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POUR N AL
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MORPHOLOGY.
EDITED BY
C. O. WHITMAN,
University of Chicago.
WITH THE CO-OPERATION OF
EDWARD PHELPS ALLIS, Penk aL LIE,
Milwaukee. University of Chicago.
HOWARD AYERS, T. H. MORGAN,
University of Cincinnati. Bryn Mawr College.
E. G. CONKLIN, E. B. WILSON,
University of Pennsylvania. Columbia University.
Vor SC VIE.
BOSTON, U.S.A.:
GINN & COMPANY.
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Volume XVII. September, 1900. No. f.
JOURNAL
OF
VOT Ol OGY
THE SPERMATOGENESIS OF BATRACHOSEPS.
PoLYMORPHOUS SPERMATOGONIA, AUXOCYTES,
AND SPERMATOCYTES.
GUSTAV EISEN, Pu.D.
TABLE OF CONTENTS. « PAGE
BTINTRO DOCTOR Ys cer erie re seen as ONE Res oh 3
Pe VERTHODS (OW TN VRSTIGATION Ge 1 eel eo re ee ee eee te. SINT 4
EAE VCS Serer eres ed eee ee Nig te rege hares eur BYTE 4
5 Fa RS RAE ARES Th YU eee oe esa Agee | 0b Aen ee 5
Optical Methods and ‘Appliances, 2308 et a 7
DMPC ONSEUTUENTS WOR REVO AC Yonge Shee Vo al ye ae Ee) 8
Remrral Plepessoms) of Cel Sirsiciuves:.- 1s 8
JES SEDS Pe is OR SRSA ote ES nie ec Le eS ee 8
LEER TPR E TE By SOU STE LD ri aR Eee Ne a AL A eI a ee 9
Archosome or Centrosomal Structures.........2.......::0c0sscsseseeeeeseeeeeeesee fe)
CFE ASOTCE ree nen RRR ee es eek te Leer tel ee Led fone Ct LR 9
Qy) LE SESE We 2 So Ngoc Ra SAS ES LD ce a 9
Bee SoS 8 HALE LA 2a 8 o8 ie ed fe)
Plasmosphere, Granosphere, and Hyalosphere. Meves’sIdioplasm 10
ae Paar Pp our ee er hE de el eee 13
Cytoplasmic Membrane or False Nuclear Membrane. Cell Wall... 15
LEE CELE Do So? RS aA Ee OS eee eee ee 16
PO i ai at, nc gO CUE ee Ee Ciel De eR 17
ACETIET ETI ATG PI eels ae ane be eed di dh, 17
2 EISEN. [VoL. XVII.
PAGE
GChromioles.icicesi ies cca ee cca hecc st pastes epee eatsnetsoever cnet 18
Chromoplasm .........-------c--c--c--eceececeesecsseececeeceecnsenenen sencereneoscsnasassuscsosearad 22
Chromomeres .........- » ASO Ra EE Sa e202 SL oth tee ea eenuer erane een ces eanaren 23
DOs Va (hfe ere eae eee sreee ce ectootee cecteu copenase roster noha hae bkecaathtaer tne eneicensene 25
ChrOMOSOMES: highs sssee ee eee dca ce teeta oa ae ree ote ae 26
Chromoplasts and Endochromatic Granules ..........0--ss1-sesceeseeceeeeees 28
Tene avoyenteyg (8 Cyber octecectccr cosenecdacoresoceen a ocebtaroccecnbacuaece 34
Linoplasts or Drie Necleola or orc cc cer ecc eases nares a2 Sacer pe ee ees 34
1 DFE esses hee eee enmeete eee dap cee occ ocece ccc anos eee Soccaccec sc cuecesacLROSE 35
Nae aur ile roa xen aie eeee sae ease aeons 37
Phylogeny of the Nucleus <2... -2.2--00.-ccs-scencte-ansereonemsnnennnnnnpsorestensnsstnse 38
AP CHOS OT70E: 2 ssste nts ee eR ee ote aaa cee aera sane eee eer cee 39
The Archosome Proper: Its Structure, Centrosphere, Somo-
Sphere, Quid Meme Gl sprees te eee ce eee acee cece ea ece tesa eee 39
Accessory Archosomes, their Structure and Functions. Expul-
sion of the Superfluous Accessory Archosomes ............::::s:e000e+ 43
TVi0 SBINDLES (AND MS BINDDID i HINBIGRIS iene seeceteneete cer ents eastern eee cae cree eee 45
General: Remankesyer ee oo aA a eee eee eae 2d eee re ease 45
Mantle Fibers, Polar Fibers, and Central-Spindle Fibers ................ 45
Contractile: Fibers is osc es ee eg a ae ere eno an sartc a arcu coaor omer en 48
Fiber Cones and Retractile Fibers of the Spindle Cones................ 49
Spindle bxidge and | Mid-Day oer oe ce arene cee eee eee reer 51
A PNR Go TAS) Tol IRU TIAN E) (CHOTIUS ohh oe ot oeneme doce st sce ep ob enoo coer eo uS RoE ase eEo oe 52
Polymotphous Sperimato ronal so: ecescecete cree sect tent etarerneeen Perera 52
PATEK OC YES Peas ace e me ce sr eee ee 56
SpermatoCytes oo iciceiitctenk ceecestsacasoe seascaetiten suet eancee oe eRe nese rear ner 59
Sperinatids 2.1170) 1 Ee eae ee ecco eene a Seer ee eenat ee aceae ca 60
WIT; IMEPTOSIS ecdee sce Sl ic AR a Toe ae ae eee ER Se ae 60
A General Review of Mitosis. The Two Parallel and Inde-
pendent Processes of Evolution and Development: The
Radiosomic and) the (Chromosome yess ee eee nen 60
The Radiosomic Process, or the Evolution of the Spheres, the
Spindle, the Fibers, and the Formation of the Cell Wall............ 63
The Chromosomic Process, or the Evolution of the Chromioles
and their Formation into Chromomeres and Chromosomes...... 67
Equations or (Reduction. css sere es eee eee eee 76
Falungey Stages inthe Mitosis sss vest eee eee 76
Villars sTRUCLURES (OFLTHE) PROTO PHASMase oe eee i)
ibers:¢Granula-andwAliveolesenc eee eee ee 77
VIII. PERMANENCY OF THE COMPOSITE STRUCTURES OF THE CELL........ 82
STEXG HS UMN R Vie ohare niet) etd OE che une nee 84
XIN OMEN CLAM URI Selec rites Se cuceelagsacet tn sates secensceedececoe taeda ee 90
Des IT URRAT URC ae tases estectes ever ofaNiae sti pec teeaees oo cubeccesadstt gens ioe yee 97
XMS EXPLANATION VON LPH E PP TGU RWS ee) eoeern ony eee) aoe eee 100
XIII. STAINS, FIXATIVES, AND OPTICAL APPARATUG........--.cccssscoosssccsleecenseees 117
Nort. SPERMATOGENESIS OF BATRACHOSEPS. 3
I. INTRODUCTORY.
OwinG to a projected and extended voyage, this paper had
to be brought to a sudden close, and much which I had in-
tended to include in it had to be left out and deferred to a
second part. This latter half will include the somatic mitosis
of the polymorphous spermatogonia, the evolutions of the
spermatids and their development into spermatozoa, and also
a discussion of the literature. In this paper I have merely
endeavored plainly and briefly to describe my own investiga-
tions, and time has hardly permitted me even to touch upon
those made by others on the same subject.
The results of the present investigations, of whatever value
they may be, are principally due to improved cytological and
optical methods, especially to the new fixatives and to the
achromatic light, all described in their proper places. With-
out them the chromioles would yet have remained a mystery,
at least as far as my own investigations are concerned. The
figures illustrating this paper have been corrected as many as
four different times, and the first thirty figures made have been
completely redrawn, in order to secure that accuracy of detail
which can only be had after repeated failures.
It is proper to state here that the testes of Batrachoseps are
very favorable for study, being small and containing large cells.
But these advantages are more than offset by the scarcity
of the material. While these batrachians are very common
almost everywhere in California, their testes are only active at
a time when it is almost impossible to procure any specimens
of the species. Batrachoseps attenuatus is only adult in the
months of June and July, at a time when, on account of the
dry season, these animals have retired down in the ground,
almost out of reach. In the summer of 1897 I had, however,
the good fortune to find in the end of June three fully adult
specimens at Monterey, Cal., in a damp meadow which had
been kept cool by the fogs from the ocean and shaded by
overhanging trees. The largest of the three specimens was
made useless by an accident in sectioning the testes; the
others, however, turned out most admirable preparations,
4 EISEN. [VoL. XVII.
which were made the material for this memoir. After-
wards I was of course able to supplement them with less
favorable material from specimens collected at other times.
In size the adult testis is about five millimeters long by one
millimeter wide. It consists of only one single lobe, undivided
and of cylindrical shape. In the central parts of this lobe
are the ripe spermatozoa, while the other cells are found
arranged on either side in the direction of the long diameter
of the testis. The four testes were sectioned longitudinally,
thus affording a comprehensive view of the arrangement of the
different cells.
It is with much pleasure that I here acknowledge my indebt-
edness to my esteemed friend, Dr. W. J. V. Osterhout, of
the University of California, for many valuable suggestions and
for assistance in correcting MS. and proof.
II. Metuops oF INVESTIGATION.
Fixatives.
The first investigations were made on testes fixed with the
classical fixatives—Flemming’s chromo-aceto-osmic mixture
and the platino-aceto-osmic mixture of Hermann, used in various
strengths, with or without admixture of water. Heidenhain’s
corrosive-sublimate-acetic was also tried, both with and with-
out addition of formalin. Experiments were also made with a
number of other fixatives, such as mixtures of Flemming’s and
Hermann’s with corrosive-sublimate and palladium-chloride.
Vanadium-chloride, uranium-chloride, and osmium-chloride were
also experimented with, all of which, with the exception of the
last, proved of no value. I soon satisfied myself that any mix-
ture containing either platinum-chloride or osmic acid, or both,
would completely ruin several of the outer rows of cells, mak-
ing them unfit for microscopic research. As the testes of
Batrachoseps are so very small and possess only a few rows of
cells, none of the above-mentioned fixatives could thus be used.
Platinum-chloride is even more injurious than osmic acid ; while
the latter destroys the chromatin, the former ruins the finer
structure of the cytoplasm. Although by the employment of
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 5
these fixatives some of the interiorly situated cells gave fairly
good images, yet it was readily seen that the cytoplasm of the
cell had become greatly contracted and distorted, to such an
extent as to represent no more the true structure of the cell.
It is comparatively easy to fix chromosomes and spindles, more
difficult to fix the cytoplasm and the linin. Osmium-chloride
is in many respects a most valuable fixative, especially in solu-
tions of from one-half to one-tenth per cent, but it always pos-
sesses the undesirable quality of blackening the tissue, though
in a lesser degree than osmic acid. I have, however, no
doubt that this chemical will be found very useful for fixing
several kinds of tissue, especially in connection with potassium-
bichromate, when it allows of intense staining and detailed
differentiation. The fixative on which I finally decided as
giving the most satisfactory results, as regards the fixation of
the testes of Batrachoseps, is a mixture of iridium-chloride-
acetic, according to the formula published in the Zeztschrift f.
wiss. Mikr., Bd. XIV, pp. 195-202. The time of fixation is
from three to twelve hours, though I think that the best
results were had with the shorter time. There is no percep-
tible shrinkage of the tissue, no blackening of the cells, and the
outer rows of cells are as perfectly fixed as those in the center.
After fixation the testes were washed in tap water for about
one hour, then passed through thealcohols. For clearing, ber-
gamot oil was found most suitable, but it was followed by xylol,
which latter was again displaced by bergamot before imbed-
ding in paraffin. The sections were cut in paraffin of 54 Fahr.
melting point, and from 4 to 6 thick, each cell being cut in
from two to three parts. This latter is of importance because
cells which are not cut into do not stain properly, making
it impossible to study the finer structures of the cell. The
sections were then fixed to the slide by the alcohol method
as described in Bd. XIV, Zeztschr. f. wiss. Mikr. (1897),
pp. 195-202.
Stains.
The majority of the sections were stained by the Benda iron-
haematoxylin method, and after-stained with congo. Another
6 EISEN. [VoL. XVII.
set was stained with congo, thionin, and ruthenium red, as will
be described below.
The liquor-ferri-sulphurici-oxidati was used diluted about six
times, and the slides were kept in the solution for about twenty-
four hours. The haematoxylin solution was used concentrated
and contained about 10% of alcohol, the solution being a year
old. The sections were kept in the haematoxylin solution for
from forty-eight to seventy-two hours, the longer time giving
the best results. The differentiation was made with a 10%
solution of glacial acetic acid in water, to which was added a
small part of the liquor-ferri, sufficient to give it a very pale
straw color. In from fifteen to twenty minutes the differentia-
tion was finished. The slides were now rinsed in water and
counter-stained with a watery solution of congo for one or two
minutes, then as quickly as possible dehydrated in absolute
alcohol, cleared with bergamot oil, and mounted in gum-thus
in xylol. Several of the slides were stained over two and even
three times before a sufficiently satisfactory differentiation was
obtained. The use of congo as a counter-stain was decided on
only after long experiments with numerous other anilin colors,
and it proved to be the only stain which gave the desired
differentiation in the highest degree. It was the only satis-
factory stain for the differentiation of the spheres and their
secretions.
Another combination of stains which proved useful is a triple
stain of congo, thionin, and ruthenium red. The slides were
first stained for a few seconds with a weak solution of congo
in water, then for about ten minutes with thionin in water, and
then differentiated with a watery solution of ruthenium red.
This latter stain was made extremely weak and of a pale rosy
tint ; still the differentiation was accomplished in a few minutes.
The ruthenium washes out the thionin, and the differentiation
should always be carefully watched under the microscope.
This combination of stains proved especially useful for differ-
entiating the chromoplasts, and also for the study of the out-
lines of the chromosomes, especially where the latter overlapped
each other, as the outlines of the separate chromosomes could
always be distinctly seen.
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 7
Optical Methods and Appliances.
No one who has not used an oil-immersion substage con-
denser can have any adequate idea of the value of such an
appliance. In the study of the finer structures of the cell it is
of equal importance with the apochromatic objective, and its
value cannot be overestimated. It is my opinion that a correct
and proper view of the structure of the protoplasm cannot be
had without the oil-immersion condenser, and that opinions
based on observations made without this condenser must neces-
sarily need to be reconsidered. An achromatic, or better yet
an apochromatic, condenser should be used, and the immersion
oil should be slightly denser than the oil used on the objective,
in order to counteract the thickness of the slide. This can
readily be accomplished by warming the oil for a short time,
or by using oil that has become thicker from ordinary exposure
to the air. The oil-immersion condenser increases the sharp-
ness of the image and brings out details not otherwise visible.
The images were studied with artificial light alone, a filter
of cyanin and methylene blue being interposed between the
Welsbach incandescent gas burner and the substage condenser.
For a more detailed account of this light see Zeztschr. f. wiss.
Mikr., Bd. XIV, pp. 444-447, 1897. The use of this light
enables us to work continuously, independent of sun and
clouds, day or night, with the same strength of light and with
the same facility. This light has also a great advantage in
not injuring the eyes, not even tiring them perceptibly after
ordinary work. The light has also another advantage in that
it differentiates structures which are not differentiated by stain-
ing. For instance, by the daylight and after staining with congo
no differentiation was had between the linin granula and the
cytoplasmic granula, but with the artificial light the linin gran-
ula were seen to be of a gray or brown color, while the cytoplasmic
granula were stained palered. A better image can be had with
this artificial light than with the best white-cloud light, and the
image is also perfectly steady, which it never is with even the best
cloud light. The sections were studied with Zeiss Apochromats,
3 mm., Ap. 1, 40, and 2 mm., Ap. I, 40; Oc. 12 and 18.
8 EISEN. [VoL. XVII.
III. CoNnsTITUENTS OF THE CELL.
General Divisions of Cell Structures.
The division of the cell structures adopted in this paper is
almost the same as the one proposed in my paper on the plas-
mocytes of Batrachoseps, the only important change being
that of the word centrosome to centriole. The principal rea-
son for this change is that many investigators have not only
used this word for different structures, but in some instances
have even discarded it altogether. The confusion is really so
great that it is in many instances impossible to know with cer-
tainty what organ or what part of the cell is referred to. W.
Flemming, in his report, “‘ Morphologie der Zelle,” 1897, rejects
the name centrosome and substitutes the word ‘“Centralkorper.”’
As this word cannot possibly be accepted by other investiga-
tors than Germans, and as Boveri has previously named this
body the centriole, I can see no valid reason why we should
drop’a really very useful word, about the meaning of which
there cannot be any misunderstanding, and which is so con-
structed that it can be adopted in every language used by biol-
ogists. Literal translations of new words often so conflict with
words already existing that great confusion results. It seems,
therefore, most appropriate that in composing new words they
should be so constructed that they may with a slight change be
used in other languages, or, better yet, be used without any
change. Words of this kind are, of course, words of Greek
and Latin derivation. I would also suggest that every biologi-
cal paper be accompanied by definitions of the nomenclature,
worded in such a manner that no misunderstanding will ensue.
If such a method had been adopted, we would not now have
had years’ wrangling about, for instance, the single little word
“‘centrosome.”
In this paper I propose to use the following nomenclature
for the divisions of the cell:
Cytosome — the purely cellular part of the cell, the cytoplasmic
parts, all parts exterior to the nucleus, except those bodies which
are known as archosomes or parts belonging tothem. The cyto-
No, 1.) SPERMATOGENESIS OF BATRACHOSEPS. 9
some thus contains such constituents as cell wall, cytomicro-
somes, the two spheres which I here designate as granosphere
and plasmosphere, metaplasmic secretions and metaplasmic
granules, various rays and fibers, and spindles.
Karyosome, or nucleus — comprises the following parts:
nuclear wall, or karyotheca, chromosomes and their constitu-
ents, linin, what is generally known as nucleoli of various
kinds. All bodies which when the cell is at rest reside within
the nuclear membrane.
Archosome — the centriole with its spheres, the somosphere
and the centrosphere, all structures which may be counted
as centrosomal structures. When there are more than two
archosomes, I refer to the others as accessory archosomes.
For the innermost dark-staining granules I have adopted
Boveri’s name, ‘“centriole.’”’ The thin zone surrounding the
centriole or centrioles is the somosphere, and the zone sur-
rounding the somosphere is the centrosphere. The archo-
somes or archosomal structures have not with certainty been
found in the higher plants.
The Cytosome.
By the cytosome I understand all that part of the cell which
is situated exterior to the nucleus, excepting those parts which
are undoubtedly of the same nature as the archosomes. The
cytosome comprises thus the following parts: the cytoplasm
proper, the plasmosphere, the hyalosphere, the granosphere,
metaplasmic secretions, the cell wall, and finally some granules
of undetermined nature, generally scattered among the cytomi-
crosomes, also the fibers, the spindle, and the mid-body.
The Cytoplasm. — During the greater part of the life history
of the cell the cytoplasm proper is difficult to distinguish from
the various granules comprising the spheres. Sometimes it is
also difficult to distinguish it from the linin granules of the
nucleus. The latter difficulty exists only when the nuclear
membrane has been dissolved, as at that time the linin gran-
ules are scattered all through the cytoplasmic part of the cell.
But even then the cytoplasmic granules may be distinguished
from the linin granules both by their staining quality and by
10 EISEN. [Vo. XVII.
the way they are arranged into threads or fibers. With the
light-filter the linin granules appear darker than the pure
cytoplasmic granules, and it is even possible under favorable
circumstances to follow the course of the linin granules from
their dispersion from the nucleus to their appearance in the
cytoplasm.
While I have included the two spheres as a part of the cyto-
plasm, I nevertheless hold that they are of a somewhat different
nature, with different functions, from the cytoplasm proper.
During the perfect resting stage of the large cell with poly-
morphous nucleus the cytoplasm proper is confined to a very
thin stratum surrounding the deeply folded nucleus. At that
time there is no distinction between the granules of the cyto-
plasm proper and the granules of the spheres (Fig. 1), and
it appears as if the latter might later on be differentiated out
of the former, though we can with equal reason assume that
they are fundamentally different, but that they are intermixed,
and that they cannot be distinguished one from the other. At
a later period in the development of the cell such a distinction
is possible, as the staining capacity is much greater in the
granules of the spheres than in those of the cytoplasm proper
(Figs. 30, 58, 60). During this early resting stage of the
polymorphous cell the cytoplasm is never accumulated close to
the cell wall, but merely forms a very thin zone around the
nucleus (Fig. 1). As the cell grows, this zone increases
in size and soon fills up all the available space between the
nucleus and the cell wall, though it is always denser in the
immediate vicinity of the nucleus (Figs. 3, 10, 12, 15, etc.).
In the early stages of this class of cells the cytoplasm proper
as well as the primitive spheres are composed principally of
granules, but at a later stage, when the spheres are formed,
the cytoplasm proper is generally distinguished by a fibrillar
structure, while the spheres are almost exclusively granular
(Figs. 34-37).
The Spheres.
By the spheres I understand that denser accumulation of
cytoplasmic substance variously designated as spheres, archo-
INO. T.] SPERMATOGENESIS OF BATRACHOSEPS. Et
plasm, aster, etc., generally containing the archosomes. The
spheres when perfect are differentiated into an inner and an
outer sphere, and at times also the outer sphere is further dif-
ferentiated into two distinct zones (Figs. 8, 9, etc.). The word
“differentiated’”’ is used in the same sense as separated and
is not intended to indicate that the two spheres are differen-
tiated from the same kind of protoplasm. The inner one of the
spheres is the most distinct and also the most permanent of
the two. It is more constant as to form, and is characterized
by a capacity to stain much deeper than any part of the outer
sphere. It is also during a part of its life cycle well defined,
having then the form of a concave disc, or a mulberry-shaped
body, one side of which is strongly concave, while the other is
more or less noticeably convex (Figs. 12, 29-31).
There is reason to believe that this inner sphere is always
concave, but that the concavity of the sphere is only perceived
when the sphere is seen from the side (Fig. 12), the con-
cavity not being visible when viewed in the other direction.
The comparison to a mulberry is yet more justified by the
structure of the sphere. It is, when perfect, always composed
of a number of alveoles of almost equal size, and so arranged
that the wall of the sphere is just one alveole thick. The cav-
ity of the sphere is not an empty cavity, but is more or less
densely filled with granules, less distinctly arranged in alveoles.
At a certain stage in the activity of the sphere and the archo-
some this inner more loosely constructed part of the sphere is
drawn out, the archosome being at its top, forming a pointed
cone of less staining capacity (Figs. 28, 35-37). The alve-
oles are non-permanent structures and formed by the peculiar
arrangement of the granules composing the spheres. It ap-
pears as if these granules secreted some distinct substance,
and that this substance was held together by the closely ap-
proached granules themselves, thus forming a bladder-like alve-
ole surrounded by a membrane of granules. The development
of the spheres will be described in another place; here it will
suffice to state that the inner sphere is during mitosis gradu-
ally dispersed, part of it being undoubtedly used up in the for-
mation of the central spindle. Similarly the outer sphere is
12 EISEN. [Vo. XVII.
dispersed at an even earlier stage, the secretions of its gran-
ules, or perhaps even the granules themselves, supplying mate-
rial for the new membrane which is formed between the two
daughter-cells.
In a paper on the plasmocytes of Batrachoseps I have de-
scribed and designated the spheres of the erythrocytes as gran-
osphere, hyalosphere, and plasmosphere, these three spheres
being of strictly cytoplasmic nature. A comparison with the
spheres of our present cells satisfies me that the inner sphere
is identical with the granosphere. For the outer sphere I use
the name plasmosphere, though it is not absolutely settled to
my satisfaction that they are in every way identical. But the
similarity is considerable, even to the extent that we find be-
tween the plasmosphere and the granosphere at times another
zone which probably is identical with the hyalosphere (Figs. 8,
16, 17, 34). In this paper I will, therefore, refer to the two
spheres as the plasmosphere and the granosphere. While in
the plasmocyte the non-staining sphere surrounding the grano-
sphere has the form of a narrow, even band, the non-staining
zone in our present cells is frequently aster-like, radiating
through the plasmosphere (Figs. 6-8, 14). The three spheres
during all their different stages of evolution possess a granu-
lated alveolar structure, the cytoplasm proper taking the form
of frequently granulated fibrilla, especially nearest the cell
wall.
When I had almost finished this paper I found that Meves
has proposed the name “idiozom”’ for the two spheres, or, as
he defines it, “for the specific covering which surrounds the
Centralkérper in the testes cells.’ The word is apparently
selected under the supposition that the spheres are especially
intended for the Centralkérper. That such is not the case I
expect to show in this paper. Moreover, the new word does
not distinguish between the two spheres, which, as I expect to
demonstrate, are distinct and independent structures. If we
are to retain one name for the two spheres, then the word
‘“‘archoplasm’”’ seems to me as good as any other. Neither of
the two words expresses the true nature of the bodies which
they are intended to designate. The names which I propose to
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 13
retain in this paper have the advantage of distinguishing between
the two spheres, and have besides the priority. Upon the
value of the latter I shall, however, not insist, and I am willing
at any time to discard any words introduced by me or by any
one else as soon as better ones are found, but not until then.
Position of the Spheres.
As will be seen from a perusal of Figs. 10-17, the spheres
are only situated on the cell axis when they are in a stage
of comparative rest, and at a time when the spheres and
the nucleus appear to balance each other. If, on the other
hand, we examine such figures as 42 and 45, we find that the
spheres, especially the granosphere, have a different position
relative to the central spindle and the nucleus. Instead of
being situated on a line passing through both the central spin-
dle and the nucleus, we find them situated ona line passing
through the equator of the central spindle. From this we can
formulate a rule that the position of the granosphere during
the radiosomic process is dependent upon the position of the
central spindle; and vice versa, that the position of the central
spindle is dependent upon that of the granosphere.. Whatever
be the relative position of the nucleus on one side, and the
granosphere and the central spindle on the other side, the cen-
tral spindle will always be so situated that a line passing
through its equator will also pass through the granosphere.
The object of this relative position of spheres and central
spindle is undoubtedly to enable the two opposite poles of
the central spindle to draw an equal amount of nourishment
or material from the granosphere.
As regards the mutual position of the two spheres, I expect
to show that they are not directly dependent on each other,
and that the position of the granosphere inside of the plasmo-
sphere is probably regulated by convenience more than by
dependence. If the granosphere were situated anywhere else
it would not be able to furnish the central spindle with the
material required for its development. The plasmosphere
again, which furnishes material for the mantle fibers and for
the new cell wall, must of a necessity be on the outside, in
14 EISEN. [VoL. XVII.
order to be able to assume its proper position near the equa-
tor of the cell, where it is most required. Again, the develop-
ment and the evolution of the cell require that as much as
possible the various parts should be arranged concentrically.
Metaplasmic Secretions.— These secretions can be readily
distinguished from the permanent elements of the cell by
proper methods of staining. Among the methods which I
have used there are only two which have proven of value.
One is the Flemming triple stain, the other is the iron-haema-
toxylin stain, with an after-staining with congo. The latter
method is much preferable, and it may almost be considered as
a specific stain for the secretions from the spheres. It has
already been stated that the ultimate visible structure of the
spheres consists of granules and that they are arranged around
alveoles. It is these alveoles which contain the metaplasmic
secretions, and the only way to explain their presence is to
assume that they are secreted from the granula of which the
spheres are composed. The secretions appear only in the
alveoles, and when these are scattered during mitosis they
carry the secretions with them. Even with the highest op-
tical powers no structure can be perceived in the secretion.
During the metaphase the alveoles, together with their secre-
tions, are found in the vicinity of the equator where the new
cell membrane is to be formed. The secretions from the
granosphere, and perhaps some of its granules, are used up
in the formation of the central spindle. At least the granules
lose, at this time, their intense staining capacity, diminish in
size, and cannot be followed any longer with any certainty.
Fibers and rays, both from the central spindle and from the
spindle cones, are frequently found ending in alveoles filled
with metaplasmic secretions, as if they were receiving nourish-
ment from them (Figs. 41, 42, 45, 61).
The metaplasmic secretions teach us, among other things,
that the two spheres are structures independent of each other,
that one sphere is not a modification of, or a secretion from, the
other, but that each is of a distinct nature. When the spheres
reconstitute they do not do so together, but often in different
places of the cell, later on to be joined together.
INO= 1:]] SPERMATOGENESIS OF BATRACHOSEPS. 15
Cytoplasmic Membrane and Cell Wall, — The cell wall is un-
doubtedly the most constant structure of the cell. I have not
made this structure the subject of any particular study and can
only say that it appears to be composed of minute granules,
closely approached to each other and evidently of the same
nature as the granula composing the cytoplasm of the cyto-
some. The formation of the new cell wall between the two
new daughter-cells will be described under the general heading
of mitosis. Here I will only mention that the new wall is
formed by the aid of metaplasmic secretions from the outer
sphere. All through the evolution of the cell we find that
wherever large vacuoles are formed in the cell, these seem to
become surrounded by athickercytoplasm or incipient membrane.
This is, I think, especially the case when these vacuoles contain
some substance differing in quality from that surrounding them,
in which instances the cytoplasm appears to thicken into a
veritable membrane, greatly resembling a thin cell wall.
At a certain stage in the mitosis of the cell, when in the end
of the anaphase the new nucleus is beginning to increase in
size, a new membrane is formed surrounding the nucleus, but
at a considerable distance from it. This membrane is not a
nuclear membrane, but a true cytoplasmic membrane, which is
again dissolved, as soon as the new nucleus has reached its
final or desired size. This membrane only serves as an attach-
ment for the cone fibers, and by being pulled outwards causes
a large vacuole to be formed around the nucleus, thus giving
the nucleus ample room to expand and to grow (Figs. 59-68,
also Fig. 70). The nuclear membrane is formed later, imme-
diately around the chromosomes, often while the cytoplasmic
membrane is still in existence, as, for instance, in Fig. 7o.
Later on this cytoplasmic membrane is dissolved. The process
of the formation of this false nuclear membrane, as well as of
the inner and thinner membranes around the vacuoles, and of
the cell wall itself, is, I think, one and the same, a condensing
of the cytoplasmic granules. In the formation of the new cell
wall the draught on the cytoplasm is so great that an extra
supply of cytoplasm and nutriment is required, which supply is
furnished by the plasmosphere and its metaplasmic secretions.
16 EISEN, [VoL. XVII.
Paracellular Bodies. —1 designate as paracellular bodies
numerous non-cellular bodies situated between the regular cells
of the testes. They appear to have been expelled from the
cells. Some of these bodies are lying free in the intercellular
space, others are more or less closely attached to the exterior
surface of the cells. These bodies are rarely found among the
polymorphous spermatogonia, or among the auxocytes, but are
quite numerous among the spermatocytes, the spermatids, and
the spermatozoa. At times we find only a few, at other times
we find them by hundreds. They may be divided in two
classes, one consisting of bodies of somewhat larger size and
which contain no granules. The other class comprises bodies
of smaller size, but which contain one or more darkly stainable
granules. The larger of these bodies are frequently attached
to the cells by thin threads (Figs. 67, 109). The smaller ones,
containing the granules, are sometimes attached, but more fre-
quently free (Figs. 85, 88). As regards the interior structure
of these bodies we find that those without any granules present
a striated appearance, as if their interior consisted of a fine
network. By the use of the congo-thionin-ruthenium method
these fibers can be stained bluish, while the other parts re-
main red. }
The structure of the smaller bodies with the granules is
quite different. There is no sign of any fibrillar structures
nor of any network, but they are seen to contain from one to
five dark-staining granules, mostly arranged along the sides of
the wall of the main body. These bodies vary very consider-
ably in size, some being many times larger than the others.
If we consider the origin of these bodies, large or small, there
seems to be only one theory that is plausible, that they are
bodies expelled from the cells. A perusal of the figures re-
ferred to above makes this supposition also probable. We see
on the surface of many cells bodies exactly similar to those
which are free; at the same time we find in the interior of the
same cells bodies of a similar appearance. From my observa-
tions I judge that the bodies with the granules are expelled
accessory archosomes, while those without granules are ex-
pelled fragments of the spheres. The increase in size can be
NG; i) SPERMATOGENESIS OF BATRACHOSEPS. L7
due to a swelling up of the bodies as soon as they enter the
intercellular liquid. Bodies of both kinds accumulate often in
very large masses between the cells and are often found in
complete dissolution. In another place I have suggested that
the expulsion of the centrosomes is affected when there are
too many archosomes in the cell, more than are necessary
to accomplish the mitosis of the cell.
Karyosome or Nucleus.
General Remarks.— The constituents of the nucleus may, in
a general way, be divided into three parts: vzz., chromatin,
linin, and nuclear wall. But as the nuclear wall is probably
only a thickening of the linin, just as the cellular wall is only a
thickening of the cytoplasm, we may dispense with the third
division and simply divide the nucleus in two distinct parts,
chromatin and linin. In this general division we must include
under chromatin such bodies as the chromoplast, directly to be
described, while under linin we must arrange the other class
of nucleoli, the linoplast, also to be further described below.
But while it seems that the true nucleoli or linoplasts are
principally of importance in furnishing or regulating the sup-
ply of linin, I must concede to the chromoplast a much more
important function, that of regulating the formation of the
chromosomes. It seems to me probable that the chromoplast
has the same function to perform inside the nucleus as the
archosome outside of the nucleus, and that while the archosome
regulates the radiosomic process or the formation of the spindle
and the final separation of the chromosomes, the chromoplast
regulates the chromosomic process inside the nucleus.
The following elements of the nucleus are distinguished
and will be described more in detail below: chromioles, chro-
momeres, chromosomes, endochromatic granula, parachromatic
granula, chromoplast, chromoplasm, linin, linoplast, and nuclear
membrane. These constituents are not of equal value and
importance. The chromioles, the chromoplast, and the linin
granula are the most permanent elements of the nucleus. All
the other constituents of the nucleus, such as chromosomes,
chromomeres, and linoplasts are only temporary and not
18 ; EISEN. [Vou. XVII.
permanent organizations. As regards the nature of the para-
chromatic granules we do not know anything with certainty,
but it seems probable that they are of great importance.
The Chromioles.— The chromioles are the smallest visible
organized parts of the chromosomes. They undoubtedly con-
stitute the most important parts of the chromosomes, the fun-
damental elements which the other parts of the chromosomes
only serve to nourish and to preserve. If we view a perfectly
fixed and stained chromosome during any of the mitotic
phases, we find that it is not a homogeneous body, but one
that shows considerable differentiation in a regular manner.
We first observe that the outline or margin of the chromosome
is not an even one, but one which shows deep indentations of
even size and number. These indentations are so arranged
that the chromosome appears to be more or less beaded; that
is, a convexity on one side corresponds to a convexity on the
other side, and a concavity similarly corresponds to a concav-
ity. We moreover find that these beads are of a constant num-
ber, at least in chromosomes of average size. A chromosome
of Batrachoseps in the beginning of the metaphase of an auxo-
cyte contains just six such beads, the beads being identical with
chromomeres. A closer study of one of these chromomeres
shows that they are not of a homogeneous structure, but that
each one of them contains several interior round granules, sur-
rounded by an apparently homogeneous substance. These
granules, for which I propose the name of chromioles, are
of globular form and of equal size (Figs. 53, 54, I12,
120, etc.). I need not point out the necessity of having the
chromosomes properly stained. If too dark, the chromioles
will not be seen, but the whole chromosome will appear as a
solid homogeneous mass of chromatin. Even when the chro-
momeres have been so fused together that the margins of the
chromosomes are only slightly wavy, the chromioles are yet
distinct enough not only to be seen, but under favorable cir-
cumstances to be actually counted. A very good view is had
of the chromioles in the chromosomes, of which Fig. 112 gives
as correct a representation as it was possible to make. Of
course, instances where chromioles are as distinct as these
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. I9
are comparatively rare. In most instances they can only be
counted here and there in the same chromosome, the trouble
generally being that the chromosome has not been properly
differentiated. But wherever glimpses of the chromioles are
had it will be seen that they are arranged in rows, one row on
either side of the chromomere, and parallel to the longer axis
of the chromosome. As is to be expected in a case like this,
where we view an object of so small a magnitude that it lies
on the limit of vision, it is a most difficult matter to count the
chromioles and to be sure that the count is correct. I have
made a number of countings, almost wherever I found a suit-
able opportunity, and the result is that I consider the number
of chromioles constant in every chromosome of regular size.
Thus in the metaphase-chromosome of the auxocytes and sper-
matocytes there are three chromomeres in each prong, or six
chromomeres in all, making six chromomeres for the whole
chromosome. Each chromomere contains six chromioles,
three at each margin, which makes thirty-six chromioles for
the whole chromosome. The regularity of the chromioles,
both as regards number, size, form, and arrangement, precludes
the possibility of their being artefacts, and we have no alterna-
tive but to assume that they are bodies of permanent structure
and of the highest importance. The question now arises, to
what extent can we trace the chromioles, backwards as well as
forwards, in the development and evolution of the chromosome.
This subject will be more particularly entered into when we
discuss the development and evolution of the nucleus, and
here it must suffice to give only a brief outline of the results
of my observations. The chromioles can be readily observed
in all the different stages through which the chromosomes pass,
except in the confluent umbrella stage in which I have so far
not been able to view them with any degree of satisfaction and
clearness. In that stage there exist in the confluent mass
besides the endochromatic bodies numerous dark staining gran-
ules, but they are irregularly scattered and stain darker than
the chromioles in other places. But while the persistence of
the chromioles in this stage has not been satisfactorily demon-
strated, it is at least highly probable, as immediately when the
20 ELSE WN. [VoL. XVII.
chromosomes begin to reappear from the confluent umbrella,
the chromioles appear at once and as well defined as ever. We
therefore must assume either that during the confluent stage
the chromioles do not stain sufficiently to be distinct one from
the other or from the chromoplasm surrounding them, or that
those globules which are observed there are actually the chro-
mioles, though less regularly arranged.
In all previous stages of chromosomic evolution the chromi-
oles are distinct in almost every chromosome, and, as I have
said, may in favorable instances be counted. Beginning with
the resting stage of the nucleus of the polymorphous spermato-
gonia, we find that the chromioles are the only parts of the
chromosomes which are distinctly visible or regularly organ-
ized. In this stage the chromioles are not united into chro-
momeres and chromosomes, but occur free in the nucleus and
separated from each other and only connected by a thread of
linin. They do not even appear to be surrounded by the usual
covering of chromoplasm, but are, so to say, strung one after
the other on linin strings, which latter apparently run in the
same general direction (Figs. 1-3).
In a somewhat later stage several, or from two to three,
chromioles are seen to congregate together and form the
beginning of a chromomere, as, for instance, in Figs. 4, 5,
etc. In a later stage the chromomeres are yet more dis-
tinct and they are then seen each to contain three chromi-
oles, situated very close together and surrounded by a thin
film of lighter staining chromoplasm (Figs. 12-14). When
again at a later stage the chromomeres have been perfectly
formed, we find that each chromomere contains six chromioles
and the supposition lies near at hand that each individual
chromiole has divided in two (Fig. 15). The chromioles are
now so arranged that three and three are on each side of the
chromomere, there appearing between them a lighter staining
line which may be followed all through the leader or spireme
segment. When this segment splits in the next stage the
splitting is carried along this line, and the newly split half will
thus only possess three chromioles in each split chromomere.
But when at a later stage the chromomeres have formed into
No: 1] SPERMATOGENESIS OF BATRACHOSEPS. Bi
their final number, then we find that each chromomere con-
tains six chromioles, just as before (Figs. 24, 48, etc.). As the
chromomeres fuse into each other, the chromioles also become
correspondingly more closely set and finally they appear in the
chromosome as two parallel strings imbedded in a common
sheath of chromoplasm. This leads us up to the very point
from which we started, the perfectly formed chromosome in
the metaphase. We can, if we wish, follow this process - all
through the evolution of the polymorphous spermatogonia, the
auxocytes, the spermatocytes, and partly also into the sperma-
tids, though the latter are so minute that their finer structure
can be less satisfactorily studied. In order to test the existence
of chromioles in chromosomes of other animals, I have fixed
testes, by the iridium-chloride method, of a number of other
animals, especially of insects, and I am thus able to state that
in every instance where the chromosomes are of sufficient size
to allow of a closer study, I have been able to demonstrate
satisfactorily the existence of the chromioles. They are espe-
cially well defined in species of orthoptera (Stenopelmatus).
From the above observations I conclude that the chromioles
are permanent structures in the chromosomes, and that they
are the smallest visible individualized and organized parts of
the chromosomes, and further that the chromoplasm, the chro-
momeres, and the chromosomes are merely structures for the
conveyance of, the nourishing of, and the partition of, the
chromioles.
There yet remains to say a few words about the division of
the chromioles. The proper increase of the chromioles is, of
course, an absolute necessity, provided we are correct in assum-
ing them to be the most important parts of the nucleus. As
the chromioles are too small to allow of any direct observation
as regards multiplication, all speculations on this subject are as
yet premature. The counting of the chromioles is a most diffi-
cult matter, as not even under the most favorable circumstances
can all the chromioles in the same chromosome be counted.
The best we can do is to approximate and average their num-
ber. I have stated that in the early anaphase we find at each
pole twelve chromosomes, each one containing about six more
22 EISEN. [Vou. XVII.
or less distinct chromomeres, and that every such chromomere
possesses about six chromioles. This makes 432 chromioles in
all for the daughter-nucleus.
When the nucleus of the following cell, the spermatocyte,
enters the metaphase we find the chromosomes in the shape of
split ”’s. The chromomeres in these are double and appear
to contain each six chromioles, or seventy-two for each chromo-
some. As there are twelve chromosomes, each equatorial plate
should contain 864 chromioles, which, after the equation-divi-
sion of the chromosomes, would again give to each daughter-
nucleus the same number as formerly, or 432 chromioles.
From this we are justified in assuming that during the conflu.
ent umbrella stage of the nucleus the chromioles have been
doubled. The easiest way to explain this increase is to assume
that each chromiole has been divided in two, thus presumably
preserving the quality while increasing the quantity. It is not
improbable that one of the objects of the confluent umbrella
stage is to allow the undisturbed division of the chromioles.
The Chromoplasm. — By the chromoplasm I understand the
apparently homogeneous substance which directly surrounds
the chromioles during all stages of their existence, except,
perhaps, while they pass through the resting stage in the
polymorphous spermatogonia (Figs. 1-3). In this stage the
chromioles appear to lie free in a linin thread, at least there is
no visual evidence of their being surrounded by any chromo-
plasm. That each chromiole is actually surrounded by a thin
film of chromoplasm is, however, probable. As soon, however,
as the chromomeres are beginning to form, then we can see
that the individual chromioles are imbedded in a homogeneous
substance for which I propose the name “‘chromoplasm.”’ It is
the chromoplasm which gives the chromosomes their general
form, appearance, and color. The chromoplasm constitutes
by far the greatest part of the chromosomes, and it appears to
be the vehicle for conveying and nourishing the chromioles.
As regards the want of chromoplasm in the polymorphous
nuclei, we may assume either that the chromoplasm has been
disintegrated or been used up as food for the chromioles, or we
may suppose that the chromoplasm has become concentrated in
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 23
the body, which I will directly describe as the chromoplast. It
is quite possible that both these processes have taken place, as
the chromoplasm found in the chromoplast is not sufficient to
account for the quantity found in the chromosomes at a later
stage. That the chromoplast has something to do with the
formation of the chromoplasm is more than probable, because
at the time when the spireme segments are being formed, the
chromoplasm is seen to be thicker nearer the chromoplast,
while at the distal end from the chromoplast the chromoplasm
is thin or very thin. It sometimes seems as if the chromo-
plasm had flowed from the chromoplast and been gradually
distributed all along the spireme segment. It seems also prob-
able that the chromoplasm is a prominent constituent in the
chromoplast — at least the only visible differentiation between
the chromoplasm in the spireme and the chromoplasm in the
chromoplast is that the former stains less intensely than the
latter. In most papers on cytology the chromosomes are
figured with their margins drawn out into the linin network.
I think this is probably an error caused by imperfect staining,
as in all my best preparations I could distinctly see that the
chromoplasm always possessed a rounded margin, and that the
points consisted exclusively of linin which at times may be so
stained that it cannot be distinguished from the chromoplasm.
The Chromomeres. — But little need be said about the chro-
momeres, as they will be again referred to in describing the evo-
lution of the nucleus. The chromomeres begin to form as soon
as the nucleus of the polymorphous cells enters the imperfect
resting stage. The chromomeres are formed in the follow-
ing manner: Two, and later three, chromioles which, during
the perfect resting stage, were suspended singly in the linin,
come together and are at the same time seen to be surrounded
by a thin layer of chromoplasm, thus forming a small isolated
body suspended in a linin network. The chromoplasm soon
increases in quantity, and the chromomere is in this way in-
creased in size. The number of chromioles present in each
chromomere is not always the same in the early prophases, and
some chromomeres may possess twice the number of chromi-
oles as some others. Still the number is fairly constant, gen-
24 EISEN. [Vor. XVII.
erally being three. There are more chromomeres in the early
spireme stages than in the later ones, and as these early ones
also are smaller, it appears as if the later chromomeres are the
results of the fusion of several smaller ones. In the perfected
bouquet stage there are, as a rule, about a dozen chromomeres
in each spireme segment (Figs. 15, 121). Those nearest the
chromoplasts are larger and possess more chromioles than
those more distant. When the chromomeres split there is
almost, without exception, six chromioles in each. With the
splitting of the spireme segment the chromomeres again lose
their identity to a considerable extent, appear smaller, and
are more numerous; the chromioles also are smaller. But
these chromomeres fuse again into larger chromomeres, and
when in the contraction stage the bretzel-shaped chromosome
is formed we find that it possesses twelve chromomeres, each
one with six chromioles (Fig. 121 £). The new or daughter-
chromosome, which results from the equation division of the
bretzel, contains only six chromomeres, each with six chromioles
(Fig. 121 7). From this time on the chromomeres gradually
lose their identity, and more and more fuse together until at
last, at the end of the anaphase, they have become so confluent
that no trace of their original form remains. But as soon as
the nucleus begins to reconstitute itself the chromomeres at
once reappear (Figs. 62, 118). The number of chromioles at
this time is uncertain. The following stage of growth of the
nucleus is characterized by a greater separation of the chromo-
meres (Fig. 119). The typical number of chromomeres in the
chromosomes of the spermatocyte is the same as in the chro-
mosomes of the auxocyte, or six in each. The exact number
of chromomeres which go to make up a chromosome sometimes
varies. Thus we now and then find chromosomes with only four
chromomeres instead of six, but we may then always expect to
find that some other chromosome possesses eight chromomeres,
and that in this way the proper number is made up. From the
above it will be seen that the chromomeres cannot be considered
as permanent organs of the nucleus or more in particular of the
chromosome, but that they are merely convenient forms of struc-
ture, the object and function of which is to facilitate the hand-
INO: Es] SPERMATOGENESIS OF BATRACHOSEPS. 25
ling of and the disposition of the chromioles. The definition
of a chromomere would thus be this: A small body of chromi-
oles surrounded by or imbedded in a matrix of chromoplasm,
the object of which is to facilitate the growth, nourishment, and
multiplication of the chromioles.
Leaders. — As leaders I designate the threads or filaments
of chromoplasm in which are suspended the chromioles in the
earliest stages of nuclear activity. The chromoplasts which
first lie free seem to attract a certain number of such threads,
which radiate out in different directions from the chromo-
plasts. In the beginning the leaders are of a varying number,
— how many is difficult to say, but decidedly more than twelve ;
but as the process goes on they diminish in number, and at
the end of the process they are found to be only twelve, or just
as many as the future chromosomes.
The exact process of this formation has not been properly
followed, but it seems as if the chromioles actually passed
through the chromoplast and were projected through it into
the leaders. At least we find at that time in the chromoplasts
granules which greatly resemble the chromioles in size and
form, besides being of the same nature as regards their staining
qualities. I have often found that the free, distal ends of the
leaders were twelve in number, while the ends attached to the
chromoplasts were more than twelve; and this fact I can only
explain by assuming that the chromioles are pushed into the
leaders from the chromoplasts, or, in other words, that the free
ends of the leaders are finished first and that their ends, which
are attached to the chromoplasts, are the last parts to be per-
fected. At the end of this process we find that there are
twelve leaders which rest their free ends on the nuclear wall
nearest the spheres, while their main parts are twisted and
bent in the cavity of the nucleus. If this supposition is cor-
rect, then the process would be something like this. The
chromoplasts attract chromioles from all sides and take them
up inits plasma. They are then again expelled into twelve
leaders, which latter are being fed with chromioles from the
chromoplasts. The leaders attached to the chromoplasts
would thus be of two kinds: one set, the genuine leaders,
26 EISEN. [VoL. XVII.
which pass from the chromoplasts, and the other set merely
strings of chromioles which pass into the chromoplasts, again
to be expelled from them into the regular leaders. The
formation of the chromomeres would, of course, take place
in the regular leaders, or possibly even in the chromoplasts.
Auxocyte in the ‘‘imperfect resting stage,’’ showing the formation of leaders consisting
of round chromioles surrounded by a film of chromoplasm. The leaders start from two
chromoplasts of unequal size, both containing endochromatic granules. The leaders are
connected by a linosomic network. Four linoplasts. In the cytoplasm are seen the two
spheres, the inner one, the granosphere, containing the archosome. There are eight acces-
sory archosomes, some in the plasmosphere, others in the cytoplasm. The two spheres
are of a foam-like structure. The cytoplasm is only partially indicated.
The Chromosomes. — The chromosomes are not in any sense
permanent organs of the nucleus. They arise, disappear, and
are re-formed as the case requires ; in fact, are mere convenient
structures for the proper division and nourishment of the
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 27,
chromioles. A chromosome is built up of a certain constant
number of chromomeres without any other additional part than
a chromoplast. A chromosome may thus be termed a string
of chromomeres attached to a chromoplast. The formation of
chromosomes is of a necessity different in the different varie-
ties of cells. In the polymorphous spermatogonia, where a
resting stage occurs in the nucleus, the chromosomes originate
from leaders or strings of chromioles, in the way that has been
partly described in the preceding paragraph. This is the case
also in the auxocytes. The leaders finally contract, their
chromomeres approach each other and finally fuse. When
the required number of chromomeres have formed, the leader
splits lengthwise, and shortly afterwards the two halves sepa-
rate and spread out. At the same time the chromoplasts
divide in as many parts as there are leaders, one part remain-
ing attached to each leader (Fig. 122). The next step is a
further contraction of the leader, which again is followed by
a twisting of its free ends, thus forming the bretzel-shaped
chromosome. The mitosis of the chromosomes will be treated
under the heading of mitosis.
In the spermatocytes the chromosomes appear from the
confluent umbrella stage in the form of staples, with strongly
marked chromomeres, and with the chromoplast attached to the
angle of the chromosome instead of to the end of one of its
arms, as in the auxocytes. The chromosome in each cell
variety is characterized by a certain number of chromomeres ;
in the auxocytes and spermatocytes they are six, though now
and then we find some chromosomes larger than others. When
such is the case we at the same time find very small chromo-
somes with a smaller number of chromomeres, thus making the
number of chromomeres and chromioles the same for every
nucleus of the same kind of cell. In the mitosis of the poly-
morphous cells we find the number of chromosomes to be
twenty-four, but in the auxocytes, as well as in the spermato-
cytes, the number of chromosomes is reduced to twelve. The
reduction in number takes place in resting stages of the auxo-
cyte, and is due to the chromoplasts which project only twelve
leaders instead of twenty-four, as in the polymorphous cells.
28 EISEN. [VoL. XVII.
In the polymorphous cells the chromosomes divide through
common or somatic mitosis; in the following stages the auxo-
cyte divides through heterotypic mitosis, while in the sper-
matocytes the mitosis is the homoeotypic one.
In the end of the anaphase of the two maturation cells the
chromosomes enter an almost perfectly confluent stage, in
which the individual chromosomes have lost their individuality,
being fused into a single umbrella-like mass. From this mass
the individual chromosomes reappear, but it seems almost
incredible that the new chromosomes should be composed,
each one of them respectively, of the same identical chromo-
meres and chromioles as before mitosis.
The changes which the chromosomes undergo in the matura-
tion cells will be more particularly described under the chapter
on mitosis. The chromosomes of the spermatocytes possess
the peculiarity to take the congo stain after the haematoxylin,
which causes them to appear reddish-black instead of pure
black, as do the chromosomes of the auxocytes.
The chromosomes of the auxocytes are bretzel-shaped, while
those of the spermatocytes are /-shaped before mitosis. The
bretzel form is due to the fact that the ends of the chromo-
somes overlap each other instead of growing together.
The chromosomes in all these varieties of cells divide by
equation division, and not by reduction division.
The Chromoplast and the Endochromatic Granules. — This
body, which I consider to be of the greatest importance in the
evolution of the nucleus, has been variously known as nucle-
olus, netknot, karyosome, etc., but as these names have also
been applied to other structures in the nucleus, I consider my-
self justified in proposing for it a new and more distinct name,
the ‘‘chromoplast,” thus indicating at least one of its char-
acteristic properties in connection with the chromosomes.
In the Batrachoseps testes the chromoplasts are most dis-
tinctly individualized in the resting stages of the nucleus, and
in those stages in which the chromosomes have not yet reached
their final and perfect form. They may, however, still be seen
in the metaphase of the auxocytes, but after that stage is passed,
they become less distinct, or may even so fuse with the chromo-
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 29
somes that they cannot always be distinguished from them. In
the resting stages, however, the chromoplast or chromoplasts, as
there may be several, stand out quite distinctly and individual-
ized and can then be studied to the best advantage. This
refers not only to the resting stages of the polymorphous
nuclei, but also to those of the auxocytes, the spermatocytes,
°
So 6°
° ary
i)
°
°
¢
°
°
°
°
A polymorphous spermatogonium in the “‘ perfect resting stage.” The form of the nucleus allows
the most perfect metabolism. Numerous chromioles are connected by a thread of chromo-
plasm. A network of linosomes is partially indicated, the individual granules being con-
nected by linopodia. A large, oblong chromoplast with endochromatic granules. Eight
parachromatic granules. A single archosome in the cytoplasm, the latter only partially
indicated by small open circles. A single large, round linoplast, with seven endonucleolar
granules.
and the spermatids. In the two first-named cells, which also
are the largest, they offer the best facilities for study.
In the perfect resting stage of the polymorphous nucleus we
find always one, but sometimes two or more chromoplasts,
easily distinguished by their capacity for intense staining.
When the iron-haematoxylin-congo stain is used the chromo-
plasts become stained, as a rule, most intensely black, while
the true nucleoli, or linoplasts, take the congo and become
red. The chromoplasts are also characterized by possessing
30 EISEN. [VoL. XVII.
in their interior several highly refractive bodies which I have
termed ‘‘endochromatic granules.” These granules never occur
in the true nucleoli, which fact always enables us to distinguish
between them and the chromoplasts, even in instances when
the true nucleoli are stained darkly, as sometimes happens.
The endochromatic granules never stain, but appear to be
naturally of a yellowish color and always highly refractive.
They vary in size, and are sometimes so small that their refrac-
tivity is not readily perceived, they appearing only as minute
granules of an intensely dark color. But as they increase in
size we begin to see in their center a light-colored, highly bril-
liant spot, which, in the larger granules, is correspondingly
large and distinct. These refractive granules are almost invari-
ably present, and they may be truly termed “landmarks,” by
which we can determine the position of the chromoplast.
