conse-
quently no data have been presented bearing on the question of
its position relative to the walls of the chondrocranium. The

386 ROBERT J. TERRY

lamina infracribrosa is a part of the antorbital division of the nasal
capsule, entering into the floor of the cranium. The course of
the ethmoidal nerve is, strictly speaking, outside the chondro-
cranial cavity, since the layer of mesenchyma (probably in part
giving rise to dura), which covers the lamina infracribrosa, stands
between it and the cerebral cavity. In the cat, in the stages
studied, there is no overhanging anterior wall of the chondrocran-
ium such as is shown in the model cf Echidna; a flat anterior
margin of the fenestra olfactoria marks the anterior limit of the
cranial cavity. Consequently, the term ‘recessus’ supracribro-
sus is hardly appropriate for the cat; the term ‘supracribrous
region’ is preferable. From these data, it seems that the eth-
moidal region of the cat, ike the orbito-temporal and otic re-
gions, gives evidence in support of Gaupp’s assertion of the non-
equivalency of reptilian and mammalian crania, and also, by its
relations to the chondrocranial cavity, indicates that the latter
is enlarged over that of reptiles by the acquisition of a region
wholly extracranial in that class. A factor having a large share
in bringing about this mammalian characteristic is the backward
growth of the nasal cavity (Weber, ’04; Gaupp, 08) whereby the
interorbital septum is encroached upon by the posterior cupola
of the ethmoidal skeleton. That this occurs to a slight extent
in the ontogeny of the cat was indicated by the difference in posi-
tion of the posterior cupola relative to the preoptic process. in
earlier and later embryonic stages.

In Lepus, according to Voit, the foramina of the lamina cri-
brosa are separated into two groups by a crista intercribrosa, ol-
factory filaments from the recessus lateralis traversing the foram-
ina of the antero-lateral group, those from the recessus posterior
(ethmoturbinal region) passing through the holes of the postero-
medial group. Voit also found the dorsal end of ethmoturbinal
I continuous with the crista mtercribrosa. Continuity between

-these two parts is present in Caluromys philander, as observed
by Dr. Denison in’ this laboratory. In the cat, at the stage
modeled, the dorsal end of ethmoturbinal I is very prominent
and stands between the group of olfactory filaments coming from
the epithelium of the recessus lateralis and those from the ethmo-

PRIMORDIAL CRANIUM OF THE CAT 387

turbinal region. The latter group is further subdivided by the
dorsal end of ethmoturbinal II into two bundles coming, one from
the area in front of, the other from the area behind this turbinal
process.

The floor of the nose and Jacobson’s cartilage. In cat embryos of
the stage modeled, the secondary palate is nearly complete, form-
ing a floor for the nasal cavities. The latter are separated from
each other by the septum nasi, excepting for a stretch poste-
riorly, where the ventral margin of the nasal partition is free
from and above the level of the palate. Between the maxillo-
turbinal dorsally and the nasal floor is a broad groove of the
lateral nasal wall, which extends from before backward to the
choanae. This groove, the inferior meatus of adult anatomy,
the lower furrow of Legal (’83) or the choanal passage of Fleisch-
mann and Beeker (’03), besides differing from the other nasal
passages by its origin from the primitive mouth, is specialized
through its relation to the naso-lacrimal duct and Jacobson’s
organ. A striking feature of this ventral part of the cavum nasi
is the variability among mammals of its cartilaginous walls and
floor. ‘This characteristic stands in marked contrast to the usual
condition of stability of the dorsal part of the ethmoidal skeleton
(Spurgat, ’96).

The peculiar characteristics of the nasal floor cartilages in the-
cat have been described by several investigators. Our observa-
tions must be regarded as confirmatory of Broom’s (’96) descrip-
tion and of Zuckerkandl’s (’08) more recent representation of the
paraseptal and related cartilages. Both of these authors found
an inner and outer division or process of the nasal floor cartilage
(lamina transversalis anterior) and a cartilage related to the
nasopalatine duct.

The significance and homology of these parts of the ethmoidal
skeleton have been much discussed. Division of the lamina trans-
versalis anterior, into medial and lateral cartilages (inner and
outer parts of the nasal floor cartilages) embracing the nasopala-
tine duct, has been observed by Broom (’96) to oceur with con-
siderable constancy in the mammalian series. The outer por-
tion of the nasal floor cartilage stands lateral to the nasopalatine

388 ROBERT J. TERRY

canal. In Ornithorhynchus and Echidna this cartilage expands

at its caudal end and unites with its fellow across the midline ~

to form a broad plate beneath the organ of Jacobson and its
cartilaginous capsule. The conditions in the Marsupialia were
traceable to those of the monotreme type. In Lepus, as repre-
senting the rodents, Broom found an independent cartilage sup-
porting the outer side of the nasopalatine canal, which was ho-
mologized with the outer nasal floor cartilage of the Monotremes,
and was regarded as a much modified form, compared with the
simple higher eutherian type. Voit has also described, under the
name cartilago nasopalatina, the supporting cartilage for the naso-
palatine duct in the rabbit, and, with Gaupp, compares it with
the processus palatinus (outer nasal floor cartilage of Broom) of
HKehidna. |

This comparison is founded by Voit mainly on the fact that in
certain mammals (horse, pig and sheep) the processus palatinus
(cartilago basalis lateralis as described by Spurgat, ’96) is united
with the lamina transversalis anterior (processus septi cartilaginei
lateralis ventralis) in the same relationship as is the case with the
processus palatinus of Echidna; and further, that in at least one
form, Vesperugo noctula, described by Grosser (’02) the ‘carti-
lagines posteriores laterales’ (cartilagines nasopalatinae of Voit)
are considerably broadened posteriorly and fused across the
median line, as is true for the palatal processes of Echidna.

Two conditions, presented by the cat, seem to indicate that the
significance of the nasopalatine cartilage and the processus pos-
terior lateralis of the lamina transversalis, is not fully brought
out by the above comparisons. These conditions are (a) the
presence, at the same time, of two separate cartilages, one in re- .
lation to the nasopalatine duct (nasopalatine cartilage) the other
in the floor of the nose next to the entrance of the nasopalatine
duct (posterior lateral process of the transverse lamina); and (6)
the independent origin of the former. Furthermore, in regard to
the first condition, it seems evident, from Grosser’s description
of Vesperugo, that both paired nasopalatine cartilages (cartilago
ductus incisivi) and posterior lateral cartilages are prepatit and
separate, the one pair from the other.

PRIMORDIAL CRANIUM OF THE CAT 389

A eartilage, having the position and relations to the nasopala-
tine duct and to the anterior transverse lamina, such as presented
by the posterior lateral cartilage of Vesperugo and the lateral
process of the lamina transversalis anterior of Felis, is of fre-
quent occurrence in the mammalian series. It stands as a sup-
port to the floor of the nose at the outer side of the entrance to
the nasopalatine duct and probably possesses, as Grosser says, a
great significance as a supplementary structure to the palate.
It is found in forms in which a nasopalatine cartilage (as here
defined) does not exist, notably in mammals having a very short
nasopalatine duct (Echidna) and also in forms where the naso-
palatine cartilage is present, in which cases it may be separate
from or united with the latter.

In accordance with this view, the processus palatinus of
Kchidna would be comparable with the posterior lateral cartilage
of Vesperugo, the lateral process of the lamina transversalis
anterior of Felis, and not with the cartilago ductus incisivi of
these forms. The primary relation of the nasopalatine cartilage
(cartilago ductus incisivi), on the other hand, appears to be
directly with the nasopalatine duct, asin the cat. There is some
evidence in the series of mammals of its correlation with the
presence of a long nasopalatine canal. Absence of a nasopala-
tine cartilage in the lower mammals and its independent origin
and late appearance in development in the cat may be interpreted
as indicating that it is phylegenetically a recent acquisition to
the palatal skeleton, and also that its connection with the lateral
posterior cartilage may be regarded as secondary.

Jacobson’s cartilage, relatively short, arises independently, as
recorded by Schwink (’88) and as observed in the present study,
and remains ununited with other parts of the chondrocranium in
embryos of the cat up to 23.1 mm. In later stages, as Zucker-
kandl has observed, this cartilage has elongated and taken on
connections with the lamina transversalis posterior, through the
development of a slender paraseptal rod. Zuckerkandl believed
that Jacobson’s cartilage represents the anterior half of a carti-
laginous ridge which is derived from the primitive floor of the
nose. This is in accord with Seydel’s (’99) conception of the

390 ROBERT J. TERRY

paranasal cartilage forming a part of the primitive nasal floor
which, by reduction, came eventually to be represented by more
or less separate parts (Jacobson’s cartilage) in the mammals.
In the light of this interpretation, the slender cartilaginous para-
septal strip which appears late in the development of the cat,
and unites Jacobson’s cartilage with the posterior transverse
lamina, may be regarded as evidence of a partial restoration of
the primitive floor.

Tectum nasi. Noordenbos has observed the beginning of the
tectum nasi in mole embryos of 9 mm. as bilateral divisions of
the anterior margin of the trabecular plate, forming curved
lamellae. In the dorsal middle line a shallow groove stands be-
tween the two halves of the tectum. In the cat the nasal tec-
tum arises apparently similarly in connection with the nasal
septum, as the parieto-tectal cartilages, although, as already
mentioned, some evidence of the independent origin of these car-
tilages was presented. ‘The groove between them, dorsad of the
septum, is the beginning of the sulcus supraseptalis. In the
cat, the parieto-tectal cartilages grow back, along the dorsal mar-
gin of the septal cartilage, as far as the fenestra olfactoria, becom-
ing gradually narrower from side to side and assuming the form
of triangular plates. These cartilages contribute the entire roof
of the precerebral division of the nose and the side wall anterior
to the recessus lateralis. What the relations of the parieto-tectal
are to the development of the lamina transversalis anterior were
not determined. Eventually a complete zona annularis is es-
tablished behind the level of the fenestra narina, the roof being
derived from the parieto-tectal cartilage, the floor from the
lamina transversalis anterior, the lateral wall from the union of
these two parts. The relations of the lateral margin of the parieto-
tectal with the anterior free margin of the paranasal cartilage are
at first similar to those in Talpa, as observed by Noordenbos.
This cartilage does not seem to be concerned in the formation of
the maxilloturbinal, although in the stage of 23.1 mm. this proc-
ess is connected with the anterior part of the lateral nasal wall
through the lamina supraconchalis. Within the nasal cavity the
atrioturbinal appears as the inrolled ventral margin of the
parietotectal cartilage.

PRIMORDIAL CRANIUM OF THE, CAT 391

Paranasal cartilage. Independent origin of a plate of carti-
lage lying in the anterior part of the lateral wall of the nose has
been observed by Noordenbos in embryos of Talpa of 9 mm.
length; also in the embryos of calf and pig. Following Mihal-
kovies, the cartilage was called cartilago paranasalis. InTalpa,
the paranasal cartilage and the tectum nasi are separated by a
fissure, bounded by the anterior border of the former and the
free margin of the latter. In the cat, also, an independent para-
nasal cartilage occurs which bears similar relations to the parieto-
tectal cartilage. It is directly over that diverticulum of the
cavum nasi which later is included in the recessus lateralis of the
ethmoidal skeleton. The little cartilaginous plate, bent upon
the convex bulging of the nasal sac, presents free margins: one
toward the side of the olfactory lobe; one backward toward the
eye; a ventral margin, and a long anterior side, opposite the free,
oblique edge of the parieto-tectal cartilage; relations comparable
with those observed in the mole. ,

Great interest attaches to the ventral and anterior margins of
the paranasal cartilage. The latter overlaps the parieto-tectal,
and, whereas in younger embryos it is separated from that car-
tilage by a fissure, it is later fused with it. The result of this
fusion is a curved, intranasal ridge, the crista semicircularis, per-
forated by the foramen epiphaniale, which is the remains of the
original fissure. Thus is explained the position and extent, quite
to the olfactory fenestra, of the semicircular crest. It follows
from its mode of formation that, in later stages, the crista semi-
circularis may be taken as the boundary between two originally
distinct territories of the nasal wall. During the period occupied
by the process of fusion of the incurved anterior margin of the para-
nasal and the hinder margin of the parieto-tectal cartilage, and
for some time thereafter, an interval of variable extent (derived
from the space of the original separating fissure) is enclosed
within the encompassing cartilaginous margins; that is, for a
time the crista semicircularis presents double walls with an inter-
vening space; this space is crossed by the lateral nasal nerve at
the level of the future epiphanial foramen.

392 ROBERT J. TERRY

Now in the nasal capsule of Lacerta, at the place where the
zona annularis joins posteriorly the broader, bulging portion of
the side wall, a conchal fold is present, projecting into the nasal
cavity; within the aditus conchae, or entrance to the conchal
fold is the foramen for the lateral nasal nerve. The fissure-like
aditus extends dorso-ventrad, its convex lateral margin overhang-
ing the medial margin made by the zona annularis. Gaupp says
’ of it (00, p. 484): An der Muscheleinstiilpung sind zwei Lameilen,
eine mediale und eine laterale, zu unterscheiden. Die mediale
Lamelle der Concha liegt in der direkten Fortsetzung der Seiten-
wand der vorderen Nasenkapselhilfte, sie endet ventral mit
freiem Rande. . . . . Die laterale Lamelle der Concha
geht ventralwiirts in den Boden des Recessus extraconchalis
tiber.

The aditus, in Lacerta, lodges the external nasal gland; its
duct passes forward across the outer side of the zona annularis
to enter the nasal mucosa through a gap in the side wall of the
nasal capsule, behind the processus alaris superior. Finally,
the concha itself forms a ventral and anterior partial partition
between the general space of the nasal capsule and a lateral
diverticulum which Gaupp has named the recessus extraconchalis.
The incomplete floor of the recessus is made by the ventral
prolongation of the lateral lamella of the concha.

It seems evident that in the stage of development of the
ethmoidal skeleton in cat when fusion is occurring between the
parieto-tectal and paranasal cartilages, certain conditions are
presented which reflect the structure of the reptilian nasal cap-
sule, as shown by.the embryo of Lacerta. The general direc-
tion of the space between the parieto-tectal and paranasal car-
tilages on the one hand, and the aditus conchae on the other,
is the same, and its boundaries are made by lamellae similarly
placed in respect to each other; it is traversed by the lateral
nasal nerve in both forms. The position of the external nasal
gland in the aditus conchae of Lacerta and of the externally
coursing duct is, apparently, impossible to reconcile, on our
present knowledge, with the lateral nasal gland of Felis and the
intranasal course of its duct, if these glands be comparable at

PRIMORDIAL CRANIUM OF THE CAT 393

all. Peter (06) seems to regard the mammalian gland as a
new acquisition. It will be remembered, however, that the lat-
eral nasal gland in the cat embryo of 23.1 mm. is located just in
. front of the base of the crista semicircularis.

Next, we may attempt to compare that part of the nasal wall
(paranasal cartilage), which stands just behind the fissure in
the cat, and the aditus conchae in lizard. We have seen that
the commissura spheno-ethmoidalis unites, in cat embryos of
17 mm., with the dorsal margin of the paranasal cartilage,
where the latter bounds the olfactory fenestra, thus presenting
relations which recall those between the posterior half of the
side wall of the nasal capsule and the cartilago spheno-eth-
moidalis of Lacerta. For, at the junction of these parts, in the
cranium of the lizard, the lateral wall limits by its upper margin
the olfactory fenestra while, medially, it passes into the posterior
wall, the planum antorbitale, as is also true for the cat. It
has been noticed that the ventral and anterior margins of the
paranasal, are continuous inrolled edges, which form the: car-
tilaginous maxillo-turbinal and, with the free posterior. margin
of the parieto-tectal cartilage, form the beginning of the crista
semicircularis. In Lacerta, the part of the side wall in question
goes over anteriorly into the lateral overhanging plate of the
bilaminar concha, the medial plate of which is the direct continua-
tion of the side wall of the anterior half of the nasal capsule.
Furthermore, the lateral plate passes ventrally into the floor of
the recessus extraconchalis. Of great interest is the resemblance
between the concha and floor of the recessus extraconchalis of
Lacerta on the one hand and the crista semicircularis and maxillo-
turbinal of the cat on the other.

_ This comparison brings out a certain degree of similarity of
form and relation between the skeletal parts of the region of the
recessus extraconchalis of Lacerta (embryo of 31 mm. total
length) and of the recessus lateralis of the cat (embryos of 17-
20 mm.). An opinion as to a possible homology between these
parts should not be ventured on a comparison limited to the
data here presented. Greater knowledge of the development of
the ethmoidal skeleton in the lizard is required, and additional

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

394 ROBERT J. TERRY

data on the history of the paranasal cartilage in mammals is
essential.

As to the origin of the lamina supraconchalis and the broad
base of the naso-turbinal, unfortunately little evidence was found.
The region of the side wall occupied by these parts corresponds
to that between the antero-inferior quarter of the paranasal
and the adjacent region of the parieto-tectal cartilage. I can-
not say to what extent, if at all, these two cartilages enter into
the lamina supraconchalis and naso-turbinal.

One other matter should be mentioned with which, possibly,
the paranasal cartilage may be related—the origin of the in-:
ferior oblique muscle. In the adult cat, this muscle arises from
the orbital surface of the maxilla behind the lacrimal bone
(Reighard, Jayne, Corning). In the embryo of 23.1 mm. its
origin is from a prominent angle of the lateral nasal wall, at the
junction of the paries nasi and planum antorbitale. In the
17 mm. embryo this angle corresponds with the ventral inferior
corner of the paranasal plate, overlapping the anterior margin
of the antorbital plate. Now, although no posterior maxillary
process is developed in cat in the stages studied, yet the angle
here referred to possibly represents this process. I have not
noted in the literature the origin of the inferior oblique from the
chondrocranium in mammals. Corning (’02), quoting Weber
on its origin in Lacerta viridis, says (p. 122): ‘‘Der M. obliquus
inferior ‘entspringt von der Cartilago ethmoidalis, wo diese sich
an den Knochen der vorderen Orbitalwand ansetzt.’ ”’

Lamina antorbitalis. Noordenbos is apparently the only one
who has observed in mammals the isolated origin of the carti-
lage forming the posterior part of the nasal capsule. This ele-
ment of the ethmoidal skeleton, found in mole embryos of 10.5
mm. and 11 mm., finds its parallel in the cat, where, as stated,
a separate plate of cartilage forms the planum antorbitale and
cupola posterior. Union between the antorbital plate and the
paranasal in the cat must take place rapidly, as no trace of an
interval between the two parts is to be seen in embryos of 20
mm. Complete union, that is, fusion, with the septal cartilage
is not present in the embryo of the stage modeled. Of much in-

PRIMORDIAL CRANIUM OF THE CAT 395

terest is the relation of the antorbital plate to the ethmoturbinal
bodies. A well developed, epithelial ethmoturbinal fold can be
seen behind the recessus lateralis in embryos of 15 to 17 mm.
We have seen that the posterior margin of the paranasal carti-
lage overlaps the anterior edge of the antorbital plate, and that
the latter projects forward and medialward into the base of the
epithelial fold of ethmoturbinal I. Sections show that the an-
terior, free cartilaginous extremity of this ethmoturbinal, in
embryos of 23.1 mm., is formed, in connection with mesenchyma,
within the fold of epithelium and independently of the wall of
the nasal capsule. The mesenchyma can be followed, however,
backward to the base of the fold and to the ridge of cartilage
derived from the antorbital plate of earlier stages, which
bounds posteriorly the opening into the recessus lateralis.

The development of the ethmoidal skeleton in the cat indicates
a certain degree of correlation between its cartilaginous com-
ponents and regions of the nose more or less sharply defined by
particular functions. The dorsal, larger, and more completely
walled division includes the olfactory and paranasal territories
and the atrium opening toward them; whereas the ventral,
smaller and imperfectly formed division stands in relation to
the respiratory air passage, nasopalatine and lacrimal ducts.
Even the original components of the dorsal division present evi-
dence of specific adaptation to functional territories. Thus, the
antorbital plate forms the wall of the ethmoturbinal territory
of distribution of the olfactory nerve, the paranasal cartilage in-
closes the diverticulum of the lateral recess, later the frontal
sinus; and the parieto-tectal develops into the wall of the atrium.
I do not wish to imply that the evidence at hand justifies the
conclusion of rigorous specificity of these components, it cer-
tainly does not; but facts are sufficient to indicate that each of
these original cartilages is, in the main, developed in relation
to recognized functional territories of the nose.

396 ROBERT J. TERRY

SUMMARY

1. The basal plate of the occipital region in the cat is derived
from a pair of parachordal cartilages and from two, probably
three, hypochordal commissures or arches. The parachordals
are continuous with the lateral occipital arches and, topo-
graphically, are to be compared with the lateral masses of
the atlas. Chondrification of the perinotochordal sheath in the
occipital region forms the apex of the dens epistrophei, which,

in certain respects, is comparable with a vertebral centrum.
2. The observations on the developmental processes of the
occipital region in the cat indicate that, in principle, they are
comparable with those of an atypical vertebra of the atlas kind.
The basal plate of the occipital region falls into the category of
arch structures, not centra.

3. In the atlas, the beginning of an atlantal foramen is very
early indicated by a notch, traversed by the first spinal nerve,
the sides of which are formed by the neural arch and a process
of the lateral mass. The possible significance of this atlantal
process was discussed. |

4. The occipital condyles are located primarily on that part
of the basal plate derived from the parachordal cartilages and,
in accordance with the interpretation of the form of the occipital
element, belong to arch structures and not to centra.

5. The position of the lateral occipital arches and the plane
of the foramen magnum, parallel with the floor of the nose in
embryos of 23.1 mm., is correlated with flexures, in a sagittal
plane, of the cranium as a whole.

6. The fissures around the otic capsule, between it and the
basal plate and walls of the chondrocranium in the 23.1 mm.
embryo, are vestiges of the spaces primarily existing between
these independently arising cranial elements.

7. The incisura occipitalis posterior of the cat embryo is in-
termediate in relative size between that of the reptile (Lacerta)
and that of man. There is apparently a tendency for this space
to increase in area from lower to higher forms.

PRIMORDIAL CRANIUM OF THE CAT 397

8. The upright position of the axis of the otic capsules in
cat embryos of the stage modeled is exceptional for mammals.
There is evidence in the literature that the obliquity of the otic
axis characteristic of the mammalian chondrocranium is attained
at somewhat different periods of development in different
species.

9. The origin of the cartilaginous pars canalicularis of the
otic capsule is independent of other parts of the cranium. The
pars cochlearis arises in connection with the pars canalicularis
and the suprafacial commissure. The latter is continuous with
the orbito-parietal commissure, and is therefore, in part at
least, to be regarded as a parietal structure. The cochlear cap-
sule forms independently of the basal plate, which in the cat is
reduced to a narrow bar in the otic region. The observations
on the relationship of the cochlear capsule to the basal plate
and suprafacial commissure are interpreted to support Gaupp’s
theory on the development of the cochlear capsule and reforma-
tion of the cranial base.

10. A single acustic fissure, transmitting the two divisions
of the acustic nerve, is situated at the bottom of a shallow inter-
nal acustic meatus. The latter results, principally, from the
elevations of the suprafacial commissure and commissura basi-
vestibularis, these forming its anterior and posterior walls.

11. The fenestra cochleae and aquaeductus cochleae result

from the division of the foramen perilymphaticum by a process
extending from the cochlear capsule.
_ 12. The cavum vestibulare of the cartilaginous otic capsule
of the cat is comparable with that of the reptile (Lacerta) in
possessing two subdivisions, a separating partition and similar
relations to parts of the membranous labyrinth.

13. The lamina parietalis seems to be derived from two inde-
pendently arising centers of chondrification, an anterior one,
which also constitutes the orbito-parietal commissure and
unites with the otic capsule in the parietocapsular commissure;
and a posterior center which unites, first, with the summit of
the lateral occipital arch and, next, with the pars canalicularis.
From the posterior center (called parietal plate in the descrip-

398 ROBERT J. TERRY

tion) the tectum posterius apparently arises as a process. The
definitive parietal plate seems to be the result of the fusion of
the anterior and posterior elements.

14. The facial nerve makes its exit from the chondrocranium
by the primary facial foramen, at which spot is located the
geniculate ganglion and the origin of the great superficial petrosal
nerve. The primary facial foramen is to be regarded as com-
parable with the foramen faciale of Lacerta.

15. The floor of the hypophyseal fossa is formed from a single
crescentric cartilage arising independently.

16. In the cat a small. space, filled with mesenchyma, existing
for a brief period, between the anterior end of the basal plate
and the hypophyseal cartilage, is identified as a fenestra
basicranialis posterior.

17. The dorsum sellae in cat is formed from the crista trans-
versa and, in addition, by chondrification of the mesenchyma
dorsad of it, probably by a separate center. There is evidence
in the literature that the dorsum sellae of the lower mammals is a
derivative of the crista transversa alone, while that of the
higher mammals includes an additional element.

18. The development of the ala temporalis of the cat, repre-
senting the type of discontinuous ala, is comparable with that
of mole, representing the type of ala temporalis continuous with
the sella turcica. The difference between these forms of ala
is an apparent one, resulting from failure of the root of the
temporal wing of the cat to form in cartilage. The synchon-
drosis between the ala temporalis and alicochlear commissure
and the incisura lacera of cat, the foramen or fissure between ala
and commissure in other forms, indicate the plane of junction
between these originally independent and different parts. The
ala temporalis of cat is comparable with the ala temporalis of
Kchidna.

19. A pterygoid element appears in the cat as a condensation
of mesenchyma, in which ossification is occurring at the stage of
the 23.1 mm. embryo. Cartilage is subsequently developed, in
which ossification proceeds. There is evidence of two ossific
centers, and from these the medial pterygoid lamella and
hamular process are formed.

PRIMORDIAL CRANIUM OF THE CAT 399

20. A cavum epiptericum and cavum supracochleare are recog-
nized in the chondrocranium of cat. The names ‘membrana
limitans’ and ‘septum transversum’ are proposed for the mesen-
chymal:sheets connected with the walls of the orbito-temporal
region. In the cat the internal carotid artery enters the mem-
brana limitans, by the carotid foramen, and secondarily into the
primitive cranial cavity. A bar of cartilage in the septum trans-
versum, lying upon the semilunar ganglion, is probably a eviaas
of the primitive chondrocranial wall.

21. The ala orbitalis arises independently in the cat na
unites secondarily with the paranasal cartilage, orbitoparietal
commissure, and trabecular plate. It is apparently primarily
adapted to the eyeball and its adnexa.

22. A region, extracranial in reptiles, is represented within
the chondrocranium of cat as the supracribrous region of the
ethmoidal skeleton.

23. The structure of the anterior part of the floor of the nose
is in agreement with the descriptions of Broom and Zucker-
kandl. The nasopalatine cartilage of mammals is interpreted
as a structure originally distinct from the lateral posterior car-
tilage of the nasal floor, and its connection with the latter
secondary.

24. Jacobson’s cartilage in the cat is the anterior, well de-
veloped, portion of a paraseptal cartilage, connected posteriorly
with the lamina transversalis posterior.

25. The cartilaginous ethmoidal skeleton of the ae is sepa-
rated on developmental grounds and physiological relations,
into a small ventral part and a large dorsal part. The former
presents incomplete walls about the inferior meatus; the latter
rather continuous walls about the paranasal sinuses and olfactory
region of the nose.

26. The dorsal part of the ethmoidal skeleton in ae to the
stage of 30. mm. is formed from the septal cartilage, parieto-tectal
cartilages, paranasal cartilages and the laminae antorbitales.

27. The parieto-tectal cartilages, paired, spring from the septal
cartilage. They contribute the roof of the precerebral division
of the ethmoidal skeleton, the side wall of the atrial region,

400 ROBERT J. TERRY

participate in forming the crista semicircularis and probably, to
some extent, give origin to the alar cartilages.

28. The paranasal cartilages, paired, arise independently and
are primarily adapted to the diverticula of the recessus laterales.
They participate with the parieto-tectal cartilages in the forma-
tion of the semicircular crests and in the origin of the maxillo-
turbinal processes. From this cartilage the inferior oblique
muscle of the eye arises.

29. The foramen epiphaniale is the vestige of the original
space between the parieto-tectal and paranasal cartilages.

30. The lamina antorbitalis, paired, arises independently,
and unites secondarily with the paranasal and septal cartilages.
From it are formed the posterior cupola and the bases of the
ethmo-turbinals I and II.

31. The ethmoidal skeleton of cat may be compared with that
of Lacerta as follows: the region of alar cartilages in the cat and
the anterior zone of the lizard; tectum nasi and lamina trans-
versalis anterior of the cat with the zona annularis of the lizard;
the combined paranasal and antorbital parts of the cat with
the posterior zone of the saurian.

PRIMORDIAL CRANIUM OF THE CAT 401

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EXPLANATION OF FIGURES

All figures are from preparations of embryos of the cat, the lengths of which
are indicated. With the exception of figures 17 and 18, the drawings are the
work of Mr. C. D. Jarrett.

In the model from which figures 1 to 5, 12, 13 have been made, cartilaginous
parts only are represented on the left side; on the right side, in addition, are
shown vessels, nerves and bones. In figures 1 and 2, the right otic capsule is
represented as partly opened. In figure 3, the incudal cartilage and part of
Meckel’s cartilage have been omitted. Figures 15 to 30 are camera lucida draw-
ings of the sections represented. Figures 19 to 30 are from sections of the 23.1
mm. embryo (H. E. C. Series 466); the number of the section is indicated in
each figure.

Fig. 1. From a model of the cranium of an embryo 23.1 mm. long (H. E. C,
Series 466) Dorsal aspect, X 32.

Fig. 2 The same; ventral aspect.

Fig. 3 The same; left lateral aspect.

Fig. 4 The same; right lateral aspect.

Fig. 5 From a van Wijhe preparation of the head of an embryo 10.5 mm.
long (W. A. C. No. 310). Dorsal aspect, x 22.

Fig 6 From a van Wijhe preparation of the head of an embryo 12 mm. long
(W. A. C. No. 311). Left side and base seen from the right, 43.

Fig. 7 From a van Wijhe preparation of the head of an embryo 15 mm. long
(W. A. C. No. 312). Dorsal aspect, x 43. The breadth of this is somewhat
exaggerated, the ala temporalis being too far toward the side.

Fig. 8 From van Wijhe preparations of the heads of embryos 18-20 mm.
long (W. A. C. Nos. 313, 314). Dorsal aspect, 4}.

Fig. 9 From a van Wijhe preparation of the head of an embryo 24 mm. long
(W. A. C. No. 315). Right occipital and otic regions seen from the left. In
this, as in all the van Wijhe preparations, the cochlear capsule is for the most
part only lightly stained. x 12.

Fig. 10 From a model of the left otic capsule. of an embryo 23.1 mm. long
(H. E. C. Series 466). The large, cut surface is in a frontal plane through the
middle of the vestibule. Dorsal and medial aspect, X 2°.

Fig. 11 The same as figure 10, excepting the level of the cut surface, which
is at the ventral part of the vestibule.

Fig. 12 Region of the foramen rotundum as it appears in the model of the
23.1 mm. embryo. Ventral and caudal aspect, * 4°.

Fig. 13 Ethmoidal skeleton; from the model of the 23.1 mm. embryo. Rep-
resents the left half from its medial aspect, the septal cartilage being omitted
and the nasal tectum, laminae transversales and lamina infracribrosa sectioned
just to the left of and parallel with the median plane. X 23.

Fig. 14 From a model of the basal plate and epistropheus in median section
showing the course of the notochord. Embryo 23.1 mm. long. X 2°.

Fig. 15 Transverse section through the occipital region. Embryo 10.6 mm.
long (H. E. C. Series 476, sect. 300). X 45.

405

Fig. 16 Frontal section through base of orbito-temporal region.
12 mm. long (H. E. C. Series 403, sect’s. 200-207).
Fig. 17 Median sagittal section through base of cranium.
long (H. E. C. Series 400).

Fig. 18 Median sagittal section through base of cranium. Embryo 15 mm.
long (H. E. C. Series 487, sect’s. 158, 161, 169). X 4°.

Fig. 19 Frontal section through occipital and otic regions. (Sect. 246).
eee

Fig. 20 Frontal section through occipital and otic regions. (Sect. 253).
ye

Fig. 21 Frontal section through the otic region. (Sect. 256). X 42.

Fig. 22 Frontal section through the otic region. (Sect. 273). X 4.

Fig. 23 Transverse section through the orbito-temporal region. (Sect. 300).
xe:

Fig. 24 Transverse section through the orbito-temporal region. (Sect. 339).
a

Fig. 25 Transverse section through the orbito-temporal and ethmoidal regions.
(Sect. 385). xX 43.

Fig. 26 The same as in figure 25 but further forward. (Sect. 404). x 4.

Fig. 27 Transverse section through the ethmoidal region. (Sect. 457).
x< 1S,

Fig. 28 Transverse section through the ethmoidal region. (Sect. 489).
ee:

Fig. 29 Transverse section through the ethmoidal region. (Sect. 492).
Baie

Fig. 30 Transverse section through the ethmoidal region. (Sect. 513).
x 15, :

ABBREVIATIONS

VI, abducent nerve Can.sem.post., canalis semicircularis

XI, accessory nerve
Ac.fis., acustic fissure
VIII, acustic nerve
Al.orb., ala orbitalis
Al.temp., ala temporalis
Alar., alar element

20
x 22.

Amp.a., ampulla anterior
Amp.l., ampulla lateralis
Amp.p., ampulla posterior

Ant.pl., antorbital plane

Aq.coc., aquaeductus cochleae

Pr.at., atlantal process
At., atlas

- Atrt., atrioturbinale
Bas.pl., basal plate

Can.sem.ant., canalis
anterior

Can.sem.lat., canalis
lateralis

semicircularis

semicircularis

Embryo
eee
Embryo 12 mm.

posterior
Car.for., carotid foramen
Cav.epipt., cavum epiptericum
Cav.coc., cavum cochleae
Cav.nas., cavum nasi
Cav.vest.ant., cavum
terius
Cav.vest.post., cavum vestibulare pos-
terius ;
Cent.at., centrum of atlas
Cent.ep., centrum of epistropheus
Ch.tym., chorda tympani
Co.cap., cochlear capsule
Co.d., cochlear duct
Com.alic., commissura alicochlearis
Com.bas., commissura basicochlearis
Com.basiv., commissura basivestibu-
laris
Com.el., commissural element

vestibulare an-

406

Com.orb.-par., commissura orbito-par-
ietalis

Com.p.-cap., commissura parieto-cap-
sularis ,

Com.sph.-eth., commissura spheno-eth-

moidalis

Com.supr.f., commissura suprafacialis

Cr.int.orb., crista interorbitalis

Cr.intervest., crista intervestibularis

Cr.par., crista parotica

Cr.sem., crista semicircularis

Cr.trans., crista transversa

Den., dens epistrophei

Dent., dentale

Dor.se., dorsum sellae

D.co., ductus cochlearis

D.sem.a., ductus semicircularis anterior

D.sem.l., ductus semicircularis lateralis

D.sem.p., ductus semicircularis poste-
rior

Endl.d., endolymphatic duct

Ep., epistropheus

Eth. I, ethmoturbinal I

Eth. IT, ethmoturbinal IT

Ext.meat., external auditory meatus

Oc., eyeball

VII, facial nerve

Fen.acust., fenestra acustica

Fen.bas., fenestra basalis

Fen.bas,post., fenestra basicranialis
posterior

Fen.nar., fenestra narina

Fen.olf., fenestra olfactoria

Fen.sphen.-par., fenestra spheno-pari-
etalis

Fen.vest., fenestra vestibuli

Fis.alicoch., fissura alicochlearis

Fis.bas.post., fissura basicochlearis pos-
terior

Fis.orb.-eth., fissura orbito-ethmoidalis

For.co., foramen cochleae

For.endl., foramen endolymphaticum

For.epiph., foramen epiphaniale

For.fac., foramen faciale

For.hyp., foramen hypophyseos

For.jug., foramen jugulare

For.jug.sp., foramen jugulare spurium

For.mag., foramen occipitale magnum

For.peril., foramen perilymphaticum

For.rot., foramen rotundum

Fos.inc., fossa incudis

Fos.oc-can., fossa occipito-canalicu-
laris

Front., frontal bone

Gen.gang., geniculate ganglion

TX, glossopharyngeal nerve

Gr.sup., great superficial petrosal nerve

Hi.sem., hiatus semilunaris °

Hyp.ar.at., hypochordal arch of atlas

Hyp.can., hypoglossal canal

XII, hypoglossal nerve

Hyph.can., hypophyseal canal

Hyph.cart., hypophyseal cartilage

Hyph., hypophysis

Inciv., incisive bone

Inciv.d., incisive duct

Inc.lac., incisura lacera

Inc.lacr., incisura lacrimalis

Inc.maz.atr., incisura maxillo-atrio-
turbinalis

Inc.occ.ant., ineisura occipitalis ante-
rior

Inc.occ.post., incisura occipitalis pos-
terior

Tnc.oval., incisura ovalis

Inc.posttr., incisura postransversalis

Inc.sing., incisura singularis

Inc.cart., incudal cartilage

Inf.ac.for., inferior acustic foramen

Inf.obl.m., inferior oblique muscle

Infr.n., infraorbital nerve

Int.car.art., internal carotid artery

J.O., Jacobson’s organ

Jug.v., jugular vein

Lam.ant., lamina antorbitalis

Lam.asc., lamina ascendens

Lam.infracr., lamina infracribrosa

Lam.par., lamina parietalis

Lam.suprch., lamina supraconchalis

Lam.trans.ant., lamina transversalis
anterior

Lam.trans.post.,
posterior

Lat.m.at., lateral mass of atlas

Lat nas.gl., lateral nasal glands

Lat.nas.n., lateral nasal nerve

Lat.occ., lateral occipital arch

Mand.cond., mandibular condensation
of ala temporalis

Mand..n, mandibular nerve

lamina transversalis

407

M, massa angularis

Mast., masseter muscle

Maz., maxillary bone

Maz.cond., maxillary condensation of
ala temporalis

Maz.n., maxillary. nerve

Macturb., maxilloturbinal

Meat.ac.int., meatus acusticus internus

Meat.inf., meatus inferior of the nose

Meat.s., meatus supraconchalis

Meck., Meckel’s cartilage

Memb.lim., membrana limitans

Met.opt., metoptic root

Mo., mouth

N.L.D., naso-lacrimal duct

Nas.ph.d., nasopharyngeal duct

Nasturb., nasoturbinal

Neu.ar.at., neural arch of atlas

Neu.ar.ep.. neural arch of epistropheus

Noto., notochord

Cond.occ., occipital condyles

ITT, oculo-motor nerve

Olf., olfactory nerve

Oph., ophthalmic nerve

Op.for., optic foramen

II, optic nerve

Pal., palate bone

Pal.mazx., palate process of maxilla

Para.pl., parachordal plate

Parna.cart., paranasal cartilage

Para.cart., paraseptal cartilage

Par.nas., paries nasi

Par.-tect., parieto-tectal cartilage

Pa.atr.; pars atrialis

Pa.can., pars canalicularis

Pa.co., pars cochlearis

Pa.lac., pars lacrimalis

Phary.pch., pharyngeal pouch I

Pl.suprch., planum supracochleare

Post.cup., posterior cupola

P.opt., preoptic root

Pre.al., processus alaris

Pre.max.art., processus maxillaris an-
terior

Prc.orb., processus orbitalis

Pre.para., processus paracondyloideus

Pre.pty., processus pterygoideus

Prm.lat., prominentia lateralis

Prm.utr., prominentia utricularis

Prm.ut.inf., prominentia utriculo-am-
pullaris inferior

Prm.ut.sup., prominentia utriculo-am-
pullaris superior

Pty.cart., pterygoid cartilage

Pty.n., pterygoid nerve

Pty.m., pterygoid muscle

Rec.amp.ant., recessus ampullaris an-
terior

Rec.amp.post., recessus ampullaris pos-
terior

Rec.lat., recessus lateralis

Rec.lat.inf., recessus lateralis inferior

Rec.lat.sup., recessus lateralis superior

Reich., Reichert’s cartilage

Sac., sacculus

Sel.iur., sella turcica

Sem.gang., semilunar ganglion

Sept., septal cartilage

Sep.sp., septum spirale

Sept.tr., septum transversum

Sph.-orb.fis., spheno-orbital fissure

Sph.p.gang., sphenopalatine ganglion

Sp.N.I, Spinal Nerve I

Sp.N.II, Spinal Nerve II

Sq., squamosal

St., stapedial cartilage

Stp.m., stapedius muscle

Sule.ch., suleus chiasmaticus

Sulc.fac., sulcus facialis

Sulc.lat.ant., sulcus lateralis anterior

Sulc.lat.post., sulcus lateralis posterior

Sulc.sig., sulcus sigmoideus

Sulc.sp., sulcus spiralis

Sulc.suprach., sulcus supraconchalis

Sulc.supr.. sulcus supraseptalis

Sup.ac.for., superior acustic foramen

Tect.nas., tectum nasi

Tect.post., tectum posterius

Temp.m., temporal muscle

Trab., trabecular plate

V, trigeminal nerve

IV, trochlear nerve

Tub.eph., tuberculum ephippii

Tub.jug., tuberculum jugulare

X, vagus

Vert.a., vertebral artery

Vo., vomer

Utr., utriculus

Zyg., zygomatic bone

408

PRIMORDIAL CRANIUM OF THE CAT PLATE 1
ROBERT J. TERRY

ee ee

i

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Com. sph. eth._

Met. opt.

ROT TO

Sel. tur, _

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1
409

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

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ROBERT J. TERRY

Fen. nario" 2 are 2

Lam, trans. ant.

Inciv.l 2 eee

= = See a)
Max... See = 2 otis or =Ere. max. ant
SS a eee Pat r

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PRIMORDIAL CRANIUM OF THE CAT PLATE 5
a ROBERT J. TERRY

JUG. Vv.

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BP LAT. OCC.

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‘ ; ; a f Z

~ NEU AR. EP

417

PRIMORDIAL CRANIUM OF THE CAT PLATE 6
ROBERT J. TERRY

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PRIMORDIAL CRANIUM OF THE CAT PLATE 7
ROBERT J. TERRY

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/
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=

421

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PRIMORDIAL CRANIUM OF THE CAT PLATE 8
ROBERT J. TERRY

: 1
(Lav. vest. post
i Endl. d
D. sem. I. ' eae
. x a ).
Sera :
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y ut. sup.
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j
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i 5
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10
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'
! M
. et !
i
: vest. ant.
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f
{
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, a
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Inf. ac. for. Sup. ac. for,

11
425

PRIMORDIAL CRANIUM OF THE CAT PLATE 9
ROBERT J. TERRY

ZAP
Co. cap. lor. co. Meck
|
i

i
!
|
|
1
t
|
\

Reich.

Fis. bas. P— Sulc. fac.

post.

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pea |
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f U j

| Nasturb. |
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t

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B@ornaspilwetire| 79
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Lam. infracr. Lam. trans. post. Para. cart.) Pre. max. ant.
13
425

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

PRIMORDIAL CRANIUM OF THE CAT PLATE 10

ROBERT J . TERRY

PRIMORDIAL CRANIUM OF THE CAT PLATE 11
ROBERT J. TERRY

Memb. lim.

Max. cond.

ay (ee Hyph.

Max. n ; Hyph. cart.
Mand. n. cS Com. el. : f
Mand. cond. Int. car. art. a : ic z : see afi? Ss = Lat. occ.
Gr. sup. - Com. bas. ett
2 Pepe Ape Para. pl.

Pa. co.