Even in places where the chromoplast itself cannot be dis-
tinguished we can judge of its presence by one or more of these
endochromatic granules, as, for instance, in the metaphase and
anaphase of the auxocytes. It is the presence of these gran-
ules which enables us to follow with certainty the evolution of
the chromoplasts, and to ascertain their presence in every stage
of the nucleus. The number of granules in each chrorhoplast
is in no way constant and seems to be of no great consequence.
Some are perfectly round, others are angular, and their general
appearance seems to indicate that they constitute secreted
matter, or metabolic products, probably for the attraction and
nourishment of the chromioles. While each granule is highly
refractive in the center, its outline is, on the contrary, very dark,
so dark indeed that it would almost seem as if it was surrounded
by a shell of some particular substance. Whether that is the
case, or whether the dark margin is only the effect of refraction,
I have not been able to ascertain. In the small chromoplasts
attached to the chromosomes in the metaphase we sometimes
find one or two endochromatic granules, sometimes also none.
In the confluent umbrella stage of the nucleus we generally
find a larger number of granules which appear to have been
newly secreted. They disappear at the end of the umbrella
stage, though a few may remain even after the nucleus has
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 31
begun to reform and after it has fairly entered its stage of
growth. For characteristic figures illustrating the endochro-
matic eranules see: Pigs: 2, 9, 21, 26, 57-62, 121.
The chromoplasts are generally rounded in outline and well
defined. When insufficiently differentiated and overstained
they frequently appear to be star-shaped and very irregular,
but this is merely an effect of the overstaining. While the
form is always rounded, it is not always globular, but, on the
contrary, oblong or beaded, especially in places where we
expect a division of the chromoplast. In the earliest stages of
the polymorphous nuclei the chromoplast is generally oblong
or consists of two distinct beads (Figs. 1-3). It lies then iso-
lated in a vacuole, only surrounded by linin threads radiating
from it in every direction. Ata later stage the chromoplast
is seen to be in more or less intimate connection with the
leaders on which the chromioles are suspended. To begin
with this connection is very slight (Fig. 3), but later on it
becomes more intimate, and leaders with chromioles are seen
to start out in all directions, radiating from the chromoplast
like the radii from the center of a circle. When there is more
than one chromoplast, leaders connect with all.
Some chromoplasts, however, may be connected with more
leaders than others (Figs. 8, 9). In the last resting stages,
when all the leaders have formed, it will be seen that all of
them connect with the chromoplasts in such a way that if,
for instance, one of the chromoplasts is connected with only
four leaders, the other is found to be connected with the bal-
ance, z.¢., eight ; there are always as many leaders as there will
be chromosomes. The chromoplasts appear thus to attract the
leaders, and my opinion is that in this manner the chromosomes
are formed. We can follow the chromoplasts with certainty
up to the end of the anaphase. In the bouquet stage, where
the spireme segments begin to separate from each other, it will
be seen that this separation is caused by a division of the chro-
moplasts into several parts. In the perfect bouquet stage we
thus find that two or more spireme segments are held together
by a single chromoplast (Figs. 14-16). The ultimate result
of this division is undoubtedly to so divide the chromoplast
32 EASE. [VoL. XVII.
that one part will remain attached to each chromosome. This
is also undoubtedly what takes place, as in the metaphase
when the chromosomes are all perfectly formed and placed on
the central spindle in the form of rings, we find that at the
center of one side of each ring is a globular body, frequently
An auxocyte in the ‘‘bouquet stage.”? There are twelve leaders starting from five chromo-
plasts. The leaders consist of chromomeres containing chromioles suspended in a
film of chromoplasm. The spheres are of a foam-like structure. There are three acces-
sory archosomes and one archosome with two centrioles. The open space between the
inner granosphere and the outer plasmosphere represents the hyalosphere. The cytoplasm
is only partially indicated.
containing one or more endochromatic granules. These bodies
attached to the chromosomes are, therefore, chromoplasts. In
the confluent umbrella stage the endochromatic granules are
the only indications of the presence of the chromoplasts. This
is the case in the auxocytes. In the spermatocytes the chro-
moplasts are much more difficult to follow, but the greater
Now rs] SPERMATOGENESIS OF BATRACHOSEPS. 33
:
thickening of the chromosomes at the place where they are
bent makes it probable that the chromoplast is situated at this
point (Figs. 118, 119). In the mitosis of the spermatocyte
I have not been able to affirm with certainty the presence
of chromoplasts, except in the umbrella stage, where their
presence is indicated by endochromatic granules. Again, in
the resting stages of the spermatid the chromoplasts, generally
one or two, are plainly definable, especially by the means
of the congo-thionin-ruthenium red-staining method. In the
resting stages of the auxocytes, which are especially favorable
for study, a stream of chromoplasm is seen to project from the
chromoplast to each leader, and each leader is more densely
stained in the parts nearest the chromoplast. I do not, how-
ever, consider it with certainty established that a flow of chro-
moplasm actually takes place, as the phenomenon of deeper
staining can also be explained by a greater attraction of chro-
moplasm in proportion as the chromoplast is approached. If
this latter supposition is the true explanation, then we must
also look for the source of the supply of chromoplasm else-
where, possibly in the parachromatic granules.
Be this as it may, the observed facts warrant us in con-
cluding that the chromoplast is of the utmost importance in
the formation of the chromosomes, and that its function seems
to be to attract the leaders, to segregate and define the chromo-
somes, and perhaps, in a general way, to supervise the formation
and evolution of the chromosomic constituents of the nucleus.
Chromoplasts are probably present in all nuclei, and probably
also in all chromosomes. They have been frequently con-
founded with true nucleoli, but their distinct nature has also
been recognized by many investigators, and in all recent bio-
logical papers they are both described and figured as being of
different nature from that of the so-called true nucleoli. In
many instances, however, they have undoubtedly been over-
looked, especially in nuclei in the bouquet stage, where they
often are so small that they can only be distinguished through
their endochromatic granules, the presence of which always indi-
cates that the object in question is actually a chromoplast, and
not a true nucleolus or linoplast.
34 EISEN. [VoL. XVII.
‘
Parachromatic Granules. — As parachromatic granules I
designate a class of dark-staining granules which, during the
resting stages of the polymorphous nucleus, are found in the
vicinity of the chromoplast (Figs. 1-8). These granules stain
in the same manner as the chromoplasts, and I have not been
able to differentiate them by color. When the leaders are
formed these granules are the first ones to join the leaders, and
it suggests itself that possibly they furnish the necessary chro-
moplasm for the leaders. But as the aggregate of all these
parachromatic granules does not equal the mass of the chromo-
somes we must suppose that, if the parachromatic granules
furnish the chromoplasm, they cause it to be evolved and that
they do not furnish it alone from the amount stored in them.
The parachromatic granules are of various sizes and forms and
vary also as regards number. With certainty they are only
found in the polymorphous cells.
Linoplasts, or True Nucleoli.— The linoplasts are that kind
of nucleoli which supply and nourish the linin during certain
stages of the mitosis. When properly differentiated with congo
they appear rather transparent and of a reddish-orange color.
They are thus readily distinguished from the chromoplasts
which take the iron-haematoxylin stain with great avidity.
The number of linoplasts is variable; sometimes we find only
one, sometimes again there are five or six. In the auxocytes
the linoplasts are most numerous just before the stage in
which the spireme segments are split, after which they gener-
ally disappear. Rarely one is left at the metaphase, and when
this is the case it is thrown out into the cytoplasm and evi-
dently dissolved. During the separated spireme stage the lino-
plasts are seen to dissolve, apparently giving off particles to the
linin network (Figs. 12-17, especially 14). This is also the
very period when the largest quantity of linin is required for
the pulling apart of the two halves of the spireme segments. If
we to this observation add the one that the linoplast consists of
apparently the same kind of granula as the linin network, both
as regards size, form, staining reaction, etc., we are, I think,
justified in assuming that the linoplast actually does furnish the
extra linin required for the pulling apart of the spireme leaders.
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 35
As regards the nature of the shell of darker granules surround-
ing the linoplasts, I have not any observations. This shell
seems to exist only during the resting stages of the polymor-
phous nuclei and not in the maturation cells. Besides pure
linin granules the linoplast undoubtedly also contains secretions
with which the linin is nourished. The function of the lino-
plast appears thus to be not only to furnish stored-up linin, but
also to nourish the general linin network. I hardly need to
point out that the linoplast has been variously termed paranu-
clein, pyrenin, true nucleoli, Kernkorperchen, etc.
Linin.— The linin network is not difficult to differentiate,
as with the congo-iron-haematoxylin method it stains reddish-
yellow, while nearly all other structures take a black or at
least a gray stain. When insufficiently differentiated it some-
times appears as if the chromatin of the chromosomes extends
far out into the linin network; and in this way it is generally
figured. With proper differentiation, however, it is seen that
this is not the case, but that the chromatin is never extended
into the linin, at least never as a fine thread (Figs. 14, 24,
I19, etc.). As long as the nuclear membrane is unimpaired
the linin always has the appearance of fine network, com-
posed of granules of equal size and form. These granules
occur either singly or in small groups, which latter may be
mistaken for larger granular units. In Figs. 14 ¢ and 26 41
have figured these granula in the way they appear under the
most favorable optical conditions, though the individual gran-
ules are perhaps somewhat more rounded than they appear in
the illustrations. We must distinguish between two distinct
periods in the life cycle of the linin, one being the periods of
rest, the other the periods of activity. There are two periods
of rest. One is found in the resting stage of the nucleus
before the leaders have properly formed, and the other occurs
later in those stages of mitosis in which the nuclear membrane
has been dissolved, and the linin been scattered away from the
chromosomes. In the former of these stages the linin gran-
ula are more regular than in the latter (Figs. 1-3, etc., also
Figs. 26, 37). After the nuclear membrane has been dissolved
the linin network is carried away from the chromosomes, and
36 EISEN. (Vo. XVII.
the granules are found both evenly distributed and arranged
in larger heaps. The active stages of the linin are to be found
during the prophases, during the formation of and the separa-
tion of the leaders. It is during this period that the lino-
plasts are dissolved in order to supply the necessary and
extraordinary linin required for this process. The linin is
then seen to consist of a network attached to the chromosomes
or spireme segments, while part of it spreads out through the
nucleus as irregular bridges between the chromatin segments.
The linin possesses thus two distinct qualities, one being
that of supporting the chromioles, chromosomes, or chromatin
parts generally, the other being that of separating the two split
spireme or leader halves from each other. As soon as this lat-
ter process is accomplished the linin is dispersed, at first all
through the nucleus, and later on through the cytoplasmic
part of the cell. The mass of the linin is composed principally
of one kind of granules—the kind here always referred to
as the linin granules. This general granule stains reddish or
gray according to the process of differentiation. But in these
granula we also find scattered isolated granules which stain
only with the iron-haematoxylin stain (Fig. 26 6). Of the
nature of these granula I have no knowledge, but it suggests
itself to me that perhaps these denser appearing granula may
serve as a support for the other kind, insuring an equal or at
least a proper distribution.
It will be seen that during the period of activity the linin
granule stains differently from what it does when in rest. This
differentiation is, however, only brought out by the achromatic
light-filter mentioned elsewhere. With the use of this filter
we find that the linin granule during its activity stains bright
and light red, while during the periods of rest it stains dark
gray. This differentiation also allows us to follow the linin
granules through the cytoplasm after the nuclear membrane
has been dispersed. What finally becomes of these linin
granules is uncertain. But I have no observations which
would indicate that they reconcentrate themselves in the new
daughter-nuclei. On the contrary, there is no sign of any
accumulation of linin granules in the immediate vicinity of the
Noe Fa] SPERMATOGENESIS OF BATRACHOSEPS. 37
new nucleus, and the first appearance of the linin in the new
nucleus is found close to the new chromosomes.
This new linin is, to begin with, of limited quantity, and
it appears as if it were actually re-formed, probably from
some linin granules with a generative function. In such
case the majority of the linin granules are either absorbed by
the cytoplasm or used up in the formation of the new nuclear
membrane.
The Nuclear Membrane.—The nuclear membrane has already
been referred to in connection with the cytoplasmic membrane
and cell wall. The most favorable cell for the study of the
nuclear membrane is the large auxocyte in the beginning of
the chrysanthemum stage. In this stage the new nuclear
membrane is being reconstituted. In case the nuclear mem-
brane is formed by a thickening of or by an accumulation of
cytoplasm, we should expect to find such cytoplasm in the
immediate vicinity of the place where the new nucleus is to be
formed. No such accumulation of cytoplasm exists at this
place. On the contrary, a false, or rather an accessory cyto-
plasmic membrane has previously been formed around the
nucleus, but at some distance from it (Figs. 62, 70). The
object of this membrane is to enable a vacuole to form, in
which the new nucleus can have ample space for development.
While this membrane is yet in existence the nuclear membrane
is formed around the new nucleus. As at this time there is
no cytoplasm between the cytoplasmic membrane and the
chromosomes, the new membrane must be formed of other
matter than cytoplasm. It is probable that this other sub-
stance is linin, of which there is at this time a fair supply
around the chromosomes.
As to the dissolution of the nuclear membrane it is most
interesting to note that, at least in the auxocytes, the mem-
brane is dissolved only after the chromosomes have formed.
The spindle fibers and mantle fibers cannot, therefore, have
anything to do with the formation of the chromosomes. The
nuclear membrane always disintegrates first at those places
where it is first touched by the fibers of the mantle. The cen-
tral spindle has apparently nothing to do with the dissolution
38 EISEN. [VoL. XVII.
of the nuclear membrane, which is fully dissolved before the
fiber of the central spindle has reached its immediate vicinity.
Phylogeny of the Nucleus.—It seems probable that the
perfect resting stage of the nucleus, such as is seen in the
polymorphous spermatogonia of the testes of Batrachoseps,
represents a phylogenetically primitive nucleus, in which the
necessity for the formation of chromosomes and chromomeres
has not yet made itself felt. In the most primitive nucleus
we should expect to find only a limited number of chromioles,
which might be readily manipulated by the chromoplast without
the assistance of chromomeres and chromosomes. But as the
development of the species progressed and more characteristics
were accumulated, we may presume that more chromioles were
required, perhaps in order to propagate these characteristics.
With this increase in the number of chromioles a more compli-
cated system of mitosis became necessary ; hence the very com-
plicated apparatus of spindles, etc., accompanying the mitosis of
all higher cells. In the lowest forms of animal and plant life
the chromioles were probably scattered in the cell itself, just as
we now find them in the nucleus of Trachelocerca, a flagellate
infusorian described by A. Griiber. In this instance there can
be little doubt as to the nature of the granules and that they
are real chromioles. The granules found in many bacteria
resemble also greatly the chromioles of the higher cells; and it
may be possible that in these low organisms the chromioles are
only suspended in the cytoplasm, without any surrounding
nuclear wall.
In the blue-green algae, the Cyanophyceae, we have probably
a similarly primitive nucleus, in which the chromomeres and
the chromosomes have not yet been developed. In a later
stage we should expect nuclei with a nuclear wall, but with the
chromioles free as in the perfect resting cells in the testes of
Batrachoseps. As is well known, many investigators deny the
existence of nuclei in the Cyanophyceae and contend that the
darker staining substance in the center of the cell is nothing
but condensed cytoplasm. But this theory seems to me unten-
able in view of the fact that the Cyanophyceae are highly dif-
ferentiated plants which certainly would require hereditary
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 39
granules for the transmission of characters. If, as I suppose,
the chromioles constitute these granules, then it is probable
that we have to identify the denser protoplasmic mass in the
cell of the Cyanophyceae as being chromioles and not cyto-
microsomes. In connection with this question it is interesting
to note that the nucleus of leucocytes, both in batrachians and
in man, contains only a few chromioles.
The Archosome.
The Archosome Proper: its Structure, Centrosphere, Somo-
sphere, and Centrioles.— As the archosome I designate that
particular structure which takes part in the radiosomic process
of the cell, and which is situated at .the very pole of the spin-
dle, at least during certain stages of the mitosis. The archo-
some consists of the following parts: One
or more interior granules — the centrioles
of Boveri. Surrounding them we find a
generally very thin zone or sphere — the
somosphere. Both the centrioles and the
somosphere stain deeply, the centrioles
much more so than the somosphere, and
it is sometimes difficult to distinguish
An archosome consisting of an
onewromythe other, 1) believe, the word « \ citer:cenaauhere fan tinier
somosphere, with two cen-
trioles.
“centrosome” might, with advantage,
be retained to designate this inner part
of the archosome, consisting of centrioles and somosphere.
Next outside of the somosphere we find a larger, generally
non-stainable, achromatic zone — the centrosphere. This
zone is, however, not always achromatic, but takes the stain
under certain conditions and stains then with plasma stains.
Usually this centrosphere is figured as a round disc, with a
perfectly circular outline, giving one the impression of being
nothing but a vacuole, in the center of which is situated the
centrosome proper. This description of the centrosphere is,
however, not quite correct. While the centrosphere is fre-
quently circular in outline, it is not always so; indeed, I
think that in the majority of instances it is not circular, but
of an amoeboid form.
40 EISEN. [VoL. XVII.
We see projections starting out just like the pseudopodia of
an amoeba, and I have no doubt that these projections must
actually be considered as true amoeboid projections, serving
the very same purpose as do the pseudopodia of the amoeba,
that is, as organs of locomotion and perhaps also of prehension.
Unless we assume the existence of a special organ for the
movement and propulsion of the archosomes and the accessory
centrosomes, their movements and migrations from one part of
the cell to the other are simply unaccountable. But if we
assume, as our observations warrant us in doing, that the
centrosphere is an organ for the propulsion of the archosome,
then these movements become easily explainable. This theory
is yet more affirmed by the fact that the centrosphere is amoe-
boid in almost every instance in which from its position we can
consider it to be in activity, and in the act of moving from
one place to another. On the contrary, when we have reaons
to expect the archosome to be at rest, we also find that the
centrosphere is globular or disc-shaped instead of amoeboid.
This holds good also in regard to the accessory archosomes,
though with them it is more difficult to determine when they
are at rest and when in activity.
We are therefore, I think, justified in assuming that the
archosome, as well as the accessory archosomes, propel them-
selves from one place to another by means of the amoeboid
centrosphere, which sphere, when at rest, assumes a globular
form, but when in activity shows an amoeboid margin, or
pseudopodia.
The position of the archosome is variable, according to the
stage of development of the cell. It may be said, as a rule,
that the archosome is situated either in the granosphere or in
the plasmosphere, when both these spheres are present. In
the prophases of the auxocyte, in which the two spheres attain
their highest development, the archosome is generally found in
the granosphere. It then generally possesses two centrioles which
are either surrounded by acommon somosphere or are sufficiently
apart to have a separate somosphere for each centriole.
The archosome seems to move around in the two cytoplasmic
spheres in a most independent manner, sometimes being found
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 41
in the granosphere, sometimes again on the circumference of
the sphere. At other times it is found a considerable distance
out in the plasmosphere. It is at times impossible to distin-
guish the true archosome from the accessory centrosomes, as
their structure is similar, though we might, with considerable
certainty, assume that the body with two centrioles situated in
or on the granosphere is the true archosome, but even about
this we cannot always be certain. Sometimes there is more
than one such body in the granosphere, while, on the other
hand, two-centrioled bodies are also found in the plasmosphere.
Even when the central spindle is being formed, and at a time
when the archosome is situated at the pole of the aster, we
find in the cytoplasm bodies in no apparent way differing
from the archosome. At other times we find what appears to
be the true archosome connected by a thread-like process with
one or more accessory archosomes (Figs. 10-17, 27-33). This
thread-like connection is the remains of the somosphere which
has been pulled out from the original somosphere surrounding
the archosome from which the budding took place (Fig. 14 a).
Such rings of somosphere are seen almost in every cell, often
in considerable numbers. Why the thread assumes the form
of a ring is not quite apparent, but may be explained by sup-
posing that it follows the inner walls of a vacuole. This will,
however, not explain all forms, as in many instances the thread
on which the centrosomes are suspended circles around the
granosphere, or seems otherwise to be entirely buried in the
cytoplasm. In other instances the granules connected by
the thread are also suspended on the rays of some fiber cone
or on some spindle cone. The granules so suspended are not
as a rule all of the same size and staining capacity, as some
will stain intensely, while others adjoining hardly stain at all.
Frequently this loss of staining capacity decreases as the gran-
ules are situated farther away from the archosome or accessory
archosome from which they budded. The same also often
holds good as regards size, those farthest away being the
smallest. To this general rule there are many exceptions;
small and large granules often alternate, and so do darkly
stained ones, with those that are lighter.
42 EISEN. [Vor. XVII.
As a result of my observations I have come to the following
conclusions in regard to the nature, position, and functions
of the archosome.
The archosome is a specialized accessory archosome, special-
ized for the purpose of conducting the radiosomic process of
the cell. During the resting stages of the cell the archosome
is generally, but not always, situated on the axis of the cell;
during mitosis the archosome is situated at the pole of the cen-
tral spindle. The archosome gives rise to the accessory archo-
somes by budding, and, vzce versa, an accessory archosome may
take the function of an archosome. As the archosome is, as a
rule, found in the concave part of the granosphere, its peculiar
and distinct qualities may depend on some particular food or
stimulus furnished by that sphere.
As regards the functions of the archosome in connection
with the spindle fibers, we find that the mantle fibers, as well
as the central-spindle fibers, start out from the outer margin of
the centrosphere and do not connect with the somosphere or
with the centrioles. I have found this to be the case in every
instance where I could see the pole of the spindle in a favor-
able manner. The fibers or rays are thus not inserted in the
somosphere, but simply join the outer surface of the centro-
sphere. The only rays which are in actual contact with the
somosphere are the contractile fibers, or those fibers which
attach themselves to the chromosomes for the purpose of pull-
ing them apart. The main part of the contractile fibers starts
also from the exterior margin of the centrosphere, but each
fiber is seen to be connected with the somosphere by a very
thin thread of dark-staining substance (Figs. 110-113).
In the early resting stage of the polymorphous cells some-
times neither archosome nor accessory archosomes can be dis-
tinguished. Whether they are at such times situated in the
nucleus or are not stainable I am unable to decide upon, but
the former seems to me the most probable. In many such
resting cells we find one or more darkly staining bodies which,
however, are seldom situated in the axis of the cell. As soon,
however, as the granosphere has assumed a definite form the
two-centrioled archosome is seen to be situated in its center,
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 43
or rather in its concavity. At the poles of the central spindle
we find always one and generally two archosomes. Sometimes
the two are connected by a thin thread of somosphere. Some-
times this thread is double, the two archosomes being situated
at the opposite ends of a dark-staining ring. At the end of
the anaphase the archosomes have gradually diminished in size
and staining capacity, and are then only visible by the most
careful optical manipulation. I have no doubt that in in-
stances where the archosome has not been figured in this
stage of mitosis, the failure to observe it is referable to insuffi-
cient optical means, and not to an actual absence of the archo-
some. In the confluent umbrella stage the archosome is,
however, not to be distinguished. But at this stage the apex
of the central spindle has also disappeared, to reappear later on
below the nucleus. With its reappearance an archosome with
a single centriole is also seen at the pole of the fibers, and we
may with some reason presume that it is the same one that was
previously situated above the nucleus, but which has followed
the central spindle and been pulled through the ring-like
nucleus (Figs. 54-61, 63, 64, 69, 70). As the granosphere is
reconstituted around or near this pole, it follows that the archo-
some will be found in or near the new granosphere. But if
the same archosome will always perform the same function in
the new cell is doubtful; it frequently appears as if the place
of the archosome in the new spermatocyte was taken by some
accessory archosome, already at the pole of some spindle cone.
The Accessory Archosomes, their Structure and Functions.
Expulsion of Superfluous Archosomes. — As the accessory arch-
osomes have already been referred to in the preceding para-
graph, I will here only describe a few points not yet touched
upon. We have seen that the accessory archosomes are quite
numerous, but of varying number. In the earliest stages of
mitosis they are more numerous than in the later ones, and it
appears that they are in some manner used up. At first they
circle around in the spheres apparently without any regularity ;
later on they arrange themselves around the archosome at the
pole of the central spindle. My observations are not conclu-
sive, but they tend to show that the accessory archosomes
44 EISEN. [Vox. XVII.
either direct or actually furnish some substance to the contrac-
tile fibers. They are, during the metaphase and anaphase
stages, found in close proximity to the points from which these
fibers start, and in several instances I have seen them actually
in contact with those fibers. It seems possible that an acces-
sory archosome is first placed in position on the outer side of
the centrosphere, and that it then gives rise to a contractile
fiber by budding (Fig. 111). Again at other times (Fig. 110)
we find these contractile fibers already formed, and yet in their
vicinity a number of accessory archosomes, arranged in a ring
around the archosome. Be this function of the accessory
archosomes as it may, certain it is that they also possess
another function of great importance, that of presiding over
the fiber cones and the pulling of the cytoplasmic membrane
away from the nucleus, while the latter is in a stage of growth
(Figs. 65-71, 114-116). Thus at the end of the confluent
umbrella stage we find them at first situated on the cytoplasmic
membrane with fibers radiating out in several directions. They
soon, however, rise from the membrane, carrying with them
the fiber cones. As the ends of the cones remain attached to
the membrane, the latter is naturally pulled away from the
nucleus. There may be one or more accessory archosomes at
the pole of each fiber cone. When the fiber cones have per-
formed their function the accessory archosomes slide down
along the fibers and congregate in the vicinity where the new
granosphere is being reconstituted. This refers to the sper-
matocytes, as I have not found any fiber cones in the auxocytes.
Towards the confluent umbrella stage in the auxocytes the
accessory archosomes diminish in size, number, and staining
capacity, just as does the archosome. They next reappear on
the cytoplasmic membrane, but are not readily detected except
on sections which pass obliquely or excentrically (Fig. 65).
A most interesting fact is that a large number of accessory
archosomes are thrown out of the cell into the intercellular
spaces, in which they sometimes remain free, sometimes re-
main attached to the outside of the cell membrane. (See the
chapter on paracellular bodies.) The centrioles in the archo-
somes vary in size and number.
No.1.] SPERMATOGENESIS OF BATRA CHOSEPS. 45
IV. SPINDLES AND SPINDLE FIBERS.
General Remarks.
The various fibers and rays which form during mitosis may
be conveniently divided into six more or less distinct classes, as
follows : central-spindle fibers, mantle fibers, polar fibers, con-
tractile fibers, cone fibers, and the retractile fibers of the spin-
dle cones. With the exception of the contractile fibers, which
possibly may be of archosomal nature, all the others are de-
cidedly of cytoplasmic origin; none can be shown to be of
nuclear origin. All these various kinds of fibers stain in
about the same manner, readily taking the congo stain, with
the exception of the contractile fibers, which retain the iron-
haematoxylin longer than any of the others, and thus under
proper treatment appear quite dark, even by their color indicat-
ing a different origin. Their structure is also from the begin-
ning different, showing distinct beads. We will now consider
each of these classes more in detail.
Mantle Fibers, Polar Fibers, and Central-Spindle Fibers.
As these fibers have the same origin and otherwise resemble
each other they may most conveniently be considered together.
The central-spindle fibers are the first ones to appear during
the radiosomic process. As the two centrioles, with their
somospheres, move apart, there appear between them two
darkly staining, narrow threads which apparently help to push
the archosomes apart. Between these two threads the lighter
staining central-spindle fibers begin to appear, but only after
the centrosphere has separated in two parts, one to each archo-
some (Figs. 37, 38). The central-spindle fibers thus originate
from the outer edge of the centrosphere, just as do the polar
fibers and the mantle fibers. But while the polar fibers and
the mantle fibers are fed only from the cytoplasm proper, the
central-spindle fibers receive, almost at once, material from
the granosphere. At a very early stage we see numerous
rays projecting from the archosome to the granosphere, and
this radiation is so arranged and limited that, on the side
46 EISEN. [Vor. XVII.
turned towards the granosphere, all rays which do not strike
the granosphere must be counted as mantle fibers and polar
fibers and not as belonging to the central-spindle fibers (Figs.
41-47). In order to supply this matter to the central spindle,
the granosphere dissolves from the side that is turned towards
the central spindle and not from the opposite side. As the
o
°
°
&
An auxocyte in the beginning of the anaphase. Only a few of the chromosomes are indicated.
At each pole there are respectively one and two archosomes and three and four accessory
archosomes. The chromosomes contain chromioles suspended in chromoplasm. At the
apex of each chromosome there is seen a chromoplast with endochromatic granules. To
the right and left in the cell are seen agglomerations of plasmosphere indicating the
position of the new cell wall, which is to separate the two daughter-cells. The chromo-
somes are seen to be connected with the centriole by contractile fibers, the latter con-
sisting of granules enclosed in a common sheath. ‘The spindle fibers as well as the polar
fibers start from the centrosphere.
central spindle grows in size, the granosphere is seen to dimin-
ish. The rays of the central spindle are also seen to end in
the granules of the granosphere, and the whole appearance is
such as to leave no doubt of the central spindle being fed prin-
cipally on the granules and secretions of the granosphere. On
the contrary, no such connection can at any time be seen
between the polar and mantle fibers on one side and the grano-
NOT] SPERMATOGENESIS OF BATRACHOSEPS. 47
sphere on the other. These two classes of fibers are apparently
only fed from the cytoplasm proper and to a limited extent also
from the granules of the plasmosphere, and this latter probably
only during the metaphase of the mitosis. At that time many
of the mantle fibers are seen to end in the granules of the
plasmosphere (Figs. 48-56). Also during the early anaphase
such connection between the mantle fibers and the plasmo-
sphere granules may be observed. The polar fibers and mantle
fibers sometimes reach the cell wall and connect directly with
it, but generally the fibers end in a marginal layer of alveoles,
which, however, is never as regular as that figured by Biitschli
and his school. These two classes of fibers at the end of
mitosis resolve themselves into plasmosphere and cytoplasm
proper, while the central-spindle fibers reconstitute themselves
into granosphere, or remain for a long time comparatively
unchanged as a spindle bridge between two cells.
There can be no doubt as to the continuity of the central-
spindle fibers from one pole to the other. In the later stages
of the anaphase when the central spindle is being contracted
we can follow without any difficulty the whole course of
one or more fibers from one pole to the other (Figs. 57-62).
hese continuous fibers are much thicker than the early fibers
of the central spindle, and it appears to me as if they origi-
nated by the fusion of several of the earlier fibers. At this
stage of the central spindle the various fibers constituting the
same vary greatly as to thickness as well as to structure.
While some are very thick, others again are as thin as they
were in the earliest stages of the spindle. Some of the fibers
are beaded like the contractile fibers, others are smoother
(Fig. 59) and show only the original structure of alternating
granules. The origin of the central spindle of the spermato-
cyte is less clear. Here the mantle fibers appear first, being
reconstructed fiber cones. These mantle fibers meet and form
a very wide spindle (Fig. 94) with very deeply sunken poles.
At a later stage the central spindle is found inside of this
wider mantle spindle, but as regards the process by which it is
formed, I have no satisfactory observations upon which to base
any theory.
48 EISEN. [Vou. XVII.
Contractile Fibers.
This class of fibers is of sufficient importance and interest
to be treated of separately. Their origin is different from that
of other fibers, and they also appear, partially at least, to con-
sist of a different kind of protoplasm. They are the only fibers
which connect directly with the somosphere and which thus
penetrate the centrosphere. As to the actual beginning of
the contractile fibers, there are no satisfactory observations,
and we do not know if the narrow thread in the centrosphere
orginates previous to the part outside of the centrosphere, but
I am inclined to think that this thin thread is formed after the
balance of the fiber. The number of contractile fibers is the
same as the number of the chromosomes, as there is a special
fiber for each chromosome. These fibers show from the begin-
ning a different structure from any of the other classes of fibers,
being from their first appearance beaded (Figs. 41-54). Each
fiber is composed of a thin outer sheath which is too small
to allow of its structure being perceived. Inside of this sheath
the protoplasm of the fiber is distinctly beaded in a manner
that greatly reminds us of the cytoplasmic arrangement of the
muscle fiber. These beads are not always of the same size,
those in the middle of the fiber often being the largest. There
is never more than one row of beads, which begins on the outer
side of the centrosphere and extends to the immediate vicinity
of the chromosome. Just before the fiber reaches the chromo-
some it divides into two tiny branches or arms, each arm con-
necting with different points of the chromosome. As soon as
the chromosome has reached the equator the contractile fiber
begins to contract, becoming thicker and shorter as well as
darker staining. When the confluent umbrella stage is reached
the fibers lose their intense staining capacity and finally disap-
pear. As regards this disappearance there are several conjec-
tures possible. Either the fibers are entirely absorbed and
changed into cytoplasm, or they are condensed into accessory
archosomes which reappear on the cytoplasmic membrane, at
this time re-forming at a short distance from and around the
nucleus. Or we may even suppose that they follow the central
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 49
spindle and are pulled through the nucleus, later to reappear
as retractile fibers, emanating from the apex of the spindle
cone. Against the latter assumption speaks the observation
that these retractile fibers are not beaded. It seems more
probable that the retractile fibers are new formations, and that
the contractile fibers have condensed into accessory archo-
somes, now appearing on the cytoplasmic membrane around
the nucleus. (See explanation of Fig. 112, p. 116.)
Fiber Cones and Retractile Fibers of the Spindle Cones.
As spindle cones and their retractile fibers, I designate
structures which appear below the nucleus at the end of the
anaphase and from which radiate numerous fibers towards the
place where the new membrane, separating the two daughter-
cells, is being formed. These fibers radiate from a small arch-
osome at the apex of the central spindle and end partly in the
granules and secretions of the plasmosphere, partly in the cell
wall. The separation of the two daughter-cells seems entirely
due to these retractile fibers (Figs. 59-61), which are the only
ones so situated that they can accomplish such a separation.
The plasmospheric granules situated in this immediate vicinity
also indicate that they are used up in the construction of this
membrane. The ultimate fate of these retractile fibers is a
reconstitution into cytoplasm, and perhaps into plasmosphere.
They disappear very soon, long before the fibers of the central
spindle.
We have yet to consider the peculiar and unusual structures
which I have designated as fiber cones, the origin of which is
as follows. A new cytoplasmic membrane is formed exterior
to the nucleus, and on this membrane are found a number of
accessory archosomes. From these archosomes fibers radiate
on the membrane in all directions. Later the archosome rises
and pulls the membrane with it, and we then get a cone-like
structure (Figs. 66-74) which in time pushes out the cell wall.
Later on these cones again move inward, and at a yet later
stage they dissolve into cytoplasm proper. I have already
suggested that these cones help to form a cavity around the
nucleus which enables the latter to increase in size and develop.
50 EISEN. [VoL. XVII.
As far as I know, similar fiber cones have not been observed
in any other animal cells, though I have some reason to think
Two daughter-cells of an auxocyte connected by a spindle bridge. There are eight accessory
archosomes at the apex of as many fiber cones. Two archosomes are connected by a cen-
tral spindle. In the latter is seen a mid-body consisting of three condensation granules.
The chromosomes are being regenerated, and the chromoplasts appear at the angle of the
chromosomes instead of at the apex, as in the last cell stage. In one nucleus are seen
five, in the other six chromoplasts with endochromatic granules. Between the true
nuclear membrane and the false membrane is an open space caused by the false mem-
brane being pulled away by the fiber cones.
that the auxocytes of Batrachoseps are not the only cells which
possess them. Dr. W. J. V. Osterhout has kindly shown me
a preparation of the testes of Triton cristatus, in which I could
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 51
plainly recognize a couple of fiber cones, though they were much
smaller than in the testes of Batrachoseps. These Triton testes
had been fixed in Flemming’s chromo-osmic-acetic mixture. The
spindle cones, which Osterhout has described from the mitosis
of the pollen cells of Equisetum, are exceedingly interesting, as
they recall the fiber-cone structures in our present cells, even if
their nature and origin be found to be entirely different. In the
pollen cells the mitosis begins with spindle cones, while in the
testes of Batrachoseps the mitosis ends with fiber cones.
Spindle Bridge and Mid-Body.
The spindle bridge is, as is now fully known, the remains of
the central spindle. After this spindle has passed through the
nucleus its fibers begin to diminish in number, several fibers
apparently fusing into one. I judge that such is the case, be-
cause as the fibers decrease in number they increase in thick-
ness without getting much shorter. At this stage the fibers
also show a beaded structure in the same manner as the con-
tractile fibers, though not quite so pronounced. This beaded
structure is also found in the fibers of the fiber cones (Fig.
116), but not in any of the mantle fibers.
The spindle bridge remains a long time after the cells have
otherwise separated, and in places we find not only one such
bridge in the same cell but two, both starting from the same
place but in different directions, and connecting several cells
with each other (Fig. 32).
The object of the cell bridge is probably to prevent the cells
from moving too far apart, and the formation of the mid-body
is perhaps only a quick way to dispose of the cytoplasm of the
cell, until it can be properly absorbed in the regular way by the
spheres.
I have in another place suggested that the contemporaneous
beginning of certain stages in the mitosis by all the cells in
the same pocket may be due to some influence exerted or
communicated by the spindle bridge. This body is the only
visible connection between one or more cells in the same
pocket. The spindle bridges are only found between cells
which simultaneously begin the same stage of mitosis.
52 ELSE IN. (VoL. XVII.
The mid-body is found on the central spindle at the end of
the anaphase and is, as has been often described, formed in a
vacuole between the two cell membranes. At the time when
the mid-body appears, the spindle bridge is always greatly con-
stricted in the middle and consists then of a lesser number of
fibers than during its earlier stages. The mid-body appears to
consist of a thickening or a concentration of the cytoplasm of
the fiber at one certain point. Thus there is either one thick
granule (Fig. 62) for each one of the thicker fibers, or there is
one granule connecting several of the fibers (Fig. 63). A solid
plate is never formed, and the individual granules of the mid-
body can always be recognized after proper differentiation. In
Fig. 62 we see how some of the fibers have become beaded
along their whole length, and we can easily understand that
the individual granules of the mid-body can consist of a con-
centration of the granules of the fibers. If this is a correct
explanation of the formation of the mid-body, then it is also
likely that the nature of the mid-body is the same as that of
the granular nodes of the individual fibers; that is, a larger
storehouse for the cytoplasm of the fibers from which the fibers
may quickly draw a supply when, through the separation of the
cells, the spindle bridge is suddenly extended. The mid-body
would thus prevent the bursting of the spindle bridge at times
of unusual strain. Again when the spindle is compressed on
account of the pressure exerted by the retractile fibers, the
cytoplasm of the fibers can be quickly concentrated in the mid-
body, there to be stored for further use. This theory of the
mid-body is supported by the fact that in extended spindle
bridges (Figs. 13, 17, 32, 109) the mid-body is always absent,
evidently then having been used up by the extension of the
spindle bridge.
V. VARIETIES OF CELLS.
Polymorphous Spermatogonia.
As polymorphous spermatogonia I designate the largest kind
of spermatogonia which, during their resting stage, possess
deeply folded or polymorphous nuclei. These polymorphous
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 53
nuclei occur only in the earliest resting stages, but as there
are no other cells possessing similar nuclei, no difficulty will
be encountered in recognizing the cells. In testes from ani-
mals killed in June and July there are comparatively few poly-
morphous nuclei, frequently only one or two, seldom more than
three or four, in each section of a pocket of cells. The other
cells in the pocket are mostly spermatogonia with round nuclei,
neaeente
eo
OR}
fe
°
°
c
°
°
A polymorphous spermatogonium in the ‘‘ perfect resting stage.” The form of the nucleus allows
the most perfect metabolism. Numerous chromioles are connected by a thread of chromo-
plasm. A network of linosomes is partially indicated, the individual granules being con-
nected by linopodia. 5. Round Cell
ee JSpermato-
eG gonia.
par 2S
> 6.4 2
> > &
° ———
eat aa
Las)
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————
SS
SS
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———
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9. Spermatozoa.
Explanation of the Diagram of the Various Generations of Cells in the Testes of Batra-
choseps.
1. Polymorphous spermatogonia, with polymorphous nucleus, somatic mitosis with twenty-four
chromosomes. The daughter-cells of these spermatogonia constitute the following generations 2-s.
2. Spermatogonia with round nucleus, somatic mitosis with twenty-four chromosomes. The
daughter-cells of the polymorphous spermatogonia. There are several generations in rapid succes-
sion, and apparently all alike. These generations are as follows:
3. Spermatogonia with round nucleus similar to No. 2.
4. Spermatogonia with round nucleus similar to No. 2.
5. Spermatogonia with round nucleus similar to No. 2.
6. Auxocytes, the daughter-cells of the last generation of round nucleated spermatogonia. The
change which caused a mitosis with twelve chromosomes takes place in the resting stage. The auxo-
cytes are characterized by twelve chromosomes, a bouquet stage, anda heterotypic mitosis. Equa-
tion division. Fiber cones after the anaphase. One generation.
7. Spermatocytes with twelve chromosomes, the daughter-cells of the auxocytes. Characterized
by the absence of a bouquet stage. Fiber cones with certainty only in the pe homoeotypic
mitosis and equation division. One generation only. The daughter-cells of the spermatocytes are
the spermatids. .
8. Spermatids.
g. Spermatozoa.
62 EISEN. [Vox. XVII.
somic process in arranging the chromosomes on the central
spindle and in pulling them apart. But the process takes no
active part in the formation of the chromosomes.
The chromosomic process again, as the name implies, refers
only to the nucleus and to the formation of chromomeres,
chromosomes, the splitting of the chromioles, and the manipu-
lation of the linin. The united object of the two processes is
to properly separate and divide the chromioles. The chromo-
somic process is presided over by the chromoplasts and the
linoplasts, just as the radiosomic process is presided over by
the archosome and the accessory archosomes.
These two processes are carried through about seven gen-
erations of cells, four of which belong to the polymorphous
spermatogonia, and one each to the auxocytes, the spermato-
cytes, and the spermatids. These five classes of cells divide
according to three distinct kinds of mitosis: the polymorphous
spermatogonia by somatic or regular mitosis (not by amitotic
division), the auxocytes by heterotypic mitosis, the spermato-
cytes by homoeotypic mitosis. As regards the mitosis of the
spermatids I am uncertain, not yet having properly studied it.
I have, however, seen mitotic figures among the spermatids,
hence my supposition that we may possibly have among the sper-
matids two generations. Only the prophases of the somatic
mitosis will be treated of in detail in this paper.
One of the most interesting parts of the chromosomic process
is the change of the mitosis with twenty-four chromosomes to
the mitosis with twelve chromosomes. This change seems
to take place in the imperfect resting stage of the auxocyte
and to be guided by the chromoplast. In the spermatogonia
the chromoplast projects finally twenty-four leaders, while in the
auxocytes the chromoplasts project finally only twelve leaders,
which latter change into chromosomes. As regards the reason
why this change is made and the particulars of how it is made,
we have no satisfactory observations upon which to base any
theories. Whether the reduction is the result of the chromo-
somic process alone, or the effect of a combination of the two
processes, is at present not quite clear; there is, however, one
fact, that would seem to indicate that the radiosomic process,
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 63
to some extent at least, influences the formation of the leaders.
I refer to the fact that at the very beginning of the bouquet
stage those ends of the leaders which are not connected with
these chromoplasts point to the granosphere, and they not only
point to the sphere, but they actually cover a surface which is
just as wide as the granosphere, this fact determining the bou-
quet form. Just before the formation of the bouquet stage the
chromoplasts are situated in that part of the nucleus which is
nearest to the granosphere, but as the leaders are becoming
more defined, the chromoplasts move away from the spheres to
the opposite end of the nucleus, leaving the ends of the leaders
resting on that part of the nuclear wall nearest the spheres.
The ends of the leaders are so placed that at the point of con-
tact with the membrane they are closer together than a short
distance from it. If there thus exists a real influence on the
leaders from the spheres, this influence must be passing through
the nuclear membrane, which at this time, and for some time to
come, remains intact. The reduction in the number of chromo-
somes is certainly not performed by any rays or fibers, as these
have not yet penetrated the nuclear wall.
The Radiosomic Process, or the Evolution of the Spheres,
Spindles, Fibers, Archosome, and Accessory Archosomes.
The radiosomic process begins in the polymorphous sper-
matogonia with the formation of the granosphere (Figs. 1-8).
The cytoplasm proper is then in the form of a very thin shell on
all sides surrounding the polymorphous nucleus. In this cyto-
plasmic envelop a denser area appears (Fig. 2), which is at first
homogeneous, but which later on differentiates into smaller
isolated areas or vacuoles, surrounded by denser staining
granules. At the same time an outer zone is forming of much
larger dimensions, but of less consistency. The outer zone
is the plasmosphere, and the inner one is the granosphere.
While this has taken place in the spheres, the cytoplasm has
spread over the larger part of the cell, having lost its thin
shell-like form. Already, with the first appearance of the
granosphere, there appears also in the cytoplasm one or more
64 ELSEN. [VoL. XVII.
dark-staining bodies, one of which enters the granosphere and
becomes the archosome, while the others remain as accessory
archosomes. The archosome, as well as the accessory archo-
somes, divides. The two-centrioled archosome soon rises above
the granosphere and carries with it a part of that sphere (Fig.
35). Metaplasmic secretions have also appeared among the
granules of the two spheres. The central spindle is formed
by the separation of the two centrioles and by the supplying
of material from the granosphere to the rays formed between
the two archosomes. The polar rays, or fibers, and the mantle
fibers are formed at about the same time. The contractile fibers
are formed, partly at least, of a different material and are from
the beginning of different structure, being beaded and of a con-
tractile nature. The relative position of the central spindle
and the nucleus is alone dependent on the relative position of
the granosphere and the central spindle. The central spindle
is always so situated that a plane passing through its equator
also passes through the granosphere. Numerous accessory
archosomes have formed which probably assist in the forma-
tion of the contractile fibers. There is always one, sometimes
two archosomes at each pole of the central spindle. Before
the poles of the central spindle have reached the opposite sides
of the nucleus, the nuclear membrane has been destroyed by
rays of the mantle fibers (Figs. 41-47). Shortly afterwards the
chromosomes are thrown on the central spindle and taken hold
of by the contractile fibers. After the anaphase or mitosis is
over, a cytoplasmic membrane is formed around the nucleus,
and as this membrane is being pulled away by a set of fiber
cones a vacuole is formed around the nucleus in which the
nucleus has ample room to develop. These fiber cones are
often numerous and as high as seventeen in a single cell. The
cones are formed as follows. The accessory archosomes ap-
pear on the cytoplasmic membrane, and fibers are projected in
various directions on the membrane. The archosomes then
rise above the membrane, pulling with them the fibers, which,
however, remain attached to the membrane with their distal
ends. The cones rise so far as to project high above the
regular circumference of the cell (Fig. 69). This formation
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 65
of fiber cones takes place only in the auxocytes. A new set
of fibers appear radiating from the poles of the spindles after
they have passed down through the ring-like nuclei of the
auxocyte. The object of these fibers is to pull the daughter-
cells apart. The latter part of the radiosomic process consists
in the reconstitution of the spheres and the reassumption of
its original position by the nucleus. With this the radiosomic
process can be considered finished in the auxocyte. In the
spermatocyte it commences in a different manner. Instead of
a central spindle being formed by the separation of the two
halves of the archosome, it is, at least in the majority of
instances, formed by the junction of two opposite spindle
cones.
The fibers of these cones dissolve the nuclear membrane and
by approaching each other form the central spindle. This part
of the radiosomic process I have, from want of sufficient mate-
rial, been unable to study as carefully as that which takes
place in the auxocytes. I do not deny that a central spindle
may be formed in the same manner as in the auxocyte, but I
have failed to find any evidence of such a formation. There
is, however, undoubted evidence that a central spindle is
actually formed by two opposite fiber cones which, receding
from the cell wall, meet in such a way as to form the spindle.
The other parts of the process are the same as that which takes
place in the auxocytes.
To the radiosomic process must also be referred the forma-
tion of the new cell walls which separate the two daughter-cells
and the pulling apart of the two new cells.
The new cell wall between the two daughter-cells is formed
in the following way. Already during the metaphase (Fig. 53)
the plasmosphere has scattered, and many of its granules and
secretions have become located along the equator of the cell.
As the anaphase progresses, this accumulation of plasmospheric
granula becomes more prominent along the line of the future
cell wall. The plasmospheric granula are never distributed
evenly along the equator, but always in isolated rounded
groups (Figs. 54-56). In the figures referred to, the plasmo-
spheric fragments are stained deeper red than any other part
66 EISEN. [VoL. XVII.
of the cytoplasm. Frequently the plasmosphere is seen on
one side of the cell (Fig. 55), and not on the other, and it
seems that this is rather the rule than the exception. The con-
traction of the cell wall commences at the place where the
plasmospheric fragments touch the equator. Just previous to
this contraction the plasmosphere has at that point divided in
two in such a way that one-half of it lies immediately above
the equator, while the other half lies under it, that is, one-half
in each of the future daughter-cells (Figs. 55, 56). In the
mean time the mantle fibers have become connected by their
ends with the individual granules of the plasmospheric frag-
ments, the other ends of the fibers being attached to the
spindle pole. The contraction of the cell wall appears to be
accomplished directly by the contraction of the mantle fibers.
At a stage a little more advanced the ends of the mantle fibers,
which were at first attached to the spindle poles, become
attached to the cytoplasmic membrane around the nucleus
(Fig. 61). Another set of fibers have also made their appear-
ance in the vicinity of the mantle fibers. These fibers, for
which I propose the name of retractile fibers, connect the arch-
osome at the spindle pole, which has now passed through the
nucleus, with individual granules of the plasmosphere (Figs.
59-61), as well as with purely cytoplasmic granules along the
equator. While this contraction is taking place in the equator
of the old cell wall, a change has also appeared in the equator
of the central spindle. Instead of being comparatively dense
and even, larger and smaller vacuoles have formed (Figs. 56,
57). These vacuoles are at first diamond-shaped, with their
longer axis parallel to the spindle axis; but later on they are
drawn out sideways, in the plane of the equator, while at the
same time plasmospheric granules appear along their mar-
gins. The new cell walls appear to be secreted out from these
granules along a double line of parallel walls of vacuoles. As
soon as the two parallel cell walls have formed they are sepa-
rated by the retractile fibers of the spindle cones. There are
thus four processes cooperating in the formation of the new
cell wall: the plasmospheric granules are placed along the
equator of the cell; the central spindle is becoming vacuoled
Nos SPERMATOGENESIS OF BATRACHOSEPS. 67
in the equatorial plane, and the vacuoles are drawn out side-
ways; a new membrane is secreted along the walls of the
vacuoles from the plasmospheric granules; the two walls are
pulled apart first by the mantle fibers, later on by the retractile
fibers of the spindle cones.
A few minor points of this process are of sufficient interest
to be noted. One of these is that in the beginning the con-
traction sinus (Figs. 56, 61) in the cell wall is rounded, while
later on (Figs. 50, 60) it is very acute, thus indicating that, to
begin with, there is only a contraction of the old cell wall,
which, of course, is single, but that later on there is an actual
pulling apart of two parallel walls. Another point is that the
first contraction never takes place all around the cell at the
same time, but always, or perhaps generally, along one side
first. This may either be due to a want of sufficient plasmo-
sphere, or to an effort to keep the cell more steady, or perhaps
to both. It will be seen that the central spindle is the pivot
upon which most all of this pressure is applied, and that the
simultaneous passing of the central-spindle poles through the
umbrella-shaped nuclei can be accounted for by the pressure
exerted by the retractile fibers on the spindle poles, coupled
with a contraction of the central-spindle fibers themselves.
The Chromosomic Process. The Formation of the Chromioles
ento Chromomeres and Chromosomes.
As has already been stated, this process is carried along inde-
pendently of the radiosomic process, but parallel to it. It
takes place in the nucleus principally before the nuclear mem-
brane has been dissolved, and is, during all this time, not influ-
enced by the action of the archosomes or by the accessory
archosomes. It is undoubtedly presided over by the chromo-
plasts and the linoplasts. It begins in the perfect resting
stage of the polymorphous spermatogonia with the formation
of the leaders, and is thence carried on through the different
varieties of cells without any cessation or perfect rest until the
spermatozoa are formed. The whole chromosomic process can
conveniently be divided into the following principal subdivisions:
68 EISEN. [Vou. XVII.
Formation of twenty-four leaders in the polymorphous sper-
matogonia.
Somatic mitosis of the same.
Formation of twelve leaders in the auxocytes.
Longitudinal splitting of the spireme segments or leaders.
Fics. a.-g. represent a broken series of leaders illustrating the formation of the leader and the
chromosome. a.— Isolated row of chromioles surrounded by chromoplasm and suspended
in a network of linosomes; 4. —Chromoplast with twelve leaders of chromioles. From
the imperfect resting stage of the polymorphous spermatogonium ; c. — Chromoplast with
five leaders. Each leader is made up of chromomeres, and each chromomere consists of
three or more chromioles surrounded by chromoplasm. A network of linosomes between
the chromomeres; d.— Three chromomeres, each with six chromioles surrounded by a
chromoplasm and suspended in a network of linosomes; e.— A bretzel chromosome con-
taining chromioles and two chromoplasts with endochromatic granules; 7— A chromo-
some from the metaphase. It contains thirty-six chromioles and a terminal chromoplast
with an endochromatic granule ; 2. — Part of a chromosome from the spermatocyte.
Contraction of the separated halves of the leaders into chro-
mosomes.
Equation division of the chromosomes by heterotypic mitosis.
Confluence of the chromosomes.
No: 1: ] SPERMATOGENESIS OF BATRACHOSEPS. 69
Reconstitution of the chromosomes and a period of growth.
Equation division of the chromosomes by homoeotypic
mitosis. .
Confluence of the chromosomes.
Reconstitution of the chromosomes and a period of growth.
Some of these stages are more composite than others and
include several more or less distinct processes, all of which will
now be considered together. For convenience’ sake and for
greater clearness I have for each one of them adopted distinct
names, under which they will now be referred to. As these
stages also mark the principal stages in the evolution of the
nucleus, the same names will be used for the various stages in
the evolution of the nucleus. It must be remarked that while
the radiosomic process in a general way goes hand in hand
with the chromosomic process, the various substages of each
do not always meet in the same nodes. Thus, for instance,
while generally the contraction of the cell wall begins before
the confluent umbrella stage in the auxocyte, it may also be
delayed until the end of this stage. This shows even more
conclusively that the two processes are, to a great extent,
independent of each other, and that they only meet in order
to perform jointly the mitosis of the chromosomes.
A. The Chromosomic Process in the Polymorphous
Spermatogonta.
Perfect Resting Stage.—In this stage the chromioles are
spread over the polymorphous nucleus and generally separated
one from the other, though they are connected by linin threads,
forming winding lines all through the nucleus. These lines
are not yet connected with the chromoplasts, which lie free in
vacuoles, only surrounded by linin. There are from one to
several linoplasts (Figs. 1-3).
Imperfect Resting Stage.— The threads of linin with the
chromioles connect with the chromoplasts and form leaders.
The chromioles begin more and more to approach each other,
and to form small chromomeres with two or three chromioles
in each (Figs. 8, 9).
7O EISEN, [VoL. XVII.
The various phases of mitosis now follow according to the
somatic process. There are twenty-four chromosomes on
the central spindle, and the result of the mitosis is also
twenty-four chromosomes carried to each daughter-nucleus.
These become confluent, after which the nucleus enters a stage
of growth. In this stage the appearance of the nucleus is very
much the same as in the imperfect stage of rest, just before
the beginning of the mitosis. This stage also marks the be-
ginning of the auxocyte. There are several generations, but
only one with polymorphous nuclei, the others having round
nuclei.
B. The Chromosomic Process in the Auxocytes.
A Stage of Growth, during which the daughter-cell of the
former mitosis increases in size and finally reaches an imper-
fect resting stage. In this stage the leaders are formed and
their ends connected with the chromoplasts, of which there
are two or more resulting from division of the original chromo-
plast. The chromioles are in groups of three, and each group
is surrounded by a film of chromoplasm. The leaders are thus
made up of numerous small chromomeres, connected by a linin
string and suspended in a linin network. There are several
linoplasts of various sizes (Figs. 10, 11). The two spheres are
perfectly formed; a perfect archosome with two centrioles is
generally present in the granosphere.
Bouquet Stage with Twisted Leaders. —In this stage the
leaders have contracted to about one and one-third the diam-
eter of the nucleus. They are bent and somewhat twisted, but
their arrangement is still so regular as to present the appear-
ance of a bouquet. One end of each leader in the bouquet is
attached to the chromoplast, of which at this stage there is one
or a few. There are many chromomeres, several linoplasts,
and a perfect network of linin. The ends of the leaders, or
spireme segments, point generally directly towards the spheres.
This is, however, not always the case, as sometimes the narrow
part of the bouquet points upwards or even in an opposite direc-
tion to the spheres. It appears, therefore, that the nucleus in
the bouquet stages regularly revolves in such a way that the
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. px
spheres remain in the equator. This revolving of the nucleus
is characteristic of all the bouquet stages (Fig. 12).
Perfect Bouquet Stage. — The leaders have contracted more,
and their length is now only a trifle longer than the diameter
of the nucleus. The chromoplasts have divided and the lead-
ers have, to a great extent, separated. Seldom more than two
leaders are connected by a chromoplast. The chromomeres
during this stage diminish in number, two and two fusing
together, so that each one finally has six chromioles instead of
three, as previously. The divided chromoplasts are recogniz-
able by the endochromatic granules (Figs. 13, 14).
Bouquet with Split Segments. — This is the last of the
bouquet stages, in which the chromomeres are twelve in each
‘leader. Each chromomere splits in two longitudinally. Gen-
erally, two leaders are connected by a dividing chromoplast.
One or more linoplasts (Fig. 15).
Separated Segments. — The bouquet stage has been passed,
the leaders have spread apart, and their free ends do not any
more point to the spheres but stretch out in various directions.
Not only the chromomeres, but the whole leader is divided,
and the separated halves twist around each other, only remain-
ing here and there connected through the non-division of cer-
tain chromomeres. Generally, only two leaders are connected
by one dividing chromoplast. Several linoplasts (Figs. 16-23).
Angular Segments. — The separated leaders have now both
contracted and straightened out in such a way as to form even
and nearly straight rods which cross each other at regular
intervals. The chromomeres are not as distinct as in previous
stages. The rods which represent chromosomes are connected,
as formerly, with chromoplasts. The linoplasts have all dis-
solved, and the linin network has become partly disarranged,
its function evidently now having ceased for the time being.
The exact process by which this straightening out of the chro-
mosomes has been accomplished is difficult to explain, but the
object is evidently to untwist the segments and to separate
them from each other. This straightening out could not be
accomplished without an almost perfect fusion of the chromo-
meres (Fig. 34).
72 EISEN. [Vor. XVII.
Irregular Bretzel. — The leaders or spireme segments have
contracted and formed bretzel-shaped chromosomes, two or
more of which are connected by chromoplasts. The chromo-
meres are reconstituting into six larger chromomeres in every
chromosome. The linin network is becoming more and more
disintegrated, separating itself from the chromosomes and
accumulating in a different part of the cell. During this stage
the central spindle is forming, and at the end of the stage the
nuclear membrane is being dissolved by the mantle fibers
(Figs. 35-46).
Bretzel Metaphase. — The bretzel-shaped chromosomes have
separated from each other, a part of a chromoplast remaining
attached to each one of them, but no two are connected
together. The nuclear membrane is entirely dissolved; the
linin granules have mixed with the cytoplasm, and the chro-
mosomes have been thrown on the central spindle and are at
the end of this stage arranged in a ring on the equator of the
spindle (Figs. 47-53).
V-shaped Anaphase.— The equation division of the chromo-
somes has taken place, and the daughter-chromosomes have
been pulled towards the poles in the form of V’’s (Figs. 54-56)
by the contractile fibers. The chromoplast remains stationary
at the end of one of the arms of the chromosome.
Confluent Umbrella Stage.— The chromosomes have con-
tinued to contract and fuse together until they have so com-
pletely fused into an umbrella-shaped, ring-like mass that the
individual chromosomes are no more definable. In this stage
the endochromatic granules become distinct in the umbrella,
indicating the presence of the chromoplasts (Figs. 57-61).
One of the objects of this stage is to allow the chromoplasts
to move from the end of the chromosome to its angle.
Chrysanthemum Stage.—In this stage the chromosomes
begin to reappear, and they are at that time bunched together
and the whole nucleus has the form of a chrysanthemum flower,
the open part being towards the daughter-cell. The chromo-
plasts appear from the start at the angle of the chromosomic
arms. The cytoplasmic membrane formed around the nucleus
is being more and more pulled away, giving the nucleus
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 73
the opportunity for a stage of growth, enabling it to
increase to about twice its former size. In this stage the
daughter-cells become entirely separated, after which they are
to be termed ‘“‘spermatocytes.”’ If we consider the spermato-
cyte to begin with the reappearance of the chromosomes, then
this chrysanthemum stage should be counted as belonging to
the spermatocyte and not to the auxocyte. If we date the
appearance of the auxocyte from the stage of growth, then we
ought also to date the appearance of the spermatocyte from
the stage of growth of the nucleus.
C. The Chromosomic Process in the Spermatocytes.
The Chrysanthemum Stage, in which the chromosomes have
the form of staples and horseshoes. This stage is similar to
the one described as the last one of the previous cell genera-
tion (Figs. 62-70). Numerous fiber cones.
Checkerboard Stage.—The staple-shaped chromosomes of
the previous stage have grown and become elongated, and the
chromomeres have become so separated as to be spread over
the nucleus almost as the squares on a checkerboard (Figs.
71-82). In the first half of this stage the fiber cones are dis-
appearing, either completely or with the exception of two,
which later join to form the new central spindle. The spheres
are being reconstituted during this stage.
Contraction Stage.— The scattered chromomeres again ap-
proach each other and form strongly beaded chromosomes.
The nuclear membrane is being dissolved by the fiber cones or
by the fibers of the new central spindle (Figs. 83-86).
Angular Chromosomes.—In this stage the chromosomes
straighten out and become narrower, cross each other at vari-
ous angles, and the chromomeres become so fused that they
can hardly be distinguished one from the other (Fig. 87).
Knotted Chromosomes. — The chromosomes have separated
from each other to a lesser or greater extent and are thrown in
a knot in the center of the cell. The chromosomes do not yet
have the regular and finished form of V’’s (Figs. 88-91, 94-97).
V-Metaphase. —The chromosomes are in the shape of per-
fect V’’s and are as such thrown on the equator of the central
74 EISEN. [VoL. XVII.
spindle. The V’’s are split and the mitosis is made by an equa-
tion division, the V’’s being exactly halved throughout their
length (Figs. 99-101).
V-shaped Anaphase. — The chromosomes are at the poles in
the form of contracting l’’s (Figs. 192, 193).
Confluent Umbrella Stage. — The chromosomes have be-
come entirely confluent. This phase corresponds entirely to
the confluent umbrella phase of the auxocytes. It possesses
the same general characteristics as that phase, but there are no
fiber cones formed (at least not to the same extent as in that
phase, nor are they as plain or as pronounced, if they actually
exist). The same kind of cytoplasmic membrane is formed
around the nucleus which enters a reconstitution stage, just as
in the auxocytes. From a want of sufficient material this stage
has not been thoroughly studied (Figs. 104-108).
Transition Chrysanthemum Stage, in which the nucleus is
reconstituted through a stage of growth, the chromosomes
passing through a chrysanthemum stage into a checker-
board stage, as in the auxocyte. This is the last stage in
the life cycle of the spermatocyte and also the first stage of
the spermatid. As I expect to make the spermatids and their
evolution into spermatozoa the subject of a special paper, I
give here only a single figure of a perfectly formed spermatid
(Fig. 109).
As regards the various stages of the chromosomic mitosis of
the auxocytes, I will only offer a few remarks.
Accessory Archosomes. — All archosome-like bodies found in
the cytoplasm, and which have the same structure as the true
archosome, that is, consist of centriole, somosphere, and cen-
trosphere. Siderophile granules of A. Bolles Lee. The acces-
sory archosomes differ only from the archosome in function, the
latter presiding over the formation of the spindle. They origi-
nate from the archosome (Fig. 69).
Alveolt. — Rounded or variously shaped vacuoles, surrounded
by granules. They contain secretions of various kinds, accord-
ing to the structure in which they are found.
Angular Segments. — The spireme segments have con-
tracted and straightened out, and have become of uniform
thickness throughout (Fig. 34).
Archosome or Spindle Archosome.— The perfectly developed
archosome which guides the formation of the central spindle.
It generally dwells in the granosphere when it is not situated
at the pole of the spindle. It is composed of an outer centro-
sphere, an inner somosphere, and one or more interior centri-
oles. It is not an integral part of the granosphere. The
archosome gives origin to the accessory archosomes by bud-
ding. The granosphere and the plasmosphere are not parts
of the archosome. The word “archosome”’ was first proposed
by me in my paper on the Plasmocytes of Batrachoseps.
Auxocytes. — This name was first proposed by A. Bolles Lee.
The first maturation cells, the last generation of daughter-cells
of the polymorphous spermatogonia. Only one generation. The
mitosis is heterotypic with twelve chromosomes, and is charac-
terized by the bouquet stage. Mitosis by equation division.
The nucleus is never polymorphous.
Bouquet Stage. — The spireme leaders have contracted and
formed twelve segments of about equal size, one end of which
is attached to the chromoplast, the other being free, and ending
in the vicinity of the spheres, thus forming a figure resembling
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. gI
a bouquet. This stage contains the three substages mentioned
below (Figs. 12-15).
Bouquet Stage with Twisted Segments.— The spireme seg-
ments are about one-third longer than the diameter of the
nucleus. Many small chromomeres (Fig. 12).
Bouquet with Split Segments. — The chromomeres are dis-
tinctly split, but are not yet separated (Fig. 15).
Bretzel Stage. — The segments have the form of bretzels or
twisted rings. These bretzel-shaped chromosomes may be
more or less regular, and their ends may only overlap each
other, or they may be actually grown together (Fig. 25).
Central Spindle. — The primary spindle by which the archo-
somes are united, and which form the center of the mitotic
figure. It does not include the contractile fibers attached to
the chromosomes, nor the mantle fibers. The spindle which
connects the two poles (Hermann, Figs. 49-56).
Centriole. —The innermost dark-staining granule or granules,
situated in the center of the archosome, and also in the acces-
sory archosome. It does not include the somosphere.
Centrosome. — On account of the many and various defini-
tions given by respective investigators, this name has recently
been discarded by several investigators, among them by W.
Flemming, who substitutes the word Centralkorper. But while
we are told that this word expresses the same thing as the word
“centriole,” we are yet at a loss to know if it includes the somo-
sphere, or the somosphere and centrosphere. When the word
“‘centrosome’’ is used in this paper, it is always left open and
undecided whether we have before us an archosome or an acces-
sory archosome. I use this word only to indicate a centriole
surrounded by its somosphere.
Centrosphere. — The more or less hyaline and indifferently
stainable zone surrounding the somosphere and centriole, the
outer sphere of the archosome, as well as of the accessory
archosomes. It is sometimes amoeboid, sometimes again cir-
cular or globular, with a perfectly even outline. It is princi-
pally an organ of locomotion.
Checkerboard Stage. — The second prophase of the sperma-
tocyte. The chromomeres have separated and scattered over
Q2 EISEN. [VoL. XVII.
the nucleus, making it appear as a checkerboard. This is the
principal stage of growth of the nucleus (Fig. 77).
Chromatin, the darkly staining substance of the chromo-
somes, applied without reference to any of the particular
structures.
Chromtioles. — The smallest visible organized parts of the
chromosomes. Possibly the bearers of heredity. They are
of constant form, size, and number in each typical and perfect
chromosome. In the perfect resting stage of the auxoyctes,
the chromioles are scattered free in the nucleus, and not col-
lected in chromioles or chromosomes. There are typically
thirty-six chromioles in every chromosome.
Chromomeres.— Small aggregations of chromioles, surrounded
by a film of chromoplasm. There are six chromomeres in each
perfect chromosome.
Chromoplasm. — The dark-staining plasma, which surrounds
the chromioles, and which unites them into chromomeres and
chromosomes. Also found in the chromoplasts.
Chromoplasts. —One or more rounded and well-defined bodies,
found in the nucleus, either free or attached to the leaders and
the chromosomes. Chromoplasts guide the formation of the
chromosomes, just as the archosomes guide the formation of
the spindles. Variously named karyosome, net-knot, Netz-
Knoten, nucleolus, etc.
Chromosomes. — The contracted leaders, with six chromo-
meres. There are twenty-four of these in the polymorphous
spermatogonia, and twelve in the two maturation cells.
Chromosomic Process. — One of the two independent pro-
cesses, the formation of the chromomeres and the chromosomes
from the chromioles and chromoplasm ; this process is presided
over by the chromoplast.
Chrysanthemum Stage.— The first prophase of the sperma-
tocyte. The chromosomes have begun to reappear, forming a
figure resembling a chrysanthemum flower (Fig. 67).
Contractile Fibers. — Fibers directly connecting the chromo-
somes with the somosphere and the centriole, and which thus
penetrate the centrosphere. There are as many contractile
fibers as there are chromosomes (Figs. I11I—I13).
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 93
Contraction Stage. — The third prophase of the spermato-
cyte. The chromosomes have again contracted and assumed
forms resembling staples or horseshoes (Fig. 83).
Cyto-Microsomes. — The most minute visible granules of the
cytosome, the granula of which the spheres and most of the
fibers are constructed.
Cytoplasm. — All the protoplasm in the cytosome. The pro-
toplasm of the cell proper. Does not refer to the protoplasm
of the archosome and the nucleus.
Cytosome. — The part of the cell outside of the nucleus and
the archosome. The two spheres are essential parts of the
cytosome.
Endochromatic Granules. — Highly refractive granules found
in the chromoplasts and in the confluent stage of the nucleus.
Probably food supply or stimulant for the chromioles.
Fiber Cones. — Cones of fibers projecting from the accessory
archosomes, and which make their appearance at the end of
the anaphase. They sometimes elevate the cell membrane,
forming large cones. The base of the cone is at first attached
to the cytoplasmic membrane around the nucleus (Fig. 114).
Granosphere. — The inner strongly granulated sphere, some-
times called the attraction sphere. It stains more intensely
than the other sphere, and it furnishes material for the central
spindle. It is the favorite dwelling-place for the archosomes.
Heterotypic Mitosis. — Mitosis, in which the chromosomes
are thrown on the central spindle in the shape of bretzels or
rings. The mitosis is by equation division. The mitosis of
the auxocytes.
Hlomoeotypic Mitosis. —The chromosomes are thrown on
the spindle in the form of V’s. The mitosis of the sper-
matocytes.
Imperfect Resting Stage.—In this stage of the nucleus the
leaders have formed, but there are no finished chromomeres,
nor any chromosomes. This stage follows the last described
stage. Is found in the polymorphous spermatogonia and in
the auxocytes.
Leaders or Spireme Segments. — Strings of chromoplasm
and linin on which the chromioles are suspended, singly to begin
94 EISEN. [VoL. XVII.
with, later on in twos and threes. There are as many leaders
as there are to be chromosomes. The leaders condense into
chromosomes. The leaders are connected with each other
only by the chromoplasts.
Linin Granules or Granula.— The smallest visible granules
composing the linin network and threads. Also found free in
the nucleus during the resting stage and after the prophases.
Linin Network. — The congo-staining network supporting
all the chromatin structures during the prophases.
Linoplast. — One or more round bodies in the nucleus,
staining like the linin and the cytoplasm. They supply the
material for the linin network, when this is in rapid increase.
Generally called true nucleolus.
Linopodia.— The thread-like or bar-like projections from the
individual granules of the cytoplasm, and from the linin and
other granules of a similar nature. By these linopodia, the
individual protoplasmic granules are able to adhere to each
other and to form network or foams. These linopodia are
retractile, very much like the pseudopodia of the amoeba, but
they are more regular and even throughout their length.
Mantle Fibers. — All fibers of the mitotic figure, which radi-
ate from the outer margin of the centrosphere, and which sur-
round the central spindle. The polar fibers and the contractile
fibers are not included in the mantle fibers.
Metaplasmic Secretions. — The various secretions confined in
vacuoles of the spheres.
Mid-Body. — A number of darkly staining granules, situ-
ated on the fibers of the central spindle, at a place where
the two daughter-cells separate. They are probably caused
by a concentration of the cytoplasmic granules of the fibers,
separated and only suspended by thin threads of linin
(Fig. 64).
Paracellular Bodies. — Bodies of various sizes and structure
found between the cells. They are probably expelled centro-
somes and particles of the spheres. Some are free, others
are attached to the cells by threads of protoplasm.
Parachromatic Granules. — Granules found in the nucleus
during the resting stage and in the immediate vicinity of the
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 95
chromoplasts. Stain as the chromatin with the iron-haema-
toxylin. Their nature is not known.
Paralinin Granules. — Larger, deeper staining granules of
unknown nature mixed in among the linin granules of the linin
network.
Paranucleolar Granules. — Dark-staining granules, forming a
shell around the linoplast or true nucleolus.
Paraplasmic Granula. — Granules of undetermined quality
found in the cytoplasm. They are often difficult to distinguish
from the centrosomes.
Perfect Bouquet Stage.— The spireme segments are only
slightly longer than the diameter of the nucleus. The seg-
ments are more parallel (Fig. 14).
Plasmosphere. — The outer, generally lighter staining of the
two spheres of the cytosome. It surrounds the inner or grano-
sphere, but is sometimes scattered. It furnishes material for
the mantle fibers and for the nuclear membrane.
Polar Fibers. — All fibers radiating from the outer margin
of the centrosphere, and which extend in a direction opposite
to that of the mantle fibers. Of the same general nature as
the mantle fibers.
Polymorphous Spermatogonia.— The largest spermatogonia
with polymorphous nuclei during the resting stage, becom-
ing less and less polymorphous, as the leaders are being
formed. They divide by somatic mitosis, and possess twenty-
four chromosomes. There are three or four generations, but
only the first one of these contains polymorphous nuclei.
Prophases. — All mitotic stages between the imperfect rest-
ing stage and the perfect metaphase. The phases in which
the chromomeres and the chromosomes are being formed, and
their structure finished (Figs. 12-44).
Radiosomic Process.—The evolution of the spheres, spindles,
and fibers ; one of the two independent processes by which the
mitosis of the cell is accomplished. This process is presided
over by the archosomes and the accessory archosomes.
Retractile Fibers. — A set of fibers radiating from the poles
of the central spindle, when the poles have descended through
the ring-like nuclei of the daughter-cells. They end on or
96 EISEN. [VoL. XVII.
near the new membrane forming between the two cells, their
function being to separate the two cells (Figs. 68-70).
Ring Stage.— The last of the bretzel stage in which the
chromosomes are ring-shaped (Fig. 25, 7.f.¢.).
Separated Segments. — The chromomeres and the segments
have separated, and the latter have twisted around each other,
and often cross each other in various directions (Figs. 16, 17).
Somatic Mitosis. — Mitosis, with twenty-four chromosomes,
dividing in the same way as the somatic cells. The mitosis of
the polymorphous spermatogonia.
Somosphere. —The thin, dark-staining zone nearest surround-
ing the centriole, and situated interior to the centrosphere. It
has sometimes the form of a narrow, even band or thread.
Spermatids. — The daughter-cells resulting from the mitosis
of the spermatocytes. Possibly two generations, the last of
which change directly into spermatozoa.
Spermatocytes. —The second maturation cells. The daughter-
cells of the auxocytes. Mitosis homoeotypic and by equation
division, with twelve chromosomes. One generation only.
Chromosomes are placed on the spindle in the form of V’s.
Spindle Cones. — The cones formed of the retractile fibers
around the poles of the central spindle, when the latter has
been pulled through the ring-like nuclei of the daughter-cells
(Fig. 114).
Spireme Segments or Leaders. — Strings of chromoplasm on
which are suspended the chromioles. There are as many
spireme segments as there are to be chromosomes. The spi-
reme segments do not form a single continuous thread, but are
individually separated.
Umbrella Stage.—The chromosomes in the amphiaster or
anaphase have become confluent, and formed an umbrella-like
body, in which the individual chromosomes cannot be distin-
guished as such (Figs. 58-61).
V-stage, in which the chromosomes have the shape of V’’s,
the apex of which is attached to the spindle. Includes a meta-
phase and an anaphase (Fig. 120).
CALIFORNIA ACADEMY OF SCIENCES,
San Francisco, California, April 26, 1898.
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 97
XI) LITERATURE,
'95 ALTMANN, R. Ueber Granula und Intergranularsubstanzen. Arch.
Jf. Anat. u. Phys., Anat. Abth.
'96 ALTMANN, R. Ueber das Wesentliche in der Zelle. Arch. f. Anat.
u. Phys., Anat. Abth.
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dina vivipara. /enatsche Zettschr. f. Naturw. Bd. xxx, N.F. xxiii.
'96-'97 BENDA, C. Neuere Mitteilungen iiber die Histogenese d. Sauge-
tier-Spermatozoen. Verh. d. Phys. Gesellsch. Berlin.
'83 BENEDEN, Ep. VAN. Recherches sur la maturation de l’ceuf, la
fécondation et la division cellulaire. Gand.
’87 BENEDEN, ED. VAN, ET NEyT, A. Nouvelles recherches sur la fécon-
dation et la division mitosique chez l’ascaride mégalocéphale. BxdZ.
de lf Acad. de Belgigue. 3° série. Tome xiv.
'96 BoLLES LEE, ARTHUR. Sur le Nebenkern et sur la formation du fuseau
dans les spermatocytes des Helix. Za Cellule. Tome xi, folio 2.
'96a BoLLEs LEE, ARTHUR. Note sur les sphéres attractives et la régres-
sion du fuseau. Anat. Anzeiger. Bd. xi, Nr. 21.
'97 BoLLES LEE, ARTHUR. Les cinéses spermatogenétiques chez Helix
pomatia. La Cellule. Tome xiii, folio 1.
'96 BoveERI, TH. Zur Physiologie der Kern- und Zelltheilung. Sztzungsber.
a. physikal.-medic. Ges. zu Wiirzburg.
'93 BRAUER, A. Die Spermatogenese von Ascaris megalocephala. Arch.
f. mikr. Anat. Bad. xiii.
’95 Braus, H. Ueber Zellteilung und Wachstum des Tritoneies, mit
einem Anhang iiber Amitose und Polyspermie. /enaische Zettschr.
J. Naturw. Bd. xxix, N.F. xxii.
'95 CALKINS, G. N. The Spermatogenesis of Lumbricus. /ourn. of
Morph. Vol. xi.
'98 CaRNoY, J. B. A propos de fécondation. Réponse a von Erlanger
eta Flemming. JZa Cellule. Tome xiv.
’'94 DRUNER, L. Studien iiber den Mechanismus der Zelltheilung. /eza-
ische Zettschr. f. Naturw. Bd. xxix, N.F. xxii.
'94a DRUNER, L. Zur Morphologie der Centralspindel. /enxazsche
Zettschr. f. Naturw. Bd. xxix, N.F. Xxii.
'97 EISEN, GusTAV. Plasmocytes. The Survival of the Centrosomes
and Archoplasm of the Nucleated Erythrocytes, as Free and Inde-
pendent Corpuscles of the Blood of Batrachoseps Esch. Prac.
Cal. Acad. Sci., Zool. Ser. 111, Vol. i, No. 1.
97a EISEN, Gustav. Notes on Fixation, Stains, the Alcohol Method,
etc. Zeitschr. f. wiss. Mikr. Bd. xiv, Heft 2, p. 195.
’96 ERLANGER, R. voN. Ueber den sogenannten Nebenkern in den mann-
lichen Geschlechtszellen der Insecten. Zool. Anzeiger. Bd. xix.
98 EISEN. [VoL. XVII.
‘96a ERLANGER, R. VON. Zur Kenntniss des feineren Baues des Regen-
wurmhodens und der Hodenzellen. Arch. f. mikr. Anat. Bd. xlvii.
’96b ERLANGER, R. VON. Neuere Ansichten tiber die Structur des
Protoplasmas, die karyokinetische Spindel und das Centrosom.
Zool. Centralbl. 3. Jahrg.
’97 ERLANGER, R. vON. Ueber Spindelreste und den echten Nebenkern
in den Hodenzellen. Zool. Centralbl. 4. Jahrg.
‘97a ERLANGER, R. von. Ueber die sogenannte Sphiare in den mann-
lichen Geschlechtszellen. Zool. Centralbl. 4. Jahrg.
'97b ERLANGER, R. VON. Ueber die Chromatinreduction in der Ent-
wickelung der méannlichen Geschlechtszellen. Zool. Centralbl.
4. Jahrg., Nr. 8.
’'97c ERLANGER, R. VON. Beitrage zur Kenntniss der Struktur des Pro-
toplasmas, der karyokinetischen Spindel und des Centrosoms.
Arch. f. mikr. Anat. Bd. xlix.
'97d ERLANGER, R. VON. Spermatogenetische Fragen. Biol. Centralbl.
Bd. xvii, Nr. 4, 15.
'97e ERLANGER, R. VON. Spermatogenetische Fragen. Ueber die soge-
nannte Sphare in den mannlichen Geschlechtszellen. Zool. Cen-
tralbl. 4. Jahrg., Nr. 5.
'97 FISCHER, A. Untersuchungen tiber den Bau der Cyanophyceen und
Bacterien. Jena, Fischer.
’87,’91 FLEMMING, W. Neue Beitrage zur Kenntniss der Zelle. Theil I,
Arch. f. mtkr. Anat., Bd. xxix. Theil II, Bd. xxxvii.
'95 FLEMMING, W. Ueber die Wirkung von Chromosmiumessigsdure auf
Zellkerne. Arch. f. mikr. Anat. Bad. xlv.
’97 FLEMMING, W. Morphologie der Zelle. Wiesbaden.
’84 GRUEBER, AUGUST. Ueber Kern und Kerntheilung bei den Protosoen.
Zettschr. f. wiss. Zool. Bd. xl, p. 121, Taf. IX, Fig. 26.
'92 HAEcKER, V. Die heterotypische Kerntheilung im Cyclus der
generativen Zellen. Bericht ad. naturf. Ges. zu Freiburg 7. B.
Bd. vi.
'93 HAECKER, V. Das Keimblaschen, seine Elemente und Lagerveran-
derungen. Nr.1. Arch. f. mtkr. Anat. Bad. xli.
'97 Hammar, J. AuG. Ueber eine allgemein vorkommende Protoplasma-
Verbindung zwischen den Blastomeren. Arch. f. mikr. Anat.
Bd. xlix.
'94 HEIDENHAIN, M. Neue Untersuchungen iiber die Centralkérper und
ihre Beziehungen zum Kern und Zellenprotoplasma. Arch. f. mikr.
Anat. Bad. xliii.
96 HENNEGUY, L. F. Lecons sur lacellule. Paris.
‘91 HERMANN, F. Beitrag zur Lehre von der Entstehung der karyokine-
tischen Spindel. Avch. f. mikr. Anat. Bd. xxxvii.
'97 HERMANN, F. Beitrage zur Kentniss der Spermatogenese. Arch. f.
mtkr. Anat. Bd. 1.
No.
"75
'98
Bout
oa
96
'97
Te] SPERMATOGENESIS OF BATRACHOSEPS. 99
LA VALETTE DE ST. GEORGE. Die Spermatogenese bei den Am-
phibien. Arch. f. mikr. Anat. Bad. xii.
LENHOSSEK, M. von. Untersuchungen uber Spermatogenese. Avrch.
fj. mtkr. Anat. u. Entwicklungsgesch. Bd. li, Heft 2.
MEVES, F. Ueber amitotische Kerntheilung in den Spermatogonien
des Salamanders und Verhalten der Attractionssphare bei derselben.
Anat. Anzeiger. 4. Jahrg.
MEvEs, F. Ueber eine Metamorphose der Attractionssphare in den
Spermatogonien von Salamandra maculosa. Arch. f. mikr. Anat.
Bd. xliv.
MeEvEs, F. Ueber die Entwickelung der mannlichen Geschlechts-
zellen von Salamandra maculosa. Arch. f. mikr. Anat. Bd. xlviii.
MeEvEs, F. Ueber Structur und Histogenese der Samenfaden von
Salamandra maculosa. Arch. f. mikr. Anat. Bd. 1.
‘97a MEVES, F. Zellteilung. Wiesbaden.
93
195
‘OT
oT
96
'93
ioe
95
96
94
7
95
96
Moore, J. E. S. On the Relationship and Réle of the Archoplasm
during Mitosis in Larval Salamander. Quart. Journ. Micr. Sct.
Vol. xxxiv.
Moore, J. E. S. On the Structural Changes in the Reproductive
Cells during the Spermatogenesis of Elasmobranchs. Qvart.
Journ. Micr. Sct. Vol. xxxviii.
NIESSING, CARL. Die Betheiligung von Centralkérper und Sphiare
am Aufbau des Samenfadens bei Séugenthieren. Arch. f. Anat. u.
Entwicklungsgesch. Bd. \xxxiv.
OsTERHOUT, W. J. V. Ueber Entstehung der karyokinetischen
Spindel bei Equisetum. /ahrd. f. wiss. Bot. Bd. xxx.
PLATO, JULIUS. Die interstitiellen Zellen des Hodens und ihre physi-
ologische Bedeutung. Arch. f. mikr. Anat. u. Entwicklungsgesch.
Bd. xlviii, Taf. XII.
RATH, O. von. Zur Kenntniss der Spermatogenese von Salamandra
maculosa. Zettschr. f. wiss. Zool. Bad. Ivii.
RAwitz, B. Centrosoma und Attractionssphiare in der ruhenden Zelle
des Salamanderhodens. Arch. f. mikr. Anat. Bad. xliv.
Rawitz, B. Ueber den Einfluss der Osmiumsaure auf die Erhaltung
der Kernstructuren. Anat. Anzeiger. Bd. x.
Rawitz, B. Untersuchungen iiber Zellteilung. I. Das Verhalten der
Attraktionsphare bei der Einleitung der Teilung der Spermatocyten
von Salamandra maculosa. Arch. f. mikr. Anat. Bd. xlvi.
REINKE, Fr. Zellstudien. Theil II]. Arch. f. mikr. Anat. Bd. xliv.
SCHLATER, GusTAv. Zur Biologie der Bacterien. Bzol. Centralbl.
Bd. xvii, Nr. 23.
WILson, Epm. B. Archoplasm, Centrosome, and Chromatin in the
Sea-urchin Egg. Journ. of Morph. Vol. xi.
WILson, Epm. B. The Cell in Development and Inheritance. New
York.
100 EISEN. [VoL. XVII.
XII. EXPLANATION OF THE FIGURES.
PLATES I~XIV, FIGs. 1-122.
General Remarks. — All the figures have been drawn to the same scale projec-
tion on the working table, by the aid of a Griinow drawing camera and with a
Zeiss Apochromat, 3mm., Ap. I, 40, Oc. 18. The details were studied with a Zeiss
Apochromat, 2 mm., Ap. I, 40, Oc. 12, the magnification thus being in both
instances about 1500. An achromatic oil-immersion substage condenser was
used for all detail work, and it was always supplemented by an achromatic light-
filter as described under the heading of methods. A few of the figures, as stated
in the text, have been drawn from Oc. 18, and with 2 mm. Objective. The stain-
ing, with the exception of a few, has been the same for all the sections: iron-
haematoxylin, with after-staining with congo. A few preparations were stained
with congo-thionin-ruthenium red. The sections were cut about 5 mw thick and
affixed to the slides by the alcohol method. All the figures are from the testes
cells of Batrachoseps attenuatus Esch. Fixative exclusively iridium-chloride-acetic.
The figures have principally been arranged according to the serial development
of the nucleus, and not according to the development of the spheres and the
spindle. In the later stages of the spermatocytes the figures have been partly
arranged according to the development of the spindle. The figures in the text
are strongly diagrammatic.
Large Polymorphous Spermatogonia (figs. 7-9).
Fic. 1. Large polymorphous spermatogonium, perfect resting stage. The
large black body is the chromoplast surrounded by filaments of linin stained red.
The chromoplast contains several highly refractive endochromatic granules. The
large red body is the linoplast. The small granules, of uniform size and dark
color, are the chromioles. The lighter stained granules are partly chromioles,
partly linin granules, all of which are suspended in the linin network. A number
of parachromatic granules are seen around the chromoplast. The cytoplasm has
the form of a thin hollow shell surrounding the much folded nucleus. Two cen-
trosomes in the cytoplasm. Remains of, or the beginning of, a granosphere at the
top of the cytoplasmic shell. The dark-staining granules which form a shell
around the linoplast are the paranucleolar granules.
Fic. 2. Large polymorphous spermatogonium, perfect resting stage; the chro-
moplast is larger and divided in two nearly equal parts, and is surrounded by an
aster of linin threads of even length; at the tips of the threads are seen more dis-
tinct linin granules. The granosphere is being reconstructed at the upper end
of the nucleus, but in the cytoplasm. No centrosomes visible. A large lino-
plast with paranucleolar granules.
FIG. 3. Polymorphous spermatogonium in a more advanced stage than Figs.
1 and 2, but still in the resting stage. The chromioles, which are strung on
threads of linin and chromoplasm, are being drawn towards the chromoplast, the
leaders thus beginning to form. Two linoplasts of unequal size stained red.
The nucleus is less polymorphous than in Figs. 1 and 2. The cytoplasmic
granules are more scattered, forming a more extended and less ring-shaped cyto-
some. Centrosome in the granosphere.
Fic. 3 4. Detail of the granular reticulum or network of the linin.
PLS.
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Spermatogenesis of Batrachoseps.
Pl. ll.
Vol. XV
Journal of Morphology.
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No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. IOI
Fics. 4 and 5 represent two successive sections of one polymorphous sper-
matogonium in the resting stage. The nucleus is more contracted, with fewer
folds. Two linoplasts. The chromioles are being drawn into the leaders and
united into chromomeres. The spheres are being reconstituted, the granular
zone being the granosphere. An archosome is seen in Fig. 5.
Fics. 6 and 7. Two detail figures of polymorphous spermatogonia with fully
reconstituted spheres, each with centrosomes. The nuclei are more advanced
than in Figs. 4 and 5. In Fig. 7 are seen several accessory archosomes, each
surrounded by a centrosphere. In each cell is a large linoplast. The nuclear
network is merely sketched in and not carried out in detail.
Fic. 8. A large polymorphous spermatogonium in a more advanced stage of
development, in the imperfect resting stage. The nucleus has changed from poly-
morphous to globular. The largest dark body is the chromoplast, the smaller
one is probably a linoplast. Many distinct leaders have been formed, and are
now connected by a network of chromioles and chromomeres. The spheres have
been almost perfectly reconstituted, consisting now of an inner granosphere and
an outer plasmosphere, an archosome with two centrioles, and several accessory
archosomes, the latter scattered in the cytoplasm.
Fic. 9. A large polymorphous spermatogonium, but in which the nucleus has
lost its folded or polymorphous nature, being now at the end of the resting stage
and just entering the prophases of mitosis. Between this cell and the one figured
in 10 there is not only a whole somatic mitosis, but at least three or four genera-
tions of round nucleated spermatogonia, all dividing by somatic mitosis, and with
twenty-four chromosomeseach. The last of these generations gives rise to smaller
oblong cells, which pass through a stage of growth and then constitute the first
or imperfect resting stage of the auxocytes. In Fig. 9 there is seen a large lino-
plast, three chromoplasts, with endochromatic granules. Leaders are séen to
emanate from the chromoplasts. The spheres are not quite reconstituted. In the
center is an archosome with two centrioles. Several accessory archosomes in the
cytoplasm. The plasmosphere is starlike, the granosphere rounded and cup-shaped.
Auxocytes: Spermatogonia with Round Nucleus, Heterotypic Mitosis, and Twelve
Chromosomes (Figs. 10-62).
Fic. 10. Auxocyte in the imperfect resting stage. Three darkly stained chro-
moplasts with endochromatic granules. Leaders are centering towards the
chromoplasts and connected with them. The spheres are reconstituted. The
granosphere is cup-shaped ; the plasmosphere is indistinct and hardly to be defined
from the cytoplasm. An archosome with two centrioles at the outer edge of the
granosphere ; several accessory archosomes in the plasmosphere, all being con-
nected by a thread and by rings of somosphere. The darker granules in the
nucleus are chromomeres, containing each from one to three chromioles. Only a
small part of the nuclear contents is sketched.
Fic. 11. Auxocyte in the imperfect resting stage more advanced than the last
figure. Two chromoplasts. The spheres are reconstituted, the inner one
stained red being the granosphere. In its center is an archosome with two
centrioles. Numerous accessory archosomes in the cytoplasm, some of them
connected by threads of somosphere. The detail figure alongside shows the chro-
matin network, each chromomere consisting of several chromioles. The leaders
are projecting from the chromoplasts.
102 EISEN. (Vou. XVII.
Fic. 12. Auxocyte in the beginning of the bouquet stage, the bouquet with
twisted spireme segments. The segments are considerably longer than the
nucleus and much twisted. They are all with one end attached to the chromo-
plast. Two linoplasts stained red. The linin network is also stained red. The
granosphere is cup-shaped ; at its upper margin is an archosome with two cen-
trioles. Several accessory archosomes in the plasmosphere.
Fic. 13. Auxocyte in the perfect bouquet stage. The twelve segments have
shortened and straightened out; some are connected, two and two, by a chromo-
plast, others are isolated. There are two dissolving linoplasts, intimately con-
nected with the linin network. The spheres not yet fully reconstituted, but in a
state of activity. A cell bridge connects two adjoining cells at the point of
reconstitution. An archosome in the granosphere and accessory archosomes both
in the spheres and in the cytoplasm.
Fic. 14. Auxocyte in the perfect bouquet stage, but a little further advanced
than the last. The segments are more contracted, and some are seen to be
attached to chromoplasts, recognizable by their endochromatic granules. One
linoplast stained red. The spheres are being reconstituted. A centrally situ-
ated archosome with two centrioles. The granosphere is concave, with the con-
cave side upwards, facing the reader. The radiations are from the cytoplasm and
plasmosphere combined, the latter being in an active state of reconstitution. The
letters a—d indicate detail figures drawn to a larger scale in order to be more
distinct, but with the same objective and ocular. Figs. 14 @ and 14 4 are froma
deeper focus or plane.
Fic. 14 a. An accessory archosome with a somosphere with centrioles, the
same one as figured in 14 é.
Fic. 14 6. The granosphere focussed deeper than in Fig.14. The centrosomes
connected by a thread of somosphere.
Fic. 14 c. Detail figure of linin network showing the linin granules and the
connection of the network with a linoplast.
Fic. 14 d. Detail of three chromomeres showing the interior chromioles.
Drawn on a somewhat larger scale than Fig. 14.
Fic. 15. Auxocyte in bouquet stage with split spireme segments. Chromo-
meres about twelve in each segment ; most of them are split, but not yet divided.
About six chromioles in each chromomere. The outer sphere not yet fully recon-
stituted, the granosphere being small, with a centrally located archosome with
two centrioles. An accessory archosome in the plasmosphere. A red-stained
linoplast in the nucleus. Several split chromoplasts connected with the spireme
segments.
Fic. 16. Auxocyte in the separated and crossed spireme stage. The divided
and partly separated segments are not any more parallel, but cross each other in
various directions. Some are attached to chromoplasts. Four linoplasts. The
plasmosphere contains numerous rounded alveoles, containing secretions around
which are seen the individual granules of the plasma. The granosphere is large
and deeply stained. A centrally located archosome with two centrioles. Three
accessory archosomes in the plasmosphere, each with several centrioles sur-
rounded by somosphere. The granosphere is cup-shaped, with the concave part
turned upwards.
Fic. 17. Auxocyte, separated spireme stage. Four chromoplasts with endo-
chromatic granules. Four linoplasts. The segments are twisted and separated
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 103
from each other, and all have been greatly lengthened out. The outer or plasmo-
sphere is in a state of evolution, showing starlike radiations emanating from the
vicinity of the granosphere. Many metaplasmic secreted granules in the plas-
mosphere. The granosphere is angular in outline, cup-shaped, with a denser
marginal wall consisting of closely packed granules of the plasma of the sphere.
A centrally located archosome with two separated centrioles. Two accessory
archosomes at the edge of the granosphere. Numerous paraplasmic granules of
unknown nature in the cytoplasm, stained darker and connected by rings. Faint
trace of a cell bridge emanating from the granosphere or from its immediate
vicinity.
Fics. 18-22. Auxocytes, all in the twisted and separated spireme stage.
The dark nodes are the chromoplasts, from which start the separated spireme seg-
ments. The two segments which twist around each other are the two halves of
one original spireme segment. The segment having split, the two halves have
separated, and becoming considerably elongated have twisted around each other
in various ways. In Fig. 21 we see one dividing chromoplast which supported
originally four undivided spireme segments, which latter have separated and
twisted around each other and also have become much elongated. The small
dark bodies are the chromomeres, containing each several chromioles imbedded
in a chromoplasm and surrounded by an irregular network of linin, here and
there stained gray by the iron-haematoxylin. It will be observed that in no
instance are the distal ends (those not connected with the chromoplasts) of the
spireme segments grown together, but simply cross each other. These segments
will soon have contracted, after which,we will find them as represented in Figs.
23 and 24.
Figs. 23 and 24. Auxocytes. Separated spireme segments which have yet
more contracted. In Fig. 23 the segments are twisted around each other. The
darkly stained nodes are the chromoplasts which hold the segments together. In
Fig. 24 we have a more advanced stage, such as is found in the beginning of the
angular spireme (Fig. 34). Only about one-half of the chromosomes have been
represented in Fig. 24, the other half having been cut away by the knife. It will
be observed that there are six original segments attached to the chromoplast, and
that each one of them has become divided and contracted. Each such pair
marked a, 4, c, d, é, f, etc., will form a bretzel-shaped chromosome, similar to those
represented in Fig. 25, a, 4, c,d, e, f,etc. The linin network has not yet separated
from the segments.
Fic. 25. Auxocytes. A series of perfectly developed chromosomes from the
metaphase and the anaphase. The figures are copies of selected chromosomes
and intended to represent the most common forms assumed by them. Ata place
marked “0” is seen the chromoplast adhering to the chromosome, while the free
ends are marked “x.” In many instances it is difficult, and in others it is impos-
sible, to determine which is the free and which is the chromoplastic end, as, for
instance, in “7.” As a rule, the separation begins at the chromoplastic node
“0.” At “yr” is seen a separated chromosome from the anaphase, the other half
having been pulled to the opposite pole. The darker globules in the chromo-
somes are the chromioles, of which there are thirty-six in each chromosome. In
some of the chromosomes are seen traces of chromomeres.
Fic. 26, a, 6, c, d, four chromoplasts with parts of leaders, from resting stages
of polymorphous spermatogonia and auxocytes. In their interior are seen endo-
104 EISEN. , [Vou. XVII.
chromatic granules. The linin is stained red, the chromioles are blue, but the
chromoplasm is not differentiated. Congo-thionin-ruthenium red.
Fic. 26%. Part of the linin network, from an auxocyte in the bretzel stage.
The linin network is disarranged and has separated from the chromosomes. The
small brown granules are the linin granula; the darker granules, of which there
are comparatively few, are paralinin granules of unknown nature. The granules
are connected by threads of the same apparent nature as the granules, and which
may be considered as projections from the granules.
Fic. 27. Auxocyte, in the bouquet stage; detail of the plasmosphere with two
large accessory archosomes, each of which consists of a slightly amoeboid centro-
sphere, a somosphere, and several interior centrioles of unequal size. The acces-
sory archosomes are connected by a thin ring of somosphere, on which are also
suspended granules of either archosomic or paraplastic nature.
Fic. 28. Auxocyte in the irregular bretzel stage. Detail of the cytoplasmic
end of the cell, showing the two spheres with accessory archosomes. The inner
part of the granosphere has been drawn out by an archosome, the outer concave
shell of the sphere being viewed sideways.
Fic. 29. Auxocyte in the perfect bouquet stage. Detail showing the two
spheres and part of the surrounding cytoplasm. The granosphere is cup-shaped,
and differentiated into two parts, the outer one of which is in the form of a deeper
stained ring, at the edge of which is seen an archosome with a faintly differen-
tiated centrosphere. The somosphere and centrioles are not differentiated from
each other ; the plasmosphere is well defined from the cytoplasm proper. The
alveoles of the granosphere are seen to be surrounded by the individual granules
of the spheres.
Fic. 30. Auxocyte in the perfect bouquet stage. Detail of the spheres and of
the free ends of some of the spireme segments, the chromomeres not yet being
split. The chromomeres and the chromioles are slightly exaggerated as regards
size, but other details are in exact proportion. The granosphere and the plasmo-
sphere are both plainly alveolated, each alveole being surrounded by a single row
of granules. An archosome with two centrioles in the granosphere. Three
accessory archosomes in the plasmosphere. Three rows of alveoles in the
plasmosphere.
Fic. 31. Auxocyte in the bouquet stage. Detail of the two spheres. The
granosphere is cup-shaped, consisting of one row of alveoles. The plasmosphere
is less regular, with one or two rows of alveoles. At least five accessory archo-
somes connected by rings of somosphere. On these rings are also suspended
among the centrosomes paraplastic granules of undetermined nature.
Fic. 32. Auxocytes in the bouquet stage. Detail figures of three adjoining
cells. Two spindle bridges connect the three cells in the vicinity of the spheres.
The spheres are not fully reconstituted, showing the chromosomic evolution
to be more advanced than the radiosomic one. The accessory archosomes are
connected by rings. The dark red spheres are the granospheres. The archo-
somes are seen at the points where the spindle bridges join the spheres. Some
of the accessory archosomes have the same structure as the archosomes.
Fic. 33. Auxocyte in the bouquet stage; detail of the sphere not yet fully re-
constituted. The archosome is connected with an accessory archosome by a fine
somospheric filament very sharply defined; four centrioles in the upper somo-
sphere and at least two in the lower one. The latter centrosome is probably the
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. 105
offshoot of the upper one. Alveoles are being formed in the plasmosphere
probably by secretion of interalveolar and metaplasmic matter.
Fic. 34. Auxocyte in the angular spireme stage. The separated segments
have first contracted and then straightened out, having been angularly bent at
the nodes, and the chromomeres have so approached that they are hardly to be
distinguished from each other. Several chromoplasts are seen attached to the
segments at the nodes, where they are joined together. Some chromioles are
distinct in the segments. The granosphere is strongly stained and is seen to
consist of one row of alveoles and several central ones. The plasmosphere and
part of the cytoplasm are alveolate with distinct granules. A large archosome
in the granosphere and an accessory archosome in the plasmosphere. There
are no linoplasts left in the cell.
Fic. 35. Auxocyte in bretzel stage, the chromosomes having the form of
bretzels and rings. Only a few of the chromosomes are figured. The cytoplasm
is alveolate with distinct granules. The granosphere is cone-shaped, with the
denser part cup-shaped as usual. Near the apex of the cone lies the archosome
with at least two centrioles. An accessory archosome at the upper left end of the
granosphere.
Fic. 36. Auxocyte in bretzel stage. Only a few of the chromosomes have
been figured; one of them has been cut by the knife. The linin has separated
from the chromosomes, and scattered to the opposite part of the nucleus. The
cup-shaped granosphere is turned sideways, and appears as a crescent with one
row of alveoles. The cone-like structure belongs probably exclusively to the
granosphere. At its apex lies the archosome with two centrioles. Four separate
accessory archosomes in the plasmosphere, the latter being strongly alveolated.
Fic. 37. Auxocyte in bretzel stage. Only a few of the chromosomes are in
the field. Several of them are connected in pairs with chromoplasts. One of
the ring-like chromosomes is free. Several chromosomes show distinct chromi-
oles. The linin network is scattered and not any more connected with the
chromosomes. The plasmosphere is in dissolution; the granosphere is elongated.
At the apex of the latter is situated the archosome, which appears to have been
divided preparatory to the radiosomic process. The somospheres connected by a
thin ring; there are three accessory archosomes.
Fic. 38. Auxocyte in bretzel stage. The section is cut so that only the cyto-
plasmic pole is seen. The archosome has left the granosphere and become
divided. A small spindle is formed between the somospheres. The centrosphere
is elongated ; from its outer margin radiate numerous mantle fibers. The plas-
mosphere is greatly shattered, and the granosphere is only partly connected with
the mantle fibers. There are numerous accessory archosomes both in the cyto-
plasm and in the spheres. At the upper right-hand corner are seen the remains of
a spindle bridge.
Fic. 3814. Auxocyte in bretzel stage. Most of the chromosomes are halved
by the knife. The linin network is scattered and retracted from the chromo-
somes. The nuclear membrane is yet intact. The archosome is entirely divided
and a small central spindle has formed outside of the granosphere. The latter is
being used up as material by the fibers. The centrosphere is stained, and the
various fibers are seen to emanate from its outer margin. The plasmosphere is
scattered, and parts of it are seen in the cytoplasm. Three groups of accessory
archosomes, some with three and four centrioles.
106 EISEN. [Vou. XVII.
Fic. 39. Auxocyte in bretzel stage. The nuclear membrane is mostly dis-
solved. The spindle is viewed from one of its poles, showing the mantle fibers to
emanate from the outer margin of the centrosphere. The granosphere is partly
used up, and the plasmosphere is mostly scattered in the cytoplasm. There are
numerous accessory archosomes, some of which are connected by filaments of
somosphere. A row of accessory archosomes is seen around the granosphere,
all connected by a filament of somosphere. Many of the chromosomes show
darkly stained chromioles. Outside of the plasmosphere the cytoplasm is fibrous,
the fibers consisting of closely packed granules.
Fic. 40. Auxocyte in bretzel stage. The chromosomes are rather heavy and
contracted. The spindle is seen from one of the poles, and is in the figure not
clearly definable. The granosphere is being used up by the spindle fibers. Much
of the plasmosphere is being scattered ; some of it is seen far down to the right
outside of the nucleus. The darker stained granules in the cytoplasm are the
remains of the metaplasmic secretions of the plasmosphere. There are several
accessory archosomes stained more or less deeply, some of them connected by a
thread of somosphere. The linin network is scattered.
Fic. 41. Auxocyte in bretzel stage. Several of the chromosomes are halved
by the knife. The central spindle is well advanced. A set of contractile fibers
has formed from both archosomes, but has not yet reached the chromosomes.
A large accessory archosome at the upper end of the central spindle below the
granosphere is situated in a much deeper plane than the archosome and is not in
a direct line between the archosome and the granosphere. The plasmosphere is
scattered in the cytoplasm. The part of the nuclear membrane nearest the man-
tle fibers is dissolved. /
Fic. 42. Auxocyte in bretzel stage. This figure, together with the previous
one and several following, is arranged according to the development of the
central spindle. The chromosomes in all these figures are in about the same
stage of development. In the present figure the spindle is upright ; its axis con-
nects with the axis of the cell. The granosphere has hardly begun to dissolve,
its concave side is upwards. In the upper archosome are two centrioles, in the
lower one is only one centriole. The contractile fibers are not deeply stained and
are thus less well definable. Eight accessory archosomes, each with a centro-
sphere and with from one to three centrioles. The plasmosphere is scattered, the
remains are seen in two isolated groups at the left margin of the nucleus. The
nuclear wall nearest the spindle is dissolving.
Fic. 43. Auxocyte in bretzel stage. This is an abnormal cell as regards the
position of the granosphere and the central spindle, the granosphere being gen-
erally so situated as to be equidistant from both the poles of the spindle. At the
upper margin are seen remains of the plasmosphere. An accessory archosome at
the periphery of the granosphere. The contractile fibers are well differentiated,
especially around the left pole of the central spindle. The nuclear membrane is
dissolved nearest the central spindle.
Fic. 44. Auxocyte in bretzel stage. The nuclear membrane is less dissolved than
in the last figure. The granosphere is being used up. The contractile fibers are
well differentiated and deeply stained ; none of them has as yet reached the chromo-
somes. An accessory centrosome at the edge of the granosphere. The mantle fibers
possess several denser nodes. The linin network has entirely separated from the
chromosomes. The contractile fibers show a strongly granulated cytoplasm.
PL. IV.
Vol. XV.
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Spermatogenesis of Batrachoseps
Noses] SPERMATOGENESIS OF BATRACHOSEPS. 107
Fic. 45. Auxocyte in bretzel stage. Only a few fragments of chromosomes
are seen in the section. The central spindle is upright, its position depending on
the position of the granosphere. At the upper pole are seen two archosomes, at
the lower pole only one. The contractile fibers are strongly granular. A few
small groups of accessory archosomes are seen to the left, the individual archo-
somes being connected by threads of somosphere. Many of the individual
granules of the granosphere are seen to be in direct connection with the mantle
fibers. At the lower right-hand margin of the cell are seen parts of the scattered
plasmosphere.
Fic. 46. Auxocyte in bretzel stage. The granosphere is very much used up
and in direct connection with the spindle fibers. The chromosomes are thrown
in a bundle, all, however, being perfectly formed bretzels. At the poles of the
spindle are seen several accessory archosomes surrounding the archosome.
What I take to be the beginning of contractile fibers are seen to start out from
the accessory archosomes. The linin network has left the chromosomes, and is
broken up into globules, each one of which consists of several granules. At the
lower margin of the cell are seen parts of the plasmosphere.
Fic. 47. Auxocyte in bretzel stage, a transition stage between the last and the
following figure in the metaphase. The last of the prophases. The central
spindle is almost perfect. The remains of the two spheres are seen at the left in
the cell. The contractile fibers are well advanced and several of them have
reached the chromosomes. The latter are in the form of bretzels and rings.
Numerous accessory archosomes as well as paraplasmic granules, difficult to dis-
tinguish from each other. The nuclear membrane is entirely dissolved and the
linin granula are scattered through the cytoplasm. The alveoli of the cytoplasm
are very large and have assumed the forms of large vacuoles.
Fic. 48. Auxocyte in a stage immediately preceding the metaphase. The
chromosomes have not yet been drawn into the equator of the central spindle.
One chromosome which is in its proper position has begun to divide. Two
superfluous or unused linoplasts are seen in the cytoplasm. An archosome and
numerous accessory archosomes are seen at each pole of the central spindle.
Four groups of plasmosphere are scattered. The contractile fibers are distinctly
beaded. In some of the chromomeres the chromioles are distinct; there are
about six chromioles in a chromomere.
Fic. 49. Auxocyte in a stage immediately preceding the metaphase. An
archosome with several accessory archosomes at each pole. Some of the chro-
mosomes are not yet in their proper position on the central spindle. There are
five or more groups of scattered plasmosphere and secretions.
Fic. 50. Auxocyte, metaphase. There are two archosomes at each pole, also
numerous accessory archosomes. Three groups of scattered plasmosphere and
its secretions. Several of the mantle fibers connect directly with metaplasmic
granules of the plasmosphere. The group to the left has assumed its final posi-
tion near the equator of the cell.