Gen. gang.
vil Memb. im. IIT

Pre. para. Jug. v. XII

PRIMORDIAL CRANIUM OF THE CAT PLATE 12
ROEERT J. TERRY

Sulc. supr.

Al. orb. | Memb. lim. III) TV Oph.

f ‘Par. nas. Nasturb.

Be Lat. nas. gl
ie Meat. s.

oe Maxturb.
be eiecmaNT AL: Ds

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= : Hyph

gem » Pre. al

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j *.\ gang.

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Lat. nas. n.

)_Sph. p. gang.
Max. n.

Temp. m.

431

PRIMORDIAL CRANIUM OF THE CAT PLATE 13
ROBERT J. TERRY

Front.
ii\ Par: nas,
Cr. sem. i

Hi. sem.

Sulc. supr.

Max.

Meat. inf,

28

For. epiph.

Par. nas. Rec. lat.

Cr. sem.
Sulc.
suprach.
Maxturb.

ant. CniCcicianEse) es ere (28 ay, : : 3 Max.

Ne ED:

29

AUTHOR’S ABSTRACT OF THIS PAPER ISSUED
BY THE BIBLIOGRAPHIC SERVICE AUGUST 18.

NOTH ON THE STRUCTURE OF THE MAXILLARY
GLAND OF CYPRIDINA HILGENDORFII

NAOHIDE YATSU
Zoological Institute, Tokyo Imperial University, Japan

FOUR FIGURES

While at Misaki in the summer of 1900 I undertook, at the
suggestion of Professor Watase, a study on the ostracods with
especial reference to the cytology of the luminous glands. In
the winter of 1900-1901 quite a number of specimens were cut
into sections and several sketches were made. But my going to
America obliged me to suspend the work. Last summer (’16)
Dr. Harvey of Princeton University came over to Japan and
carried out at the Misaki Biological Station biochemical experi-
ments upon the Juminous substance formed in the maxillary
gland of Cypridina hilgendorfii. In connection with his study
it may be of some interest to publish the results of my obser-
vation on the morphology of the gland carried out sixteen years
ago.
In Cypridina hilgendorfii (Miller ’90, p. 228) the maxillary
gland (Oberlippendriise) attains a considerable development,
consisting of a number of large gland cells. These cells open to
the exterior on five protuberances, one unpaired anterior and
two pairs of posterior ones (figs. | and 2). The anterior process
has five or six pairs of openings. The middle pair is shorter
than the anterior one and each has only three or four openings.
The hindmost pair is the longest of all, projecting over the an-
terior wall of the mouth cavity, and each has seven or eight
openings along its side. The last pair of protuberances alone
is provided with fine hairs. .

The maxillary gland is a group of unicellular glands, as have
often been described by previous writers. The longest cells
measure nearly 0.7 mm. in length and reach as far up as the

435

436 NAOHIDE YATSU

supraoesophageal ganglion. Their diameters vary naturally
according to their secretory activity. The gland cells usually
assume a club shape, tapering towards the openings. In this
form as in other marine ostracods, the gland cells are not differ-
entiated into the gland proper and the duct, contrary to those of
fresh water forms (Bergold, ’10). The secretion granules fill

Fig. 1 Upper lip of C. hilgendorfii seen in an oblique view from the anterior
side. One of the middle pair of protuberances is behind the anterior one. X
115.

Fig. 2 Upper lip of C. hilgendorfii (9) seen from the right side. Fresh.
material treated with methylgreen acidulated with acetic acid. Mucous gland
cells are stippled. 90.

up a greater part of the cells, if specimens are killed quickly,
that is, before the oozing out of the contents. But in indi-
viduals from which the secretion products have been discharged,
the lower portion of the cells has a large space containing a
coarse spongy coagulum. ‘This space, especially in poorly fixed
preparations, is liable to give a deceptive picture, as though
there were a large reservoir common to all the gland cells.

MAXILLARY GLAND—CYPRIDINA HILGENDORFII 437

The maxillary gland is composed of two entirely different ele-
ments, namely the mucous gland cells and the yellow gland cells.
The posterior protuberances have the openings of the former
alone, while both the anterior and middle ones have those of two
kinds of cells (fig. 2). The secretion product of the mucous
cells of the maxillary gland stains intensely green with methyl-
green, as in the gland cells found in the appendages and the

3

Fig. 3. A portion of a vertical section through the maxillary gland of C.
hilgendorfii (6). Alcohol-acetic preparation. X 247.

Fig. 4 Cross section through the anterior process of the upper lip (@).
Flemming’s fluid preparation. 247.

mantles. In sections the cytoplasm of the mucous cells is finely
granular. The other kind of gland cells I shall call the yellow
gland cells, since they are yellow in life, due to the color of the
secretion product they contain. The yellow substance, which
emits light, is in the form of coarse, somewhat angular, granules.
The size of the granules varies considerably, often attaining the
diameter of 10 to 15 uw. Im general it may be said, that the
nearer the openings, the larger the granules. Their seat of
formation is in all probability near the nucleus, inferring from
the fact that a small number of minute granules of the same

438 NAOHIDE YATSU

nature is usually found there. The cytoplasm of the yellow
gland cell is fibrillar, in contrast to that of mucous cells, which
is granular as has already been mentioned. Figure 4 shows a
section through the anterior protuberance near the openings.
Here we see very clearly the relative position of both kinds of
gland cells.

In comparison with Cypridina hilgendorfii, the maxillary gland
of Pyrocypris japonica (Miller ’90, p. 233') was studied. The
protuberances of the latter differ both in shape and number from
those of the former, one unpaired one being added in front.
But so far as the interna] make-up of the glands is concerned,
it is so similar that its description would be simply the repe-
tition of what has been stated above. The only difference is the
presence of pigment cells in the upper lip of P. Japonica.

In conclusion, I would like to emphasize once more the two
points, that is, the presence of two kinds of gland cells and the
absence of a reservoir for secretion granules common to all the
gland cells. It should be mentioned that Watanabe was the
first to direct especial attention to the luminous glands of ostra-
cods at Misaki. He read a paper on this subject before the
meeting of the Tokyo Zoological Society on January 23, 1897, an
abstract of which appeared in Japanese (’97). He states that
the maxillary glands secrete colorless transparent fluid and
yellow homogeneous substance. But he does not say whether
each gland cells produces these two substances or whether there
are two different glands for them. Miller (90, p. 248) clearly
states that he saw two groups of gland cells of different nature,
1.e., the secretion product of the upper group is found in the form
of droplets and does not take carmine stain at all, while that of
the lower group takes it. Furthermore he advanced the view
that light is produced by the interaction of these two substances.
He, however, seems to have failed to observe the correct topo-
graphical relation of these two kinds of cells.

1 The general outline of the shell of Pypocypris japonica is more like that of
P. chierchiae (Miiller, ’90, pl. 25, fig. 3) the posterior process being longer than
in the figure for this species.

MAXILLARY GLAND—CYPRIDINA HILGENDORFII 439

One other point, which I would like to call attention, is the
absence of common reservoir for gland cells. Although all the
students of ostracods maintain that the maxillary glands are
unicellular, yet curiously enough those who have studied the
luminous glands entertain an erroneous idea that there is a special
cavity to store up the secretion product. Miller (’90, p. 248),
for instance, states that ‘‘die Ausfiihrunsgiinge samm+tliche
Driisenzellen vereinigen sich zu einem gemeinsamen Hohlraum.”’
Doflein published a paper on the maxillary glands of a Japa-
nese species of ostracod, which he provisionally calls Halocypris
(?) and gives a semidiagrammatic figure (06, p. 134). Since
pigment cells are drawn in his figure, his material may have
possibly been Pyrocypris japonica. At any rate he inter-
preted the section as though there were a spacious reservoir
for secretion granules. Probably influenced by Doflein’s de-
scription, Liiders (’09) a’so mentions the presence of a special
reservoir in Gigantocypris agassizi. It should be mentioned
that the above authors seem to have studied specimens from
which a greater part of the secretion products had been dis-
charged, and it is, I think, quite natural that they have come to
such an interpretation. The lower part of each gland cell
functions as a temporary reservoir of the secretion granules it is
true, but this cannot be called a special organ at all. As a
matter of fact, as I have expressly mentioned above, there is no
reservoir in the sense of previous writers.

January 9, 1917

440, NAOHIDE YATSU

LITERATURE CITED

Bercotp, A. 1910 Beitraige zur Kenntnis des inneres Baues der Siisswasser-
ostracoden. Zool. Jahrb., Abt. Anat., Bd. 30.

Doruein, F. 1906 Uber Leuchtorganen bei Meerestieren. SB. der Gesell. f.

Morph. u. Phys. Miinchen, Bd. 22.

Livers, L. 1909 Gigantocypris agassizi (Miiller). Zeit. wiss. Zool., Bd. 92.

Maneoup, E. 1919 Die Production von Licht. Winterstein’s Handbuch d.
verg. Physiol., Band 3, Heft 2.

Mituer, G. W. 1890 Neue Cypriniden. Zool. Jahrbuch., Abt. Syst., Geogr.
ty [roll IBcl, 5.

Watanabe, H. 1897 Umihotaru no Hakké6 ni tuite (On the phosphorescence of
Cypridina hilgendorfii). Ddébutugaku-zassi 9 also in Annotationes
Zool. Japon. 1 and Zool. Jahresbr. fiir 1897, Arth., 24.

AUTHORS’ ABSTRACT OF THIS PAPER ISSUED
BY THE BIBLIOGRAPHIC SERVICE SEPTEMBER.

THE PERIOD OF SYNAPSIS IN THE EGG OF THE
WHITE RAT, MUS NORVEGICUS ALBINUS

BENJAMIN HARRISON PRATT AND J. A. LONG
From the Laboratory of Zoology, University of California

TWO TEXT FIGURES AND ONE PLATE

CONTENTS
flininsrivel Wed GIN Soe Ceo at eee dee tye las. o.oo a Fe RRS eae ee ORR 441
AVG ria ete MVE COU y eee. se WSE Patac es fo sk snc yeh ches See preteen axe, cles ga 442
Genernlgconsidenaclonserrie we ene een ae | Oe erage Se Aero 442
The last oogonial division and early pre-leptotene changes..............-- 443
Ponr eC HOMME Be are ein cier o fs ceo 2 «ane 3 5b et ee Me Seo) tee 446
Be Me DW HOEINCHS GAC tm cee) eee spose Sia chase = > one! Soca pc > ACERT CIe rue ee) ts 447
Maine Mey MMAR GETICNS GAR Cr clo ects Mente otic isin s = « Fa ols a5 een eee nee age: ete ener nese ene 447
Muhiemromtelin he Mens EM Geer ny fen. ere, 5 eee sain 2.2 ao tiy dials vce ee neem teenedenca ake eral ste 448
MCRD LO FEMERSHARC Ac seth ies gis 6.6 veep s aw 8 a re eee le epee rbepet oe apie 450
ithe nuclerotanhereathy erowtl PeMod......252 2. 1s. - vaccetoe soem ae ae os oe 451
MnerceniTosoMmerancachromeapoldlbOdiyeeeenc 2c. = + sir eee eieiee cele ie 451
DiscusslonsandaconcluslOnsey amen esste dass. 2s. o- jn oe Soetoro tare do oeeee 453
IPH ence AUDREY OM NeVOLA cee dona bra bees lord ne titty Cec Cee a Reece oie ob Sooo puomo a todc 455
INTRODUCTION

Of the very considerable literature on synapsis much relates
to vertebrates, but only a small amount to mammals. In nearly
all of the publications on mammals synapsis in the male is de-
scribed, the process in the ovary being investigated in only a very
few cases. In view of the importance of synapsis in its relation
to theories of heredity and to the behavior of the chromosomes it
has seemed worth while to extend the study to the female of an-
other mammal. Of particular interest have been the problems
of the presence of an accessory chromosome, of the identity of the
chromosomes throughout the series of changes, and of whether or
not an actual pairing of chromosomes takes place.

1 Aided in the preparation of most of the figures by the Department of Anatomy
of the University of California.

441

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

442 BENJAMIN H. PRATT AND J. A. LONG

The rat was selected because of its interest in connection
with other studies and because of the possibility of obtaining a
chronological series of embryos of known ages, and, consequently,
of securing a natural series of stages.

MATERIAL AND METHOD

Since the period of synapsis in the egg of the rat is well along
toward completion at birth, it was found necessary to obtain
embryos of known age in order to complete the necessary series
of slides. These were obtained in the following way. It having
been clearly demonstrated that the female albino rat normally
ovulates within twenty-four hours after having given birth to a
litter (Long, 712), mother rats were taken from their young im-
mediately after parturition and placed with sexually active
males. Twenty-four hours later these females were taken from
the males and left alone or with females only. Upon subsequent
examination about 50 per cent of the rats so treated were found
to be pregnant, and the age of their embryos was consequently
known to within a fraction of a day. For the most part the sex
organs were dissected out of these embryos before fixing, but in
a few cases the entire embryo was fixed and sectioned. For those
stages occurring after birth the ovaries of young of appropriate
ages were used. The fixing solutions employed were Zenker’s,
Flemming’s strong solution, Bouin’s formol-picro-acetic, and
sublimate acetic. The first two gave the best results and were
used almost exclusively. The material was sectioned from 3
to 10 micra thick and for the most part stained in Heidenhain’s
iron haematoxylin. Usually a counterstain was employed,
orange G or acid fuchsin, or a mixture of the two being most
satisfactory. Erythrosin was used to some extent. A few slides
were stained in safranin and gentian violet.

GENERAL CONSIDERATIONS

The process of synapsis in the rat Jasts for approximately
ten days, starting about seven days previous to birth and being
practically completed by three days thereafter (table, p. 444).
Following von Winiwarter (’00) it has been found possible to

SYNAPSIS IN THE EGG OF THE WHITE RAT 443

distinguish clearly leptotene, synaptene, pachytene, diplotene,
and dictyé stages, together with more or less complicated transi-
tion changes to be mentioned Jater. These various stages suc-
ceed each other with considerable regularity throughout the
entire ovary, so that at any one time most of the germ cells are.
in the same stage of the synaptic process. While it is true
that those nuclei least advanced in the general process of change
are most likely to be found at the periphery of the ovary, there
is an absence of that clear distribution of stages in concentric
zones so evident in the cat, rabbit, and man (Winiwarter ’00,
and Winiwarter and Sainmont 708). Because of these features
of the process, the difficulty of determining the sequence of
stages has been reduced to a minimum.

THE LAST OOGONIAL DIVISION AND EARLY PRE-LEPTOTENE
CHANGES

The last oogonia] division occurs about seven days before
birth. In the ovaries of embryos from female 389 (table, p. 444)
there are a large number of division figures together with numer-
ous nuclei which have not yet passed through the last oogonial
division and also many that belong to the early stages of the
oocytes. Some few division figures may still be found in embryos
from female 451-6, at six days before birth. The nuclei of the
oogonia in the typical resting condition are spherical. They are
approximately equal to or perhaps a little smaller than the lepto-
tene nuclei to be described Jater, and are supplied with a large
amount of chromatin in irregular blocks. Often one or more of
these blocks is comparatively large and conspicuous, somewhat
suggestive of the chromatin nucleoli of the post-synaptic stages,
though they never have the definiteness of outline characteristic
of these later chromatin bodies. A heavy discontinuous spireme
is formed during the prophase of the last oogonial division, and
often the nuclei appear slightly oval at this time. The chromatin
is very closely massed together during the equatorial plate stage
as well as during the anaphase, so that it is extremely difficult
to distinguish individual chromosomes. The last oogonial divi-
sion may be distinguished from previous ones by the numerous

444 BENJAMIN H. PRATT AND J. A. LONG

deeply staining granules found in the cytoplasm during the ana-
phase, and by the character of the chromatin in the daughter nuclei.
In the very young daughter nuclei, when the nuclear wall is first
appearing, the chromatin forms a somewhat flattened, closely-
packed aggregation of blocks exceedingly varied in size and shape
(fig.1). No linin is evident in such nuclei. <A conspicuous, very
elongate, spindle-shaped remnant of the interzonal fibers and
the zwischenkérper extends over the two adjoining margins of
the two daughter cells containing such nuclei. These cells may
be regarded as the very first stages of the primary oocytes.

Table showing time of occurrence of synaptic changes

DAYS

DAYS AFTER), . vs arTER| BEFORE OR|NUMBER OF

PARTURI- CONDITION OF GERM CELLS

TION MATING are FEMALE

12 11 11 418 Gonad barely distinguishable

15 14 8 437 Gonad well formed, multiplication di-
vision

16 15 t 389 Last oogonial division and pre-leptotene
stages

17 16 6 451-6 | Pre-leptotene and contraction figures

18 17 5 577 Contraction figures and early leptotene

20 18} 33 454 Leptotene and synaptene

20 19 3 472 Synaptene and some pachytene

21 20 2 376 Synaptene and pachytene

215 20% 13 481 Pachytene

22 21 1 446 Pachytene

223 214 3 596 Pachytene

23 22 0 Young | Pachytene

233 224 $ Young | Pachytene and diplotene

24 23 1 Young | Pachytene and diplotene

25 24 2 Young | Diplotene and dictyé

26 25 3 Young | Dictyé

In the same ovary with these late telophase nuclei and often
immediately adjacent to them are other nuclei which, for the
following reasons, may be considered as directly derived from
them and as constituting the early stages of the preleptotene
nuclei. Although these preleptotene nuclei may lie side by side
with the late telophase nuclei they are slightly larger, almost
spherical and contain chromatin stiJ] in the form of numerous

SYNAPSIS IN THE EGG OF THE WHITE RAT 445

blocks of irregular size and shape (figs. 2, 3, and 4) which are dis-
tributed over the inner side of the nuclear membrane. The out-
line of the blocks is clear cut and definite. A few linin threads
may be attached to one or more of the blocks at this stage (figs.
3and4). Asin the case of the late telophase nuclei, here, too, the
preleptotene nuclei are evidently intimately associated in pairs,
as is clearly proved where remnants of interzonal fibers and
zwischenkorper persist between the cells of two such nuclei.
It may be concluded then that the late telophase nuclei increase
in size and become more spherical; and at the same time the
chromatin blocks separate and become arranged about the inner
surface of the nuclear membrane. In the early stages the num-
ber of these blocks of chromatin varies from twenty-two to
thirty-five and seems therefore not to be significant, except in
indicating a fragmentation of the original chromatin masses.

The comparatively simple condition of the contents of the
nucleus represented by the peripherally arranged chromatin
blocks changes gradually into an extremely complex, chromatin-
linin network dispersed more or less regularly throughout the
entire nucleus. The changes represented by these closely simi-
lar conditions involve a regularly progressive increase in the
number of chromatin blocks, a gradual augmentation of the :
number and complexity of arrangement of the linin threads,
and a more or less equal distribution of the chromatic material
throughout the entire nucleus. (figs. 4, 5, and 6). In the earlier
phases of this series of changes it may be readily seen that all of
the linin threads are attached to chromatin bodies, or, that the
many small, almost powdery particles of chromatin are arranged
along linin threads. There is no distinct chromatin element con-
stant in size or shape throughout this series of changes.

This whole series of changes, from the very first form of the
primary oocytes to the most complex condition of the chromatin-
Jinin network, is strongly suggestive of the migration of chroma-
tin aJong linin filaments which later probably become incorpo-
rated in the leptotene threads. It is very difficult to explain in
any other manner the gradual decrease in average size and the
increase in number of the chromatin blocks, simultaneously with

446 BENJAMIN H. PRATT AND J. A. LONG

the appearance of the linin filaments. A study of the oldest
nuclei alone would hardly lead one to such an inference, but the —
complete series seems very convincing. Such an elaborate
series of transformations intervening between the last oogonial
division and the leptotene stage has not been described in the
ovary of any other mammal carefully studied, though there is a
slight indication of such changes in the cat (Winiwarter ’00, and
Winiwarter and Sainmont ’08).

CONTRACTION FIGURES

Immediately preceding the leptotene stage, or possibly coin-
cident with the earlier portion of it, there is a clearly defined
contraction stage. This occurs about six days before birth.
The chromatin-linin is eccentrically arranged in a confused mass
closely packed against the nuclear wall (fig. 7). Such figures
may be found throughout the entire ovary after either Zenker’s
or Flemming’s fixation, fixation that is evidently good in all other
portions of the same tissue. Since these figures are found in all
portions of well fixed ovaries, and since there is no constancy
whatever in regard to the direction of contraction, it is not pos-
sible to agree with Schaffner (’07), Von Hoof (’12) and others,
who contend that this so-called contraction stage is an artifact
due to poor fixation. It seems rather that this stage is quite as
normal as those stages immediately preceding or following it. In
these figures it is obvious that the eccentrically placed darkly
staining mass is not of the same consistency throughout, but is
composed of chromatin blocks, granules, and linin threads.
Finely attenuated linin threads often extend from the chromatin
knot to the opposite wall of the nuclear cavity. The whole
picture strongly suggests that the complex chromatin-linin
network has somehow been concentrated at one side of the
nuclear cavity, and that those strands of linin attached to the
opposite side of the nucleus have not entirely shared in the
process.

SYNAPSIS IN THE EGG OF THE WHITE RAT 447

THE LEPTOTENE STAGE

The leptotene stage (figs. 8 and 9) which follows the con-
traction stage, occurs about five to three and one-half days pre-
vious to birth. It may even persist to a later date, as illus-
trated by figure 9, from an ovary three days before birth, in
which most of the nuclei had passed over into the pachytene
stage. The chromatin threads are either regular in outline
with a constant size in cross-section or slightly moniliform, ex-
ceedingly fine, and very numerous. Many definite visible ends
suggest that a large number of individual threads are present.
As indicated in figures 8 and 9 the greater part of the threads
lie at one side of the nucleus. This arrangement may well be
considered as determined by the previous contracted state of
the chromatin and as leading to the subsequent polarized orien-
tation of the pachytene. In fact, the above figures show a tend-
ency for many of the ends of threads to reach the nuclear mem-
brane in the region near which the so-called centrosome is found
when demonstrable at this stage. In figure 9 are a number of
confused clumps of chromatin characteristic of early leptotene
nuclei, but no definite chromatin body, uniform in either size or
shape could be found at this period. A tendency toward paral-
lel arrangement of threads is very apparent in all nuclei closely
examined, and in many cases (figs. 8 and 9) figures indicating
the side by side approximation of individual threads are clearly
demonstrable. Where the moniliform character of the threads is
appreciable, the enlargements into which the chromatin is col-
lected tend to lie exactly opposite to each other in the more closely
approximated parallel threads. These leptotene nuclei are not
appreciably larger than those of the stages immediately preced-
ing. It was not possible to determine the number of individual
threads in these nuclei.

THE SYNAPTENE STAGE

The synaptene stage may be found from three and one-half
to about two days before birth. It often happens that some
portions of the threads may show the bipartite nature at a much
later period, but, for the most part, do not do so as late as a couple

448 BENJAMIN H. PRATT AND J. A. LONG

of days before birth. The orientation of the threads first dis-
cernible in the leptotene stage is distinctly more advanced.
Figure 11 is a lateral view while figure 10 is a polar view of a
nucleus in the late synaptene stage. In figure 10 the nucleus is
viewed from the pole opposite the so-called centrosome. It is
clearly evident from figure 11 that the loops of the synaptene
threads are of different lengths, some of them extending barely
half as far out into the nucleus as do the others. Counts of the
loops as seen in polar views or sections have not been made at
this stage. Moreover, since it has not been possible to deter-
mine the number of leptotene threads, a comparison of the num-
bers in these two stages cannot be made as evidence of pairing.
Nevertheless a consideration of the sizes and structures of the
leptotene and synaptene threads give reasons for believing that
the latter are derived from the former. A comparison of figures
8 and 9 with 10 and 11 makes it evident that the synaptene
threads are about double the width of the leptotene. The synap-
tene is further clearly composed of distinct moniliform halves sep-
arated by a longitudinal split (fig. 10). Each half of the double
synaptene thread is very similar to the leptotene threads, and
bears much the same relation to the other half which some lepto-
tene threads have to other leptotene threads. That is, the spin-
dle shaped and laterally flattened enlargements in each half are
usually opposite and nearly or quite in contact with those of the
other half. Also the portions of each moniliform half, between
the deeply staining enlargements, are almost or quite devoid of
chromatin. It seems then that each of these synaptene threads
was formed by the side by side approximation of two leptotene
threads.

Throughout this period as in the preceding ones a chromatin
body in any way simulating an accessory chromosome is not

evident.
THE PACHYTENE STAGE

The disappearance of the longitudinal division in the synaptene
thread marks its transformation into the typical thread of the
pachytene stage. This stage begins two days or thereabouts
before birth and persists for about a day thereafter. The ori-

SYNAPSIS IN THE EGG OF THE WHITE RAT 449

entation of the previous stage is retained, though it becomes more
indefinite (figs. 12, 14 and 15). The nuclei sometimes appear
more oval, in contrast to the former spherical shape, and the
thread is more regularly distributed throughout the entire nu-
cleus (fig. 15), with a tendency, perhaps, toward a peripheral ar-
rangement. The thread itself is of about the same thickness as
that of the preceding stage. It is distinctly moniliform, and in
early pachytene nuclei it is clear cut and definite in outline (figs.
12 and 14). The enlargements of the thread stain heavily and
show no evidence of their double origin except in very early
threads (fig. 12). In the intervals of the thread between these
enlargements, there is a paucity of chromatin, and in some cases
it seems entirely wanting, only the linin framework being left.
In the later stages of the pachytene nuclei, the outline of the
thread becomes less distinct due to the extension laterally of
numerous very fine linin strands connecting these enlargements
of the thread.

Figure 13 represents a pole view of a nucleus similar to figure
11 or 12 cut through the equator. The threads are accurately
drawn as they are seen near the sphere or centrosome. They
show no sign of being double and each one undoubtedly repre-
sents one end of a loop. They number 40. Consequently there
would be 20 loops; and, if each loop represent paired chromo-
somes, the diploid number of chromosomes is 40, the haploid 20.
Too great reliance, however, must not be put on the number
obtained by this single count.

For the first time in this series of stages, a distinct chromatin
body becomes distinguishable in the nucleus (figs. 12 and 15).
This chromatin body, however, is constant neither in shape nor in
size, and is often distinctly connected with one or more pachy-
tene threads. It can hardly be regarded with reason as an
accessory or sex chromosome, but is rather to be looked upon as
the first appearance of the large chromatin nucleoli which char-
acterize the nuclei of the early growth period.

450 BENJAMIN H. PRATT AND J. A. LONG

THE DIPLOTENE STAGE

Nuclei in the diplotene stage may first be distinguished at the
time of birth, or possibly a little earlier, and persist in com-
paratively large numbers for a couple of days thereafter. At
three days after birth they are but infrequently met with, prac-
tically all of the nuclei having passed over into the stage char-
acteristic of the early period of growth and designated by Wini-
warter as ‘Noyoux dictyé.’ The early diplotene nuclei (figs. 16
and 17) show numerous contorted threads, more or less irregular
in outline, but often distinctly parallel in arrangement or wound
about each other in spirals. Fine strands of linin are often dis-
tinetly visible passing from thread to thread. The number of
individual threads is clearly greater than in the pachytene stage,
though the exact relations in this respect could not be definitely
determined. Thediplotene threads are also clearly only about half
as wide as those of the previous stage. The orientation, so con-
spicuous in the threads of synaptene and pachytene nuclei, is
almost entirely lost. A large chromatin body is present in each
of these nuclei, and very often an additional one or two may
be discovered. The chromatin threads very commonly are
united to the chromatin body in large numbers (fig. 16). Some
of the threads are always connected with these bodies. It seems
from an examination of a large number of these diplotene nuclei,
that the individual threads are formed by a longitudinal splitting
of the pachytene threads, and that the chromatin is rapidly being
assembled in the large chromatin bodies. The appearance of
the later phases of the diplotene stage gives further evidence of
the validity of these inferences: the individual threads are no
longer distinctly visible as such; often rows of granules indicate
their probable former course; the linin may still be apparent, in
arrangement strongly suggesting the course of the former threads.
The chromatin bodies, chromatin nucleoli, are more definite in
outline and typically number one to three. These later stages
gradate imperceptibly into the nuclei characteristic of the early
growth period.

SYNAPSIS IN THE EGG OF THE WHITE RAT 451
THE NUCLEI OF THE EARLY GROWTH PERIOD

By three days after birth, most of the nuclei have passed
over into the resting stage, so-called, and in this condition they
remain, with certain modifications, up to the period of sexual
maturity. Typically from one to three large definitely outlined
chromatin nucleoli are present. Throughout the remainder of
the nucleus a fine achromatic network is dispersed, with an
occasional deeply staining block or particle suspended within it
(text fig. 1). There is a decided increase in the size of the
nucleus coincident with the beginning of the enlargement of the
cell itself. The amount of achromatic material in these nuclei is
strikingly greater than that of any preceding period. Its ar-
rangement is without constant order and gives no hint of its
relation to the previous stages. If it be the linin of previous
stages, certainly there is here little evidence in support of that
theory which postulates that the individuality of the chromosome
is maintained through the constant discreteness of the linin
framework.

THE CENTROSOME AND CHROMATOID BODY

While no attempt has been made to analyze carefully the
cytoplasmic changes which occur simultaneously with the series
of nuclear alterations just described, our attention has been
drawn to two distinct structures which appear in the cytoplasm
very constantly during a part of the process. These are the
so-called centrosome or body of Balbiani and the chromatoid
bodies. The centrosome appears as a roughly spherical or elon-
gated condensed portion of finer texture than the remainder of
the cytoplasm, lying never more than half way from the nuclear
wall to the periphery of the cell. It has no definite mem-
brane and its outline is uneven. It is first discernible in the
early leptotene nuclei (fig. 9) where it may occur in only a
comparatively small percentage of the cells. Throughout the
synaptene stage it is more conspicuous, and only rarely at this
time is there within it a darkly staining granule, perhaps the
centriole. It is very evident in most of the cells in the pachy-

452 BENJAMIN H. PRATT AND J. A. LONG

tene stage, and the granule above referred to as the centriole
here becomes more constantly apparent (fig. 15). At this
period, in ovaries fixed in Flemming’s solution, this internal
granule seems to be surrounded by a narrow zone of less dense
material. During the diplotene stage the centrosome can still

5

Text fig. 1 One of the largest cells from the ovary of a rat three days old.
Fixed in Flemming’s fluid and stained in iron haematoxylin. X 1830.

Text fig. 2 One of the largest cells from the ovary of a rat nine days old.
Fixed in Zenker’s fluid and stained with iron haematoxylin and erythrosin.
X 1830.

SYNAPSIS IN THE EGG OF THE WHITE RAT 453

be distinguished in a fairly large percentage of the cells, but it
has not been found in any of the nuclei of the later stages. It
will be seen that this body is evident throughout the period in the
process of synapsis, when there is a distinct orientation of the
chromatin threads. This orientation seems to have a definite
relation to the position of the centrosome, the bent portion of
the loops being, in all clear cases, directed away from that side
of the cell where it occurs (fig. 12). As has already been clearly
pointed out (von Winiwarter and Sainmont, ’08) it cannot be
asserted on the evidence here available that this body actually is
the centrosome and its enclosed granule the centriole. On the
other hand the converse is just as difficult of demonstration.

The chromatoid body here referred to is a deeply staining
body of small size appearing, seemingly, in any region of the cyto-
plasm. It is rarely to be found in the cells with synaptene nuclei.
During the pachytene stage (figs. 12 and’15) it is common, and
here not infrequently two such bodies may be found in the same
cell. From this time on throughout the period involved in this
paper, it is a constant feature of a large percentage of the cells.
During later stages there may be quite a number of these bodies
(text fig. 2). Neither the origin nor the fate of these two
structures has been determined.

DISCUSSION AND CONCLUSIONS

As a whole the series of changes associated with synapsis in
the egg. of the rat rather closely resembles the same period of
development in other mammals carefully studied (von Wini-
warter, ’00, and von Winiwarter and Sainmont, ’08). There are,
however, some very noticeable differences. Those changes
taking place subsequent to the last oogonial division and just
previous to the formation of the leptotene threads, are much
more elaborate in the rat than in any of the other forms de-
scribed. In the case of the cat there is some slight suggestion in
the figures (von Winiwarter and Sainmont, ’08) of such a series
of changes but they seem much less complex than in the rat.
Particularly in the rabbit and in man there is a complete ab-
sence of those transition nuclei with the chromatin in irregular

454 BENJAMIN H. PRATT AND J. A. LONG,

blocks peripherally arranged, and in none of the three forms
described by these authors is there that finely graded series of
nuclei showing the fragmentation of these blocks and the simul-
taneous appearance of linin threads. In the case of the rat, the
contraction stage certainly must start earlier than in these other
forms. It would seem from the figures that this stage persists
longer in the rabbit and in man (von Winiwarter, ’00).

It has already been mentioned that distribution of nuclei in
zones—the most advanced stages being in the interior and the
least advanced at the periphery with the intervening stages in
more or less definite concentric areas—is almost completely
lacking in the case of the rat. It would seem that this phenome-
non might be correlated with the comparatively shorter period
over which these nuclear changes extend in this form.

In the case of the cat (von Winiwarter and Sainmont, ’08)
there is a clearly defined chromatin element, fairly constant in
appearance, persisting throughout this entire series of changes.
There is certainly no such body in the case of the rat; and von
Winiwarter finds none in either the rabbit or man. In all
other respects, particularly in reference to the gross as well as
the more detailed appearance of the chromatin threads through-
out the entire series of changes, the four forms are closely
_ similar.

Of particular interest throughout this study has been the
relation of the chromatin to the linin threads, and of the chroma-
tin nucleoli of the later periods to the synaptene and diplotene
threads. During the first part of the series of stages here de-
scribed, the evidence is very strongly in favor of the conception
that fragmentation of the original chromatin blocks and migra-
tion of these chromatin fragments along the linin threads then
evident, contribute largely to the formation of the leptotene
threads. This process is almost exactly reversed at the other
end of the process of synapsis. The chromatin nucleoli seem to
be merely the closely compacted clumps of that same chromatin
which has now migrated back along linin threads to one or more
common points. The contact of the synaptene and diplotene
threads with these chromatin bodies, and the persisting linin

SYNAPSIS IN THE EGG OF THE WHITE RAT 455

threads in the remainder of the nuclei, point to this conclusion.
Such a phenomenon has been elaborated upon by McGill in the
case of the Dragonfly (McGill, ’06), and has been described by
numerous other authors.

In regard to those questions which attracted attention in the
first place, it seems: (1) There is no evidence, during the period
of synapsis, of the presence of an accessory chromosome or sex
chromosome. (2) If it be assumed that the individual leptotene
threads represent chromosomes, chromosomes seem to pair dur-
ing synapsis; and this is a side by side pairing, or parasynapsis.
(3) Under this same assumption, it would seem that individual
chromosomes maintain their identity throughout this period up
to and including the diplotene stage, although there is oppor-
tunity for mixture of material in the chromatic enlargements
during the pachytene stage. There is, however, no satisfactory
evidence that these individual leptotene threads do represent
chromosomes.

LITERATURE CITED

ARNOLD, Geo. 1908 The prophase in the ovogenesis of Planaria lactea. Arch.
f. Zellforsch, Bd. 3.

Browne, E.N. 1910 The relation between chromosome number and species in
Notonecta. Biol. Bull., vol. 20.

CarpirFr, I. D. 1906 A study of synapsis and reduction. Bull. Torrey Botan.
Club, vol. 33.

Davis, H. 8. 1908 Spermatogenesis in the Acrididae and Locustidae. Bull.
Mus. Comp. Zool., vol. 53.

DuessurG, JuLES 1908 Les Divisions des Spermatocytes chez le Rat. Arch.
f. Zellforsch., Bd. 1, pp. 399-449.

Foot, K. anp Srropety, E. C. 1910 Pseudo-reduction in the oogenesis of
Allobophora foetida. Arch. f. Zellforsch., Bd. 5.

Von Hoor, Lucten 1912 Laspermatogénése dans les mammiféres. La Cellule,
a2.

Jorpan, H.E. 1911 The spermatogenesis of the opossum, Didelphys virginica,
with special reference to the accessory chromosome and the chondrio-
somes. Arch. f. Zellsforsch., Bd. 7.

Kine, Heten D. 1908 The oogenesis of Bufo lentiginosis. Jour. Morph.,
vol. 19. ;

Lone, J. A. 1912 The living eggs of rats and mice. Univ. of Calif. Pub.
Zool., vol. 9, no. 3.

McGiti, Caroutine 1906 Behavior of the nucleoli during the oogenesis of the
dragonfly with especial reference to synapsis. Zool. Jahrb. Abt. Anat.,
Bd. 28.

456 BENJAMIN H. PRATT AND J. A. LONG

McIzuroy, A. Louise 1910 The development of the germ cells in the mammalian
ovary with special reference to the early phases of maturation. Proc.
Roy. Soc. Edin., Bd. 31.

Reeavp, Cu. 1901 Etudes sur la structure des tubes séminiféres et sur la sper-
matogénése chez les mammiféres. Arch. d’Anat. Mier., v. 4.

ScuaFFner, J. H. 1907 Synapsis and synizesis. Ohio Naturalist, vol. 7.

Sxrosansky, K. 1903 Beitrige zur Kenntnis der Oogenese bei Saiugethieren.
Arch. f. mik. Anat., Bd. 62.

Stevens, N. M. 1911 Heterochromosomes in the guinea-pig. Biol. Bull.,
vol. 21.

Witson, E. B. 1911 Studies on chromosomes, VIII. Observations on the
maturation phenomena in certain Hemiptera and other forms, with
considerations on synapsis and reduction. Jour. Exp. Zodél., vol. 13.

Von WINIWARTER, Hans 1900 Recherches sur l’ovogenése et l’organogenése
de l’ovaire des mammiféres. Arch. de Biol., Bd. 17.

Von WINIWARTER, Hans ET Satnmont, G. 1908 Nouvelles recherches sur
l’ovogenése et lVorganogenése de l’ovaire des mammiféres (chat).
Arch. de Biol., Bd. 24. :

WopbsEDALEK, J. E. 1913 Spermatogenesis of the pig with special reference
to the accessory chromosomes. Biol. Bull., vol. 25.

1914 Spermatogenesis of the horse with special reference to the ac-
cessory chromosomes and the chromatoid body. Biol. Bull., vol. 27.

PLATE

PLATE 1

_ EXPLANATION OF FIGURES

Figures 1, 2, 3, 7, 9, 11, 12, 16 and 17 are drawn to the same magnification
(X 2290) with a Zeiss 2 mm. 1.4 n. a. apochromatic objective; figures 13, 14 and
15 (X 2270) with a Zeiss 1.8 mm. achromatic objective; and figures 5, 6, 8 and 10
(X 2490) with a Leitz +s achromatic objective; a no. 12 Zeiss compensating ocular
being used in all cases.

Figures 1 to 4, 6, 7, 9 to 11, 16 and 17 prepared by Dr. H. M. Gilkey; and fig-
ures 12, 18 and 19 by Mr. Willard Shepard.

1 to 6 Successive phases of the transition nuclei between the last oogonial
division (fig. 1) and the contraction stage. From young of female 389, fixed
in Zenker’s fluid and stained with Heidenhain’s iron haematoxylin and acid
fuchsin.

7 Two nuclei in the contraction stage. Fixed in Zenker’s fluid, from young
of female 451-6 and stained with Heidenhain’s iron haematoxylin and acid
fuchsin.

8 Side view of nucleus in the leptotene stage. Material from female 454,
fixed in Zenker’s fluid and stained in Heidenhain’s iron haematoxylin and
orange G.

9 Lateral view of a nucleus in the leptotene stage. Material from female
472, fixed in Zenker’s fluid and stained with iron haematoxylin and orange G.

10 and 11 Nuclei in synaptene stage, 10 polar view, and 11 a lateral view.
Material from female 376, fixed in Zenker’s fluid and stained with iron haematoxy-
lin and orange G. :

12, 13,14 and 15 Nuclei in the pachytene stage. Material of 13 from female
376, and that of 14 from female 481, both fixed in Zenker’s fluid and stained in
iron haematoxylin and orange G. Material of 12 and 15 from young at birth,
fixed in Flemming’s fluid and stained with iron haematoxylin. Figure 12, an
early pachytene, and figure 14 a later, both in side view. 13 isa pole view. 15
a very late pachytene in which polarized arrangement of threads is lost.

16 and 17 Nuclei in the diplotene stage. Material from young one day
old. Fixed in Zenker’s fluid and stained with iron haematoxylin and orange G.

458

SYNAPSIS IN THE EGG OF THE WHITE RAT PLATE 1
BENJAMIN H. PRATT AND J. A. LONG

AUTHOR’S ABSTRACT OF THIS PAPER ISSUED
BY THE BIBLIOGRAPHIC SERVICE SEPTEMBER.

THE EARLY DEVELOPMENT OF A STARFISH, FATERIA
(ASTERINA) MINEATA

HAROLD HEATH

From the Leland Stanford Junior University, California

FIVE FIGURES

During the past summer a small number of gastrulae were dis-
covered in the plankton of Monterey Bay, California, which
exhibited a unique combination of characters, relating them on
one hand to the Echinodermata and on the other to the Enterop-
neusta. To discover their true relationship all were placed in
balanced aquaria where they subsequently developed into bi-
pinnariae. Ova of various species of shore-dwelling starfishes
were then artificially fertilized and reared for a sufficient length
of time to show that the first captured specimens were the
young of Pateria (Asterina) mineata.

Judging from artificially fertilized material the segmentation
and early blastula stages do not exhibit any especially note-
worthy features, but beyond this point certain structures arise
that have no known counterpart among starfishes. The first
of these unique organs is the apical plate. In the late blastula
stage the cells about the animal pole commence to elongate
and, in the gastrula, form a thickened area, more or less lens-
shaped in form, having approximately one half the diameter of
the transverse axis of the embryo. As indicated in the drawings
(figs. 3, 5) its center is exactly opposite to the blastopore and
therefore is strictly apical.

Sections show the component cells to possess a height fully
three times that of the average ectoderm cell of the animal half .
of the embryo. Passing outwardly the altitude diminishes at a
fairly uniform rate until the outer limits are reached. The
nuclei are distally located and therefore similar in this respect

461

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

462 HAROLD HEATH

to the ectodermal elements generally. Furthermore all of the
cells of the apical plate are packed with granules, evidently
yolk, and thus are in marked contrast to the remaining ectoderm
where the granules are relatively few and minute.

Generally speaking, this condition of affairs continues to the
close of gastrulation. In specimens entering upon the initial
stages of enterocele formation, where the walls of the blind end
of the archenteron have grown thin, a few of the cells of the
apical plate are usually to be seen in the act of migrating into
the blastocele. As will be seen later these and other migrants
from the apical plate form mesenchyme.

The formation of the enteroceles (hydroceles) proceeds in the
typical fashion. In practically every case they arise independ-
ently of each other, and from the outset the left is almost in-
variably the larger of the two (fig. 1). Mesenchyme cells arise
as usual from the walls of the enteroceles as well as from the
intervening portion of the archenteric wall. Their numbers,
when compared with those in Asterias ocracea for example, are
relatively small, and, in comparison with the migrating cells of
the apical plate, they are distinctly smaller and far more hyaline
in appearance—features which enable one to distinguish the
two types of mesenchyme (ectodermal and entodermal) through-
out the stages described in this paper.

In fully 50 per cent of the specimens in hand a few of the mesen-
chyme cells arising from the blind end of the archenteron, be-
tween the enterocele pouches, unite to form a small vesicle (fig.
1, av). This usually occurs after the enterocele pouches are well
differentiated though not completely cut off. In a relatively
short space of time this anterior, unpaired vesicle is rapidly
enlarged by the addition of other mesenchyme cells from the
archenteron, and ultimately attains a diameter equal to that
of the gut. In a few surface views it is clearly seen to be entirely
enclosed, with walls everywhere complete, and, though it is
closely attached to the distal wall of the archenteron, it is never-
theless distinctly separated from it. In other casés the vesicle
is so closely applied to the archenteric wall that it 1s not pos-
sible to determine whether the vesicular walls are complete. In

EARLY DEVELOPMENT OF A STARFISH 463

every instance, however, the distal wall of the archenteron is con-
tinuous, and the evidence is perfect that this anterior vesicle is
entirely formed from mesenchyme and not as an outpouching
of the archenteric wall.

By the time that the anterior vesicle has attained a diameter
equal to that of the archenteron the mesenchyme migration
from the apical plate is at its height. Many cells in sections are
seen to have become entirely free, while others are in the act of
slipping past what are to become the final ectodermal elements,
and are making their way into the blastocele. In several larvae
they come in contact with the anterior vesicle (fig. 1), and cover
it like a roof. Where the mesenchyme-is more scattered, a
relatively small number of cells rest upon the vesicle, while the
others pass around it, especially in the region of the future
oesophagus.

Beyond this stage in the development, the walls of the anterior
vesicle usually disappear, the mesenchymal elements separating
and migrating to other regions. In the oldest stage where the
vesicle has been found to exist the stomodaeum had completely
formed, and the enterocele pouches had severed their connec-
tion with the gut. The vesicle in question showed slight signs of
disintegration on its posterior face, but, as figure 4 indicates, it
is fairly complete, and has a diameter approximately equal to
that of the middle section of the body. Here it is a question
whether it has a complete wall next to the gut, but there is no
doubt whatever about its Jack of communication with the
digestive tract.

Surface views under fairly high magnification show the wall of
the vesicle to be.made up of a relatively small number of cells.
These possess highly ramified pseudopodial processes which
appear to form an extremely delicate granular meshwork.
Whether the meshes are bridged by a non-granular ectoplasm
or by some intercellular material has not been determined, but
it is evident that the bounding wall, as a whole, is fairly com-
plete, since neither the pseudopodia of other cells nor minute
granules which appear to have escaped from some of the apical
cells make their way into the cavity of the vesicle. In some

464 ‘ HAROLD HEATH

specimens the blastocele contains a ground substance distinctly »
stained by Delafield’s haematoxylin, and is to that extent in
contrast with the fluid contained in the vesicle, which has only a
slight affinity for dyes of this character.

After cells of the anterior vesicle have separated and migrated
into the blastocele, many of the mesenchyme elements from the
apical plate move to the wall of the gut, especially in the region
of the oesophagus. In the oldest larvae in my possession (about
twenty hours later than the stage represented in figure 2) a few
of these apical mesenchyme cells, more or less bipolar in form,
rest upon the wall of the anterior half of the oesophagus at right
angles to its long axis. Between this point and the stomach
other mesenchyme cells of entodermal origin are taking up similar
positions. Both types of mesenchyme doubtless become trans-
formed into circular muscles.

The left hydrocele, after separating from the archenteron, is
not only larger than the right, but its subsequent growth is more
rapid, and it soon develops a pore canal and hydropore which
have no counterparts on the opposite side; at least none Bee
been discovered in the material at hand.

A posterior enterocele pouch (fig. 4) arises from the left side
of the gut at about the middle of the future stomach. It is a
hollow outgrowth, nearly as thick-walled as the gut itself, and
after severing its connection with the digestive tract, it be-
comes a flattened vesicle wedged in between the stomach and
body wall. Ina stage slightly older than the one represented in
figure 2 the left hydrocele forms a diverticulum at its posterior
end which ultimately comes in contact with the posterior en-
terocele pouch and fuses with it. Before this fusion takes place
the posterior enterocele vesicle, in several larvae, assumes the
form of a rather narrow ellipse with its long axis extending
from a point slightly behind the left hydrocele to the base of the
intestine. Nothing is known regarding its subsequent history.

Comparisons. Since the year 1869, when Metschnikoff first
called attention to the resemblance between the echinoderms and
Balanoglossus a vast amount of data has accumulated. This
tends to support the original theory that the two groups in ques-

EARLY DEVELOPMENT OF A STARFISH 465
tion are genetically related, but the interpretation of certain
details is not completely satisfactory. For example there is a
lack of agreement relating to the homologies of the coelomic
cavities. It will be remembered that Balanoglossus develops
five pouches, an anterior unpaired vesicle and two succeeding
pairs which become the proboscis, collar and trunk coelom re-
spectively. In Balanoglossus clavigerus, according to Heider
(09) the anterior vesicle arises as a diverticulum from the distal
end of the archenteron, and after separating completely, forms
the future proboscis pore, before coming in contact with the
apical plate. After a time the vesicle withdraws from the plate,
though retaining its connection by means of a muscular strand,
whitle mesenchyme cells from the strand and undetermined neigh-
boring regions migrate to the oesophageal region where they
become transformed into circular muscles.

The resemblance in the behavior of the anterior vesicle in Balano-
glossus clavigerus and Pateria mineata is decidedly striking. In
the starfish the vesicle arises in the form of mesenchyme cells
which subsequently unite; in Balanoglossus it originates as a
direct outgrowth of the archenteron. In Asterias rubens and a
few other species of starfishes Gemmill (14) has described the
rudiments of posterior enterocele pouches which either fuse with
the left hydrocele or break up into mesenchyme (and possibly.
unite later with the hydrocele, though this is not indicated).
In other words it is well known from this and numerous other
instances that there is no fundamental difference between a vesicle
formed as an outpouching of the gut and the precocious develop-
ment of mesenchyme with subsequent fusion. In Pateria mine-
ata the anterior vesicle soon disappears, the component mesen-
chyme cells wandering off into the blastocele, but before its dis-
appearance it has come into close contact with wandering cells
from the apical plate. No pore unites this anterior vesicle with
the exterior, but its behavior is such that I am convinced it is
the homologue of the proboscis coelom of the Enteropneusta.

There is, so far as I know, no other starfish which develops a
distinct, independent anterior vesicle. In several species the
blind end of the archenteron becomes expanded, thin-walled and

466 HAROLD HEATH

develops laterally the two well known enteroceles, so that the
median section between the pouches may possibly be considered
an incipient unpaired vesicle as certain authors have suggested.
On the other hand it is equally possible that some of the mesen-
chyme cells migrating from the distal end of the archenteron
represent the anterior vesicle though they may never actually
fuse. In Pateria mineata, for example, not over 50 per cent
of the embryos form a complete vesicle; in a few cases, rela-
tively, it is imperfect, and it appears probable that in the others
it is represented by isolated mesenchyme cells which arise in
the proper position but never unite. Furthermore, it is a signifi-
cant fact that in all of. these cases, even where the anterior
vesicle is perfectly formed, the enterocele pouches are separated
by a thin section of archenteric wall which therefore can scarcely
be regarded as representing the anterior vesicle.

Gemmill’s discovery of a pair of posterior enterocele pouches in
the starfish is of the highest importance. They have the same
origin as the trunk coelom in Balanoglossus, and as Gemmill
states ‘“We have here, I think, rudiments of a paired posterior
enterocoelic outgrowth, which in the common ancestor of
Balanoglossus and the Echinoderms gave rise to the coelom of
the body or trunk.” In some of the species studied by Gemmill
‘‘this rudiment takes no part, or only a small part, in the forma-
tion of the wall of the posterior coeloms, but it still retains the
function of producing mesenchyme.” In Pateria mineata, on
the other hand, it is a relatively large vesicle, present on the
left side only, and in the future an attempt will be made to de-
termine its fate. It is possible that, in this species and in the
others where it forms mesenchyme, this posterior outgrowth does
play a more or less important part in the history of the left entero-
cele from which the hydrocele arises, and that some of the diffi-
culties in homologizing this last named cavity are due to its
compound character.

To sum up: I am strongly inclined to look upon the anterior
vesicle in Pateria mineata as the homologue of the proboscis
coelom of Balanoglossus, while the posterior outgrowth corre-
sponds to the trunk coelom, and the intermediate pair of vesicles

EARLY DEVELOPMENT OF A STARFISH 467

in the echinoderms, often with two hydropores in certain species,
is the equivalent of the collar coelom.

A word remains to be said regarding the apical] plate. In
certain crinoids and echinoids it becomes a well developed organ
in fairly old larvae, in which definite ganglion cells appear. As
the adult nervous system arises from the ectoderm in close
proximity to the hydrocele, it would appear that these embryonic
nerve cells play no part in the process. Whether they degener-
ate or become mesenchyme remains undetermined. It is fairly
certain, however, that they furnish a strong bit of evidence in
favor of the theory that the apical plate of the trochophore
larva and of the echinoderm Jarva are homologous structures.

In Pateria mineata it has been shown that many of the cells
of the apical plate completely lose their connection with the
ectoderm and, as mesenchyme, migrate through the blastocele
to the oesophageal section of the gut where they probably be-
come transformed into circular muscles. All signs that they
ever functioned as nervous elements appear to be wholly Jost.
In this connection one calls to mind the work of Katschenko (’88),
Platt (94) and others who find that numerous cells leave the
neural crest in the head region of various vertebrate embryos and
become mesenchyme. It is possible that such cells represent
ganglionic elements in the primitive ancestor which formerly
innervated preotic structures now vanished or rudimentary.
The matter, however, remains unsettled for the vertebrates; such
is emphatically the case with the echinoderms where the species
‘studied are few indeed and the data far too scanty to enable one
to draw trustworthy conclusions.

LITERATURE CITED

GemmiLh, J. F. 1914 The development and certain points in the adult structure
of the starfish Asterias rubens. Phil. Trans. Royal Soc., v. 205,
Series B.

Herwer, K. 1909 Zur Entwicklung von Balanoglossus clavigerus. Zool. Anz.,
Bd. 34, 1909.

KatscHenko, N. 1888 Zur Entwicklungsgeschichte des Selachierembryos.
Anat. Anz., Bd 3.

Piatt, J. B. 1894 Ontogenetische Differenzirung des Ectoderms in Necturus.
Arch. mikr. Anat., Bd. 48.

,

PLATE 1

EXPLANATION OF FIGURES

1 Late gastrula or early bipinnaria stage showing mesenchyme migrating
from the apical plate (ap) and coming in contact with the anterior vesicle (av).
The archenteron bears the usual two enterocele pouches and a single-left poste-
rior one.

2 Anterior end of bipinnaria showing the completion of the mesenchyme
formation at the apical pole and its migration to the esophageal region. The
left hydrocele is provided with pore canal and hydropore. lp left posterior
vesicle.

3 Section of gastrula showing apical plate with signs of mesenchyme
formation.

4 Bipinnaria showing mesenchyme migrating past the anterior vesicle (av)
to the esophagus. The left hydrocele has severed its connection with the archen-
teron. lp left posterior vesicle in process of formation.

5 Surface view of gastrula immediately before mesenchyme development
from apical plate.

468

EARLY DEVELOPMENT OF A STARFISH PLATE 1
HAROLD HEATH

<p

469

a ee a.
We pee ic eet!

AUTHORS’ ABSTRACT OF THIS PAPER ISSUED
BY THE BIBLIOGRAPHIC SERVICE SEPTEMBER.

SYNAPSIS AND CHROMOSOME ORGANIZATION IN
CHORTHIPPUS (STENOBOTHRUS) CURTI-
PENNIS AND TRIMEROTROPIS
SUFFUSA (ORTHOPTERA)

D. H. WENRICH

Department of Zoology, University of Pennsylvania

THREE PLATES

CONTENTS
Peeper COG CROWES. pPeNe eS je: 55. . v5 5s Se ed aS Do oe do ke 472
AO Sek set tO Maes epee tsa, seca Skee ta Ws « «+9 « 20S ning RMON Cee lot hance od 474
A. Chorthippus (Stenobothrus) curtipennis......................... 474
De Jin OC hCiOM 7 DUCA cagsosedenusddtacc ds sucbcaccogancnde 474
b:) he post-apireme chromosomes. .\. 585. )chactetds vac ve eee es 475
(oatohaolh Os sive We cia Rae ee eat are Re et, ae en ee 476
Ga Chroma tigumovementsi.v....2>.. 5... 1 lateness vas os 479
ex the planes. o1-tne fitstGlvisiol. ....crn <2 geese t= ers 480
f. The apical constrictions and the chromomere-vesicles....... 481
po ltheraccessonyachromosome®....1. <1. ..4u sonore as oe eee: 483
FR EINTT t Vee eeer tees yee oS 2... . 16. 2 ree oc et ch he 483
Be Erimero,ropis Suiusnt ee 25... «ete eee = tes ae 484
algo du ChomyvestabeM Clibe tery. 4705.,; i. «ses eens ecto 3 = 484
bavthelpost-spiremelchromosomes... .:.):2 -- seen eae: oo oe 484
Cae the evidence Gn SYNAPSIS,; . 46 <. .°. 2 4. eee eee shoes - 486
dm ChromatidumovementsS 42.050. +. cle Rees secede 487
es Dheyplamesiotstme, first sean Vvision:. . .). <2. eae sie hoe sat 490
f. Additional observations on organization.................... 492
FROUITIT VA PEARL Renee is a va ashes eee eaten eas De 493
TUCO NSCS Oa a 2 Bente Ate 0/0 ta aS J, ee 494
TNSISS GE 6] Wine ay eer IR J aCe eg =. 5 Oe 494
bs Ee re-rednctionavs..pOst-reGuchlony @. .....- 0 .. << ews nc see 498
@eEChromosomeronrranizationeme eet |. ae ac emeiesnctoee) dal 1 505
ae Atelomiitic CUROmMOsOIMeS i: .. «2. ph tae eee nee ores 505
bseRherchromomene-vesiclestss..:... <:.0 2. -etee eeeiee chsc ie sie = 507
De Sammary, of conclastons:.. 22.2.4 - =... ss. 2 2)ceee Pe sascha: 509
LiWe JIA Per ey TUES CNet Re. OOM eS Ooo.) Oe ae 510

471

472 D. H. WENRICH
I. INTRODUCTION

In a recent paper (Wenrich, ’16) the writer presented what
seemed to him conclusive evidence that parasynapsis occurs
in at least three pairs of first spermatocyte chromosomes of
Phrynotettix magnus. Although only these three chromosomes
were studied in great detail, sufficient attention was given the
other members of the complex to assure the writer that para-
synapsis occurs in all. Phrynotettix, however, like many of the
Oedipodinae, possesses only rod-shaped, or telomitic chromo-
somes. It seemed advisable, therefore, to investigate the con-
ditions to be found in species of grasshoppers in which the
chromosomes are V-shaped, or atelomitic. Chorthippus (Steno-
bothrus) curtipennis was chosen for this study because it is
readily obtainable, gives clear figures when fixed and stained,
and because various species of the genus have been the subject
of investigation in the past. Sufficient study of this species,
which has three pairs of atelomitic chromosomes, was made be-
fore the publication of the paper on Phrynotettix to assure the
writer that the chromosome relationships in synapsis are essen-
tially the same as in that form with respect to both types of
chromosomes. This is indicated by the following statement
(Wenrich, 716, p. 98):

I have recently made a study of the conditions in Stenobothrus and
may say that I found parasynapsis for both forms of chromosomes,
and that the V-shaped chromosomes divide reductionally in the first
maturation mitosis as Davis (’08) described, but that the rod-shaped

chromosomes divide equationally in the first division as I found that
they did in Phrynotettix.

No drawings were presented to support these statements at
the time, but the evidence (with additions) on which the conclu-
sions as to parasynapsis were based is presented in the present
paper. Unfortunately, more careful study of the material makes
it impossible to be so confident as to which division is reductional
for the two types of chromosomes. This point will be discussed
later.

The same conclusions as to parasynapsis in Chorthippus, to-
gether with the same kind of evidence, in part, has recently

SYNAPSIS AND CHROMOSOME ORGANIZATiON 473

been presented by Robertson (’16). In many respects the evi-
dence and conclusions which have been independently reached
by Robertson and myself will be mutually corroborative. In
regard to some points, however, differences of interpretation
exist which will be discussed in an appropriate place.

In view of the very interesting conditions in Trimerotropis
and Circotettix, where telomitic chromosomes are paired with
atelomitic ones, as found by Dr. E. Eleanor Carothers (’17)
it seemed worth while to examine stages which would indicate
what form of synapsis occurs between these chromosomes of
diverse form. Dr. Carothers very kindly permitted the use of
her slides for this purpose. It may be stated at once that para-
synapsis was found to occur for all the chromosomes of Trimer-
otropis of whatever form, just as it does in Chorthippus and
Phrynotettix. In addition to the subject of synapsis the topics
of pre- and post-reduction and chromosome organization will
be considered.

In this paper new terms will be used in accordance with those _
‘recently adopted by Dr. Carothers (717), asfollows: (1) Telomitic—
chromosome with terminal fiber-attachment, i.e., rod-shaped;
telomitic and rod-shaped will therefore be used interchange-
ably; (2) atelomitic—chromosome with non-terminal fiber-attach-
ment = V-shaped; V-shaped and atelomitie will be used inter-
changeably; (3) heteromorphic—those pairs of chromosomes (tet-
rads) of which one member is telomitic and the other atelomitic,
or, of which one member is noticeably different in form or size
from its mate; (4) chromomere-vesicle—the plasmosome-like ap-
pendages formerly called ‘vesicles’ by Carothers (713), and called
appendages and plasmosome-like structures by the writer (’16).
I shall also make use of McClung’s (’14) term, euchromosome as
equivalent to Montgomery’s ‘autosome.’

All drawings have been outlined with a pencil under the
‘camera lucida and then inked while the cell remained under
observation.

A474 D. H. WENRICH

II. OBSERVATIONS
A. Chorthippus (Stenobothrus) curtipennis .

a. Introductory statement. Chorthippus (Stenobothrus) curti-
pennis belongs to the sub-family Truxalinae of the Orthopteran
family Acrididae. The material from which nearly all the draw-
ings were made consists of a single smear prepared during the
summer of 1914 at Woods Hole, Mass., near which place this
species was abundant. Through the kindness of Professor
McClung I was afforded facilities for preparing and staining
cytological material at that time. The smear was fixed in
Flemming’s stronger solution (at a temperature of about 4°C.).
One part was stained with Zwaardemaker’s safranin, the other
with Heidenhain’s haematoxylin. Figures 12, 13, and 14, plate
3, are from sectioned material, fixed in cold Flemming’s fluid and
stained with Heidenhain’s haematoxylin.

While: this material was studied some during the summer of
1914 and at. Harvard University during the winter of 1914—
1915, it was carefully re-examined in 1915-1916 at the Univer-
sity of Pennsylvania and again at Woods Hole during the sum-
mer of 1916, when most of the drawings were made. I am in-
debted to the University of Pennsylvania and to the director
of the Marine Biological Laboratory for facilities for pursuing
this study at Woods Hole.

Although material from a number of individuals was studied,
nearly all the drawings are made from a single smear derived
from one animal as stated above. It was deemed desirable to
represent conditions from a single specimen in order to avoid any
possible confusion arising through individual variations, since
recent studies on such forms as Phrynotettix, Trimerotropis,
Hesperotettix, ete., have shown that individuals within a species
may vary as to certain features of their chromosomal constitu-
tion, but: the conditions in each individual remain constant. In
the second place, a smear was used in order to insure the pres-
ence of whole complexes in each cell and thus to avoid the diffi-
culties incident to the study of sections, where most of the cells
are cut and distributed into two or more sections with frequent

SYNAPSIS AND CHROMOSOME ORGANIZATION 475

disarrangements or cuts in the chromosomes. Some distortions
naturally arise as a result of the smearing process, but the prepa-
ration used was more than usually free from such disturbances
and in this case the advantage gained through the study of
whole cells far outweighs the disadvantages arising from the
smearing process.

In plate 1 all of the chromosomes in each cell are represented.
It is believed, therefore, that, although identifications of any
chromosome in any cell might sometimes prove doubtful, the
chances for error, with all members present, is reduced to a
mininum. This method also has its disadvantages, because
only occasionally are all of the chromosomes in any particular
cell in favorable positions for drawing.

b. The post-spireme chromosomes. The post-spireme stages
have received the most attention and are represented on plate 1.
As a glance at the plate will show, there are nine chromosomes
in the reduced series. This number has been reported for all
the species of the genus which have been studied except the
doubtful member reported by McClung (’14) and which he now
thinks may be Circotettix in which there were eleven. In plate
1, the chromosomes of eight cells are represented, those from
each cell being arranged in a vertical column according to size,
with the smallest at the bottom. The cells are lettered A, B,
C, ete. Each horizontal row therefore presents examples of a
particular chromosome, and successive stages in development
from the end of the spireme stage to early anaphase can be read
from left to right. These horizontal rows correspond in develop-
mental stages to figures 62 to 65, plate 6, of the paper on
Phrynotettix.

_ Of the nine chromosomes in the first spermatocyte one is the
unpaired accessory chromosome (no. 3); the others are tetrads,
consisting of three pairs of atelomitic (nos. 7, 8, and 9) and five
pairs of telomitic chromosomes (nos. 1, 2, 4, 5, and 6). Column
A represents the chromosomes of a cell at the stage when the
spireme of the growth period has just become distinguishable as
individual segments, each segment being the direct forerunner of
a tetrad (except the acccessory, no. 3). Each of the segments is

476 D. H. WENRICH

an attenuated thread with a longitudinal cleft, and more or less
coiled or bent, according to its length. The longitudinal cleft
is what has been called the primary longitudinal split.

In cell B, a second split is seen at some points, where four
threads are visible (e.g., at a). In cell C all of the segments
(except no. 1 and the accessory) have the four chromatids, indi-
cating that the secondary longitudinal split has become complete.
The other cells, D to H, represent the farther progress of chro-
matid transformation and condensation, through characteristic
tetrad figures, to the metaphase or early anaphase of the first
maturation mitosis. As nearly as possible, all of the tetrads in
cells D to H have been given the same orientation; those in cells
A, B, and C could not be definitely oriented, partly because the
synaptic points could not be determined and, in the case of
numbers 7, 8, and 9, partly because of lack of space on the plate.

c. Synapsis. The point to which especial attention should be
directed is that all of the autosomes, or euchromosomes, show
the same fundamental conditions, whether they be pairs of telo-
mitic or atelomitic chromosomes. All come out of the spireme as
elongated threads with one longitudinal cleft visible; all develop
a second longitudinal cleft at right angles to the first, giving rise
to tetrads, each with four chromatids. And since, as is generally
believed, each tetrad represents a pair of spermatogonial chro-
mosomes, it would appear that each of the spireme segments in
cell A represents a pair of chromosomes which have been ex-
tended axially and united side-by-side throughout their length.

I have already shown (716) how this side-by-side union of
attenuated leptotene threads takes place in Phrynotettix. Evi-
dence of the same nature for Chorthippus is presented in figures
1 to 4, plate 3. In figure 1 a nucleus is shown with one double
thread (5)—that attached to the accessory—and another thread
which is double at the end nearest the accessory (proximal end)
but divides distally into two single threads. Numerous single
threads are visible in the other parts of the nucleus. In figures
2 and 3 a considerable number of these partially conjugated
pairs of threads are shown. In none of these drawings (figs. 1
to 4) was it possible to represent all of the threads because they

SYNAPSIS AND CHROMOSOME ORGANIZATION 477

are so long and so extensively curved and coiled that they ap-
pear at first glance to be hopelessly tangled and to constitute a
network. It was possible, however, by careful study, to follow
some of the threads for considerable distances, but others only
short distances. On this account these drawings are, in part,
diagrammatic.

In these lepto-zygotene nuclei there is always a tendency

toward an orientation of the threads just as was found at the
corresponding stage in Phrynotettix (’16, figs. 29, 30, 31, plate
3). This orientation appears to be confined mostly to the region
near that end of the thread to which the spindle-fiber is at-
tached (proximal end) and therefore that side of the nucleus
toward which these ends are directed is called the proximal side.
From this proximal side the threads run more or less parallel
toward the opposite side of the nucleus, thence turning to trav-
erse the nuclear space in various curved or convoluted courses.
The amount of curving depends, apparently, on the length of the
threads, though even the shorter ones have a tendency to form
a loop as is indicated by the short, deeply staining thread (5),
attached to the accessory chromosome in figures 1 and 4. In
general, only the proximal ends of the threads exhibit orientation
and this orientation, I believe, facilitates the initiation of the
pairing process and causes its inauguration to occur at the
proximal ends, as shown in figures 1 to 3. In the distal part of
these figures most of the threads are single. The accessory (X),
usually has one end attached at the proximal pole, as shown in
figures 2 and 3. In figure 4 the position of the nucleus was such
that the orientation could not well be shown without interfering
with other features which it was desired to represent.
- The nuclei in figures 2, 3, and 4 were chosen for drawing be- —
cause they show, in addition to the partially conjugated threads
already mentioned, certain others to which small plasmosome-
like bodies, or chromomere-vesicles, were appended. ‘These
structures, (c), as will be pointed out later, mark the synaptic
points on one of the pairs of V-shaped chromosomes.

The question has naturally arisen as to the behavior of these
V-shaped chromosomes in synapsis. Does the process of conju-

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

478 D. H. WENRICH

gation begin at the apices of the V’s and proceed toward the
ends, or does it begin at the free ends and proceed toward the
apices? The drawings shown are not entirely conclusive on
this point, though very suggestive. In figure 2 the two synaptic
points are marked by deeply stained knobs to which the ‘ves-
icles’ are attached. These knobs are not situated at the proxi-
mal side of the nucleus, but appear to have been pulled away
from this position which they undoubtedly held in the telophase
of the last spermatogonial division (figs. 7 and 8). The knobs
are at the apex of an angle made by a sharp bend in the threads
at that point, and while the knobs themselves stand somewhat
apart, the threads appear to be conjugated for a short distance
on either side of them. When I attempted to follow these con-
jugated threads they soon became lost in the maze of unconju-
gated, single threads. The appearances, however, indicate that
the only parts of these threads which had conjugated at the
time were those immediately adjacent to the appendage-bearing
knobs, and therefore at the apices of the V’s.

In figure 3 a situation is presented somewhat similar to that
in figure 2, except that here conjugation has taken place on
only one side of the apical knobs, the remainder of this pair of
threads apparently consisting of unpaired leptotene strands.
In figure 4, conjugation of this pair has gone further, but even
in this: case the conjugated part is confined to the region on
either side of the synaptic points. These cases, together with
others which have not been drawn, tend to support the idea that
conjugation of the atelomitic chromosomes begins at the apex
of the V, which, as the point of spindle fiber attachment, is
homologous with the proximal end of the telomitic or rod-shaped
chromosomes. |

As soon as conjugation is complete, all of the chromosome
threads appear double, as shown in figure 5, which represents
the pachytene stage. In this nucleus, the usual orientation of
the chromatic elements has been lost. There is some tendency
for the threads to be centered toward the side of the nucleus
which is uppermost in the drawing, but the accessory chromo-
some (X), which is customarily attached at the proximal role

SYNAPSIS AND CHROMOSOME ORGANIZATION 479

of the nucleus, is here removed a considerable distance, and
separate from the deeply stained loop (5), to which it is usually
attached. This deeply-staining thread is found in the later
stages to be that of chromosome 5 (see plate 1) and it very com-
monly lies near, and often attached to, the accessory. This
association may be seen in figures 1, 4, and 6.

Figure 6 represents a nucleus at abot the same stage a as cell
A on plate 1 and shows the separate spireme segments. Each
of these has but one longitudinal split, but each represents a
tetrad. The segments are numbered according to the arrange-
ment on plate 1. <A series of successively older stages may
therefore be recognized, beginning with figure 1, extending
through figure 6 on plate 3, and continuing through cells A to H
on plate 1.

The series of stages just mentioned constitute, it seems to
me, a sufficient body of evidence to indicate that in Chorthippus
parasynapsis is the rule.

d. Chromatid movements. Attention may be directed to the
different rates of change in the chromatid relationships experi-
enced by different chromosomes in the.same cell and by the
same chromosome in different cells. The typical form of the
metaphase chromosome’ of the telomitic type seems, in this
* species, to be the rod extended parallel to the spindle axis. Such
a form is taken by chromosomes 1, 2, 4, and 6 of cell G on plate 1.
Although number 5 has not been pulled out in the direction of
the mitotic poles sufficiently to make it a rod, it is readily ap-
parent that only a small amount of movement of the oppositely
directed pairs of chromatids would produce the forms seen in
chromosomes 4 and 6. As an example of the different degrees to
which the chromatid movements have brought about an ap-
proach to the extended-rod condition of the metaphase, atten-
tion may be called to cell E, where chromosome 4 seems to be
lagging much behind the other chromosomes, though in cells F,
G, and H, such is not the case. In cell D, on the other hand,
chromosomes 2 and 5 seem to be farther advanced toward the
metaphase-rod condition than any of the others.

480 D. H. WENRICH

When we examine a particular chromosome as it appears in
different cells we do not always see a consistent progress in de-
velopment in the successively later stages. Chromosome 4 in
cell E seems to be in about the same condition, so far as chroma-
tid movement is concerned, as it is in cell C; that is, either one
could, by the simple rotation of the free arms, assume the con-
dition seen in cell G. However, it is just possible that in cell
D a valid intermediate stage is represented and that this chromo-
some in the condition found in cell C would have to pass through
a stage such as that in cell D before reaching the condition seen
ims or G.

e. The planes of the first division. In the absence of well-
marked polar granules it is impossible to determine which are the
proximal, or synaptic, ends of the chromatids, but if we may
assume for the time being that the ends at the left in cells B
to E are the synaptic ends, we may trace for chromosome 4 suc-
cessive steps as follows: In cell B the longitudinal split on the
right (the only one visible for two-thirds the length of the
tetrad) is probably the primary longitudinal split. The split
just forming at the left and continued to the point a is probably
the secondary split. In cell C, then, we may consider that the
formation of the secondary split has been completed and that the
chromatids have separated along this split almost to the distal
end. Such an element might remain in this condition, con-
densing through a stage such as is shown in cell E and finally
opening out to form an element in the metaphase like the one in
cell G. In cell D we may have a stage in which the secondary
split has become complete but the separation along its plane has
not. If the progress of separation along this plane were to be
impeded by gradual condensation, this stage might be followed
by a cross formed by the proximal ends (left) of the two pairs of
chromatids becoming extended in opposite directions in the same
plane (as shown in chromosome 2, cell D), which cross might
reach the metaphase in some such form as shown for chromo-
some 5 and 6, cell F, or even chromosome 4, same cell. A simi-
lar series of stages occurs for chromosome 2 in cells B, C, and D.
Series of movements such as have been suggested would corre-

SYNAPSIS AND CHROMOSOME ORGANIZATION 481

spond in all essentials to the series of changes found to occur for
chromosome A in Phrynotettix (see 716, fig. 62, plate 6), and
would indicate an equational division. Other interpretations,
indicating a reductional division are, of course, possible, and
cannot be excluded.

In chromosome 6 a similar series of stages may be traced.
In cell B the split running through most of the length of the
element from the right is probably the primary split, while that
just beginning at the left and extending to point a would be the
secondary split. A continuation of the secondary split and a
separation along its plane would give rise to such a stage as
that seen in cell C, or, if the separation were delayed, to that in
cell D. A rotation of the arms of the tetrad in cell C would
give rise to a stage such as is shown in cells E and G, while a
similar rotation of the arms of the example in cell D would give
rise to the condition seen in F.

It is regrettable that the polar granules, which do occur to
some extent, are not sufficiently differentiated by the staining
method used to make the orientation of the tetrads certain.
In sectioned material stained with iron-haematoxylin polar
granules are, in fact, better differentiated than in the safranin
stained smear, but in this instance little study has been made
of sections, where identification of all the chromosomes is not
so certain.

In the case of the pairs of atelomitic chromosomes (nos. 7,
8, and 9) variations in rate and extent of chromatid movement
are not so apparent in the examples drawn on plate 1. Such
variations do exist, however, as will be seen by comparing num-
ber 8 with three ‘rings’ in cell C, and two ‘rings’ in cells D, E,
and F, and figures 9 to 14, plate 3. i

f. The apical constrictions and the chromomere-vesicles. In
these atelomitic chromosomes the synaptic point is in many
cases very clearly marked by a constriction, as Robertson (’16),
has emphasized. This constriction (point b in the figures, plate
1) is not visible in all cases, as is indicated in the figures. Chro-
mosome 9 in cell E for example, shows scarcely any evidence of
a constriction, although it is plain enough in chromosomes 7

482 D. H. WENRICH

and 8. In cell F chromosomes 7 and 9 show the constriction,
while it is not apparent in chromosome 8. Again in cell G
chromosome 9 did not reveal the constriction as did chromosomes
7 and 8. All three show evidences of a constriction in cell C.

In connection with this synaptic point, as already mentioned,
there is a small plasmosome-like appendage, or chromomere-
vesicle (marked c in the figures), which seems, in the earlier
stages at least, to be as constant in its occurrence as is the con-
striction just described. It disappears in the later tetrad stages
as such structures usually do. Similar appendages are occa-
sionally seen attached to the synaptic points of chromosomes
7 and 8, as is indicated for the former in cell D and for the
latter in cell A, but their occurrence on these chromosomes is
rather infrequent.

It will be noticed that only one appendage is to be seen on a
single chromosome. in the figures on plate 1. In earlier stages,
however, there are two such bodies as is indicated in figures 2,.
3, 4, 6. 7, 8, and 9, plate 3. Figure 5 shows the two partially
fused together and many times they appear to be entirely fused
at these stages. It could not be determined whether the single
appendage in plate 1 and in figures 10 to 14 on plate 3 repre-
sent two fused together, or whether one of them disappears
before the other. The latter possibility is suggested by a con-
stant difference in size in all cases where two are in evidence
and by the fact that the single ones in figures 10 and 11 do not
appear to be equal in bulk to two such as are shown in figure 9.
In figures 12, 13, and 14, they appear larger, but these figures
are taken from sections from another individual, which fact may
account for their larger size. That these structures are con-
stant elements of this pair of atelomitic chromosomes is well
illustrated by the spermatogonial telophases shown in figures 7
and 8. In each case the ‘vesicle’ is attached at the apex of a
V-shaped chromosome with a marked disproportion between the
lengths of the arms, comparable to that seen for chromosome 9
on plate 1. In figure 8, the smearing process has resulted in a
slight distortion of one of the atelomitic chromosomes (at the
left) to which an appendage is attached. It seems fairly safe to

SYNAPSIS AND CHROMOSOME ORGANIZATION 483

regard these chromomere-vesicles as diagnostic for the apices in
this largest pair of V-shaped chromosomes.

In-the figures from sections (figs. 12 to 14, plate 3) the ap-
pendage is attached to only one member of the pair of knobs
which mark the synaptic point, and, further, the attachment is
always to the knob nearer the middle of the chromatid. In
the smears this position is not so evident owing to the lack of
definite knobs showing at the synaptic points. However, chro-
mosome 9, cell A, does show such knobs and it will be observed
that the appendage is attached to the one nearer the middle of
the chromatid. Chromosome 8, cell A also shows such a rela-
tionship. The possible evidence that these structures furnish
toward an understanding of the planes of first spermatocyte
division will be considered in the discussion.

g. The accessory chromosome. The accessory chromosome
does not require description or discussion in this paper, but
attention may be called to the vesicular appendage attached to
it. This appendage is similar to those Just mentioned which are
attached to the atelomitic chromosomes. This structure seems
to have been overlooked by all those who have studied this form,
except Davis (08).

h. Summary. In summarizing the observations on Chor-
thippus we may call attention to the following:

1. The number of chromosomes in the reduced series (first
spermatocyte) is nine, consisting of one unpaired accessory chro-
mosome and eight pairs of autosomes or euchromosomes. Of
the latter there are three pairs of atelomitic and five pairs of
telomitic chromosomes.

2. The leptotene threads conjugate two-by-two throughout
their length during the zygotene, or lepto-zygotene, stages.
They remain conjugated through the pachytene stage and until
the tetrads are formed. This condition of parasynapsis holds
for all the euchromsomes, both telomitic and atelomitie.

3. The process of parallel conjugation (parasynapsis) appears
to be inaugurated at the proximal ends of the leptotene threads
as was the case in Phrynotettix, and it appears to begin at the
apices of the atelomitic chromosomes.

484 D. H. WENRICH

4. A constriction occurs at the synaptic points in most of
the tetrads of the atelomitic chromosomes.

5. A small plasmosome-like appendage, or chromomere-
vesicle, is attached to the conjugants of the largest pair of
atelomitic chromosomes (no. 9) at the apex of the V (synaptic
point. A similar appendage is occasionally found at the homol-
ogous point on the other two atelomitic pairs, and occurs very
constantly on the accessory chromosome.

B. Trimerotropis suffusa

a. Introductory statement. Trimerotropis belongs to the sub-
family Oedipodinae of the family Acrididae. A discussion of
some systematic problems connected with this genus will be
found in the paper by Dr. Carothers (’17). The material
from which the drawings were made consisted of a single
smear made by Dr. Carothers and loaned to the writer for
study. This individual corresponds to her number 34 (plate 6)
(17) and cell E on my plate 2 is the same as that drawn by her.
Other individuals were studied but no drawings from them are
used in the plates.

The reasons for using a smear preparation in this case are
the same as those already stated in connection with Chorthippus.
This smear was fixed in Flemming’s solution and stained by
Flemming’s tri-color method. The chromatin was not so
deeply stained in this smear as it was in the smears of Chor-
thippus, and this difference appears in the drawings.

b. The post-spireme chromosomes. As Carothers has found,
the reduced number of chromosomes in this genus is twelve.
Occasionally, however, supernumerary chromosomes occur, as
she discovered, and one such supernumerary occurs in this in-
dividual, making the number of first spermatocyte elements
thirteen instead of twelve.

The arrangement of the chromosomes in plate 2 is the same
as for Chorthippus in plate 1. Each vertical column repre-
sents the complete series of chromosomes from a single cell ar-
ranged in the order of size with the smallest at the bottom.

SYNAPSIS AND CHROMOSOME ORGANIZATION 485

The differentiation on the basis of size is not always easy to
make. This difficulty is made more apparent by the differences
between the order used on this plate, where the accessory is
made number 3, and the order used by Carothers, who made
the accessory number 4. Such differences, however, are without
significance so long as other means of identification are avail-
able to obviate confusion. The supernumerary is placed at the
top of the plate to avoid any possibility of its becoming con-
fused with the smaller tetrads. From left to right are shown
successive stages in the transformation of the spireme segments
to tetrads, and their condensation, final orientation, and partial
division in the spindle of the first maturation mitosis.

A glance at the metaphase figures shows that the complex of
this individual consists of four pairs of atelomitic chromosomes
(nos. 7, 10, 11, 12), five pairs of telomitic ones (nos. 2, 4, 5, 6,
9), two heteromorphic pairs (nos. | and 8), the atelomitic acces-
sory (no. 3), and the supernumerary. In other individuals of
the species the relative numbers of pairs of atelomitic, telomitic,
and heteromorphic pairs may be different, as found by Carothers
and described by her.

It is not possible in every case always to identify each chromo-
some in a cell. This is due to similarities of size and organiza-
tion. Chromosomes 11 and 12, for example, appear very similar
in size and organization in the earlier stages, so that it is not
always possible to tell which is which. In the metaphase and
anaphase, however, these two are distinguishable by the dif-
ferent proportions between arm-lengths of the V’s. Number
12 has the greatest disproportion between arm lengths; in num-
ber 11 the disproportion is less, and in number 10 still less.
The proportions between arm-lengths for these atelomitic
chromosomes can the more readily be determined by reason
of the occurrence in many of the metaphase examples of con-
strictions or transverse clefts at the points of spindle-fiber at-
tachment. Such clefts are to be seen, for example, in cells E,
F, and G for chromosomes number 11 and 12, and cells E and
F for number 10. Such clefts or constrictions (marked 6 in
the figures) can sometimes be distinguished in the earlier stages

486 D. H. WENRICH

as, for example, one cleft for number 12 in cell D, two clefts for
number 11 in cell D, two clefts for number 10 in cell C, and in
the ease of the atelomitic member of number 8 the cleft shows
very plainly in cell D. Clefts are likewise indicated for number
7 in cells C and D, and still more plainly in the metaphase cells,
E and G. These clefts or constrictions appear to correspond in
all respects to those found in the atelomitic chromosomes of
Chorthippus. ,

Chromosomes 5, 6, and 7 are somewhat similar in organiza-
tion, each possessing polar granules at both ends. This gives
rise to some uncertainty as to identity, especially in cells B
and C. In cell A the differences in length are more apparent.

Number 4 in cells A, B, and C, and number 8 in cells A and
B are readily identified by the peculiar clusters of granules (c)
attached to them. In the later stages these disappear and
this gives rise to some difficulty in identification in the case of
chromosome 8. Number 4, however, possesses an additional .
means of identification by reason of its staining power which is
constantly greater than in the other euchromosomes.

In spite of the difficulties of identification, it is felt that with
all the chromosomes present in each cell, and with a careful
consideration of the size and structure relations of the various
chromosomes, very few mistakes in serial arrangement have
been made.

c. The evidence on synapsis. The evidence for parasynapsis,
as presented on plate 2 is of the same nature as that for Chor-
thippus, and consists in the facts: (1) that all the euchromosome
pairs, irrespective of the point of spindle-fiber attachment,
come out of the growth period as longitudinally split, attenuated
threads, and (2) that from these split threads tetrads arise by
the formation of the secondary longitudinal split. Figure 21,
plate 3, gives the evidence for parasynapsis as it occurs in the
lepto-zygotene stages and the conditions shown are quite similar
to those already described for Chorthippus and shown in figures
1to4. Figure 21 does not represent nearly all of the chromatin
threads in the nucleus and is partially diagrammatic. However,
the condition indicated—namely, the presence of double threads

SYNAPSIS AND CHROMOSOME ORGANIZATION 487

with one end at the proximal pole of the nucleus and the other
end separating distally into two single threads—was clearly
seen for a number of those represented and indicated for the
others. The deeply staining body near the accessory (X) is
regarded as the supernumerary chromosome. In this stage in
this material none of the atelomitic chromosomes could be iden-
tified and, while the tendency for conjugation to begin at the
proximal ends of the threads is clearly indicated, the behavior
of the atelomitic chromosomes could not be followed.

d. Chromatid movements. Differences in rates of development,
or progress toward separation at anaphase, in different cells
find some striking éxamples in the series drawn on plate 2.
Chromosome number 1 seems to be lagging somewhat behind
the others in cells B and C, though in cell D it is as far advanced
as any. In cell D, number 2 is not so far along toward its
typical metaphase condition as it is in cell C. The same rela-
tions appear to hold for chromosome. 5 in these two cells, yet
all of the chromosomes in cell D are more condensed and there-
fore presumably nearer metaphase than they are in cell C.

In the metaphase there are also some striking differences.
Number 4 in cell G is very far behind the other members of the
complex and seemingly little advanced in chromatid movement
beyond the condition seen in cell A. In cell F, too, separation is
not so far advanced for this chromosome as it isin cell E. Cell H
is in early anaphase, and cells E, F, and G are at about the
same metaphase stage, yet chromosome 9 is not so far advanced
toward complete separation in F as it is in EK, and in E it is not
so far along as in G, yet in G it seems further along than in H.
Again number 6 is lagging in cells F and G, as compared to the
conditions in E and H. The examples of this chromosome in
cells F and G are at about the same stage, but in G a ring exists
through the contact of the ends of the arms at the right which
are seen to be free in cell F.