Fic. 51. Auxocyte, metaphase. Only a few of the chromosomes are figured.
One archosome at each pole, but several accessory archosomes. A number of
linin granules as well as paraplasmic granules are seen in the cytoplasm. The
contractile fibers are well defined, and one of them in the upper right-hand corner
has been torn by the knife and has been bent outwards, a fact illustrating the
independent nature of the contractile fiber.
108 EISEN. [VoL. XVII.
Fic. 52. Auxocyte, metaphase. The section is cut at an angle with the cell
axis and consequently the upper pole is seen slightly from above, while the lower
pole is so viewed that the archosomes are not distinctly seen. The circle of dots
around the upper pole are the starting points of the contractile fibers, which are
seen to be connected with the somosphere and the centriole by a fine bar of dark-
staining plasma. Several accessory archosomes in the cytoplasm. The red spots
in the cytoplasm are the scattered remnants of the plasmosphere. The chromo-
somes show here and there distinctly the chromioles and the chromomeres. This
cell is unusually small for an auxocyte.
Fic. 53. Auxocyte, metaphase. The chromosomes are regularly placed on
the central spindle, all being in about the same stage of development. The spin-
dle is halved and presents its inner concave surface to view. Chromioles are
seen in all the chromosomes and chromomeres. Most of the chromosomes have
commenced to separate. The red blotches are parts of the plasmosphere. The
contractile fibers are all well defined, and some of them are seen to connect with
the somosphere by a fine bar of darkly staining plasma. At the upper pole is
seen one archosome, while at the lower pole there are two. The upper archo-
some is connected with the contractile fibers in that part of the section which is
not figured here. This archosome is darker and refractive, the two centrosomes
being of a dull color and not refractive. The cytoplasm contains no accessory
archosomes, but numerous dark-staining granules, which perhaps may be inter-
preted as linin granules. Many granules are connected by rings or threads. See
also Fig. 51.
Fic. 54. Auxocyte, metaphase. Most of the chromosomes have separated,
and some have begun to contract. The contractile fibers have also contracted ;
they are strongly beaded. Chromioles are seen in the chromomeres. The archo-
somes are large and distinct. A few accessory archosomes in the cytoplasm. In
the central spindle is seen a separated chromatin granule. This figure is a com-
posite one as regards the poles. A few chromosomes found in the following sec-
tion were added to the lower pole. The accessory archosomes were also added
from that section.
Fic. 55. Auxocyte, anaphase. A stage succeeding that shown in Fig. 54. The
chromosomes are drawn much nearer the poles. Chromioles are seen plainly in
many places. An archosome at each pole. The contractile fibers are disappear-
ing. The plasmosphere is accumulated at the left side of the equator. The
central spindle is beginning to dissolve, and shows irregular vacuoles along a line
where the coming new cell wall is to appear. A chromatin fragment in the cen-
tral spindle. Numerous paraplasmic and linin granules in the equator of the
central spindle.
Fic. 56. Auxocyte, anaphase. The chromosomes are further advanced,
approaching the confluent umbrella stage. On account of improper washing out,
this figure does not show the details as well as the preceding and following
figures. The cell is lengthening out and the central-spindle poles have been
pulled down through the chromosomes. A few chromosomes are not yet sepa-
rated from each other, but connected by chromoplasm.
Fic. 57. Auxocyte, anaphase. The chromosomes are entering the confluent
umbrella stage. The individual chromomeres are yet distinguishable, but the en-
dochromatic granules of the chromoplasts have already come into plain view.
The archosomes have diminished in size, now appearing as very faint points.
PLY.
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PLVI.
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Spermatogenesis of Batracho:
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Nori] SPERMATOGENESIS OF BATRACHOSEPS. 109
The plasmospheric granules are seen near the equator of thespindle. The future
cell wall is outlined, and several mantle fibers are seen connected with the plas-
mospheric granules in the vicinity of the contraction in the equator.
Fic. 58. Auxocyte, anaphase. The chromosomes in the umbrella stage. The
chromosomes have lost their individuality, and only here and there does a pro-
jecting point indicate theirformer outline. The distribution of the endochromatic
granules of the chromoplasts indicates that the confluence is perfect. At the
upper pole is seen the apex of the central spindle, with the remains of the con-
tractile fibers under the form of four granules, corresponding to as many acces-
sory archosomes. The archosome is seen at the very apex of the central spindle.
The red blotches are part of the scattered plasmosphere. The alveoli of the cen-
tral spindle are widened along the equator and along a line where the new cell
wall is to appear. -
Fic. 59. Auxocyte, metaphase. The confluent umbrella stage in which the con-
fluence is perfect. Inthe umbrella are seen vacuoles and endochromatic granules.
A cytoplasmic or false nuclear membrane is formed around the nucleus. Numer-
ous polar fibers and mantle fibers connect the cytoplasmic membrane with the cell
wall. The plasmosphere, now fragmented, appears as four agglomerations along
the new cell wall separating the spermatocytes. The spermatocytes are more sep-
arated than in Fig. 61, but this separation is only apparent as the cell in Fig. 61 is
seen from the side, while the present one is viewed from the front. The spindle
is much contracted in the middle, and the muscular nature of some of the fibers
is indicated by the beading. A few accessory archosomes are seen below each
nucleus. The poles of the central spindle are not visible.
Fic. 60. Auxocyte, anaphase, ring-like, confluent umbrella. The two new
spermatocytes are almost separated. The cytoplasmic membrane around the
nucleus is being pulled away from the umbrella, and numerous fibers are seen to
connect with the membrane. Numerous fibers from the poles of the spindle
connect with the cell wall, separating the two spermatocytes. Several accessory
archosomes are seen on the cytoplasmic membrane.
Fic. 61. Auxocyte, metaphase, and confluent umbrella stage. The central
spindle has contracted in the middle, and has been pulled through the um-
brella. A large vacuole has appeared around each nucleus, the cytoplasmic
membrane around the nucleus is being pulled away allowing the nucleus to
expand. On the membrane are several accessory archosomes, from which start
out fibers singly and in bundles. The fragments of the plasmosphere are in the
equator at points where the new cell wall is being formed. The granules of
this sphere are seen to be connected with fibers both from the poles and from the
cytoplasmic membrane. This and several of the following figures are from differ-
ent slides from the previous ones, the tissue having been stained much more
intensely by the congo. The fibers of the central spindle are all strongly granu-
lar and beaded like muscle fibers. The contraction from the old cell and the
formation of the new cell wall is seen to proceed from one side only, which
process appears to be normal.
Spermatocytes or Spermatogonia of the Second Maturation Stage.
Fic. 62. Spermatocytes. Two cells not yet entirely separated. The chromo-
somes in the beginning of the chrysanthemum stage, emerging from the confluent
IIO EISEN. [VoL. XVII.
stage. Darkly stained bars indicate the new chromosomes in the confiuent mass,
all pointing in the direction of the cell axis. The spindle shows several con-
tractile fibers ending on the cytoplasmic membrane which has receded from the
chromosomes. On this membrane are seen several accessory archosomes, from
some of which radiate fibers. From one of these archosomes proceed the
remains of retractile fiber cones. The reddish blotches are the remains of the
plasmosphere. Some of the accessory archosomes are furnished with distinct
centrospheres. In the chromosomes are seen a few endochromatic granules,
characteristic of the chromoplasts. The cell wall is made up of cytoplasmic
granules.
Fic. 63. Spermatocyte, in the chrysanthemum stage, having entered the pro-
phase in which the individual chromosomes are being reconstituted. Only a
small section of the nucleus is seen. Only one cell is figured. The cytoplasmic
or false membrane has been pulled back in order to allow the growth of the
nucleus. The central spindle is fully retracted and the archosome has assumed
its position at the apex of the fibers. Several accessory archosomes pulling fiber
cones towards the cell wall. Numerous accessory archosomes attached to cone
fibers, others are seen on the cytoplasmic membrane. Many of the accessory
archosomes are seen to have a centrosphere.
Fic. 64. Spermatocyte. Spindle bridge ; remains of the central spindle which
has greatly contracted, many of its fibers showing muscular beading. One of the
dark granules is probably the archosome, it being situated where the granosphere
is being reconstituted. The cells which were connected by this bridge were in
about the same stage as the cell figured at 63.
Fic. 65. Spermatocyte in the chrysanthemum stage, more advanced than Figs.
63 and 64. The chromomeres and chromosomes are plainly indicated and partly
individualized. The section passed obliquely to the central spindle, showing
the cytoplasmic or false nuclear membrane with three or more accessory archo-
somes, from which radiate several fiber cones. This is not a free cell, but one
which was connected with another cell by a spindle bridge.
Fic. 66. Spermatocyte in the chrysanthemum stage. The cells are not yet
separated, but connected by a cell wall and a spindle bridge. Several fiber cones
are formed on the cytoplasmic membrane, pulling the latter away from the
nucleus. The accessory archosomes are not as distinctly stained as in the other
cells, which is due to the greater washing out of the iron stain. A mid-body in
the center of the spindle bridge. The retractile fibers are emanating from the
apex of the upper spindle pole.
Fic. 67. Spermatocyte in the chrysanthemum stage; the cells are not yet sepa-
rated. The central spindle is greatly contracted, the fibers at each pole are being
retracted and condensed into a reconstituting granosphere. The fiber cones have
advanced towards the cell wall, the accessory archosomes actually resting on the
cell wall. Several paracellular bodies are seen on the cell wall, some being con-
nected with the cell by fine threads. Retractile fibers emanating from the poles
of the central spindle. The accessory archosomes at the poles of the fiber cones
are too much washed out to be distinct. From two to three fragments of the
plasmosphere in each cell, easily identified by their deeper stain.
Fic. 68. Spermatocytes in the chrysanthemum stage. The two cells are more
separated than in the preceding figures. The fiber cones have reached the cell
wall, and some of them have receded from the cytoplasmic membrane, The
Journal of Morphology Vol. XVI. j PLVIL
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Lith. Werner & Winter Frankto
Spermatogenesis of Batrachoseps.
No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. III
granospheres are being reconstituted at the poles of the central spindle. In the
upper cell are seen three fragments of plasmosphere near the cell wall. The pole
of the upper central spindle rests on the cytoplasmic membrane, while the pole of
the other cell ends in the cytoplasm. A linin network is forming between the
chromosomes in the lower nucleus. Archosomes and accessory archosomes are
too much washed out to be distinctly visible. The mid-body consists of a double
row of granules.
Fic. 69. Spermatocyte in the chrysanthemum stage. The linin network is
appearing among the chromosomes. The fiber cones are pushing out the cell
walls in both cells. The accessory archosomes at the poles of the cones are well
defined; some are also seen on the cone fibers. The fragments of the plasmo-
sphere are seen in both cells, stained dark red. There are two archosomes at the
pole of the central spindle of the lower cell. At a deeper level the false nuclear
membrane was distinctly seen in each cell.
Fic. 70. Spermatocytes emerging from the chrysanthemum stage and entering
the second prophase. The two cells are only connected by a spindle bridge.
The chromosomes are separated, though some are yet connected by chromoplasts,
which latter are now located at the angle where the two prongs of the chromo-
some meet. The cytoplasmic membrane is yet seen around the nucleus, the latter
having filled out the vacuole. But a true nuclear membrane or karyotheca has
also been formed directly around the chromosomes, showing that the two mem-
branes are of different origin. Accessory archosomes are seen on the cytoplasmic
or false nuclear membrane; some are also seen on the cone fibers. Two fragments
of plasmosphere in the lower cell along the new cell wall. The granosphere is
being reconstituted, especially around the pole of the central spindle in the upper
cell. The chromosomes in the lower cell are further advanced than those in the
upper cell.
Fic. 71. Spermatocyte in the checkerboard stage, the chromomeres being
much separated. The fiber cones are yet pushing out the cell wall, though some
of them have evidently begun to dissolve. The new nuclear membrane has
formed around each nucleus. A large plasmosphere in each cell. Accessory
archosomes at the pole of each fiber cone. A mid-body on the spindle bridge.
Fic. 72. Spermatocytes connected by a spindle bridge on which is seen a mid-
body. The fiber cones are disappearing. The two spheres are reconstituting
separately, later on to be united. Many accessory archosomes on the fibers as
well as in the cytoplasm.
Fic. 73. Spermatocytes in the checkerboard stage, though further advanced
than the last figured cell. The fiber cones, however, are less degenerated, and the
granosphere is less advanced. A comparison of the two figures, 72 and 73, shows
that here, as elsewhere, the chromosomic process and the radiosomic process do
not run quite parallel, but that one may be in advance of the other. Thus in
73 the nucleus is further advanced than the nucleus of 72, but the cytosome of 72
is further advanced than the one of 73.
Fic. 74. Spermatocyte, free and in the checkerboard stage. The fiber cones
are yet faintly traceable. Several rings of somosphere with accessory archo-
somes. An unusually small cell.
Fics. 75 and 76. Spermatocytes, free, in the checkerboard stage. These two
figures represent two sections of the same cell. The numerous fiber cones have
not yet begun to recede. Several rings of somosphere with accessory archosomes.
112 EISEN. [Vou. XVII.
The chromomeres are seen to be of different sizes and to contain a variable num-
ber of from nine to three chromioles each.
Fic. 77. Spermatocyte, free and with chromosomes in the checkerboard
stage. The chromomeres are well separated and contain about three to nine
chromioles each. The spheres are being reconstituted together, the inner one
being the granosphere and the outer one the plasmosphere. An archosome with
two centrioles on the plasmosphere. The fiber cones have not yet disintegrated,
the upper one with a distinct accessory archosome at the apex.
Fic. 78. Spermatocyte, free and with the chromosomes in the chrysanthemum
stage. The chromomeres are much separated, though the staple-shaped form of
one of the chromosomes is distinct. The spheres are reconstituting in the upper
left corner of the cell. Accessory archosomes connected by a ring of somo-
sphere. The remains of the fiber cones are recognizable in the four projecting
corners of the cell. A linin network is stained reddish.
Fic. 79. Spermatocyte, free, the chromosomes in the beginning of the con-
traction stage or the third prophase. All traces of fiber cones have disappeared.
The spheres are being reconstituted, the darkly stained one being the granosphere.
Numerous accessory archosomes in the plasmosphere.
Fic. 80. Spermatocyte, free and the chromosomes in the beginning of the con-
traction stage. The two spheres are being reconstituted. Numerous accessory
archosomes on the plasmosphere. Figs. 80-82 are in very much the same
stage of development, but representing a serial development and contraction of
the chromosomes. In Figs. 81 and 82 the plasmosphere is reconstituted in the
opposite end of the cell from the granosphere. This is frequently the case in the
spermatocyte, and saves the redistribution of the sphere to the equatorial of
the new spindle.
Fics. 81 and 82. See Fig. 80.
Fic. 83. Spermatocyte. Contraction stage in which the chromosomes are
again assuming their staple form, and in which the linin network is separating
from the chromosomes. This stage corresponds to the bretzel stage of the auxo-
cytes. Figs. 83 and 84 are in nearly the same stage. The plasmosphere is recon-
stituted in the opposite part of the cell from the granosphere. Numerous acces-
sory archosomes around the granosphere. The similarity of all is so great that it
cannot be decided which of them is the archosome. Chromomeres show the
interior chromioles.
Fic. 84. See Fig. 83.
Fic. 85. Spermatocyte in the beginning of the angular chromosomes, the
fourth prophase. The chromosomes have become narrower and the margins are
more even. This stage corresponds to the angular segments of the auxocytes,
though there are some important differences. The chromoplasts, for instance, are
very prominent in the auxocyte, while in the spermatocyte they are only now and
then to be distinguished from the chromosomes. Only a few of the chromosomes
are figured. At the lower margin of the cell are seen the spheres, but it is doubt-
ful if the round mass is anything but the plasmosphere. The linin network is
disintegrated and retracted from the chromosomes. Several of the superfluous
archosomes have been expelled from the cell and are now seen attached to the
exterior of the cell wall. They have also swelled up and increased perhaps five-
fold in size, but to what extent their inner structure has become modified by the
swelling up is not clear. It seems, however, most probable that the somosphere
PL.VII..
Vol. Xvi
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Spermatogenesis of Batrachoseps.
PLIX.
Journal of Morphology. ae ol.XI UW.
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78. ¢ Fe
Spermatogenesis of Batrachoseps
re |
No. I.] SPERMATOGENESIS OF BATRACHOSEPS. I13
has filled out the centrosphere, and that the centrioles have separated from each
other.
Fic. 86. Spermatocyte in the angular chromosome stage. This and the previ-
ous figure are very much in the same stage as regards the nucleus. The spheres
are not distinct and there are no expelled archosomes. Three accessory archo-
somes at the upper part of the cell.
Fic. 87. Spermatocyte in the beginning of the knotted chromosome stage.
The chromosomes are separated and, have not yet accumulated in the center of
the cell. Numerous accessory archosomes, each one surrounded by an amoeboid
centrosphere. A very small granosphere. Chromioles are seen in the chromo-
somes.
Fic. 88. Spermatocyte in the knotted chromosome stage. A distinct grano-
sphere, a scattered plasmosphere, and numerous accessory archosomes in the
cytoplasm. Some of the archosomes are being expelled from the cell. Chromi-
oles are seen in the chromosomes.
Fic. 89. Spermatocyte in the knotted chromosome stage. Several fiber
cones are yet seen, and it is probable that two of them will form the central spin-
dle. Numerous accessory archosomes on the fibers of the cones, some of the
fibers evidently dissolving the nuclear wall.
Fic. 90. Spermatocyte in the knotted chromosome stage. The nuclear mem-
brane is completely dissolved by two fiber cones. The individual chromosomes
are so tightly knotted that they are difficult to segregate one from the other.
The chromosomes are only approximately correctly figured. These two fiber
cones are probably the beginning of the central spindle. A sphere is seen in the
upper apex of the cell; many accessory archosomes and an archosome with an
amoeboid centrosphere.
Fic. 91. Spermatocyte in the knotted chromosome stage. Only a few chro-
mosomes are seen in the section. The nuclear membrane has been dissolved by
the fiber cone emanating from the upper apex. The linin network is scattered
and the granules are mixing with the cytoplasm. Accessory archosomes on the
fibers and one at the lower pole of the cell. Each one is furnished with an amoe-
boid centrosphere. Some of the chromioles in the chromosomes are distinct.
Fic. 92. Spermatocyte in the V-stage; the chromosomes are in the center of
the cell. Only one pole of the central spindle is developed, there being no trace
of the other pole. The nuclear membrane is dissolved. A plasmosphere to the
left of the future equator. A dividing archosome in the pole of the spindle.
Fic. 93. Spermatocyte in the beginning of the V-stage, the chromosomes being
in the center of the cell. A central spindle is being formed out of two old fiber
cones. At the apex of each cone is an accessory archosome which is now assum-
ing the function of an archosome.
Fic. 94. Spermatocyte. Chromosomes in the knotted stage, but the central
spindle has already formed out of two opposing fiber cones. This is the charac-
teristic form of the spindle in this stage, the two poles being greatly depressed.
An archosome at each pole. There is no distinction between the mantle fibers
and the central spindle fibers. I found several cells like this one, but no interme-
diate stages with Fig. 93.
Fic. 95. Spermatocyte. In the V-stage, not yet in the metaphase. The
upper pole with several accessory archosomes, one of which is the spindle archo-
some. The lower pole has probably been cut off by the knife.
II4 EISEN. [VoL. XVII.
Fic. 96. Spermatocyte in the beginning of the V-stage. Half of the spindle
has been cut off. There are three accessory archosomes at the upper pole, one
of which probably has the function of a spindle archosome. The plasmosphere
is scattered in the equator. The archosomes at the pole have a remarkable simi-
larity to the expelled archosomes figured elsewhere (Fig. 85).
Fic. 97. Spermatocyte in the beginning of the V-stage, or the end of the
knotted chromosomes. The central spindle is finished, but the chromosomes are
not yet in position. The plasmosphere is in the equator. The accessory archo-
somes lie in a ring around the poles of the spindle.
Fic. 98. Spermatocyte in the V-stage just before the beginning of the meta-
phase. The chromosomes in the form of perfect V’s, which, however, are not
yet distributed’ along the spindle. The mantle fibers are connected with the
granules of the plasmosphere. An archosome at each pole, also a large accessory
archosome with an amoeboid centrosphere. Contractile fibers are forming and
projecting from the centrosphere of the archosomes.
Fic. 99. Spermatocyte in the perfect V-metaphase. The contractile fibers are
formed and connect with the chromosomes. An archosome at the upper pole;
the lower pole is cut off. A trace of the plasmosphere to the left of the equator.
Only a few of the chromosomes are figured.
Fic. 100. Spermatocyte in the perfect V-metaphase. Only a few of the chro-
mosomes are figured. The chromosomes are splitting at the bottom or angle of
the V. An archosome at each pole surrounded by a pale centrosphere. The
contractile fibers are plainly beaded. Blotches of plasmosphere stained pink.
Many chromioles are seen in the chromosomes.
Fic. 101. Spermatocyte in the perfect metaphase; some of the chromosomes
are separating, while others are not yet in their proper position on the central
spindle. Several larger groups of plasmospheres along the equator. An archo-
some at each pole, surrounded by several accessory archosomes, each one with
developed centrosphere.
FIG. 102. Spermatocyte in the beginning of the anaphase. An archosome at
each pole, and a few accessory archosomes in the cytoplasm. Chromomeres and
chromioles visible in the chromosomes.
Fic. 103. Spermatocyte in the perfect V-anaphase. The chromosomes have
separated, the chromomeres have mostly disappeared, but the chromioles are yet
distinct, and arranged in two parallel rows in each chromosome. The plasmo-
sphere is scattered along the equator of the contracting spindle. The mantle
fibers are seen to be connected with the plasmospheric granules. An archosome
at each pole.
Fic. 104. Spermatocyte in the beginning of the confluent stage of the ana-
phase. The contractile fibers have shortened and the chromosomes have become
partly confluent. The chromomeres have disappeared, but the chromioles can
yet be distinguished here and there. Parts of the plasmosphere along the
equator.
Fic. 105. Spermatocyte in the beginning of the confluent stage of the ana-
phase. The cell has already begun to divide and a new membrane is being
secreted along the vacuolated equator by the plasmospheric granules. The polar
cones of the central spindle have so shortened as to be hardly distinct. The
archosomes are reduced in size and barely visible. A few of the chromioles are
distinct in the chromosomes.
Journal of Morphology. Vol.Xvil ; ane
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Spermatogenesis of Batrachoseps.
Journal of Morphology. Vol. XVII.
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No. 1.] SPERMATOGENESIS OF BATRACHOSEPS. I15
Fic. 106. Spermatocyte in the confluent stage, but the confluence is not yet
perfect. The polar cones are mostly gone and the archosomes so faint as to be
indistinct. The new cell membrane has formed along the equator of the central
spindle. The latter has contracted, several of its fibers being beaded. Many
plasmospheric granules along the new membrane, especially on the left side.
Fic. 107. Spermatocyte in the perfectly confluent umbrella stage. The cells
are almost separated and are only connected with each other by the central
spindle. The spindle is greatly contracted, showing some beaded fibers. No dis-
tinct archosomes, and the polar cones have so descended into the nucleus as
to be no more visible. A false nuclear membrane is being formed around the
nucleus. The pole of the lower spindle is just above the nucleus; at the apex is
a small archosome. In the upper cell is a large accessory archosome.
Fic. 108. Spermatocyte in the end of the confluent stage, the chromosomes
just beginning to reappear in the chrysanthemum stage. The cytoplasmic mem-
brane is fully formed around the nucleus, and is now being pulled away by the
centrosomes. The granospheres are being reconstituted around the poles of the
spindle. Parts of the plasmospheres are seen along the new cell walls. A mid-
body on the central spindle, which latter has been greatly contracted. The poles
of the central spindle are connected with the cytoplasmic membrane by a few
fibers.
Fic. 109. Spermatid. In a rather advanced stage of development, the nucleus
having assumed its full size. The two spheres have been reconstituted. An
archosome is seen to the left of the granosphere. The nucleus is in the checker-
board stage. Several paracellular bodies are attached to the exterior of the cell.
These are probably expelled particles of the spheres, which have become inflated.
They show in their interior a fibrous structure. There are two distinct chromo-
plasts in the nucleus, recognizable by their endochromatic granules. The remains
of a spindle bridge at the upper pole of the cell.
Fic. 110. Auxocyte. Detail figure of one of the central spindle poles, show-
ing the formation of the contractile fibers and their connection with the somo-
sphere of the archosome. In the center of the field is seen a large archosome
consisting of a darkly stained inner centriole and somosphere, surrounding which
is a large unstained centrosphere. Twelve fine bars connect the centriole with
the contractile fibers which begin on the outer margin of the centrosphere. On
the upper ends of the centrosphere only the ends of the contractile fibers are
seen. Several accessory archosomes in a ring around the archosome. The red,
granular plasma, divided in three groups, is the remains of the plasmosphere.
Each accessory archosome possesses a centrosphere. The contractile fibers are
strongly beaded.
Fic. 111. Auxocyte. Detail figure of a pole of the central spindle, showing
the archosome and its connection with the central spindle fibers and the con-
tractile fibers. The archosome is large and contains two centrioles, each sur-
rounded by a somosphere. Several accessory archosomes, one of which appears
to be the starting point of a contractile fiber. The contractile fibers are strongly
beaded. Zeiss Apo. 2 mm., Apert. 1, 40, Oc. 18.
Fic. 112. Auxocyte. Detail figure of an archosome; the contractile fibers
start from the outer margin of the centrosphere. The chromosomes are in the
anaphase, with the contractile fibers greatly contracted. They are strongly
beaded, the beads being situated between a covering of granulated fibers, evi-
116 EISEN. [Vo. XVII.
dently forming a casing to the granules. The beading of the contractile fibers
is probably of the same nature and origin as the mid-body. That is, the beads
may serve as storage reserves of plasma to be used when the contractile fiber is
lengthened or shortened. When suddenly lengthened on account of strain the
plasma is probably supplied by the beads, and vice versa; when the contractile
fiber requires to be suddenly shortened its superfluous plasma is quickly accumu-
lated in the beads. Chromioles are plainly visible in the chromosomes, especially
in the one to the left. Zeiss Apo. 2 mm., Apert. 1, 40, Oc. 18.
Fic. 113. Auxocyte. Detail figure of an archosome and six of its contractile
fibers, showing them to start from the outer edge of the centrosphere. Some of
the fibers connect with the inner centriole by a fine bar of somosphere. The
contractile fibers are strongly beaded, somewhat of the nature of a muscle fiber.
The beads are situated in zigzag fashion and covered by a sheathing of fibrous
nature. There are three strongly stained accessory archosomes at the pole. The
chromosomes are only indicated. The figure is drawn to a larger scale.
Fic. 114. Spermatocyte. Detail figure of a fiber cone showing the connection
of the fibers with the accessory archosomes. Several of the latter possess amoe-
boid centrospheres. The nucleus is in the checkerboard stage.
Fic. 115. Spermatocyte. Detail figure of a fiber cone. The outer edge of
the cone forms also the outer cell wall. An accessory archosome with several
centrioles is near the apex of the cone. This cone is less advanced in dissolu-
tion than the one figured in Fig. 114, though it is from the same cell.
Fic. 116. Spermatocyte. Detail figure of a fiber cone in dissolution, showing
the granulated and beaded structure of the fibers. At the apex is an accessory
archosome. The outer edge of the cone is closely pressed against the cell wall.
Fic. 117. Spermatocyte. Detail of a fiber cone in dissolution. The accessory
archosomes have left the apex of the cone and are now congregating around the
reconstituting granosphere. Each centrosome possesses an amoeboid centro-
sphere. Some of the centrosomes are yet attached to the cone fibers. The outer
lining is the cell wall.
Fic. 118. Spermatocyte. A nucleus in the chrysanthemum stage, showing
the staple-shaped chromosomes in a stage of growth. The nuclear membrane is
formed in the immediate vicinity of the chromosomes. The chromomeres and
some of the chromioles are distinct. The linin network is stained red.
Fic. 119. Spermatocyte. A nucleus and two detail figures of chromosomes.
The details are drawn on a slightly larger scale, but with the same magnification
and objective. The chromosomes are further advanced than in Fig. 118. The
chromomeres are separating. Some of them contain eight or ten, others only
three to four chromioles.
Fic. 120. The homoeotypic mitosis by equation division of the spermatocyte
from the perfectly split / to the confluent umbrella stage. a@ to fshow the V-
shaped chromosomes as they are thrown on the central spindle; some are seen in
front view, others in side view. The fibers connecting with the chromosomes are
contractile fibers. . to 4 show the chromosomes in the act of separation, being
pulled apart by the contractile fibers. At 7 is seen one of the daughter-chromo-
somes in which the chromioles are very distinct. z to £,chromosomes after the
halves have separated and the daughter-chromosomes have formed. J/, m,
chromosomes in the confluent umbrella stage; in 7 no endochromatic granules
are seen on account of too dense staining. In m many endochromatic granules.
PLXMI.
Journal of Morphology Vol. Xvi.
108.
105.
11+.
T11.
i
110.
109.
115.
Spermatogenesis of Batrachoseps
ar
No:\5.] SPERMATOGENESIS OF BATRACHOSEPS. PE
All the above chromosomes are copies from actual chromosomes and not dia-
grammatic.
Fics. 121 and 122. The heterotypic mitosis by equation division. A diagram-
matic representation of the development of leaders of an auxocyte into chromo-
somes, their splitting and equation, in a progressive series from a to/. a, two
leaders connected by a divided chromoplast, the latter marked c. Numerous
chromomeres on the leaders, each with several chromioles. 6, the same two
leaders, the chromomeres having contracted into a smaller number, each chromo-
mere having more chromioles, which latter have now been arranged in two
parallel rows in each chromomere. This is the beginning of the stage in which
the leader splits. c, the same two leaders, but which have now split into four
leaders, each one of which will become a single chromosome in the daughter-
nucleus. The two halves of one leader form the bretzel-shaped chromosome.
Observe that the chromomeres have again separated and become smaller. d, the
same two leaders, the chromomeres having contracted anew, the whole leader
having shortened. ¢, the same two leaders, which have yet more shortened, and
the chromomeres have contracted into a smaller number; the two chromoplasts
are seen at the junction of the two leaders. /, a single leader which has become
separated through the division of the chromoplast. It now forms a perfect bretzel-
shaped chromosome, consisting of two prongs connected by a dividing chromo-
plast. The two prongs of the leader have crossed each other and thus formed
the bretzel. g to & are various forms of bretzel chromosomes, some of which
have their free ends overlapping, while two of them have the ends actually grown
together. 7, a chromosome which has just undergone equation division. The
parting has taken place through the chromoplast; cc, the two ends which were
grown together, are yet united by two fine threads of chromoplasm. m, two
chromosomes in the confluent umbrella stage, with several endochromatic
granules.
XIII. STAINS, FIXATIVES, OPTICAL APPARATUS, Etc.
Congo, No. 1209, The Substantive Colors Co. Actien Gesellschaft fiir Anilin-
Fabrication.
Thionin, Cogit & Co., Paris.
Rutheniumroth, Dr. G. Griibler & Co., 200, Leipzig.
Iridium Chloride, Merck & Co., Darmstadt, Germany.
Apochromat No. 412, 2 mm., Apert. 1. 40, Homog. Immers. Carl Zeiss, Jena.
Apochromat No. 262, 3 mm., Apert. 1. 40, Homog. Immers. Carl Zeiss, Jena.
All the chemicals and optical apparatus furnished by Charles C. Riedy, San
Francisco, Cal.
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PLXIV;
journal of Morphology. Vol.Xvit.
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PROFESSOR COLLETIT ON THE MORPHOLOGY. OF
THE CRANIUM AND THE AURICULAR OPEN-
INGS IN THE) NORTH-EUROPEAN SPECIES O8
SHE PAMIMICY (StTRIGID A:
R. W. SHUFELDT, M.D.
One of the most extensive and valuable contributions to
the subject of the anatomy of owls, and their classification,
was given to science by Prof. Robert Collett of the Zodlogical
Museum of Christiania, Norway, in 1881. This brochure was
read by him before the Scientific Society of that city on
December 9, and published in its Proceedings for the same
year. This memoir printed nearly forty pages octavo, and is
illustrated by three folding lithographic plates, giving thirty-
five figures of the skulls and ear-parts of various species
of the family considered, the whole being entitled Cvanzets
og Oreaabningernes Bygning hos de nordeuropeiske Arter af
Familien Strigide. Appearing, as it did, in the Norwegian
language, the usefulness of this very excellent piece of work
was to a great extent limited, and many comparative anato-
mists all over the world could not readily employ it or avail
themselves of its results, both of which uses it so amply
merited, for the very reason that it was in Norwegian, a
language rarely mastered by naturalists at large. With the
view of obviating all this, and bringing the investigations of
Professor Collett in the osteology and taxonomy of the Strigz-
de before the English-speaking world, I have long planned to
have his memoir in these fields translated, but, from one cause
or another, the task had to be postponed. Events of a partic-
ularly unfortunate nature stood in my path during the entire
summer of 1895 and late into the following autumn, but with
the opening of the year 1896, circumstances became far more
propitious for the resumption of all my work in comparative
1 ae)
120 SHUFELDT. [VoL. XVII.
morphology, and among the first tasks undertaken by me was
the translation of this worthy contribution to avian anatomy
by my esteemed colleague in Christiania. This has been ren-
dered possible through the kind assistance of my young Nor-
wegian friend, Miss Alfhild Dagny Lowum, now my wife, who,
with great patience, made the literal part of this translation.
With this before me, Professor Collett’s memoir was given
its English version in the language of science. My private
osteological cabinets contain the skeletons of many species
of owls, and the crania of these I have compared with his
researches as the labor of translation progressed, giving such
additional information as was thus obtained in footnotes, and
signed by my own initials. JI have also seen fit to rearrange
his figures, redrawing some of them for text-figures, and retain-
ing those for lithography that especially demanded that kind
of reproduction.
The present contribution, then, consists in a full and com-
plete English translation of Collett’s memoir, supplemented
by footnotes of my own, and a reproduction of all the figures
given in the original Norwegian work. And to this I have
added some of the more recent opinions of recognized authori-
ties upon the subject, relative to the systematic position of
the Strigide, thus bringing the whole up to date and ren-
dering the entire memoir available to students of comparative
morphology everywhere; it being, as it were, a comprehensive
treatise upon the value of certain structures to be found in
the head and cranium in owls in the classification of that
family, together with their relations to other groups of birds,
as those relations are understood at the present time.
Professor Collett says :
«The ten North-European species of the family Strzgzde, all
of which belong to the subfamily Lwbonine (the other sub-
family, which is represented by Stvzx flammea, does not occur
in Scandinavia), can be arrayed in six (6) groups based upon
the morphology of the cranium and upon the structure of the
external ear-openings and their dermal appendages.”
It is clear from the following table that only the first of these
groups, which includes Surnia funerea, Glaucidium passerinum,
Kit
LE CRANIUM TIN TRE, OWES.
No: T.]
Family, Bubonine.
Order, Striges:
A. Dermal F
aGHGtlaT I. Cranium
flaps symmet-
absent. | rical.
I. Cranium
symmet-
rical.
B. Dermal
auricular
flaps
present.
II. Cranium
asymmet-
rical.
I. sect. ‘Process
. Group. Auric- dexclaped ee
ular openings jueae [
symmetrical.
2. Sect. Jugal lin-
Cale eae
2. Group. Auricular opening largest
upon the right side ... .
3. Group. Auricular openings asymmet-
rical; resembling a gill-slit; aural
skin-flaps of equal size, as are also
the auricular openings.
4. Group. Auricular openings asymmet-
rical; reniform ; the skin-flap larg-
est upon the right side. . .
5- Group. Cranium asymmetrical upon [
the right side; ear-openings reniform
4
in outline ; and the skin-flap largest
upon the right side.
a. Supraorbital processes
Styliformi esos oe
6. Supraorbital processes
broad and short. . .
a. Frontals narrowly sculpt.
6. Frontals broadly sculpt.
a. Os squamosum slightly
asymmetrical. =.
6. Os squamosum markedly
asymmetrical. . . .
6. Group. Bilateral asymmetry of the cranium; auricular openings wide;
equal in size; dermal flap similar to cranial asymmetry . .. .
a
o>
Io.
Surnia funerea (Linn.) 1776.
1776.
Wyctea scandiaca (Linn.) 1766.
Bubo ignavus (Forst.) 1817.
Asio accipitrinus (Pall.) 1771.
Asio otus (Linn.) 1766.
Syrnium aluco (Linn.) 1766.
Syrnium uralense (Pall.) 1776.
1789.
Wyctala tengmalmi (Gmel.) 1788.
122 SHUFELDT. [VoL. XVII.
and Vyctea scandiaca (all lacking ear-flaps), have perfectly
symmetrical auricular openings and crania. In all the other
groups, including seven species, the auricular apertures are
unequal in size or asymmetrical in other ways. On the two
last groups, which include Syrntum uralense, Syrnium lappont-
cum, and Nyctala tengmalmi, the asymmetry is so pronounced
that even the cranium is more or less involved.
This asymmetry of the auricular openings, their dermal
flaps, or the cranium, commonly exhibits itself as an anoma-
lism of the right side of the head, so the opposite or left side
in these must be regarded as the normal one.
This anomalous condition in the majority of our species, so
far as the auricular openings and their dermal flaps are con-
cerned, consists in these strictures being larger and of greater
width on the right than on the left side. Where this condi-
tion also exists in the cranium, it is again the right side which
exhibits the anomalous development. It is only in Wyctala
tengmalmi wherein we find that both sides present the con-
dition referred to, and perhaps the most so upon the left side.
In the two species of Aszo, where the irregularity is confined
to the dermal parts of the aural apertures, the right side must
again be regarded as the normal side. /¢ would appear that in-
asmuch as the internal ear and the brain cavity are perfectly
symmetrical, neither of these parts enter into this anomalous
state of affairs.
The six groups into which the North-European species fall
can be briefly characterized as follows :
Group I. Dermal ear-flaps absent. Cranium and auricular
openings symmetrical.
a. Jugal with an elevated osseous apophysis.
I. SURNIA FUNEREA (Linn.). 2. GLAUCIDIUM PASSERINUM (Linn.).
Auricular openings of medium size or small. Osseous crests on os
Sguamosum conspicuously individualized; viewed anteriorly they come
into plain sight at the posterior aspect of either orbit. Posterior periphery
of either orbit sharp where formed by the frontal bone. The greatest
NO: 'k.]] THE CRANIUM IN THE OWLS. 123
vertical height of the cranium is posterior to the orbits. Vomer rudimen-
tary. Jnfraoccipital foramen present, and large in the case of G. pas-
serinum. The supraorbital processes in S. fumerea long and styliform.
Crania lack the superficial median furrow upon their superior aspects.
6. Jugal linear.
3. NycTea scanpiAca (Linn.).
Auricular openings of medium size and placed inferiorly. Osseous crest
of os sguamosum comparatively small, and xon-united superiorly ; viewing
the skull from in front, they are almost entirely concealed by the orbits.
Vomer rudimentary. Supraoccipital foramen present. Median furrow on
superior aspect of cranium present.
To this first group, then, which includes species without
dermal ear-flaps, and where no asymmetry is present in any
part of the head, belong Surnia funerea, Glaucidium passert-
num, and Nyctea scandtaca.
Of these three, the two first-named species constitute a
subgroup of themselves, since in certain of their cranial char-
acters which they exhibit in common and in which they differ
from the Norwegian species, they must doubtless be con-
sidered, systematically speaking, as allied to each other. Both
Surnia funerea and Glaucidium passerinum develop, superiorly,
upon the jugal bone an elevated, oblong process of some
length, while this bone in all the remaining North-European
species is linear. Further, the superior aspect of the skull is
flat and entirely lacking in a median furrow, which latter in
_all the other species is present. Within this group the crania
can be distinguished in the two species one from the other, in
addition to the difference in size, by the feebler development
of the mandibles in Glauctdium passerinum, which in its case,
as compared with the cranium proper, are shorter than are the
mandibles in any other species. Further, the supraoccipital
foramen in this species is unusually large, both relatively and
absolutely ; in fact, larger than it is in any other form. In
addition thereto, Surnia funerea has the supraorbital processes
long and spiculiform, approaching in this respect the diurnal
Raptores.
Nyctea scandiaca, constituting the second subgroup, has
124 SHUFELDT, [Vou. XVII.
another type of cranial structure. In it the orbits are notably
large, and the mandibular part strong. The jugal bone is
linear, and the supermedial furrow of the cranium is well
marked. The auricular openings in most of their characters
agree with those forms already described, in being relatively
small or of medium size, and in lacking any external dermal
conch, or ear-flap.
Group II. Aural skin-flaps absent. Cranium symmetrical.
Auricular apertures largest upon the right side.
4. BugBo 1GNAvus (Forst.).
Ear-openings of medium size; nearly of the same dimensions. Osseous
crest of the os sguamosum comparatively small, completely free above ;
viewed anteriorly, they are almost concealed by the orbits. Posterior
periphery of either orbit sharp where formed by the frontal bone. Cranium
has a supermedial furrow present; its greatest height is posterior to the
orbits. Jugal linear. Vomer present. Supraoccipital foramen present.
To this, the second group, belongs Bubo zgnavus, which is
further characterized by possessing a symmetrical cranium, and
the lack of dermal ear-flaps, but in this species the first evi-
dence of asymmetry exhibits itself in an insignificant differ-
ence in the size of the two ear-openings. Here the cranium
has a structure most like Wyctea scandiaca, and has, as in that
species, powerfully developed mandibles, a conspicuous median
furrow on the supero-external aspect of the cranium, broad
and prominently outstanding orbital wings, markedly capa-
cious orbits, and feebly developed osseous crests on either
os Squamosum.
Owing to the feeble development of these processes we may
infer that the sense of hearing in this owl is comparatively
less acute than it is in any other North-European species.
The similarity in the structure of the cranium in these two
species is, upon the whole, so close that doubtless they would
have both been relegated to the same group had not the
right ear-opening in B. zguavus been a little larger than the
left, a state of affairs that I have not been able to demonstrate
with certainty in the case of Vyctea.
No. I.] THE CRANIUM IN THE OWLS. 125
Group III. Lar-flaps present. Cranium symmetrical. Ear-
openings asymmetrical, resembling a gill-slit, but the aural
skin-flaps of equal size.
5. ASIO ACCIPITRINUS (Pall.). 6. Asio oTus (Linn.).
Auricular fissures or slits carried high up. The entrance to the ear is
on the right side below, and on the left side above an outstretched fold
of the skin. Osseous crest of the os sguamosum, upon either side, meets
with the frontal bone above, without any intervening notch. Viewed from
in front they are wholly visible beyond the orbits. Frontal bones obliquely
sculptured at the posterior margins of the orbits; the sculpturing being
most marked in A. ofws. External supermedial furrow of the cranium
present ; greatest vertical depth of cranium lies in the postero-orbital plane.
Jugal linear. Vomer present. Supraoccipital foramen generally found.
The third group contains the two species of Aszo, viz. :
A. accipitrinus and A. otus. In the case of these also is the
cranium symmetrical, while the auricular openings and their
dermal appendages exhibit in their structure a very remarkable
asymmetry. The apertures to the ears are so markedly wide
that they remind one of gill-slits, inasmuch as they extend
from the nether side of the mandible, upon either side, up to
a point near the middle of the forehead, where they are sepa-
rated only by a small interval of space. Upon either side of
this long slit-like aperture there is a raised fold of skin, the
two resembling a pair of lids, of which the supero-anterior one
is the real ear-flap. Crossing the aperture is an elevated fold
of skin, and it is in its neighborhood that the asymmetry is
especially observable. To its left side, and above it, we find
the entrance to the ear, while on the right side of the head
it lies below this fold. So far as the cranium itself is con-
cerned it does not exhibit any special asymmetry. The
osseous crests of the squamosal bones are peculiar in form,
inasmuch as they ascend up to the frontal, upon either side,
without any intervening notch, whereby they are endowed
with an unusual amount of superficial surface, and with great
depth; this, taken in connection with the unusual development
of the external ear-openings, accounts for the sense of hearing
having attained to its greatest acuteness in this group. The
126 SHUFELDT. [VoL. XVII.
difference in the cranium of the two species is not very
marked, it being confined principally to the oblique osseous
plane formed by the frontal, upon either side, that extends to
form the posterior periphery of the orbit. This is greater in
A. otus than in A. accipitrinus.
Group IV. Larflaps present. Cranium symmetrical. Auritc-
ular openings reniform in outline, and the earfiap largest
upon the right stde.
7, SYRNIUM ALUCO (Linn.).
Auricular openings wide, carried high up, and with broad ear-flaps.
Osseous crest on os sguamosum completely free above. Viewed anteri-
orly, they are almost concealed by the orbit upon either side. Posterior
periphery of orbit, where formed by the frontal, rounded. Median furrow
present upon superior aspect of cranium; and the greatest depth of the
latter is at a point just over the center of the orbit. Jugal linear. Vomer
rudimentary. Supraoccipital foramen present.
In Syrnium aluco, which belongs to the fourth group, the
cranium, ear-openings, and ear-flaps are constructed upon a
very different type as compared with the other species. We
find the cranium still symmetrical ; but the auricular openings,
which are slit high up, and are reniform in outline, are larger
upon the right side. The same obtains with the broad, almost
door-shaped ear-flaps, the form of which is somewhat different
upon either side of the head.
To this group also belong the other two North-European
species — S. wvalense and S. lapponicum. In them the cra-
nium is alike in form, and the auricular openings and the ear-
flaps are as they occur in S. aluco. In these species, however,
the asymmetry is extended even to include the cranium, while
in S. aluco the cranium is perfectly symmetrical. S. aluco
has the margins of the frontals evenly rounded where they go
to form the posterior peripheries of the orbits, and the hinder
part of the cranium is prettily dome-shaped, with a conspic-
uous, nail-like, anteriorly projecting process upon either os
sguamosum. The thinner part of the interorbital septum,
which until now has been comparatively thick, is beginning
No. I.] THE CRANIUM IN THE OWLS. 127
to be less extensive, inasmuch as the orbits themselves are,
comparatively, not very large.
Group V. Ear-flaps present. Cranium asymmetrical upon
right side. Auricular openings reniform in outline, and,
as in the case of the ear-flaps, largest upon the right side.
a. Crania with slight asymmetry.
8. SYRNIUM URALENSE (Pall.).
Auricular openings wide, carried high up, with broad ear-flaps, with the
difference between the two flaps not as marked. Osseous crest on os
sguamosum completely free above, more conspicuously bent forwards
upon the right than upon the left side, though without coming in contact
with the posterior surface of the alisphenozds in either case. Frontal
bones rounded at the posterior margins of the orbits, with a deep concavity
behind either supraorbital process. Longitudinal median furrow present
upon the superior aspect of the cranium, and the greatest height of the
latter is situated somewhat posterior to the middle of the orbital cavity.
Interorbital septum quite thick. Jugal linear. Vomer rudimentary. Supra-
occipital foramen absent.
6. Cranium decidedly asymmetrical.
9. SYRNIUM LAPPONICUM (Hunt.).
Ear-openings wide, slit high up, and with broad ear-flaps. Asymmetry
slight. Osseous crest on os sguamosum normal on left side, conspicuously
individualized. Osseous crest on right side has its supero-external angle
inclined forwards and codssified with the posterior margin of the alisphe-
noid, which is strongly developed laterally. Frontal bones completely
rounded off at the posterior borders of the orbits, and with a profound
notch posterior to the supraorbital processes. Cranium with a longitudinal
median furrow on its superior aspect, and the greatest depth of the former
is posterior to the orbits. Interorbital septum short and thick; orbital
diameter comparatively small. Jugal linear. Vomer rudimentary. Supra-
occipital foramen absent.
The fifth group, which, as above noted, is closely related to
the fourth, and contains the two other North-European species
of Syrnium, is characterized by having the cranium as well as
the auricular openings and ear-flaps asymmetrical. So far as
the two last-named parts are concerned, they have a structure
128 SHUFELDT. [VoL. XVII.
similar to what occurs in S. al/uco, but the difference between
the two sides is, strangely enough, upon the whole, less decided
than in the last-named species, although always noticeable. It
is here likewise that it is the right side wherein the auricular
openings and ear-flaps are the larger. The asymmetry of the
cranium is similar in either species, owing to a peculiar struc-
ture of the right osseous crest of the os sguamosum, which is
the case in a more marked degree in S. lapponicum than it
is in S. wvalense. In the last-named species the asymmetry is
but feebly pronounced, although always present ; the osseous
crest of the os sqguamosum is somewhat more produced for-
wards upon the right side, but nevertheless does not quite
come in contact with the hinder border of the alisphenoid.
On the other hand, this is the case in S. /apponicum,; the
osseous crest is more lofty and wider, and extends its superior
margin quite to the above-named bone, with which it coésifies.
At the same time the entire right side of the head is more
drawn out laterally, and exhibits a greater vertical compres-
sion than it does upon the left side, and this is especially to
be observed when the cranium is viewed upon its anterior
aspect. In both these species the orbital cavity is compara-
tively small, and the interorbital septum low and thick, which
is especially the case in S. lapponicum.
In the last-named species the cranium is, upon the whole,
smaller as compared with the beak than it is in any other
species, and this, notwithstanding the fact that the beak is
not very powerfully developed, as it is, for example, in Budo
and Vyctea.
Group VI. Lar-flaps present. Cranium decidedly asymmet-
vical. Auricular openings wide, uniform in size, and
together with the ear-flaps exhibiting an asymmetry agree-
able with that of the cranium.
10. NycTALA TENGMALMI (Gmel.).
Auricular openings very wide, with crescent-formed ear-flaps; Asym-
metry of aural entrance agreeing with that of the cranium. Osseous crest
of os sguamosum large, deep, and distorted upon both sides; especially
N@nT:] LHE CRANIUM IN THE OWLS. 129
lofty upon the right side, and situated far posterior to the orbit ; on the
left side greatly compressed, and comes in contact with the hinder margin
of the orbit above. Anteriorly, both osseous crests are produced as long,
forward-projecting processes ; that on the right side meets the posterior
border of the orbital crest of alisphenoid, and on the left is deflected,
so as to come in contact with the mandible. Medio-longitudinal furrow
exists upon superior aspect of cranium ; the skull’s greatest depth being post-
orbital. Jugallinear. Vomer rudimentary. Supraoccipital foramen present.
In the last group, which is created to contain WVyctala teng-
malmt, the cranium sees its greatest asymmetry, as this asym-
metry occurs in the left as well as in the right side. It is here
also that the os sguamosum with its osseous crest exhibits its
maximum amount of anomalous development. On the right
side the osseous crest is lofty, approaching the same plane
above in which lies the superior contour line of the head. On
the left side it is as decidedly drawn downwards, and with the
tongue-like process on the osseous crest likewise so markedly
inclined in the same direction that the apex of the latter is in
direct contact with the lower jaw —a condition which is per-
haps unique for this genus in the class Aves.
I have already availed myself of the opportunity to point out
the cranial asymmetry in JV. tengma/mz in an article that has
since appeared in the Proceedings of the Zoological Society of
London for 1871, p. 739, entitled ““On the Asymmetry of the
Skull in Strix tengmalmi”’ (it having been sent in June of the
same year); and also in Vzd. Selsk. Forh. Chria., p. 68, 1872.
Auricular openings are broad and wide, and have a depth equal
to that of the head; both these and the ear-flaps, which are not
very broad, are of the same dimensions upon either side, other-
wise they present no asymmetry other than that which pertains
to the cranium itself. Apart from the asymmetrical structures
seen in the latter, it is perhaps most like that part of the skel-
eton in Syruium aluco, and has, as in that species, a notably
wide interorbital septum, part of which is transparent, and a
uniform convexity of its posterior aspect.
The three resident species occurring in south and middle
Europe, vzz., Strix flammea (Linn.), 1766, Athene noctua
(Retz), 1800, and Scops giu (Scop), 1769, together with Aszo
capensis (Smith), 1835, which occurs as a straggler in the
130 SHUFELDT. [VoL. XVII.
countries about the Mediterranean, are not found in Norway.
The two first-named species have been found as far north as
Jutland and the southern part of Skaane, but are, like Scops
giu, principally south and middle European forms. Aszo
capensis belongs to the Ethiopian region. I have not had the
opportunity to examine the heads of any of these in the flesh;
and, as the dermal structures of the auricular openings cannot
with entire safety be described from dried or steamed heads,
the following remarks will have reference only to the cranial
characters in these species. Strix flammea, which is the type
of the first subfamily of Striges, belongs, as is well known, toa
special group, different from the other six groups of North-
European Bubonine just described. Its principal characters
are a symmetrical cranium, and a broad ear-flap, which is much
larger than the comparatively small (symmetrical ?) ear-open-
ings. The cranium, which appears to be entirely lacking in
asymmetry, is peculiarly lengthened, with a long and slender
mandibular portion, and with a marked development of the
dipléic tissue in several of the cranial bones, to an extent not
approached by any of the other North-European species.
As in Syrnium lapponicum, the forehead slopes conspicu-
ously downwards, but here, to such a high degree that the
line becomes almost concave. The medio-longitudinal furrow
on the top of the cranium is deeper than it is in any of the
other groups, and the forehead is raised almost pyramidically
above the orbits upon either side of this deep median furrow.
No distinct fossa stands between the crest upon the os sqgua-
mosum and the parietal bone, as is seen to be the case in most
of the other groups of Bubonine, and this crest has, upon
the whole, no extraordinary or very pronounced development ;
but the cranium is especially remarkable on account of the
great thickness of the interorbital septum, which here presents
no point where it is thin, as is the case in all the other species.
The orbits, relatively speaking, are notably incapacious; the
lacrymals are disproportionately large and swollen, and are
found beneath the frontal, upon either side, and not as in the
subfamily Bubonine, partly (or often quite) beneath the supe-
rior mandible.
Nor T.| THE CRANIUM IN THE OWLS. I31
Finally, it may be said that the mandible is markedly wid-
ened beneath the ramal vacuity; that the pars plane of the
mesethmoid are thick and swollen at their apices, and widely
spread out ; that the palatine bones are narrow, and the vomer
well developed and mesially swelled ; and, lastly, the large
orbital wings of the alisphenoid are so long that they almost
reach the linear os jugale.
Taking into consideration the depression of the cranium, its
small orbits, and the marked development of the dipldic tissue
in all the bones, Stvzx flammea, of all the North-European spe-
cies of owls, stands nearest to Syruzum lapponicum, though in
the latter the interorbital septum is very far from being as
thick as in Strix flammea, and the lateral processes of the
ethmoid are not swollen at all.
Upon the whole, then, when taking into account the struc-
ture of the cranium in Strzx flammea, although this exhibits no
asymmetry, this form occupies an isolated place among the
owls, and these peculiarities of its cranium, when taken in
connection with the characters obtained from the structure of
the sternum and furcula, doubtless contribute towards sustain-
ing the opinion of placing this form in a separate sub-
family.
As far as the auricular openings in Strix flammea are con-
cerned, they are small or of medium size, and probably sym-
metrical (or very little asymmetrical). The ear-flaps, which
are both superiorly and inferiorly squarely truncated, and are
about as broad as they are high, give them, upon the whole,
a resemblance to the right ear-flap in the Syrvnzum group ; on
the other hand, these ear-flaps are larger than the apertures
they are intended to cover, and consequently they overlay the
auricular margins. Further, we observe the characteristic long
and broad fold of skin, overgrown with stiff feathers (the veil),
which stretches, as an oblong semi-arc, from the base of the
superior mandible above the eyes, down behind the ear-open-
ing upon either side, from thence quite out to the symphysis
of the lower jaw. This fold of skin corresponds to the verti-
cal fold that surrounds, posteriorly, the slit-like ear-opening in
the genus Aszo.