All these differences seem to indicate that the extent of chro-
matid movement is variable, not only for different chromosomes
but also for the same chromosome in different cells, so that in
some cases the movement which ends in the separation accom-

488 D. H. WENRICH

plished in the anaphase may be well advanced before the ele-
ment reaches the metaphase, while in other cases these move-
ments are largely deferred until after the element has been
oriented in the metaphase spindle.

There are some pronounced differences in shape of the atelo-
mitic chromosomes in the metaphase. In the case of chromo-
some 12, for example, a different shape is seen in each of the
cells, E, F, G, and H. It is easy to see how a simple move-
ment of the oppositely directed dyads in cell E toward their
respective poles would give rise to the condition in cell H; but
no such simple movement would account for the shapes in F and
G. The explanation of these various shapes, I think, may lie in
the statement made above as to the variations in chromatid
movement in the earlier stages. A search among the tetrad
figures of these earlier stages should reveal the forerunners of the
shapes seen in metaphase. In cell C, for example, is a condition
of chromosome 12 which would readily give rise to that in cell
E if the shorter arms of the V’s are toward the right and the
apices of the V’s are pulled out toward opposite poles. Simi-
larly for chromosome 11, the tetrad in cell C might easily take
its place in the spindle in the form shown in cell E and the
tetrad of number 10 in cell D could, by orientation, assume the
shape in cell E. In cell D, on the other hand, occurs a condi-
tion of number 12 which in many respects is similar to that in
cell F. The chief difference is that in the latter the short arms
of the V’s have been reflexed toward the longer arms. The
tendency for the shorter arms to bend back in this way
when they are free is not infrequent among the atelomitic
chromosomes, as shown by McClung (’14). A somewhat similar
metaphase of number 11 or 12 from another cell is shown in figure
18, plate 3. Figure 17 shows an earlier tetrad which could give
rise to it by the separation of the ends on the right and their
flexure backwards toward the left.

None of the earlier stages for chromosome 11 or 12 as seen on
plate 2 indicate a condition which could by any simple move-
ment give rise to the shapes seen in cell G. Here the curious
condition is found of the shorter arms remaining in contact,

SYNAPSIS AND CHROMOSOME ORGANIZATION 489

while the longer arms have become free. From the standpoint of
simple mechanics it would be difficult to understand how a
tetrad such as is seen in cell C, for example, could give rise to
the condition in cell G. It would be natural to suppose that the
crossed longer arms (at the left) would require a greater amount
of force for separation than the shorter arms in contact at the
right; the pull of the spindle fibers would be expected to be
exerted more strongly on the shorter ends. The conditions in
cell G are the exception rather than the rule, and I have not found
an earlier tetrad which showed the longer arms free as they are
in this cell. However, in figure 19, plate 3, there is a ring-
shaped tetrad which, by the mere separation of the lightly at-
tached ends of the long arms at the left, would provide a condition
analogous to that in figure 20, which resembles those in cell G,
plate 2. A condition which is the reverse of that in figure 20
is shown in figure 16, where the short arms are free. Such a
shape could readily arise from that in figure 15 by a little more
separation along the plane between the arms at the right and
their flexure at the point of spindle-fiber attachment.

It might be remarked that one cannot be certain whether
chromosome 11 or 12 is represented in figures 15 and 17 because
the synaptic points are not indicated by clefts as they are
in figure 19. Figure 16 is doubtless number 12, with its great
disproportion between arm lengths, while figure 20 is more
probably number 11. Figure 18 is problematical.

In cells E and G chromosome 7 (plate 2) seems to have the
shorter arms united and the longer arms free, while in F the
longer arms are attached to each other and in H they have
been the last to separate. In cell E the difference between arm
-lengths seems much less than in the other cells. This is to be
accounted for by the foreshortening of the longer (free) arms
and by the stretched conditions of the attached shorter arms,
shown by their smaller diameter.

As a net result of such observations one may conclude that the
movements of the constituent chromatids of a tetrad are sub-
ject to great variation and that with respect to the separation
of the ends, there is sufficient evidence to show that either the

490 D. H. WENRICH

longer or the shorter ends may become free in advance of the
other end. Just why the chromatids should assume the vary-
ing relationships to each other in similar stages of the tetrad
transformation period is of course not easily determinable, but
the metaphase figures seem to be derived from similar ones in
the earlier stages without much movement of the chromatids
during the later condensed prophases, nor until the forces in
metaphase and anaphase are at work. One may suppose that the
movement of the chromatids takes place at different rates in
different cells and that, as condensation in the later prophases
progresses, such movements are retarded; the result being that
whatever stage in transformation has been reached in a late
prophase is the one in which the element enters the spindle.
The further movements then must be the result of the forces in
operation during metaphase and anaphase.

e. The planes of the first division. In Chorthippus, as de-
scribed on pages 480 and 481 the evidence seemed to favor an
equational division for chromosomes 2, 4, and 6 (plate 1) which
are telomitic. Evidence of equational division among the telo-
mitic chromosomes of Trimerotropis can be found on plate 2.
Chromosome 2, for example, as it appears in cell A, has a very
characteristic arrangement for the parts of this element. It has
very pronounced polar granules at both ends, those at the
distal end being the larger. That.the larger granules represent
the distal end is shown very well in the metaphase figures E, F,
G, and H.- A further indication that these larger granules are
at the distal end is their behavior toward each other. In all of
the cells studied which were at stages corresponding to cells.
A and B, these large granules stood widely apart from each other.
The example in cell A shows this especially well. It would
hardly be supposed that the proximal ends of a pair, being the
first to conjugate, would behave in this manner, while the distal
ends might easily fail of complete pairing. Now, since it is
possible to determine which end is proximal and which distal,
it is also possible, I believe, to trace the entire series of changes
into the metaphase. In cell A the primary split is visible at the
distal end* (at the right in the figure) of this chromosome, but

SYNAPSIS AND CHROMOSOME ORGANIZATION 491

not through the middle. A split is seen in the proximal end
(at the left) but it cannot be determined whether this represents
primary or secondary split; in cell B, however, both splits are
easily seen and it is further observable that the separation at
the proximal end (left) is along the plane of the secondary split.
The tendency for the proximal granules to diverge with further
separation along the secondary split is seen in cell C. In cell
D the relation of the chromatids is much the same as in cell B
but they are more condensed. In cells E, F, and H, as I have
already noted, smaller knobs or enlargements occur at the
proximal ends, while a bulging at the middle of the oriented
tetrad indicates the larger distal granules. It seems fairly safe,
then, to assume that a tetrad in the condition seen in cell C would
become oriented in the metaphase without further change in the
relationships of the chromatids, except their further separation
along the plane of the secondary split. There seems to be good
reason for concluding, therefore, that division is equational for
this chromosome.

There is also some evidence that chromosome number 4 di-
vides equationally in this first division. In the metaphase
cell E the horizontal components of the chromatids on the right
side of the tetrad have stained differently from those on the
left. They failed to retain the stain so well and appeared finely
granular, as indicated in the drawing, in contrast to the compact,
deeply staining chromatids on the left. It is reasonable to sup-
pose that those two chromatids which show this peculiarity
belong to the same parent chromosome, and, therefore, that
halves of chromosomes are being separated in this division, con-
stituting an equational division. Attention may be directed
to the cluster of granules attached to this chromosome. In the
examples in cells A, B, and C, plate 2, it cannot be determined
just what relation this appendage bears to the chromatids. In
figures 22 and 23, plate 3, however, it is plainly indicated that
the structure is attached to a chromomere of only one of the
conjugated threads. Presumably this condition holds true for
all stages. If that be true, then these appendages may be at
the distal end, if it be permitted to associate the peculiar stain-

492 D. H. WENRICH

ing condition of the example in cell E with the presence of this
appendage in the earlier stages.

In the cases of chromosomes 5, 6, and 9, there is no method of
distinguishing distal from proximal end in the earlier stages and
therefore no deductions can be drawn as to which plane of sepa-
ration prevails in metaphase.

For the heteromorphic pairs of chromosomes (nos. 1 and 8)
there seems to be little doubt that the first division is a segre-
gating one, because of the striking difference in shape of the
segregating parts. In this respect they are analogous to the
unequal pairs found in Phrynotettix and other forms which
divide reductionally in the first division.

f. Additional observations on chromosome organization. Some
additional points of interest on the subject of chromosome or-
ganization may be indicated. In the first place outstanding
chromomeres are much more abundant than in Chorthippus, and
this is particularly true of those occurring at the ends of the
chromosomes. These polar granules (chromomeres) have al-
ready been noted in chromosomes 5, 6, and 7, but they are also
prominent in the earlier stages, at least, in numbers 2, 4, 8, and
9. The terminal chromomeres are less prominent but easily
distinguishable in number 10, still less so in numbers 11 and 12.
In most cases, with the gradual condensation ot the entire chro-
mosome, these prominent chromomeres become difficult to de-
tect in the later stages (cell D, e. g.). In the case of number 2,
however, the polar granules are relatively very large and they
continue to be recognizable even in the metaphase (cell E).

Secondly, the presence of the appended bunches of granules
(c) on chromosomes 4 and 8, already noted, may be considered
further. As characters for identification of these chromosomes
they have been mentioned on a previous page. An examination
of the pachytene stages shows these appendant structures to be
prominent. Figures 22 and 23 (plate 3) show them (c) attached to
their respective spireme segments. Chromosome 4 is further
identified in these figures by its greater capacity for holding
stain. In both of these figures the appendages appear to be
attached to only one of the conjugants of each pair of threads,

SYNAPSIS AND CHROMOSOME ORGANIZATION 493

and furthermore, they appear to be joined to single chromomeres
in three of the four illustrations. In both cells, that end of the
chromosome, near which the appendages are attached, is united
with the end of another chromosome, the opposite ends being
free in each case. In figure 23 the burdened ends of these two
chromosomes are joined together, the appendages are in contact
and, so far as could be determined, may possibly be fused at
the point of contact. It will be noted that the chromomere to
which the appendages are attached appears to be in about the
same position with reference to the end of the segment in both
cells.

A study of still earlier stages to determine whether these ap-
pendages may be double, that is, one for each conjugant, was
not made. In the stages shown on plate 2 the bunches of gran-
ules were so disposed as to make it impossible to determine
whether or not their attachments were restricted to one pair of
chromatids. Structures which were interpreted as representing
these appendages were seen in the nucleus from which figure 21
was made but were not drawn because to have done so would
have confused the other features which were to be emphasized.

A third point on the subject of organization is the occurrence
of the transverse clefts or constrictions at the points of spindle-
fiber attachment in the atelomitic chromosomes. These clefts
have been described in another connection so that it will be
unnecessary to repeat’ a description of them.

In passing, it may be noted that the distribution of the
accessory chromosome with reference to the members of the
heteromorphic pairs follows the law of chance, as discovered by
Carothers (17). (See chromosomes 1, 3, and 8, plate 2.)

g. Summary. In this individual of Trimerotropis the fol-
lowing conditions have been found:

1. The reduced number in the first spermatocyte is twelve
(plus one supernumerary). The complex consists of five pairs
of telomitic chromosomes, four pairs of atelomitic chromo-
somes, two heteromorphic pairs, and the atelomitic accessory
besides the supernumerary. These facts were all previously

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

494 D. H. WENRICH

%
determined by Carothers, and the present observations corrob-
orate those made by her.

2. Synapsis consists in a side-by-side union of leptotene
threads, which parallel association persists until the breaking
up of the spireme into its constituent segments and the pro-
duction of tetrads by the formation of the secondary longitudinal
split. .

3. The process of parallel conjugation appears to begin at
the proximal ends of the leptotene threads, as was. found in
Chorthippus.

4. The great variety of metaphase shapes for the same tetrad
appears to be correlated with variations in the extent and char-
acter of the movements of the chromatids with reference to each
other in the earlier tetrad stages.

5. At the point of spindle fiber attachment (synaptic point)
in the pairs of atelomitic chromosomes there occurs a transverse
constriction, or cleft, similar to those found for the atelomitic
chromosomes of Chorthippus.

6. Chromosomes 4 and 8 (plate 2) each bears near one end a
cluster of granules which is thought to be homologous with the
chromomere-vesicles seen in Chorthippus and other grasshoppers.

III. DISCUSSION

On the basis of the foregoing observations it seems worth
while to discuss briefly the following topics: (A) Synapsis, (B)
pre-reduction vs. post-reduction, (C) chromosome organization.

A. Synapsis

In considering the subject of synapsis it may be well first to
summarize the evidence gained from the study of Chorthippus
and Trimerotropis, together with that previously recorded for
Phrynotettix, and then to compare these evidences with the
results recorded by others who have studied Chorthippus (Steno-
bothrus). An extended discussion of the literature on synapsis
would be superfluous in view of the consideration given the
subject by McClung (’14), Robertson (716) and the writer (16).

SYNAPSIS AND CHROMOSOME ORGANIZATION 495

The evidence for parasynapsis as it has been presented for
Chorthippus and Trimerotropis on the previous pages is very
much of the same nature as that presented in the paper on
Phrynotettix (’16). The chief differences are as follows: In
Phrynotettix three particular first spermatocyte chromosomes
were selected for intensive study because they possessed charac-
ters which made their identification possible at most of the
stages concerned. For these three chromosomes stages in the
transformation of the double-thread spireme segment to the
tetrad in metaphase or anaphase were traced. In the present
study similar stages have been traced for all of the chromosomes
in both species. In Phrynotettix the leptotene and zygotene
stages were carefully studied and one of the selected pairs of
chromosomes traced through these stages. In Chorthippus and
Trimerotropis, lepto-zygotene stages have been found which
demonstrate the phenomenon of parallel conjugation, beginning
at the proximal ends of the threads, just as was found for
Phrynotettix.

In the latter species all of the chromosomes are of the rod-
shaped or telomitic type, while in Chorthippus there are both
telomitic and atelomitic types and in Trimerotropis there are,
in addition to the two types named, heteromorphic pairs with
one member telomitic and the other atelomitic. I think the
evidence presented shows very conclusively that parasynapsis
occurs for all the chromosomes of whatever type in these three
species.

When we consider the papers of others who have studied the
male germ cells of various species of Chorthippus (Stenobothrus)
we find that not all have expressed an opinion on the subject of
synapsis, and among those who have considered the subject,
there are some differences of opinion.

The work of Carnoy (’85), who studied the male germ cells of
Stenobothrus along with those of a large number of other Ar-
thropods, was of a pioneer kind and did not concern itself with
the subject of synapsis.

Davis (’08) was the first among those who have studied
Stenobothrus to consider seriously the subject of synapsis, and

496 D. H. WENRICH

on account of a misinterpretation of the looped condition of the
pachytene threads he decided that synapsis consisted in an
end-to-end union. He regarded the longitudinal cleft ot these
threads as having arisen by a splitting of the individual chromo-
meres of the single leptotene threads, instead of arising from a
pairing of chromomeres, as I have shown. He failed to detect
the formation of the secondary split, confusing it with the
primary, and also failed to notice the zygotene stages with their
partially conjugated pairs of threads.

Gerard (’09), on the other hand, did notice the zygotene stage
with the partially paired threads and correctly interpreted them
as evidence of parallel conjugation. He regarded one of the con-
jugating threads as more prominent “principale” than the other
“secondaire” but I have failed to find evidence for such a dis-
tinction. Gerard also noticed that pairing began at the proxi-
mal pole and progressed distally, as I have described, and
further that orientation was not complete nor entirely persistent
in the pachytene stages.

Meek (’11), in his first paper on the spermatogenesis of Steno-
bothrus viridulus, does not commit himself on the subject of
synapsis further than to point out the reduction in number of
chromosomes in the first spermatocyte and then to say (p. 12):
“This reduction must be effected before the breaking up of the
spireme, for I have found no evidence of lateral association of
filaments after this has occurred,” and then (p. 15): ‘“‘ Probably

: a numerical reduction takes place as a result of
Taeual association of chromatin granules or masses on the retic-
ulum of threads prior to the spermatocyte prophase of mitosis.”
In a later paper (712) he concludes that conjugation in pairs
actually does take place, though he offers no proof for the state-
ment and it is apparent that he has not observed the critical
stages.

McClung (’14) in considering a Stenobothrus-like form along
with numerous other species of Acrididae admits the possibility
of parasynapsis, but did not make a study of the earlier stages
where conclusive evidence is to be found.

SYNAPSIS AND CHROMOSOME ORGANIZATION 497

Robertson (’16) considers the subject of synapsis in Chorthip-
pus at some length. His figures 163 to 180 represent about the
same stages as those shown on plate 1 of the present paper.
The evidence in the two sets of drawings is of the same general
nature and consists in the facts that each of the early post-
spireme segments is a slender filament with one longitudinal
split and that a second longitudinal split appears in a plane at
right angles to that of the first, giving rise to the tetrads. So
far as this evidence goes, therefore, my work, though done
independently serves only to corroborate his.

In regard to the actual process of conjugation Robertson has
made no observations, but assumes, in accordance with the work
- of the Schreiners (06) on Tomopteris and Salamandra and the
work of Janssens (’05) on Batrachoseps, that, in the V-shaped
chromosomes at least, the process of pairing begins at the distal
ends and proceeds toward the apices of the V’s. He is further
led to this conclusion by finding interlocking pairs, the peculiar
relations of which could readily be explained on such an as-
sumption. He then carries the analogy over to the rod-shaped
chromosomes and considers that they probably also begin pairing
at the distal end.

My observations, as well as those of Gerard, show that, in a
general way, the reverse process takes place, namely, that con-
jugation is initiated at the proximal end and proceeds distally.
In the case of the atelomitic chromosomes the evidence is not
quite so conclusive, but that shown in figures 2, 3, and 4, plate 3,
indicate that here conjugation begins at the apices of the V’s,
and proceeds distally. However, I am inclined to believe that
the progress of pairing may not always be uniform along the
whole length of the threads, but that chance association of the
distal ends of a pair would result in their union, even if the
region between the ends and the apices had not completely
united. Such a condition is shown very clearly in the case of
chromosome A in Phrynotettix (see ’16, figs. 73, plate 6, and
figs. 75 to 78, plate 7), and the interlocking of chromosomes
such as that shown by Robertson in his figures 163 and 177
could be explained by such behavior.

498 D. H. WENRICH

In conclusion it may be said that parasynapsis has been
amply demonstrated for Chorthippus through the work of
Gerard, Robertson, and myself. The evidence is just as con-
clusive for Phrynotettix and Trimerotropis as found by me,
while Robertson found clear evidence in Syrbula. Besides these
examples from among the Acrididae, parasynapsis was also
found among Orthoptera by Otte (07) for Locusta, by Morse
(09) for blattids, by Vejdovsky (11-12) for locustids, by
Stevens (712) for Ceuthophilus, and by Robertson (15) for
Tettigidae. ;

B. Pre-reduction vs. post-reduction

The old controversy over pre-reduction and post-reduction ~
which has agitated the minds of cytologists for so long a time
seems still far from a settlement. Even without considering the
subject of synapsis there has been little tendency to agreement
and with the assurance that parasynapsis is the rule in a large
number of animals (Wenrich, 716) the uncertainty becomes
more acute. There is one thing, however, about which I believe
we can be certain, and that is that there is no general rule
which is followed by all chromosomes at all times, and a failure
to appreciate this fact has had much to do with the present un-
settled state of this subject. I have shown for Phrynotettix (716)
how chromosome-pair C (type C,) divided by pre-reduction half
the time and by post-reduction half the time. In the case of
chromosomes A and B the rule was post-reduction, and I be-
lieved that post-reduction was the rule for the remainder of the
euchromosomes. In that paper (quoted on page 472) I was also
bold enough to declare my belief that pre-reduction was the rule
with the atelomitic chromosomes of Chorthippus. My greater
familiarity with the atelomitic chromosomes since my study of
Chorthippus and Trimerotropis has somewhat shaken my faith
in some of the criteria used to determine this point. I am
strongly inclined to believe that the mode of division in the first
spermatocyte cannot be determined with absolute certainty in
the absence of recognizable differences between the two conju-
gants of a pair.

SYNAPSIS AND CHROMOSOME ORGANIZATION 499

In this connection it may be .of interest to review the evi-
dence on this subject as found in the three forms that I have
studied (Phrynotettix, Chorthippus, and Trimerotropis), and
then to compare the opinions of some other investigators, espe-
cially those who have studied Chorthippus (Stenobothrus). It
will be necessary to consider only the chromosomes of the first
spermatocyte, for the behavior in this first division will govern
the subsequent behavior in the second spermatocytes.

In the case of the telomitic chromosomes of Phrynotettix,
unequal chromosome-pair C, type C, divided half the time
- reductionally and half the time equationally. Chromosome-pair
B, unequal type, always divided equationally while the equal type
behaved in precisely the same manner and presumably also
divided equationally. Chromosome-pair A divided equationally
- with the possible exception of the ring-shaped forms, which were
not traced to the metaphase and their behavior not determined.

In the case of the telomitic chromosomes of Chorthippus no
very conclusive evidence is available, but a probable behavior
leading to an equational division has been described on a previous
page (480). Among the telomitic chromosomes of Trimero-
tropis, number 2 (plate 2) exhibited convincing evidence of an
equational division, and good evidence for a similar type of
division was found for number 4.

When we come to consider the pairs of atelomitic chromosomes,
a decision as to pre- or post-reduction is not so easily reached.
The evidence in relation to the chromomere-vesicles found in
Chorthippus may be made to favor pre-reduction. In plate 1,
it will be remembered, whenever a vesicle occurred it was always
single and attached to but one pair of chromatids. This single
one might be accounted for in one of two ways: either the two
that are found in the earlier stages (figs. 2, 3, and 4, plate 3)
have fused together to form a single body, or there may be a
normal difference between the two causing one to disappear
before the other. In all cases where two are seen, One is slightly
larger than the other. This is well shown, for example, in figure
9, plate 3, which presents one of the few cases encountered in
which both vesicles appeared at so late a stage. Figures 7 and 8

500 D. H. WENRICH

also show this difference. In figures 10 and 11, the vesicle that is
present does not appear to be any larger than the largest one in
figure 9, and this fact lends support to the idea that the smaller
one disappears early instead of fusing with the larger. The
cases shown in figures 12, 13, and 14 are from section of another
individual and can therefore not be discussed in this connection.
If we assume, then, that the pair of chromatids to which vesicles
are attached in chromosome 9, cells E and F, and in chromosome
7, cell D (plate 1), for example, represent one of the conjugants,
then the evidence seems clear that a reductional division should
take place.

On the other hand, if it be assumed that the two vesicles have
fused to form one, then one of them must have broken loose
from its former attachments when the pairs of chromatids sepa-
rated, as they do in the tetrads, whether or not the separation is
along the primary or the secondary plane. When it is consid-
ered that these structures are eventually destined to disappear
in the later tetrad stag’es, as shown by the fact that many of the
tetrads observed in the stages represented by cells C to E (plate
1) do not show any vesicles, the assumption made above does not
seem unreasonable. But, if ‘these vesicles are to be regarded
as shifting in their attachments, then it might be objected
that such structures offer uncertain bases for deduction. On
this aceount, deductions made on the basis of the behavior of
these vesicles in the later tetrad stages may have to be con-
sidered as not entirely satisfactory. Nevertheless, because of
the constancy of occurrence of these bodies throughout the
pachytene stages, and the constant difference in size between
them, as already mentioned, the most reasonable conclusion
would appear to be that the one remaining vesicle, as found
in plate 1, and figures 10 and 11 on plate 3, 1s attached to one
conjugant and that therefore, a reductional division is fore-
shadowed. ;

We may attack this problem of reduction in the atelomitic
chromosomes from a different angle. In chromosomes 2, 4, and
6, plate 1, a probable behavior of telomitic chromosomes was de-
scribed which paralleled that of chromosome A in Phrynotettix,

SYNAPSIS AND CHROMOSOME ORGANIZATION 501

and consisted in a first separation (though sometimes very slight)
along the primary split, followed by a progressive separation of a
more pronounced nature along the plane of the secondary split.
When we attempt to find an analogous behavior in the atelomitic
chromosomes we meet with difficulties. If, however, we follow the
example of Robertson (’16) and consider each of the atelomitic
chromosomes as composed of two telomitic ones joined at their
proximal ends and then consider that the behavior of these com-
ponent rods is analogous to that described above for the telomitic
chromosomes, we would have to conclude that division of these
pairs of V’s was equational.

If we carry this idea of the compound nature of the atelomitic
chromosomes over to Trimerotropis, further difficulties await us.
Robertson uses the idea of compound chromosomes in Chorthip-
pus to indicate that the real number of chromosomes is 23 ()
instead of the apparent 17 (<), and that, consequently, Chor-
thippus possesses the number typical of the Acrididae. If we
assume that the atelomitic chromosomes of Trimerotropis
also are compound then we should have 34 as the total
number of telomitic chromosomes in this particular individual
(see p. 506). However, if we are to consider the number of
chromosomes in the Acrididae to be constant or nearly so we
must conclude that the atelomitic chromosomes of Trimerotropis
are not compound and therefore we cannot carry over the analogy
of behavior from the possibly compound chromosomes of
Chorthippus.

On the other hand the behavior of the chromatids may be
considered as variable, so that at one time separation in any
pair of atelomitic chromosomes could be along the primary
-plane and at another time along the secondary plane. In this
connection, consider for a moment figure 11, plate 3. Here, there
are three successive ‘rings’ with a potential fourth at the right—
that is, if the two free ends were in contact, as they are at the
left. Each succeeding ring is in a plane at right angles to those
adjacent.. If we may number these rings | to 3 beginning at the
left and consider the incomplete ring on the right as number 4
it will facilitate discussion. We might consider either plane as

502 D. H. WENRICH

primary or secondary but let us assume that number 3 has the
chromatids separated along the primary plane, with the vesicle
attached to the chromatids of one conjugant. This tetrad is at
a stage early enough so that it could be expected to undergo
chromatid movements before it became condensed and oriented in
the metapase. If ring 3 has arisen from a separation along the
primary split, then the free ends (no. 4) must have separated
along the secondary split. So, also, number 2; while number 1
would have separated along the primary split. Now the question
may be asked if there is any reason why the further separation of
chromatids should prevail along one plane rather than along the
other. Does not, for instance, the greater extent of the separa-
tion in ring 2 and the smaller size of ring 3 indicate that further
movement is likely to be in the plane of separation of rings 2 and
4 which we have assumed to be the secondary plane? Would
not such a process give us a condition similar to that in figure 10
with the long free arms at the right having opened out beyond
the apical point? Again, could not separation proceed to the
enlargement of ring 3 at the expense of 2 and 4 and give rise to
such a form as occurs in figure 14?

Similar situations are presented in the series from Trimero-
tropis in figures 15 to 19. In figure 15, so far as can be ob-
served, there would be just as much chance of separation along
one plane as the other, since we cannot recognize the synaptic
point in this element. In figure 17, the middle ring might be-
come enlarged so as to produce a condition such as is shown in
figure 19, or the ends at the right might be separated and re-
flexed toward the left -as indicated in figure 18, as previously
mentioned (p. 488). In any case the primary cannot be differ-
entiated from the secondary plane of separation, and in many
ways it seems as reasonable to assume one as the other as likely
to prevail in anaphase.

From the heteromorphic pairs another line of argument may
be developed. If we assume as established that the hetero-
morphic pairs in Trimerotropis always divide reductionally as
they appear to do, we have a basis upon which to argue that the
other atelomitic chromosomes should behave in the same man-

SYNAPSIS AND CHROMOSOME ORGANIZATION 503

ner and thus divide reductionally. As a matter of fact, chromo-
some 12 in cell D, plate 2, shows a constriction in one pair of
chromatids (b) and not at the homologous point in the other
pair. This might be considered as evidence that the constricted
pair represented one conjugant which showed this peculiarity
without its being shown by its partner, and that therefore a re-
ductional division was foreshadowed.. The results of Carothers
(17) also go far to support pre-reduction for the pairs of atelo-
mitic chromosomes. She finds that for each of the chromosomes
1, and 4 to 9 inclusive one of three conditions may exist in ‘dif-
ferent individuals: (1) there may be a pair of atelomitic chromo-
somes, or (2) a heteromorphic pair, or (3) a pair of telomitic
chromosomes. Since the members of the heteromorphic pairs
separate in the first division, it is reasonable to suppose that in
another individual the two members of a pair of atelomitic
chromosomes, both of which were homologous to the one atelo-
mitic member of the heteromorphic pair, would also separate
in the same way. And further, it might be presumed that even
the telomitic homologues, when both are present in the same
tetrad, would have a similar behavior. The strongest evi-
dence, then, in both Chorthippus and Trimerotropis seems
to support the pre-reduction hypothesis for the atelomitic
chromosomes.

I have gone into all these suppositions and analogies for the
purpose of showing how difficult it is to arrive at any general
conclusion with regard to the behavior of the chromatids and
the consequent plane of separation at the first division. It is
my belief that only in those cases where the two conjugants of a
pair can be differentially recognized can the plane of separation
in the first spermatocyte division be absolutely determined for
these atelomitic chromosomes.

The method of analogy is perhaps too generally used in the
discussions of the subject of reduction. Gregoire (10) at-
tempted, unsuccessfully, to align most of the results published
up to the time of the completion of his paper into an agreement
on the side of pre-reduction. Davis (08), taking the V-shaped
chromosomes of Stenobothrus as a type, concluded that pre-

504 D. H. WENRICH

reduction occurred in them, and then by analogy, probably
occurred in all the others. Gerard (’09), though somewhat un-
certain, likewise concludes that the plane of separation of the
atelomitic rings is along the primary plane and is therefore re-.
ductional and then says (p. 579): “‘ Personne ne contestera cepen-
dant que tous les chromosomes doivent se comporter a ce point
de vue de la méme facgon et que l’on est autorisé a appliquer, a
tous, ce que l’on a vu d’une facon irréfutable chez quelques uns
d’entre eux.”’ I think there is danger in drawing such analogies.

Meek (’11) says he is not able to discover whether reduction
occurs at the first maturation division or the next but thinks
possibly both divisions are equational and a numerical reduction
takes place only as a result of lateral association of chromatin
granules or masses on the reticulum of the threads prior to the
primary spermatocyte prophase. Meek thus failed to see the
parallel conjugation (though he assumes it may occur) and
does not recognize the primary longitudinal split (along which
one division takes place) as the space between conjugants.

McClung (’14) mentions the difficulty in determining the plane
of division in the first spermatocyte and says, p. 665-666: “It
is probably true that until the relations of the chromosomes
during the synaptic phase are definitely determined it will not
be possible to assert unequivocally that the longitudinal axes
of the paired chromosomes of the first spermatocyte represents
the coincident axes of the spermatogonial chromosomes consti-
tuting it, for if there be a parasynapsis at any period there is a
possibility that the doubly split thread may open out along
the plane of the equational cleavage instead of along the. space
between chromosomes. In either event the form of the re-
sulting chromosome would be the same.’’ However he believes
that (p. 667): ‘‘The sister halves of a chromosome remain closely
united here as in other generations of cells, and that separation
between parts of a tetrad is much more likely to occur along spaces
between whole chromosomes.” If one were to apply the reason-
ing in the last sentence quoted to the cases under discussion one
would get variable results. Besides, I think I have sufficiently
demonstrated parasynapsis and therefore the existence of the
basis for the uncertainty mentioned.

SYNAPSIS AND CHROMOSOME ORGANIZATION 505

Robertson (716) is persuaded that all the autosome pairs
divide reductionally in the first division. He bases this conclu-
sion on the interlocking tetrads which he found in Chorthippus,
the behavior of the ‘bi-tetrads’ in Jamaicana (Woolsey, 715),
the segregation of unequal rods in the first division described
by Hartman (13), Carothers (’13), and Robertson (’15), and the
pre-reductional division of the multiples in Hesperotettix and
Mermiria (McClung, ’05).

He says (p. 246): ‘From the instances which I have here given
it seems to me the inference may possibly be drawn that all
autosomal tetrads will be found to divide reductionally in the
first maturation division.”

In Phrynotettix I found one unequal pair which apparently
always divided equationally in the first division and another
’ which did so half the time. I was also able to show that Chromo-
some A in Phrynotettix, though the conjugants were of equal
length, nevertheless divided equationally in the first division,
and I believe that a similar behavior is clear for chromosome 2
in Trimerotropis. With these different facts established, the
variability of behavior in the telomitic chromosomes with regard
to reduction must be recognized, and, further, in the case of the
atelomitic chromosomes it seems unwise to attempt to establish
a general rule.

C. Chromosome organization

a. Atelomitic, or V-shaped chromosomes. ‘he idea of multiple
or compound chromosomes was first presented for Orthopteran
material by McClung (’05). In a paper in this journal Dr.
McClung considers this subject in a comprehensive manner so
that it will be unnecessary to discuss here more than a comparison
between the chromosomes of Chorthippus and Trimerotropis.

The occurrence of a constriction or transverse cleft at the
apices of the atelomitic chromosomes has been noted several
times and I have already mentioned the view that Robertson
(16) has taken in regard to the possibly compound nature of the
atelomitic chromosomes of Chorthippus. In drawing his conclu-
sion that these chromosomes are compound, Robertson makes

506 D. H. WENRICH

two assumptions, namely, (1) that the number of chromosomes
for the Acrididae is constant (i.e., 23, diploid series) and (2) that
the ‘achromatic bridge’ or constriction at the apex represents
the point of union between two telomitic chromosomes joined
at their proximal ends. Were we to generalize on these as-
sumptions and apply them to Trimerotropis a difficulty would
immediately arise. In the first place, this form possesses the
number of diploid chromosomes typical for the Acrididae (23)
in spite of the presence among them of V-shaped members.
If we should assume that each of these V’s represents two for-
merly separate rods, then the total number of rods in the indi-
vidual studied would be 34, as follows: for the 4 pairs of ate-
lomitic chromosomes, 16; for the 2 heteromorphic pairs, 6; for the
5 pairs of telomitic chromosomes, 10; and for the atelomitic acces-
sory, 2. This number (34) would be a radical variation from the
supposedly constant number of 23, and in other individuals the
number might be more (or less). As shown by Carothers (717),
the range in number of rods on this basis could extend from 30
(individual no. 62) to 40 (individual no. 6). From the stand-
point of constancy in number, therefore, the V’s in Trimero-
tropis should not be considered compound.

On the other hand, if 1t is to be assumed that the ‘constric-
tion’ is a criterion for the recognition of compound chromo-
somes, then the majority, at least, of the atelomitic chromo-
somes:in the individual studied would have to be considered com-
pound (plate 2). It is true that the assumption of a compound
nature for the atelomitic chromosomes of Chorthippus enables
one to recognize the number typical for the group (23), but a
similar assumption for Trimerotropis only causes a wide diver-
gence from the typical number which is already present. Per-
haps the way out of the difficulty may lie in the suggestion made
by Robertson (’16, p. 221) that there are two types of V-shaped
chromosomes, one type representing two rods joined at their
proximal ends and the other type a bent rod with spindle-fiber
attachment in a non-terminal position.

On this supposition the typical Acrididian number may be
conserved by assuming that the atelomitic chromosomes of

SYNAPSIS AND CHROMOSOME ORGANIZATION 507

Chorthippus are of the compound type and that those of Tri-
merotropis belong to the other type. Considering the similarity
of organization of these chromosomes in the two species, i.e., the
presence of the apical constriction in the two types, it will be
seen that such a constriction cannot be used as a criterion for the
recognition of the compound type.

Robertson seeks to extend this compounding idea to the
V-shaped chromosomes of other groups of animals. It seems to
be unsafe to generalize so extensively, considering that such a
generalization does not seem to hold in all cases, even among
the Acrididae. It would appear, rather, that each group would
have to be considered by itself and conclusions drawn only from
a study of numerous species within a group. Such a study has
been made by Metz (14) in which case the compound nature of
the V-shaped chromosomes of Drosophila seems to be established.
But in this case, as Metz has pointed out, it is as admissible to
consider two rods to have arisen from the transverse cleavage of
a primitively V-shaped chromosome as to assume that a V-shaped
type arose by an end-to-end union of two of the primitively rod-
shaped type. As Robertson has noted, Agar (’12) found very
decidedly constricted chromosomes in Lepidosiren and that (p.
295): “The constancy of the position at which transverse seg-
mentation takes place indicates a constant differentiation of the
chromosomes in a lengthwise direction.”’ But he considered that:
“The presence of transverse constrictions or joints in chromo-
somes is not, without special evidence, to be taken as an indica-
tion of bivalency or of a future division plane.” This note of
caution ought, I think, to be especially emphasized.

b. The chromomere-vesicles. The plasmosome-like chromo-
-‘mere-vesicles were first called ‘vesicles’ by Carothers (’13). In
16 I called attention to their plasmosome-like appearance, at
least in certain stages, and emphasized the point, already noted
by Carothers, that they are related to definite regions of chromo-
somes. Dr. Carothers (17) now calls them’ ‘chromomere
vesicles’ (p. 473), a term which emphasizes their relationships to
separate chromomeres and distinguishes them from the chromo-
some vesicles found in the spermatogonia where each vesicle

508 D. H. WENRICH

represents an entire chromosome. ‘These structures will be con-
sidered here only as further evidences of the exact organization
of each chromosome.

As pointed out in the observations, these chromomere-vesicles
are attached to the chromomeres at the apices of the V’s in
Chorthippus—quite regularly in chromosome number 9, less so
in numbers 7 and 8—and near one end of the telomitic chromo-
somes 4 and 8in Trimerotropis. In Chorthippus one is practi-
cally always attached to the accessory.

The relationship of the vesicle to a particular part of this
accessory is not readily observable in the growth period, as
shown in figures 1 to 6, plate 3, but on plate 1, it is readily seen
that the vesicle (c) is attached to a point near the middle but
always nearer one end than the other, indicating that in this
case, also, the relationship is to some definite region or chromo-
mere of the accessory.

Whenever the chromomeres at the apices of the V’s in Chor-
thippus can.be distinguished in the same tetrad which shows
a vesicle, it is found that the vesicle is always attached to that
one of the pair of chromomeres which belongs to the longer
arm of the V. This is seen especially on plate 3 in figure 9
from the smear and in figures 12 to 14 from sections. It is also
seen in in chromosomes 8 and 9, cell A, plate 1.

Similarly, in Trimerotropis, the relationship of the granular _
appendage is constant in the two chromosomes to which they
are attached. In plate 2 the relationships are not so definitely
ascertainable, because of the more condensed condition of the
chromosomes and of the granules in the cluster, but it is notice-
able that the cluster is closer to the end in chromosome 8 than
it is in chromosome 4. This is better seen in figures 22 and 23
in plate 3. In both cells the clusters are attached to chromo-
some 8 at or near the last chromomere but one, near the end
and in chromosome 4 to the fourth chromomere from the end.
In figure 23 the ends of chromosomes 4 and 8 are in contact.
The two appendages are also in contact, but it could not be defi-
nitely determined whether or not they had fused together.
Taken all in all, this brief study of these slightly-understood,

SYNAPSIS AND CHROMOSOME ORGANIZATION 509

plasmosome-like chromomere-vesicles adds considerable to the
evidence indicating a constant and definite organization of each
chromosome.

D. Summary of conclusions

1. Parasynapsis occurs in all the chromosomes of Chorthip-
pus and Trimerotropis, whether they are pairs of rods, pairs of
V’s, or heteromorphic pairs.

2. The pairing begins at the proximal end fof the rods and
at the apices of the V’s and proceeds distally. It is probable
that the distalward progress is not uniform, but that the distal
ends may occasionally become conjugated before intermediate
parts have united.

3. In the telomitic chromosomes of Chorthippus and in
chromosomes 2 and 4 of Trimerotropis there is evidence that the
first maturation division may be an equational one. The
heteromorphic pairs probably divide reductionally. In the case
of the atelomitic chromosomes the bulk of evidence favors pre-
reduction, but no definite conclusions on this point seems to be
_ possible.

4. There are probably two types of atelomitic chromosomes,
one, found in Chorthippus, consists of compound chromosomes,
representing two rods joined at their proximal ends, the other,
in Trimerotropis, is a bent rod. This is in agreement with
Robertson’s (16) suggestion.

5. Chromomere-vesicles are constant in position in the chro-
mosomes to which they are attached, and go to support the
idea that the chromosomes are constant in their internal
organization.

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

510 D. H. WENRICH

IV. LITERATURE CITED

Acar, W. E. 1912 Transverse segmentation and internal differentiation of
chromosomes. Quart. Jour. Mic. Sci., vol. 58.°

Carnoy, J. B. 1885 La cytodiérése chez les Arthropods. La Cellule, tome 1.

CarotHers, E. Eveanor 1913 The Mendelian ratio in relation to certain
Orthopteran chromosomes. Jour. Morph., vol. 24.

1917 The segregation and recombination of homologous chromosomes
as found in two genera of Acrididae (Orthoptera). Jour. Morph.,
vol. 28, no. 1.

Davis,,H. 8S. 1908 Spermatogenesis in Acrididae and Locustidae. Bull.

: Museum Comp. Zool., Harvard College, vol. 43.

GeERARD, Pot 1909 Recherches sur la spermatogenese chez Stenobothrus
biguttulus (Linn.). Arch. de Biol., tome 24.

GREGOIRE, Victor 1910 Les cineses de maturation dans les deux régnes. La

Cellule, tome 26.

Hartman, Frank A. 1913 Variations in size of chromosomes. Biol. Bull.,
vol. 24.

Janssens. F. A. 1905 Evolution des auxocytes males du Batrachoseps atten-
uatus. La Cellule, tome 22.

McCuivunea, C. E. 1905 The chromosome complex of Orthopteran spermato-
cytes. Biol. Bull., vol. 9.

1914 A conan ee study of the chromosomes in Orhopteran sper-
matogenesis. Jour. Morph., vol. 25.

Meek, C. F. U. 1911 The spermatogenesis of Stenobothrus viridulus with

special reference to the heterotrophic chromosome as a sex determi-
. nant in grasshoppers. Linnean Society’s Jour., vol. 32.

1912 A metrical analysis of chromosome complexes, showing corre-

lation of evolutionary development and chromatin thread width

throughout the animal kingdom. Philos. Trans. Roy. Soc. London,

Series B, vol. 203.

Merz, Cuas. W. 1914 Chromosome studies in the Diptera. I. A preliminary
survey of five different types of chromosome ery in the genus
Drosophila. Jour. Exp. Zool., vol. 17.

Morse, Max 1909 The nuclear basiboncats of the sex cells of four species of
cockroaches. Arch f. Zellforsch., Bd. 3, pp. 482-520.

Orrr, H. 1907 Samenreifung und Samenbildung bei Locusta viridissima. -
Zool. Jahrb. Abt f. Anat. u. Ontog., Bd. 24.

Rosertson, W. R. B. 1915 Chromosome studies. III. Inequalities and de-

ficiencies in homologous chromosomes: their bearing upon synapsis
and the loss of unit characters. Jour. Morph., vol. 26.
1916 Chromosome studies. I. Taxonomic relationships shown in
chromosomes of Tettigidae and other subfamilies of the Acrididae,
Locustidae, and Gryllidae: Chromosomes and variation. Jour.
Morph., vol. 27.

ScHREINER, A. unp K. E. 1906a Neue Studien iiber die Chromatinreifung der
Geschlechtszellen. I. Die Reifung der méannlichen Geschlechts-
zellen von Tomopteris onisciformis, Escholtz. Arch. Biol., tome 22.

SYNAPSIS AND CHROMOSOME ORGANIZATION 511

ScHREINER, A. uND K. E. 1906 b Neue Studien. II. Die Reifung der minn-
lichen Geschlechtszellen von Salamandra maculosa (Laur.), Spinax
niger (Bonap.), und Myxine glutinosa (L). Arch. Biol., tome 22.

Stevens, N. M. 1912 Supernumerary chromosomes and synapsis in Ceutho-
philus sp. Biol. Bull., vol. 22.

Vespovsky, F. 1911-12 Zum Problem der Vererbungstraiger. Béhm. Gesell.
Wiss., Prag.

Wewricu, D. H. 1916 The spermatogenesis of Phrynotettix magnus with
special reference to synapsis and the individuality of the chromosomes.
Bull. Mus. Comp. Zool., vol. 60.

Wootsey, C. E. 1915 Linkage of chromosomes correlated with reduction in
numbers among the species of a genus, also within a species of Lo-
custidae. Biol. Bull., vol. 28.

EXPLANATION OF PLATES

All figures in the three plates were drawn under a camera lucida at a magnifi-
cation of 3000 and reduced one-half in reproduction.

PLATE 1

EXPLANATION OF FIGURES

All drawings made from a smear from a single male of Chorthippus (Steno-
bothrus) curtipennis. Vertical columns represent separate cells, each hori-
zontal row represents one chromosome in different stages. Figures 1 to 9, at the
left, refer to the separate chromosomes arranged in order of size. The letters
A to H at the top refer to individual cells. a, Refers to four strand condition,
indicating two longitudinal clefts; b, refers to transverse constrictions in the
atelomitic chromosomes; c, refers to the chromomere-vesicles.

512

SYNAPSIS AND CHROMOSOME ORGANIZATION
D. H. WENRICH

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PLATE 1

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PLATE 2

EXPLANATION OF FIGURES

All drawings from a smear of a single male of Trimerotropis suffusa. Figures
1 to 12, at the left, refer to the different chromosomes arranged in order of size.
Letters A to H at the top refer to separate cells. The supernumerary chromo-
some in the row at the top of the plate is unnumbered. 6, Refers to the transverse
clefts or constrictions in the atelomitic chromosomes; c, refers to appendant
clusters of granules (chromomere-vesicles) in chromosomes 4 and 8.

514

PLATE 2

SYNAPSIS AND CHROMOSOME ORGANIZATION

D. H. WENRICH

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PLATE 3

EXPLANATION OF FIGURES

Small numerals in figures 1, 4, 5, and 6 correspond to the numbers of the
chromosomes in plate 1. The small numerals in figures 22 and 23 correspond to
the numbers of the chromosomes in plate 2. c, indicates the chromomere ves-
icles; X, indicates the accessory chromosome.

1to1l From the same smear of Chorthippus that was used for the drawings
on plate 1. Figures 12 to 14 are from sections of another individual of the same
species.

1 to 4 Zygotene stages, showing partially conjugated threads. In figures
2 to 4 the apices of the atelomitic chromosome no. 9 are marked by chromomere-
vesicles (c).

5 Pachytene stage. Chromomere-vesicles (c) partially fused.

7 and 8 Telophases of spermatogonia showing chromomere-vesicles (c) at-
tached to chromosomes no. 9. Chromosome vesicle of accessory at X.

9to1l Tetrads of chromosome 9, illustrating variation in chromatid arrange-
ments at about the same stage.

12 to 14 Tetrads of no. 9 from sections showing chromomere-vesicles and
variety of chromatid arrangement.

15 to 23 Trimerotropis; from same smear as that used for drawings in plate 2.

15, 17,.and 19 Prophase tetrads which may be considered forerunners of the
metaphase figures 16, 18, and 20, respectively.

21. Zygotene stage showing partially conjugated threads.

22 and 23 Late pachytene stages showing chromomere-vesicles on chromo-
somes no. 4, and no. 8.

516

PLATE 3

SYNAPSIS AND CHROMOSOME ORGANIZATION

D. H. WENRICH

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AUTHOR’S ABSTRACT OF TH1S PAPER ISSUED
BY THE BIBLIOGRAPHIC SERVICE JULY 21.

THE MULTIPLE CHROMOSOMES OF HESPEROTETTIX
AND MERMIRIA (ORTHOPTERA)

CLARENCE E. McCLUNG

Department of Zoology, University of Pennsylvania

EIGHT PLATES

CONTENTS

GS Terat TO GUT CH Tha Nae are etc Se PM ests, 5s 2s! ols Sed tare Re ee ea 519
II. Chromosome conditions in the genus Hesperotettix.................... 521
ioe Generalvobsenvablonsee saa o.cs 205 sss ae Ae ee ee IT era ae 521
Peabhe coMmplexyOl EL sSpECIOSUS. ... <b... sm los «osise Sees ee se OS
Sel eEcomp exaolotlaspnahensiss. 2.4 «4c ee doe aes: © Olt
APesWherconiplex Ole sore va PeMniS’:./\.4.29244 006 2 ee ee 525
DeEheIcomplexsOlM He MeStIVUS =. ..2< cs 2-5 cis a aa ea eee 526

Os mlthexcomplexyoteHee viridis... 2 25.5.:%.4 Roca Ses Ae eRe ion Ss 526

ITI. Chromosome conditions in the genus Mermiria........................ 530
NiVeeGenenaleconsrderatlONs eer cea. hc oss ta <a ee eae 536
jmChromosomemumibersmni the Acrididaes..45.. 2s seen ee ees: 538

2a Chromosome mumperssmyrencrale: ..41. .ssee eee eee reece 545

Son © DOM OSOIM CESIZES tee neN Nir fo mee ac, : 2a sk A ee alee 504

Axe OhOMOSOMeEMOLIMS aya. 06 5. hcnis baa En ee 558

Oem OATOM OSOMe" DEM avd Olea earch evs. «cates soc ARE ee ee a eae Sy/ll

Gre Chromosome distimbpuoiOne. 1... ..4.. 42 cor eee enters. oe 573
Chromosomes aivadmalitiyas.. - >: sc se een eee eee ole: 577

Ss SMCGMIGSOMIE SPCEMICTE Vier < oo. si = Se sieciseets ean eee dee ae cote 585

AO SUTTATH ETAT Ta ate eal et aes PR STS kc Se 587
Wilk s* TBs 0} boyea cia) 0) shy Aihara Pe Cane ea Oe ele PR Ree CP oy ici nan ert ee ive 589

I. INTRODUCTION

Under the title ‘‘The chromosome complex of Orthopteran
spermatocytes” (’05) I described certain unusual conditions in
these cells, among them the union between the accessory chromo-
some and particular euchromosomes to form multiple chromo-
somes. At the time my material was limited and I was able to
present only a partial account. Since then I have been accumu-
lating a large series of specimens which have been studied both

519

520 CLARENCE E. McCLUNG

cytologically and taxonomically. In the course of this study of
the more extensive series of preparations a number of facts have
been determined which were obscure in the early stages of the
investigation. Although it is not yet possible to present a
complete study of the two genera, owing to failure to secure cyto-
logical material from all the species, there are some facts known
which should be presented in order to add what has definitely
been determined and to correct errors in the earlier description.

Since the appearance of my former paper (705) upon multiple
chromosomes, a number of observations upon similar structures
have been reported by different investigators. Some of these,
such as the ones of Voinov (14), are not clear in their nature, but
recent papers by Robertson (’16) and his student, Woolsey, (’16)
have made distinct contributions to our knowledge of chromo-
some relations which will certainly prove valuable. These are
strongly confirmatory of the view expressed in my former papers
(05, 08) regarding the persistent organization of chromosomes
even in the face of apparent numerical reductions. Very strik-
ing is the discovery of a structure, the octad, which I was not
then able to find, but whose existence I anticipated so strongly
that I gave it a name in advance of its actual observation. The
occurrence of such a multiple chromosome I am now abundantly
able to confirm, as well as the steps in its formation reported by
Woolsey. The underlying principles of chromosome organiza-
tion, permitting the anticipation of yet unobserved conditions,
stands in as striking contrast to the conception of chance asso-
ciation of undifferentiated masses as does the periodic law of
chemists to the vagaries of the alchemists.

In this reéxamination, advantage has been taken of the un-
usual opportunities for a study of the taxonomic characters of
the two genera, especially Mermiria, offered by the splendid
collections at the Philadelphia Academy of Natural Science
under the charge of Messrs. Rehn and Hebard. Much good is
sure to come from their active interest in all that concerns the
group upon which they are specializing and from their cordial
and generous coéperation with other students. By their very
careful studies of large numbers of excellently preserved speci-

MULTIPLE CHROMOSOMES BVA |

mens they reach conclusions regarding the relationships of indi-
viduals and groups which are soundly based upon well defined
external characters and upon personal knowledge of the habits
and distribution of the materials. Working quite independently
of them I reach conclusions regarding the relationships of indi-
viduals and groups from the study of their germ cells and, in
most cases, find that there is no difference in our estimate of
these relationships. Since the discrimination between nearly
related forms, upon cytological characters, sometimes reveals
groupings that have been overlooked by earlier taxonomists, the
feeling of confidence in the validity of the theories upon which
such determinations are made is much strengthened. I feel con-
-fident that a full agreement between cytology and taxonomy de-
pends only upon the quality of the criteria of differentiation
and upon the accuracy of observation on the part of the followers
of these two methods of gaining a knowledge of the organization
of biological units of different degrees of complexity and extent.

Il. CHROMOSOME CONDITIONS IN THE GENUS HESPEROTETTIX
1. General observations .

When the observations on Hesperotettix were first announced
I had only a few specimens, and, because of unfamiliarity with
taxonomic characters, my assistants failed to distinguish the
species and confused the sources of the material used for study.
It was only when the germ cells were examined that it became
apparent that all the specimens regarded as H. viridis did not
belong to that species. Later and more careful collections
enabled me to determine that H. viridis and H. pratensis were
both represented. No difficulty is now experienced in discrim-
inating between these species by germ cell characters. Together
with H. speciosus, these represented the full extent of my ac-
quaintance with the genus. Although the chromosome complex
was, in its major features, consistently alike in the three species,
I published no further observations, because I hoped to obtain
preparations from the other North American forms in order to
make the presentation complete. After waiting a number of

522 CLARENCE E. McCLUNG

years I am now in a position to give a much fuller account of
the chromosomal characters of the genus, although I have not
yet seen all the species. Much to my surprise some of the new
material shows marked departures from the uniformity preva-
lent in all my earlier slides. As a result, some of my generali-
zations are now rendered invalid, but it is hoped that fuller knowl-
edge may make possible the formulation of principles having even
wider application.

At present I have preparations from five different species,
but in this article I shall discuss fully only the three of which
earlier mention was made, for it is only in these that multi-
ples have so far appeared. The number of specimens in each
case, except brevipennis, is possibly sufficiently large to be -
representative.

2. The complex of H. speciosus

The observations recorded for H. speciosus are essentially
correct and need only amplification here. It will be recalled
that the accessory chromosome is united with one of the tetrads
in the first spermatocyte to produce a hexad element. In the
spermatogonium the union with one half of the tetrad also exists
and is carried over into one of the second spermatocytes. This _
association was invariable in all the specimens studied, affecting
always the same elements. So far as could be observed the
unusual relations of the accessory chromosome did not modify
its peculiar character and behavior in other respects. The
striking appearance of a chromosome, one part of which is con-
densed and safraninophilous while the other portion is granular
and tinged with the violet in Flemming’s tricolor, is presented
to our view in prophase and telophase of the first spermatocyte.
As was pointed out at the time, an apparent reduction in chromo-
some number occurs without there being any real difference in
this respect from other Acrididae. The diploid number of
twenty-two becomes the normal twenty-three when it is noted
that the accessory chromosome, instead of being free, forms one
limb of a V-shaped element, easily distinguished among the

MULTIPLE CHROMOSOMES 523

twenty-one ordinary rods. That there is here a true preserva-
tion of the physical identity of each member of the complex is
evident from the continued characteristic behavior of the mem-
bers which are apparently fused together. The conception of
genetic continuity is therefore not merely formal, ‘but expresses
the actual morphological conditions of the species. Aside from
the presence of the multiple chromosome the germ cells show no
marked difference from most other Acrididae.

To complete my former account of the chromosomal charac-
ters of this species the following facts may be given: In the sper-
matogonium appear twenty-one rod-shaped chromosomes which
are generally characteristic of the Acrididae. Besides these
there is a V-shaped element with arms of unequal length (fig.
9, pl. 3). That this is not a simple euchromosome is indicated
by the observation that one member becomes highly vesicular
during the prophases. Such a condition is uniformly charac-
teristic of the accessory chromosome under these circumstances
and is sufficient to identify this arm of the V as the accessory
chromosome. During the synapsis stage there is joined to this
heterogeneous pair a third member, the homologue of the euchro-
mosome portion. In the late prophase the accessory chromo-
some is precocious in condensation and appears as a dense,
homogeneous rod, more or less bent, joined to a granular tetrad
by endwise union. The contrast is most evident in preparations
by the tri-color stain. In the first spermatocyte metaphase this
hexad element. goes on the spindle with its long axis parallel
to that of the spindle and having fibers attached at the ends of
the tetrad. This brings one fiber to the point of union between
the accessory chromosome and the tetrad. There are visible,
at this time, eleven separate chromosomes, of which ten are
quite like the ordinary Acrididaean type while the eleventh is the
cane-shaped multiple (complex 6, pl. 1).

The anaphase groups resulting from this division each show
eleven chromosomes, but in one there is a V which has no like
mate in the sister group. This is constituted of the accessory
chromosome and one half of the tetrad. In the second sper-
matocyte into which the V goes, the nature of this is again like that

524 CLARENCE E. McCLUNG

of the spermatogonitum—the member which was added during
synapsis having been removed in the first spermatocyte mitosis.

The second spermatocytes are accordingly of the usual di-
morphic character, one with the accessory chromosome—here
permanently joined to a euchromosome—and the other without
it. Since the V is made up of a dyad plus the accessory chromo-
some dyad, it is, in effect, a tetrad, but of unusual type since
its parts are not homologous. It divides here just as do tetrads
in the first spermatocyte, and the anaphase shows a V going to
each pole along with the ten rods. The union of the accessory
chromosome with one euchromosome is therefore not lost dur-
ing all the changes of the maturation period, but persists into
the spermatozoon and, by it, may be handed on to the female
line of the next generation from which it passes into the male
line upon the following fertilization.

3. The complex of H. pratensis

In this species, as in H. speciosus, there is uniformly present
a multiple chromosome which differs from the speciosus form
only in the proportion of its parts. Without some more defi-
nite criterion for the homology of the euchromosomes than we
now possess it is not possible to say that it is the same mem-
ber of the complex with which the accessory chromosome unites
in the two species. If size only were used as a basis for judg-
ment, then it would be necessary to say that different tetrads
are involved, because the euchromosomes are much larger in
speciosus than in pratensis. From the fact that the accessory
chromosome itself may vary considerably in different species, it
would appear that size is not alone a safe indication of homology.
Leaving out of consideration the question of whether it is a
particular one of the eleven tetrads with which the accessory is
joined, we face the concrete fact that so far as our observations
have gone, there is always such a multiple element present in
the germ cells of the two species.

When we come to observe the character of the multiple ele-
ment in the different generations of cells it is found to exhibit

MULTIPLE CHROMOSOMES 525

throughout essentially the same features as mark its history in
speciosus. The only observable difference is in the size of the
parts. One individual, however, exhibits a variation in ap-
pearance of the multiple, which makes the conditions in Ana-
brus, already described (05), directly comparable to those of
Hesperotettix (fig. 23, pl. 4). Instead of the accessory being
attached to the end of a rod-shaped tetrad it is joined to one ex-
tension of a ring. This relation appears in the prophase and is
carried over directly to the metaphase, so that multiple chromo-
somes of very different shape from the ones commonly present
are produced. Both forms appear, not only in the same animal,
but also in a single cyst. It is probable on this account that the
variation does not represent any fundamental difference, but
only a divergence in some rate of movement of the parts.

The spermatogonial complex shows practically the same con-
ditions which characterize the corresponding stage in H. speciosus.
Minor differences of relative size of the elements are the only
ones of note.

Figure 23, plate 4 exhibits the complex in the first spermato-
cyte. It is at once noticeable that the chromosomes are strongly
of the Hippiscus type and in polar view appear as rings or V’s
lying in the equatorial plate. The only unusual feature is the
tetrad, elongated in a plane of the spindle axis, with the acces-
sory chromosome joined to one end at a more or less acute
angle. The behavior of the chromosomes during division pre-
sents no unusual features and my general description of these
types of chromosomes, given at length in a former paper (’14)
may be he'd to apply here. The second spermatocyte mitosis
likewise is typical for the euchromosomes, and the multiple

_chromosome behaves like the same structure in speciosus.

4. The complex of H. brevipennis

There is nothing in the specimens of this species, so far ex-
amined, to indicate the existence of any of the unusual conditions
of chromosome association which occur in speciosus, pratensis
and viridis. As may be seen by an examination of plate 3, figure

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

526 CLARENCE E. McCLUNG

8, the complex is strictly of the Hippiscus type. There are
neither multiple nor atelomitic! 1 chromosomes. It is pos-
sible that a more extensive series might show some variation,
but this is doubtful. If multiple chromosomes are characteristic
of the genus—which might fairly be said from their prevalence
in the species so far studied—then brevipennis departs here
from the type. Since this paper deals only with the question of
multiple chromosomes, no further consideration will be given:to
species in which they are absent, except to note that the seriation
in size is uniform.

5. The complex of H. festivus

This striking and characteristic species, of which numerous
specimens have been studied, is like brevipennis and shows no
trace of multiple chromosomes. The nature of the complex in
the first spermatocyte may be observed in plate 1, complex 2.
It seems therefore to have no immediate bearing upon the sub-
ject of the present discussion.

6. The complex of H. viridis

This species, like speciosus and pratensis, may possess a
multiple chromosome, a hexad, constituted of a tetrad joined to
the accessory chromosome dyad. ‘The euchromosome portion is
larger than those of the other species. This was the condition
present in the first specimens which I studied and which served

1H. viridis. In a former paper I found it convenient to refer to various
forms of chromosomes and to note that their forms depend upon the fiber at-
tachment. Following de Sinety, the position of this attachment was designated
as terminal, subterminal, or median. In the case of the annular chromosomes
terminal attachment apparently results in rings whose plane in metaphase coin-
cides with that of the equatorial plate, while with subterminal, or median, at-
tachment the rings are so placed as to lie parallel with the spindle axis. For
convenience these were spoken of as the Hippiscus type and the Stenobothrus
type respectively. With the discovery of additional complexity of forms it has
been found desirable to have general terms for the two conditions represented
by the ring chromosome, and so it has been agreed in this laboratory to speak of
chromosomes with terminal fiber attachment as ‘telomitic,’ while those with
non-terminal attachment receive the name of ‘atelomitic.’ These terms may
therefore be used to designate chromosome conditions similar to, but more
general than, the ones involved in the two types of ring formation.

MULTIPLE CHROMOSOMES VAT

as the basis for my earlier discussion, although at the time they
were not fully identified individuals. Now, with an extensive
series secured for me by Miss Carothers, I find that the uni-
formity of association, so marked a feature of my early slides,
has, for certain chromosomes, given way to an order character-.
ized by multiples or non-multiples in equal proportions for the
individuals studied. For any individual animal however there
is no variation. But this species possesses added interest be-
cause of associations between euchromosomes to produce octad
multiples in which the accessory chromosome does not occur.
This is the first unquestionable instance of any such condition
in the Acrididae, but its occurrence in a genus of the Locustidae
has recently been reported by Miss Woolsey, working under the
direction of Robertson. So clear and unequivocal is this con-
dition in viridis that its interpretation can not be escaped, and
that it should have failed to appear in my early material is
most surprising. A careful restudy of my preparations makes
it evident that no other multiples than those involving the
accessory chromosome are to be found there. In some more re-
cently prepared slides of earlier lots I was however somewhat
chagrined to find individuals with the accessory chromosome free.
These various modifications of the complex are most interesting
and suggestive and merit extended consideration.

The following conditions of the first spermatocyte complex
have been encountered so far (plates 1 and 2).

Class (1 )-12 separate chromosomes = 11 tetrads + the accessory dyad
Class (2 )—-11 separate chromosomes = 10 tetrads + one hexad
Class (3 )-10 separate chromosomes = 8 tetrads + one octad + one hexad
Class (4 )— 9 separate chromosomes = 6 tetrads + two octads + one hexad
Class (5 )-10 separate chromosomes = 7 tetrads + two octads + one dyad
Class (5a)-11 separate chromosomes = 7 tetrads + two octads + one dyad
and supernumerary
Class (6 )-11 separate chromosomes = 9 tetrads + one octad + one dyad

While the number of chromosomes varies from nine to twelve,
the number of chromatids, morphologically recognizable, re-
main in all cases forty-six. The particular form of chromosome
which I called an ‘octad’ in my former study (05) presents
itself very commonly in the new material.

528 CLARENCE E. McCLUNG

A discussion of these various classes of complexes will serve
to bring out most clearly the conditions prevailing in the species.
Of these the first shows no unusual conditions whatever, and had
specimens of this nature been the only representatives of the
genus examined, they would have been regarded as coming from
a group entirely typical of the family. There are the usual
twelve chromosomes in the form of rings, V’s, crosses and rods
as found in Hippiscus, all of the telomitic type. The accessory
chromosome is free and early passes undivided to one pole of
the spindle. Of thirty-eight individuals studied, five had this
chromosome constitution.

Seven of the thirty-eight belong to the second class and were
the only kind of which I had preparations when my first study
was made. Conditions here are as in class 1, with the striking
exception that the accessory chromosome is joined permanently
to one of the tetrads, forming a hexad element. The structure
and behavior of this complex of eleven chromosomes instead
of twelve, has been fully described and will not need further
consideration here.

Very different is the aspect of the complex in the five indi-
viduals in class 3. Instead of twelve separate chromosomes as
in class 1, or eleven Jike class 2 there are but ten. We recog-
nize at once the hexad multiple of the second class and, in addi-
tion, eight telomitic tetrads of characteristic forms. The tenth
element is much the Jargest and is otherwise strikingly different
from its mates. In shape it is a much elongated ring of the
Stenobothrus type, but, like the rings of Chloealtis, usually
lacking any lateral extensions. Not infrequently there will be a.
separation on one side of the ring producing a C-shaped structure.
The character of this element will be considered later in con-
nection with other chromosome forms.

Members of class 4, of which I have seven individuals, show
still further modifications. The number of chromosomes is
reduced to nine, among which are distinguishable six tetrads of
usual types, two large Stenobothrus rings and a hexad multiple.
The two differential rings are of unequal size. The larger is
directly comparable to the similar element of class 3, but the

MULTIPLE CHROMOSOMES 529

smaller is always recognizable by its minor size and also by its
variability of form. In this !atter respect it may appear as a fully
formed ring, or it may show varying degrees of separation at one
of the polar angles, resulting in a large V-shaped structure.
Any one individual animal however shows either a ring or a V
and this does not suffer variation in any cells.

In class 5, represented by seven individuals, we encounter
again the number ten as in class 3, but it is constituted in a dif-
ferent manner. The absence of the hexad multiple is at once
apparent, for the accessory chromosome is free and occupies a
characteristic polar position. Its sometimes associated tetrad
appears among the seven chromosomes of this type and there
are in addition, two large rings as in cells of class 4. So far as
can be seen, these two elements are as directly comparable with
the corresponding two of the preceding class as are similar struc-
tures within either of these classes.

To the complexity resulting from combinations of separate
elements into multiples, thus reducing the number of independ-
ent structures, there is added the opposite condition of a super-
numerary chromosome in the animal found in class 5-a. This
has a complex similar in its composition to the ones in class five —
to which is added a smal], extra element with the usual charac-
teristics of the supernumerary chromosomes. For the third
time there appears the number eleven, but its make-up is different
from the complexes of either class 2 or class 6.

The number eleven reappears in celJs of the six individuals in
class 6, but once again there is lacking the hexad multiple char-
acteristic of classes 2, 3, and 4. Nine ordinary tetrads, a free
accessory chromosome and one large Stenobothrus ring make up
_ the complex in this group. In place of the smaller ring, or V,
of classes 4 and 5 there are present two rod-shaped chromosomes
of corresponding size. The large ring occurs in five of the six
individuals and is directly comparable to the element falling in
the same place in complexes of classes 3, 4 and 5. The sixth
specimen of this group has, in place of the ring, a large V of the
same construction as the smaller octad in class 4. This is the
only individual in which the larger tetrads were not united at

530 ‘ @GLARENCE E. McCLUNG

both extremities and, until it appeared, I was inclined to believe
that the unipolar union, rather common in the case of tetrads
nine and ten, was lacking and that some modification of the
association force existed. It is now evident that the conditions
are essentially the same in both cases, except that the more
frequent occurrence of the large ring and its complete char-
acter would suggest a longer history of multiple constitution.

III. CHROMOSOME CONDITIONS IN THE GENUS MERMIRIA

At the time of my first report (05) upon Mermiria I had
studied a'l the available Acrididaean species and, in every indi-
vidual, found only one type of chromosome—a telomitic rod in
the spermatogonium, which, after synapsis with its mate, ap-
peared in the form of a Hippiscus-type ring or in some modifi-
cation of the type. Although familiar with the atelomitic form
of chromosomes in other material, I had never seen it in the
Orthoptera and had no reason to suspect its occasional appear-
ance. Failure to consider the possibility of such chromosome
forms was responsible for my misinterpretation of the multiple
chromosomes in Mermiria, through which I made the serious
error of reporting the segregation of whole tetrads. Although,
with increased knowledge of the conditions in the group, it is
now possible to determine with certainty the nature of the mul-
tiple chromosomes, at the time of my first acquaintance with the
phenomenon of chromosome combinations the constancy of
chromosome structure and behavior was so marked as to make
quite unjustifiable any assumption of variation. Added to this
is the fact, which seemed at the time very significant and which
even yet is not satisfactorily explainable, that in certain indi-
viduals the multiple has a series of definite constrictions corre-
sponding in number and position to what would exist in a decad
element. Finally; actual separation in the first spermatocyte
metaphase at the level of these constrictions in certain cells per-
suaded me of their value as an indication of chromosome bound-
aries. The theoretical difficulties involved in explaining the
preservation of the complex on the assumption of tetrad segre-
gation finally convinced me that I was probably mistaken, but

°

MULTIPLE CHROMOSOMES 531

it was not until the discovery of the J-shaped chromosome in
Trimerotropis by Miss Carothers that any explanation, consistent
with the other known conditions in the group, was made possible.
Meanwhile I had accumulated an extensive series of specimens
and had studied the complex of the female and needed only the
conception of the J-shaped tetrad to bring all the observations—
with the exception just mentioned—into conformity.

In Mermiria, as in Hesperotettix, the fixity of combinations
which seemed to mark the genus has failed to prevail throughout
al] its species. While such variation as is shown by H. viridis
does not obtain in any species of Mermiria studied, multiples
are lacking in texana and neomexicana. These results empha-
size strongly the necessity of an extensive series of specimens in
any investigation—a requisite | have always appreciated and
sought to meet. Our recent work in the Orthoptera has shown
that numbers of considerable magnitude are required for extensive
generalizations.

Mermiria bivittata

It is not my purpse in the present paper to enter into a com-
parative history of the chromosomes in the various species of
Mermiria. I wish merely to consider the multiple chromosome
found in bivittata, with its modifications in certain groups of
individuals which seem to have specific value. My former re-
port on this species stated that the multiple chromosome con-
sisted of two tetrads joined to the accessory chromosome. This
is a mistake the occasion for which is discussed elsewhere. More
extended study upon a large series of specimens has shown that
in this genus, as in Hesperotettix, there is a hexad multiple in-
-stead of a decad. While there is a striking difference in con-
figuration of the element in the two groups, it is due entirely
to the form of tetrad involved. In Hesperotettix this is an ordi-
nary extended rod with the accessory chromosome joined at
approximately a right angle on one end. Mermiria has, on the
contrary, a tetrad already of just this shape, to the straight end
of which the accessory chromosome unites. Thus, while the
composition is the same, the appearance is very unlike. How

Hae CLARENCE E. McCLUNG

this configuration is established, appears very definitely when the
chromosome complex of the different cell generations is studied.
Conditions of the spermatogonial metaphase are presented in
figures 44, 46, 47, 49, pl. 6. First it may be noted that the num-
ber of chromosomes present is twenty-two instead of the usual
twenty-three, and that, of these, two differ from the remainder
and from the usual spermatogonial rods in being atelomitic V’s,
with more or Jess unequal arms. Even a casual study of these
differential elements reveals their divergence in both size and
structure. One is distinctly larger, and; under favorable con-
ditions, it may clearly be seen that its shorter arm is irregular in
outline and more lightly staining. In these respects it conforms
to the behavior of the accessory chromosome in many Orthop-
tera. So characteristic are these appearances that there can be
no doubt whatever in the identification of this arm of the V chro-
mosome as the accessory. The V chromosome, then, is a mul-
tiple, a tetrad, consisting of the two rod-shaped chromatids of
the accessory chromosome joined to the two corresponding rods
of a euchromosome, just as in Hesperotettix. At the angle of
the V, where the fiber is attached and where the chromosomes
join, there is, not infrequently, a clear break in outline.. The
compound nature of this V is clearly evident from these facts.
Inspection of the smaller V reveals no such indications of
heterogeneity, and only in shape does it differ from the remain-
ing elements of the complex. Its position in the metaphase
plate is commonly near the multiple V. For convenience of
comparison several of these pairs of V’s in different stages are
shown in figures 47 and 49. The number of chromosomes pres-.
ent in the complex is therefore found to be twenty free telomitic
rods of various lengths, two rod chromosomes joined at their
inner extremities forming a V and one other V-shaped chromo-
some—a total of twenty-three, the number characteristic of the
family. ‘The internal morphological evidence of the complex in
. this generation is sufficient proof to establish this conclusion. In
addition however we have two confirmatory lines of evidence
which are of great value, viz., the subsequent history of these
structures in spermatogenesis and the conditions of the female

MULTIPLE CHROMOSOMES 533

diploid complex. Before following out the later spermatogenetic
history I will briefly indicate the conditions in the female cell.

Unfortunately it has not been possible to work out the history.
of the female germ cells, but the egg follicle cells show beautiful,
clear chromosome groups, some of which are represented in figures
43, 45 and 48. It is at once observable that the resemblance to
the male diploid group is very marked. Here again there are
twenty-two chromosomes, among which are also two V’s. A
more careful study however reveals a significant sexual difference
in the case of the two V’s. Instead of being unlike in size they
are of practically identical proportions. Owing to their some-
what sinuous course through the cell, with consequent foreshort-
ening, it is difficuit, if not impossible, to represent them accu-
rately in drawings. Where they lie more nearly in the same
plane, as in figure 48, pl. 6, their equivalence is clearer. Under
the microscope there is no difficulty in appreciating the close
resemblance existing. On comparing these two V’s with the ones
of the spermatogonium (figs. 47, 49, pl. 6) it is seen at once that
in size and proportion they agree with the larger one of the male
celis. In other words these are two multiples, the short arms
of which are the accessory chromosomes. The count for the
female complex, instead of the apparent twenty-two, is therefore
twenty-four, corresponding to the conditions in other species.
No differential behavior of the sex chromosomes was observed
in these female somatic cells and but little evidence of separation
at the point of fusion.

Other species of Mermiria show no multiple chromosomes in
the first spermatocyte, and when the spermatogonial complex
is observed there are found twenty-three rod shaped chromo-
~ somes of the usual type. Absence of a multiple chromosome in
the spermatocyte is accompanied by the absence of V-shaped
chromosomes in the spermatogonium. Animals of this type
are not classified as bivittata, but, quite aside from their exact
taxonomic disposition, it is plain that they must be very nearly
related to bivittata. In such material, then, the direct rela-
tion between V chromosomes of the spermatogonium and mul-
tiple chromosomes of hexad nature in the first spermatocyte is

534 ' CLARENCE E. McCLUNG

strongly suggested. Because of the constancy of chromosome
organization, indicated among other ways by the constancy of
fiber attachment, we would be justified in saying that the V’s
of the spermatogonium unite in synapsis to form the first sper-
matocyte multiple and that this should appear with two non-
terminal fiber attachments. Such a condition is realized in the
structure of the hexad in the first spermatocyte mataphase.
The conditions of the first spermatocyte complex in meta-
phase are readily determined, particulariy if sections of sufficient
thickness are used, and in smears are almost diagrammatic.
Here there are clearly eleven chromosomes present, among which
is a very large and distinctly different shaped one (figs. 55, 56,
57, pl. 7). This is characteristically in the form of a rod with
the two ends of slightly different length bent sharply back in
the same plane. One or both of the ends may exceed, or fail
to reach, the common angle, producing some variety in form.
Greater or less extension, preparatory to division, may result in
considerabie variation in length, but commensurate and opposite
changes in diameter show that the volume remains very constant.
Indications of internal composition are afforded by the contour
of the element, although, as will be shown later, they are not
entirely trustworthy. At each of the bends, where the fibers
attach, there is a constriction, and nearer the shorter bent end,
at about its length down the shaft, there is a pronounced fissure.
At the time of division, separation occurs at this point, pro-
ducing two unequal V’s in the anaphase. Although the chromo-
somes are much shorter and thicker than in the spermatogo-
nium, relative proportions are preserved, and if these two parts _
of the long chromosome (figs. 47a, 50a, pl. 6) be compared with
the two V’s of the spermatogonium they will be found to corre-
spond almost exactly. That is to say, two V-shaped chromo-
somes of certain proportions found in the spermatogonium re-
appear in the first spermatocyte (united by one limb) and are
there separated at this point and segregated into different second
spermatocytes. Since one limb of one V is the accessory chromo-
some, it remains undivided, as usual. Attached to the accessory
chromosome is the rod portion of a J-shaped chromosome which

MULTIPLE CHROMOSOMES 535

has separated from its V-homologue to which it was joined in
synapsis. The only differences between Mermiria and most
other Orthoptera are (a) the multiple chromosome V and (b) the
euchromosome V. That the union of the accessory to a euchro-
mosome is not a fundamental change of the nuciear state is in-
dicated by the fact that certain species of Mermiria lack the
association. No change in the distribution of the accessory re-
sults from its union, and, as we have seen in Hesperotettix
viridis, the combination may be so weak as not to occur in some
individuals.

Evidence that the euchromosome V is of like transitional
character is not wanting in certain well marked members of this
loosely constituted species. In these (figs. 58, 59, pl. 7) the
multiple chromosome of the first spermatocyte metaphase is much
like that of Hesperotettix except in proportions. There is a
pronounced bend at one end at the point of fiber attachment,
but the other extremity is almost straight, only a slight sub-
terminal flexure indicating the place of the other fiber insertion.
In some instances this point is almost at the end of the chromo-
some. Individuals with this peculiarity are clearly distinguish-
able by somatic characters and, I believe, constitute a distinct
species. It is possible that, with fuller representation, forms
similar in the constitution of their multiple chromosomes to those
of Hesperotettix might appear.

This type of hexad caused me much difficulty and led to the
conception of a decad chromosome. As will be noticed in fig-
ures 58 and 59, pl. 7, there are a number of constrictions along
the length of the chromosome quite constant in position, and so
placed as to indicate that there are five divisions or parts. It
_will also be observed that the chromosome may be divided at
more than one of these levels. I can not now find any expla-
nation for these separations at various levels on the chromosome,
but that they are evidences of unions between various tetrads
is not indicated by the fuli history of the chromosome complex.
Again, in the anaphase and telophase of the first spermatocyte,
the composite nature of the larger V becomes marked. As may
be seen in figure 13 of a former paper (05), one member of the

536 CLARENCE E. McCLUNG

_ V consists of two granular rods of the same character as the re-
maining chromatin elements, while the other arm is composed
of two dense and homogeneous rods of smooth. contour. All
these parts tend to diverge widely except at the level where the
unlike portions join, which is the point of fiber attachment in
the preceding cell generations and its site in the one to follow.
This difference in constitution is the reverse of the one in the
spermatogonium, but corresponds to the relative degree of con-
centration of the nuclear elements in the first spermatocyte
prophase. The intervai between the two spermatocyte mitoses
is very brief and the chromosomes may be followed through their
changes without any loss of identity.

The metaphases of all second spermatocytes show eleven
separate chromosomes of which one isa V. On observing these
V-chromosomes (figs. 63, 64, pl. 7), however, it is found that they
are of two sizes which correspond in proportion to the two V’s
of the spermatogonium and to the two of the first spermatocyte
anaphase. Upon division these are distributed to the spermatids
which are accordingly of two classes, equal in number. It is clear
from this very evident history of the two V-chromosomes that
they go into different spermatozoa and so, upon fertilization,
are contributed to different individuals. Of some theoretical
interest is the fact that the rod-shaped homologue joined to the
accessory chromosome has a criss-cross inheritance while its
V-mate is confined to the male line. The presence of the ac-
cessory chromosome as a portion of one V means the addition of
one chromosome to the count of eleven separate elements, and
so conforms to the conditions in other Orthopteran species.

IV. GENERAL CONSIDERATIONS

The very extensive and detailed studies of chromosomes which
have been in progress for many years would not be fully justi-
fied if the result were merely a record of interesting but non-
significant protoplasmic manoeuvers. It is the belief that the
substances of the chromosomes are specific materials which are
intimately concerned with the development of a multitude of

MULTIPLE CHROMOSOMES joe

dissimilar cells from a single cell that renders‘a knowledge of the
finest details of their structure and behavior of the utmost im-
portance. That this belief is well founded would seem to be
clearly indicated by cumulative evidence from many sources.
The fundamental concept involved is the Roux-Weismann hypo-
thesis that the chromatin is the idiopiasm, which is differentially
organized and linearly arranged. As an indication of this dif-
ferential organization and linear arrangement, the existence of
definite aggregates of the chromatin substance into more or less
thread-like chromosomes is regarded as most important.

Details of chromosome structure and behavior are significant,
therefore, as indexes of the precision of organization in the ma-
terial of which they are composed. Since it is the existence and
perpetuation of this definite series of differentiated materials
that is primarily required by the hypothesis, it is conceivable,
and possible, that it may vary in the nature of its aggregates
into definite masses (chromosomes) without affecting the manifes-
tation of its various specific effects, except in their combinations.
It is not the existence of a certain number of these aggregates
that is of first importance, but the presence of the varied materials
which enter into their composition. While this is true, it is to be
expected that a somewhat exact correspondence should be main-
tained between the ultimate units of differentiated substances
and the units of higher order into which they are assembled.
But such a fundamental arrangement may be maintained in the
presence of both lower and higher numbers of chromosomes
through secondary combinations into units of still higher value
in one case,.or through duplications of the normal series in whole
or in part, in the other. Numerical variation is not of itself
-prima facie evidence of altered organization—it must be shown
that something of the complete series is lost, or new and unrep-
resented materials added, in order to demonstrate the existence of
altered organization. The maintenance of the morphologically
recognizabie units of the original series in the face of changed
conditions is indeed added proof of the exactness and stability
of structural conditions in the chromatin substance. Evidence
of a very important character in support of this position is fur-

538 CLARENCE E. McCLUNG

nished by the facts disclosed in the study of Hesperotettix and
Mermiria. For convenience these facts may be taken up under
a number of different headings.

1. Chromosome numbers in the Acrididae

It is claimed by those who criticise the so-called chromosome
theory of heredity that the maintenance of the specific number
of chromosomes is required and that variations in number are
direct disproof of the theory. There is an element of truth in
this argument which has always been granted by students of
cellular phenomena, but stated baldly and without reservation it
may lead to entirely erroneous conclusions—indeed has done so
in conspicuous instances. The fallacy in the argument lies in
the circumstance that a primary organization may be maintained
while having superimposed upon it secondary modifications.
Instances of this are very common in organic structures. Itis no
argument against the reality of the pentadactyl type of limb that
duplications or combinations or reductions occur in certain groups
or individuals. Polydactyl or syndactyl individuals reproducing
their modifications of the primitive type are not regarded as
illustrations of the absence of a fundamental organization of
limb bones. The diplopod condition is rightly considered as
secondary to the usual arthropod arrangement—not a disproof of
its existence. While it is true that these instances of organiza-
tion are of a different order from those found in cellular structures
they are true examples of meristic variation in individuals in
the presence of a persistent type. Ail that is claimed by those ~
who believe in the hereditary significance of nuclear structures is
that the chromosomes are, in themselves, indications of structural
organization in the materials of which they are composed. Pro-
vided the full complex of elements be preserved, the essentials
of idioplasmic control of development exist, even in the pres-
ence of combinations or duplications. From this point of view,
in the event of apparent variation in chromosome numbers in
an individual or group, it is essential to discover whether any
of the normal chromatic units are lost or others of different

MULTIPLE CHROMOSOMES 539

nature added before it can be established that there is not main-
tained a specific organization.

The belief in such an organization as this has, for brevity,
been called the theory of chromosome individuality. This has
perversely been much misunderstood or misrepresented. Ac-
cording to some the theory demands an ‘independent existence’
of the chromosomes, although how this could seriously be main-
tained in the entire absence of any independently existing chro-
mosome or claim for such, it is difficult to see. In the minds of
others the theory demands that the chromosome shali ‘make the
ceil/—whatever that may mean. Of coursé no such views are
entertained by any cytologist and no fair interpretation of the
theory of chromosome individuality would give occasion for
such statements. Because it is desired to examine the nature of
the evidence in favor of this theory, under conditions which
might apparently controvert it, a statement of the facts, involved
and an outline of the theory may be given to avoid useless dis-
cussion. They might take this form in the present state of our
knowledge (1) The cell is a complex of organs-having various
functions; (2) of these the nucleus, is most concerned in reproduc-
ing the characters of the cellular organization; (3) of nuclear
substances those involved in the structure of the chromatin are
most important in carrying out this function; (4) these substances
are likewise differentiated and have various réles; (5) an indica-
tion of this differentiation is afforded by the aggregation of these
substances into certain definite masses which are characterized
by individual peculiarities of size, form and behavior; (6) these
ageregates maintain their organization and reproduce them-
selves in each cell division; (7) their derivatives are characterized
_ by similar attributes of size, form and behavior under given con-
ditions; (8) such complexes therefore occur in all the celJs of an
individual, both germ and somatic; (9) because members of a
species are related by descent their complexes are essentially the
same; (10) the fact that a type of organization, which holds in-
variably for the imdividual and almost as constantly for the
species, prevails with slight variations through genera and even
a family is very strong evidence for exactness of organization:

540 CLARENCE E. McCLUNG

(11) the behavior of the chromosome in maturation and fertili-
zation is strictly in accord with the necessary mechanism for
alternative inheritance; (12) the imner constitution of the
chromosome is such as to afford an explanation for the linear
arrangement of factors and for their variations; (13) in the in-
stance of the most thorough analysis of characters in any one
animal, Drosophila, the groups of linked characters and their
magnitudes correspond to the number and size of the chromo-
some; (14) experimental disturbance of chromosome conditions is
followed by the expected modifications of characters during de-
velopment; (15) from the known conditions of nuclear organiza-
tion in relation to character development predictions with re-
gard to new characters and combinations of characters may be
made.

As has been stated before, the number of diploid chromosomes
in the various species of Acrididae is usually twenty-three in the
male. Exceptions to this have been announced by Granata (’10)
for Pamphagus and by various authors for Chorthippus, and by
myself for Hesperotettix and Mermiria. Montgomery gave the
number twenty for Syrbula acuticornis, but this is unques-
tionably an error, as Robertson has shown. In no case has a
variation been reported for cells of the individual. The gametic
complex therefore maintains itself, according to the reports of
all investigators. Similar constancy prevails in the species, in
almost all instances, except for the wide variation of eighteen to
twenty-three here reported for Hesperotettix viridis. In the
face of the admitted validity of numerical constancy as one test
of the theory of chromosome individuality, how can it be upheld
when actual variations of this magnitude exist? This would
seem to be as severe a strain as it could be subjected to, and if it
can be shown that the conditions in H. viridis are capable of
explanation without invalidating the hypothesis, then other
cases of apparent exceptions would be less weighty as evidence
until their full character became known beyond question.