132 SHUFELDT. [VoL. XVII.
That Athene noctua is doubtless especially closely related to
the genus Swrnza can plainly be discerned from the structure
of the cranium alone.
It appears that Kaup, in a paper (Zvans. Zogl. Soc., Vol. IV)
to which I have not had access, has shown that Athene noctua
presents an asymmetry (although slight) in the development of
these dermal structures. This asymmetry cannot, with cer-
tainty, be pointed out in a dry head that I possess, but in any
case must have been very slight. They are of medium size, or
relatively of about the same size as in Survnza funerea, with the
flap absent. The cranium itself, which is symmetrical, agrees
in its main characters with the cranium in the last-named spe-
cies. The jugal bone is furnished with an elevated process ;
the osseous crest of the os sguamosum resembles that struc-
ture as it occurs in Surnia funerea; but the greatest resem-
blance to this species is especially exhibited in the slender,
spine-like supraorbital process, which goes far towards making
clear the affinity these forms have with the diurnal birds of
prey (of the genus Astur); this also extends to the structure
of the cranium in these two species.
In this particular the genus A¢hkene comes nearer to the
genus Surnia than to Glaucitdium,;? on the other hand, it is
unlike both in possessing an evident median furrow.
Scops giu has also relatively small or medium-sized auricular
1 Kaup’s figure appears in A History of North-American Birds (Baird, Brewer,
and Ridgway), vol. iii, p.97. Boston, 1874.
In this connection compare the pterylography of the so-called “ Burrowing
Owls” of the American continent, reference being made to one of them in my
memoir entitled “ Notes on the Anatomy of Speotyto cunicularia hypogoea”
(Journ. Morph., vol. iii, No. 1, June, 1889, pp. 115-125, Pl. VII), also in a very
excellent paper by Mr. Hubert Lyman Clark, entitled ‘“ The Pterylography of cer-
tain American Goat-suckers and Owls,” Proc. U.S. Mat. Mus., vol. xvii, 1894,
Pp. 551-572. Many figures in text. The comparison of the feather-tracts of
Speotyto and Athene would be especially interesting. — R. W. S.
2 The supraorbital processes are also spine-like and well developed in Sfeotyto,
as may be seen in my figures of the skeleton of that species (Aud/. U. S. Geog.
and Geol. Surv. of the Terr. Dept. of the Interior, vol. vi, No. 1, Washington, Feb-
ruary, 1881, Pls. I-III), but they are quite rudimentary in Micropallas whitney,
one of the smallest owls in the world, and belonging to a genus related to Glauci-
dium. Speotyto, Glaucidium, and Micropallas all possess the elevated process
upon the jugal.— R. W. S.
Nos. I.) THE) CRANIUM IN THE OWLS. 133
openings that are lacking in dermal coverts. The structure of
its cranium makes it clear that it belongs to a different type
as compared with the other North-European species, even if it
does appear in one of the first two of the above-arrayed
groups. The cranium, which is symmetrical, has the osseous
crest of the os sguamosum terminating in a pointed process,
that almost comes in contact with the hinder margin of the
alisphenoid, and to which it is united by ligament. Therefore
the structure of this crest corresponds to what we find in the
right side of the cranium in Syruium lapponicum. The aural
entrance is contracted, quite slit-like, on account of the fusion
of the crests with the posterior orbital margin.
As to the remaining characters it may be said that the cra-
nium’s greatest depth is found to be at a point situated unusu-
ally far forwards, almost in the region of the supraoccipital
processes ; that the jugal is linear; vomer, rudimentary ; and
the orbital cavities notably large.
That these characters of the crania, and the structure of the
external auricular openings, can be shown to be present toa
great extent in all the species of the same genus, is probable,
and the few examinations that I have had the opportunity to
make of the heads or crania of non-European species have
sustained this. Of the genus Vyctala, in which form the
asymmetry of the cranium is most evident, there is, at this
time, but a single species known that belongs to the nearctic
region, vzz. — lV. acadica (Gmel.), 1788, with the exception of
the circumpolar WV. tengmalmz. It is quite probable that the
asymmetry seen in the former is also similarly exhibited in
the last-named species. Ina note in the Proc. Acad. Phila.,
1870 (p. 73), Mr. Hale Streets invites attention to the fact
that a pair of crania in the collection of the Academy, which
were thought to belong to Wyctala acadica, exhibited an asym-
metry in their cranial structure which from the description
corresponds with that seen in WV. Zengmalmi.
The second species exhibiting asymmetry in its cranium,
Syrnium lapponicum, is represented in the nearctic region by
a related species, S. czzereum (Gmel.), 1788, which was de-
scribed one year earlier than S. /afponicum. That this species,
134 SHUFELDT. [Vo. XVII.
characterized in the main only by its darker plumage, will
present about the same structure in the cranium as the palzo-
arctic S. dapponicum, is evident.!
This is further shown in two figures, which are given in
Baird, Brewer, and Ridgway, A History of North-American
Birds, Vol. III, pp. 99, 100.
Finally, Syrnzum uralense, the third species having an asym-
metrical cranium, is represented in the eastern part of the
palzeo-arctic region (Japan) by a similar race or subspecies,
S. rufescens (Temm. and Schl.), 1850,? which is smaller and
darker in plumage than the type species, but nothing is known
of the structure of its cranium.
It is not improbable that there are still other species of the
genus Syrnium that will furnish examples of cranial asymmetry.
Of this genus, Sharpe has in his Catalogue of Birds, British
Museum, Vol. II, 1875, described twenty-seven species, besides
various subspecies, to which are to be added two others, old
species that of late years have been transferred into this
genus.
I. SURNIA FUNEREA (Linn.), 1766.
(Plate XV, Figs. 1-3.)
Both the auricular openings and the cranium are symmetrical, flap being
absent in the former.
The skin-like auricular openings are of medium size, sym-
metrical, and comparatively lowly situated, inasmuch as their
upper edges barely ascend above the middle of the eye, the
lower reaching down to about the mandible. They are evenly
rounded above and below, perpendicular, and in an adult female
specimen (collected in West Aker, Christiania, Nov. 12, 1881)
measure 12 mm. in height and 9 mm. in breadth. There is no
evidence whatever of the presence of any dermal flaps, or of
any raised dermal folds about the margins.
1“ One point of note is to be observed, however, and that is, in some species
of Syrnium the skull is symmetrical, while in some others asymmetrical distortion
to a moderate degree is observable. Of the first condition S. xebulosum is an
example, and of the latter, S. cézereum furnishes us an instance.” (Shufeldt in
MSS., March 20, 1896.) —R. W. S.
2 « Referred to as Strix rufescens in the text, and S. fuscescens on the plate.”
No: a.) LEE (CRANIUM LN \ LAE OVCES. 135
The zostrils are of medium size, situated low down com-
paratively; their height is 3 mm. and very little more than
their width, which is 2mm. A tuberous cere is situated above
the nostrils.
The cranium, which is quite symmetrical, attains its greatest
height posterior to the orbits.
The deak is short and very much curved; the mandibles,
not taking into account their horny sheath, measured from the
frontal bones, will enter 2.6 times into the total length of the
cranium. The superior surface of the cranium is even and
smooth, without any median furrow, a character which, among
the North-European species, it possesses in common with G/lau-
cidium passerinum
The supraorbital process is, in the older individuals, espe-
cially long, and is seen to be a narrow, stiletto-formed, osseous
process, that is directed obliquely backwards.
The forehead, posterior to the supraorbital processes, is
broad, of the same breadth as is that region in front of those
apophyses; that is to say, the frontal borders are very nearly
parallel.
Frontal bones are sharp where they go to form the poste-
rior periphery of either orbit. The zuterorbital septum has
its thinner, semitransparent part especially extensive; in the
middle of the alzsphenoid there is a vacuity caused by non--
ossification? that in size about equals the foramen opticum.
The osseous crest of the os sguamosum is completely free
superiorly and juts out sharply from the cranium. It is broad-
est in the middle, where it develops an apophysis, directed
forwards, that conceals the posterior extremity of the quad-
rate, when the cranium is viewed upon its lateral aspect.
Regarding the cranium anteriorly, the osseous crests are seen
in plain view standing out beyond the orbital wings (that is,
the osseous crests of the alisphenoids).
1 While making this translation I have before me three skulls of adult
specimens of Surnia ulula caparoch, and three skulls of adult specimens of
Micropallas whitneyi. The median furrow is entirely absent in the former, but
there is a slight indication of one in the skulls of A/icropallas. — R. W. S.
2 This is referred to in the following words, vzz.: “et hudagtigt parti,” which,
being literally translated, means “a membraneous part.” — R. W. S.
136 SHUFELDT. [Vou. XVII.
Supraoccipital (squama occipitis) has a small, round supra-
occipital foramen, the size of which varies in different indi-
viduals (diameter 4%-1% mm.).
The jugal bone is broadest in the middle, inasmuch as
its superior border develops a rather long, low, but distinct
process. The pterygoid bones are slender, becoming pointed
in front, where they offer but small articular facets, for articu-
lation with the palatines.
The palatine bones are notably broad; pars plana of the
mesethmotd comparatively short, not coming out beyond the
external margin of the palatine bone, upon either side, when
the cranium is viewed upon its basal aspect. Vomer rudi-
mentary, and present as a slender osseous spine, or (in younger
individuals) completely unossified.!
2. GLAUCIDIUM PASSERINUM (Linn.), 1766.
(Plate XV, Figs. 4-6.)
The auricular openings, which are without flaps, are, as well as the cra-
nium, symmetrical.
The dermal parts of the auricular openings are small, sym-
metrical, and, comparatively speaking, placed high up, inasmuch
as their inferior extremities do not descend further down than
the lower border of the eye, the superior extremities ascending
to a point opposite the center of that organ, upon either side.
They are oval in form, with the longitudinal axis, in each case,
obliquely directed backwards. In an adult female specimen
(collected at Lillehammer, Dec. 9, 1876) the longest diameter
measured 6 mm., and the transverse diameter 4.5 mm. The
flaps were absent, and the skin did not create an elevated fold
about the borders.
The xostrils are small, with a comparatively broad space
between them, and are directed forwards, inasmuch as they are
situated in the fore part of the much swollen cere. Their ver-
tical diameters slightly exceed their transverse ones.
The cranium, which is symmetrical, agrees, upon the whole,
1 Literally translated this reads “fuldkommen hudagtigt,” meaning “ fully
membraneous.” —R. W. S.
No. 1.] THE CRANIUM IN THE OWLS. R37
with the corresponding characters as they occur in the cranium
of Surnia funerea; its greatest height, as in that species, lies
posterior to the orbits.
The deak is short, thick, and very much hooked; the mandi-
bles, not taking their horny sheath into account, measured
from the frontal bones, will enter almost two times (2.8—2.9)
into the total length of the cranium; thus it is shorter than in
any other North-European species.
The surface of the cranium is smooth, without any median
furrow; the forehead, posterior to the supraorbital processes,
is very slightly convex, its surface being broad behind them,
but progressively narrower in front of them. The frontals form
sharp borders at the posterior parts of the orbits ; the thick-
ness [| fortykkelse| of the forehead in the neighborhood of the
supraorbital processes is less than it is in any other species.
The thin, semitransparent part of the interorbital septum is
extensive; in the middle of the alisphenoid there is an unossi-
fied point, that is occasionally as large as the optic foramen.
The osseous crest of the squamosal agrees with what we
found in Suruza funerea, and though standing well outwards,
its process is less produced. When we view the cranium upon
its lateral aspect, then the crest conceals from view the poste-
rior extremity of the quadrate bone, and, viewed from the
front, this is seen outside the orbital wings (that is, the osse-
ous crests on the alisphenoids).
The jugal is, as in Surnia funerea, broadest in the middle,
inasmuch as its superior border develops in that region a long-
ish, low apophysis; in all the other North-European species
the jugal is linear.
Supraoccipital (squama occipitis) has an oblong supraoccip-
ital foramen, that is relatively, as well as absolutely, larger
than in any other inland species (vertical diameter 3 mm.,
transverse diameter 2% mm.).}
The pterygoid bones are somewhat broader at their anterior
ends, and are there furnished with better developed articular
facets for the palatines than they are in Surnia funerea.
1 Micropallas also presents this foramen, and in this species it attains a size
equal to one-fourth the size of the foramen magnum. — R. W. S.
138 SHUFELDT. [Vou. XVII.
The palatine bones are quite broad ; pars plane of the meseth-
moitd comparatively short, and are concealed by the palatines
when the skull is viewed upon its basal aspect.
Vomer rudimentary, being developed only as an almost
invisible osseous spicula, or, as in the younger individuals,
completely unossified.
The maxillo-palatines are notably small, and well separated
in the median line.!
3. NycTEA sScANpIAcA (Linn.), 1766.
(See Figs. 1 and 2.)
The auricular openings, which are without flaps, are, as well as the cra-
nium, symmetrical.
The dermal parts of the auricular openings are of medium
size, symmetrical, and situated comparatively low down, as
their lower extremities do not pass the superior borders of the
mandible, upon either side, and the superior tips ascend only
about to the middle of the eye. They are evenly rounded off
both above and below, with their longer axes somewhat ob-
lique. In an adult male specimen (collected in Ringebo, Oct.
19, 1876) the vertical diameter is 20 mm., and the transverse
diameter 11 mm. There is no evidence of any flap, but the
skin on the anterior borders forms, in either case, a somewhat
raised fold. The wostri/s are quite large, roundish, and placed
high. Vertical diameter is 6 mm., and the transverse diameter
the same. Posterior to the nostrils, the cere is very little
swollen. The cranium, which is symmetrical, possesses espe-
cially large orbital cavities, and its greatest height is posterior
to the latter.
The decak is of medium length and comparatively strong.
The mandibles, not including their horny theca, measured from
the frontal bones, will enter slightly more than twice (2.1) into
the total length of the cranium. On its superior aspect the
1 These ossifications are also comparatively small in Micropallas whitney, and
owing to the relatively as well as absolutely shorter superior mandible in this
pygmy species, these spongy masses of bone are brought closer together medi-
ally; indeed, they come very near being in contact. —R. W. S.
No. 1.] THE CRANIUM IN THE OWLS. 139
cranium has a longitudinal median furrow, which is especially
well marked in the region of the base of the superior mandible,
and between the parietal bones.
The supraorbital processes are situated comparatively far
forwards (anterior to the middle of the orbits).
The forehead, posterior to the supraorbital processes, is
somewhat contracted, narrower in fact than it is anterior to
these apophyses, and
the orbital borders
are here about par-
allel to each other.
The frontal bones are
sharp where they
form the posterior
borders of the orbits ;
the forehead is espe- !
Fic. 1.— Left lateral view of the skull of Nyctea scandiaca
cially thick in the (Linn.) ; two-thirds natural size.
region of the supra-
orbital processes.
The thinner, semi-
transparent part of
the zzterorbital sep-
tum is extensive; in
the middle of either
alisphenotd there is an
unossified area, and
in the cranium of one
Fic. 2. — Left lateral view of the plucked head of a specimen
of the specimens BNE of Myctea scandiaca (Linn.); two-thirds natural size. (Both
figures by Shufeldt, after Collett.)
hand there are, more
anteriorly, in the direction of the ethmoid two other minute
areas of a similar character.
The osseous crest of the squamosal bone is, comparatively
speaking, more feebly developed than it is in the other groups.
Superiorly, it terminates in a pointed process, that is directed
somewhat anteriorly, which, when the cranium is viewed upon
its lateral aspect, conceals from view the distal end of the os
gquadratum.
The broad orbital wings (that is, the osseous crests of the
140 SHUFELDT. [VoL. XVII.
alisphenoids) hide those structures upon the os sguamosum of
either side, when the skull is looked at from in front.
The supraoccipital (squama occipitis) possesses an exceedingly
small, round supraoccipital foramen (the diameter being about
I mm.).
The pterygoid bones are narrow both anteriorly and posteri-
orly, while their upper and lower margins are sharp.
Their facets for the palatines are triangular in outline.
The palatine bones are of about medium width; the pars
plana, upon either side of the mesethmoid, long and strong,
and, when viewed from beneath, are seen to extend laterally
well out beyond the external borders of the palatines.
Vomer rudimentary, or else unossified (that is, in all the
five specimens examined up to the present time, all of which
are probably subadult individuals). In older or adult birds,
ossification, to some slight extent, may take place. Mesially,
the maxillo-palatines are not widely separated.
4. Buso 1GNAvus (Forst., 1817).
(See Fig. 3.)
The auricular openings, which are without flaps, slightly asymmetrical ;
the cranium is symmetrical.
The dermal parts of the auricular openings are rather large
and subequal in size, inasmuch as the right one is somewhat
larger than the left. They are oval in outline ; a male speci-
men (collected at Western Aker, Sept. 23, 1875) has its right
ear-opening measuring 30 mm. in height, and with a width of
19 mm., the left aperture possessing a height of 26 mm. and
a width of 16mm. There are no ear-flaps, but the anterior
border upon either side develops a slightly elevated fold of
skin.
The nostrils are subcircular in outline, and, as in the genus
Nyctea, situated rather superiorly. The cranium, which in all
its main characters agrees with the cranium in WVyctea scan-
diaca, is large and coarsely constructed, being symmetrical, and
with comparatively large orbital cavities; posterior to which
latter we find the greatest height of the cranium to be situated.
No. 1.] THE CRANIUM IN THE OWLS. I4I
The deak is somewhat long and strong, the mandibles, when
not covered by their horny theca, measured from the frontal
bones, will enter a little more than twice into the total length
of the cranium. The superior surface of the cranium exhibits
a median furrow, which, as in /Vyctea, is deepest in the frontal
region at the mandibular base and between the parietals.
The ordzts are markedly capacious, the diameter in each being
twice as long as the postorbital part of the cranium. The
crest of the alisphenoid (posterior orbital process) is conspicu-
ously broad and prominent above, and powerfully developed.
Fig. 3. — Left lateral view of skull of Buso zenavus ; two-thirds natural size.
(Shufeldt, after Collett.)
The forehead is, as in Wyctea scandiaca, somewhat contracted
posterior to the supraorbital processes, and the latter are
situated comparatively far forwards (anterior to the middle
of the orbits).
The frontals, where they enter into the posterior peripheries
of the orbits, are sharp; the thickening of the frontal region
in the vicinity of the supraorbital processes is especially well
marked. The thinner (transparent) part of the zzterorbital
septum is less extensive than it is in Wyctea scandiaca, from
the fact that the alisphenoid is thicker in front of the optic
foramen than it is in that species, which is likewise the case
with the mesethmoid element. The osseous crest of the os
Squamosum is, comparatively speaking, feebly developed, but,
upon the whole, somewhat stronger than it is in /Vyctea; it
is, as in that genus, completely free superiorly, and develops
in the margin there a semi-anteriorly directed sharp-pointed
I42 SHUFELDT. [Vo.u. XVII.
process, which, when the cranium is viewed laterally, conceals
the distal extremity of the quadrate. Viewed from in front,
they are almost completely hidden behind the broad orbital
wings (that is, the osseous crests of the alisphenoids).
The supraoccipital (squama occipitis) has a very minute and
circular supraoccipital foramen (diameter barely I mm.). The
pterygoid bones are, as in Nyctea, narrowed both before and
behind, and develop cultrate margins both superiorly and
inferiorly ; the articular facets for the palatines are triangular
in form. The palatines themselves are comparatively slender ;
the pars plana, upon either side of the mmesethmoid, long and
stout, and extends far out beyond the external border of the
palatine bone, when we view the skull upon its basal aspect.
Vomer rudimentary, and somewhat enlarged mesially. In-
feriorly, the maxtllo-palatines are separated but by a small
interval of space.
5. ASIO ACCIPITRINUS (Pall.), 1771.
(Plate XV, Figs. 7 and 8. — Plate XVI, Figs. 9-11.)
Auricular openings and their flaps asymmetrical ; cranium symmetrical.
The dermal parts of the auricular openings are asymmetrical,
remarkably long, being almost level with the top of the head,
and resemble gill-slits. They extend from the frontal region
in a curved direction (Za/vbue) down to the nether side of the
lower jaw, where they reach or even pass beyond the angle
of the gape (the superior angles of these slits are separated
at the vertex of the head by a very narrow interval). Their
vertical height in an adult specimen (collected at Krogskoven,
Oct. 16, 1876) is about 35 mm.
The auricular opening, both in front and behind, is bounded
by a raised fold of skin, that extends the entire length of the
aperture, performing the function of the ear-flap, although the
true ear-flap is here, as well as in the other species possessing
it, composed of the anterior, which is at the same time the
larger fold of skin. This, the true ear-flap, is crescentic in out-
line (narrowing upwards and downwards), and broadest in the
middle (about 12 mm. wide). While, on the whole, this ear-flap
No. 1.] THE CRANIUM IN THE OWLS. 143
is symmetrical for the two sides, the tensor muscle that closes
them, and which transversely divides either auricular opening
at about its middle, exhibits a peculiar asymmetry. This
muscle arises symmetrically on the right as well as on the left
side, near the center of the lid’s inner surface, while its
attachment, upon either side, to the cranium posteriorly is
thoroughly asymmetrical. On the right side the tensor muscle
is attached posteriorly, at a point about in the middle of the
osseous crest of the os sguamosum, or rather so high up that
the entrance to the ear upon this side must necessarily be
below the transverse fold formed by the muscle, and that part
of the entrance above the muscle consequently closed. On
the left side the muscle is directed more obliquely downwards
and makes an inferior attachment posterior to the mandible,
at the lowest extremity of the osseous crest of the os sgua-
mosum,; consequently the aural entrance is found above the
muscle, while the lower part of it is closed over. The muscle’s
attachment to the ear-flap, as already described above, is seen
to be upon the inner surface of the latter, near its center,
after first having passed and received support from the short
but distinct process which occurs upon the posterior aspect of
the osseous crest of the alisphenoid.
In addition to the tensor muscle proper, there is a feebler
one lower down, which, upon either side, passes from the
mandibular border to the lid’s inner surface, in the direction
of the gape of the mouth.
The nostrils are oblong, elevated, close together, and com-
paratively large, besides being longer than they are high
(length 6 mm.; vertical diameter 4 mm.).
That part of the beak posterior to the nostrils, and covered
by the cere, is somewhat raised and of oblong form. The
cranium, which does not exhibit any notable asymmetry, is, if
viewed upon its superior aspect, seen to be strikingly pointed,
or almost triangular, inasmuch as such parts of the margins
of the orbits formed by the frontals are obliquely sculptured ;
therefore the postorbital region of the cranium is more con-
tracted, and lacks the rounding off which takes place in the
other groups. The greatest vertical height of the cranium is
144 SHUFELDT. [VoL. XVII.
posterior to the orbital cavities. The beak is comparatively
feebly developed, being powerfully deflected from the frontal
region, obliquely downward, in addition to being quite short.
The mandibles, omitting their horny sheath, and measured from
the frontal bones, will enter almost 2.2 times into the total
length of the cranium. The cranium’s superior surface ex-
hibits a median furrow that is especially well marked in the
frontal region, posterior to the supraorbital processes.
The orbital cavities are relatively small, due to the fact that
their posterior borders, where formed by the frontal bones, are
obliquely truncated; and, moreover, the alisphenoids are short
and thick. The osseous crest of the alisphenoid (proc. orbit.
poster.) aS we pass upwards, is seen to become rapidly nar-
rower, it having its greatest width about its center; upon the
broadest portion there is, on the external border, a process
directed backwards and outwards, and which affords attach-
ment for the superior portion of the tensor muscle that passes
to the ear-flaps. This process is symmetrical upon either side,
although the muscle referred to is asymmetrical at its distal
extremity. The frontal region is comparatively narrow, partic-
ularly so posterior to the supraorbital processes, where, indeed,
it is narrower than is the part in front of them; while the
orbital borders are nearly parallel to each other. The frontal
bones of the posterior orbital peripheries slope obliquely away,
being abruptly truncated above and below, and have a height
that is somewhat less than the length of a pterygoid bone.
Inasmuch as both the alisphenoid and mesethmoid are thick-
ened bones, the interorbital septum is necessarily so, the only
exception to this being a place just above the sphenoidal ros-
trum, where the septum is seen to be thin (semitransparent).
The osseous crest of the os sguamosum is not especially well
individualized superiorly (by an evident and deep groove sepa-
rating it from the alisphenoid), but is continuous in the upward
direction without any intervening cleft, or glenoid fossa, quite
up to the frontal; as the crest thus becomes somewhat long,
and is likewise rather deep, and possesses a semi-anteriorly
directed border, it forms a fossa, opening anteriorly, which is
larger than the similar cavity seen in the other species having
No. 1.] THE CRANIUM IN THE OWLS. 145
a symmetrical cranium. Therefore they are enabled to appre-
ciate the least evident vibrations of sound far easier than the
others, and this, moreover, becomes even still easier inasmuch
as they possess, too, such conspicuously large dermal parts to
their auricular openings.
The external border of this osseous crest is quite even, and
no process is developed upon it, and, as mentioned above, it is
but slightly deflected forwards, so that it does not come quite
opposite to the quadrate bone when the skull is viewed upon
lateral aspect. Regarding the cranium from in front, the osse-
ous crests, in their entirety, project, lateral-wise, beyond the
orbital wings (that is, the osseous crests of the alisphenoids).
Supraoccipital (sguama occipitis) has in some specimens a
very small supraoccipital foramen, while in others the bone is
not perforated at all.
The pterygoid bones are, especially in front of the basiptery-
goid processes (proc. pteryg. oss. sphenoid.), broad and flat, their
borders being even and their distal ends presenting extensive
and compressed articulatory facets for the palatines.
The palatines are of medium width; the pars plana upon
either side of the mesethmoid is widely spread out and, if the
cranium is viewed from beneath, is seen to come out beyond
the externo-lateral margins of the palatines. Vomer present ;
usually, but not always, somewhat mesially enlarged.
The maxillo-palatines are large and come almost in contact
in the median plane.
6. Asio otus (Linn.), 1766.
(Plate XVI, Fig. 12.)
Auricular openings and their flaps asymmetrical ; cranium symmetrical.
The dermal parts of the auricular openings agree exactly
with what was found in A. accipitrinus, and the transverse fold
(tensor muscle) presents precisely the same asymmetry in its
posterior attachment as in that species. On the other hand,
the ear-flap, as well as the corresponding posterior fold of integ-
ument, is perhaps somewhat a little higher, and consequently
the entrance to the ear is larger. This really insignificant
146 SHOUFE EDT. [VoL. XVII.
departure agrees with such other differences as are to be found
in the structure of the crania of the two species under consid-
eration. The flap is 13 mm. wide, and the posterior integu-
mental fold about 8 mm.; the height of the ear-slit in an adult
male specimen (collected at Hamar, May 23, 1880) is, as in
A. accipitrinus, about 35 mm. The nostrils, the structure of
the beak, and its relation to the total length of the cranium
are identically the same as in A. accipztrinus. The cranium
likewise, in the main, agrees with the cranium of A. acczpi-
trinus.
Its pointed, triangular form is here even better marked,
inasmuch as the obliquely sculptured part of either frontal is
more extensive and reaches further backwards. The greatest
vertical height of the cranium is found in the posterior orbital
region.
The superior surface exhibits the same median furrow as in
A. accipitrinus. The orbits are comparatively even of less
diameter than they are in A. accipitrinus, due to the fact that
their obliquely sculptured portions at their posterior borders,
which are contributed by the frontal bones, are, in the present
species, more extensive than in A. acczpitrinus.
The longitudinal diameter of the postorbital part of the cra-
nium is here almost as great as is the diameter of the orbit; in
A. accipitrinus it is considerably less.
The osseous crest of the alisphenoid (proc. orbit. post.) is
notably small and narrow ; while the apophysis upon its poste-
rior surface (at least in the specimens examined by me up to
the present time) is either rudimentary or absent. The frontal
region is somewhat broader than it is in A. accipitrinus ; its
width is greater posterior to the supraorbital processes than it
is in front of them, while the reverse of this is the case in
A. accipitrinus.
The frontals form at the posterior borders of the orbits, as
in A. accipitrinus, a slanting surface, which is abruptly trun-
cated both above and below; but this surface is deeper than in
the species named, inasmuch as its height is equal to the length
of a pterygoid bone. The interorbital septum is transversely
thick, as in A. accipitrinus, and, as in the species named,
No. I.] THE CRANIUM IN THE OWLS. 147
exhibits only a single, limited, thin (semitransparent) area just
above the sphenoidal rostrum.
The structure of the osseous crest of the os sguamosum cor-
responds exactly with what was found in A. acczpitrinus, but,
inasmuch as the truncated portion of the frontals posterior to
the orbits is more extensive than it is in that species, and the
big orbital wings (on os alisphenoides) being, as a consequence,
situated further forwards, the distance between the osseous
crest and the orbit is greater, and the fossa thus created, more
capacious, particularly above, than A. accipitrinus.
The supraoccipital (sguama occipitis) is pierced by an ex-
tremely minute supraoccipital foramen, which, as in the spe-
cies just mentioned, is situated at the base of a little oblong
fossa, and in some individuals it doubtless will be found to be
absent.
The pterygoid bones seem to be somewhat narrower than
they are in A. accipitrinus and offer a less extensive articular
surface for the palatines than in that species. The palatine
bones are perhaps a little broader than in A. accipitrinus,; pars
plana of the mesethmoid barely passes beyond the external
border of the palatine, upon either side, when the cranium is
viewed upon its nether aspect. Vomer present, and developed
as in A. accipitrinus. The maxzillo-palatines are large and
come near being in contact in the median plane of the skull.
7. SYRNIUM ALuco (Linn.), 1766.
(Plate XVII, Figs. 13, 14. — Plate XVIII, Figs. 17-20.)
Ear-openings, as well as the ear-flaps, asymmetrical ; the cranium sym-
metrical.
The dermal parts of the auricular openings are of subequal
size, and they possess asymmetrical flaps. These openings are,
upon the whole, wide; their borders giving them a reniform,
or oblong bean-shaped, outline; on the right side, where the
1 While this translation was being made, I have had before me a complete
skeleton of Asio wilsonianus (Asio Brisson; Strix otus Linn.), collected by me at
Fort Fetterman, Wyoming, in April, 1881, and I find the characters it presents
agree, in so far as the skull is concerned, with the corresponding ones so correctly
given above by Professor Collett for Asio otus. —R. W. S.
I 48 SHUFELDT. [VoL. XVII.
aperture is the larger, it has, in an adult female specimen (col-
lected at Aker, Nov. 10, 1876), a height of 25 mm. and a width
of 12-13 mm. ; the entrance is smaller upon the left side, and
has a height of 22 mm. and a width of 11-12 mm. Compara-
tively speaking, they are situated rather high up, inasmuch as
their lower extremities do not fall below the inferior arc of the
eyeball, upon either side. Superiorly, the right opening passes
above the eyeball; the left being situated a little lower down
than this. The distal border of an ear-opening is bounded by
a thickened integument, approaching in its nature a low, free
fold of skin. The ear-flaps are also asymmetrical. On the
right side, where the aperture is the larger, it is broad, being
squarely truncated both superiorly and inferiorly, and has an
average width of about 12 mm.; on the left side the flap nar-
rows as it ascends, but below is carried out as an irregular,
inferiorly directed point; in this locality the flap sees its great-
est breadth, being about 11-12 mm. The nostrils are markedly
small, elevated, and almost circular; their diameter, in either
case, being about 2mm. The cranium, which is symmetrical,
is comparatively large, and the posterior region is prettily
dome-shaped ; its greatest vertical height being comparatively
far forwards, that is to say, about over the middle of the orbits.
The beak is of medium size, with flattened sides; the mandi-
bles, measured from the frontal bones, not taking into consid-
eration their horny covering, will enter 2.3 times into the total
length of the cranium. The superior aspect of the cranium has a
longitudinal, median, shallow furrow that becomes more distinct
in the frontal region between the supraorbital processes.
Posterior to the supraorbital processes the frontal region is
notably broad, and considerably (sometimes almost double the
width) broader than the forehead is in front of the processes.
The latter diminishes rapidly in width as one passes anteriorly,
and, when the cranium is viewed from above, it is seen that
1 At this writing I have at hand the skeleton of a specimen of Syrazum nebu-
losum, a ‘bird of the year,” collected by me at New Orleans, La., in July, 1883.
In it the furrow, as usually seen in owls on top of the cranium, is replaced by a
sharp, linear, deep-seated crease that is distinctly carried from the base of the
superior mandible to the supraoccipital prominence behind. —R. W. S.
INO.) THE CRANIUM IN THE OWLS. 149
here the lateral borders are quite concave. Where the frontals
enter into the formation of the posterior peripheries of the
orbits their borders are rounded off ; and, if we view the skull
from behind, the supraorbital processes are concealed from
sight by the vertex of the cranium.
The thinner (transparent) parts of the wall of the inter-
orbital septum are quite extensive. The osseous crest on
either squamosal bone is of medium size only. Above, it is
completely free, and there develops a curved process, directed
forwards and upwards, which, when the cranium is viewed
lateral-wise, is seen to be opposite to the posterior border of
the quadrate. Regarded from in front, it is only their outside
edges that become visible to the outer side of the large orbital
wings (that is, the osseous crests on the alisphenoids). An
extremely minute supraoccipital foramen pierces the supraoc-
cipital bone (sguama occzpitis), the diameter of which in the
subadult individuals is equal to about 1 mm., while in the older
birds it is barely more than % mm.
Anterior to the basipterygoidal processes (proc. pteryg. oss. |
sphenoid.) either pterygoid is compressed from above down-
wards, having a uniform width, and with its cultrate edge
directed anteriorly. The palatine bones are quite broad; the
lateral processes of the os ethmoides pass outwards so as to be
about opposite the external margins of the palatines, when we
regard the cranium from beneath. Vomer is rudimentary, as
only its posterior moiety ossifies as a minute spicula of bone;
ossification not being extended to its anterior end. It is very
likely that in still younger individuals it does not ossify at all.
The maxillo-palatines are of unusually large size and come
very near being in contact in the middle line, below.
8. SYRNIUM URALENSE (Pall.), 1776.
(Plate XVII, Figs. 15, 16; Text-fig. 4.)
Auricular openings and their flaps asymmetrical, the cranium slightly
asymmetrical.
The dermal parts of the auricular openings are of subequal
size, with a somewhat asymmetrical lid; upon the whole,
150 SHOFELDT. [VoL. XVII.
these structures agree with the corresponding ones as they
occur in S. aluco, only being relatively a little smaller. -The
auricular openings may be said to be quite wide, and have a
reniform outline. On the right side, where the opening is
the larger, it has, in an adult specimen (collected at Lojten,
Nov. 1, 1881), a vertical height of 26-28 mm. and a width of
about 14mm. The aperture upon the left side is somewhat
smaller, the height being 23 mm., the width about 14 mm.
Comparatively speaking, they are placed pretty well up on the
side of the head, inasmuch as on the right side the lower end
descends to a point slightly below the inferior arc of the globe
of the eye; superiorly, they are carried up, upon either side,
to a point in the same plane with the top of the eyeball.
The hinder border of either auricular opening is, as in
S. aluco, bounded by a thickened fold of integument, infe-
riorly. An asymmetry of the ear-flaps, also agreeing with what
we find in S. aluco, is present; on the right side, where the
aperture is the larger, it is broad ; both above and below it is
transversely truncated, and, upon the whole, has a consider-
able breadth, which corresponds in size to that of the ear-
opening. On the left side the flap is somewhat irregularly
drawn downwards, and terminates in a shorter projection,
though it still agrees with what we find in S. aluco. The
nostrils are of medium size, oval, and with their breadth and
height about equal (nearly 4mm.). The cranium, which is
almost but not completely symmetrical, is, in its main char-
acters, like the cranium of S. a/uco, although the mandibular
portion is more powerfully developed as compared with the
cranium, and the orbits are comparatively smaller. The asym-
metry, to which reference has been made, and which is almost
imperceptible, is due to the fact that the osseous crest of the
squamosal bone is inclined slightly more forwards upon the
right side than it is upon the left, thus foreshadowing the very
decided asymmetry which will be found to be present in these
structures in S. lapponicum. The greatest vertical height of
the cranium is at a point posterior to the orbital cavities.
The bill is moderately long, though not of a powerful build;
it will enter twice into the total length of the cranium, measur-
No. 1.] THE CRANIUM IN \ THE. OWLS. I51
ing from the frontal bones, and not including the horny theca
that covers it. Upon the superior aspect of the cranium there
is a very distinct median furrow, which, in the three specimens
examined, is best marked at the cranial vertex in the inter-
parietal region.
The orbital cavities are comparatively smaller than they are
in S. aluco, inasmuch as the os alisphenoides is here shorter and
thicker. Taken upon the whole, the orbital diameter is of
about the same length in the two species. The big orbital
wings (the osseous crests of the alisphenoids) are in both
these owls comparatively broad and large. The frontal region,
posterior to the supraorbital processes, is conspicuously wide,
and even much wider than it is in front of them, where it
gradually narrows anteriorly, but not in as marked a degree as
it does in S. aluco. The frontal bone is, upon either side,
thoroughly rounded off where it forms the hinder border of
the orbit, but it is seen to slope obliquely away in the direc-
tion of the large orbital wing, so that we are enabled to see
the supraorbital processes
when the cranium is
viewed upon direct pos-
terior aspect.
The zxterorbital septum
is quite thick transversely,
inasmuch as both os al-
Sphenotdes and os eth-
motdes enjoyasimilar con-
dition throughout all their
parts; as in Aszo there is
only a localized area, situ-
ated above the rostrum of
the sphenoid, where the
Fic. 4. — Cranium of Syrnzum uralense, seen from above,
septum is thin and semi- and showing slight asymmetry of the crests of the os
transparent. The osseous squamosum ; compare this with same view of cranium of
S. lapponicum. (Adapted by the author from Collett.)
crest of the os sguamosum
agrees entirely with what was found in S. a/uco, being an out-
standing, nail-like, and superiorly free process; but at the same
time it exhibits in the slight forward inclination of its anterior
152 SHUFELDT. [VoL. XVII.
border of the right side, as has already been pointed out above,
a disposition to approach the asymmetry which is present in
S. lapponicum.
The difference seen in the two sides is better marked in
the crania of some specimens than it is in others, and can
in the adult individual vary between 1 and 2 mm., this differ-
ence being interesting rather than remarkable, inasmuch as it
is just here that in S. /appontcum such decided asymmetry is
present. This difference can best be appreciated when the
cranium is viewed from above (see Fig. 4), although even then
it is seen to be very slight, though it is invariably present.
The occipitale superius (squama occipitis) has no supraoccip-
ital foramen.
The pterygoid bones are, as in S. aluco, broad in front of the
basipterygoid processes, and quite compressed.
The palatine bones are, comparatively speaking, narrower
than in S. aluco; pars plane on os ethmotdes reach a little
beyond the outer margin of either palatine, when the cranium
is viewed from below.
Vomer is almost rudimentary, inasmuch as it is present only
as a thin osseous spicula posteriorly, and non-ossified in front.
Maxillo-palatines are very large, and meet in the line below.
9. SYRNIUM LAPPONICUM (Thunb.), 1780.
(Plate XIX, Fig. 27; Plate XX, Figs. 28-30. Text-figs. 5-7.)
Auricular openings ; ear-flaps; and cranium asymmetrical.
The dermal parts of the auricular openings, structurally,
about agree with the two other species of Syruzum and present
a similar asymmetry. Upon the whole, they are quite large,
being subequal in size, although this asymmetry is apparently
less than in S. aluco.
Upon the right side, where they are of the greater size, the
ear-opening has in an adult female specimen (collected in
East Aker, Nov. 17, 1881) a vertical height of 30 mm. and
a width of 15 mm.; on the left side the height is 28 mm.
and the width 14mm. They may be said to be placed high
up on the side of the head, being situated just back of the
No: 1.) TAECRANIOM TN TIPE OWLS. 153
eyes, and consequently their upper and lower ends (more par-
ticularly upon the right side) extend slightly past the ees:
and lowest points in the eyeball.
The distal border in either auricular opening is surrounded
by a thick and somewhat raised fold of integument similar
to what is found in the other species. The flaps are large
and somewhat asymmetrical, though in a less degree than in
S. aluco. The flap is larger on the right side, and has a
length that somewhat exceeds that of the ear-opening, being
about 35 mm. The width is 17 mm., and this flap is less
obliquely truncated than it is upon the left side; its lower
end is, transversely, quite straight. The ear-flap is, upon the
left side, greatly narrowed above and broadest below, where it
forms a long, produced, and deflected extremity. The length
and breadth of this flap do not materially differ from the same
measurements given for the right side.
Across either auricular opening there is stretched a fold of
skin or tensor muscle! that is attached at a point somewhat
above the middle of the lid; on the right side this arises from
the tuberous and comparatively inferiorly situated superior
border of the osseous crest of the alisphenoid (or the large
orbital wing); on the left side this tubercle is found higher
up and less prominent, and the tensor muscle passes this, its
origin being found upon the posterior aspect of the osseous
crest of the squamosal bone, at its superior extremity. Owing
to the formation of the cranium, the entrance to the ear, or
the canal leading from the same to the parts within, has a
different direction upon the two sides. On the right side this
canal passes almost directly into the cranium immediately be-
neath the tensor muscle of the ear-flap; on the left it passes
obliquely downwards beneath the muscle.
The zostrils are comparatively large, elevated, somewhat
oblong ; their longitudinal diameter is 7 mm., the height 5 mm.
The cranium, which is asymmetrical, resembles in its struc-
1] presume Professor Collett means the “tensor muscle,” the same having
the appearance of a “fold of skin.” It reads in the original “Strekker sig en Hud-
fold eller Lukkemuskel.” To be sure, the muscle is included within a fold of
skin. — R. W. S.
154 SHUFELDT. [VoL. XVII.
ture the cranium in Syruium uralense, but in it the mandibular
parts are more powerfully developed ; the parietal region is
more pyramidal in contour, and with comparatively smaller
orbits than in that species. The cranium sees its greatest
height opposite the posterior margins of the orbits. The
asymmetry is chiefly due to the somewhat distorted develop-
ment of the osseous crest of the
right os sqguamosum. The beak
is laterally compressed, but is not
especially strong; the mandibular
portion has a greater length than
in any other inland species, and
does not quite enter twice (1.9)
into the total length of the cranium,
ie.) epee earn not taking into account its horny,
Skull seen from in front; mandible at- integumental theca. The median
eee natural size. (Shu furrow upon the superior aspect of
the cranium is quite well marked
its entire length, being especially
so in the frontal region, posterior
to the supraorbital processes.
The orbit has a comparatively
less diameter than in S. wvalense,
inasmuch as os alisphenoides is
notably short and thick, which is
likewise the case with that part
Fic. 6.— Syrnium lapponicum (Thunb.). . ;
Skull seen from behind; mandible at- of either frontal which forms the
tached; two-thirds natural size. (Shu- margin of the orbit superiorly
i -
feldt after Collett.) k
The supraorbital processes are
situated far back, so much so that their apices, upon either
side, reach to a point upon the orbital crest of the os alisphe-
noides. Further, either one of these processes is very broad, and
develops as a long frontal extension, which is connected by a
membrane with the tubercle of the orbital wing, superiorly, and
in this manner contributes towards the formation of the hinder
roof of the orbital cavity.
The osseous crest of the alisphenoid (frocessus orbitalis
posterior) is on the right side somewhat asymmetrical, as is
No. 1.] THE CRANIUM IN THE OWLS. 155
also the os squamosum, inasmuch as it is here drawn out in
a greater degree laterally, and also more depressed than upon
the opposite side, in such a manner that the crest becomes
broader above, on the right side, and more tuberously swollen
than upon the left side.
The orbits thus become a trifle wider, but at the same time
lower, than upon the left side. Upon the posterior aspect of
the apex of the osseous crest there is to be found a process
that is not especially conspicuous.
The frontal region, posterior to the supraorbital processes,
is profoundly concaved,! but, upon the whole, particularly
broad, and much broader than the surface in front of these
processes, which, relatively speaking, is also of considerable
width. Either frontal bone slopes obliquely downwards from
the middle of the cranium towards the hinder border of the
orbit, and is very deep posterior to the supraorbital processes.
If the cranium is seen upon direct posterior view, the supra-
orbital process of the right side, including its upper border, is
in view beyond the limiting profile line of the frontal, while
the left one is hidden behind it. The interorbital septum is
notably thick and of limited area, and this thickness is to be
found over its entire extent, and it is only just above the
rostrum of the sphenoid that there is to be found a thinner
place, which only in a very limited degree is semitransparent.
The osseous crest of the squamosal bone is normal upon
the left side, having the same structure as in S. a/uco and
S. uralense, forming there a supero-anteriorly directed process,
that is, above, perfectly free. This crest is particularly lofty
upon the right side, where it extends upwards and forwards
as a prominently curved apophysis that reaches to the upper
border of the os alisphenoides; this latter is decidedly massive,
and, as has before been remarked, stands out from the side of
the skull in a most abnormal manner. The two processes do
not fuse at their point of contact, but are simply joined there
by membrane. The fossa formed by the osseous crest, the
entrance to which is in front, thus becomes more capacious, and
1 I take this to refer to the superior orbital borders, they being roundly concaved
in most species of Syrzium, just behind the supraorbital processes. — R. W. S.
156 SHUFELDT. [Vou. XVII.
especially more lofty than upon the left side. Regarding the
cranium upon its anterior aspect, it will be seen that the promi-
nent orbital wing completely conceals from view the osseous
crest of the right squamosal, while upon the left side the ex-
ternal border comes into sight beyond the orbital wing. Upon
the whole, the asymmetry of the cranium in this species can
best be appreciated by viewing it from above; while thus seen,
one can also more easily compare the powerfully anteriorly
directed superior bor-
der of the osseous crest
of the right side with
its retreating border
upon the deft: | (ee
Fig. 7.)
Supraoccipital (sgua-
ma occipitis) lacks, as
in S. uvalense, a supra-
occipital foramen.
The pterygoid bones
are more slender than
in) S:/ alaco: andi
uvalense, and possess
smaller articular facets
Fic. 7.— Cranium of Syrxium lapponicum seen from above, i i ;
and showing the degree of asymmetry of the squamosal for articulation with
on Sere aie Me of ee thie) pala ea aa
paratively speaking,
the palatine bones are especially slender ; the lateral processes
of the ethmoid are well developed, and have an unusually high
point of origin, being upon a level with the olfactory foramen,
or slightly below the superior border of the lachrymal bone,
upon either side; they are widely spread out, and when the
skull is seen from below, nearly the whole of either one of
them can be seen beyond the external border of the palatine
of the same side.
The vomer is, as in other species of this genus, nearly rudi-
mentary, as it is only represented posteriorly by a minute
osseous spicula, being otherwise unossified (in subadult indi-
viduals, perhaps entirely so).
No. 1.] THE CRANIUM IN THE OWLS. 157
The maxillo-palatines are unusually large, and are in contact
in the mesial plane, below.
10. NycTALA TENGMALMI (Gmel.), 1788.
(Plate XIX, Figs. 21-26.)
Auricular openings and flaps asymmetrical ; the cranium profoundly so.
The dermal parts of the auricular openings are nearly of
equal size upon the two sides, but in other respects exhibit
an asymmetry that agrees with the asymmetry assumed on
the part of the cranium itself; they are very large, occupying
as they do the whole side of the head, upon either side ; they
are somewhat semilinear or oval in outline, but less pointed
above and below than in Aszo, and therefore not as gill-slit-like
as in that genus. Their vertical height in an adult specimen
(collected at Hamar, Sept. 20, 1876) is about 28 mm., the
greatest inner width being about 12 mm.; but they frequently
have a greater width than this.
Hither of these openings extends from beneath the mandible
or lower jaw (close to the mandibular commissure) up to the
side of the frontal region, where the space separating the one
from the fellow of the opposite side is comparatively wide,
being but a little less than the height of either ear-opening.
The ear-flap that closes the aural aperture in front is of a semi-
lunar outline, but is not very broad, as at a point opposite the
center of the eyeball it barely exceeds 6 mm.; in the frontal
region, and below the eye, it is alittle broader. Posteriorly the
opening is closed by a very well developed integumental fold
resembling an ear-flap, which, with a breadth coequal with that
of the true ear-flap, extends the entire length of the auricular
opening, and both above and below indistinguishably merges
into the ear-flap proper. Thus the entire aural aperture is
surrounded by a continuous, free, and rather high dermal fold.
The contour assumed by this posterior integumental fold is
that given it by the form of the cranium; thus it is high on
the right side, and comparatively as low on the left, where the
osseous crest of the os sguamosum holds such an abnormally
low position.
158 SHUFELDT. [Vor XVII.
The nostrils are small and oblong; their height, which is
hardly 3 mm., is greater than their width; they are subvertical
in position, with their openings somewhat anteriorly directed.
Posterior to the nostrils, the cere constitutes the swelled part,
and this, superiorly, develops two tubercle-like elevations.
The cranium, which is profoundly asymmetrical, is compara-
tively large, with orbits of about medium size.
The asymmetry is present upon both sides, but the left is
the more abnormally so. In its structure generally it agrees,
perhaps, in so far as the inland species are concerned, most
nearly with the cranium of Syrnzum aluco, although it widely
departs even from it. Its greatest vertical height is at a point
posterior to the orbits. Longitudinally the superior aspect
of the cranium presents for its entire length a feeble median
furrow, which is best marked in the frontal region, between
the supraorbital processes. A rather well marked cranio-facial
hinge stands between the not very powerfully developed supe-
rior mandible and the frontal bones; this mandibular portion
is comparatively short, for, upon being measured from the
frontalia, it will enter 2.6 times into the total length of the
cranium, provided its horny theca is not taken into account.
Posterior to the supraorbital processes the frontal region is
rather broad; the area anterior to the processes rapidly nar-
rows as we pass forwards, and it has quite concave borders.
The asymmetry.— The bones that take part in the asym-
metry of the cranium are principally the os sguamosum, and in
a lesser degree the adjacent parts of the frontal, the parietal,
and the alisphenoid.!
The frontal bones are smoothly and very completely bounded
off where they enter into the posterior peripheries of the orbits,
1 The internal configuration of these bones can only be examined with certainty
in the very young. If the individual has arrived at maturity, even if the downy
plumage (the first feathers, which are moulted shortly after the bird becomes full
grown) is still worn, the sutures among the separate bones have already disap-
peared. Although I have made every effort to obtain the young just taken from
the nest, I have not succeeded in securing them, having only obtained a pair of
indifferent specimens of nestlings, and in these obliteration of the sutures had
already partly taken place. So perhaps the above description of the defining of
the separate bones in certain instances can be corrected or supplemented.
No. 1.] THE CRANIUM IN THE OWLS. 159
and have the appearance of being almost quite symmetrical.
Thus, their orbital portions do not seem to offer any difference
upon the two sides, as both descend about an equal distance
upon either posterior orbital wall; on the other hand, the lat-
eral portion on the right side, where it articulates with the
anteriormost apex of the parietal bone, and the here abnor-
mally developed and much uptilted crest of the os sguamosum,
is more elevated than on the left side. Otherwise the differ-
ence is very slight.
The osseous crests on the os sguamosum, where the asym-
metry is most evident, are, upon the whole, so abnormally
large, deep, and conspicuously outstanding, that they, almost
in their entirety, can be seen beyond the orbits, if the cranium
be viewed from in front. As in the genus Aszo, they are not
distinguished from any of the bones with which they articulate
above by any distinct groove or depression, but enter into the
uninterrupted lateral contour of the cranium, where it is seen
from in front. Both sides are distorted, the left side being the
more so. On the right side, the osseous crest is extended up-
wards to a height quite coequal with that of the superior border
of the orbit, but it abruptly terminates here, as it comes in con-
tact with the frontal, at a considerable distance (7.2 mm.) pos-
terior to the orbit, and in this manner crowding far backwards
the apex of the parietal bone. In the middle the osseous crest
is produced in such a way as to form an anterio-inferiorly
directed and rounded process, which with its point impinges
upon the hinder border of the orbital crest of the os alisphe-
noides. The combined heights of the osseous crests upon this
side are equal to 20 mm. On the left side the osseous crest
is abnormally vertically compressed ; it commences at a point
above, at about opposite the middle of the orbit, and close to
the latter’s hinder border, thus being farther forward anteri-
orly than it is upon the right side, as the crest is here sup-
ported by the superior extremity of the orbital crest upon os
alisphenoides. Here also, froma point a little below its middle,
the crest is produced in a long, inferiorly directed process; but
its apex is found as low down as the mandible, where, with a
feeble, yet with an easily distinguished articulatory facet, it
160 SHUFELDT. [Vot. XVII.
meets the jaw, as well as the os guadratum and the os jugale,
at their point of articulation. It is in this way that the cra-
nium itself comes in contact with the lower jaw, a phenomenon
which is certainly without parallel in the class Aves, outside of
this genus. Owing to the unusual development of this osseous
crest, the fossa, in which the aural entrance is found, is of con-
siderable width, particularly upon the right side. On the other
hand, the entrance to the ear itself is normal upon both sides,
and quite symmetrical; and, as the asymmetry is thus mainly
confined to the external osseous crest and its neighboring struc-
tures, while the os sguamosum, internally, is normally devel-
oped, upon either side, it follows as a result that the inner
walls of the brain casket are symmetrical, and the brain itself
does not appear to offer anything anomalous in so far as its
superficies are concerned.
The parietal bone upon the left side, on account of the lowly
situated osseous crest of the os sguamosum, is quite pointedly
produced anteriorly, though it extends forwards quite to the
hinder margin of the orbit ; on the right side, where the osse-
ous crest is situated higher up and at the same time placed
farther backwards, it is less pointed, though crowded farther
to the rear, and as a consequence does not reach to the poste-
rior border of the orbit. The alzsphenozd is, upon the right side,
larger and posteriorly broader than it is upon the left side; in
other respects the orbital crest does not present any asymmetry,
that is, beyond the fact that its superior border is extended a
little higher up on the right side than it is upon the left.
The zuxterorbital septum is, anteriorly, quite thin and trans-
lucent ; the os ethmotdes has a comparatively thick wall.
The supraoccipital (squama occipitis) is pierced by a small
supraoccipital foramen (diameter 34 mm.).
The pterygotd bones are slender, being somewhat compressed
from above downwards, thus causing their cultrate edges to
turn obliquely outwards and downwards.
The palatine bones are very broad; the pars plane upon the
mesethmoid are quite short, and do not extend beyond the ex-
ternal palatine borders, when the cranium is viewed upon its
basal aspect.
No. 1.] THE CRANIUM IN THE OWLS. 161
Vomer is present, but is very slender; in subadult individ-
uals it is probably unossified (that is, Aadagtigt, or skin-like).
The maxillo-palatines are, mesially, almost in contact upon
their inferior side.
[Conclusion of the translation. ]
Opinions upon the Position of the Strigide in the System.
Huxley, in his celebrated paper ‘‘On the Classification of
Birds,” published in the Proceedings of the Zovlogical Society
of London in 1867, says that his Aetomorphz is a division
which is equivalent ‘to the ‘Raptores’ of Cuvier —an emi-
nently natural assemblage, and yet one the members of which,
as the preceding enumeration of their characters shows,! vary
in most important particulars.”