On first thought the conditions in this group would seem to
be a particularly strong argument against the theory. Here is a
species, beyond question intimately related to many others of a

MULTIPLE CHROMOSOMES 541

group in which the number of chromosomes is almost constant,
and yet, within the one species, there are wide departures from
the normal number. If such changes may occur without pro-
ducing any effect upon bodily characters that will serve to mark
individuals by their variations, then surely it may be argued that
there can be no direct relation between chromosomes and somatic
structures. This would indeed be a vital objection to the theory
if, under its terms, the existence of a fixed group of free chromo-
somes of unchanging behavior were postulated. Such how-
ever are not the conditions of the theory. If it can be shown
that the smaller numbers present in some individual are not
caused by the loss of any chromatic units, and further that all
the conditions in the group are consistent with the maintenance
of certain associations between chromosomes and their chance
combinations in fertilization, then the conditions of the theory
are not violated. In effect this position would extend the theory
beyond the observed conditions of the chromosomes to their
subdivisions. It would be most exact if it could be based upon
constancy of chromomeres, the limit of our observational analy-
sis, as has been done for certain chromosomes in Phrynotettix
by Wenrich (16).

The genus Hesperotettix, so far as our studies have gone, has
two species, brevipennis and festivus, in which the normal hap-
loid number in the male is twelve; two species, speciosus and
pratensis, In which the number is eleven; and one, viridis, in
which both of these numbers are represented and, in addition,
nine, ten and thirteen. There can be little doubt that the
oecurrence of the typical family number in the genus is signifi-
cant of conformity to type; the presence within one species of
this number, and of variations from it, most strongly indicates
that, whatever differences there are, they must not be due
to any fundamental disturbance of the chromosome organiza-
tion. This a priort argument, while in no sense conclusive, has
its value and must be considered. Fortunately however. there
is strong objective evidence to support it.

First of this evidence is the case where the number is reduced,
from twelve to eleven. This I have already considered at length

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

542 CLARENCE E. McCLUNG

(02, ’05), and the case is supported by observations of Sinety
(01) and others. In this instance an element, so well marked
by peculiarities of form and behavior as to be unmistakable in
every cell generation, is found to be united to one of the euchro-
mosomes at all times so as permanently to reduce the haploid
number to eleven. There is actually one less free and inde-
pendent chromosome in cells of these animals than in those of
other members of the group. This however is a far different
thing from saying that there is one less chromosome present.
In fact there is no difference at all in the number of chromo-
somes—the sole variation being the union of the accessory chro-
mosome with one euchromosome. To put the case thusis to
make a plain statement of fact and not to create an hypothesis.
The apparently missing element is just as clearly present as in
any other Orthopteran cells. Irrefutable proof is thus afforded
of the process of the fusion of chromosomes without loss of their
identity. As a principle of nuclear organization we have there-
fore to reckon with the ability of chromosomes to unite together
while still retaining their morphological integrity.

It is also conceivable that where a tendency of this kind mani-
fests itself between certain chromosomes in a species, it may
also obtain between other members of the complex. Such com-
binations are more difficult to detect on internal structural evi-
dence, because there is no such differential behavior as charac-
terizes the accessory chromosome. Nevertheless there are valid
criteria which may be employed and these make certain the
existence of such multiple chromosomes. The conditions dis-
played in H. viridis are peculiarly fortunate and may now be
considered in detail. From the study of thirty-eight individuals
of H. viridis it is apparent that (a) the number of chromosomes
in the first spermatocyte may vary from nine to thirteen and
that (b) the same number may be present in two or three indi-
viduals and yet in each case be differently constituted. The
necessity for a careful and detailed study of the complex before
passing judgment upon the significance of numerical variation,
is certainly apparent from these circumstances. In view of the
fact that most explanations of changes in the number of chromo-
somes have concerned the smaller members of the series, it is of

MULTIPLE CHROMOSOMES 543

much interest to find that in Hesperotettix this portion is rela-
tively stable while the larger elements may be variously combined
together. But however much difference there may be in num-
bers there is apparent no loss of any morphological structures in
any of the classes. A comparison of homologous series of
chromosomes, based on size, may be made on inspection of plate
2 where I have attempted to arrange the chromosomes of dif-
ferent classes in order so that homologous chromosomes are in
vertical rows. In the case of multiple euchromosomes they are
placed in an intermediate position between the columns where
their members would properly come. The accessory chromo-
some, when in a multiple, is drawn as it is attached to its tetrad.
Even a casual inspection of this plate will show that, aside
from the accessory chromosome, the seven smaller chromosomes,
(nos. 1 to 8) constitute a graded series in which variation is not
great. The eighth chromosome, however, may or may not
have the accessory chromosome attached to form a multiple.
In classes 4 and 5 there are above this chromosome only two
other separate ones, but these are of a character to attract atten-
tion at once. Unlike most of the remaining elements of the
complex, they lie extended, parallel with the spindle axis and are
in the form of open rings, each half of which is greater than the
whole of chromosome eight. There are a number of considera-
tions which make it practically certain that these are multiples
composed respectively of chromosomes 9 and 10, 11 and 12.
First, it is to be noted that if these are counted as octad
multiples, the number of chromosomes becomes exactly twelve.
In weighing the value of this piece of evidence it must be re-
membered that this number is characteristic of almost the en-
_ tire family to which Hesperotettix belongs. This fact makes it
certain that in this respect we deal with such a fundamental
feature of organization as to require us to consider any varia-
tion, not as prima facie evidence of a lack of precision in organi-
zation, but rather as a modification of the form of it.2. In the

2 One of the most unjustifiable and unscientific attitudes imaginable is that
which would regard the effort to interpret the form of organization in its vari-
ous aspects only as an attempt to force a real divergence into a seeming agreement.
Such a style of argument has been resorted to by a number of those whose belief

544 CLARENCE E. McCLUNG

case before us the individual animals in class 1 have twelve
chromosomes, those in class 4 have nine while the ones in class
5 have ten. The question we have to decide is, whether these
conditions represent absolute differences in organization, or
whether, within the nine and ten groups, the twelve elements
of class 1 are morphologically present. On inspecting a com-
plex of class 4 we find that the accessory chromosome is miss-
ing from its usual position in the series, but upon looking further
it is discovered, with al] its usual characteristics of structure
and behavior, attached to one of the tetrads. As a structural
element of the cell it is demonstrably present and must be
counted, although it is not a free chromosome. In a complex
which is of almost identical composition otherwise, (class 5) the
accessory chromosome is a free element and would of course be
counted. In both cases the entire history of the accessory
chromosome in all cell generations is typical, whether free or
attached. The remaining two chromosomes of classes 4 and 5
are strikingly different from al] the others, and upon careful
inspection are found to have morphological subdivisions, which
if counted in the usual way, restore the apparently missing two.
In other words, if the number of chromatids is counted the
total is forty-six, just as it is in class 1. So far as the number
of elements is concerned, therefore, we are dealing with the
same series in each case. It is obvious that if the differences in
number were the result of an unordered variation there would
be every reason to expect numbers in excess of twelve, together
with modifications of all the elements and not of precise changes
in particular ones.

In a similar way, when the numbers in classes 2, 3 and 6 are
considered, the same evidences of ordered change are seen. Only
eleven separate chromosomes are found in class 2 but the largest
of these shows very clearly the accessory chromosome as a con-

is that the chromosomes are unstable and indefinite structures of the cell. Back
of such a position is the implication that evidence must be taken at its face
value without interpretation. This I consider entirely wrong. The essence of
observational work is interpretation, and in microscopical investigations it
reaches its fullest development. The value of:evidence submitted by a micro-
scopist is in direct proportion to the quality of his interpretative ability.

MULTIPLE CHROMOSOMES 545

stituent part and thus demonstrates the completeness of the
series. In class 3 there are ten separate chromosomes, of which
one is a multiple involving the accessory chromosome as in class
2, besides which there is a very large octad similar to the one
in classes 4, 5, and 6. Class 6 differs from 3 only in respect to
the non-union of the accessory chromosome with a tetrad. The
one individual of class 5 a, of which I have only a smear prepa-
ration, presents the second instance of a supernumerary chro-
mosome which has appeared in my material up to the present.
Aside from this, the complex is like that of class 5. From all
these considerations I think it may be said that the numerical
variations within these specimens of H. viridis, instead of being an
indication of lack of stability in organization of the chromosomes,
are, in fact, very strong proof to the contrary. There is noth-
ing whatever to indicate that the integrity of any element is
lost, or, aside from the case of the supernumerary, that any
additional members are added to the complex. Variation is not
a question of Joss or gain, but of relations.

2. Chromosome numbers in general

Variations in chromosome numbers, within the species and
larger groups certainly exist, as is clearly manifest in the work
of numerous investigators. The constancy of numbers is more
definitely established in some groups of animals than in others.
Thus the Acrididae have a common number for many of the
genera, but in the Hemiptera, as Wilson and Montgomery have
indicated, the families are much less uniform numerically. In
using the conditions of the family which I have most studied as
an indication of chromatin organization, I have recognized
that the nature of this organization might be different in other
groups, and I have not attempted to apply generally the imme-
diate conclusions to which I inclined. - Not only is this true but
the specific statement to that effect appears in an early. paper
of mine (’08 a) in these words:

Iam quite prepared to admit also that in one species even, there

may be a variation in the integration of the chromatin material, result-
ing i some numerical variation of the chromosomes, without losing

546 CLARENCE E. McCLUNG

my belief in the necessity for this definiteness in the grasshoppers.
We do not yet know how much difference there may be in the organi-
zation of the various chromosomes of a complex nor how variable in
importance they may be.

A more careful) reading of my papers would have saved some
of my critics much futile argument.

While I have thus avoided any consideration of the general
topic of chromosome variations in other papers, I should like -
now to examine some of the data relating to this subject. It is
important that this be done, because most of the attacks upon
the theory of chromosome individuality have proceeded from
investigators who either found, or think they found, variations
in chromosome numbers within individuals or species. Such
attacks have run the gamut, from assertions that chromosomes are
merely physical aggregates without morphological value, down to
questions regarding the definition of the term chromosome. In
undertaking such a general discussion I shall base my opinion
largely upon material with which I have personal familiarity.
Much harm has come from attempts to homologize results from
widely different materials by persons who have no first hand ac-
quaintance with the conditions discussed. With our present
knowledge of cellular phenomena as slight as it is, such lengthy
critiques, involving the interpretation of other investigators’
interpretations, can accomplish little good and may greatly
retard progress by fixing attention upon relatively unimportant
details. A striking instance of this has been the controversy
regarding pre- or post-reduction, extended long past the time
when it was definitely known that the question of the segrega-
tion division is one of the individual chromosome and not of
a whole mitosis. The matter of chromosome organization is,
however, fundamental to all our present conceptions of the cell
in relation to the larger problems of biology, and the evidence is
cumulative that the essential assumptions of our hypotheses
are justified. On the other hand it seems clear that the nature
of chromosome integration varies with different groups and that,
for this reason, we must be cautious in carrying over the con-
clusions reached from a study of one population of organisms to

MULTIPLE CHROMOSOMES 5A7

another. It is in full realization of this need for care in generali-
zation that I wish to examine the conclusions of others regard-
ing chromosome numbers in the light of my own and my
students’ studies.

In making such an examination I can profitably take up
only the most general questions, because, in matters of detail,
it becomes a case of interpretation of phenomena, and many
times one is not justified in criticising the work of others without
himself knowing the objective conditions. For this reason I
should like to consider the work of Della Valle on the subject
of chromosome numbers. I do not choose this author as repre-
sentative, because of any inherent strength apparent in his
papers, nor am I impressed by their number and size. On the
contrary they appear to me weak, because of the small amount
of observational basis and the large development of theory. For
instance in the paper of 1909 of the hundred and seventy-seven
pages, only forty pages are included under the heading ‘‘ Data of
observation” and, of these, twenty are concerned with matters
of technique. Throughout all of his publications, indeed, there
is apparent a painful lack of judgment regarding the distinction
between fact and theory, and were he alone in his position he
could fairly be dismissed with little attention.*

3 ‘Objective analyses,’ accomplished by the translation of morphological
facts into terms of physical chemistry, carry their own indictment of lacking
experience and judgment, and could safely be left without comment. Such
an attitude toward chromosome organization is, however, but an extreme case
of the position assumed by a number of biologists who would seek to discredit
the hard won facts of cytology by an appeal to conditions or forces beyond ob-
servational control or. by an arrogation of the whole problem to their own
‘chosen field. It would seem that, in almost every case where such attitudes are
assumed, there is some animus or prejudice in the mind of the writer which be-
trays itself in his injudicious or intemperate language. All those who fail to
agree with his particular extreme views are depicted as banded together for the
establishment of dogma and the suppression of truth. With much vigorous
language and the plentiful use of exclamation marks all such are consigned to
scientific oblivion with their obsolete methods and narrow views.

This is very unfortunate. It is rarely the case that scientific investigators
are not honestly in search of the truth with regard to the subject of their en-
quiry, and to accuse them of conspiring for its suppression is most absurd. It
is true that new views sometimes prevail but slowly, but it does not hasten their

548 CLARENCE E. McCLUNG

~The work of Della Valle is open to criticism from two sides.
It may in the first place, well be questioned whether the knowl-
edge of colloid chemistry, and of fluid crystals in particular, is
sufficiently established to justify the extension of its principles
into the operation of cellular phenomena. Certainly one is in-
clined to doubt the basis on which such application is made
when the complicated phenomena of chromosome division are
declared to be ‘absolutely identical’ with the cleavage of fluid
erystals, or when the involved changes of the chromatin in the
telophase are described as ‘identical’ with the solution phe-
nomena of a gelatin cylinder in warm water. It is of course
not to be doubted that in the activities of the chromosomes,
and all parts of the cell indeed, chemical and physical laws are
operative. Such a belief is however far removed from the one
which conceives some particular manifestation of chemical or
physical energy as ‘identical’ with the behavior of the chromo-
somes in mitosis. Much might properly be said with regard to
this phase of Della Valle’s work, but I desire rather to consider
the nature of what he advances as direct evidence against the
theory of chromosome individuality. Since this involves a
thoroughgoing denial of all the facts and theories relating to the
subject, such a discussion will touch upon most of the objections
that have been raised by other critics and will avoid the neces-
sity for repeating arguments involving only minor differences of
material or opinion. A summary of his position with regard
to matters relating to chromosome individuality follows:

He asserts that the number of chromosomes in a cell is due to
the constancy in the amount of the chromatin and the median
size of the single chromatin aggregates. This number suffers
variation according to the law of fluctuating variations and is

acceptance to attack the motives of those who hold other opinions. A method
does not commend itself as an instrument of value merely because it is termed
an ‘objective analysis’ when it is obviously the application of a series of anal-
ogies.. Neither does an observed fact cease to be such on being termed a ‘hy-
pothesis’ or even a ‘subhypothesis.’ It is in fact not infrequently true that
much of good in the work of certain biologists issues under a severe handicap
because of the inherent evidence of poor judgment in their estimation of values
in the work of others.

MULTIPLE CHROMOSOMES 549

subject to conditions within the system of which the chromosomes
are a part. The chromosomes are temporary and variable or-
ganizations of the chromatin, which form in the prophase and
dissolve in the telophase. Variations in size of chromosomes
are within the Jimits of observational error and are of the order
of size variations in the droplets of an emulsion. Correspond-
ence in size between chromosomes and nucleus finds its explana-
tion in the physical condition of adsorption. The fact that
chromosomes shorten proportionally to their original length
shows they are homogeneous and indicates the identity of all
the chromosomes in a mitosis. The previous history of the
chromosomes in a line of cells can have no effect upon later
generations because there is no continuity. Definite or specific
organization is lacking and there is no perpetuation of a series
through reproduction of individual chromosomes. All expla-
nations of variations in number (called ‘sub hypotheses’) are
declared to be untenable upon ‘accurate examination’ and cer-
tain determination of numbers in sections is stated to be im-
possible. As is customary with critics of this type, Della Valle,
after decrying the spirit and purpose of those who do not agree
with him, proceeds to attack their methods and declares that
only his own technique yields infallible results. Sections can
not give accurate enumerations of chromosomes, and only
counts made upon stretched membranes are of value. Having
thus put out of count the bulk of the work already done, he
next makes a comparatively limited number of observations
upon one type of material and arrives at the ultimate general
conclusion that chromosomes are fluid crystals. With this
solution of the problem accomplished, all minor questions are
easily settled, because upon this major premise that chromo-
somes are fluid crystals and subject to all the laws known to
pertain to such physical aggregates, certain variations of num-
ber, size, form and behavior must exist. I should like now to
consider some of these assertions in the light of work known to-
me personally, first pointing out that all-instances of order and
system under varying conditions are direct evidence against his
position.

590 CLARENCE E. McCLUNG

The number of chromosomes within cells of an organism, he
states, is variable, according to the law of fluctuating variations,
because the number in any cell is due to the constancy in the
amount of chromatin and the median size of the chromatin
aggregates. Opposed to this is all the evidence, already given,
regarding the high degree of regularity in the Acrididae where so
many genera are alike in number, although the amount of chro-
matin varies widely. In this large group, the family, variation
is infrequent, but in one species, Hesperotettix viridis, variation
is common. Certainly under the terms of Della Valle’s argu-
ment the greater variation should occur where there are the
greater differences in amount of chromatin. But if there is any
truth in the assumption, some variation would be expected in
the cells of the individual and this does not occur in these
Orthoptera. As reported for Culex by Whiting (’17) in the
germ cells the diploid number is constantly six, Hance (’17)
finds the same conditions generally true of the somatic cells,
but Holt (17), working upon the same material, discovers a
range of variation extending from six to seventy-two in certain
intestinal cells. It is very clear that the amount of chromatin
is here not constant, while the median size of the chromosome
remains practically unchanged. There is no correspondence,
either, between the size of the nucleus, or of the cell, and the
number of chromosomes. No evidences whatever of any bal-
anced physical system, such as Della Valle advocates, appears
in these cells of Culex.

Hertwig’s outworn nuclear-plasma relation theory receives
just as little support. In H. viridis the amount of chromatin
is much the same in all the cells of a given generation and yet ~
the number of chromosomes in the haploid condition ranges from
nine to thirteen. Along with this fixity in the amount of the
chromatin and variation in chromosome numbers, goes a con-
stancy of size series up to certain chromosomes, beyond which
there is a sudden change. The phenomena relate to no means or
averages, but concern definite morphological entities. In place
of fluctuating variations there is definite and determinable
order. What happens is explainable, not upon circumstances of

MULTIPLE CHROMOSOMES Sat

chance relations between masses of substance in different
‘phases,’ but through a knowledge of the history of certain
individually recognizable chromosomes traced through a large
group of animals. Worthy of note is also the fact that in such
cases as H. viridis the range of variation is strictly defined and
falls within the limits set by the organization established in the
family, except in the occasional instance of supernumerary
chromosomes—two instances in the thirty-eight individuals
studied.! .

It is only upon the basis of entire identity of all chromo-
somes in a complex and of their temporary character that the
Italian author has any argument at all. Building upon this he
seizes upon every reported instance of difference of chromosome
numbers as a support for his thesis. Every descriptive fact is
labeled a ‘sub hypothesis,’ and so many of these are secured in
this way as to convince him that the main hypothesis of chro-
mosome individuality has no standing. Curiously enough, he
conceives a great importance for the fact that one explanation
for all the reported cases of numerical variation is not sufficient.
On the contrary, he says, there are so many ways of accounting
for such variation that there can be no constancy and no indi-
viduality. Perhaps in no other way is the quality of his argu-
ment better indicated than here. The fact that an error in
observation has been made, and even admitted, is only an indi-
cation of variation; when it is shown that a reported difference
in number is due to the inclusion of more than one species in a
study this is a subhypothesis weakening the main one; the pro-
duction, by hybridization, of chromosome numbers different
from those of the parents is accounted as an example of varia-
tion, as is the case of asymmetrical mitoses in neoplasms. ‘The

4 Tf a chromosome is but a chromosome without character or distinction, there
is in this case a violation of the rule stated. But if the nature of the element
be significant, the rule holds, for the entire history of the supernumerary chromo-
some demonstrates that it is of a different order from the euchromosomes. It
may in many ways depart from the history of typical chromosomes and finally
end in complete elimination. Arguments, such as Della Valle’s, require that
such a structure be considered identical with all other bodies called chromo-
somes, without in any way regarding its individual history of ultimate extinction.

atis4 CLARENCE E. McCLUNG

clear cut description by Wilson of the failure of certain chromo-
somes to enter into synapsis is not an explanatory fact but an-
other ‘subhypothesis.’ Similarly, early separation of conju-
gants, delayed divisions of certain elements, the presence of
supernumeraries are merely so many condemnatory ‘subhypoth-
esis.’ The exact determination of the union of the character-
istic and well marked accessory chromosome, with a tetrad to
form a multiple is not a fact at all, not even a hypothesis, but
only a ‘subhypothesis.’

From this it is clear that Della Valle, and others like him,
have set up in their minds the conception of an absolutely fixed
and invariable number of chromosomes of constant and un-
changing form as the hypothesis of chromosome individuality.
This is a man of straw, fathered by no biologist of standing or
character. His destruction in no way affects the existence of
the real image of a constancy in chromosome organization
consistent with our other knowledge of the living substance of
which these structures are a part. Such misinterpretation merely
condemns the judgment of the one who has no better discernment
of the real problem. It seems incredible that a biologist should
be capable of twisting the truth in such a way as to turn an in-
vestigator’s meaning entirely around so as to make his results
support a converse. Only when his basic conception of chromo-
some constitution is fully appreciated does an explanation of
Della Valle’s attitude appear. This is expressed by him in sey-
eral places in some such terms as these: The chromosomes are
temporary and variable aggregates forming in the prophase and
disappearing in the telophase (’09). Between two mitoses the -
chromosomes are so completely lost as individuals that finally
no trace of them can be found (713). It is easy to see that,
with such a view of chromosome organization, no constancy is
possible and the quickest way to dispose of variable numbers is
to consider them the result of chance.

But such a disposition of the case neglects certain objective
facts which can not be disposed of by consignment to the class.
of ‘subhypotheses.’ It has long been known that the accessory
chromosome, and other heterochromosomes, preserve their mor-

MULTIPLE CHROMOSOMES 553

phological identity from one generation of cells to the other. All
through the spermatogonial divisions each chromosome lies in
its own vesicle and can be clearly recognized. Recently Wen-
rich (16) has carefully traced certain differentiated chromo-
somes in Phrynotettix through much of the history of the
maturing germ cells, without loss of their physical identity. In-
stead of appearing as ‘‘temporary and variable structures”
they are just the opposite, being persistent and exact in or-
ganization to the highest degree. Not only are the chromosomes
constant in number, but also, and more fundamentally, the
chromomeres. Such conditions are probably unknown to Della
Valle and are certainly unappreciated or he could not make such
sweeping assertions regarding chromosome instability.

Perhaps one of the most striking and extensive instances of
variation in chromosome numbers yet reported is the one de-
scribed by Miss Holt (17) for the intestinal cells of Culex.
Here, in one individual, there may be a range from six to sev-
enty-two. Without extending the analysis of the case beyond
the simple determination of the numerical conditions, one would
be justified in believing that no significance attaches to the
mere number of the nuclear bodies. This would follow on the
major premise that indefinite and fluctuating variations in
numbers are direct evidence of lack of definiteness in organiza-
tion. This might presumably be admitted for the somatic cells
without entirely invalidating the theory of individuality so far
as it applies to the germ cells, for it is possible that, among other
evidences of differentiation in cells, correlative changes in the
nature and integration of the chromatin substance might occur.
Especially might this be the case in pupal Culex intestinal cells,
because these are on their way to disintegration in preparation
for the new epithelial lining of the enteron. Meanwhile the
germ cells of the species preserve an unvarying constancy in
number. But, as Miss Holt shows, the matter is not so simple as
it appears. True, there is variation, but it is not indefinite and
unordered. There are not always six chromosomes present,
but, if more occur, the numbers are multiples of three and repeat
in corresponding series the sizes of the primitive complex. Not

554 CLARENCE E. McCLUNG

only this, but the grouping is maintained and the derivatives
of each of the original series remains associated with its: fellows
and, with them, forms a common vesicle. So far as prophase
and telophase conditions are involved it would not be observed
that anything unusua] in numerical relations obtains. Even
in the matter of this multiplication the chromosomes exhibit
individual differences, and one may have advanced in the proc-
ess beyond the others and in this way produce a total number
not strictly a multiple of three. But no matter how many
or how few there may be, each one of the individual groups repeats
the characters of the original member. How far removed from
mere chance crystallization out of an indifferent matrix is the
ordered and definite reproduction of distinct morphological
entities which we see here. In the very face of what seems at
first glance to be the grossest of variability there appears only
another marked instance of exact organization. It is of interest
to observe also that division of the chromosome may occur
independently of mitosis, which suggests, in connection with the
observation that the actual splitting of the chromosome is a
prophase change, that mitosis may be more concerned with cell
division than with chromosome separation.

3. Chromosome sizes

If the total amount of chromatin is constant for each cell and
if the number of chromosomes is unchanged, it might reasonably
be expected that the same series of sizes would always appear.
These conditions are certainly realized in the individual, where
the closest correspondence exists between the series and between’
individually recognizable elements. That like correspondence
exists between individuals seems probable when the seriation in
the complex is noted. An exact determination of chromosome
sizes is however a very difficult undertaking, owing to the variety
of forms they assume. One is forced to estimate relative vol- _
umes, and an exact determination between two nearly equal
sizes of different form can not be made with certainty. Fortu-
nately the difficulty of comparing sizes is less in the case of the

MULTIPLE CHROMOSOMES 555

larger elements, owing to their volume and more uniform shape,
and we may be sure of the series in this part of the complex.
Since it is between these chromosomes that combinations occur,
the members may easily be identified. The value of the evi-
dence with regard to the constancy of chromosome organiza-
tion as shown by size relation is best appreciated by a comparison
of the different classes shown in plate 2.

In the one containing twelve chromosomes (1) there is a grad-
ual increase in size from the smallest to the largest without any
marked breaks. Class 2 shows the same condition, with the
exception of the multiple chromosome, but if the presence of the
accessory chromosome there be disregarded, the disproportion
vanishes. Class 3 however presents a different aspect. There
is the same gradation up to the largest element, which, in turn,
is more than twice the size of the next one of the series. Similar
conditions prevail in each of the other classes, with additional
distinctness in classes 4 and 5 where the element succeeding
number 8 is like the largest in class 3. In each of these cases
there is an abrupt and disproportional increase in size, if these
structures are regarded as simple units, which entirely disappears
if their multiple constitution is recognized. Such jumps of size
in the complex are lacking in any species of this family where
the twelve chromosomes are present, and it is not reasonable to
consider that they represent any great change in the organiza-
tion of the chromosome such as would be involved if these huge
chromosomes were in fact of the same value structurally as the
lower ones of the series. However much difficulty there may be,
for example, in locating chromosome 4 or 5 in the series, there
can be no mistake made in judging the relative size of the largest
-element in classes 3, 4, 5 and 6. It is also easy to see that
either half of this ring exceeds the dimensions of the next chro-
mosome in size in somewhat the same degree as chromosome 11
does chromosome 10 of class 6. Similarly the members of the
smaller ring in class 5 are related to chromosome 8 of class 6.
The relations in size of the upper members of the series are
demonstrated most conclusively by a comparison of them in
classes 4, 5 and 6.

556 CLARENCE E. McCLUNG

While these unequivocal conditions certainly obtain and jus-
tify the effort to homologise the chromosomes on the basis of
size, it must be admitted that there appears to be some fluc-
tuation in volume, both absolute and relative, between the
same members of the series in different individuals. How much
this may signify it is difficult to say. There are so many ways in
which the size of a chromosome may be affected in the processes
of microscopical technique that a just estimate of the significance
of size variation is hard to reach. Thus it is known, for in-
stance, that very marked differences in size may result from the
method by which the animal is killed. If this be true, there are
doubtless other ways in which these delicate structures may be
similarly affected. Since however the animals themselves may
vary greatly in dimensions without in any other way modifying
their character, the same may be true of their chromosomes.

A very careful study needs to be made of chromosome dimen-
sions, based upon material prepared with the utmost refinement
of technique and studied with most careful mensuration. Under
ordinary conditions there are many circumstances which would
serve to obscure differences between nearly related members
of a series and make their identification uncertain. While this
is true, most of our observations would indicate that agencies
affecting the size of chromosomes operate more or less uniformly
on the entire complex, so that a proportionate change is found in
each element. With the subject as difficult as it is there is no
wonder that views as widely divergent as those of Meek and
Della Valle exist. The former author thought at one time that
he had detected a uniformity so great that only two diameters —
appeared in all the Metazoa, but a more extended experience did
not confirm this opinion. It is true that there is much uniformity
in the diameter of the chromosomes of a complex, and Meek’s
careful measurements disclosed this; but, on the other hand,
there are extensive movements in the chromatin substances and
the diameter varies inversely with the length. There is always
the possibility of such movements and the extent of them at
any given time is variable, so that we may expect to find differ-
ences in dimension although the volume remains constant.

MULTIPLE CHROMOSOMES By

Meek has done good service in pointing out the facts, but it is
unfortunate that he should push his generalizations so far upon
a limited experience. Very different are the methods and
conclusions of Della Valle.

Variations in size, according to Della Valle, fall within the
limits of observational error and are of the order of size varia-
tions of droplets in an emulsion. Correspondence in size between
chromosome and the nucleus finds its explanation in the physical
condition of adsorption. As in the case of numbers, the appeal
is from an explanation based on order of determinable character
to one in which only the chance circumstances of physical rela-
tions obtain. Opposed to this conception stand all the careful
investigations in which definite size relations are shown to be
preserved, not only in a single series but in a duplicate one.
Within this occur occasional inequalities, which, in turn, are of
definite character, pertaining to certain chromosomes and so
recurring as to be accounted for most readily through genetic
continuity and chance distribution and recombination. Upon
this point again the circumstances in H. viridis offer important
evidence. The smaller members of the complex form an ascend-
ing series which, in class 1, is continued without breaks through
the larger members. But in the remaining classes there are sharp
breaks in seriation of exactly the same character in all the cells of
the individual, entirely beyond the range of observational error
and past the possibility of chance variation. The conditions are
altogether of the character of order and system common to liv-
ing structures and foreign to purely physical phenomena. The
material upon which the Italian author worked is not nearly so
favorable for size determinations as are many other kinds, be-
eause of the great length and irregular contour of the elements,
but even here much more accurate results could have been ob-
tained by the exercise of such care as was employed by Meek.
From some studies being pursued in this laboratory by Mr.
Parmenter I feel certain that the Amphibia are no less exact in
their size relations than are other groups of animals.

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

558 CLARENCE E. McCLUNG

4. Chromosome forms

In a previous paper (’14) I have considered at length the
subject of chromosome forms in the Orthoptera and do not here
desire to go into the subject beyond what is necessary to an
understanding of the multiples. A glance at plate 2 will show
how strongly these elements differ from the tetrads in metaphase.
The typical Orthopteran chromosome is telomitic and, in polar
views of the spermatogonium and second spermatocyte meta-
phase, it appears as an approximately straight rod which, in
the anaphase, becomes divided into daughter rods of similar
nature. In the first spermatocyte these rods, joined in pairs to
form tetrads, show a great variety of'shapes in metaphase, but
in the anaphase again become reduced to the form of two rods
joined at one end to form a simple V, the enclosed space of which
lies between two chromatids of the former tetrad. Upon divi-
sion of the hexad in the first spermatocyte of Hesperotettix this
condition is again realized for the rod-portion, but opposite this
in the other anaphase group stands a V, the arms of which are not
simple rods but double ones, and the enclosed space of this lies,
not between chromatids, but between whole chromosomes. ‘The
nature of this double-V I have considered fully in former papers.
Its peculiarity of form is due to the fact that fiber attachment is
non-terminal—a condition resulting from the union of non-
homologous chromosomes and not from a real shift of the fiber.
All this is very clear in Hesperotettix, and the character of the
double V is beyond question and easy of determination. From
this one would be inclined to generalize and to say that where
fiber attachment is shifted from the terminal position, producing
double V’s in the first spermatocyte anaphase, it is due to the
union of non-homologous chromosomes. Of course to make this a
valid argument there would have to be a corresponding reduction
in the group number of free elements. This condition is fully
met in Hesperotettix and is confirmed by the differential mor-
phological characters of the elements involved. In the absence
of such criteria based upon structure, the sole test regarding
the character of the double V’s would be that of numerical
conformity.

MULTIPLE CHROMOSOMES 559

Upon turning to Mermiria bivittata we encounter these con-
ditions: a spermatogonial complex of twenty-two free elements
among which are two atelomitic V’s. If it were assumed that
the latter are always multiples, then the male diploid complex
would be twenty-four. There are two arguments against this
conclusion however. First there is the circumstance that the
genus—a, well marked one—has species with the normal twenty-
three free chromosomes. The value of such evidence has already
been considered. A second piece of evidence is the actual
morphological structure of the V’s. One of them shows by all its
history that it is directly comparable to the similar structure in
Hesperotettix—it is a multiple composed of the accessory chromo-
some and a rod-shaped euchromosome. The other V is found
in the first spermatocyte attached to this multiple element.
Unless this combination be of greater valence than a hexad, the
second V can be only a dyad. Strong evidence that this V is
indeed only a simple dyad appears from a study of certain in-
dividuals which I have called the ‘green’ bivittata. In these
specimens the multiple chromosome is almost the shape of the
one found in Hesperotettix, the fiber attaching near the free
end instead of toward the middle (figs. 58, 59, 60, pl. 7). The
valence of the part is very clearly indicated in this way. Owing
to mistaken enumeration in the spermatogonium, because of in-
sufficient material, I regarded the multiple as a decad instead
of a hexad in my earlier work. In this opinion I believed my-
self confirmed by the persistent type of chromosomes in the
family. It was only when new material revealed to Miss Caroth-
ers that, in a full complex of twenty-three chromosomes, there
might be numerous double V’s, and that one such an element
might be united to a rod, producing a J-shaped tetrad, that I
found it possible to account for the form of the Mermiria mul-
tiple. With plenty of favorable material I was also able to de-
termine accurately the diploid number of chromosomes in the
male to be twenty-two. Having all these facts it was not diffi-
cult to solve the problem.

It is apparent, therefore, that form alone is not sufficient to
establish the nature of a chromosome. The double V may or

560 CLARENCE E. McCLUNG

may not be a multiple. In Mermiria, in the same chromosome
of the first spermatocyte, we have two such V’s, one of which is
multiple, the other not. In Trimerotropis double V’s are nu-
merous although the complex is not reduced in number. But
the form of the chromosome, taken in connection with the
number in the complex, the relative sizes of the elements, their
structure and behavior, is important. With these limitations
on the value of chromosome form in mind, I wish to consider the
evidence they afford regarding the nature of the Stenobothrus
type of rings and V’s in H. viridis.

In such a study the occurrence of the incomplete ring is very |
helpful because it constitutes an intermediate form between the
two rod condition and the ring. An examination of these ele-
ments in classes 4, 5 and 6 (plate 2) will demonstrate these rela-
tions. In the last class, chromosomes 9 and 10 are rods ar-
ranged on the spindle parallel with its axis, and there divide at
the middle constrictions. Similar structural conditions pre-
vail in class 4, with the exception that, in place of chromosomes
9 and 10 as free elements, their position in the size series is occu-
pied by a single chromosome in the form of a V placed in the
same relation to the spindle. Upon division, the elements of this
unusual chromosome separate at their middle constrictions just
as did free chromosomes 9 and 10, and in one of the anaphase
groups exactly the same conditions obtain as in cells of class 6
(fig. 28, pl. 5). The other group has, in place of two rods, a
double V corresponding in the number and size of its subdivisions
to the sum of those in the two rods from which it separated. All
the circumstances of the case indicate that the only unusual con-.
dition here is the union of chromosomes 9 and 10 at one end,
producing, in the diploid condition, a V, whose arms are unequal
in size and otherwise non-homologous. The origin of such a
combination has not yet been determined, but it is not a tempo-
rary condition during the maturation period, for it is found in all
generations of the cells and is undoubtedly present in the so-
matic cells. Since it is present in half of the sperm it may
as readily perpetuate itself as the two rod condition. If like
relations exist during the maturation of the egg, then a means

MULTIPLE CHROMOSOMES 561

for producing all the chromosomal arrangements. found in H.
viridis is at hand. Thus a two rod spermatozoon and a two rod
egg would produce a complex having chromosomes 9 and 10
free as in classes 1 and 6. A double-V spermatozoon and a
two rod egg would bring about the condition shown in class 4
where these chromosomes are joined at one end, while such a
spermatozoon, united with an egg of similar composition, would
result in the complete ring of class 5. It seems evident there-
fore that the forms of chromosgmes found in the male germ cells
may be accounted for on the ae of persistent fusions, segre-
gations and recombinations.

Similarly, if chromosomes 11 and 12 are compared, we find ie
two rod, incomplete ring, and ring, and the argument’ for their
relation is the same as for the preceding case. There are how-
ever two notable differences between the series. Of the six
classes, only two show multiples of chromosomes 9 and 10, while
four classes have combinations between d1 and 12. Again, the
incomplete ring is as frequent as the complete in classes 4 and
5, while only one individual out of twenty-six belonging to classes
3 to 6 failed to have a union of the two tetrads at both ends.
Thus we learn that the tendency of the large elements. to unite
is more pronounced and complete. In this connection it may
be noted that in class 2 the largest element, although failing to
form a union with a euchromosome, is united to the accessory
chromosome. Only four individuals of the thirty-seven show this
element not joined to another chromosome. Of similar import
is the combination between the accessory with the largest free
euchromosome in class 4. It is possible that the largest free
tetrad is involved in class 3, although I judged it to be next to
the largest when the drawing was made. Another thing to be
noted is that only tetrads of nearly equal size unite together.
The accessory chromosome is never joined to a chromosome of
lesser size.

The form of the multiples, as represented on the tabular
series of plate 2, is the one best adapted to serve as a means of
comparison between them and the free chromosomes of other in-
dividuals. ‘This relatively simple configuration is, however, not

562 CLARENCE E. McCLUNG

the only one assumed, and some of the figures would be difficult
of conception in the absence of acquaintance with the possible
range of chromosome movements. For a number of reasons
these variable forms are of importance and require consideration.
It is to be noted that this extended ring may be the final shape
assumed by other metaphase forms just previous to the ana-
phase, or it may represent the status attained by chromosomal
movements antecedent to the metaphase. Probably all that is
involved throughout is a differenge in relative movements of the
chromatids. An examination of figures 14b, 16c, plate 3 will
reveal a chromosome, one part of which is extended over the
spindle as are the members of the flattened ring already de-
scribed, while, embraced between its ends, lies another ring
within the plane of the equatorial plate. By comparing this
chromosome with others shown in photomicrographs Q-V,
plate 8 it is seen that this second ring may be progressively
reduced until it corresponds in form and position to the extended
element to whose ends it is attached—the sole remnant of the
equatorial ring being an enlargement at the middle of the curved
rod. It is apparent that the enclosed spaces in these two rings,
lying at right angles to each other, can not be the same morpho-
logically, unless the chromatids in synapsis have shifted. One
must represent an interchromosomal space, the other the longi-
tudinal split of the chromosomes. In this respect the element
is similar to the double ring figures in certain Orthopteran tetrads.

Another form of not infrequent occurrence is, similar in out-
line to the hexad of Mermiria and consists of a curved rod applied
conformably to the spindle, with the fibers attached at the ends.
From these ends also there spring at various angles more or less
straight chromatin rods equal in length, approximately; to half
the curved rod to which they join. Superficially such an element
is almost the counterpart of the Mermiria hexad, but is nothing
more than the large extended ring whose shorter half has divided
at the equatorial constriction in advance of the longer (fig. 24).
A more puzzling case is that of the curved rod extending from
one pole of the spindle to the other and almost equalling the
combined length of the two halves of the ring or V (fig. 19, pl.

MULTIPLE CHROMOSOMES 563

4 and photomicrographs P., Y., pl. 8). Such a structure would
result if the V were unfolded on the spindle with fibers attach-
ing at each end, but in this case the parts on either side of the
equatorial constriction would be unequal and division at this
place would mean separation of whole tetrads. Because of ‘the
relatively slight difference in size of the joined tetrads, I have not
yet been able to satisfy myself of the exact relation of parts in
this elongated chromosome, but I suspect that separation of
chromatids has occurred in a plane at right angles to that which
obtains in the V. A full study of the prophase history should
clear up this matter.

Emphasis needs to be placed upon the statement already
made that the mere form of the chromosome is not conclusive
evidence, either of its valence or its method of division. Valence
can be determined only by a study of the element through the
various generations of cells and in numerous individuals of the
species. Planes of division are certainly identified only by some
morphological character which marks one of the synapsed
elements. Instances of the exactness in configuration of chromo-
somes of tetrad, hexad and octad valence have already been given,
but it would seem desirable to consider the ring chromosome a
little more at length. In former papers I have called attention
to the importance of such elements as indicators of the planes of
division, and in one (714) I pointed out the distinction between the
Hippiscus and Stenobothrus types and indicated how failure to
recognize such distinctions has led to much confusion. At the
same time it was recognized that, in the presence of parasynap-
sis, the opening in the ring might represent either the space be-
tween homologous chromosomes or their longitudinal division.
Since there was, so far, nothing to suggest two types of ring
formation, it was considered that only one exists and the avail-
able evidence would indicate that the annular space lies between
“homologous chromosomes. In the presence of one type of ring
there must necessarily be two forms of first spermatocyte divi-
sion, for the Hippiscus ring divides along the length of the ring
while the Stenobothrus type separates transversely. Owing to
the fact that, up to that time, all rings of the Stenobothrus type

564 i CLARENCE E. McCLUNG

has been found in complexes of less than the full twenty-three
numbers, some uncertainty existed regarding the connection
between these two circumstances. That this connection was not
necessarily causal was indicated by the case of the unidentified
‘Stenobothrus-like’ species with a complex of twenty-one and
numerous rings of this species-type. But not until the work of
Carothers on Trimerotropsis was it certain that there is no
necessary relation between the Stenobothrus ring and lesser
chromosome numbers. It is now clear that this form of chro-
mosome is not in itself evidence of multiple constitution above
the tetrad. Structurally all that is involved, apparently, is an
atelomitic fiber attachment.

But if it is not true that such rings and the double-V’s which
unite to form them, and which reappear upon their division, are
criteria for octads, it is very suggestive of such composition to
find them so frequently in cases of reduced numbers. Where it
can be shown that progressive steps in such unions occur within
a species, as in H. viridis, and that morphologically recognizable
divisions of these elements which, if counted as units, exactly
restore the reduced number to that characteristic of the species
and family, then the form of the chromosome is of value in
determining composition. Especially is this true if by such means
always the exact number characteristic of the group is restored,
and if, in groups of different chromosome numbers, the distinc-
tive numerical relations are preserved. All of these desiderata
are realized in Hesperotettix of the twenty-three chromosome
family and in Jamaicana of the thirty-three and thirty-five group
as reported by Woolsey. The parallel between the two cases
seems to be very exact, with the exception of a more marked ~
tendency toward combinations in Hesperotettix.

The circumstances appear unequivocal in the cases of Hespero-
tettix and Jamaicana where multiples may or may not exist within |
one species and where intermediate steps indicate the method of
combination. The question which next presents itself is with
regard to the application of these criteria to cases, such as Chor-
thippus, where there appears to be a permanent and fixed re-
duction of number, not only for the species, but also for the

MULTIPLE CHROMOSOMES 565

genus and related genera. In a recent paper Robertson (’16) has
considered this matter with great care and has advanced strong
arguments in support of the position that the family number
may be maintained in the face of apparent reduction. His argu-
ment may be thus summarized. (1).The number of chromo-
somes for the family is twenty-three in the male; (2) the form
of the chromosomes, when uncombined, is that of a rod with
terminal fiber attachment; (3) size relations are constant and
valid indications of homologies; (4) in the presence of less than
the typical number of chromosomes certain ones of the com-
plex are V’s with non-terminal fiber attachment; (5) if the limbs
of the V’s are counted as units, the number twenty-three is re-
stored; (6) the behavior of the limbs of the V’s in maturation is
parallel to that of corresponding free elements in other species
of the family; (7) the morphological composition of the V is
indicated by a non-chromatic bridge at the angle where the fiber
attaches.

I believe that in the species studied by Robertson the criteria
are largely applicable and the conclusions essentially justified.
The evidence is, to a considerable extent parallel to that of H.
viridis, with the exception of intermediate steps in linkage.

There is clearly a permanent reduction in the number of free
chromosomes—it then becomes a question as to whether there
is a definite loss of morphological entities in the chromosome
complex, or whether all the twenty-three elements are poten-
tially present, even though in combinations. It must be recog-
nized, I think, that, however fundamentally alike are the cases
of Hesperotettix and Chorthippus, they stand on a somewhat
different basis morphologically. In the former, independence
_of certain chromosomes is strongly evidenced by their free con-
dition in some individuals and their partial union in others; in
the latter the number of free elements is constant, not only for
this genus but for others nearly related, and evidence of com-
binations must be more indirect. Considering the criteria which
I have employed in Hesperotettix and Mermiria I would regard
the following as probably applying in the case of Chorthippus:
(1) The number of chromosomes, so strongly indicated in the

566 CLARENCE E. McCLUNG

family, is made exactly normal by counting the limbs of V’s as
units, (2) the graded size series, sharply broken if the V’s are
considered as simple units, is restored if they are compound
elements, (3) the form of the univalent chromosomes is so gen-
erally a rod in the family that the occurrence of V’s, in connec-
tion with the circumstances in (1) and (2), is strongly suggestive
of multiple constitution. To these should be added the con-
formatory evidence of cases like H. viridis which establish on
direct observation the principle of chromosome combinations.

That these circumstances justify the generalizations which
Robertson draws regarding the multiple nature of V-chromosomes
in general seems much less certain. Because of the great im-
portance which attaches to the exact determination of chromo-
somal conditions in the germ cells it is essential that our cytologi-
cal evidence be most carefully considered. I should like there-
fore briefly to indicate where it appears that limits should be
placed upon the extension of the principles indicated by condi-
tions in Hesperotettix, Mermiria, Anabrus and Jamaicana.
Since Robertson has made the widest application of these by his
conception of the multiple constitution of V-shaped chromo-
somes, an examination of his presentation will illustrate the
nature of the difficulties attending such generalizations, into
some of which I was myself led. It is fortunate in this con-
nection that there is no question regarding the accuracy of the
observations. His work is very carefully done and the eselannece
are clear and definite.

Agreement has already been indicated with the first two prem-
ises of his argument, ie, that the number twenty-three is
typical for the family, and that the form of the univalent chro- —
mosome is a rod with terminal fiber attachment. Like most
other biological generalizations, however, these are not without
exceptions in the Acrididae. Pamphagus, with telomitic ele-
ments, has only nineteen chromosomes and Trimerotropis with
numerous and variable V’s has a full complex of twenty-three.
My unidentified Acridian reported in a former paper (14)
(which may be a species of Circotettix) has nine atelomitic
chromosomes in twenty-one chromosomes, while Circotettix, as

MULTIPLE CHROMOSOMES 567

reported by Miss Carothers, has similar conditions of less than
the typical family number and more than enough V’s to com-
pensate. Despite these exceptions the value of the evidence for
constancy of number and form is strong because of the few
departures from type.

With regard to size as a test for homology there is much less
certainty. No chromosome is more definitely to be determined
than the accessory chromosome and this falls in no constant size
position, either for the family, genus or species. Robertson re-
ports it varying in size from number 1 to number 5 in the Tet-
tiginae and from number 8 to number 10 in the subfamily
Oedipodinae. It seems to vary from number 3 to number 5 in
the genus Hesperotettix and from number 4 to number 5 in the
species viridis. Variation in size of the individual chromosomes,
recognizable by other morphological characters, has been reported
by Wenrich (’16) after a most careful study of Phrynotettix..
In this latter case variation appears to be the result of actual loss
of certain parts of the chromosome, but in general it is due to the
extent of condensation and possibly to the amount of more
fluid substance held within the chromosome. All our observa-
tions indicate the existence of a fairly definite series of sizes
throughout the group, and the extreme members of the complex
can not be confused, but it is clear that no certain identification
‘of neighboring elements can be made by size alone. For this
reason, even if the achromatic bridges did mark the limits of
joined chromosomes, it would not be certain that specific num-
bers united as is indicated by Robertson. Here it may be noted
that in H. viridis chromosomes of nearly equal size, and the
largest in the series, are joined together. Practically the same
_ conditions are reported by Woolsey in different species of Jamai-
cana. Judging from her figures I should be inclined to say that
it is not improbable that neighboring chromosomes, and those
of the largest size, are united here. Measurement of the chromo-
somes as drawn is not a very accurate way of determining their
size, since the amount of foreshortening can not be known, but
it is so frequently the case that the element marked ‘14’ in her
figures of the multiple, is clearly larger than the free number
‘15,’ that the possibility of confusion exists.

568 CLARENCE E. McCLUNG

The significance of the form of V-chromosomes, as an indi-
cation of multiple constitution, is bound up intimately with the
question of numbers. .Only when the limbs of the V, counted as
units, with the rod chromosomes, total the number characteristic
of the family can there be such evidence of multiple constitution,
according to the terms of Robertson’s argument. If it appears
that such elements exist under other circumstances, then it is
necessary to assume that there may be more than one type of V.
This Robertson does and uses as a criterion for the V, indica-
tive of multiple composition, the presence of a distinct achro-
matic bridge at the apex of an acute angled structure. The final
test of the validity of his generalization becomes therefore a
structural one. There is no doubt of the accuracy of his deter-
mination of such a condition and he has with great care traced
it through all the stages of maturation. It is unfortunately
true, however, as Carothers and Wenrich have shown, that
equally clear non-staining bridges occur in atelomitic chromo-
somes of Trimerotropis where the full complex of twenty-three
is present. Conversely, in cases where undoubted combina-
tions exist, as in H. viridis, no distinct achromatic bridges at
the point of fiber attachment appear. This seems to be true
of Jamaicana also, judging by the figures of Woolsey and of
Robertson himself. It seems certain therefore that the V-form
of chromosomes, is, in itself, no indication of a multiple condi-
tion. If this be true for the Acrididae it is quite useless to
consider its value in other groups where the chromosome con-
stitution is less well known.

The form of certain first spermatocyte chromosomes and the
behavior of their parts in this mitosis is regarded by Robertson ~
as further confirmation of his belief in their multiple character.
He draws a close parallel between them and free elements of
other species through homologies of size and form. Since the
limits of these supposed elements are fixed by the achromatic
bridges at the point of fiber attachment, their validity as tests
for chromosome boundaries is questioned for the same reasons as
were given above. I should however like to speak more at
length regarding this form of chromosome—the double rings.

MULTIPLE CHROMOSOMES 569

These are represented very exactly in Robertson’s (716) figures
174, 179, 180 and 182, and the achromatic break is considered the
point of union between tetrads. I believe that the weight of
evidence supports this interpretation: that these are indeed po-
tentially multiple chromosomes, but at the same time I feel
that there is no justification for the belief that this form of chro-
mosome is the result of the union of two tetrads of such shapes
that this configuration results. My evidence for this is that just
such shapes occur in full complexes of twenty-three chromosomes,
of both telomitic and atelomitic type. They are found in many
species and have been figured by Sutton, Granata, and myself.
As I have pointed out, the two rings lie in planes perpendicular
to each other and their origin is easily conceived if the chromo-
some is constituted of four parallel rods. A similar conception
appears in the interpretations of the other two authors cited.
The same difference between double rings of the telomitic and
atelomitie types holds as in the ease of simpler annular chromo-
somes of the two types, for the fiber attachment is persistent
and determines the position of the chromosome on the spindle.
Therefore such structures are very much alike in Trimerotropis
and Stenobothrus and are so placed on the first spermatocyte
spindle that the ring to which the fiber attaches lies parallel
with its axis, while in forms with telomitie chromosomes only,
such as Hippisecus, Tropidolophus, Brachystola and others, the
ring to whose ‘lugs’ the fibers attach lies in the equatorial plate.
Such differences are however entirely independent of simple or
multiple composition of the diploid chromosomes.

Finally I consider them valueless as criteria of multiple con-
stitution, because in Chloealtis, a genus nearly related to
_Chorthippus, the same numerical and size relations obtain, and
there are no double rings to suggest preservation of chromosome
forms such as are found in more widely removed genera. So far
as the form of the chromosomes is concerned, the conditions in
the Tryxaline, Chloealtis, are much more nearly like those in
H. viridis, of the Acridiinae, than they are in Chorthippus, a
very nearly related genus.

570 CLARENCE E. McCLUNG

At this point it may not be out of place to speak of the condi-
tion of cross segmentation as an index of chromosome bound-
aries, since this is a matter that has led many, including myself,
into mistakes. These non-chromatic segments are doubtless
definite indications of structure in the chromosome and prob-
ably are always of the nature of the spaces lying between the
chromomeres, as in the ‘selected’ chromosomes described by
Wenrich (’16). Such regions are more pronounced in appear-
ance and more persistently free of chromatin where the fiber
attaches than elsewhere in the chromosomes, but probably do
not differ otherwise. Even this distinction may be lacking, as in
Mermiria (figs. 58, 59, pl. 7) where the chromosomes seem not
infrequently to separate at different levels. It was this strong
cross segmentation at definite levels, with subsequent division,
that led me to believe in the. decad constitution of the multiple
in Mermiria. 3

Another thing which has contributed to Robertson’s mis-
interpretation of the V-chromosome is his belief that only in
their presence do pachytene loops appear in the nucleus. No one
feature is more characteristic of the prophase condition in all
Acrididae (from which the Tettiginae should be removed, as I
suggested in 1908 and as Robertson believes) than the bending
of the chromosome so that both ends lie at one side of the nu-
cleus. Even the univalent, accessory chromosome takes this po-
sition, as was shown in an earlier paper (’02, fig. 12). Wenrich
finds that the looped condition is not confined to the large ele-
ments, but is characteristic of the small chromosomes of which
he made careful, detailed study. It is of interest to note that,
in this respect, the members of the octad in H. viridis behave as ~
though they were independent, each forming its own loop.
This is a very strong indication, indeed, of their multiple nature.
The conditions at this time in the Tettiginae are unique so far
as my experience goes. Here, as Robertson states, the chromo-
somes are extended in a more or less straight line, and since they
are much longer than the nuclear diameter, the whole nucleus is
drawn out, producing very irregular shaped structures. It

MULTIPLE CHROMOSOMES 571

was this circumstance, of which he had detailed knowledge, that
led Robertson to believe that loops are unusual.

The form of the chromosome is conceived by Della Valle to be
uniformly that of a rod with rounded ends. Such is frequently
the shape of metaphase chromosomes, particularly in the dip-
loid condition, but no one who has studied the complicated
changes through which the members of the haploid series pass
at the synaptic period, could entertain the simple conception
of a homogeneous rod spontaneously dividing along its length,
advocated by this author. The most remarkable and striking
phenomena of biology are entirely ignored by this explanation.
Precision of organization, shown by: Wenrich to extend to the
limit of our observational powers, is entirely disregarded by the
gross conception of a formed and homogeneous rod cleaving like
an unorganized colloid mass. The extensive and significant
changes of the prophase, when the division actually occurs, re-
celve no recognition in this crude explanation of chromosome
division. The form of the chromosome .is a much more in-
volved question than would appear from the statement of the
case by Della Valle.

5. Chromosome behavior

Of very great importance for the theory of chromosome in-
dividuality is the behavior of the elements united into mul-
tiples. If the chromosomes are merely colloid masses—products
of the cell—it would not be expected that they should exhibit
any differential characters. The very fact that such differences
of behavior exist is a disproof of all theories which postulate
complete loss of identity and reformation of chromosomes at
-each mitosis. Unless there is continuity of substance there
can not be continuity of organization, because we know of no
organization independent of material basis. Besides. such per-
sistence of structure and substance is observable. As indicat-
ing the high degree of this specificity of chromosome characters,
the multiples are of much value, especially when they involve
the accessory chromosome. If all the elements of a mitosis are

are CLARENCE E. McCLUNG

‘identical’ and ‘homogeneous,’ as Della Valle asserts, there
would not be the marked difference in behavior of the euchromo-
some and the accessory chromosome which we always witness in
the Orthoptera. Most especially would this be true where the
two types constitute a single mitotic element. What a con-
trast the actual facts regarding exactness and differential char-
acter of the chromosomes present to the crude and vague gen-
eralizations of those who conceive the cell to be only a micro-
scopic laboratory for the play of the chemical forces involved in
colloidal crystallizations. It is however fortunate that there are
minds not content with a half way denial of the facts relating
to nuclear constitution and the substitution of indefinite generali-
zation about the activity of the cell as a whole or of specific
enzymes, etc., but which push the denial of precision of organi-
zation to an unconscious reductio ad absurdum in some field of
chemistry. For through this service we are brought to see the
contrast between clearly defined facts, gained through re-
searches of the most exacting and painstaking character and the
uncertain and contradictory theories springing from impatient
and prejudiced minds.

The facts regarding the differential behavior of the chromo-
somes, together with those relating to numbers, sizes and forms,
are, many of them, now commonplaces of observation and are
regularly determined by beginning students in microscopie
anatomy. Others, such as those exhibited by the euchromosome
multiples described in this paper, are no less striking and sig-
nificant. ‘They all speak clearly and unequivocally in favor of
an order, in terms of morphology, and against one of a more ~
remote and molecular character. But no single feature of
chromosome behavior possesses the significance and fundamental
importance which attaches to the unquestioned reproduction of
each individual chromosome during mitosis. Why, unless there
be something in the organization to be preserved, should the
elements so carefully reproduce themselves down to the most
minute structural peculiarities? It is inconceivable that the
complexity and exactness of this process should exist unless there
is some correspondingly important function to be carried out.

MULTIPLE CHROMOSOMES Sia

If the chromosomes are homogeneous and identical, as Della
Valle asserts, their substance could most easily be divided while
they were in ‘solution.’ The complication of the mitotic proc-
ess is all out of proportion to the simple end to be served under
such an assumption.

6. Chromosome distribution

In most mitoses it would seem that every step of the process is
directed toward securing the exact distribution of the chromatin
elements. The outstanding exception to this rule has been the
independent movement of the accessory chromosome in one of
the maturation mitoses, where it goes into one cell entire without
division. This is clearly a differential mitosis, featured by an
asymmetrical distribution of the chromosomes. One of the
elements possesses a distinctive character not shared by the
others—it has an individual and more or less independent move-
ment which takes place at only one time in all the history of the
organism. Up to this one point it is distributed in mitosis lke
the other chromosomes, but just here it betrays the inherent
difference of its nature. So much of the chromatin substance
acting as a unit in mitosis, possesses distinctive characters. Are
these the consequence of this separate unity, or is there some
specific nature of the material? The history of the hexad mul-
tiple chromosome answers this question definitely in favor of
the latter alternative, for, although joined to another element,
the same characteristic features of behavior and distribution
mark the accessory chromosome as when it is free. It is incom-
prehensible that there should be this definiteness of action on
the basis of mere chance—such a conclusion is foreign to all our
_experience with living structures. Taken in connection with the
parallelism between the development of sex and sex linked
characters, and its distribution during maturation, all the his-
tory of the accessory chromosome speaks for specific organiza-
tion and self perpetuation. The fact that it violates the practi-
cally universal rule of a complete division of all the members of
the complex in each mitosis in order to accomplish its necessary
distribution and self perpetuation is an unanswerable argument

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

574 CLARENCE E. McCLUNG

for its specific individuality. That this distribution is properly
maintained, although the element is no longer free in the mul-
tiples, is only another confirmation of the conclusions otherwise
determined. )

Another evidence of specific organization through acts of dis-
tribution comes from the studies, upon unequal and hetero-
morphic chromosomes by Miss Carothers (717). Organization,
expressed in size or form, is perpetuated by a distribution and a
conceivable recombination according to chance movements,
There is no indication that any indefinite variation exists.
While it is true that no explanation of the origin of the hetero-
morphic condition is strongly suggested by the facts so far ob-
served, it may be noted that Wenrich’s work affords objective
evidence regarding inequalities in size. Always a means for
the maintenance of given conditions appears in the mechanism
of mitotic distribution.

The same precision in distribution which marks the accessory
chromosome is true also of the elements which unite to form the
euchromosome multiples. No difference exists between the
distribution of these members of the complex, whether free or
combined. It might be thought that the intimate and appar-
ently permanent association of two chromosomes, resulting in
the formation of a new mitotic unit of different value, would ma-
terially change the activities of the components. So far as I
can see this is not the case, and even the details of movements
in the prophase are preserved in the face of the multiple
condition.

The problem of accounting for the occurrence of a given vari-
able series of heteromorphic chromosome combinations in>
Trimerotropis has been considered by Miss Carothers and she
properly arrives at the conclusion that segregation and chance
recombination of components offer a competent explanation of
the observed phenomena. At the same time there is not ex-
cluded the possibility of a readjustment of relations between the
chromosome complex and the new cytosome at the time of fer-
tilization, which, within a limited range of possibilities, would
result in a similar variable series. The conditions within the

MULTIPLE CHROMOSOMES 0 5

species of H. viridis would not be fully met by the explanation
through segregation and recombination, without assuming a
heterogeneous character of the material or a lack of survival of
certain classes. While both of these possibilities exist they are
remote, and the phenomena, taken in their entirety, are much
more suggestive of a reconstitution of relations in the new indi-
vidual, probably at its origin on fertilization. This is a prob-
lem which concerns the most fundamental activities of the
chromatin substances, and about which we lack information on
all the stages of fertilization and maturation of the egg. Breed-
ing experiments should serve to decide between the possibilities
suggested, and these will be carried out, but the nature of the
processes will not be clear until the complete cycle of the chromo-
some complex has been studied. This fact has been realized
since the beginning of the work on the Orthoptera, but the
technical difficulties involved are great and so far have not been
overcome.

While, therefore, it is not possible to draw any definite conclu-
sions from our present knowledge, it may be desirable to direct
attention to the conditions which confront us. Reasons are
given elsewhere for considering the individuality of the chromo-
somes as well established by the observed uniformity of num-
ber, size, form, behavior, etc., but in the case of the multiple
chromosomes we face a series of variations. As has been
pointed out, variability is a universal property of living matter
and is a subject for investigation, not an evidence of lost indi-
viduality. Taking into consideration, first, the accessory chro-
mosome, whose individuality is marked so definitely as to be
unquestionable, we find, that, within the species H. viridis, it
may possibly vary slightly in size although this may be only
apparent. From this we would draw the conclusion that, for
the species, size is a fairly safe criterion of homology, although
not absolutely exact. Using size to identify homologues, then,
we discover that the accessory chromosome is joined to the
largest chromosome in class 2 (plate II), to the third or fourth
from the largest in class 3, and to the fifth from the largest in
class 4. With persistent union, segregation and chance com-

576 CLARENCE E. McCLUNG

bination it is apparent that there could be no union between a
spermatozoon of class 2 and an egg of classes 3 or 4, for instance,
without synapsis of non-homologuos chromosomes. Still using
size as a test for homology, we find no such indication of non-
homologous chromosome unions in this species.

This difficulty entirely disappears, however, if we assume
that the formation of multiples takes place at fertilization.
Such a view is in strict accord with our knowledge of the im-
portance of this step in the production of differences between
individuals and of constancy of character exhibited by each of
these variants throughout its subsequent history. Also there
is offered a ready explanation of the formation of multiples,
which would, at the same time, explain the variety of elements
sometimes involved, as in this case; for if there be a period at
which chromosomes are brought into intimate relations in a
linear series, multiples would be merely persistent cases of such
associations. The contrary might also be true, the multiples
showing a tendency to overcome forces keeping the chromosomes
apart, but, in view of the variety of elements involved in H.
viridis, this would seem less reasonable than the first explana-
tion. There are also other considerations, into which I have not
the time to enter here, which incline me to believe that mul-
tiples indicate the operation of a common principle of chromo-
some association. The alternative for this explanation of the
conditions in H. viridis, by reason of associations established at
the time of the union of the spermatozoon and egg complexes,
is the assumption that, at some time, each of the classes repre-
_ sented in plate 2 became established in some way and has since
maintained itself by the segregation of its elements and their
chance recombinations, with the elimination of all the unrepre-
sented conditions. By this we are still left without an expla-
nation of the first instance of each class and must confront a
selective mortality of considerable magnitude, for which there is
no evidence. f

Such an explanation, as that to which I incline, for the condi-
tions of the multiple chromosome in H. viridis does not make
impossible another for the case of Trimerotropis, and it may

MULTIPLE CHROMOSOMES yer

well be that in the latter instance, which concerns questions of
fiber insertion or other variation between homologous chromo-
somes, the simple method of segregation and chance recombina-
tion obtains, while in H. viridis, where non-homologous chromo-
somes are involved, another mechanism is operative. Genetical
experiments will shed some light on these difficulties and it is
hoped that these may be completed before long.

7. Chromosome indimduality

As has been stated elsewhere in this paper, the circumstances
relating to the multiple chromosomes are strong proofs of the
theory of chromosome individuality, as indeed are all facts indi-
cating order and definiteness in form and behavior. So far as
I can see there is no half way ground between the assumption
that the chromosomes are definite, self-perpetuating organic
structures and the other which presents them as mere incidental
products of cellular action. According to one view individual
chromosomes are descendants of like elements and possess cer-
tain qualities and behavior because of their material descent,
the visible mechanism for which is the process of mitosis: ac-
cording to the other any similarities that may exist in the com-
plexes are the result of chance aggregations of non-specific ma-
terials. It is a choice between organization and non-organiza-
tion in the last analysis, at least in terms of cellular structures.
To attempt the substitution of a conception of molecular or-
ganization, which is beyond the experience of the biologist and
which exceeds the present powers of the chemist to analyse, is
to cast aside all hope of solving the problem of cellular action,
because it is necessary to understand, not only the physical and
_chemical phenomena involved, but also their different forms in
the various parts of the cell. It is readily admitted that these
are not the same in the nucleus and in the cytosome, but some
hesitate to recognize differences between parts of the nucleus,
and more are disinclined to grant specific activities to the
chromosomes. . '

Since it is not possible to observe directly the action of the
chromosome we are obliged to make use of indirect evidence,

578 CLARENCE E. McCLUNG

seeking parallels between elements of structure and action in the
chromosomes, and the mass effect of cellular action as exhibted
in the so-called body characters. Such a method is justified by
all our other experience in tracing relations between structure
and function in organisms, and while it apparently resolves the
individual into parts of greater or less independence, has given
us our best conceptions of it as a whole. Homologies have been
much more significant of relationship than analogies when con-
cerned with organic parts, and I do not doubt that conclusions
drawn from structural relations will greatly exceed in value the
remote and equivocal analogies between nuclear structure and
colloidal phenomena. On the basis of our experience we antici-
pate a commensurate relation between structure and function,
but this does not mean a fixed and exclusive correspondence—
it does not signify that a function necessarily entirely lapses in
the absence of a certain structure. All our observations indi-
cate that the relatively few functions of the living substance—
irritability, contractility, metabolism and reproduction—are
shared by all its parts in varying degrees, and when we speak of
the function of any somatic organ or cell part we mean its
outstanding and preponderant activity.

With this understanding of the relation between morphology
and physiology, we speak of the chromosomes as having to do
with the process of reproduction, and conceive of them as
non-homogeneous within themselves and individually unlike.
_ In this sense they bear factors, or have parts, which are most
concerned with certain peculiarities which, through cumulative
action in cell reproduction, come to fullest expression in regions
of the complete soma. Through what manner a factor operates
to produce a cell structure which, in a given cell aggregate,
summates in the form a somatic character, we do not know,
and that is not the question immediately at issue in the indi-
viduality hypothesis. What is postulated there is that the
chromosomes are self perpetuating entities with individual pecu-
liarities of form and function to identify them. Characteristics
of form and behavior we see; certain very definite parallels be-
tween these and the manifestations of somatic characters exist

MULTIPLE CHROMOSOMES 579

beyond question; provision for the perpetuation of the organic
unity of the individual chromosomes is found in the process of
mitosis; the actual direct result of its operation appears in the
uniform conditions of the complex in the individual animal; the
extension of this beyond the organism to the group and the
means for it in the phenomena of maturation and fertilization
are easily established by observation; the age old existence of all
these circumstances is revealed by the near approach to uni-
formity in the chromosome complex of the multitude of species
of unnumbered individuals constituting afamily. And yet, in the
face of this overwhelming mass of evidence indicative of order,
system and specific chromosome organization, some conceive only
the action of ordinary chemical forces, or the chance associa-
tion of indifferent substances, while others, over impressed with
the thought of a general coordinating force in the organism,
deny significance to the orderly play of its cellular parts.

While opponents of the individuality hypothesis differ thus
widely in what they would substitute for it, they almost invari-
ably seize upon one supposed condition of the chromosome as
a basis for discounting the remaining positive evidence which is
presented for the hypothesis. Even some well informed cytolo-
gists who accept the implications of the facts, regard this cir-
cumstance as a severe weakness in the chain of evidence. That
the chromosomes do not maintain a compact and easily recog-
nizable form in the interval between mitoses is accepted by
many such biologists as proof that they no longer exist as en-
_ tities. All the other manifold indications of character and con-
tinuity do not weigh against this apparent loss of identity.
Doubtless it would be more satisfying if we could at all times
- perceive the chromosomes in unchanging form in all stages of
cellular activity, but why we should demand this condition as a
test for individuality in the chromosomes when we unhesitat-
_ ingly admit the unity of an organism in all the varied changes of
its development from a single cell, through such complexities of
change and metamorphosis as to give rise to doubts of even the
phyletic position of some stages, it is difficult to see. Being
organic, the chromosomes must change their form, they must

580 CLARENCE E. McCLUNG

suffer division of their substance and they are obliged to re-
store this loss through metabolic changes. Since these changes
of substance take place at surface contacts there is an obvious
advantage in increased superficies and, in common with other,
larger structural elements, the chromosomes become extended
and their substances are diffused. In this state their bound-
aries may not be well defined and this circumstance has been
seized upon as a disproof of their continuity.

For myself, even were the visible limits of the chromosome
completely lost, this would not appear as a convincing disproof
of persistent individuality in the face of the large number of
facts pointing in the opposite direction. Of such facts those
relating to the history of the multiple chromosomes, outlined in
this paper, are of great importance. Their bearing upon the
various aspects of numbers, sizes, forms and behavior, has been
mentioned under these different headings. At this point how-
ever I wish to summarize this evidence upon the general topic of
individuality. But before doing so I should like to repeat state-
ments previously made that the accessory chromosome in the
germ cells of the male presents us with the history of a particu-
lar chromosome, at all times distinct and well delimited, whose
physical identity suffers no eclipse during the various metabolic
changes of growth and division. It is readily distinguished
where it occurs, not alone in a given cell, but in all the germ
cells of the species, genus, family and order. The same element,
always recognizable by reason of its structural character, is
identified in different phyla and is shown to have a definite rela-
tion to the development of sex characters. It would seem im-
possible to conceive any more definite marks of individuality
than is possessed by this chromosome, in whose history there is
no confusion of character or break of continuity, and yet it
does not receive even mention in some attacks upon the theory of
individuality.

Again, its position may be granted, but with the reservation
that it is unique and no criterion for other chromosomes.
Upon this point it is now merely necessary to say that the
accessory chromosome differs only in degree from the euchro-

MULTIPLE CHROMOSOMES 581

mosomes, and general conclusions regarding the nature of
chromosome organization may properly be drawn from its his-
tory. That its condition is indeed not unique is shown by vari-
ous approaches to it on the part of certain chromosomes in
Phrynotettix, as demonstrated by Wenrich (16). The great
similarity to the euchromosomes is also indicated by the union
with the accessory chromosome in multiples, and by its entirely
typical nature in the female when paired.

The mere academic question of individuality is not here im-
portant, the practical matter before us is to decide whether the
metaphase chromosomes of two cells are individually identical
organic members of a series because they were produced by the
observed reproduction of a similar series of the parent cell, or
whether the resemblance is independent of this genetic relation
and due to chance association of indifferent materials, or to a
reconstituting action of the cell as a whole. It is my belief that
the observed act of reproduction, by which the organization of
the chromosomes is materially transmitted in each mitosis,
together with all facts indicating extensive distribution of given
conditions, definiteness of organization, uniformity of behavior
and consistency of deviation from the normal, are so many
clear indications of the individual character of the chromo-
somes. ‘Transmutation of form, even to an extreme degree, can
not be held as a valid argument against a persistent individu-
ality. A consideration of the criteria applied to larger organic
aggregates well supports this view. Such objects are said to
possess individuality when they exhibit a more or less definite
unity which is persistent and characterized by peculiarities of
form and function. Most clearly defined is this individuality
_when it may be perpetuated through some form of reproduction
to find expression in new units of similar character. The term
does not connote unchangeability, and there may be fusions with
more or less loss of physical delimitations, followed by separation,
even after exchange of substances. The test of individuality is
material continuity, but it does not necessarily involve com-
plete or entirely persistent contiguity. An organism may bud
off new individuals similar to itself, the substance of its body

582 CLARENCE E. McCLUNG

differs from time to time, movements of parts take place, frag-
mentation occurs, extreme attenuation or extension of substance
is found, even separation and recombination of parts may
happen and yet the individual maintains itself. What it may
have been in the past, what its possibilities of future develop-
ment are, what potentialities of multiplied individuality it
suppresses do not affect the reality of its individuality. It is, —
as Huxley says, ‘‘a single thing of a given kind.” If one such
thing divides into two, there are two individuals; if two unite
into one indistinguishably there is a single individual; if a
fusion of two things occurs in part, without loss of physical
configuration, there are still two individuals in existence. Only
when the substance of one thing disappears or becomes incor-
porated integrally into the organization of another does its
individuality depart.

If all these variations of physical state may occur in the his-
tory of an organism without sacrifice of individuality, there can
be no reason for urging them against a conception of the indi-
viduality of the self perpetuating chromosomes. Especially is -
this true in face of the facts recorded here and in other papers
showing the high degree of chromosome constancy, for any given
period, in all the attributes by which we usually judge indi-
viduality. The conditions in Hesperotetix and Mermiria at
first seem to be a contradiction to this generalization, but, when
examined with care, show, not an instance of fundamental
change, but merely of modified detail. From these results it is
very clear that a chromosome number less than normal for the
group is not a necessary evidence of lost elements. In a similar |
manner the studies of Miss Holt on the intestinal cells of Culex
indicate definitely that numbers in excess of the normal do not
signify the addition of anything not previously represented.
Loss or gain in chromosome numbers is a condition to be inves-
tigated, not implicit evidence of an altered organization with
loss of organic individualities. That the chromosomes are not
the ultimate structural units is, however, indicated in many
ways, but it remained for Wenrich to show the nature of this
more minute portion of the chromosome architecture. From

MULTIPLE CHROMOSOMES 583

his results it would appear that all chromosomes are, in a sense,
multiples, and it is conceivable that these parts might be vari-
ously associated, producing even extensive numerical variation,
still without loss or gain of essential structural elements.

The peculiar case of Ascaris megalocephala, where evident
multiple chromosomes are retained intact in the germ cells while
they suffer fragmentation in the somatic cells, is an extreme in-
stance of numerical variation which occurs in one individual.
How common such relations may be we do not know, since so
little has been done in the study of the complete history of a
single organism; but it is obvious that the Orthoptera stand at
the opposite extreme from Ascaris in the persistence of chromo-
some organization, for here all the cells of an individual seem
to be invariably the same, and the individual is representative
of the group. But even in this stable assemblage we encounter
the conditions which I have described for H. viridis. This
case, with its diminution in number, and that of Culex, with its
great increase, are alike in the fact that the measures of differ-
ence are entire chromosomes and not parts of such, as seems to
be the case in Ascaris, unless indeed these. chromosomes be
multiples of a high order of complexity.

If it were possible for chromosomes to reproduce themselves
and still preserve their physical configuration unchanged, there
. would probably be little question of their continuity and indi-
viduality—the demonstration would be self evident. But it
happens that the necessities of the case require that each newly
produced chromosome should take part in the formation of a
new nucleus, through whose activities the cell as a whole and
each chromosome, individually, is enabled to restore the volume
- diminished by the act of division. During this process the out-
lines of the chromosomes become materially changed and in
their extreme diffusion can no longer be traced in many cases.
Because of our limitations in observational power they appear
to be lost as separate individuals and we are thus deprived of
the simple test of observed continuity. Later, in the same cell,
there reappears a series of chromosomes severally like those which
seemed to disappear during the period of metabolic activity.

584 CLARENCE E. McCLUNG

We confront two alternative explanations for this re-integration
of the chromosomes; either they actually persist as discrete
units of extremely variable form, or they are entirely lost as
individual entities and are reconstituted by some extrinsic
agency. ‘There is no other possible explanation and we must
weigh the evidence for one or the other of the alternatives.

All facts which indicate order and system in chromosome
features speak for the former, those which demonstrate varia-
bility and indefiniteness, for the latter. The case for discontin-
uity is strongest in the absence of any chromosome order, and
becomes progressively weaker with the establishment of definite-
ness and precision in form and behavior. Evidence has already
been given in other papers on the Orthoptera to show the exact-
ness in organization of chromosomes, their persistent continuity
between mitoses in certain cases, the uniformity in number and
behavior through large groups, and the parallel behavior of
chromosomes on one hand, and of somatic characters on the
other. In this paper are discussed what appear to be the
widest departures from normal conditions so far found in the
group. Accepting as most important, next to actual observed
continuity, the evidence afforded by constancy in number, size,
form and behavior of the chromosome, I have been able to show
that these criteria are here applicable and that variation is only
apparent and not real. It seems to me that the facts disclosed |
in Hesperotettix and Mermiria not only fail to weaken the case
against individuality, as tested by constancy in number, size,
ete., of the chromosomes, but, on the contrary, greatly strengthen
it, for the reason that all of the distinguishing features of the
individual chromosomes are maintained, even in the presence of |
unions into multiples of higher order. The fact that, although
the number of independent units is reduced, nothing is lost from
the complex, is most important and significant.

Finally, the main feature of chromosome individuality must
not be lost in a discussion of whether it is the chromatin or the
linin that persists with less change. However great in impor-
tance this distinction may be, it does not alter the aspect of the
problem of individuality in its present phase. One or both of

MULTIPLE CHROMOSOMES 585

these substances may be responsible for the integration of the
chromosomes, but it is the fact that there is a definite structure
to be identified which concerns us most. The substances of the
chromosome divide into new units of similar relative sizes, and
these structures, now of half the original content, take up unlike
materials and replace the missing portions. The complexes of
the daughter cells are now equivalent to that of the mother
unit. It is obvious that, since the chromosomes, as such, divide,
all of their substances must be involved. There may be some
question whether one may be lost as a morphological entity
while another persists—although this is much open to question
—but something maintains the organization which we recognize
in the chromosome and it is this organization which we study.
In view of the fact that our microchemical tests are so far from
- specific in their action, it is not the part of wisdom to build very
extensive theories upon their evidence. It is quite possible that
one substance, in different phases of its activity, may present
alternately the aspects of chromatin and achromatin, and some |
conditions of the staining reaction suggest this, so that it would
be unwise to involve the whole question of chromosome organi-
zation in a dispute regarding the nature of their substance,
based merely upon uncertain staining reactions.

8. Chromosome specificity

That chromosomes might be genetically continuous and still
be of the same nature, without differential character, is, of course,
conceivable. In fact it is more than probable that, in a sense,
they are all alike, for they probably share the general properties
_ or functions of protoplasm. But that they carry out these activi-
ties in the same manner is a conclusion quite foreign to the evi-
dence. Just what the nature of this differential action may be
has not yet been discovered, but the action of the sex determin-
ing chromosome and the groupings of characters in Drosophila
are suggestive. Male and female possess the same series of
parts, and the difference between them is one of relative develop-
ment. Nothing unique for either sex exists and such a thing

586 CLARENCE E. McCLUNG

as an ‘exclusively male’ or exclusively female character is not
to be found. The evidence here would indicate that the ‘fac-
tors’ for maleness, are such controls of the developmental proc-
esses as will eventuate in a certain degree of differentiation of
each cell of the body. The sum of all these, in any somatic
region, produces a condition which we call a male character,
and the total complex of these constitutes an individual which is
a male. In another individual the same series of elements ob-
tains, but each cell and each part is slightly different and the.
sum total of the characters produces an assemblage which we
recognize as a female. Should the conditions be varied, even by
the internal secretion of the gonad, in some eases, these may be
altered to resemblance of the opposite sex.

However much the entire complex is involved in the produc-
tion of characters which are called sexual, it is apparent from
the history of the accessory chromosome in the Orthoptera that
it is a differential agent. All other things apparently being
equal, the presence of one accessory chromosome so shapes the
‘developmental processes that a male results, while if two are
involved a female is produced. In some way, not now apparent,
the action of this particular one of the chromosomes differs
from all the others in producing an effect of which they are not
capable—that is, it has a specific action. Apparently it is un-
like them in being concerned with the entire body, including
the germ cells, which are differentiated into eggs or spermatozoa.
A further indication ‘of the specific nature of this particular
chromosome is afforded by sex-linked characters whose develop-
ment is conditioned by exactly the same circumstances of dis-
tribution as those which mark the alternatives of maleness or
femaleness. ‘The facts relating to the accessory chromosome are
the strongest evidence we have in support of chromosome
specificity, because the history of this element is. so clear, its
continuity so unbroken and its relations to certain characters so
definite. But any evidence for specificity of one chromosome is,
at the same time, support for the general conception of the dif-
ferential nature of chromosomes, and for this reason the facts
concerning the accessory chromosome have additional value.

MULTIPLE CHROMOSOMES 587

The only direct evidence for any such a differential nature of
the other chromosomes is afforded by the work on Drosophila.
In this case a whole group of characters follows the rule of distri-
bution governing sex. This is the only element that can cer-
tainly be identified, but the groups of observed characters, not
sex linked, correspond to the three remaining pairs of chromo-
somes, and the numbers of characters in each group are in pro-
portion to the size of the chromosomes. Of these one pair is
very small and there is a corresponding small group of charac-
ters. As is well known, the analysis of the conditions in Dro-
sophila has gone so far that the relative loci for the different
factors have been calculated. It would seem from these results
that there is every reason to regard the chromosomes of this fly
as qualitatively different. While there is no correlation of this
sort known for the Orthoptera, the actual history of the chromo-
somes which their germ cells exhibit affords a mechanism ade-
quate for the facts of alternative inheritance and for the segre-
gation and chance recombinations of characters. While the
multiple chromosomes do not afford any direct evidence for
‘specificity of function, it would seem, because of all the facts,
that the purpose for which these studies on the Orthoptera were
begun—a correlation between germ cell structure and somatic
characters—is much more feasible of accomplishment than
appeared at the beginning.

V. SUMMARY OF RESULTS

1. Chromosomes are definitely organized chromatic bodies
acting as units in mitosis.

2. These units are of unlike morphological value in the dif-
ferent generations of germ cells.

3. While any one cell generation is marked by one general
type of chromosome organization, individual chromosomes may
differ from the type in higher or lower degree, by definite steps
or intervals.

4. In a given species the integration of the chromosome com-
plex may vary from individual to individual.

5. For any one individual this integration is fixed.

588 CLARENCE E. McCLUNG

6. Despite this individual variation in the composition of the
mitotic units, there is no loss in the total morphological elements
of the specific complex, or departure from the usual habits of
synapsis and segregation of homologous elements.

7. The maintenance of the original complex in the presence of a
variable number of mitotic units results from associations of
these to produce others of higher valence.

8. Where variation between individuals exists for any one cell
generation, it is the result of differences in association between
certain definite mitotic units.

9. Such variations are not indefinite, but occur in a fixed order
between certain units. |

10. The occurrence of associations between units of lower order
into those of a higher results from the operation of a common
integration principle. .

11. The union of homologous chromosomes to produce te-
trads is temporary and is terminated in one of the following
maturation divisions; multiples of non-homologous chromosomes
are permanent for the individual and the union does not end in
either maturation mitosis.

12. Associations in the first spermatocyte of a higher order
than tetrads are the result of lower associations which are per-
sistent throughout all cells of the individual.

13. Associations into tetrads in the first spermatocyte occur
between. homologous chromosomes.

14. Higher associations than tetrads in the first spermatocyte
are necessarily non-homologous.

15. Associations may be complete and persistent, or only
approximations.

16. Associations may be complete in parts of chromosomes and
incomplete in other regions.

17. The point of union between associated units in metaphase
is at the ends of the chromosomes.

18. In telomitic chromosomes this is at the point of fiber
attachment.

19. Atelomitic chromosomes of unit value have not yet been
observed in multiples, except in that part of the tetrad of Mer-
miria not joined to the accessory chromosomes.

MULTIPLE CHROMOSOMES 589

20. Multiple chromosomes are of two types (a) those between
euchromosomes and heterochromosomes and (b) those between
euchromosomes alone.

VI. BIBLIOGRAPHY
A. Additions to my former list (’14) of papers on Orthopteran spermatogenesis

CaroTuEers, EH. Exeanor 1917 The segregation and recombination of homol-
ogous chromosomes as found in two genera of Acrididae (Orthoptera).
Jour. Morph., vol. 28.

Harman, Mary T. 1915 Spermatogenesis in Paratettix. Biol. Bull., vol. 29.

McCune, C. E. 1914 A comparative study of the chromosomes in Orthop-
teran spermatogenesis. Jour. Morph., vol. 25.

Monr, Orro L. 1915 Sind die Heterochromosomen wahre Chromosomen?
Archiv f. Zellforsch., Bd. 14. 4

PayNE, FERNANDUS 1914 Chromosomal variations and the formation of the
first spermatocyte chromosomes in the European earwig, Forficula sp.
Jour. Morph., vol. 25.
1916 A study of the germ cells of Gryllotalpa borealis and Gryllotalpa
vulgaris. Jour. Morph., vol. 28.

Ropertson, W. R. B. 1915 Chromosome studies III. Inequalities and de-
ficiencies in homologous chromosomes: their bearing upon synapsis
and the loss of unit characters. Jour. Morph., vol. 26.
1916 Chromosome studies I. Taxonomic relationships shown in
chromosomes of Tettigidae and other subfamilies of the Acrididae: —
V-shaped chromosomes and their significance in Acrididae, Locustidae
and Gryllidae: chromosomes and variations. Jour. Morph., vol. 27.

Senna, ANGELO 1911 La spermatogenesi di Gryllotalpa vulgaris Latr. Moni-
tore Zoologico Italiano, Anno 22.

Vortnov, D. 1914 Recherches sur la spermatogenese du Gryllotalpa vulgaris
Latr. Archives. de Zool. Exp., T. 54.