«They appear to me to fall naturally into four well-defined
primary groups—the Strigid@, the Cathartide, the Gypetide,
and the Gypogeranide. But this arrangement is so different
from that ordinarily adopted that I shall proceed to justify
it by enumerating the principal circumstances in which the
members of the several divisions agree with one another and
differ from the rest.”
This is first followed by a fairly complete résumé of the
osteological and other characters of the owls; but as many
important skeletal strigine characters have, since that paper
was published, been described by ornithotomists, I will com-
plete Professor Huxley’s opinion by what he thought of the
systematic position of the Caprimulgide, which he believed
“come near Zvogon, and more remotely approach Podargus
and the Owls”’ (p. 460).
This is important, for as early as 1867 so keen an observer
as Huxley saw the affinity between the goat-suckers and the
owls. In his admirable article “Ornithology,” in the ninth
edition of the Excyclopedia Britannica (Vol. XVIII, p. 47), Pro-
fessor Newton says that “it has so long been the custom to
1It has not been thought necessary to give these characters here; they are
surely not of a nature to convince one that a typical hawk, an American vulture,
and an owl all belong to the same group; for example, Accipiter + Cathartes
+ Strix!—R. W. S.
162 SHUFELDT. [VoL. XVII.
place the owls next to the diurnal birds of prey that any
attempt to remove them from that position cannot fail to incur
criticism. Yet when we disregard their carnivorous habits, and
certain modifications which may possibly be thereby induced,
we find almost nothing of value to indicate relationship be-
tween them. That the S¢vzges stand quite independently of the
Accipitres as above limited can hardly be doubted, and, while
the Pszttaciz, or parrots, would on some grounds appear to be the
nearest allies of the Accipztres, the nearest relations of the owls
must be looked for in the multifarious group Pzcarze. Here
we have the singular S¢eatornis, which, long confounded with
the Caprimulgide, has at last been recognized as an inde-
pendent form, and one cannot but think that it has branched
off from a common ancestor with the owls.’’ But the same
eminent authority, in the volume just quoted, under the article
« Owl,” further says, on page 89, that “the owls form a very
natural assemblage, and one about the limits of which no doubt
has for a long time existed. Placed by nearly all systematists
for many years as a family of the order Acczpztres (or whatever
may have been the equivalent term used by the particular tax-
onomers), there has been of late a disposition to regard them
as forming a group of higher rank. On many accounts it is
plain that they differ from the ordinary diurnal birds of prey
more than the latter do among themselves; and, though in
some respects owls have a superficial likeness to the goat-
suckers, and a resemblance more deeply seated to the Guac-
haro, even the last has not been made out to have any strong
affinity to them.” !
«A good deal is therefore to be said for the opinion which
would regard the owls as forming an independent order, or, at
any rate, suborder, S¢viges. Whatever be the position assigned
to the group, its subdivision has always been a fruitful matter
of discussion, owing to the great resemblance obtaining among
all its members, and the existence of safe characters for its
division has only lately been at all generally recognized.”
1 Nevertheless, Professor Newton believes, at least, that Steatornis ‘has
branched off from a common ancestor with the owls.” (Compare first quota-
tion above.) —R. W. S.
No. 1.] THE CRANIUM IN THE OWLS. 163
Upon consulting the plates and text of so distinguished an
authority as Professor Max Fiirbringer, ‘“‘ Untersuchungen zur
Morphologie und Systematik der Vogel,’ we are to note that
there the Caprimulgi and Striges are considered as arising
from a common ancestral stock, the suborder Coracizformes
of the order CoORACORNITHES, and this last-named division is
quite apart from the order PELARGONITHES, which contains -
the Accipitres.
In 1892 a no less careful examiner of the structure of birds
than Prof. Hans Gadow published in the Proceedings of the
Zoological Soctety of that year a very excellent article, in
many respects, upon the “Classification of Birds,” and in the
scheme set forth in that work Gadow placed the STrRIGEs in a
group by themselves, standing between the parrots and the
goat-suckers, and far removed from the Accipitres. Huxley,
Newton, Fiirbringer, and Gadow must have especial weight
attached to their opinions in the matter of the classification
of Aves, for each and all of them carefully looked into and
compared the anatomical structure of the members of this
puzzling division of the Vertebrata. Many of the taxonomers
of birds have not done this, and consequently are often guilty
of classifying these forms upon such characters as strike their
eye after a superficial examination of the general characters
presented on the part of “series of museum skins.”
In as yet unpublished MSS. the present writer has said :
“Regarding the owls as a whole, they are to be considered as
forming a group of nocturnal birds of markedly raptorial habits.
Some of the species, however, are largely diurnal in their
ways. They are not especially related to the Acczpztres, but
are, on the other hand, remotely allied with the Caprimulgz.
What we now know of the structure of such forms as Stea-
tornts and Podargus sufficiently indicates this much.”
This opinion is based upon an examination of the anatomy
of the last two forms mentioned ; upon the osteology of all
the species of North-American owls, Acczpztres, Caprimulgt,
and a host of forms suspected of having alliance with these
groups.
In 1894 Mr. Hubert Lyman Clark published in the Pro-
164 SHUFELDT.
ceedings of the United States National Museum (Vol. XVII,
pp. 551-572 (many cuts)) a very able paper entitled “The
Pterylography of Certain American Goatsuckers and Owls,”
in which all the principal North-American forms were ex-
amined. At the end of this memoir Mr. Clark said: ‘The
conclusion, then, to which this study of their pterylography
has brought me is that the Caprimulgi are related to Striges,
and not very distantly either— probably a branch from the
early part of the Strigine stem” (p. 572).
My own opinions have been based upon a study of a// the
characters of the groups we have under consideration; this, to
a considerable extent, was the case likewise with Huxley;
certainly so with Fiirbringer and Gadow, while Professor
Newton gave the external characters and the skeleton the
greatest weight. This being the case, the results arrived at
by Mr. Clark very aptly fill in a gap that long stood greatly in
need of the very kind of treatment he has bestowed upon it.
As to what relations may exist between the owls and the
parrots, I am, just now, not prepared to give a decided
opinion; certain it is, however, that we have both “owl-
parrots” (S¢viugops) and parrots in Australia that are suffi-
ciently “rapacious” to make good enough use of their claws
and hooked beaks to prey upon living sheep, and that display
quite as much taste for the habit as a Budo does when he
kills and devours a hare. —R. W. S.
166 SHUFELDT.
EXPLANATION OF PLATE XV.
(All the figures of the plates are by Professor Collett.)
Fic. 1. Skull of Surnia funerea; anterior aspect, with mandible attached;
natural size.
Fic. 2. Skull of Surnia funerea ; left lateral aspect, with mandible attached ;
natural size.
Fic. 3. Head of Surniza funerea ; feathers removed and showing ear-opening; -
natural size.
Fic. 4. Skull of Glaucidium passerinum ; anterior aspect, with mandible
attached ; natural size.
Fic. 5. Skull of Glaucidium passerinum ; \eft lateral aspect, with mandible
attached; natural size.
Fic. 6. Head of Glaucidium passerinum ; feathers removed and showing ear-
opening; natural size.
Fic. 7. Skull of Aszo accipitrinus ; anterior aspect, with mandible attached ;
natural size.
Fic. 8. Skull of Aszo accipfitrinus ; superior aspect, with mandible attached;
natural size.
Journal of Morphology. Vol. XVII PEXY.
B Meisel, hth,Boston
ie
ru)
vat
7 ” +
168 SHUFELDT.
EXPLANATION OF PLATE XVI.
Fic. 9. Skull of Asio accipitrinus ; right lateral aspect, with mandible attached ;
natural size.
Fic. 10. Head of Asio accipfitrinus ; left lateral view, with feathers removed
and showing ear-opening; natural size.
Fic. 11. Head of Asio accipitrinus ; right lateral view, with feathers removed
and showing ear-opening; natural size.
Fic. 12. Skull of Asio otus; left lateral aspect, with mandibie attached;
natural size.
Journal of Morphology. Vol. XVij PLXVI
‘
EIEN
ti
} ay
aN
170
FIG. 13.
natural size.
FIG. 14.
natural size.
FIG. 15.
natural size.
Fic. 16.
natural size,
SHUFELDT.
EXPLANATION OF PLATE XVII.
Skull of Syrnium aluco ; left lateral aspect, with mandible attached ;
Skull of Syrnium aluco; anterior aspect, with mandible attached;
Skull of Syrnium uralense ; anterior aspect, with mandible attached :
Skull of Syrnium uralense ; left lateral aspect, with mandible attached;
Journal of Morphology. Vol. XVII Jae OIE
>
vo
ie
fl!
172 SHUFELDT.
EXPLANATION OF PLATE XVIII.
Fic. 17. Head of Syrnium aluco; right lateral view, with feathers removed
and showing ear-opening ; natural size.
Fic. 18. Head of Syrnium aluco; \eft lateral view, with feathers removed
and showing ear-opening; natural size.
Fic. 19. Skull of Syrnium aluco; basal aspect, with mandible attacned ;
natural size.
Fic. 20. Skull of Syrnium aluco; superior aspect, with mandible attached ;
natural size.
PLXVI,
Journal of Morphology. Vol. XVII
B. Meisel, lith,Boston
174 SHUFELDT.
EXPLANATION OF PLATE XIX.
Fic. 21. Skull of Myctala tengmalmi ; anterior aspect, with mandible attached ;
natural size.
Fic. 22. Skull of Vyctala tengmalmi ; posterior aspect, with mandible attached;
natural size.
Fic. 23. Skull of Myctala tengmalmi; right lateral aspect, with mandible
attached; natural size.
Fic. 24. Skull of Myctala tengmalmi; \eft lateral aspect, with mandible
attached; natural size.
Fic. 25. Head of Myctala tengmalmi; right lateral aspect, with feathers
removed and showing ear-opening; natural size.
Fic. 26. Head of Wyctala tengmalmi; \eft lateral aspect, with feathers
removed and showing ear-opening; natural size.
Fic. 27. Skull of Syrnium lapponicum ; \eft lateral view, with mandible
attached; natural size.
Pl. X1X.
gy. Vol. XVI
holo
Journal of Morp
5, Meisel, lith Boston
. oF '
—
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:
:
'
'
.
i
I
.
rs
'
a
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4 Fb,
i
176 SHUFELDT. °
EXPLANATION OF PLATE XxX.
Fic. 28. Head of Syrnium lapponicum ; left lateral aspect, with feathers
removed and showing ear-opening; natural size.
Fic. 29. Skull of Syrnium lapponicum ; right lateral aspect, with mandible
attached ; natural size.
Fic. 30. Head of Syrnium lapponicum ; right lateral aspect, with feathers
removed and showing ear-opening; natural size.
Journal of Morphology.
Zi
d.
B Meisel, lith, Boston
Volume XVII, June, IQOL. Vo.
LN}
JOURNAL
OF
MOK EHO Ogi
NOTES ON AEOLOSOMA TENEBRARUM.
EDITH M. BRACE.
Acolosoma tenebrarum, a fresh-water oligochaete belonging
to the Aphaneura, has been supposed to hold a unique posi-
tion among annelids, having been described as having a brain
but no ventral nerve cord.
Vejdovsky, Maggi, and Beddard have given the more de-
tailed accounts of its structure. Vejdovsky! found a few cells
supposed to represent a rudimentary nerve cord which was not
connected with the bilobed brain: “ Bei A. tenebrarum treten
auf der Bauchseite zerstreute Elemente hervor, die auf eine
nervose Natur hinweisen.’”’ And again: “Man erkennt in der
Centrallinie der Bauchseite, eine kurze Strecke hinter der
Pharyngealregion, eigenthiimliche, aber sehr undeutliche Zellen-
und Fasserstrange, die jedoch mit dem Gehirnganglion nicht
zusammenhangen.”’ From the plates it is impossible to tell
just what cells are referred to, but as they were found in the
median line, they could not have been a part of the ventral cord.
Maggi” has described a brain, ventral cord, and lateral nerves
for Aeolosoma: ‘Un cordone schiacciato che si estende lungo
1 Vejdovsky, F. System und Morphologie der Oligochaeta. 1884.
2 Maggi, L. Intorno al genere Aeolosoma. 186s.
177
178 BRACE. [Vou. XVII.
tutto la linea mediana ventrale dell’ animale mandando laterala-
mente degli esili fili nervosi, ed un ganglio cefalico consti-
tuiscono per quel che potei scogere, il sistema nervoso degli
Aeolosoma.” This description has not generally been credited.
He gives no illustrations of the nervous system, and his drawing
showing the mouth at the end of the prostomium, with the space
inside the prostomium designated as the buccal cavity, leaves
no place for a brain and is incorrect, as well as the statement
that the nerve cord extends along the median ventral line.
Beddard! says of A. tenebrarum: “This species alone shows
any traces of a ventral cord, which is very short and is not
connected with the brain.”
A further study of the subject was undertaken in the Zo6o-
logical Laboratory of the University of Chicago, at the sug-
gestion of Professor C. O. Whitman, to whom I am indebted
for the supervision of my work.
Material for study was found among the water plants in the
park ponds of Chicago, where it was especially abundant around
the water hyacinth and Vectorza regia.
The worm is not an active swimmer, but prefers to lie among
the algae or to crawl between the meshes of a decaying leaf.
It is white and semi-transparent, and the integument is studded
with innumerable green oil drops contained in gland cells
which have their large nuclei flattened against the cell wall,
similar to the gland cells of the Turbellaria. A delicate chiti-
nous covering may be seen after treatment with reagents. The
worms feed upon algae or bits of decayed leaves and have a
tendency to collect on the sunny side of the aquarium. They
vary in length from 3 to 10 mm.
A number of worms will frequently get together, twist them-
selves into a ball, and remain so fora long time. It has been
suggested that this was connected with conjugation, but that
is improbable; they are presumably feeding upon each other,
as one worm is usually found partly eaten, if the ball is pulled
apart. They have great powers of regeneration; in one case,
where the head had been eaten away to the first pair of setae,
a new head was regenerated in about three days.
1 Beddard, F. E. A Monograph of the Order Oligochaeta. 1895.
No.2.] MWOTES ON AEOLOSOMA TENEBRARUM. 179
The head segment, which is broader than the following
segments, is separated from them by a constriction, and seen
from above, it appears to have a ciliated pit on each side like
those of the Turbellaria. The mouth is on the ventral side
and is overhung by the prostomium, which is ciliated on its
lower surface, and serves as a tactile organ. There is no
proboscis.
Intersegmental septa were not found, but the segmentation
is defined by the nephridia and the setae. Each segment has
one pair of nephridia and four bundles of setae, placed dorso-
and ventro-laterally. There is also a segmental arrangement
of single, nucleated muscle fibers which extend from the ali-
mentary canal to the body wall between the setae sacs.
The alimentary canal comprises a circular mouth opening
into a bell-shaped pharynx, followed by a narrow oesophagus,
which extends through two segments and leads to a broad
stomach with glandular walls, which extends through the sixth
segment where it narrows into a straight intestine. As the
worms are transparent the movements of the cilia lining the ali-
mentary canal may be seen in the living specimen.
The muscular system is comparatively simple. There is one
layer of longitudinal and one layer of circular muscle fibers just
beneath the epidermal wall, and single nucleated fibers are con-
nected with the setae and hold the various organs in place.
These single nucleated fibers are especially numerous in the
head and resemble the muscle plates of the Turbellaria.
The worms were under observation from October until July,
and during that time they were constantly reproducing by fis-
sion, with sometimes as many as three zodids developing at
once. Back of the seventh setigerous segment there is a fis-
sion zone in which all the tissues of the epidermal wall are
greatly thickened, especially on the ventral side, where they
nearly obliterate the body cavity. The new brain arises as a
dorsal thickening of the epidermis. No sexual reproduction
was observed.
Methods. — At the slightest irritation the worms will coil in
a circle, throw off the contents of the gland cells, and con-
tract so violently that the tissues are injured for study. To
180 BRACE. (Vou. XVII.
secure good specimens for sectioning they were mounted ona
slide and held in place by a cover-glass that pressed on them
slightly. They were then placed on ice for a few moments
until chilled and unable to contract any portion of the body,
when they were treated with the fixing fluid. The cold also
prevented abnormal activity of the glands, so that very perfect
preparations were obtained, although the worms will go to.
pieces if left on the ice too long.
The fixing fluid after the second formula of vom Rath (picric
+ acetic + osmic + platinum-chloride) was found most effect-
ive in demonstrating the nervous system. Specimens were
left in this for fifteen minutes, washed in alcohol, and placed
in a 20 per cent solution of tannin in acetic acid for periods
of time varying from twenty-four hours to four days, or else
they were stained in section with safranin or iron-haematoxylin
after vom Rath.
Paraffin was used for imbedding, and sections were cut from
3-20 thick. Sections from 10-15 uw thick were found most
favorable for study.
Nervous System. — The brain lies in front of the mouth in
close contact with, and partly imbedded in, the epidermal wall
(Pl. XXI, Figs. 1, 6-8), the lower part projecting more or less
into the cavity of the prostomium. Its ventral and lateral sur-
face, so far as free from the epidermis, is covered by a delicate
nucleated membrane which may be seen in section. It hasa
slightly bilobed appearance, as seen from above, each half
having a rounded anterior margin and a large posterior lobe,
the latter composed entirely of nerve cells (Pl. XXI, Figs. 2, 3).
Closely packed nerve cells with large granular nuclei cover the
whole dorsal surface, and are from three to four cells deep in
the anterior and posterior lobes, but only one layer deep in
the middle region where the anterior lobes meet (Pl. XXI,
Figs. $,o00):
A pair of nerves composed of fibers partly from the brain
and partly from the oesophageal commissure, runs forward
from the brain into the prostomium, and another pair runs
back from the angle between the posterior lobes and the com-
missures (Pl: XI, Pigs. 1512595520) 9):
No.2.) MOTES ON AEOLOSOMA TENEBRARUM. 181
Commissure. — Immediately after leaving the brain the oeso-
phageal commissure passes into an accessory ganglion, from
which a nerve runs forward into the prostomium (Pl. XXI,
Fig. 1). It then passes downward and backward, in close con-
nection with the epidermal wall, to the ventral side, where it
expands into a second ganglion before passing into the ventral
cord (Pl. XXI, Fig. 1). The fibers of the commissure form a
broad band which is clearly distinguishable, but it is often
difficult to determine whether the cells along its course belong
to it or to the epidermis.
Ventral Cord. —The two parts of the ventral cord are sepa-
rated by about one-fifth of the diameter of the body and com-
municate with each other by fibrous commissures, forming the
ladder type of nervous system (Pl. XXI, Figs. 1, 12).
There is one pair of ganglia in each segment, and each
ganglion is deeply bilobed, the anterior lobe being somewhat
smaller, while the posterior lobe extends out farther in the
body wall. The fibrous portion forms the greater part of the
ganglion, and is covered by cells one layer deep (Pl. XXI, Fig.
11). Inthe posterior segments the ganglia are crowded together
more closely than in the anterior segments (Pl. XXI, Fig. 1).
Lateral Nerves. — Four distinct lateral nerves are given off
from each ganglion, two from the anterior and two from the
posterior half (Pl. XXI, Figs. 1, 11).
This whole system of brain, ventral nerve cord, commissures,
and nerves is connected throughout with the epidermal wall,
no portion of it being entirely free in the body cavity. The
cells of the ventral ganglia, as well as those of the brain, are
often so closely connected with the epidermis that it is hard to
find the boundary line between them. The nuclei of the gan-
glion cells are of about the same size as those of the epidermis,
but stain a little more deeply.
Ciltated Pits.— Vejdovsky! states that in Aeolosoma we
find the only instance of an oligochaete possessing a pair of
lateral ciliated pits, and he compares them with the ciliated
pits of the Turbellaria. From the dorsal side the appearance
is very similar to these organs in the Turbellaria, but frontal
1 Vejdovsky, F. Thierische Organismen der Brunnenwisser von Prag. 1882.
182 BRACE. [Vou. XVII.
sections of the ventral side show that they are not pits at all,
but the terminations of deep ciliated grooves which curve for-
ward and outward from the mouth to the edge of the pro-
stomium (Pl. XXI, Fig. 13).
The mouth is circular, bordered posteriorly and laterally with
a thick swollen lip, which may be greatly extended, and which
is continued as the posterior wall of the ciliated furrows. The
cilia of the grooves, and those around the mouth, are excep-
tionally long. Sense organs are as numerous along either
side of the furrows as on the prostomium.
Vejdovsky describes a nerve connecting the lateral pits with
the brain. I find muscle fibers here, but no nerve, and from
the nature of the structure should not expect to find one.
Sense Organs.— There are many large pear-shaped cells,
that have the appearance of sensory cells, lying in all parts
of the prostomium and disposed through the body segments
(Pl. XXI, Fig. 14). The cytoplasm of these cells is finely gran-
ular and deep-staining, the nucleus is of medium size, coarsely
granular, and usually eccentric, taking its position at the base
of the cell. Between the nucleus and the opposite end of the
cell there is a large, sharply outlined, clear space containing
a refractive body with peculiar granulations at its periphery
(Fig. 14) which may represent an otolith. These cells are
sometimes isolated, but are often collected into small groups
(Fig. 15), as seen to best advantage in the prostomium. They
suggest sense organs of some kind. They have no pigment.
At the anterior end of the prostomium there is a group of
about fifteen of these large compound organs, crowded together
so closely that their sides are somewhat flattened against each
other (Fig. 16). Back of these there are smaller compound
sense organs, some distance apart, arranged in rows across the
ventral surface of the prostomium, and there are large sense
organs along both sides of the ciliated furrows leading to the
mouth (Fig. 16). The smaller compound sense organs are
also found on the ventral side of the segments back of the
mouth. All of these sense organs lie immediately under the
epidermis, so that they project slightly into the body cavity.
Aeolosoma undoubtedly possesses the essential annelidan
No. 2.] NOTES ON AEOLOSOMA TENEBRARUM. 183
characteristics, although Vejdovsky favored classifying it with
the Turbellaria on account of the similarities which he found
between the ciliated pits, muscle plates, and gland cells of these
forms, together with the structure of the brain and the sup-
posed lack of a ventral cord.
The course of the large nerves running back from the brain
has not yet been traced for an annelid; they present an anom-
alous feature which is most interesting from its suggesting a
possible transitional form of nervous system between unseg-
mented and segmented worms. The position of the brain in
the first segment, the continuity of the entire nervous system
with the epidermis, and the wide separation of the halves of
the ventral cord are primitive characteristics which would be
consistent with such a form.
REFERENCE LETTERS.
ag. accessory ganglion. mo. membrane lining the body-cavity
@ -brain: and covering the free, lower
c. connecting commissures of the surface of the brain.
ventral nerve cord. mf. tauscle fibers attached to the
cl. cluster of large sense organs in brain and connecting it with the
the end of the prostomium. epidermis of the ventral side.
d. second ganglion of the oesopha- %. nucleus.
geal commissure. 7.1.3 first, second, and third pairs of
ep. epidermal cells. cephalic nerves.
f lateral ciliated furrows leading to | zm. nuclei of the lining membrane.
the mouth. o. refractive body.
g. gland cells. oc. oesophageal commissure.
/. lip bordering the mouth and the . posterior ganglionic lobes.
ciliated furrows. v. vesicle containing a refractive
7x. lateral nerves. body.
m. mouth. ve. ventral nerve cord.
184 BRACE.
EXPLANATION OF PLATE XXI.
Fic. 1. Frontal view of the central nervous system, reconstructed from sec-
tions. (X 210.)
Fic. 2. Ventral view of the brain. (x 1200.) ,
Fic. 3. Dorsal view of the brain, showing its bilobed form. (x 1200.)
Fic. 4. Frontal section near the middle of the brain, showing the first pair of
nerves. (X 800.)
Fic. 5. Frontal section next above Fig. 4. (x 800.)
Fic. 6. Sagittal section of the brain in the plane of the anterior nerve and the
posterior lobe. (x 800.)
Fic. 7. Sagittal section of the brain a little nearer the middle than Fig. 6.
( x 800.)
Fic. 8. Sagittal section near the middle of the brain, showing a single layer of
cells on the dorsal side. (x 800.)
Fic. 9. Oblique section of the brain, showing the posterior lobe and the roots
of the first and second cephalic nerves. (x 800.)
Fic. 10. Cross-section of the brain in the plane of the commissure. (x 800.)
Fic. 11. Frontal section through a segment of the ventral nerve cord, showing
the roots of the lateral nerves and of the connecting commissures. (X 1200.)
Fic. 12. Cross-section of the ventral nerve cord in the thoracic region, show-
ing the ganglia connected by a commissure. (x 800.)
Fic. 13. Drawing showing the mouth with the furrows leading to it, and the
prostomium, ciliated on the ventral side. (x 1200.)
Fic. 14. Pear-shaped sensory cell, with vesicle containing a refractive body.
(X 1200.)
Fic. 15. Sense organs composed of several cells similar to those of Fig. 14.
(X 1200.)
Fic. 16. Partial diagram showing the position of the compound sense organs
on the ventral surface of the prostomium. (x 1200.)
Saud of Morphology. Vol. XVI.
Ci
“U )ef
:
is : 7 Tih Werner @Weter, Franktore if,
MOK PHOLOGY ‘OF THE MY XINOIMDET.
I SKELETON AND MUSCULATURE.
HOWARD AYERS anp C. M. JACKSON.
CONTENTS. PAGE
TST OND ODEO Nf esac aie ctivece es daa enncc homes eucbcnesienuch caitonsbuoe OAS cae hs Le ma ee ee 185
Alera RoeE: MONG (UIN RGN RUA TS) | oo. 2 noc as5.t nc collee cave asuzsonec-Oohcsueceeeseee ce ate eeene one 189
a. Endoskeleton (general) Intermuscular Septa...............0.c2.ceccecssseeeeeeneesseeeees 190
a. Notochord, Structure, and Position, Sheaths, Neural Canal.............. 190
B. Skeleton of Head Region (skull as a whole)..................csssssenesssssessees 193
neem branousy © ramus se .02e Ss ae ee ae eee ee 194
2. Parachordals, Auditory Capsules, and Trabeculae................000--+- 194
BrEiypophysial aelaterands (Cam ally esse ence seee nee ase ee ee 196
AaOltactonye Capsule ance Nasal wien ss eesst ee nena 196
5. Cornual and Subnasal Cartilages ......... beaolie ia eee 200
Owleabialyand Mentaculars Cartila ges: seer cebe ee ene ence 201
7basalyPlaterand, Mandibular Cartilacesii sss 202
8. Palato-Pterygoid and Epi-Hyoid Arches .......................- areas e207,
© Anterior branchials and) Velar)@antilagesy sss sce ene 209
HOw GillPancdiMiuscles Gartilag es. see2 ice. ceecs eee eer a 212
py sm AUG al C1 OM bee ecco oe even decet dees casves coe eee ee 214
1. Median Dorsal and Ventral Bars, Neural Ring.............s.ssccee-0e---- 215
PB RAY Se hea cases gst: ech cnsedencna ionnensictnet cotsctsnst 171 43-
mies set a from the coast of Chili, 10 gills, 11 | 1
(Lacépéde), 12|42, 13
paeneeee from the ae of California, 11 to 13 gills, 3 | 8,
In the California series examined by Dr. Ayers the dental
formulae were as follows: In 22 individuals with 11 gills,
10 sh 10 | _9 10]10 10/10 pay ee) alt) |) aL
1 1 10 lio et TOE || eee 1 9 [0 1 KOM SO? 1 ro | One
i i i) jf ata JE ae) plat ta) dat |) gia aba eat
1 9 oe 1 a ete 3 +o | to 1 rt law 5 154d 1 4 40
IEPA Wa Wey || ab eA
1 3 esas 2 relat
No. 2.] MORPHOLOGY OF THE MYXINOIDET. 219
In 62 individuals with 12 gills the following dental formulae
occurred: 1 8/18, 18/8, 8 2/10, 1/49, 1/19, 2121/2
0110? 9) 192
L4$]8 148i 10 WA 4 4g] ae 6 BLES T ARLES,
Lett, LARA LAL 1 ALAR 10 HIE 8 44 4b
L abt 149143.
On combining the dental formulae of the 11-gilled and 12-
gilled variations, the following numbers were found to obtain
in the 86 individuals whose dental formula was carefully
examined on both sides of the dental plate.
NuMBER oF INDI- TAGLAR. NuMBER CH Mor Thane Renee
VIDUALS. VIDUALS.
1 318 2 [44
8 sit? 1 rakes
1 fol ? 81th
1 oot 1 tg. [3h
3 18 1 th |
1 1818 13 14
2 18 | 1 1/4
. Wty 8 5/44
8 a8 1 HLH
4 ak 1 5148
7 +8148 1 1B |
: aoe 3 elke
Total number 86
In the series of 162 specimens from Monterey Bay examined
by Mr. Jackson, the following dental formulae were observed:
Branchial formula, 1o-10:—1 g| 2.
i 1) OT A | ao) 10 |10 a) || EL
Branchial formula, 11-11: —1 10/10, 11 12|19, 4 19/19,
play (gl Ds 20 aly) aeae At) |) Lo) BLO cals WAL |) SLL
Lit ites 8 the 4 dbl 4h 2 thle 1 Plat, 1 aa,
ea eg (ae, JLal |} aL) LAL) ala Ua) Let Ye | Ee JUL |) 2s
275150 8 45/40 T4ablth 1 ab] 1 bh 1 41
226 AVERS AND JACKSON. [VoL. XVII.
Branchial formula, 12-11:—3 1 |4f, 3 42|13, 3 18) 108,
1 i0)ta, 219/10, 2 14/49 8 11 |1it. Total, 17.
Branchial formula, 12-12:—1 2/8, 1 3|,%, 2 2|43,
16 30/18, 4 IP|4G, 1 ARH LABIAE 8 APIS 8 ALLA,
28 49/48, 8 14h 4 dh|4h 2 4b] 1 gldb 1 48) M
23g |4e, 244 be 18 44/4 2 Ag BE 1 ES 1 44H
1 12| 12. Total, 88
Branchial formula, 12-13:—1 1] 1%.
Branchial formula, 13-12 :—1 12/48, 1 14)14
Branchial formula, 13-13:—1 1°|19, 1 42/418, 1 10\16
Total, 3.
The following table is a summary of all the variations found
in the 162 specimens observed.
whee eo Lis DENTAL FORMULA. SIUM EE GE DING E DENTAL FORMULA.
VIDUALS. VIDUALS.
2 alg 6 x | 4h
1 $|70 - 45 | 4
2 he 2 48 [3
1 3 |e 1 04h
31 1 |p 24 ab lt
10 ap | 44 9 1148
4 ae 9 1814
2 tolis 1 45 | 4?
6 wag 1 15134
4 a 1 1b )F
1 ag | AL 1 16148
1 1 [gh 1 tlt
1 1A 1 +148
6 1 4 1 12 |g
31 +8148
Total number 162
No. 2.] MORPHOLOGY OF THE MYXINOIDEI. 221
From a comparison of the above dental formulae, including in
all 248 specimens, we conclude:
(1) That there is an exceedingly great variation in the num-
ber of the teeth, even more striking than in the case of the
gills. Thus these two characters (the number of teeth and
gills), the only two “constant” characters which Johannes
Miller could find upon which to base his classification, are both
proven to be extremely variable.
(2) In a large number of cases the two sides of the dental
plate are not symmetrical with regard to the number of teeth.
It is to be feared that the dental formulae given in systematic
accounts of Bdellostoma are, in many cases, based upon counts
of one side only of the dental plate.
(3) There is no constant relation between the number of
teeth and the number of gills. If there is any difference at all
worthy of note, the individuals with the larger number of gills
have a smaller proportion of teeth than might be expected.
(4) There is no constant relation between the number of
teeth and the size or sex of the individual. The size and sex,
though not given in the above tables, were noted in every case.
While we should naturally expect that the larger individuals
would have a larger number of teeth, this is usually not the
case. Ina 23-inch specimen, for example, which is considerably
above the average size, the dental formula was 3 | 1).
(5) The outer rows of teeth have in a majority of cases
a greater number of teeth than the inner. In 312 cases the
teeth of the outer row were more numerous than those of the
corresponding inner row. In 178 cases they were equal. In
only 6 cases had the inner rows a greater number - teeth.
Bat, The dental formulae eon oftenest are: 1,°| 4° (45),
& (88), 44/44 (82), 44]48 (22). It is ae that we
eaniot ek HY ‘ony one “4 @eypiedl” or predominant formula.
More than half the rows of teeth number 10 however, and in
nearly half the cases the corresponding outer and inner row
each contains 10 teeth. The number g is given next in fre-
quency, but occurs less than half as often as 10. More than
95% of the rows include either 9, 10, or 11 teeth.
The Chilian specimens seem to average a larger number of
222 AYERS AND JACKSON. [VoL. XVII.
teeth, for Girard counted in his type specimens with 14 gills
12/12, while Putnam found +3 |13 or 42] 42 in the material he
studied from Talcahuano Bay (Hassler expedition), reported as
having 10 gills.
Lacépéde’s example from Chili had the very unusual dental
formula of 14-| 41.
A critical histological study of the dental structures of
Bdellostoma is reserved for a separate paper. But it may be
mentioned that the hollow bases of the corneous teeth rest
upon soft dental papillae, which are fused together below into
a bar extending the entire length of the row of teeth. These
papillae are epidermal in origin, and the teeth are simply corni-
fied sheaths of the epidermal elevations upon the dental plate.
They are easily sectioned when imbedded in celloidin, and
show no traces of dentine, enamel, bone, or calcareous matter
of any kind.
March, 1808.
(To be continued.)
Nov2.] MORPHOLOGY OF THE MYXINOIDEL. 223
SYNONYMOUS TERMS FOR SKELETAL PARTS.
AYERS AND JACKSON.
Notochord ;
Cellular sheath of same .
Fibrous core
Notochordal sheath
Skeletogenous layer, elastica externa
Neural tube .
Auditory capsule
Parachordals
Trabeculae
Hypophysial plate
Subnasal cartilage .
Transverse labial cartilage .
Lateral labial cartilage
Nasal tube
Olfactory capsule .
Cranium . Ale
Tentacular cartilages .
Dental plate .
Teeth .
Anterior segment of basal plate .
Middle segment of basal plate
Posterior segment of basal plate .
Palatine bars
Cornual cartilages .
Pterygo-quadrate .
Hyoid arch
Superior lateral cartilage
Inferior lateral cartilage.
First branchialarch . . . .
Second branchial bar.
External lateral bar
Internal lateral bar
Suprapharyngeal plate
JOHANNES MULLER.
Gallertsaule.
Innere Schicht.
Faser-Faden.
Innere Scheide der Gallertsaule.
Aeussere Scheide der Gallertsaule.
Riickenmarksrohr.
Gehorkapsel.
Knocherne Basis cranii.
Fliigelfortsatze derselben.
Gaumenplatte.
Knocherne Stiitze der Schnautze.
Innerknorpel.
Knorpel-Fortsatz am vordern Ende des
Zungenbeins.
Nasenrohr.
Nasenkapsel.
Gehirnkapsel.
Mundknorpel.
Zunge.
Zahne.
Vordere Reihe der Zungenbein-Kno-
chenstiicke.
Hintere Reihe der Zungenbein-Kno-
chenstiicke.
Knorpeliger Kiel des Zungenbeins.
Gaumenleisten.
Knorpel-Fortsatz am vorderen Ende der
Gaumenleiste.
Unterer Fortsatz der Gaumenleiste.
Verbindung der Fortsatze mit der
Gehorkapsel.
Oberer Fortsatz des Schlundkorbes.
Unterer Fortsatz des Schlundkorbes.
Grosses Horn des Zungenbeins.
Kleines Horn des Zungenbeins.
Hauptsttick des Schlundsegels.
Mittel-Riemen des Schlundsegels.
(In part-) Aufsteigende Fortsatze des
Mittelriemens.
224 AYERS AND JACKSON.
EXPLANATION OF PLATE XXII.
Fic. 1. A cross-section of the notochord, spinal cord, and sheaths of
Bdellostoma a short distance behind the cranial region (x 10, camera lucida
outlines).
Fic. 2. A cross-section of the notochord, spinal cord, and sheaths of
Bdellostoma in the posterior gill region (xX 10, camera lucida outlines).
Fic. 3. Section of the notochord and its envelope.
Fic. 4. A cross-section of the cranium of Bdellostoma through the region of
the auditory capsules (Xx 20, camera lucida outlines).
Fic. 5. Dorsal view of the skull of Bdellostoma (x 2).
Fic. 6. The skull and the skeleton of the pharyngeal region of Bdellostoma,
lateral view. The roof of the spinal canal, the oesophagus, the gills and gill
passages, and the retractor mandibuli muscle are outlined with dotted lines (x 2).
A. = auditory capsule. mp. = internal process of lateral
a. = anterior connecting process. labial cartilage.
B. = anterior segment of the basal A# = notochord.
plate. 2. = nucleus.
B’ =middle segment of the basal #.s. = notochordal sheath.
plate. 4V. = subnasal bar.
BY” = posterior segment of the basal .7. = nasal tube.
plate. Oes. = oesophagus.
é. = superior lateral cartilage. oes.c. = oesophago-cutaneous duct.
b! = inferior lateral cartilage. O.C. = olfactory capsule.
ér4 = Ist “branchial” arch. P.Q. = pterygo-quadrate.
ér.. = 2d “branchial” arch. fi. = palatine bar.
By: — prem pc. = parachordal cartilage.
Cr. = cranium. S. = supra-pharyngeal plate.
¢.¢. = cornual cartilages. sc. = neural tube.
¢.s. = superior chondroidal bar. s.6. = basal process.
¢.. = inferior chondroidal bar. sk. = Skeletogenous layer.
D. = dental plate. Sh.y = internal layer of notochordal
d.t. |= median dorsal tooth. sheath.
éx. = external cellular layer. Sh.g = middle layer of notochordal
F. = “fatty” tissue of the neural sheath.
tube. Sh. = external layer of notochordal
#’ =similar layer within the cra- sheath.
nium. Sf. = spinal cord.
Fc. = fibrous core. 24, t.2, 43, 4.4 = Ist, 2d, 3d, 4th tentac-
f.s.._ = fascia superficialis interna. ular cartilages.
gb. = gill bar. Zr. = main bar of the trabecula.
Hy. =hyoidarch * tr. = anterior horn of the same.
fff. = hypophysial plate. Z = tendon of retractor mandibuli
t.m.s. = intermuscular septum. muscle.
Z.c. = lateral labial cartilage. ve. = vacuole.
Z.. = lateral (ethmoidal) plate. V. = external lateral velar bar.
m.j.e. = membrana limitans externa. V’ = internal lateral velar bar.
m.d.s. = median dorsal septum. I, 2, 3, 4 = fenestrae of skull.
m. = median connecting process.
AVI.
Vol
ogy.
1
.
es ren Ce ee
Winter, Frankcore Oe
bith Werner &
226
AYERS AND JACKSON.
EXPLANATION OF PLATE XXIII.
Fic. 7. A dorsal view of the skull of Bdellostoma, cranium, olfactory capsule
and nasal tube removed (X 23).
Fic. 8. The basal plate of Bdellostoma, ventral view (x 1).
Fic. 9. A dorsal view of the basal plate of Bdellostoma (x 1).
Dorsal view of the teeth and the dental plate of Bdellostoma (x 2).
The dental plate of Bdellostoma, ventral view ( x 2).
A gill bar of Bdellostoma, stretched out (X 8).
The cartilage of the oesophago-cutaneous duct of Bdellostoma (x 4).
The skeleton of the posterior region of Bdellostoma (x 1).
A cross-section of the tail of Bdellostoma, taken just in front of 7,
Dorsal and ventral portion of section not shown (xX Io).
FIG. 10.
Fic. 11.
FIG. 12.
FIG. 13.
FIG. 14.
FIG. 15.
Fig. 14.
A.i. = internal bars of anterior seg-
ment.
A.c. = external bars of anterior seg-
ment.
a.a. = lateral dental plate.
av. = Cloacal cartilage.
a.6. = anterior transverse velar bar.
bv. = blood vessel.
¢.m. = palatine commissure.
é. = process of median ventral
cartilage.
cm. = connective tissue.
D.m. = dermal muscle layer.
D.#. = dorsal fin.
é: = posterior external process of
lateral plate.
ex.g.p.= external gill passage.
Vi = auditory foramen.
je. = tin-tay.
£- = dorsal tendon groove.
h. = superior process of oesophago-
cutaneous cartilage.
posterior internal process of
lateral plate.
anterior process of hypophysial
plate.
median dorsal bar.
median ventral bar.
median cartilage bar.
median piece of dental plate.
myotome.
the oesophago-cutaneous bar.
posterior transverse velar bar.
posterior arch of dental plate.
anterior connecting process of
lateral plate.
sheath of fin-ray.
epidermis.
transverse labial cartilage.
anterior process of trabeculae.
ventral fin.
posterior connecting process
of lateral plate.
Journal. of Morphology. Vol.XVU.
‘Lith Werner RWinter, Frankfort 7
18
Ill.
IV.
GONTENTS OF V@EUMES Sy ir
No. 1. — September, 1900.
GusTAV EISEN, PH.D.
The Spermatogenests of Batrachoseps .
R. We SHUFELDT, M.D:
Professor Collett on the Morphology of the
Cranium and the Auricular Openings in
the North-European Spectes Oe the ii
Strigide
No. 2. — June, rgor.
Epity M. Brace.
Notes on Acolosoma Tenebrarum
Howarp AYERS AND C. M. Jackson.
Morphology of the Myxinotdet. TI. Skeleton
and Musculature
FRANK R. LILLIE.
The Organization of the Egg of Unio, based
on a Study of tts Maturation, Fertilization,
and Cleavage .
HELEN DEAN KING.
The Maturation and Fertilization a the |
of Bufo Lentiginosus
PAGES
I-117
119-176
177-184
185-226
227-292
293-350
iv
i,
Ti
IV.
CONTENTS.
No. 3. — July, Igo.
PAGES
W. S. NICKERSON.
On Loxosoma Davenporti (Sp. Nov.) . . . 351-380
MARGARET LEwis NICKERSON.
Sensory and Glandular Epidermal Organs in
Phascolosoma Gouldit. . . . . . 381-398
Aaron L. TREADWELL.
The Cytogeny of Podarke Obscura Verrill . 399-486
R. W. SHUFELDT, M.D.
On the Osteology of the Pigeons (Columba). 487-514
KATHARINE Foot AND ELLA CHURCH STROBELL.
Photographs of the ee o es
Fretatan IE 6658 i 2 eo (eS kee eee
THE ORGANIZATION OF THE EGG OF UNIO,
BASED ON A STUDY OF ITS MATURATION,
FERTILIZATION, AND CLEAVAGE.
FRANK R. LILLIE.
TABLE OF CONTENTS. PAGE
TIN'TRODUCTION cccccsccccccssnccecccee soecce cence ene cececcensnocnn=snnnmerenennannnedacon@anesencnmenmaneconanssocoGiocs 227
J. THE BEHAVIOR OF THE SPERMATOZOON IN THE EGG UP TO THE
TIME OF EXTRUSION OF THE SECOND POLAR GLOBULE........ 229
r. The Sperm-Nucleus ........-.-.---------2cscscvsseneccccssensenenssneeneerenncnceasertansennasss 229
2. The Sperm-Aster and Amphiaster: Origin and Disappearance.... 231
@. Observations .........-----..-cc2-c2cccceceee co ceeeecseneeeececeneceeemeneanenessscnnaneneners 231
B. Weiterature —.o222---ccccc.nccsenscceeeceeeseccnc sererdeenseecbaeanernenennecnrrssencentnanscnc 233
II. THE MATURATION OF THE EGG ..........22-.---------------ceccececesecercences ereeneneneanane 235
1. The Chromosomes ....... SF ok ee es ee ee ssdpeeesesteeveeacs 235
2. Achromatic Structures.........-..--2.-2-c-csscecesees cee cneeeneeectne teeeneeneenmenennc neces 236
III. GrowTuH, MIGRATION, AND UNION OF THE GERM-NUCLEI; BEHAVIOR
OF THE SPHERE SUBSTANCE; ORIGIN OF THE CLEAVAGE. CEN-
ARO SOMES oo occcececcecscseeecdes ewan wctsesen de cucesrsecesheeet artes ste ee nanan Rae eee pemareasrs 245
Ti) @PSCLV ACO eee oe cess onan canara achat ono aa ea eee aes toeaeees 245
2. Literature and Theory of Fertilization. ............---.-:-1-2ee-errees 250
IV. MovEMENTS OF THE FIRST CLEAVAGE SPINDLE. FIRST AND SECOND
GTR MVIC ES occ eee caa ee nccde cee ced apse see cencsn cay debe nee raeeeeam ta een ae na
V. CONCERNING THE SPHERE SUBSTANCE ©....-2..----:-2--eceesessesesereesereneeceesennecrscs 256
VI. Two RECENT THEORIES OF UNEQUAL CLEAVAGE .....----:-1--s-eoeeseesererteeteees 258
VII. ORGANIZATION OF THE EGG .....-....------ ’ Ary) rin ; \ al,
Bes: a
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344 KING.
EXPLANATION OF PLATE XXVIII.
All figures were drawn with the aid of the camera lucida. Plate XXXTJ is
reduced one-third.
Fic. 1. Vertical section through the black pole of a young ovarian egg, show-
ing the distribution of the yolk (Y) and pigment (PZ) and the position of the
germinal vesicle (GV) just before the beginning of the hibernation period. Diam-
eter of the egg, 1.1 mm. Size of the germinal vesicle, 0.24 mm. x 0.36 mm.
Zeiss AA., Oc. 4.
Fic. 2. A portion of the upper surface of a young ovarian egg, showing the
egg membranes. A and C, membranes belonging to the wall of the ovary; ZR,
Zona radiata; /, perivitellin; 2, blood corpuscles. Zeiss apoc. 2 mm., Oc. 8.
Fic. 3. Transverse section of the germinal vesicle in the same stage as that
of Fig. 1, showing the position of the chromatin threads and the nucleoli. C,
chromatin threads ; Cy, fluid substance surrounding the lower part of the ger-
minal vesicle; /V, nucleoli. Zeiss D., Oc. 2.
Fic. 4. Nucleoli from the germinal vesicle of an ovarian egg at the stage of
Fig. 1. Zeiss apoc. 2 mm., Oc. 4.
Fic. 5. Chromatin threads from the germinal vesicle of an ovarian egg at the
stage of Fig. 1. Zeiss apoc. 2 mm., Oc. 8.
Fic. 6. Vertical section through the black pole of an ovarian egg, showing
the position of the germinal vesicle just before the beginning of its dissolution.
Diameter of the egg, 1.1 mm. Size of the germinal vesicle, 0.31 mm. x 0.39 mm.
Zeiss AA., Oc. 2.
Fic. 7. The germinal vesicle of an ovarian egg at the beginning of its dissolu-
tion. ZA, line of radiation; 4, granular substance below the line of radiation.
Zeiss D., Oc. 4.
Fic. 8. Paired arrangement of the chromatin threads at the stage of Fig. 7.
Zeiss apoc. 2 mm., Oc. 8.
Fic. 9. Youngest stage of the large nucleolar-like bodies found in the germi-
nal vesicle at the end of the hibernation period. Zeiss apoc. 2 mm., Oc. 4.
Fic. to. Later stage of the same. Zeiss apoc. 2 mm., Oc. 4.
Fic. 11. Ordinary nucleolus found in the germinal vesicle at the end of the
hibernation period. Zeiss apoc. 2 mm., Oc. 4.
Fic. 12. Stages in the disintegration of the nucleoli during the dissolution of
the germinal vesicle. Zeiss apoc. 2 mm., Oc. 4.
Fic. 13. The lower pole of the germinal vesicle after the disappearance of the
nuclear membrane. ZAR, line of radiation from which fibers extend both above
and below; J, nucleoplasm breaking up into coarse granules; 4, granular sub-
stance below the line of radiation. Zeiss apoc. 2 mm., Oc. 4.
Fic. 14. The lower pole of the germinal vesicle at a somewhat later stage
than that of Fig. 13. The line of radiation is composed of a dense lower part
sharply defined below, and an upper looser meshwork from which fibers extend up
between the granules of nucleoplasm. Zeiss apoc. 2 mm., Oc. 4.
Fic. 15. Beginning of a pronounced radiation extending from the line of
radiation. Zeiss apoc. 2 mm., Oc. 4.
Fic. 16. Filamentous chromosomes found in the germinal vesicle of the
youngest ovarian eggs obtained at the end of the hibernation period. Zeiss apoc.
2mm., Oc. 8.
: . DD a =
fournal of Morphology Vol. XVt.
+
= Sith Wemer «Winter Frankfort 7M.
346 KING.
EXPLANATION OF PLATE XXIX.
Fic. 17. Vertical section through the black pole of an ovarian egg, showing
the migration of the nuclear débris towards the upper pole after the breaking
down of the nuclear membrane. Zeiss D., Oc. 4.
Fic. 18. A high magnification of the region of the line of radiation at the
stage of Fig. 17. The radiation has reached its greatest extent, and the coarse
granules found both above and below the line of radiation at an earlier period
have entirely disappeared. Zeiss apoc. 2 mm., Oc. 4.
Fic. 19. Vertical section through an egg at a later stage than that of Fig. 17.
The nuclear débris has taken a position directly under the black pole. Zeiss D.,
Oc. 4.
Fic. 20. A somewhat oblique section through an egg in the stage succeeding
that of Fig. 18. The radiation is decreasing and the line of radiation has short-
ened considerably. First appearance in the radiation of rounded granules stain-
ing like chromatin. Zeiss apoc. 2 mm., Oc. 4.
Fic. 21. A later stage than that of Fig. 20. The granular masses seen in
Fig. 20 have increased in size and number and take a much deeper stain. Zeiss
apoc. 2 mm., Oc. 4.
Fic. 22. Next section in the same egg as Fig. 21, showing the rest of the
granular substance in the radiation. Zeiss apoc. 2mm., Oc. 4.
Fic. 23. Masses of granular substance near the first polar spindle. From
the same egg as Figs. 25-27. Zeiss apoc. 2 mm., Oc. 4.
Fic. 24. The twelve chromatin rings with accompanying asters, found in the
nuclear substance at the stage of Fig. 19. Zeiss apoc. 2 mm., Oc. 8.
Fic. 25. A somewhat oblique section of the first polar spindle before its
migration to the periphery of the egg, showing the longitudinal division of the
chromatin rings and a distinct aster at one pole. Zeiss apoc. 2 mm., Oc. 4.
Fic. 26. Next section in the same egg as the preceding. Zeiss apoc. 2 mm.,
Oc. 4.
Fic. 27. Next section to the preceding. Zeiss apoc. 2 mm., Oc. 4.
Fic. 28. The first polar spindle migrating towards the periphery, with its
longitudinal axis parallel to the upper surface of the egg. The asters at the spin-
dle poles have entirely disappeared, and the double chromatin rings have separated
into four parts. Zeiss apoc. 2mm., Oc. 4.
es
Vol.XVu.
f Morphol
FE
:
i
:
3
348 KING.
EXPLANATION OF PLATE XXX.
Fic. 29. Vertical section through an egg from the body cavity. The first
polar spindle occupies a radial position at the surface of the egg directly under
the black pole. The chromosomes are arranged at the equator of the spindle.
Zeiss apoc. 2 mm., Oc. 4.
Fic. 30. Vertical section through an egg from the body cavity at a stage pre-
ceding that of Fig. 29. Z/P, Zona pellucida; YM, inner yolk-membrane. Zeiss
apoc. 2 mm., Oc. 4.
Fic. 31. Next section in the same egg as Fig. 30. Zeiss apoc. 2 mm., Oc. 4.
Fic. 32. Vertical section through an egg from the upper part of the oviduct.
Anaphase of the first polar spindle. Zeiss apoc. 2 mm., Oc. 4.
Fic. 33. Section through an egg from the middle part of the oviduct. Cutting
off of the first polar body. Zeiss apoc. 2 mm., Oc. 4.
Fic. 34. Vertical section through an egg from the lower part of the oviduct.
The second polar spindle lies at the periphery with its chromosomes arranged at
the equatorial plate. Zeiss. apoc. 2 mm., Oc. 4.
Fic. 35. Vertical section through an egg from the lower part of the oviduct.
Separation of the sister chromosomes which were apparently fused in the first polar
spindle. PB, first polar body. Zeiss apoc. 2 mm., Oc. 4.
Fic. 36. Next section to the preceding. Zeiss apoc. 2 mm., Oc. 4.
Fic. 37. Horizontal section through an egg from the lower part of the oviduct,
showing the first polar body and the equatorial plate of the second polar spindle.
Zeiss apoc. 2 mm., Oc. 4.
Fic. 38. Vertical section through a newly fertilized egg, showing the late ana-
phase of the second polar spindle. Zeiss apoc. 2 mm., Oc. 4.
Fic. 39. Section of a newly fertilized egg, showing the second polar body.
Zeiss apoc. 2 mm., Oc. 4.
Fic. 40. The chromosomes remaining in the egg after the cutting off of the
second polar body preparing to form the female pronucleus. Next section in the
same egg as Fig. 39. Zeiss apoc. 2 mm., Oc. 4.
Fic. 41. The spermatozoon of Bufo lentiginosus. A, apex; A, head stained
black with iron-haematoxylin; J/, middle-piece; 7, tail. Zeiss apoc. 2 mm., Oc. 8.
Fic. 42. Depression in the surface of an egg caused by the entrance of the
spermatozoén. There has been an extrusion of egg-plasm at this point to form an
“entrance cone.” Zeiss apoc. 2 mm., Oc. 4.
FIG. 43. Penetration of the spermatozo6n into the egg and the formation of
the astrosphere at its anterior end. Zeiss apoc. 2 mm., Oc. 4.
Fic. 44. The sperm-head after it has entered the egg breaking up into rounded
chromatin granules preparatory to the formation of the male pronucleus. The
astrosphere has become decidedly oblong and a radiation marked by pigment
granules is forming around it. Zeiss apoc. 2 mm., Oc. 4.
Fic. 45. The middle-piece and tail of the spermatozoén after their entrance
into the egg. Zeiss apoc. 2 mm., Oc. 4.
Fic. 46. Vertical section through an egg about one-half an hour after fertili-
zation. A pigment trail marks the path taken by the spermatozoon in the egg.
Zeiss AA., Oc. 2.
Fic. 47. Division of the astrosphere into two parts, each surrounded by a pro-
nounced radiation marked by rows of pigment granules. Zeiss apoc. 2 mm.,
Oc. 4.
7. .
Journal of Morphology. Vol. XVI. om i
Tak. Werner & Winter; Frankfort 7M
a
Ee ma
17
Ay
ey a"
eet! ii ”
350 KING.
EXPLANATION OF PLATE XXxXI.
Fic. 48. The male pronucleus about fifteen minutes after the egg has been
fertilized. The radiation around the pronucleus centers in the astrosphere which
is in the next section of the egg. Zeiss apoc. 2 mm., Oc. 8.
Fic. 49. The female pronucleus beginning its migration from the surface.
About fifteen minutes after fertilization. Zeiss apoc. 2 mm., Oc. 8.
Fic. 50. The two pronuclei approaching each other about one-half hour
after fertilization. The male pronucleus lies between the two centers into which
the astrosphere has divided. Zeiss apoc. 2 mm., Oc. 8.
Fic. 51. Apposition of the two pronuclei about three-quarters of an hour
after fertilization. Zeiss apoc. 2 mm., Oc. 8.