Wenrico, D. H. 1916 The spermatogenesis of Phrynotettix magnus with
special reference to synapsis and the individuality of the chromo-
somes. Bull. Mus. Comp. Zool. Harvard, vol. 40.
1917 Synapsis and chromosome organization in Chorthippus (Steno-
bothrus) curtipennis and Trimerotropis suffusa. Jour. Morph., vol.
29.

Wootsey, CarRigE E. 1915 Linkage of chromosomes correlated with reduction
in numbers among the species of a genus, also within a species of the
Locustidae. Biol. Bull., vol. 28.

B. Articles cited on other than Orthopteran material

Detta Vatie. Paoto 1909 L’orgamizzazione della chromatina studiata
mediante il numero dei Chromosomi—Archivio Zoologico, vol. 4.
1911 La continuita della forme di divisione nucleare ed il valore
morphologico dei chromosomi. Archivio Zoologico, vol. 5.

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

590 CLARENCE E. McCLUNG

Dewtua VaLtteE. Paoxra 1912 La morphologia della chromatina dal punto di
vista fisico. Archivio Zoologico Italiano, vol. 6.
1913 Die Morphologie des Zellkerns und die Physik der Kolloide.
Zeitschrift fiir Chemie und Industrie des Kolloide, Bd. 12.

Hance, R. T. 1917 The somatic mitoses in the mosquito, Culex pipiens. Jour.
Morph., vol. 29. —

Hout, Carotine 1917 Multiple complexes in the alimentary tract of the
mosquito. Jour. Morph., vol. 29.

Wuitine, P. W. 1917 The chromosomes of the common house mosquito, Culex
pipiens, Linn. Jour. Morph., vol. 28.

DESCRIPTION OF PLATES

All figures are drawn at an initial magnification of 2860 diameters under the
camera lucida, and appear in the reproduction at a magnification of 1800. The
photomicrographs were obtained with a Zeiss 2 mm. objective of 1.40 N. A.,
projection ocular 4 and a Watson ‘Holoscopic’ oil immersion condenser. The
original magnification of 1000 diameters is here reduced to 666, except fig. IX.

PLATE 1
EXPLANATION OF FIGURES

Horizontal rows represent complete first spermatocyte complexes, usually in
lateral view, numbered 1 to 6. These are arranged so that chromosomes _ of
homologous size are brought into vertical rows, numbered from 1 to 12. Blank
spaces in vertical rows represent the normal position of the accessory chromosome
which is joined to a tetrad.

1 A complex of Hesperotettix brevipennis. All twelve chromosomes are
free.

Hesperotettix festivus, polar view.

Hesperotettix viridis, class 1—twelve chromosomes plus a supernumerary.
H. viridis, class 2.
Hesperotettix pratensis.

Hesperotettix speciosus.

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PLATE 2
EXPLANATION OF FIGURES

Complexes, arranged as in plate 1, of representatives of the various classes of
first spermatocytes in Hesperotettix viridis. The classes are indicated by the
figures at the left, 1 to 6. Euchromosome multiples are arranged between the
rows to which their tetrads belong. Not all conditions are represented here
but may be found in other figures. Thus the smaller octad of class 4 may also
be a ring in some individuals; the smaller ring of class 5 may be a V; and the
ring octad in one individual of class 6 is a V.

592

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593

PLATE 3
EXPLANATION OF FIGURES

1 to 5,7 to 9 Polar views of spermatogonial metaphase complexes. 1 to 7
are of Hesperotettix viridis, 8 of H. brevipennis and 9 of H. speciosus.

1, is of class 2, showing twenty-two chromosomes, of which one is a multiple.
The accessory chromosome portion of this is marked ‘X.’

2 An example of class 3. The members of the large first spermatocyte
euchromosome multiple ring are the larger V-shaped elements, while the smaller
V includes the accessory portion of the hexad. Twenty separate chromosomes.

3 A complex of class 4, in which the largest two V’s are parts of the first
spermatocyte ring, the next largest one of the octad V, and the smallest of the
hexad. Nineteen separate chromosomes.

4 In this group, representing class 5, there are three V’s belonging to two
octads of the first spermatocyte, the smaller of which is a V. The accessory
chromosome is free. Twenty separate chromosomes.

5 From an individual of class 6 with a free accessory chromosome and one
octad ring in the first spermatocyte. Twenty-one chromosomes.

6 An anaphase group of class 4 showing the 4 V’s (fig. 3 above).

7 A complex of class 6 in which the octad of the first spermatocyte is a V
instead of a ring. The one V in this spermatogonial group is involved in the
formation of this multiple. Twenty-two free chromosomes.

8 From H. brevipennis in which all specimens studied showed twenty-three
rod shaped chromosomes.

9 The one V in this complex of twenty-two chromosomes will constitute a
part of the hexad in the first spermatocyte. The accessory chromosome forms
one limb.

10 An octad ring of H. viridis in the late prophase. It will commence to
separate at the apex.

11 Late prophase condition of such a chromosome as shown in figure 10.

12 Shows metaphase condition of such octad rings. These are from dif-
ferent cells.

13. Two metaphase octad rings of H. viridis from the same cell. Class 5.

14 Similar elements from another cell of the same individual as shown in
figure 13. The large octad b has one tetrad forming a ring lying in the equatorial
plate at right angles to the other member. The small octad a shown edgewise.

15 Five examples of the V-shaped octad of class 4. The inequality of the
constituent tetrads shows clearly.

16 Multiples of class 4; a the large octad and the hexad; c the two octads, the
larger like figure 14 b.

594

CLARENCE E. \.CCLUNG

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PLATE 4
EXPLANATION OF FIGURES

17 Examples of octad rings in late prophase showing various aspects during
the process of opening out. These are arranged somewhat in the order of
progress from a to k.

18 Lateral view of first spermatocyte metaphase, class 6. One octad ring,
and accessory chromosome at one pole.

19 Three examples of extended V’s, such as shown in Photo Y.

20 Lateral view of first spermatocyte metaphase of class 5 with the V por-
tion of the smaller octad going to same pole as the accessory chromosome. Ten
free chromosomes.

21 A complex of a first spermatocyte of class 6 in which the one octad is a V.

22 Two first spermatocyte octads from one cell.

23 A complex of H. pratensis in which the hexad is similar in shape to that
of Anabrus.

24 <A complete complex of Hesperotettix viridis, class 3, in which the octad
has opened at one side, simulating the appearance of the hexad in Mermiria.

25 The three multiples from a complex of class 4.

26 An entire complex of class 3, from the same animal as in figure 24.

27 A representative complex of class 5 with one V.

596

MULTIPLE CHROMOSOMES PLATE 4
CLARENCE E. MCCLUNG

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PLATE 5

EXPLANATION OF FIGURES

28 First spermatocyte anaphase, class 4 with one V, showing the distribu-
tion of the rod and V parts, in black. The entire complex, including the other
multiples is shown.

29 to 42 Various second spermatocyte metaphase complexes (except fig. 33)
in polar view, of H. viridis.

29 Class 1 with accessory chromosome.

30 Class 2 without accessory chromosome.

31 Class 2 with accessory chromosome in multiple.

32 Class 4, (one ring, one V and hexad in first spermatocyte) no accessory
chromosome, two rods of V, and half of ring.

33 First spermatocyte anaphase of class 4, no accessory chromosome.

34 Class 6 (in first spermatocyte one ring, free accessory chromosome) no
accessory chromosome.

35 Class 6 with accessory chromosome.

36 Same condition as figure 35, same animal.

37 Same condition as figure 35, another animal.

38 to 42. From one animal of class 6 with the octad in the form of a V, acces-
sory chromosome free.

38 With V and no accessory chromosome—ten chromosomes.

39 With V and with accessory chromosome—eleven chromosomes.

40 No V and no accessory chromosome—eleven chromosomes.

41 As in figure 40.

42 No V, but with accessory chromoseme—twelve chromosomes.

598

PLATE 6
EXPLANATION OF FIGURES

43 to 54 From Mermiria bivittata.

43 Somatic complex of the female with twenty-two free chromosomes and
two similar multiples, each containing an accessory chromosome. The euchro-
mosomes are all telomitic.

44 <A spermatogonial complex of twenty-two free chromosomes with two
unlike V’s, in one of which the accessory chromosome betrays its presence by its
characteristic granular condition. The other V is smaller and is confined to the
male line by always going into the opposite cell from the accessory chromosome
in its segregation division.

45 Another female somatic complex.

46 Spermatogonial complex.

47 Pairs of spermatogonial V’s in different stages showing disproportion in
size.

48 A female somatic complex—one V foreshortened.

49 Spermatogonium, V-chromosomes. a and c associated pairs.

50 a The multiple in first spermatocyte anaphase, lateral view; b, en face;
c, as these elements would appear in second spermatocyte metaphase.

51 Multiples in late first spermatocyte prophase showing the marked dif-
ference in appearance between the smooth, homogeneous, condensed accessory
chromosome and the yet granular tetrad to which it is joined.

52 First spermatocyte multiples, 6 almost fully condensed and showing
non-chromatic clefts. These are about in the relative positions of the fiber
attachments and the plane of division.

53 As in figure 51.

54 Like 52 b.

600

PLATE 7
EXPLANATION OF FIGURES

55 to 65 From Mermiria bivittata.

55 First spermatocyte metaphase showing the multiple and the five smaller
chromosomes divided.

56 Three multiples of first spermatocyte metaphase.

57 Like figure 56.

58 Three multiples of the ‘green’ variety of M. bivittata in which fiber
attachment is almost at the end of the bent portion. At a complete separation,
in 6 and c beginning stages.

59 Similar to figure 58. Note the various constrictions, simulating a decad
constitution, emphasized at a by separation at two levels.

60 Complete separation of bent rod opposite accessory chromosome.

61 Polar view of second spermatocyte metaphase.

62 Lateral view of same stage.

63 to 65 Polar view of second spermatocyte metaphase. All have eleven
chromosomes, one of which is a V, but in one case, figure 63, this is a simple
chromosome and in the other, figure 64, it is a multiple involving the accessory
chromosome.

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PLATE 8
EXPLANATION OF FIGURES

A to Z and II to III are photo micrographs of Hesperotettix viridis cells and
IV to IX of Mermiria bivittata. A to D and IV to VI smears, the remainder
sections.

A, B, C show the appearance of multiple rings with the longitudinal split
and numerous clefts, D is a lateral view of a first spermatocyte metaphase show-
ing the multiple ring in profile and the accessory chromosome at one pole.

E Polar views of spermatogonial metaphase with telomitic and atelomitic
chromosomes.

F, G, H_ Profile views of hexad multiple.

Ito N Lateral views of V-shaped multiples showing characteristics of form
and movement.

O Ring and V. multiples.

P, A V-multiple with one limb out of position.

@ to T Ring multiples in which one tetrad has the plane of its ring perpen-
dicular to the other.

U, V_ Late stages in the movement of such rings as appear in Q to T.

W, X Late metaphase stage of ring multiples.

Y An extended V similar to that of P.

Z A ring multiple about to divide.

II Anaphase condition of a V-multiple (ef. fig. 28).

III Late anaphase condition of a divided ring. The resulting V’s are double.

IV Prophase condition of a hexad showing the accessory chromosome con-
densed and the tetrad thin and granular.

V, VI Metaphase hexads showing constrictions.

VII, VIII Profile views of hexads.

IX Lateral views of mitoses X 400.

604

PLATE 8

MULTIPLE CHROMOSOMES

CLARENCE E. MCCLUNG

605

AUTHOR’S ABSTRACT OF THIS PAPER ISSUED
BY THE BIBLIOGRAPHIC SERVICE, SEPTEMBER.

MULTIPLE COMPLEXES IN THE ALIMENTARY
TRACT OF CULEX PIPIENS

CAROLINE M. HOLT

Simmons College, Boston, Massachusetts

THIRTY-THREE FIGURES (FOUR PLATES)

CONTENTS
TO CUG WON emer mcs re tere terete ks oon sg eee eeeeterter cae Mite er Nem aeons ee ee 608
ZOLDER Rees eb eek 0 Pees Cd ae ie on 8 ee 608
Previous observations on the Jireera tract otiCules 2.525. ide So Aust «- 609
Behavior of the gut cells during metamorphosis...................02000000- 609
Mitosisemprmultiple-complexicells....... 2... g0eeamae ceess onetime scien «certs « 611
iiearerrarton or tae celles... 2. . Qu. he Uelee. FAR eRe ae. Fah. 615
UN ae SE LIST PARA 3 05 OMNES 61 a) oc 2 eR ew SRE el ee Rap cme Sameer nS eee 615
RUA AGC GNC MRIs te cook x «, «/<in neared ater «ok cat aak me wales es 617
BIDNOGTADITY. ....<< cease ees os a8. 68:5 (ha So RPE Neate Clare ORE Pa ner es 618
INTRODUCTION

The phenomena discussed in this paper first came to our
attention in the course of a systematic study of the chromosomes
of Culex pipiens under ‘the direction of Dr. McClung in the
Zoological Laboratory of the University of Pennsylvania.
The work was undertaken by a group of graduate students for
the purpose of verifying certain accounts of this species already
published. But in the course of the investigation so many
interesting questions arose that it was decided to make a more
thorough study of the cells of Culex than had originally been
planned. Accordingly, after a general investigation of all the
tissues, each student directed his attention to some particular
phase of the work. At the same time, each contributed what-
ever came under his observation which would be of use to the
others. 7

I wish here to acknowledge my indebtedness, first of all, to
Dr. McClung for the encouragement, the invaluable counsel

607

608 CAROLINE M. HOLT

and the thoughtful criticism which he has given so generously
throughout the progress of the investigation; to Miss Eleanor
Carothers to whom I am indebted for a part of the slides; and
to my co-laborers, Dr. Phineas Whiting, and Mr. Robert
Hance, whose reports on other phases of the study have ap-
peared separately.

TECHNIQUE

Larvae and pupae of Culex pipiens were taken during the fall
and winter from tubs of water in the University greenhouses
and from the alligator-tank in the vivarium. These were kept
in jars in the laboratory and a certain number of adults allowed
to emerge, to be identified as a check in the identification of the
pupae and larvae. Nothing but Culex pipiens was ever found in
this material.

The observations for this portion of the work were all made
upon sections of pupae. The abdomens were cut off just pos-
terior to the thorax and immediately placed in fixing fluid.
Some twenty methods of preparation were tried out, including
fixation in six different modifications of Bouin and Flemming;
with heat, cold, and room temperature; and for varying lengths
of time. The method which gave the best results and which was
finally adopted was as follows:

Fixation. One to six days at about 100° F. in “P. F. A. 3.”
Picrie acid 75 parts
Formalin 15 parts
Acetic acid 10 parts
Length of fixation after the first twenty-four hours seemed to make little
difference in the results.
Dehydration. Very gradual, by drop method.
Clearing in xylol.
Embedding in paraffin.
Staining. Iron haematoxylin, twelve to twenty-four hours. Cleared in
xylol and mounted in balsam.

All of the slides upon which this study is based are in the col-
lection of the Zoology Laboratory of the University of Pennsyl-
vania, except one prepared by Dr. Stevens and now in the Bryn

ALIMENTARY TRACT OF CULEX PIPIENS 609

Mawr Laboratory. This material has proved favorable for
the study of all somatic tissues as well as of the germ cells. It
includes sections of a large number of individuals in which vari-
ous parts of the alimentary tract are undergoing metamorphosis.

PREVIOUS OBSERVATIONS ON THE ALIMENTARY TRACT OF CULEX

M. T. Thompson has described in detail the changes which
take place during the metamorphosis of the digestive tract of
the mosquito. But while he notes the fact that mitotic iizgures
are very numerous toward the end of these changes, he does
not discuss the complexes.

Miss Monica Taylor, while seeing the great importance of
working out the somatic complexes thoroughly, seems to have
been handicapped by a difficulty in finding dividing somatic
cells. She makes no mention of any variation in the number
of chromosomes in the gut tract, and her figures show only
cells previous to the beginning of metamorphosis or after its
completion.

In fact, in all the work which has been done upon the chromo-
somes of Culex, observers have overlooked, or at least have
failed to mention, an interesting phenomenon which occurs in
connection with metamorphosis of the gut tract—the appearance
of multiple complexes in cells which are about to give place to
the new adult tissue.

BEHAVIOR OF THE GUT CELLS DURING METAMORPHOSIS

During the pupa stage, the entire gut, posterior to the oesoph-
agus, undergoes metamorphosis. The larval tract degenerates
_ and is absorbed, while the new tract is formed from cells, the
nuclei of which appear between the bases of the larval cells.
As the new epithelium forms, a marked activity develops in the
old cells. There is some cell division accompanied by rapid
multiplication in the number of chromosomes. While the
normal somatic number in material prepared by the ordinary
methods, is apparently three, as Miss Taylor (’14) states, the
constant occurrence of splits in these chromosomes gives weight

JOURNAL OF MORPHOLOGY, VOL. 29, No. 2

610 CAROLINE M. HOLT

to Dr. Stevens’ view that we have here three bivalent chromo-
somes—the same condition found by Metz (’14) in Drosophila,
where parasynaptic union of homologous chromosomes takes
place between mitoses. Hance (’17) has demonstrated that the
normal somatic number may, by improved technique, be clearly
shown to be six.

The four normal complexes shown in figure 21, a,b, c, and d,
may be interpreted in two ways. 21d seems to represent an
early metaphase before the final equatorial arrangement and
division of bivalent chromosomes, while a, b, and ec may be
groups in which homologous bivalent chromosomes are separat-
ing and are about to pass to the poles; in fact in a, they are
already moving away from the center. Under such an interpre-
tation, the six chromosomes in a, b, and ¢, are in each case,
bivalent, representing fused homologous elements. The enlarged
ends, which not infrequently are split, suggest such a condition.
The other interpretation of these four groups is that each of
the six chromosomes in a, b, and ¢ is a univalent chromosome,
lying in the equatorial plate, ready for division. The work of
other investigators indicates that the latter is the true interpre-
tation. As in normal somatic cells, homologous chromosomes
tend to fuse during the resting stage; so in the metamorphosing
gut cells, the same condition apparently obtains.

In Culex, the degenerating intestinal cells frequently show
thirty-six or forty-eight elements; and in one case, at least
sixty-eight chromosomes appear in a metaphase group. ‘This
particular cell probably contains seventy-two, although it is
not possible to determine the exact number (fig. 23, y and 2).
But whatever the number, approximately four divisions of half |
of each of the original chromosomes must here be represented,
and three of the other half.

It is possible that cytokinesis does not always follow karyo-
kinesis, though there may be an increase in the amount of cyto-
plasm, since some of the cells containing multiple complexes are
larger than the normal (fig. 8). But, if this be the case, we
might expect to find multinucleated cells, and there is no evi-
dence of such a condition, save in a few possible instances where

ALIMENTARY TRACT OF CULEX PIPIENS 611

cells are on the point of disintegration and cell boundaries can
not be definitely determined. On the other hand, a cell con-
taining a complex of three or four times the normal number of
chromosomes may be of about the same size as one with six
chromosomes (figs. 27 to 30). It would seem therefore, as if
the growth of chromatin might be greatly accelerated in the
‘resting stage,’ followed by rapid splitting in the prophases, so
that the chromosomes retain their normal size, while the cyto-
plasm grows, with or without division, at the normal rate.
However that may be, it is evident that there is a great increase
in the amount of chromatin in the old cells of the alimentary
tract, preparatory to their absorption by the new.

MITOSIS IN MULTIPLE-COMPLEX CELLS

In the late anaphase of cells in which the number of chromo-
somes is not large, the chromosomes appear to lie in groups of
three. Where the number is great, it is not possible to make
out the exact arrangement, but from conditions in the early
prophases, it is believed that the chromosomes pass into the
resting stage in three groups, each group made up of the indi-
viduals derived from one of the three pairs of chromosomes of
the original complex. Now and then a pair of chromosomes
lags behind on the equatorial plate. An interesting case of this
appears on Dr. Stevens’ slide, on which such a pair occurs in
several cells of the intestinal epithelium of the same individual
(figs. 5 and 31). In telophase, the nuclear wall can not be dis-
tinguished, but the region of the nucleus is suggested by a light
space about the telophase masses.

As the chromosomes pass into the ‘resting stage’ they grad-
ually lose their staining power and become indistinguishable
within an irregular mass taking a pale blue-gray stain with
haemotoxylin (figs. 3, 4, and 5). For a time, scattered bits of
chromatin remain visible within this mass, but these eventually
disappear, and only a pale nucleolus can be seen. The chro-
matin next makes its appearance in granules about the periph-
ery of the nucleus and in faintly staining threads centering

612 CAROLINE M. HOLT

in the nucleolus. At this period the nucleolus may take a pale
stain so that the chromatin can be clearly seen collected about
it (fig. 6) or, as the chromatin threads become more distinct, a
deeply staining mass may appear in the region of the nucleolus.

The chromatin threads are gathered into an irregular mass
which becomes three-lobed and finally resolves itself into three
vesicles in which the granular chromatin threads are fairly dis-
tinct (figs. 7, 8, and 9). The vesicular appearance is then lost,
but the chromosomes remain in three distinct groups of very
long, folded, and somewhat twisted threads (figs. 10, 11, 12).
These threads immediately begin to straighten and condense
(figs. 11 to 16). This process of condensation is very interest-
ing. Not enough cells at exactly the same stage of condensation
could be found to make it possible to decide definitely, but com-
parison of the longest pairs of chromosomes in figures 13, 15,
16 and figure 14, and of the medium chromosomes in figures 13,
15, and 16 and of the short chromosomes (especially c) in figure 13
with the short one in figure 15, certainly do suggest very strongly
that condensation takes place in a very definite and orderly
manner, and that in all nuclei at the same stage of condensation,
we should find the same number of granules in corresponding
chromosomes. Duting this period the chromatin threads split.
Whether, in the resting stage, the multiples of a given chromosome
really become fused into a single thread, it is not possible to
say. But the fact that in individuals which show complexes of
thirty-six or forty-eight chromosomes in metaphase, early pro-
phases in adjoining cells show but three or six splitting threads,
with far too much chromatin for a like number of chromosomes,
suggests that a parasynaptie. union of sister chromosomes takes
place in the telophase and also that the re-separation may come
at any time during prophase (figs. 10 to 16 and 19).

There is nowhere any evidence of anything but a longitudinal
splitting of the threads. Figures 10 and 11 appear to be cases
in which an early division has occurred, while figures 13 to 16
show division taking place in threads in which the chromatin
has become condensed to comparatively few granules. Since each
normal complex is made up of three pairs of chromosomes, and

ALIMENTARY TRACT OF CULEX PIPIENS 613

since the homologous members of each pair show a tendency to
fuse and form a single bivalent chromosome, we should expect
to find the chromosomes of the multiple complexes also con-
jugating, not in three pairs, but in three groups of homologous
individuals. It is believed that such is really the case.

We find the fully condensed chromosomes still arranged in
groups of three, the difference in size of the three kinds making
it easy to see that we have sister chromosomes in each group.
' Compare figures 21 A, B, C and D for relative size of the three
chromosomes in normal complexes. But the individuals of a
group do not always divide at the same time, which accounts
for the finding of nine, eighteen, and thirty-six chromosomes in
some cells, whereas, simultaneous divisions of all the members
of a complex would give twelve, twenty-four, ete. It is interesting
to note that when an early division takes place in one of the mem-
bers of a given group, the same thing occurs in the corresponding
member of each of the other two groups. A good many com-
plexes have been found in which this point is brought out very
clearly through inequality in thickness of the individual threads.
In figure 17, A and B are evidently sister chromosomes, possibly
derived from the mate of E; C and D show the same relation to
F. Figure 19 brings this out even better. A, B, and C evi-
dently represent one pair of which one member has divided
into two, A and B. Figure 20 illustrates the same point.

It is obvious, since every group counted belongs either to a
“six series’ or a ‘nine,’ 1.e., six, twelve, twenty-four, forty-eight,
or nine, eighteen, thirty-six, seventy-two, ete., that, when
irregularity in the time of division of members within a group does
occur, it must come with the first splitting of half of the threads,
and that otherwise all the derivatives of each of the daughter
threads of the first split must divide simultaneously. If this
were not the case, we should get multiples of numbers other
than six and nine. We might suppose an early division of either
the maternal or paternal element of each pair to have given us
the nine chromosomes which we find in some complexes. The
fact that in some individuals we find only the ‘nine series’—
nine, eighteen, thirty-six, could be explained by supposing the

614 CAROLINE M. HOLT

maternal or the paternal group to be more precocious, either
dividing earlier or, in the first division dividing twice.

The chromosomes grow so rapidly that in most cases the indi-
viduals of a multiple complex show the same sizes as those of
‘normal’ chromosomes found in the larva] gut or the newly
formed cells of the adult intestine (fig. 21 A). But even in meta-
phase we may find evidence of precocious splitting, giving ab-
normally slender chromosomes (fig. 23).

In the metaphase, we find the triplex arrangement still holds
though here it is much more difficult to make out (figs. 24, 26,
27). In figure 26, for example, the two groups of six chromo-
somes on the lower side of the figure suggest that they may have
been derived from the division of the small chromosomes of the
original group. The individual at the extreme right seems a
little larger and possibly belongs to the group above. The re-
maining twenty-four fall quite naturally into two groups. And
so, with careful study, it has been found possible, in nearly all
cases, to separate even the metaphase complexes into three
component groups.

As in ‘normal’ cells, the chromosomes of the multiple com-
plexes arrange themselves horizontally upon the spindle, where
they split lengthwise and pass to either pole as V’s (figs. 31 and
32. Compare with ‘normal’ somatic groups—fig. 21). Note
even in multiple complexes the tendency on the part of the.
chromosomes to arrange themselves in triangular groups in
metaphase.

DISINTEGRATION OF THE CELLS

After several multiplications of the chromosomes, the cells
begin to show signs of degeneration. Apparently this usually
comes after the third or fourth division. Vacuoles appear at
first as lighter spots in the stained cytoplasm (fig. 8). Later
these vacuoles have the appearance of empty spaces in the cell
body, which is rapidly losing its staining power. The chromatin,
meanwhile, becomes liquid and takes the form of black-stamimng
drops of varying sizes, which may finally run together into one
or two large masses. The nuclear wall breaks down (fig. 8)

ALIMENTARY TRACT OF CULEX PIPIENS 615

and the chromatin flows out. In the lumen of the newly formed
gut appear great numbers of vacuolated ‘ghost cells’ whose
outlines can barely be discerned. And in the midst of these,
streams of a gray-blue substance appear, filled with tiny black
granules. This is evidently the chromatin from the disintegrat-
ing cells. All this material is apparently digested, for it has
never been found in the very posterior part of the alimentary
tract.

Such then appears to be the history of the cells of the larval
gut tract while that tract undergoes metamorphosis. For a
time, metabolism is greatly increased; disintegration follows, with
final absorption by the newly-formed imaginal cells.

Discussion

These facts with regard to the intestinal cells of Culex may
possibly have some bearing upon two of the unsettled cytological
questions at present under discussion—the ‘Individuality Hy-
pothesis’ and the ‘Kern-plasma Relation.’ It might be urged
that this is degenerating tissue and that therefore abnormal
conditions prevail, but the uniformity and consistency in the
behavior of all these intestinal cells lead to the belief that these
conditions are normal, that they have a definite place in the life
cycle of each intestinal cell of the larva, and that, in question of
individuality of chromosomes or ‘Kern-plasma Relation,’ these
cells conform to the laws governing other cells of the body.

One of the arguments urged against the Individuality Hy-
pothesis has been variation in number. But certainly here,
variation in number instead of arguing against the theory, seems
to give added weight, as has been the case in many of the other
exceptions to the rule of constant number. To be sure, we
have here a wide variation in the chromosome number, ranging
from [six] to a possible seventy-two, but always multiples of
three—six, nine, twelve, eighteen, twenty-four, thirty-six, forty-
eight. With the exception of one cell, (fig. 27 and the possible
exception of fig. 23), no other number was ever found. In some
individuals, the ‘six series’ appears, and in others the ‘nine

616 CAROLINE M. HOLT

series’ is consistently present, which could be explained if we
were to suppose a difference in initial rhythm between the
maternal and paternal elements of each original chromosome pair.
If multiple complexes were simply the result of the breaking
up of chromosomes in degenerating cells, then we should expect
to find, not simply the multiples of three, but any other number.
Neither should we expect to find the chromosomes of uniform
size, had they arisen by fragmentation.

We are led to believe, from the behavior of the chromosomes of
these metamorphosing cells, that the three pairs of chromosomes
which appear in the original gut cell are made up of quite distinct
individuals, differing from each other to such a degree that
chromatin split from one can not associate itself with that from
another pair. So, all through the series of divisions which precede
the final disintegration, we find the daughter chromosomes of
each of the original chromosomes maintaiming the size and
appearance of the original structure; and moreover, we find each
group of daughter chromosomes so closely associated that they
behave as a single individual. Chromosome individuality,
alone, can account satisfactorily for these conditions.

In the intestinal cells at least, there is no question of Boveri’s
Law of cell size being determined by the number of the chromo-
somes. A glance at the figures on plate 4 shows conclusively
that no such relation exists, nor can the converse be true—that
nuclear size is dependent upon amount of cytoplasm. Hert-
wig’s idea of a definite fixed ratio existing between cytoplasm
and nucleus does not hold here. It is true that the intestinal
cells increase in size as they approach the time for disintegration,
but this would seem to be due to the general acceleration in the
metabolic processes, and to have no direct connection with size
of nucleus or number of chromosomes. Cytoplasm and nucleus
appear to be acting more or less independently. ‘Kern-plasma-
spannung’ could scarcely be the cause for the division in two cells
of equal size, of which one has a nucleus of twelve chromosomes
and the other forty-eight. In these metamorphosing cells, at
least, we must look for a cause for cell division other than the
Kern-plasma Relation which is here extremely variable.

ALIMENTARY TRACT OF CULEX PIPIENS 617
SUMMARY AND CONCLUSION

1. During metamorphosis in Culex pipiens, the number of
chromosomes in the cells of the pupal intestine is considerably
increased.

2. Before disintegration of the cells begins, the chromosomes
of each pupal gut cell pass through a number of longitudinal
divisions resulting in three or four multiplications.

3. The number of chromosomes in the multiple complex is
always a multiple of three—oftenest twelve, twenty-four, forty-
eight; but frequently nine, eighteen, thirty-six, and even seventy-
two may appear.

4. The triplex divisions of the chromosomes apparently arise
through premature splitting of one member of each pair of chro-
mosomes in the original complex or by a precocious division of
one of each of the homologous elements of the bivalent chro-
mosomes.

5.-The size relation between nucleus and cytoplasm is ex-
tremely variable.

6. It appears that in the resting stage of those cells of normal
size which contain multiple complexes, there must be an accel-
erated growth of each chromatin thread which splits into normal
sized chromosomes in prophase, or else the cytoplasm of such
cells must fail to divide and to grow while the chromosomes
continue to do both. The former seems to be the probable
explanation.

7. There is evidence of a parasynaptic union of sister chromo-
somes in the resting stage, followed by re-separation through
longitudinal splitting in the prophase.

8. These sister chromosomes, the multiples of each member
of the original complex, tend to remain together throughout the
mitotic changes.

9. The individuality of the chromosomes is maintained until
the cell disintegrates.

10. The disintegrated cells appear to be digested by the cells
of the newly formed lining of the adult alimentary tract.

618 CAROLINE M.. HOLT

All of these facts suggest that increased metabolism of the
older epithelial cells may be a means of supplying needed food
material to the developing cells of the adult gut durimg the pupal
changes. That this great increase in the amount of chromatin
in cells which have attained their growth, functioned for a time,
and are about to be absorbed, is not accidental, or simply a
process of degeneration, seems reasonably clear from the uni-
formity and universality of this increase in the intestine of Culex.
Every cell of the larval gut epithelium apparently passes through
the whole series of changes above described before it reaches
the stage of disintegration. If this were simply a process of
degeneration, it would be hard to account for the tremendous
growth in the chromatin material and for the retention of the
individuality of the chromosomes to the end. One would expect
the processes observed in the disintegration of the cells, to come
directly without these elaborate preparatory phenomena. It
would seem that we have here, not the hit-or-miss phenomena
of degenerating cells, but a definite adaptation to provide for
the support of the organism during metamorphosis.

BIBLIOGRAPHY

Boveri, T. 1902 Ueber mehrpolige Mitosen als Mittel zur an Analyse des
Zellkern. Verh. d. phys. med. Ges. Wiirzburg.
1905 Zellen Studien, 5.

Hertwic, ©. 1903 Ueber Korrelation von Zell- und Kerngrosse und ihre Be-
deutung fiir die geschlechtliche Differenzierung und die Teilung der
Zelle. Biol. Centralbl., Bd. 22.
1908 Ueber neue Probleme der Zellenlehre. Arch. f. Zellforschung,
Bas.

Hancr, Ropert T. 1917 The somatic mitoses of the mosquito, Culex pipiens.
Jour. of Morph., vol. 28.

Metz, C.W. 1914 Chromosome studies in Diptera, I. Jour. Exp. Zoél., vol.
Ve

Stevens, N. M. 1910 The chromosomes in the germ cells of Culex. Jour.
Exp. Zoél., vol. 8.

Taytor, Monica 1914 The chromosome comPlex of Culex pipiens. Quart.
Jour. Mic. Sci., vol. 60.

Tuompson, M. T. 1916 Alimentary canal of the mosquito. Proc. Boston
Soc. Nat. Hist., vol. 32.

Wuitine, P.W. 1917 The chromosomes of the common house mosquito, Culex
pipiens L., vol. 28.

PLATES

619

PLATE 1

EXPLANATION OF FIGURES

All drawings were made with camera lucida, Spencer homogeneous immersion
lens 1.8 mm., Zeiss no. 12 compensating ocular. All, except figure 6, were then
enlarged two diameters, giving a magnification of 5800. In reproduction, the
drawings have been reduced one-third.

land 2 Late anaphases from intestinal epithelium of Culex pipiens, showing
six pairs of chromosomes passing to each pole. Figure 1 from stomach (fig. 33,
region8). Figure 2is from Dr. Steven’s slide, position not known. Note pointed
tips of V’s. Compare 31 from same individual. ;

3and4 Telophases from stomach (fig. 33, region 6).

5 Early telophase showing two lagging chromosomes. This cell is from the
same individual as 2 and 31. Position not determined but probably stomach.

6 Resting stage from stomach (region 7) showing chromatin scattered about
periphery of nucleus and collecting around the nucleolus. The magnification
is one-half that of .all other figures. Compare with Miss Taylor’s ‘clock face
figure.’ ,

7,8, and 9 Very early prophases showing successive stages in the formation
of three separate vesicles containing the chromatin threads. Figure 7, from
stomach (region 6). Figure 9, from colon, (region 2). Figure 8 shows a cell
about to disintegrate. Note the vacuoles, V, V, just appearing in the cytoplasm
and the break in the nuclear wall.

620

ALIMENTARY TRACT OF CULEX PIPIENS

CAROLINE M. HOLT

PLATE 2

EXPLANATION OF FIGURES

10 and 11 Early prophases from cephalic part stomach (region 10) showing
threads shortening, straightening and thickening. The lower group of figure
10 shows the ends of chromosomes lying to the left. Both figures show early
division of the thread. The two groups of long chromosomes, L and M, in figure
11 have straightened, while the group of short chromosomes is still folded.

12 Early prophase from ileum (region 4) showing threads in three groups
surrounded by nuclear membrane.

13, 14, 15, and 16 Early prophases showing chromatin collecting in granules
as the threads shorten. From stomach (region 10). Figure 13 shows two sec-
tions of the same cell, A and B in one, C, D, EH, and F in the other.

17, 18, 19 Prophases. Figures 17 and 18, stomach. Figure 19 ileum. Fig-
ures 17 and 19 show three groups of six chromosomes each. The small group in
each case suggests the derivation of six instead of four or eight through longitu-
dinal division of the original short bivalent chromosome. In figure 17, A and
B, C and D probably represent the completed division of two chromosomes
corresponding to # and F which are still elongated and have not completed the
division. In figure 19, A and B, D and £, probably represent the same condition
and the larger groups in this cell also show such an early division of one chromo-
some of each pair. Figure 18 shows a group of eighteen chromosomes, of which
two are nearly divided.

ALIMENTARY TRACT OF CULEX PIPIENS PLATE 2

CAROLINE M. HOLT

623

PLATE 3

EXPLANATION OF FIGURES

20 Prophase from stomach (region 6) showing eighteen chromosomes in
three groups. The middle group shows clearly the early splitting of two of four
chromosomes, A and b. The size difference indicates that the division has just
taken place and the chromosomes have not had a chance to grow to normal size.

21a, b, ec, d Normal somatic metaphase complexes. Figure 21 a metaphase
group from stomach epithelium showing size of chromosomes in the ‘normal’
gut cell. Figure 21 b, e and d, groups from nerve tissue showing typical group-
ing found in all somatic tissues.

22 Metaphase group from stomach (region 6). 2x, y and < represent three
sections of the same cell. When superimposed, the group is found to contain 36
chromosomes.

23 Metaphase group from ileum (region 4). Y and Z are two sections of the
same cell. The number in this group is probably 72, although there appear to
be but 68 chromosomes.

24 Metaphase, showing 24 chromosomes—from Dr. Stevens’ slide—region
undetermined.

25 Metaphase from ileum (region 3)—24 chromosomes. Three in center of.
group show splits.

26 Metaphase from stomach (region 6) showing 36 chromosomes, grouped in
three groups of 12 each.

624

PLATE 4

EXPLANATION OF FIGURES

27 Metaphase from ileum (region 4). G and H are two sections of the same
cell. When superimposed, 42 chromosomes may be counted. This number
is possibly due to irregularity in time of division.

28 Metaphase from ileum (region 4). 12 chromosomes.

29 Prophase from ileum (region 5). 6 chromosomes.

30 Metaphase from ileum (region 5). 18 chromosomes, only 17 show in
drawing. Figures 27, 28, 29, 30 show loss of typical size relations between cyto-
some and chromatin mass.

31 Anaphase from Dr. Stevens’ slide. 12 pairs chromosomes. Note two
lagging chromosomes.

32. Early anaphase from colon (region 2) 6 pairs chromosomes. These
chromosomes seem to be smaller than those of other regions drawn.

33 Diagram of alimentary tract of pupa showing regions included in sec-
tions studied. 1, rectum; 2, colon; 3, 4, 5, ileum; 5, region of entrance of Mal-
pighian tubules into gut; 6, 7, 8, 9, 10, stomach in abdominal region.

626

SUBJECT AND AUTHOR INDEX

NATOMY of arachnids. Notes onthe.. 1
Arachnids. Notes on the anatomy of.. 1

UXTON,B.H. Notesontheanatomy of
Pie Yel enerG (5) nGospacico ds saeneeers CODAOEEAOO

One The primordial cranium of the...... 281

Chorthippus (Stenobothrus) curtipennis and
Trimerotropis sufiusa (Orthoptera). Syn-
apsis and chromosome organization in... 471

Chromosome organization in Chorthippus
(Stenobothrus) curtipennis and _ Tri-
merotropis .suffusa (Orthoptera). Syn-

APSISHAL Ca rctare oes eee ele Mra ee = She's ais 471
Chromosomes of Hesperotettix and Mermiria
__ (Orthoptera). The multiple.............. 519
Ciliated cells. Studies on.................... 217
ConeL, JessE LE Roy. The urogenital sys-
LOT Ofe My RIT OLGSs ee ienie ieteies eiclers te. ccy ease, 75
Culex pipiens. Multiple complexes in the
alimoentanyatlaet Oli. ssc cidlesioecicieiaeess: 607

Cypridina hilgendorfii. Note on the struc-

ture of the maxillary gland of............ 435
EVELOPMENT of a starfish, Pateria
(Asterina) mineata. The early......... 461

GG of the white rat, Mus norvegicus al-

binus. The period of synapsis in the.. 441
ALLUS domesticus. Studies on the
Byles Ol eames teas tects ainrs mie ose aterene 165

EATH, Haroup. The early develop-
ment of a starfish, Pateria (Asterina)

Lrara(s tif eae se cdoce bon arid re eee em paC 461
Hesperotettix and Mermiria (Orthoptera).
The multiple chromosomes of............. 519

Hort, Carotine M. Multiple complexes in
the alimentary tract of Culex pipiens....._ 607

NSECTS. On the physiology of the nucle-

LT aaa SAAS RO beCOS SEBO S OTS ROR Sera 5 Us)

Lone, J. A., Pratt, BensamMin HaRRIson,
AND. The period of synapsis in the egg
of the white rat, Mus norvegicus albi-
PLUG Sogo ete ci oioiece ots ote ayatocnievaze, eisseiehsyete: aid sore 441

1A Genes CuiaReENcE E. The mul-
tiple chromosomes of Hesperotettix

and: Mermiria (Orthoptera)............ 519
McInvdoo, N. E. The olfactory organs of
IDS PIG OPEN As. peer ae | Acttreiearowses 6 33
Maxillary gland of Cypridina hilgendorfii.
Note on the structure of the.............. 435
Mermiria (Orthoptera). The multiple chro-
moses of Hesperotettix and............... 519

Multiple complexes in the alimentary tract

Of Culex piplenstca-ae mae iste iors aces 607
Myers, Jay ARTHUR. Studies on the syrinx

Of GalltisidOMeStiCUsi a. seaceene sclne cite cieters 165
Myxinoids. The urogenital system of........ 75

INES Waro. On the physiology

of the nucleoli as seen in the silk-gland
cells of certain insects................... 55

Nucleli as seen in the silk-gland cells of cer-
tain insects. On the physiology of the... 55

(Orthoptera). Synapsis and chromosome or-
ganization in Chorthippus (Stenoboth-
Tus) curtipennis and Trimerotropis suf-
RE SiS Be Aon REO eicic Oo Care ORD ODONG 471

(Orthoptera). The multiple chromosomes
of Hesperotettix and Mermiria............ 519

pee (Asterina) mineata. The early
development of a starfish................. 461
Physiology of the nucleoli as seen in the silk-
gland cells of certain insects. Onthe.... 55
Pratt, BrenJAMIN HARRISON AND Lona, J.
A. The period of synapsis in the egg of
the white rat, Mus norvegicus albinus.... 441
Primordial cranium of the cat. The......... 281

GeGusst S. Studies on ciliated cells ..... 217

Silk-gland cells of certain insects. On the
physioology of the nucleoli as seen in the 55
Starfish, Pateria (Asterina) mineata. The
early development of a............- eoccuns Gul!
Synapsis and chromosome organization in
Chorthippus (Stenobothrus) curtipennis
and Trimerotropis suffusa (Orthoptera).. 471
Synapsis in the egg of the white rat, Mus nor-
vegicus albinus. The period of........... 441
Syrine of Gallus domesticus. Studies on ee
GLC centres atc letete ee restates sictetatateleverelais)ele7ai=)~iebiniere

IERRY, Rozert J. The primordial cra-
Mitimvof the leAbesseeme esas seals = -igieialnieie> 281

Trimerotropis suffusa (Orthoptera). Synap-

sis and chromosome organization in Chor-
thippus (Stenobothrus) curtipennis and.. 471

ROGENITAL system of Myxinoids.
BT Ceo spe Ean soda conrt GC en OAOGbOereNOnr

ENRICH, D. H. Synapsis and chro-
mosome organization in Chorthippus
(Stenobothrus) curtipennis and Tri-

merotropis suffusa (Orthiptera)....... 471
White rat, Mus norvegicus albinus. The
period of synapsis in the egg of the....... 441

ATSU, Haonimer. Note on the struc-
¥y ture of the maxillary gland of Cypri-
Gime bil wend ora sce. ae os cles se ssl 435

629

JOURNAL OF MORPHOLOGY, VOL. 29, NO. 2

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