Fic. 52. A somewhat oblique section showing the resting daughter nucleus
with its astrosphere preparing to divide into two parts in preparation for the sec-
ond cleavage. Zeiss apoc. 2 mm., Oc. 8.
Fic. 53. Formation of the segmentation spindle by the union of rays from the
two astrospheres. The segmentation nucleus has rounded up and occupies a posi-
tion at the equator of the forming spindle. Zeiss apoc. 2 mm., Oc. 8.
Fic. 54. The segmentation spindle after the breaking down of the segmenta-
tion nucleus. The chromosomes lie at the equatorial plate of the spindle; the
astrospheres have reached their greatest extent. (A combination of two sections.)
Zeiss apoc. 2 mm., Oc. 8.
Fic. 55. Metaphase of the segmentation spindle. Decrease in size of the
astrospheres and disappearance of many of the rays. (A combination of two
sections.) Zeiss apoc. 2 mm., Oc. 8.
Fic. 56. The segmentation nucleus. The section is cut somewhat obliquely,
so that only one astrosphere is shown. Zeiss apoc. 2 mm., Oc. 8.
Journal. of Momphology Vol. XVI.
0
2.
5
2
28
wate:
a
3%
3
Ke)
Volume XVII. July, Igor. Vo. 3.
JOURNAL
OF
MOK PHO OC
ON LOXOSOMA:’ DAVENPORTEI ‘SP. NOV.
AN ENDOPROCT FROM THE NEW ENGLAND COAST.
W. S. NICKERSON.
CONTENTS. PAGE
intro diictiony .2e224 sey eG lL eae ia ad ct er Ly ee 351
OTemia tone ee eee La Sas cals uscenasne inn secon sseabeah atuee uetacuartuanraresi ae oededeees 352
Hirgbertvall \C War aCteliStieS ieee cca. ssaesatenc curs anuntinsies axa soateyen onan one settee sae cee eee 352
Morphology:
Body=W allvand Modifications: sisi. ss cecsarersansestceacemenresectanec tea aean cea aeeceecea eee 353
IMGUSCUIAPOT EC. e. .cccc os) sedh tt ccabstsceatbssanshsecsssemestuncssbotandatessacstaed Vana seuesutersueaseteapeseatces 359
AON CE GINA bo... 202 casa acu dcscniancsionyvouascetstts wat sonencteir setae Seacapeen sceatan ameet eae eee 361
MOIS CSELVE: SY SECM: secs case sescccete sccotssetces sence Seceatenseat nema taaeeaec sence eae ee 362
INET VO UES “SV SECUE a5 2. has ccclec totes ace stnucanden sp sod eysnnedenetssasebuneansccetnensarsiareeaneae aay eee 363
FREPEOGUCHIVE Sy Sten se. i225. 5. tadashresuslteaedensnarsatens cor sthanetoeecsethy ene aeeaseeeserasae eee 364
Excretory Ongans.0-, ieact ohare acca gute daa aatl arcs eatsaed avarearee vactza incor s chon ee 371
HVE lAONEtOVOLH eT SPECIES) sac cesetccesseseee see cece eet ce aeue aaa bes seyates cn ataa reset cn aaeneapeeee oe 373
Material and) Method sisi i 2cios soe see cece ccesatancnecsusedasu conv sesewuda abecsssesssvedvcentaeeetuceaseeen 373
SOUT ALY ceeee ces, selecreduas svssonseuuvesses oes dwasceeceatauetae tures tauecas Messomencasvsoussanaacsstastuventneraoneezes 374
TELCO TAPULO YE oof silo cete ceca dace ci ak URC ea a as Sa Se nL ea a seven 376
Explanation Of Plates, 22:....3<.sconctvsscsccssssssntsssadeaossnsssussaesustoiescaeaon Pe a vf Oil i
Vi AA, ay 1
Mt er ie i
4 rail ba AAs
380 W. S. NICKERSON.
EXPLANATION OF PLATE XXXIII.
Fic. 16. Longitudinal section of a mature flask organ. X 495.
Fics. 17, 18. Sections showing two stages in the formation of flask organs.
x (o7/tF
Fic. 19. A flask organ in which the gland cells have discharged their contents.
x 495.
Fics. 20-22. Three consecutive transverse sections showing relative positions
of the gonads and their ducts, the median unpaired chamber (sem. ves.), the shell
gland, the brain, and the duct from the excretory organ. %X 250,
Fic. 23. Portion of sagittal section showing manner in which young embryos
are attached to parent. xX 250.
Fic. 24. An optical frontal section of stomach showing lateral glandular tracts
near basalend. x I14.
Fic. 25. Rounded corpuscles from parenchyma. x 675.
Fic. 26. Two mature spermatozoa from seminal vesicle. x 1280.
Fic. 27. Portion of nearly sagittal section through upper portion of body to
show relations of oesophageal gland cell. x 250.
Fic. 28. Oesophageal gland cell shown in Fig. 27, more highly magnified.
xalOvi5s
Fics. 29-31. Three consecutive sections through brain and adjacent organs of
bud still attached to parent ; showing a pair of bipolar cells connecting brain and
ventral wall of body. x 675.
Fic. 32. Section through stalk of bud showing attachment to parent. x 495.
Fic. 33. Section through excretory organ and duct. x 495.
Fic. 34. Portion of margin of foot showing sucker-like openings of gland
cells. X 250.
loural of
it Morpholog
ology Vol. XVit
iz
SENSORY AND GLANDULAR EPIDERMAL ORGANS
IN PHASCOLOSOMA GOULDII.
MARGARET LEWIS NICKERSON.
DurinG the summer of 1897, while enjoying the advantages
of the Marine Biological Laboratory at Woods Holl, Mass., I
had an opportunity to apply the methylene-blue zztva vitam
nerve stain to a study of the epidermal organs of the Gephy-
rean worm Phascolosoma Gouldii. This form lends itself well
to this method of study, as the tough body wall is not easily
torn in the process of injection, and the copious body fluid
surging back and forth quickly carries the injected stain to
all parts of the peritoneal cavity. The use of methylene blue
gave as results some facts regarding the peripheral nervous
system which could probably not be obtained in any other way.
These were supplemented and confirmed, as far as possible, by
maceration preparations and by sections prepared by the ordi-
nary histological methods, as well as by the picro-osmic-acetic-
platinic chloride method of Vom Rath (95). This latter method
was found to be especially useful in the study of glandular
structures.
A brief description of the structure of the body wall will be
given, not with the idea of presenting anything new, for the
general anatomy of the worm is well known (Andrews, ’90), but
for the purpose of making clearer my account of the epidermal
organs.
The body wall consists of three parts: the cuticula, the epi-
dermis, and the muscular layers. In the regions of the probos-
cis and of the tail the cuticula is thrown into elevations or
papillae, but in the middle region of the body it forms a com-
paratively smooth covering. If the cuticula from this middle
region is studied in sections, it will be seen to show numerous
large excavations upon its inner surface. The epidermis, which
consists of a single layer of columnar epithelial cells resting
381
382 MARGARET LEWIS NICKERSON. [Vot. XVII.
upon a basement membrane,! rises at frequent intervals above
its general level to follow the inner surface of the cuticula.
On the proboscis and tail it lines the cuticula covering the
papillae, while in the body region it follows the contour of the
excavations mentioned. Between the epidermis and the circu-
lar muscle is a quantity of loose connective tissue. Scattered
abundantly over the proboscis and body of the worm are found
the well-known epidermal organs which form the subject of
the present paper. On the introvert and tail these organs
occupy the papillae already described, while in the body region
they are partially included in the large excavations in the under
portion of the cuticula. They are ovoidal in shape; the
smaller end is directed outward, while the base rests upon
the circular muscle.
The Epidermal Organs.
The epidermal organs may be divided into two classes: one
containing gland cells, the other not. Each class may be sub-
divided into two types. The two types belonging to the first
or non-glandular class are distinguished by the presence or
absence of a bulb over the organ; the two types belonging to
the second or glandular class by the presence or absence of
intracellular sacks in the gland cells. Each of the four types
contains sensory cells. Except in these organs I obtained no
indication of nerve cells or nerve terminations in the epithelium
covering the animal. Nerve endings are probably present in
the tentacles surrounding the mouth, but no observations upon
these structures are included in the present paper. Each
epidermal organ is flask-shaped and is surrounded by a deli-
cate membrane, probably an invagination of the basement
membrane, and in each type considerable variation is shown
in distribution and appearance, corresponding to the different
regions of the body in which they occur. For convenience,
the two types of non-glandular organs will be first consid-
ered, and afterwards the two types of glandular organs. This
1 Andrews’s statement, that no basement membrane is present, is certainly a
mistake, as a basement membrane can always be demonstrated in material which
has been well preserved and stained.
No.3.] ORGANS IN PHASCOLOSOMA GOULDII. 383
classification has no reference to the distribution of these
bodies ; for in the integument of the worm glandular and non-
glandular organs are found intermingled with one another, with
no definite arrangement.
Organs of the First or Non-Glandular Class (First Type).
The organs of this type are most abundant on the anterior
end of the introvert, in which region, indeed, none of the other
types are found. Above each organ the cuticula is much re-
duced in thickness, the reduction being made from the inner
surface. Each organ has quite a large number of sensory cells,
as many as six or seven of these often responding to the blue
stain. Moreover, in nearly all cases there is evidence that
there are sensory cells which have not taken the stain or which
have taken it only in a slight degree. A drawing of one of
these organs (Pl. XXXIV, Figs. 3 and 10) shows that the group
of sensory cells is situated near the middle of the flask, and that
the long axis of the individual cells is perpendicular to the ring
muscles. The sensory cells are spindle-shaped and are all
bipolar. The peripheral process is stouter than the central
process, and at a short distance below the cuticula, is somewhat
broadened and thickened, making a club-shaped end. From
this expanded end a slender sensory hair ascends to the cutic-
ula and passes through it to the exterior. It is only in exceed-
ingly fortunate preparations that the sensory hairs have retained
the stain, but it is probable that in all cases such hairs are
present. The central processes from the sensory cells emerge
from the flask in one bundle, pass inward across the band
of circular muscles, and enter one of the main nerves coming
from the ventral cord. So far as these central processes were
followed they were never seen to branch.
Organs of the First or Non-Glandular Class (Second Type).
These organs, like those of the first type, are strictly non-
glandular and evidently have some marked sensory function.
Like those of the first type, again, they are each flask-shaped.
They are to be distinguished, however, even under a low power
384 MARGARET LEWIS NICKERSON. [Vot. XVII.
of the microscope, by the presence of a bulb-like structure pro-
jecting above the general surface of the cuticula. It is this
bulb which constitutes the distinction between the first and
second types of epidermal bodies. In other respects there is
much similarity, and the two types are perhaps to be regarded
as fundamentally the same. A comparison of the two types
might suggest that the bulb is a temporary structure produced
by the effect of reagents or by a violent muscular contraction ;
but examination of a large number of sections from specimens
preserved in different ways showed that no matter what the
method of killing, organs exhibiting these bulb-like protuber-
ances were always present, even when the cuticula had been
removed before placing the tissue in the fixing fluid. Again,
pieces of the body wall cut from living worms and examined
under the microscope showed the presence of these bulbs.
The organs of this type first appear on the introvert some-
what anterior to the nephridial openings. Here they are very
rare. They increase in number, however, backward, until in the
region of the nephridia they are so numerous that several are
found in one transverse section. In the tail region they are even
more abundant. Occasionally there may be found in a section
two successive organs belonging to the same type, but far more
often they are separated by a considerable distance. They are
found at intervals in all parts of the body of the worm except the
most anterior portion of the introvert. In sections they are more
conspicuous in the middle region of the body than upon the intro-
vert, hence the projecting bulb appears more prominent.
These organs gave a very successful reaction to the blue stain,
and frequently single sections were obtained which showed all
the details here presented regarding the individual cells and
their connection with the main nerves coming from the ventral
cord. The number of cells stained by the blue showed consid-
erable variation, but the best effects were obtained when not
more than six cells had taken the blue color. Organs in which
only one or two sensory cells were stained were best for study-
ing the peripheral endings (Pl. XXXIV, Figs. 4 and 6). The
enlarged inner portion of the flask contains a group of bipolar
nerve cells very similar in shape to the sensory cells of the
No. 3.] ORGANS IN PHASCOLOSOMA GOULDII. 385
organs of the first type. The body of each of these bipolar
sense cells is of an elongated spindle shape, and it possesses
a large nucleus which is often differentiated by the stain
(Pl. XXXIV, Figs. 6 and 7). The group of cells lies in the mid-
dle or just above the middle of the flask, and the long axes of
the cells are perpendicular to the ring muscles. The peripheral
processes of the cells are longer than those of the sensory cells
belonging to the first type of organ, as they must traverse both
the upper portion of the flask and the entire length of the bulb
before reaching the exterior. In passing through the neck of
the flask the peripheral processes of these sensory cells some-
times show spiral twists and turns very difficult to reproduce
(Pl. XXXIV, Fig. 6).
The fibers passing inward from the group of sensory cells
lie close together and occupy the central axis of the organ.
Emerging in a bundle from the base of the flask, they run for
a longer or shorter distance in a horizontal direction under the
epidermis and, crossing the circular muscle, enter one of the main
nerves coming from the central nervous system (Pl. XXXIV,
Figs. 4 and 6).
The peripheral process of each sensory cell passes up through
the neck of the bulb and at a little distance from the surface
becomes broadened and thickened in the manner described for
the sensory cells of the first type of organ. From this periph-
eral expansion a delicate process or hair extends through the
cuticula covering the bulb (Pl. XXXIV, Figs. 6 and 11). In
some instances this sensory hair could not be traced quite through
the cuticula to the exterior, but such appearances were probably
due to defective staining, as in a large number of instances the
hair could be seen distinctly projecting beyond the surface. Im-
mediately over the center of the bulb in the region through which
the sensory hairs pass, the cuticula shows a marked concavity
of the outer surface, in some cases being so reduced in thickness
that only a line was visible (Pl. XXXIV, Figs. 6 and 7).
The organs of both types possess cells which are evidently
not sensory but supporting epidermal cells. No particular
attention has been paid to such cells and no description of
them appears necessary.
386 MARGARET LEWIS NICKERSON. [Vot. XVII.
Organs of the Second or Glandular Class (First Type).
The structures belonging to this class are rather small, glan-
dular bodies, containing a few — probably never more than eight
or ten— large gland cells, each of which is rudely pyramidal
in shape. Fig. 20 (Pl. XXXV) represents a section through
one of these organs from a preparation made by the Vom Rath
method. Over the middle of the organ is a tubular excavation
in the outer surface of the cuticula, which probably represents
the common duct of the gland cells. Besides the large gland
cells, two nuclei are shown situated near the base of the organ,
* and another lying close to the periphery of the upper portion
of the flask. These nuclei are best interpreted by comparison
with Fig. 5 (Pl. XXXIV), which represents a section through
one of these same organs froma worm injected with methylene
blue. It is here demonstrated that sensory as well as glandu-
lar cells are present, and that the nuclei near the base of the
first figure, in all probability, correspond to the sensory cells
which are colored blueinthe second. These cells are evidently
bipolar with a small cell body. They are situated near the
base of the organ, and in its central axis, or else close to the
limiting membrane of the organ, outside the gland cells.
The peripheral as well as the central process is evidently very
slender, and the small cell body is almost entirely occupied by
the nucleus. The exact method of termination of the periph-
eral process was not determined by this method, and indeed the
results of the methylene-blue staining were in all respects far
less satisfactory for this type of organ than for any one of the
other three types. This was probably due, in some cases, to
the fact that the glandular secretion was stained somewhat
diffusely with the blue and so tended to obscure the sensory
cells. In sections stained by the Vom Rath method the
nuclei belonging to the large gland cells were not visible, but in
sections from material treated with methylene blue and after-
wards stained by alum carmine a small round nucleus was
demonstrated near the base of each gland cell.
Fig. 22 (Pl. XX XV) shows one of these organs containing
about the maximum number of cells and presenting a condition
INO! 3.) ORGANS IN PHASCOLOSOMA GOULD/I. 387
in which the different cells show varying phases of activity.
While in most of the cells the contents appear finely granular,
in one the secretion is formed into spherules, and these spher-
ules I believe to represent a very late stage in the activity of
the cell.
Organs of the Second or Glandular Class (Second Type).
This type, by far the most interesting of the four classes,
includes certain large glandular organs characterized by the
presence of some remarkable intracellular canals within the
gland cells. These organs are found abundantly in all parts
of the body of the worm, with the exception of the anterior
portion of the proboscis. In the region of the nephridial open-
ings and the anus they are the most common of the four types,
as many as ten different organs often being shown in a single
section. Fig. 16 (Pl. XXXV) represents a section through
one of these bodies, and shows that, as in case of the other
three classes, a thin membranous sack encloses the whole
organ, which contains at least two types of cells, vzz., gland
cells and sense cells. By ordinary methods of preparation the
sense cells would probably escape notice entirely, but by the
use of the blue stain they are rendered conspicuous, the gland
cells as a rule remaining entirely unstained. Figs. 9 and 12
(Pl. XXXIV) are drawings from methylene-blue preparations.
As figured here, the sensory cells are bipolar and resemble in
some respects those of the first type of glandular organ, the
peripheral and central processes being both very slender. The
peripheral endings are similar to those found in the non-glan-
dular organs, for at a little distance below the cuticula the ex-
ternal process of the cell shows an expansion, and from this
expanded end a sense hair ascends to the cuticula and passes
through it to the exterior. The long axes of the cell bodies
are, as a rule, nearly vertical to the cuticula, and the central
processes either take a course perpendicular to the ring muscle,
through the middle of the organ, or else lie close to the mem-
branous covering of the organ, the processes seeming, as it were,
to creep over the gland cells. In sections of material prepared
388 MARGARET LEWIS NICKERSON. [Vot. XVII.
by the Vom Rath mixture, the cell body with its characteristic nu-
cleus can be distinguished readily as that of a nerve cell, although
neither process of the cell can be followed for any distance.
Besides these sensory cells, each organ contains a large num-
ber, often as many as twenty or thirty large gland cells, each of
which is broadened at the base and narrowed somewhat toward
the outer end. The nucleus lies near the base of the cell, and
above the nucleus is an intracellular ampulla opening into a
canal which unites with similar canals coming from the other
gland cells of the organ. By the union of all these canals a
duct is formed which communicates with the exterior by means
of a pore in the cuticula situated over the summit of the
organ (Pl. XXXV, Fig. 15). As the sacks are nearly always
plump, it is inferred that they are filled with a fluid secreted
from the gland cells, although the sack contents were unaffected
by any of the stains used.
So much may be said in the way of a general description of
these organs; but for a correct understanding of the individual
cells and intracellular structures, the various conditions pre-
sented by the different phases of activity must be noted. At
what is probably a comparatively early stage in the activity of
one of these gland cells, there are present outside each of these
membranous sacks a very large number of delicate radiating
threads which form a rather broad radial zone or vesicle be-
tween the sacks and the general cytoplasm of the cell. These
threads are attached by one end to the sack wall, and are lim-
ited at the other end by the general cytoplasmic reticulum, with
which they are probably continuous. The width of this radial
zone may be equal to that of the sack (Pl. XXXV, Fig. 16).
A condition considerably later than the one described is
shown in Pl. XXXV, Fig. 17. As figured here, there appear
to be large vacuoles in the protoplasm, which in some cases
occupy nearly the whole of the cell. The sack within now
almost or quite fills the vacuole, and the delicate threads shown
in the first figure are not visible in case of the enlarged sacks.
The ducts from the different sacks unite as before and finally
form a single tube. In the case of two of the cells the con-
dition shown in the first figure is retained. Other organs show
No. 3.] ORGANS IN PHASCOLOSOMA GOULDII. 389
a condition in which the radial zone is enlarged, and extends
down into the protoplasm of the cell, while the sack within
remains small and surrounded by an extensive zone of delicate
threads. At what appears to be a very late phase the walls of
some of the sacks are seen to be broken down, the sacks are
confluent, and in all probability entire cells disintegrate.
After a comparative study of a large number of these organs
representing many conditions, the following explanations of the
different appearances seemed justified. The transparent zone
traversed by radial fibers as shown in Pl. XX XV, Fig. 16, enlarges
and occupies more of the cell. The sacks within enlarge in turn,
and finally, as the periphery of the cell is approached, the sack
comes to occupy the whole space. The enlargement of the sack
within the radial zone is the result of the secretory activity of
the cell —the sack being filled with a clear secretion which is
conducted to the outside by means of the common duct aris-
ing from the union of the several smaller canals. The delicate
radiating threads surrounding the sack probably represent the
protoplasmic reticulum filling the cell, the threads of the
reticulum in the vicinity of the sack being perhaps stretched
by the accumulation of the secreted material in this region and
thus caused to assume the radiating character shown. That
the space between the sack and the wall of the vacuole, as
figured in Pl. XXXV, Figs. 15, 16, and 19, is not an artifact
due to the action of reagents, is proved, I think, by the exami-
nation of fresh tissue under the microscope, in which case the
sack appears as a highly refractive body, surrounded by a sec-
ond clear zone which evidently represents the region traversed
by the delicate radiating threads.
Comparison with other accounts of the epidermal organs of
Gephyreans. — Of the various accounts which have been given
of the epidermal organs of the Gephyreans, the only ones which
will be considered here are those of Andrews (90), Ward ('91),
and Jourdan (’91), these being the only papers, so far as I know,
which offer observations upon the epidermal organs, interesting
for comparison with the results here presented.
Andrews, who deals with the same worm as the one treated
in the present paper, divides the epidermal organs into three
390 MARGARET LEWIS NICKERSON. [Vot. XVII.
classes——two glandular and one sensory and non-glandular.
The two glandular classes which he mentions are probably to be
identified with the glandular organs described in this paper,
although he makes no mention of intracellular sacks and ducts.
In regard to his third class, the sensory organs, I am not able
to infer such a correspondence, as he limits these organs to the
anterior and posterior extremities of the body, while in the pres-
ent account sensory organs have been described for the mid-body
region as well as the extremities of the worm. The histological
details of the epidermal organs, as given by Andrews, possess
but little in common with the observations here presented.
The sense cells of both types of glandular organs are not men-
tioned by him, and the large sensory organs with protruding bulb
seem also to have escaped his notice entirely, as he neither de-
scribes nor figures anything of the sort. His statement (p. 393)
that the delicate processes of the vacuolated gland cells of the
multicellular organs are to be regarded as nerve processes are
not supported by the observations here presented, and in view
of the modern conception of nerve fibers and their relationships,
such a condition as continuity of gland cell and nerve process
is highly improbable. The structure of the cells in the second
type of glandular organ has been very incompletely described
by Andrews ; the intracellular sacks and ducts and the relation
of these sacks to one another being unnoted, as well as the
extreme variety of conditions presented by these structures.
Ward (91), in his paper on the anatomy and histology of
Sipunculus nudus, describes a condition of the bicellular
glands of this Gephyrean which resembles to a slight extent
the condition found in the second type of glandular organs
described in this paper. He says (p. 153): ‘“ Whether resting
or active, a clear zone of plasma forms the periphery of the cell
on all sides, and is, therefore, adjacent to the vacuole as well as
to the external surface of the cell. This zone is traversed radi-
ally by delicate fibrils, the beginnings of the plasma reticulum
which fills the cell, but which is ordinarily seen only in this clear
zone.” These delicate fibrils are probably to be compared with
the filaments surrounding the intracellular sack in the gland
cell, as figured in this paper. Ward states that the gland cells
No. 3.] ORGANS IN PHASCOLOSOMA GOULDII. 391
of the multicellular glands are in direct connection with nerve
fibers. This view, which harmonizes with that of Andrews,
seems to me untenable, and to be due to the lack of special
nerve methods.
Jourdan (91), who investigated the peripheral sensory and
glandular organs of several Gephyreans, has given a detailed
account of the sensory apparatus of these worms, and figures
some conditions which present interesting similarities to the
condition which I have found in Phascolosoma Gouldii. In case
of Sipunculus nudus he finds several types of glandular organs
which possess no sensory cells, and also certain organs which
contain both sensory and glandular cells ; these sensory cells
he describes and figures as possessing sense hairs which pass
through the cuticula, and as being supplied by nerve fibers.
Technique of the Methylene-Blue Method.
The methylene-blue method was employed as follows: a con-
siderable quantity of B. X. methylene blue was injected into
the bodies of several freshly dug worms. The worms were not
previously narcotized, and after injection were returned to the
dishes of sea water and put away in a dark place for three and
a half or four hours. Then an examination was made by cut-
ting out small pieces from the body wall and observing them in
sea water under a cover-glass. When the fresh tissue showed
evidence that the right reaction had taken place, the blue color
was fixed by the ammonium molybdate method of Bethé (96).
The tissue, after being imbedded in paraffin, was cut into sec-
tions from 30 to 50 in thickness, and the sections were
mounted in balsam. Some of these sections were afterwards
stained with alum carmine. It was necessary, in order to obtain
favorable results, to use freshly dug worms. Specimens which
had been in the laboratory for more than one day, even if
kept in running sea water, did not, in any case, give positive
results.
392 MARGARET LEWIS NICKERSON. [Vou. XVII.
SUMMARY.
I. The sensory nervous system of Phascolosoma Gouldii,
posterior to the tentacles surrounding the mouth, is to be found
entirely in the epidermal bodies distributed abundantly through-
out the body of the worm and in the nerve fibers connecting
them with the central nervous system.
2. These epidermal bodies may be grouped into two classes,
and each class into two types. One class contains gland cells ;
the other is non-glandular. The second type of glandular ©
organ may be distinguished from the first by the presence of
intracellular sacks and canals in the gland cells. The second
type of non-glandular organ is distinguished from the first by
the possession of a bulb-like structure projecting above the
general level of the cuticula.
3. All four types of epidermal organs possess sensory cells.
4. Nerve fibers are never found in continuity with the gland
cells of either type of glandular organ, though the contrary
has been several times asserted by different investigators.
5. The sensory cells of all these organs are bipolar in shape,
the cell body in the non-glandular organs being larger than
that in the glandular organs.
6. Each of the peripheral processes of the sensory cells ends
in a delicate sensory hair, which, in some cases at least, is pro-
longed beyond the surface of the cuticula. In one type only,
the second type of the glandular organs, the exact form of the
peripheral ending was not made out.
7. The central processes of all these sensory cells enter the
large nerves passing from the ventral nerve cord.
8. One type of glandular organ possesses a very remarkable
structure consisting of a communicating set of intracellular
canals, each canal leading from an otherwise closed pouch. All
these communicating canals finally open to the surface of the
worm through a common duct.
g. The peculiar sacks or pouches belonging to these glandular
organs are reservoirs for the secretion from the gland cells
and show much variation in size and appearance in correspond-
ence with the phases of functional activity of the cells. The
No. 3.] ORGANS IN PHASCOLOSOMA GOULDII. 393
ducts are the channels by which the secretion is conveyed to
the surface of the animal. The radiating threads surrounding
the sacks are probably to be regarded as continuations of the
reticulum of the cell.
After the preceding part of this paper had been written and
the figures sent away to the lithographer, I had an opportunity to
obtain new material. In preserving this material, I took the
precaution to remove the cuticula from the tissue as soon as it
was placed in the fixing reagent, thus securing a very rapid
penetration of the fluid. The fixing reagents employed in-
cluded Hermann’s and Flemming’s fluids, corrosive sublimate,
and Graf’s chrom-oxalic mixture. For staining, a number of
aniline dyes were employed, and the results obtained, besides
confirming the facts already presented, furnished some addi-
tional details regarding the cells in which the intracellular sacks
and canals are found. These new details have been presented
fully with figures in another place! and will be only briefly
reviewed here. Especially clear pictures were obtained from
material fixed in chrom-oxalic acid and stained with the Ehrlich-
Bionditriple mixture. With this stain, both when it is employed
upon material fixed in Hermann or upon that fixed in chrom-
oxalic, the wall of the intracellular sack is stained red, and is
seen to be surrounded by a second membrane, which also takes
the red color. Between the sack and this enveloping mem-
brane stretch the delicate radiating filaments which have
already been described as surrounding the sack. This mem-
brane surrounding the sack and limiting the filaments is always
present, even when the sack within has become so large as to
occupy almost the whole cell, and it is as well defined as the
sack wall itself. It is no mere boundary or limit of the proto-
plasm of the cell, as has been suggested in the first part of this
paper, but a sharply defined membrane distinguished by its
staining reaction from the cell protoplasm. The staining re-
action of the delicate radiating threads cannot be so positively
stated, for the exceeding fineness of these threads renders the
determination of their color a difficult matter. In some cases
1 Zool. Jahrb., Bd. xiii, Heft i.
394 MARGARET LEWIS NICKERSON. [Vot. XVII.
they were certainly stained red, but at other times the question
of their color could not be decided.
The cytoplasm of the cells containing the sacks shows a
variety of conditions, corresponding, I believe, with the stage
of activity. Those cells in which the intracellular canals are
large, and the surrounding radial zones narrow, show a coarse
condition of the cytoplasmic reticulum, which stains green, while
cells containing small intracellular sacks, with a broad surround-
ing zone of radial filaments, possess a much finer structure and
show the presence of abundant red granules. The latter con-
dition is, I believe, a young stage in the activity of the cell, the
former an advanced stage.
The several canals leading from the intracellular sacks and
the common duct resulting from their union are stained deep
red with the Biondi-Ehrlich mixture and are seen to be en-
veloped in a sheath which also takes the red color. This
sheath, which is directly continuous with the radial vesicle sur-
rounding the intracellular sack, envelops each small canal from
its point of union with the terminal sack and beyond the junc-
tion of the several canals forms a common sheath for the main
duct. The sheath widens considerably near the mouth of the
main duct, while the duct itself close to the exterior often shows
a contracted lumen. Although no mention of the sheath was
made in the first part of this paper, a reéxamination of the
Vom Rath preparations shows that it is always present, but,
owing to the lack of a differential stain, is difficult to see except
with the highest powers.
By the side of the main duct, close to the point of junction
of its branches, is situated a large nucleus within the sheath.
The sheath broadens markedly where it encloses this nucleus.
The nucleus is surrounded by a very clear, transparent, sharply
limited area, which probably represents a vacuole. This nucleus
within the sheath of the main duct is, I believe, always present,
but may of course lie outside the section which contains the
duct; for this reason it was not noted in the sections studied
and drawn for this paper.
UNIVERSITY OF MINNESOTA, MINNEAPOLIS,
January, 1900.
No.3.] ORGANS IN PHASCOLOSOMA GOULDII. 395
EITERATURE (CITED:
'90 ANDREWS, E. A. Notes on the Anatomy of Sipunculus Gouldii Pour-
talés. Stud. Biol. Lab. Johns Hopkins Univ. Vol. iv, pp. 384-430,
Pls. XLIV-XLVII.
’96 BeTHE, A. Eine neue Methode der Methylenblaufixation. Avat.
Anzeiger. Bd. xii, No. 18, pp. 438-446.
’'91 JourRDAN, E. Les corpuscles sensitifs et les glandes cutanées des
Gephyriens inermes. Azz. Sct. Nat. 7¢ série. Tome xii, pp. I-13,
EE fs
95 Ratu, O. vom. Zur Conservirungstechnik. Anat. Anzeiger. Bd. xi,
No. 9, pp. 280-288.
91 Warp, H. B. On Some Points in the Anatomy and Histology of
Sipunculus nudus L. Bull. Mus. Comp. Zool., Harvard College.
Pp. 143-182, Pls. I-III.
EXPLANATION OF PLATES.
The figures in Plate XXXIV are from methylene-blue preparations. The fig-
ures in Plate XX XV, with the exceptions of 18 and 21, are from preparations
made by the Vom Rath method. Most of the drawings were made with Leitz
objective 7, ocular 2, the finer details being filled in with the aid of Zeiss Apo-
chromatic 2 mm. immersion lens and compensating ocular 6. All figures were
drawn with the aid of the Abbé camera lucida.
ABBREVIATIONS.
616. Bulb. mu.crc. Circular muscle.
cad.n. Nerve cord. mu.tg. Longitudinal muscle.
cl. gl. Gland cell. pap. Papilla.
cl. sms. Sense cell. sac. Sack.
cta. Cuticula. set. sas. Sense hair.
h’drm. Hypodermis. vac. Vacuole.
396 MARGARET LEWIS NICKERSON.
EXPLANATION OF PLATE XXXIV.
Fic. 1. Section through non-glandular organ of second type showing four
sensory cells. x 460.
Fic. 2. Section of non-glandular organ of first type. X 512.
Fic. 3. Section through non-glandular organ of first type showing two sen-
sory cells and their connection with nerve from ventral cord. X 512.
Fic. 4. Section of non-glandular organ of second type showing sensory hair
and connection of sense cells with nerve from ventral cord. x 460.
Fic. 5. Section of glandular organ of first type showing five sensory cells.
Mgt.
Fic. 6. Section through non-glandular organ of second type showing two
sensory cells. x 460.
Fic. 7. Section of non-glandular organ of second type. x 460.
Fic. 8. Section of glandular organ of second type showing four sense cells
and refractive bodies representing the intracellular sacks. xX 460.
Fic. 9. Section of glandular organ of second type. x 460.
Fic. 10. Section through non-glandular organ of first type. X 512.
Fic. 11. Section of non-glandular organ of second type showing two sensory
cells and peripheral terminations. x 460.
Fic. 12. Section from glandular organ of second type showing one sensory
cell with its peripheral ending and intracellular sacks. x 512.
Fic. 13. Section through glandular organ of first type showing three gland
cells and one sense cell. x 512.
Fic. 14. Section showing relation of main nerve to ventral cord. These main
nerves contain the central processes from the sensory cells. x 84.
Journal of Morphology. Vol.XVi.
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Ai
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Bie pati Me) Wp
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ia Ay i
398 MARGARET LEWIS NICKERSON.
EXPLANATION OF PLATE XXXV.
Fic. 15. Section through glandular organ of second type showing the intra-
cellular sacks with their communicating ducts. x 620.
Fic. 16. Section through glandular organ of second type showing appearance
of cell contents. The plane of section was not such as to show connection of
intracellular sacks. x 575.
Fic. 17. Section through glandular organ of second type to show late condi-
tion of enlarged sacks. Cell contents shown only on left. x about 550.
Fic. 18. Optical section of bulb belonging to second type of non-glandular
organ. Drawn from living tissue. x 250.
Fic. 19. Section through glandular organ of second type representing early
phase of activity. x 550.
Fic. 20. Section through glandular organ of first type showing two nerve
nuclei at base. X 575.
Fic. 21. Portion of section of Phascolosoma Gouldii in region of retracted
proboscis to show arrangement of epidermal organs. X 33.
Fic. 22. Section through glandular organ of first type showing cells in various
stages of activity.
rs
AT
PLAX
Sela To)
MU.ErC-
Journal of Morphology Vol.XVu.
Sith. Werner @Winter Frankfort 7M.
THE
CYTOGENY OF PODARKE OBSCURA VERRILL.
AARON L. TREADWELL.
CONTENTS.
PART I.—DESCRIPTIVE. PAGE
Mntroducto ry ieee ce. 2sccnceccostcuacecnscocscueceseosseebecnes,nechateheacatcat eseeetaeee a autos aeeseee eee 399
Beoceaying and) Methods it. aacassesecsccuseiceccstestvtcere cee nateeun cena Phe ta ener ea tesa 400
@nerto ili wor Gell si ose ce ee tee ei cae cada s tak te ee aa an a 404
PwortorHour Cell sis ects ceca fccecctect bce cpaccehcagoe coos Ne cae eat eee te ee 404
OUT COMP SHER C OMS oo ae rad cea nas ct ceasise nec rst sages ecaae eum ae ee 406
MiphtitoysixteenuCell sit sess es oes ee eee ne 407
SIxteens CO) UN Mitty-twoi Cells o.oo ccc cssece eceraocean tunseseoecssecueere te ceaeeeeaee eee ee 407
PUHInty-EWO-CO, SIxXty tour Cells sooo casas bac cuszsecccecen cect eee eee eee 408
nS by Gro Up Ole CEOMLCLES i arre ee codec cece oe eee ne re ee 412
SecondiGrouploOksHctomenres) osx iscss eee he oase ee ee 419
sDhirduGroupOfMH CLOMEKCS es. taasee cece -ecea wens susan nde ee meee ce 25
WWarval Meso las ties eecce eo crc ctescaccsecteenceae ee ceee eee see ee ee 427
BIO TUE NG OUP Ole CEOMICTES teewte ces cera ne rears scenes te ee 42
Bitchy Gro uprob, eCtOMenes sate ssscat vies seuss aston ceceettes beetles treats eee neen a nee a 433
LUVGOXEHRG) 0) a0) (Ieee ete Bare alr ee or nana ee deabdssaage Ula Ohasnteoneumen tees Oeeteaae oh 434
PACT ANRC LACIO NS Soe ce Sea cs sce ss ces se cecuee ed cect coerce eee nee eee ee cee ne ue ec 438
pityipes- Of Cleavares: ta tiths pet AU Ae eee BURA A DOES tee yas ee area) eee ne 438
SMG MS Chan Cis 2s eee ae ee Bese oe eae 440
Hovaland UnequaliiCleavage:j.. sth ly We eae aust ee ae aes 441
Mesoblast and Warval :Mesoblast::22-5 22221 c20sJ#i. 82-year cae eae A
CellFancl PN S10 mall ETO mi OO Oy teers tae eee ese eee 455
Tue following investigation, begun in 1891, has been carried
on at the Marine Biological Laboratory at Woods Holl, Mass.,
in the Zodlogical Laboratory of the University of Chicago, and
in the intervals of teaching at Miami University. For many
helpful suggestions I am indebted to my friends, Drs. C. M.
Child, E. G. Conklin, and A. D. Mead. I desire especially
to acknowledge my indebtedness to Professor C. O. Whitman,
without whose friendly encouragement the work would hardly
399
400 TREADWELL. [ Vou. XVII.
have been completed. In the preparation of my drawings I
am indebted to my wife, who has finished from my camera
sketches all of the figures which illustrate this paper.
Podarke obscura is a small Hesionid, abundant in various
localities at Woods Holl, Mass. The species was described
and named by Verrill (No. 30), who says that at night during
July and August they come to the surface and swim about “in
vast numbers.” I have never been able to confirm the latter
observation and have found only a few when towing at night,
these seeming rather to be attached to bits of floating eelgrass
than swimming free. In the “Eel Pond” and in “Little
Harbor” they are abundant, lying in the soft, flocculent sur-
face mud and clinging to the eelgrass a short distance from
the bottom. It is almost hopeless to attempt to pick the
animals from the mud, and I have found the best way to collect
is to sweep through the grass with a strong net. (I used
for this purpose a wooden-rimmed flour sieve.) The animals
remain in the sieve and can easily be jarred into a bucket,
while the finer dirt passes through with the water. They were
then transferred to clean water in glass dishes in the labora-
tory, where with only an occasional change of water they will
live indefinitely. Both in their natural environment and in
captivity they seem rather sluggish, though if irritated they
will swim rapidly away from the disturbing object. They will
burrow quickly into any dirt or sediment that may be in the
dish, but seem in no way inconvenienced if forced to live in
clean water. The occurrence of bifid monsters is very com-
mon, a number of such cases having been described by
Andrews (No. 1).
Specimens in captivity lay their eggs from 7.30 to 9 P.M.,
usually on the second or third, rarely on the first, night after
they are brought into the laboratory. The eggs have no albu-
minous coat, and hence when extruded sink rapidly to the
bottom of the dish, where, if the water be clean, they may
easily be recognized and picked out with a pipette. A simpler
expedient is to strain the water through a fine cloth, through
whose meshes the eggs will pass, leaving the adult annelids
behind.
No. 3.] PODARKE OBSCURA VERRILL. 40I
Artificial fertilization, though tried repeatedly and at various
times of the day, was never successful, unless the eggs had
been laid in the normal manner by the female. Then it was
perfectly possible to cut sperm from the body of the male and
fertilize. Since, as already stated, the normal time of laying
is from 7.30 to 9 P.M., many important early stages are
passed through before daylight (the embryo begins to swim
at the completion of the 64-cell stage, or about the fifth hour
of development), and since the small size and opacity of the
embryo make it an unfavorable object for study by artificial
light, an attempt was made to delay the process of laying.
Although a number of devices which had proved successful in
other forms were tried, they were wholly without success. If
the females are put on ice, or in a very cool place, overnight,
they will hold their eggs until about daylight the next morn-
ing, but such eggs almost invariably developed abnormally ;
and the same result followed if for any reason the eggs were
laid at other than the regular time. In one case only did I find
eggs which must have been laid about 4 a.m. developing nor-
mally. It is not at all improbable that modifications of the
cooling method might have proved successful, but for the pur-
poses of this paper preserved material was so much more satis-
factory than fresh that I have relied almost entirely on that,
merely using the fresh, where possible, for corroboration.
Cilia can of course be seen better in living than in preserved
material, but the history of cells can best be made out on
stained specimens where the karyokinetic figures give abso-
lutely accurate evidence of cell origin.
When the sexual products are ripe, the sexes may be easily
distinguished by the characteristic color of the ova and sperm
seen through the semi-transparent body wall; the females
being a seal brown, the males a cream color. I found that
the most convenient way was to isolate the sexes, which
seems in no way to affect the time of egg-laying, and when
laid to transfer the eggs to fresh water and fertilize with sperm
cut from the body of the male. In this way the precise time
of fertilization can be controlled, something which cannot
always be done if the sexes are together; and the difficulties
402 TREADWELL: (VoL. XVII.
arising from an excessive number of sperm collected on the
surface of the egg can be avoided.
While emitting the sexual products, the female usually
crawls slowly along the bottom of the dish, the eggs stream-
ing out from both sides of the body through openings at the
base of the parapodia. Occasionally one will be found swim-
ming with considerable rapidity during this process. The
males are usually much more active at this time, though there
is never anything like the amount of activity displayed by some
other free-swimming annelids, ¢.g., Nereis.
Material obtained and fertilized in this way was preserved
at intervals of fifteen minutes for the first twelve hours, and
at rather longer intervals for the later stages. There is so
much variation in rate of development in the different lots,
due apparently to temperature conditions, that time records
are of little value, and I have not attempted to keep them
after the first few divisions.
For preserving, I have found Kleinenberg’s picro sulphuric
(dilute) and picro acetic (made with 1% acetic) the most
useful, the latter especially, when followed by Delafield’s
haematoxylin ! (acidified), giving beautiful results with surface
views. Flemming’s fluid, though practically worthless for sur-
face views, preserves cilia well, and gives better preserva-
tion for sectioning than the picro acetic. The specimens,
preserved and stained as above, were cleared in clove oil and
mounted in the same medium underneath a long cover-glass,
supported at one end by a bit of capillary glass tubing. This
method, for which I am indebted to my friend Dr. C. M. Child,
has proved much more satisfactory than to mount in balsam,
as the specimens can be rolled into any desired position and
drawn with a camera as soon as they are mounted.
In the main I have followed Mead’s nomenclature (No. 22)
with certain modifications suggested in conference with Dr.
Child, whose work on Arenicola has been carried on at the
same time as this. The successive generations of ‘ macro-
meres” we propose to designate by capital letters, with the
1] am under great obligations to Dr. Conklin for suggestions as to the use of
this method.
NOs 3:1 PODARKE OBSCURA VERRILE. 403
generation indicated by a coefficient, while the ‘“ micromeres”’
are indicated by small letters, each with a coefficient indicating
the generation and a subscript indicating its position in the
generation. Thus, A, B, C, D form the 4-cell stage. At
their next division from A arises tA and 1a; from B, 1B and
Ib, etc. IA then divides into 2A and 2a, while ta divides
into Ia and Iaz.
We have continued the use of the terms “ dexiotropic”’ and
‘‘leiotropic’”’ to indicate the direction of the spiral cleavages, but
propose the terms “dextral”’ and “sinistral”’ to designate the
respective daughter-cells resulting from a spiral cleavage,
reserving the terms “right” and “left” to apply to the sides
of the bilaterally symmetrical body. Thus, in a dexiotropic
cleavage, the upper cell when viewed from the animal pole
would lie to the right, and is the ‘dextral”’ cell, the other is
“sinistral,” and vice versa in a leiotropic cleavage. In all
cases the cell nearer the vegetative pole has the larger expo-
nent, regardless of absolute size. When a cleavage is merid-
ional, the sinistral cell receives the smaller exponent.
This method has one disadvantage, in that symmetrically
placed cells which arose by a meridional division do not receive
corresponding subscripts. Thus (see Pl. XX XVIII, Fig. 27),
3c2 and 3dz2 divide in a meridional direction and so that their
products are symmetrically placed with respect to the median
plane of the embryo. After one more division their larger
daughter-cells become the larval mesoblast. One of these
cells is 3c2.1, and the other 3dz2.2, according to the proposed
system. I believe, however, the advantages of the system
will outweigh any disadvantages resulting from a_ possible
confusion. This nomenclature differs from that adopted in
my preliminary paper (No. 29, a), but seems enough of an
improvement over that to warrant the change.
Cleavage.
The eggs are small, measuring 62.9 mw in diameter, and are,
in the fresh condition, very opaque. As already stated, they
are not provided with any albuminous coating, and when laid
404 TREADWELL. [Vou XVII.
sink rapidly to the bottom of the dish. They are usually more
or less irregular when first laid, but rapidly become spherical
or nearly so. In some cases there has seemed to be a certain
amount of axial differentiation, but these differences are not
constant. A thin membrane surrounds the egg, and remains
attached to it until the latest stage I have studied. Whether,
as is commonly stated to be the case among annelids, it
becomes the cuticle of the adult, I cannot say. It is smooth
in the living egg, but becomes more or less wrinkled under the
influence of reagents. Except in Fig. 1, I have not attempted
to represent it in the plates.
Soon after laying, the first polar spindle appears, and the
eggs remain in this condition until fertilized. A study of the
maturation and fertilization stages is reserved for a future
paper, and the present account begins with the first cleavage.
The first cleavage begins, with very slight variations in time,
one hour after fertilization. At this time the animal pole is
indicated by the position of the polar globules and by a certain
amount of protoplasmic differentiation easily seen in stained
material. The vegetal pole of the egg stains very slightly with
haematoxylin, and has a granular appearance, while the animal
half is much more homogeneous in texture and stains more
deeply. The first spindle lies slightly nearer the animal than
the vegetal pole. (See PI OCI isa)
The first cleavage furrow cuts rapidly through the egg,
sinking down more rapidly at the upper than at the lower pole
(cf. Wilson, No. 34, d, and Mead, No. 22), and the 2-cell stage
results. (See Pl. XXXVI, Fig. 2.) Here it will be seen that
the first cleavage is exactly equal. The two nuclei are directly
opposite one another, there being no indication of the rotation
described by Conklin in the 2-celled stage of Crepidula. A len-
ticular cleavage cavity is formed, which persists and becomes
the large cleavage cavity of the later stages. (See Text-Figs.
I and 2.)
Two to Four Cells.— The next three cleavages follow one
another at intervals of approximately fifteen minutes, but be-
yond this, time records are of little value. The eggs of the
same lot are usually in practically the same stage at any one
No. 3.] PODARKE OBSCURA VERRILL. 405
time, but owing doubtless to temperature conditions, different
lots vary considerably in rapidity of development. (See Mead,
No. 22, p. 269.) The 4-cell stage arises from the 2, by the
equal division of both cells, there being no large D, as in
other annelids. (See Pl. XXXVI, Fig. 3.) The spindles
are not quite parallel with one another, so that two cells rotate
upward and two downward. As a result, the familiar ‘cross
furrow”’ appears. This is found at both poles, that at the
upper being at right angles with the lower, and considerably
shorter than it. The origin and significance of this furrow
have been discussed by Conklin (No. 5, a), and I can add noth-
ing to what he has said. It is of considerable practical impor-
tance in Podarke for purposes of orientation. The direction of
this furrow at the lower pole is positively the only means of
orientation before the completion of the 56-cell stage. I have
taken a good deal of pains to ascertain if it remains constant in
direction up to that time. There is no doubt that it does,
although soon after the completion of the 64-cell stage this
direction may be lost, owing to movements of the entomeres
whose position determines the existence of the furrow.
The relation of the two first cleavage planes to the body
axes is a point on which most investigators have laid consider-
able stress. In the cytogeny of annelids and mollusks two
apparently distinct relations are found. In Nereis (No. 34, 2),
Crepidula (No. 5, a), and Limax (No. 17), for example, the sec-
ond cleavage furrow is said to coincide with the future median
plane, while in Amphitrite (No. 22) and Arenicola (No. 4) the
quadrants are anterior, median, right, and left. This apparent
discrepancy has been explained by Lillie (No. 21) and Conklin
(No. 5, 2) as arising from the fact that only a small part of the
furrow, that between the entomeres, has been considered in
determining the orientation. Conklin has shown that in anne-
lids and mollusks there is no exception known to the rule that
the second and fourth quartettes lie in the median and trans-
verse planes, while the first and third lie between them. An
examination also of Wilson’s figures of Nereis will show that
the second cleavage furrows, zf traced between the ectomeres,
lie at some distance from the median plane of the embryo.
406 TREADWELL. [Vou. XVII.
In orienting the embryo of Podarke, it is impossible to rely
on the constancy of direction of the polar furrow after the
64-cell stage. Even before they divide to form the fifth group
of micromeres, shiftings in position occur (see Pl. XX XVIII,
Fig. 27), and immediately after this division invagination begins.
From this time on it is impossible to determine their position
with any accuracy. Evidently, then, the arrangement of the
ectomeres must be considered here, and that offers no excep-
tion to the rule formulated above. The second and fourth
generations of micromeres lie in the median and transverse
planes, the first and third lie between them. The relation of
the entomeres to the ectomeres, as is shown before the latter
shift their position, is exactly as in Amphitrite and Arenicola.
They lie anterior, posterior, right, and left. Owing to the
absence of a large D-cell, however, it is not possible to dis-
tinguish between the two ends of the second furrow.
Four to Eight Cells. — The spindles of this division appear
about fifteen minutes after the completion of the last, and the
cells all divide at approximately the same time. The cells are
rarely in exactly the same stage at any one instant, and I tried
to find some indication of an acceleration of development in one
quadrant, such as has been described, e.g., in Unio (No. 21).
Such an acceleration, if present, would be of great aid in orien-
tation, but I do not believe that any exists. In later stages, at
the lower pole, the C and D quadrants divide a little more
rapidly than either A or B, but precisely the opposite occurs at
the upper pole (see Pl. XX XVII, Figs. 19 and 23, showing the
history of the cross), and in no case was there any constant
difference between C and D. Neither was it possible, by any
staining reactions, to distinguish between the quadrants.
The result of this division is the formation of the first group
of ectomeres, which lie on top of the macromeres, but are ex-
actly equal to them in size, or so nearly equal that their differ-
ences lie within the limits of error of observation (Pl. XXXVI,
Figs. 4 and 5). The division is dexiotropic, and it is interest-
ing to note that here, as in Nereis (No. 34, d, p. 387), the spin-
dles show an inclination from the vertical before any external
trace of segmentation is visible.
No. 3.] PODARKE OBSCURA VERRILL. 407
The upper pole is indicated by the presence of the polar
globules, which lie between the cells, almost inside the seg-
mentation cavity (Pl. XXXVI, Fig. 5).
Light to Sixteen Cells. — The 16-cell stage is reached by the
division of each cell of the 8 in a leiotropic direction, the divi-
sions all occurring at about the same time (Pl. XXXVI,
Figs. 6 and 7). The division at the lower pole is equal and
leads to the formation of the second group of ectomeres. It is
of importance to note here that all of the cells of this second
group are equal in size, as compared with many other anne-
lids, in which a very large 2d,
“the first somatoblast,” appears.
Inasmuch as the history of this
cell 2d in Podarke is similar to
that in other annelids, I shall
also call it the “first somato-
blast.”” At the upper pole the
division is more unequal, the
upper cell being the larger. (See
Diy KOO EeiPigs: 6) and 7.)
Since the eight cells were all
equal, it follows that now the
jangest cells are at the supper me.z.opacal ection obzecIltstee tion
pole; and this'relation:holds yntil, 7 te ceavanecenty ae, eles stoke:
the cross has been broken up into small cells (Pl. XX XVIII,
Pies 235 Pla XXX EX, Fig-37).. The smaller:cellsaacieub>
IC2, Id2, divide twice more and form the primary prototroch
of the larva. I shall call them, after Mead, the primary trocho-
blasts. The segmentation cavity present as a lenticular space
in the 2-cell stage is continued through the later cleavages,
and is present as a good-sized cavity at this time. Its pro-
portions a little later than this are shown in Text-Fig. 2.
Sixteen to Thirty-two Cells.—The 32-cell stage is reached by
the dexiotropic division of each of the sixteen cells, the transi-
tion falling into three well marked subdivisions. 7. The division
of the macromeres to form the third group of ectomeres, which,
as we shall see, are not purely ectodermal in destiny, and the
division of the upper cells of the embryo giving rise to the
408 TREADWELL. [Vou. XVII.
”
‘“‘intermediate girdle”’ cells, which occupy the spaces between
the arms of the cross (Pl. XXXVI, Fig. 8). 2. The division
of the primary trochoblasts (Pl. XXXVI, Fig. 9). 3. The divi-
sion of the second group of ectomeres (Pl. XXXVI, Fig. 10).
At the 32-cell stage, although well-marked size differences have
appeared among the cells, the quadrants are still radially sym-
metrical, and it is impossible, by any differences in size or
arrangement of cells, to distinguish them. The polar furrow
retains its original direction and enables us to distinguish
between the two cleavage planes, but no other orientation
mark appears.
At the 32-cell stage the polar globules, which until this time
have occupied a position at the upper pole of the egg lying
on the inner face of the rounded ectomeres, pass into these
latter cells, where they may be seen as small, deeply staining
bodies, lying in the protoplasm of the cell (Pl. XXXVI,
Fig. 11, pg, and Text-Fig. 4). This position they retain for
some time. There seems to be no regularity in the process,
the bodies sometimes passing into one and sometimes into
another of the large cells. Similar observations have been
recorded by Mead (No. 22) in Lepidonotus, where, also in the
32-cell stage, the polar globules pass sometimes into one,
sometimes into another of the cross cells, or they may even
be found in the segmentation cavity ; and in Chaetopterus,
where the polar globules are ingested by the rosette cells.
Grobben (No. 10) finds in Cetochilus that at least one polar
globule wanders into the segmentation cavity, where it, pre-
sumably, is absorbed. Hatschek (No. 11) in Eupomatus, and
Eisig (No. 8) in Capitella, have described a similar fate for the
polar globules. (See p. 417.)
Thirty-two to Sixty-four Cells. —The 64-cell stage is “actual ”’
in Podarke, and is reached by the leiotropic division of each of
the thirty-two cells. Here, as before, there are three well-marked
subdivisions. 7. Thirty-two to forty cells. The fourth group
of micromeres arise at the lower pole (Pl. XX XVII, Fig. 13),
and four very small cells, the apical rosette, are divided off from
the large cells at the upper pole (Pl. XXXVI, Figs. 11 and 12).
It is important to note that the cells of the fourth quartette
No. 3.] PODARKE OBSCURA VERRILL. 409
are exactly equal in size; in other words, there is no large
4d, and so far as we can tell from observation, the cell contain-
ing the mesoderm might be either of two cells lying one at
either end of the second cleav-
age furrow. The spindles at
the upper pole are inclined
downward a little from the
horizontal (Text-Fig. 2). This,
combined with the small size
of the rosette cells, causes the
latter to lie somewhat below
the surface (see Pl. XX XVII,
Fig. 16, and the Text-Fig. 4).
Later, as a result of the pres-
sure of the dividing cross cells,
Bit or ent shown they are forced :stull srarther
below the surface. (See Text-
Fig. 3.) A similar process has been described by Mead for
Lepidonotus (No. 22). Asacomparison of Fig. 12 (Pl. XXXVI)
with Fig. 27 (Pl. XX XVIII) will show, one result of this divi-
sion is further to increase the p av
difference in size which has = -
before been noticed between
the cells of the upper and
those of the lower hemisphere.
2. Forty to fifty-six cells. (@)
A division of the trochoblasts
to form four cells in each
quadrant (Pl. XXXVI, Fig. 12,
Pl OGY ig, 14,: td2-1,
ido 2acerc.).) hese do not
divide again, but soon develop
cilia and function as the pri-
Fic. 3.— Optical section of stage shown in
mary prototroch (PI. XXXVII, Fig. 15, Pl. XXXVII. az, apical rosette;
: , polar globules.
Fig. 15, Id2.1.1, 1d2.1.2, 1d2.2.1, a
1dz2.2.2, etc.). This band of ciliated cells is at first broken
at four points, but is afterwards completed in a manner to be
described later. (6) A division of the intermediate girdle
410 TREADWELL. [VoL. XVII.
cells, Iar.2, Ibr.2, IC1-2, Idi.2 ; and (c), a division of the third
group of micromeres. See Pl. XXXVI, Fig. 12 5 PL OOeeViaiL
Fig. 14, where the spindles of all these divisions are shown.
3. The second division of the second group of ectomeres
(Pl. XXXVII, Fig. 24). This is a most important division, for
by it arises the first indication of a difference between the quad-
rants. It marks, in other words, the first appearance of bilat-
eral symmetry. In three of the quadrants the mode of division
is that shown in Pl. XXXVIII, Fig. 25 (2br-1, 2b1.2; 2b2-1,
2b2.2, etc.). In the fourth quadrant the case is different.
The dextral cell, 2d1, has divided, as in the other quadrants,
ar with a smaller cell above. The
— sinistral cell, on the other hand,
SANE has divided in precisely the op-
posite way. The larger cell is
above, and the smaller cell,
which is very much smaller
than any products of the divi-
sion in the other quadrants, is
below. This cell lies a little
to the right of the second
cleavage plane, and nearly
over one of the fourth group
a of micromeres. It can easily
be distinguished by its small
Fic. 4.— Optical section of stage shown in Fig. ° 1 2.05
16, Pl. XXXVII. In this and later draw- SIZE and deeply staining nu-
ings the nuclei of the prototroch cells are cleus (Pl XOXO aE Fig 26)
stippled. i Z i ‘
Later study shows that the
“4” micromere, near which it lies, contains the mesoderm.
Orientation is now complete, and the quadrant in which the
cell in question occurs is the “D” quadrant. A similar cell,
occupying a similar position, has been described by Mead (No.
22), Lillie (No. 21), and Conklin (No. 5, a) in other annelids
and mollusks. The polar furrow retains its original direction
up to the time when this cell appears, and this enables us to
orient the early cleavage stages.
At about the 4o-cell stage strands of protoplasm can be
plainly seen reaching across the cleavage cavity, running from
No. 3.] PODARKE OBSCURA VERRILL. A4II
the cross and rosette cells to the upper ends of the entomeres
(Text-Figs. 3 and 4). From the pointed upper ends of the
entomeres in Text-Fig. 5, I believe that the connections exist
also in later stages, though I have not been able to make
them out on preserved material. Professor E. A. Andrews,
who kindly examined some of my preparations at my request,
informs me that these processes are undoubtedly protoplasmic,
but that he is unable to determine from preserved material
whether they are protoplasmic streamings, such as have been
described in other animals (see No. 2), or remnants of the
primitive continuity which has never been lost. For our
present purpose the question is immaterial. Of importance is
the fact that protoplasmic connections do exist between blasto-
meres of relatively late cleavage stages.
The embryo is now composed of sixty-four cells, divided as
follows :
rst. -Ouartette) a: .0 45) vas cee
2d Z Sop ceh) talacee LO
3d &“ an Sy scas cg ES
4th th Shed, Se asl) cee creme
JDO. 5 Gg o 6 6 o eh
64
Three of the quadrants are exactly alike and the fourth differs
from them merely in the possession of the small cell, Xr.2,
which lies at what will be the posterior end of the body.
Up to this stage it is evident that Podarke agrees in the
character of its segmentation with other annelids and with
gasteropods and lamellibranchs. In all cases three quartettes
of ectomeres arise in alternating directions. In all cases one
member of a fourth quartette is budded off, and this cell is
wholly or partially composed of the definitive mesoblast. Usu-
ally but not always (e.g., Nereis) the other three members of
this fourth quartette appear. Inasmuch as they, together with
the remaining macromeres, give rise to the entoderm, the dif-
ference is merely that in the one case this division takes place
at the surface, in the other, after invagination.
On the other hand, Podarke differs from most other annelids
in two important features. The cells of the second and those
412 TREADWELL. [Vou. XVII.
of the fourth quartettes are all equal in size, whereas in nearly
all annelids there is a large 2d and a large 4d. The entomeres
also are much larger in other annelids than in Podarke.
These differences are important and will be discussed later.
(See p. 441.)
Let me repeat that up to the time when the small cell X1.2
appears, the polar furrow at the lower pole of the egg retains
its original direction. At the 64-cell stage, however, the
entomeres elongate inward to a greater or less extent, and
the shiftings of position thus caused among the cells may pro-
duce a change of direction in the polar furrow. (See PI.
XXXVIII, Fig. 27.) The condition shown in Pl. XXXVIII,
Fig. 27, appears only rarely, but often enough to show that
the polar furrow can no longer be relied on for orientation.
Since the regular geometrical progression is now lost (some
cells, ¢.g., trochoblasts, do not divide again, while others divide
repeatedly), the later history can best be treated by considering
each group by itself.
First Group of Ectomeres.— At the 64-cell stage these are
arranged as follows :
Trochoblasts 16
Intermediate cells 8
Cross cells 4
Rosette cells 4
The trochoblasts, as already stated, do not divide again, but
form the larval locomotor organs. They become elongated
as development proceeds, prominent nucleoli appear in their
nuclei, and they stain with great difficulty. They are very
much narrower than in Amphitrite, agreeing in this respect
very closely with Lepidonotus (No. 22). (See Pl. XX XVIII,
Figs. 29, 30, etc., af’, etc.) Cilia appear on these cells soon
after their last division, about four and a half to five hours after
fertilization, and the embryos at first rotate slowly and later
swim at the surface, being at first positively heliotropic. The
primary prototroch thus formed is at first divided into four
distinct areas, the openings between being later filled with cells
having a different origin. As long as the separate cells could
No. 3-] PODARKE OBSCURA VERRILL. Aihe
be distinguished I have designated each by 9’, with the appro-
priate letter and number (Pl. XX XVIII, Fig. 25—Pl. XL, Fig.
58). In later stages, where the primary and secondary, and
still later, where also the tertiary prototroch cells are not to
be distinguished from one another, I have indicated the proto-
troch merely by #, with the appropriate letter to show to
which quadrant each portion belongs.
The Intermediate Cells. — The last division of these cells was
leiotropic. The next is dexiotropic and leads to the forma-
tion of four cells in each quadrant (Pl. XXXVII, Figs. 17
and 18). In three of the quadrants (a, b, and c) the lower
product of the division of the dextral cell Icr.2.2.2, etc., com-
pletes the primary prototroch (Pl. XX XIX, Figs. 37 and 38, a",
etc.). They pass into the space between the sets of primary
trochoblasts, become ciliated, and function as prototroch cells.
I propose to call them the secondary trochoblasts. The other
products of this division fill the space between the arms of the
cross and become a part of the umbrellar ectoderm. For some
few divisions I have been able to follow their history, but after
the cross cells begin to divide into small cells the two sets
intermingle so that it is not possible to distinguish them.
In the fourth quadrant the history of the intermediate cells
is very different from that just described. Their first division
into four cells is the same, but a little later the lower product
of the division of the dextral cell, z.2., the one corresponding to
the cell which in other quadrants becomes a part of the pro-
totroch, begins to migrate through the opening in the proto-
troch, and thus forms a portion of the lower hemisphere. In
this migration it is accompanied by part, at least, of its sister-
cell, but I think by none of the descendants of the other inter-
mediate cells. These migrating cells push through the break
in the prototroch, dividing as they go (Pl. XX XIX, Figs. 42, 44,
and 45; Pl. XL, 53, 57, and 58, lx, lz, etc., and the cells just dorsal
to them). Since the opening persists until late in the develop-
ment, the process of migration lasts for a considerable time, or
until the trochophore is fully formed. In Pl. XL, Figs. 53,575
and 58, it will be seen that these cells flatten out as they pass
downward, one of them, |: (Pl. XL, Figs. 53 and 57), elongating
414 TREADWELL. [Vou. XVII.
very considerably. It immediately adjoins the cell X3.2, and the
two form a landmark which is unmistakable. Figs. 58 and 59
(Pl. XL) show that the cells which have migrated through the
prototroch eventually comprise a large portion of the sub-
umbrella, fully three-fourths of it being formed from them.
The cell 1; divides transversely. (See the products of its divi-
sion, ly.1 andlz.2,in Pl. XL, Figs. 58 and 59.) Beyond the latter
stage I have not followed it. All of these cells become excess-
ively thin and their outlines difficult to follow, so that in the
later figures I have indicated only the nuclei. The entoderm
cells lie close under the ectoderm, the two being dorsally in
actual contact, and it frequently becomes impossible, except in
optical section, to determine whether a given nucleus belongs to
ectoderm or entoderm. In Pl. XL, Figs. 58 and 59, I have
intended to represent only ectoderm nuclei.
A similar migration has been recorded in Amphitrite by
Mead (No. 22), but there the number of migrating cells is
much less than in Podarke, and they play a much less impor-
tant part in the formation of the subumbrella.
The Cross. —In the 64-cell stage the cross is composed
of four equal cells, radially arranged. At the next division
bilateral symmetry appears. It is interesting to note that this
is accomplished by a dexiotropic cleavage ; the direction which
it ought properly to assume according to the law of alternating
cleavages. Fig. 16 (Pl. XX XVII) shows the beginning and
Fig. 17 (Pl. XX XVII) the completion of this division. In the
latter is seen, also, the beginning of the next divisions of the
cross cells in two quadrants. In the latter figure, also, is shown
the division of the upper (sinistral) intermediate cell in each
quadrant. The result of the first bilateral division of the cross
cells is shown in Pl. XXXVII, Fig. 17. Two of the cells
have divided unequally, two very nearly equally, so that a ver-
tical plane can be drawn which would cut the embryo into
bilaterally symmetrical parts. This plane of symmetry coin-
cides with the plane marked out by the small cell X1.2, pre-
viously described at the 64-cell stage. The median plane
of the embryo is now fully indicated, and orientation is com-
plete. The constant position of the polar furrow up to
No. 3.] PODARKE OBSCURA VERRILL. AI5
the 64-cell stage, the appearance of the cell X1.2, and the
bilaterally symmetrical cross form a series of orientation
marks which are unmistakable. We may say, therefore, that
in A and B quadrants the first division of the cross is very
unequal ; in C and D quadrants it is nearly equal.
The Appearance of Bilaterality.
This marking out of a bilateral plane by cleavages which
follow a true radial ! type is important to my mind as indicat-
ing that the bilateral divisions have nothing to do with shift-
ings of material into the median plane, but rather that the
bilateral and the radial are distinct in origin. The former
having been, so to speak, superimposed upon the latter, the
bilaterality of the organism may express itself even in the
spiral cleavages.
Bilateral cleavages have not in Podarke such direct refer-
ence to the form of the body, as distinct from the head, as
Conklin (No. 5, a) has described for Crepidula. The first bilat-
eral cleavage is at the lower pole (Pl. XX XVIII, Fig. 27), but
bilateral divisions appear early and are very prominent at the
upper pole as well. Further, as we have seen, bilateral sym-
metry is established before bilateral cleavages appear, and is as
marked at the upper as the lower pole.
Of interest in this connection are the following observations:
I have seen a few (not more than three were carefully studied)
cases where the cross, when formed, is radial and not bilateral.
Each arm has three equal cells, like the anterior cross arms
represented in Pl. XX XVII, Fig. 18. In these same embryos
2d: and 2dz2 divided just like the other second quartette cells,
and no small X1.2 appeared. In this stage, therefore, the
embryo was still radially symmetrical. In one other case three
cross arms were alike in having three equal cells, while the fourth
was of the posterior cross-arm type. These facts are signifi-
cant to my mind as indicating a reversion toa radial type of
a cleavage which had secondarily become bilateral. The fact
1 In this and later discussions I have followed Conklin in classing both “ ortho-
radial” and “ spiral ” cleavages under the general head of “ radial.”
416 TREADWELL. [VoL. XVII.
that the reversion is always to the radial from the bilateral
(from the type of the posterior arm to that of the anterior)
and not in the opposite direction is suggestive. The facts are
perhaps too few in number to warrant wide inferences, but so
far as they go they seem important.
The next division of the cross cells emphasizes still more the
bilateral symmetry. The division of the basal cells in A and
B quadrants, begun in Pl. XX XVII, Fig. 17, is completed in
Pl. XXXVII, Fig. 18, and there result three subequal cells
in arow in each arm. In C and D quadrants the upper cells
divide next, but divide bilaterally, the cells sloping inward
(Pl. XXXVII, Fig. 18). In C quadrant the division is equal,
in D quadrant unequal. (See Pl. XXXVII, Fig. 19.) This
result was so unexpected that I suspected it might be an
abnormality, but in examining a large number of prepara-
tions I found always the same result.
While this last division is in progress in the basal cells of
the posterior arms the terminal cells divide, Ic1.1.2.2 usually
a little in advance of Idy.1.2.2. The division is bilateral, and
there result two small cells, lying a little farther from the
median plane than the center of the large terminal cell. These
small cells are very little larger than their nuclei, which stain
very deeply, and they lie on top of the cross, between it and
the basal cells of the arm. They are excellent landmarks for
later study of the embryo, as it is possible at a glance to recog-
nize the C and D quadrants by means of these small deeply
staining cells (Pl. XX XVII, Fig. 20).
In Nereis, Wilson (No. 34, @) described cells similar to these
in origin and position, which he called, provisionally, “head
kidneys.” In Amphitrite corresponding cells were found by
Mead (No. 22), from which arise the huge mucous glands of
the trochophore, and Wilson (No. 34, f) has since suggested
that possibly they are slime glands in Nereis also. In Podarke
the next division of the dorsal arms of the cross (Pl. XX XVII,
Figs. 20 and 21) buds off one other cell on either side. This
cell is very little larger than the first one, and the two pairs
remain in this position until very late in the development.
The last stage in which I was able to recognize them with
No. 3.] PODARKE OBSCURA VERRILL. 417
certainty was that represented in Pl. XXXVII, Fig. 23. I
believe that they become slightly larger in the later stages and
form a part of the general ectoderm of the umbrella. Once
and only once did I see an indication of a division in one of
these cells, Idr.1.2.2.2.1. This I believe was abnormal. They
certainly do not become slime glands (excretory glands?) in
Podarke, unless the small deeply staining cells scattered over
the surface have that function, for there are no such large
glands as Mead has described for Amphitrite.
The anterior arms of the cross next divide meridionally.
(See the division begun in Pl. XXXVII, Fig. 19, and com-
pleted in Pl. XX XVII, Fig. 20.) At their next division! a
number of small cells appear (Pl. XX XVII, Fig. 22). Note
especially the small size of these cells and their deeply staining
nuclei. To avoid tedious description I have indicated by junc-
tion lines in Pl. XX XVII, Fig. 22, the origin of many of these
cells, and have put their divisions in the table, p. 438. In Pl.
XXXVII, Figs. 18-23, the outline of the cross is indicated
by the heavy line.
Beyond the stage represented in Pl. XX XVII, Fig. 23, I
have not attempted to carry the lineage of the anterior (ven-
tral) portion of the umbrella. The cross cells become inextri-
cably confused with the descendants of the intermediate group,
and, with possible exceptions, all contribute to the formation
of the ventral ectoderm. The exceptions are these. I believe
that some of the very small cells are pushed into the cleavage
cavity and finally absorbed. Immediately after they are formed
they sink below the surface, lying near the bottom of the rather
thick ectoderm. A little later dark bodies are seen lying inside
the segmentation cavity, and later still they touch the en-
toderm (see Text-Fig. 8, ec?). The point needs reinvesti-
gating before it can be considered absolutely proven, but
PE believe the fate of the cells: is) as: | have desembeds) 4
similar process occurs in Crepidula (No. 5, a2), where, however,
the cells are thrown outside the body, and more recently Miss
Langenbeck (No. 20) has described, in Microdeutopus, cells
which are taken into the segmentation cavity. In Lepidonotus,
Mead (No. 22) states that the polar globules ‘pass into the
418 TREADWELL. [VoL 2evil:
cross cells (see above, p. 417), and he figures them in Figs. 93
and 105. In Podarke, as already stated, the polar globules have
a similar fate, but long before the stage corresponding to
Mead’s Fig. 105 they have completely disappeared. On the
other hand, these small cells derived from the ectoderm migrate
inward and occupy a position very similar to that of the “ polar
globules” of the latter figure. This leads to the suggestion
that possibly both processes may occur in Lepidonotus also,
and that the small cell figured in Fig. 105 is derived from the
ectoderm.
In the dorsal arm of the cross, the cells Icr.1.2.1.2 and
Idy.1.2.1.1 next divide (FI: XXXVII, Fig. 20), and this is
followed by the division of Ic1.1.2.1.1 and Id1.1.2.1.2. (See
Pl. XX XVII, Figs. 21 and 22, and table, p.438.) The large termi-
nal cells of the dorsal arms divide considerably later, the divi-
sions being nearly equal. Figs. 22 and 23 (Pl. XX XVII) show
the division in C quadrant. (See also Pl. XXXIX, Fig. 42,
Idi.1.2.2.2.2.) Later than this I have not attempted to follow
the cells in detail. They all enter into the formation of the
ectoderm on the dorsal side of the umbrella, in which I have
been able to make out no specialized organs. Ventrally there
are two ‘“eye-spots’”’ and the large “problematic” organs
which develop from either the ventral cross cells or from the
intermediate cells. It is impossible to tell from which.
The Rosette Cells.— At the 64-cell stage these are four in
number, lying between the cross cells and considerably elon-
gated imward. | (See Pl Xx XXVIL) Bigse16;17, anc ais,
and Text-Figs. 3 and 4.) Soon after the stage represented
in Pl. XXXVII, Fig. 17, one of them, invariably the one of
the A quadrant, comes to the surface and divides equally
(Pl. XXXVII, Fig. 18, av). Next, the one in the D quadrant
divides (Pl. XX XVII, Fig. 20, dr). Later, the two remaining
cells divide, and the resulting plate of eight cells is shown
with stippled nuclei in Pl. XX XVII, Figs. 22 and 23. These
cells differ so little in size from those around them that the
two are hard to distinguish, but I think the arrangement
given in Pl. XXXVII, Fig. 23, is correct. The cells elongate
slightly inward (Text-Figs. 5 and 6, av). From them arises the
No. 3.] PODARKE OBSCURA VERRILL. 419
tuft of apical cilia which from now on is a prominent feature of
the larva. I think that all of the eight cells become ciliated.
The Second Quartette. — At the 64-cell stage there are sixteen
of these cells, four in each quadrant, and a difference between
the quadrants has shown itself by the peculiar division of one
cell, leading to the formation of X1i.2, already mentioned.
Since the fate of the second group of micromeres in the
dorsal quadrant is different from that in the others, it will be
advantageous to consider it by itself, and turn first to the
second quartette in quadrants A, B, and C.
The first division concerns the upper dextral and lower
sinistral cell (Pl. XX XVIII, Fig. 29). This is followed some-
what later by a division of the upper sinistral and lower
dextral cells (Pl. XXXIX, Fig. 37). These divisions follow
the law of alternation of cleavages only in the dextral cells,
the sinistral dividing in precisely the same direction as their
preceding division. Neither can the divisions be called bi-
lateral, since the cells are not bilaterally arranged ; and,
indeed, from the 64-cell stage on, while some of the divisions
of cells which lie near the median plane may be bilateral,
the majority are not. They develop so as to produce in the
end an embryo with bilaterally symmetrical organs; but data
concerning the precise direction of each spindle, except in so
far as they bear on the identification of cells, seem to me of
little value. Cleavages may follow the law of alternation, or
they may not, and neither case in itself is of any importance.
The divisions of the dextral cells are of interest, for by them
are produced three cells, which correspond to the “secondary
trochoblasts”’ of Amphitrite, the cells 2a1.1.1, 2a1.1.2, 2a1.2.1,
etc. (Pl. XXXIX, Fig: 38).. In Amphitrite, however, the
division of the upper cell is equal, while in Podarke it is very
unequal (Pl. XX XIX, Figs. 37 and 38).
In each quadrant, then, there are three cells, two large and
one small, corresponding in origin to the secondary trocho-
blasts of Amphitrite, (See Pl. XX XIX, Figs. 37, 38; 41,,etc.,
appa! ap2!”, 2a1.1-1y box; bp2!”, 2 Tt. 15 epi! Epa! ZCY Tet)
Fig. 56 (Pl. XL) shows the relation of these cells to the rest
of the prototroch : cp1!”’, cp2!”", 2cr.1.1.. While, however, 2cr.1.1,
420 TREADWELL. [Vou. XVII.
and 2c1.1.2 (cp1’’ and cp2!’) have elongated considerably, their
nuclei have become swollen and contain prominent nucleoli,
and the whole cell stains with difficulty, —agreeing in this
respect with the cells of the primary prototroch, — the small
cell 2c1.1.1 remains very small and with a very deeply stain-
ing nucleus. Later, as a result of the shifting of cell areas,
this small cell is shoved out of the prototroch ring, and, I
believe, forms a part of the ectoderm of the subumbrella,
though its later history is difficult to follow. This process
occurs in all three quadrants. Compare Pl. XL, Fig. 56, an
embryo of 12 hours 35 minutes, with Pl. XXXIX, Fig. 48,
an embryo of 24 hours (2b1.1.1 and 2c1.1.1). These figures
show two stages in the shoving of this small cell out of the
prototroch ring. Later embryos show it lying entirely below
the prototroch. The other two cells form a part of the com-
pleted prototroch, though they acquire their cilia very late.
In the stage represented in Pl. XXXIX, Fig. 48, they are
still without cilia. A little later they push up into the proto-
troch ring and all the cells elongate still more, this latter
process coinciding with the closure of the dorsal interruption.
They stain very poorly, so that their outlines are impossible
to follow in later stages.
The other divisions of the second quartette are as indicated
in Pl. XXXVIM, Pig? 365°R1 XRT, Missa a2; eae
Pl. XL, Figs. 50, 51; andin the table, p. 438. One cell is, how-
ever, of especial interest. This is the cell 2bz.2.1 shown in
Pl. XXXIX, Fig. 41. Here it is seen at some distance from
the edge of the blastopore. It divides once only. (See the
products of the division in Pl. XL, Fig. 51.) While the corre-
sponding cell in quadrant A divides vertically and equally
(Pl. XXXIX, Fig. 41), this division is horizontal and unequal,
a small cell being budded off dorsally. The ventral product,
2bz2.2.1.2, does not divide again at the surface. Gradually the
cells between it and the blastopore, — descendants of 2bz2.2.1,
—invaginate to form a part of the stomodaeum, and this
1In Pl. XXXIX, Fig. 46, I have indicated by the numeral on each cell the
share which the second and third quartettes take in the composition of the ven-
tral ectoderm.
No. 3.] PODARKE OBSCURA VERRILL. 421
cell, 2bz.2.1.2 , approaches closer and closer to the blastoporic
margin, and finally invaginates. (See Pl. XX XIX, Figs. 43,
4ar Pl. XL, Pigs 40,50; Sy $2,545.55.) ln thesstace repre-
sented in Pl. XX XIX, Fig. 47, it lies underneath the surface
in the wall of the stomodaeum, where its nucleus is indicated
by the dotted line. It later divides, but I have not been able to
follow its subsequent history farther than to say that it forms
a part of the stomodaeal wall.
The history of the second quartette cells in the dorsal quad-
rant is of especial interest for purposes of comparison, since
in many annelids and mollusks they give rise to a large part
or all of the ectoderm of the body, and in Amphitrite and
Arenicola, at least, the paratroch of the larva is formed from
descendants of this group. I shall follow Wilson and Mead
in giving to these cells the especial name “ X.’”’ For the sake
of clearness I have enclosed the X-cells in a heavy outline.
The first divisions of X have already been described,
the small X,., arising in the 64-cell stage. (See Pl. XX XVIII,
Fig. 26, where I have labelled the figure to correspond with
Mead’s nomenclature for the X-cells.) The next divisions
occur in X,, and X, (Pl. XX XVIIT, Fig. 30;and Pl Oris,
Fig. 39), and these are soon followed by a division of X, (PI.
XXXVIII, Figs. 31 and 32), where the completion of this
division is shown. X,,,,, next divides (Pl. XX XIX, Fig. 39),
and there results a larger cell above, X,,., and a smaller,
Kyeas, below (Pl; XXXITX, Fis. 40). At, mearly) the same
time X,,, divides (Pl. XX XVIII, Fig. 35, and Pl. XXXIX,
Fig. 39). In Pl. XXXIX, Fig. 40, is shown the division
of X,.,/and Xj5,and Xiao. PlwWXX XD Bice 42, shows) the
division completed. X,,;,, next divides and at about the
same time division occurs in X,,,. These divisions are shown
as completed in Pl. XX XIX, Fig. 42. These cells with their
descendants now become difficult to distinguish from the cells
of the third quartette near them, and as nothing of importance
was to be gained from such a study, I have not attempted to
carry them farther. X,,., amd X,1:22 next divide equally
(Pl. XXXIX, Fig. 43), and X2., (Pl. XXXIX, Fig. 44), very
unequally, the latter budding off a small cell to the left of
AZe TREADWELL. [Von. XVII.
Xoo5 Later, Xia27, and X,52,2 divide very unequally, each
budding off a small cell downward, and at the same time X,,
sends a small bud upward (Pl. XX XIX, Fig. 45, and Pl. XL,
Fig. 53). These small cells, formed from X,, and X,1.21.,
have very deeply staining nuclei, and are excellent landmarks.
The general rotation, which all the dorsal cells undergo, affects
lie underneath X,,, while its sister-cell lies to its right
(Pl. XX XIX, Fig. 48). Meanwhile the small cell, X,,., has
migrated inward, and forms a part of the wall of the procto-
daeum, while its sister-cell lies at the edge of the blastopore.
This afterwards divides again (Pl. XX XIX, Fig. 46).
As a result of the divisions described above, the condition
of the X-group is as shown in Pl. XXXIX, Fig. 47. At the
dorsal edge of the blastopore are three cells, one of which is
dividing. X,.. divides next, unequally and in a meridional
direction. The smaller product lies to the outside, and later
Xi1221 buds off a small cell dorsally, which lies just below
X32. These cells occupy this position for some time, but
subsequently divide, and the ventral edge of the X-group is
composed entirely of small cells. (See Pl. XL, Fig. 59.)
In Pl. XXXIX, Fig. 47, X3.. is shown very much flattened
and elongated, having remained undivided from the stage
shown in Pl. XXXIX, Fig. 39. Together with the ectoderm
cells which have migrated from the upper hemisphere, it has
become excessively thin and transparent, but can always be
recognized by means of its large vesicular nucleus and promi-
nent nucleolus (Pl. XL, Fig. 57). As already stated, it and
the “2,” cell just above it are excellent landmarks in follow-
ing the shiftings of position which the dorsal ectoderm cells
undergo. Finally 7, divides, and immediately afterwards
X,. divides bilaterally. Pl. XL, Fig. 58, shows the spindle
of this division with the products of the division of 7, lying
just above it on either side. The daughter-cells of X,. elon-
gate considerably, and push apart (Pl. XL, Fig. 59). They
may be recognized in later stages lying in this position, one
on either side of and dorsal to the protodaeum. Each soon
buds off a small cell downward and outward. In a considerably
No. 3.] PODARKE OBSCURA VERRILL. A23
later stage I have seen, occupying the position of these
cells on either side, a row of two or three small cells, which
apparently have come from a division of X3.214+ and X3..,, but
I am unable to give any positive statements about their
origin or destiny. They have an appearance which strongly
suggests teloblasts, but I do not know if they have that
character. Indeed, the cells X32. and X28 (Plea Ris:
59) look very like teloblasts, but if they are their teloblastic
growth must begin much later, for none of the ectoderm
anterior to them has, in the stage figured, come from their
division. Their later position also resembles very much that
of the paratroch cells figured by Mead (No. 22) in Amphi-
trite, but in the latest stages I have seen no cilia are found
on them.
I have described these divisions of the X-cells at some length
because of their value for purposes of comparison with other
annelids. Amphitrite and Arenicola (No. 4) are the only annelids
where the exact origin of the paratroch is known. Podarke,
as said before, probably has no paratroch, but so important an
organ might, on one theory of cleavage, be supposed to be
present as an ancestral rudiment ; and I was interested to
follow the cleavages in the three genera to see if any similari-
ties appear. The divisions of the X-cells in Podarke beyond
the stage of Pl. XX XVIII, Fig. 30, have no similarities what-
ever to those of Amphitrite (No. 22) nor to those of Arenicola,
as I learn from a comparison with figures kindly given me
by Dr. Child.
I have already spoken of the way the dorsal ectoderm cells
flatten out and spread apart. It is as if the cells from the
upper hemisphere spread out like a fan, with their center near
the upper edge of X3.2, and carried the X-cells with them around
towards the ventral side. The direction in which the forces
which produced this shifting must have acted is shown in
Pl. XL, Fig. 59, by the elongated cells X3.2.1 and X 3.2.2.
The break in the prototroch remains open much later than
in Amphitrite, and is represented as just closing in Pl. XL,
Fig. 58. Whether or not this be regarded as the cause, the
result is that a much larger portion of subumbrellar ectoderm
424 TREADWELL. [Vor. XVII.
comes from these cells than from the corresponding cells in
Amphitrite. In fact, a very limited portion of the subumbrella
is formed from the X-cells,as is shown in Pl. XX XIX, Fig. 48 ;
Pl. XL, Figs. 58 and 59. To this point, which is mainly of
importance in a discussion of homologies, I shall return. (See
p. 467.)
As a result of this migration and expansion of the dorsal
ectoderm cells, the X-group are forced ventrally and finally
concresce on the ventral surface (Pl. XX XIX, Figs, 46-48).
I am not absolutely certain that some of the cells figured as
lying just outside the X-group may not really belong to the
latter. The descendants of the third group of micromeres lie
close to the X-group on either side, and so many shiftings
occur that it is impossible to follow every cell. For our present
purpose the precise history of every cell is not absolutely neces-
sary. The point of importance is that the X-cells surround
the proctodaeum and, if it be safe to rely on analogy, make up
the budding zone of the larva. I have thus far been unable to
rear larvae, though they will live in confinement for as many as
ten days. Probably connected with the lack of proper food
(for the small amount of yolk in the egg must be rapidly used
up) is an exceedingly slow rate of development during the time
that they will live in captivity. Similar difficulties with other
annelids have been described by Hatschek (No. 11) in Eupo-
matus, von Drasche (No. 7) in Pomatoceros, and Mead (No. 22)
in Lepidonotus. Beyond a slight increase in length, practi-
cally no growth takes place after the second day. In Amphi-
trite, Mead has proved that all of the body behind the first
segment arises from descendants of 2d. For reasons above
mentioned, I am unable to make any positive statements about
their fate in Podarke, but in view of their position I think the
presumption is strong that here also the body ectoderm arises
from 2d.
Of interest in this history of the X-cells in Podarke is the
fact that their divisions are not bilateral, so that until at least
a very late stage the cells are not symmetrically placed with
regard to the sagittal plane. Pl. XX XIX, Fig. 46, for example,
shows a marked asymmetry. This asymmetry is partly due to
No. 3:] PODARKE OBSCURA VERRILL. 425
asymmetrical divisions, and partly due to shiftings of positions
which the cells undergo. In Pl. XXXIX, Fig. 42, for example,
the cells Xr.1.1.1 and Xz.1.1 are seen to lie close against
the prototroch cells in C and D quadrants respectively. Just
to the left of X2.1.1 are two small cells, 2a2.1.1 and 2a2.1.2
(Pl. XX XIX, Fig. 43). When the cell areas shift so that the
prototroch cells take their final position, I believe that the
cell 2a2.1.1 is pushed up between Xz2.1.1+ and the proto-
troch (Pl. XX XIX, Figs. 44 and 45), while, on the other hand,
the cell X1.1.11.+ is pushed up between the prototroch cells
(PR DOCG Bie 45; Ply XL, Fiey 56). Pheinesulteomthis
movement is that on the left side the X-cells occupy a broader
area, when seen from below (Pl. XXXIX, Fig. 48), than do
those of the right of the median plane. In much later stages
(Pl. XL, Figs. 57 and 58) a small cell lies wedged in between
the cells of the prototroch in the C quadrant, This cell, I
believe, is a descendant of X1.1.1.1, which has been separated
from the X-group by the migrating cells from the upper hemi-
sphere. In later stages the large X3.2 divides symmetrically
(Pl. XL, Fig. 58), but I have been able to discover no other
symmetrical divisions. Neither could I find any divisions, such
as Mead has described in Amphitrite, which, though themselves
asymmetrical, had direct reference to the symmetry of the
trochophore.
The Third Quartette.— At the 64-cell stage these are eight in
number, two in each quadrant. . We have already seen that the
next division establishes bilateral symmetry at the upper pole.
Symmetry also appears at the same time at the lower pole as a
result of the peculiar division of two of the third group and one
of the fourth. Leaving the latter for the present with merely
the remark that it is 4d and contains the mesoderm, let us
notice the division of the third quartette cells (Pl. XXXVIII,
Figs. 26 and 27). Here 3d2 and 3cz, lying one on either side of
4d, are dividing in a bilaterally symmetrical fashion. (The sec-
ond line of cleavage in the specimen from which Pl. XX XVIII,
Fig. 27, was drawn had changed its direction. This is rare in
this stage and I have never found it in earlier stages before
X1.2 is formed.) The outer product of the division in both
426 IREADWELL. [VoL. XVII.
cases is the smaller and may be neglected in the further de-
scription. The inner products show from the first a tendency
to invaginate (see Pl. XXXVIII, Fig. 28), where their nuclei
lie beneath the surface. Later each cell divides dorsally a
small cell, coming to the surface to divide (Pl. XX XVIII,
Figs. 35, 3d2.1 and 3d2.2, and 36, 3C2.1.2 and 3d2.2.2). Their
nuclei immediately start to invaginate again. Finally each
nucleus comes to the surface and a very small cell is budded
off (Pl. XL, Figs. 50 and 51), and all four of the cells thus
formed invaginate to give rise to a large part of the /arval
mesoblast, which is entirely the functional mesoblast of the larva.
As we shall see immediately, the larval mesoblast is completed
by the addition of other cells from another quadrant.
Of the other products of 3d and 3c little need be said; 3dr
and 3cr divide meridionally soon after the first division of 3dz2
and 3cz (Pl. XX XVIII, Fig. 28, 3dr), and a number of later
divisions have been noted. (See Pl. XX XIX, Figs. 40, 42,
44, 46, and table, p. 438.) They form a portion of the ventral
ectoderm of the trochophore, take part in the closure of the
blastopore, and make up a part of the proctodaeal wall. (See
Pl. XXXIX, Fig. 46.)
The first division of the third group of micromeres in the A
and B quadrants is shown in Pl. XX XVIII, Fig. 28, where 3a2
and 3b2 are dividing meridionally. A little later 3a1 and 3b:
divide also meridionally (Pl. XX XVIII, Figs. 34 and 35). The
next division in A quadrant is of cell 3a2.2 (Pl. XX XIX, Fig.
At). This divides unequally, sending a small cell upward,
3a2.2.1 (Pl. XL, Fig. 50), while the larger lower portion begins
to invaginate (Pl. XL, Figs. 50 and 51). This cell, 3a2.2.2,
passes into the segmentation cavity and becomes /arval meso-
blast. Originally situated at the left of the median plane, it
passes forward and lies directly in this plane. Its next division is
equal. (See Pl. XL, Fig. 52, and Text-Fig. 7.) From this time
on its products lie symmetrically on either side of the median
plane. A corresponding cell in B quadrant divides at about
the same time as this and apparently invaginates (Pl. XL,
Figs. 49 and 51). I at first supposed that this also becomes
larval mesoblast. Careful examination, however, fails to show
No. 3.] PODARKE OCBSCURA VERKILE: 427
any trace of this cell lying in the segmentation cavity, and all
the larval mesoblast of the anterior end of the body, as is
unmistakably shown by the specimens, comes from the cell
3a2.2.2. I have been unable to trace the cell 3bz.2.2 with any
accuracy after the stage shown in Pl. XL, Fig. 51, but from its
position I suppose that it aids in the formation of the stomo-
daeum. The entoderm cells have divided repeatedly, and at
this time are no larger than the cells at the edge of the blasto-
pore, so that it is difficult to distinguish between the two sets.
The further history of the other descendants of 3a and 3b, so
far as I have followed it, is given in Pl. XX XIX, Figs. 46 and
47, and in the table, p. 438. Detailed description would be
profitless. They form a part of the stomodaeum and the gen-
eral ectoderm of the subumbrella.
Larval Mesoblast.
This arises in Podarke, as we have seen, from descendants of
3d, 3c, and 3a. The two former are symmetrically arranged
from the beginning, while the latter only become so placed
after invagination and division. It is important to note that
this division, which occurs in 3a2.2.2, after its invagination, cor-
responds to the division which in the other cells gave rise to
the small cell ventrally, and which takes place at the surface.
In both cases both products of the division become mesoblast,
so that all the cells of the larval mesoblast belong to the same
generation. I have indicated these cells as right, l.m.r., left,
Lm.l., and median, l.m.m. After the next division, immediately
to be described, the smaller product of the posterior larval mes-
oblast, when seen from the side, lies over the large 4dz cells
(Pl. XL, Fig. 56), while the others have spread farther apart
in the cleavage cavity.
The larger products of the posterior larval mesoblast divide
next, and there is formed a band of three cells on either side
of the median line (Pl. XL, Figs. 52 and 54, and Text-Fig. 7).
Since the posterior end of each band lies very close to the defin-
itive mesoblast (colored a deeper pink in the figures), the effect
is that of two well-developed mesoblast bands, lying in the
428 TREADWELL. [Vou. XVII.
usual position in the segmentation cavity, and they would
undoubtedly be described as such by any one who saw merely
the preparation figured in Pl. XL, Fig. 54. Very soon, how-
ever, the larval mesoblast cells begin to migrate (Pl. XL, Figs.
53, 55, 56). In Pl. XL, Fig. 56, is shown the position of the
posterior larval mesoblast, while the anterior, at this stage, is
composed of four cells on a side. The cells elongate and
become the larval musculature. They are especially well
developed in the region of the prototroch, under which the
long, spindle-shaped cells may easily be recognized in later
stages. ‘(See Pext-Fig:/3:)
Comparative. — A larval mesoblast was first discovered by
Lillie (No. 21) in Unio, where it arises asymmetrically in the
A quadrant only, from the second group of micromeres, 2a2 +.
This migrates so as to lie symmetrically in the cleavage cavity,
and by its division are formed cells which become metamor-
phosed into the “myocites” and larval adductor muscles,
which are functional only during larval life. Later Conklin
(No. 5, a), in Crepidula, found larval mesoblast arising from
the second quartette in three quadrants, A, B, and C. In the
left-wound gasteropods, Physa and Planorbis, which have the
“‘reversed”’ type of cleavage, Wierzejksi (No. 31) and Holmes
(No. 15, 4) found it arising from the third quartette in B and C
quadrants ; in these reversed cleavages, therefore, symmetri-
cally arranged. In annelids, thus far, the structure in ques-
tion has been found only in Aricia, Capitella, and Podarke. In
Aricia, Wilson (No. 34, g) finds two cells arising symmetrically
from either the second or third quartette. Through lack of
material he was unable to discover its exact origin. In Capi-
tella, Eisig (No. 8) finds it arising from the ventral products
of the second division of 4d, thus corresponding in origin to
cells which in other annelids become entoderm. (See p. 451.)
To this point I shall return later.
From the figures which Hatschek gives for Eupomatus, it
seems to me extremely probable that a larval mesoblast is pres-
ent there also, although the point is not one to which Hatschek
paid any attention. His figures (Pl. XX XIX, Fig. 42 to Pl. XL,
Fig. 49) show scattered muscle cells in the upper hemisphere of
No: 3.] PODARKE OBSCURA VERRILL. 429
the larva, which could hardly have come from the feebly devel-
oped mesoderm bands at the posterior end of the body. The
same suggestion would apply to Pomatoceros, as described by
von Drasche (No. 7), where Pl. XXXVII, Fig. 20, shows a
muscle cell just underneath the apical pole, and the small
compact mass of seven mesoblast cells, showing no trace of
differentiation, quite at the other end of the larva.
The cell origin of the larval mesoblast in the forms where it
has been thus far described is as follows :
WWmlOUr es pox este outa:
Grepidulay “a sy 2ag2b.2c;
Bhysas ts ey a. BE BE.
RIANOE DISH. J58 Be KS be
MAGICIAN tea) Ve .. = -2ndsor 3rd quartette:
Capitellay ty. |. Ads. Adio
POdAr Kelana co fe «Zab SOa pe oOo
Fourth Quartette. — At the 64-cell stage the fourth group of
micromeres has just been formed, and, so far as one can tell
with the microscope, are all exactly alike. Very soon, how-
ever, as we have seen, one of the cells divides bilaterally, thus
aiding in the establishment of the bilateral symmetry of the
body. These cells, like those of the third quartette just adjoin-
ing them, early show a tendency to invaginate, and they divide
at the same time as the latter, each budding off ventrally and
posteriorly a very small cell (Pl. XL, Fig. 51). The two then
invaginate and can be seen through the transparent X-cells
lying just underneath the surface. It is important to notice,
however, that at the same time that these cells invaginate a
gastrulation begins, and the entoderm cells push in at the
same time as the cells 4d, and 4d2. (Since until the stage of
Pl. XL, Fig. 57, the mesoderm is not fully differentiated, I have
retained the designation 4d,, etc., for the descendants of 4d in
the earlier figures. The small cells which enter into the arch-
enteric wall I have indicated by ez in Pl. XL, Figs. 51-57.)
This accounts for the fact that the descendants of 4d undergo
such extensive shiftings of position without at the same time
1 Here, as elsewhere in the comparative portion of this paper, I have modified
the nomenclature to conform with that adopted for Podarke. (See also p. 465.)
430 TREADWELL. [VoL. XVII.
losing their connection with the wall of the archenteron. The
two small cells described as budded posteriorly from 4d, and 4d2
form a part of the wall of the archenteron. Since the greater
part of 4d gives rise to the
definitive mesoblast, it is
therefore, to use Conklin’s
term, a mesentoblast cell.
The cells 4d,,; and ade
at first lie in the wall of
the archenteron, though
they protrude considerably
into the segmentation cav-
ity. Consequently, in a
section passing a little to
one side of the sagittal
Fic. 5.— Beginning of entodermal invagination. £7, ee cn Soom so) I
entoderm: Zw, larval mesoblast; JZ, 4d before Wholly im this cavity (Text-
he soe eee oe a ig (0) Baca abade aie
the “anal ” cell. second small cell (Pl. XL,
Fig. 56), and the larger
portion is the definitive
mesoblast, M, and M,.
Considerably later (Fig.
57,.Fl. XL, and Dext-Pig:
8) each divides equally.
Only until this last divi-
sion do these cells entirely
lose their connection with
the archenteric wall. Text-
Fig. 8 is an optical section
of the specimen drawn in
Fig. 57, and shows that
the descendants of 4d are
Fic. 6. — Later stage of invagination. still connected with the
a, archenteric cavity.
entoderm. I have actual
sections of this stage which show exactly the same thing. The
products of the last division migrate rapidly through the
segmentation cavity, retaining approximately their original
No. 3.]
PODARKE OBSCURA VERRILL.
431
direction, at right angles to the prototroch, and eventually lie
on either side the ventral surface, just underneath the adoral
zone of cilia) (FI XGLy Pigs sa):
which I have carried
the mesoderm cells
in what I am posi-
tive were normal
embryos. In older
embryos I have
found a large pole
cell occupying a
position like the
posterior one of the
two cells figured
in Fig. 59, while a
row of small cells
extended anteriorly
The diffi-
culties experienced
in getting larvae to
develop after the third day
have as yet prevented me
from securing any complete
details of the later history
of these cells, and since the
study of the trochophore
development has been taken
up by another worker, I
have thought it best to leave
the subject at this point. In
calling these cells the germ
bands, I am not relying en-
tirely on analogy with other
annelids, although the re-
semblance is close, but on
the fact that both ectoderm
from it.
Pl. XL.
This is the latest stage to
Fic. 7. — Horizontal optical section through Fig. 52, Pl. XL, taken
at level of larval mesoblast.
median larval mesoblast.
Zmr, lml, Imm, right, left, and
Other letters as before.
Fic. 8.— Sagittal section through stage of Fig. 57,
ec, ectodermal cell; JZ, definitive meso-
blast, in its first division after eliminating all the
entodermal elements ; stom, stomodaeum.
and entoderm are fully differentiated at this stage, and these
cells, lying in the segmentation cavity, are the only source from
432 TREADWELL. [Vou. XVII.
which mesoderm can arise, unless we assume an ectodermal
origin, which is not probable. Hence I have no hesitation in
saying positively that they are the germ bands.
The second pair of small cells, like the first, enter into the
wall of the archenteron.
Comparative.—In all annelids, gasteropods, and lamelli-
branchs thus far studied, with one exception, the definitive
mesoblast arises from 4d. The exception is Capitella, where,
according to Eisig, 4d contains only a little larval mesoblast,
while the greater part of the cell is ectodermal and enters into
the ventral plate. The definitive mesoblast in this form arises
from 3c and 3d. (Seep. 451.) In Nereis, Wilson (No. 34, @)
described small cells budded off ventrally from 4d, and 4d,,
which he at first called “secondary mesoblast,’ and supposed
they lay on the dorsal wall of the archenteron. In Aricia
only one of these cells appears on either side. Later, how-
ever, Wilson has shown (No. 34, g) that the so-called second-
ary mesoderm cells do not form mesoderm at all, but really
become a part of the wall of the archenteron. In Amphitrite
(No. 22), Polymnia! (No. 34, @), and Arenicola (No. 4) this
entodermal portion is lacking in the cell 4d. In Amphitrite,
Mead described a very small cell at the anterior end of the
germ band, which he suggests may be a reminiscence of the
superficial budding which takes place at the surface in other
forms, and Wilson has definitely homologized the two sets of
cells. Inasmuch, however, as these cells always remain in the
mesoderm, such a comparison seems to me doubtful, and, if ves-
tigial at all, they represent rather some mesodermal structure.
As I have pointed out on p. 472, the small size of cells when
first formed is no proof of their vestigial character, since they
may subsequently undergo any amount of growth. In Clyme-
nella, Mead (No. 22) described the first division of 4d, and 4d,
as equal instead of the very unequal division of Nereis or Aricia.
Wilson (No. 34, g) has suggested that the posterior portion of
each of these cells is entoderm. While this is possible, it has
not been proved, and hence the structure is of little value for
comparison.
1 See, however, Wilson (No. 34, g), p- 12 of reprint.
Nov3:] PODARKE OBSCURA VERRILL. Ase
Among the mollusks Conklin (No. 5, a) has shown that 4d
in Crepidula is more than half entoderm. It is not impossible
that a portion of this cell in Unio may have a similar fate, and
a close relation between mesoderm and entoderm has been
described for Cyclas (No. 28) and Patella (No. 26), though the
precise cell origin of the mesentoblasts in the latter cases was
not determined. These observations seem to indicate a lack
of uniformity in the mode of origin of the mesoblast and also
show an apparently close relation between mesoblast and ento-
blast. To this point I shall return later. (See p. 449.)
The other members of the fourth quartette apparently invagi-
nate. (See their small superficial area in Pl. XX XVIII, Figs.
33 and35.) In Pl. XX XVIII, Fig. 34, the nucleus of 4a shows
underneath the 2a cells. In some cases I was unable, in the
stained specimens, to see the outlines of the cells. This fact
led me to the erroneous statement in my preliminary paper
(No. 29, a) that they invaginate before dividing. As a mat-
ter of fact, the cells come to the surface and divide equally
(Pl. XXXVIII, Fig. 36), and then immediately invaginate,
entering into the wall of the archenteron.
The Fifth Quartette.— A fifth series of four cells arising
from the entomeres has been called the fifth quartette of. micro-
meres by other workers, and in my preliminary note (No. 29, a)
I emphasized the fact that in Lepidonotus, as in Podarke, such
a quartette appears. The term, however, is misleading, since
the cells thus formed are entodermal in destiny ; and we must
regard this division as corresponding to the division which, in
other forms, takes place after invagination. The only differ-
ence between the two cleavages is that one takes place at the
surface and the other below it. The one is as truly a fifth
quartette of micromeres as the other.
This division in Podarke is shown in Pl. XX XVIII, Fig. 33,
occurring in C and D quadrants, and later it appears in quad-
rants A and B (Pl. XXXVIII, Fig. 34). The eight cells thus
formed, together with six derived from the division of three
members of the fourth quartette, make up an invaginating plate
of fourteen cells, which rapidly invaginates, its cells meanwhile
dividing again; and the alimentary canal of the embryo is
434 TREADWELL. [VoL. XVII.
quickly mapped out. The details of this process I am unable
to give, for it is impossible on surface views to see the outlines
of the cells; and on account of the small size of the embryos,
sections are very unsatisfactory objects for study, the difficulties
in the way of accurate orientation being too great. I can only
say that the alimentary canal is rapidly formed, being practi-
cally completed by the twenty-third hour of development. As
in Nereis (Nos. 34, @ and g), the posterior ectoderm cells bud
off some small cells, which enter into close relations with the
entodermal portion of 4d. Some stages in the invagination and
hollowing out of entoderm cells are shown in Text-Figs. 5, 6,
7, and 8.
The stomodaeum, as already stated, is formed by cells from
both the second and third quartettes. The invagination which
some of these cells undergo is shown most clearly by the aid of
the landmark furnished by the cells 2b,.,.,,. already described
on p. 420. Theanterior portion of the blastopore becomes the
mouth, and its sides are closed by cells from both the second
and third quartettes. The proctodaeum arises at the posterior
end of the blastopore, which I do not believe ever completely
closes. Thus both mouth and anus arise from it (cf Conn,
No. 6). The cell X,.,.., as already stated, early invaginates to
form a part of the proctodaeal wall, but the exact origin of the
other cells which invaginate I was unable to determine. From
their position in earlier stages, I believe that the cells 3c., and
3d., are the ones most deeply concerned, but the small size of
the cells and the shiftings of position which they undergo make
it impossible to be certain. (See Pl. XXXIX, Fig. 46.)
The trochophore is now fully formed. The apical tuft of
cilia still remains at the anterior end of the umbrella, and about
midway between this and the prototroch is a second tuft. (See
Pl. XL, Fig. 60.) The prototroch is now a complete ring, the
origin of its cells having already been described. An adoral
zone of cilia extends from the mouth to the anus (“ Neurotro-
choid”’ of Eisig), but no paratroch is present. On the ventral
surface of the umbrella are the two orange-colored ‘‘eye-spots,”’
and the large clear spaces, which are undoubtedly similar in
origin and function to the “frontal bodies” of Nereis and the
No. 3.] PODARKE OBSCURA VERRILL. 435
“problematic bodies”’ of Amphitrite. In Nereis, Wilson sup-
poses each to arise from a single cell, which becomes vacuolated
and probably has a glandular function. In Podarke there are
two on a side, closely crowded together just in front of the eye-
spot, and a fifth very small one on the median line in front.
They stain very deeply with haematoxylin, an outer portion
(Wilson’s “duct ’”’) staining much more deeply than the inner.
From the number of nuclei surrounding each “body”’ in the
early stages, I think they are formed from more than one cell.
Their staining reactions indicate that they have a glandular
function, and they are apparently the only glands in the body.
In the case of these glands, as well as in that of the so-called
‘slime glands”’ in other annelids, I agree with Eisig (No. 8),
that they probably have an excretory rather than a slime secret-
ing function, the necessity for the one and not for the other
being apparent. —
A marked feature of the larva of thirty hours and later is a
circular shelf, which extends around the cavity of the archen-
teron and, when seen from the side, apparently divides it into
distinct compartments (Pl. XL, Fig. 60). Careful observa-
tion shows, however, that this is really a broad, very thin shelf
of tissue. The opening through it is at first at the center of the
ectoderm cavity ; later it lies at the dorsal side of the enteron.
Just above it is a tuft of long cilia, a modification of the general
ciliation of the archenteron. (See Pl. XL, Fig.60.) The first ap-
pearance of this structure is at about twenty-three hours, when a
slight constriction appears at about the middle of the archenteron.
Partly by the swelling out of the archenteron above and below it,
and partly by an active growth of the cells involved, is formed a
circular shelf of tissue extending out into the cavity of the ali-
mentary canal. In embryos of about thirty hours, if the speci-
men be rolled so that the proctodaeum looks upward, careful
focusing through the proctodaeal opening shows this circular
shelf running entirely around the archenteron, and extending
about one-half the way across its cavity. The organ at this
stage bears a very striking resemblance to the velum of a
medusa. Later it becomes very thin and vacuolated, and the
details of its structure are difficult to make out. The original
430 TREADWELL. [VoL. XVII.
opening, as I believe, moves backward to the position described
above, and I think other openings break through it, but of this
I am not certain. When first formed, the partition is ciliated
above and below. I do not know how long that condition lasts.
(See Pl. XL, Fig. 60.) The section passed a little to one side
of the central opening, which therefore does not show in the
drawing.
The suggestion has been made that this partition represents
the first septum, but I do not believe that is so. So far as
I can discover, only entoderm cells enter into it. It seems to
me rather to lie at the boundary line between “stomach” and
‘“intestine”’ of the larva, and to be merely an exaggeration of
the constriction found at that point in other annelid larvae.
(See No: 7, Pl. SX RVI, Pig. 26)
As already stated on p. 435, the wall of the archenteron swells
out so as to lie close under the ectoderm. Since dorsally both
layers are very thin and transparent, it becomes difficult, on
surface views, to make out the outlines of the cells. Indeed,
it frequently is impossible, except by rolling the specimen so
as to get an optical section, to determine to which layer a
given nucleus belongs. Ventrally (Pl. XL, Fig. 60), the ecto-
derm is much thicker.
At this point the cell lineage naturally ends, and the study
of the trochophore begins. Since the problems of the latter
subject are so different from those of the former, it has seemed
best to reserve the metamorphosis of the trochophore for
another paper.
Comparison with other Annelids having “equal” Cleavage.
— The most complete account of the cleavage of an equally
segmenting annelid previously published is that of Mead
(No. 22) on Lepidonotus. To Dr. Mead’s generosity I have
been indebted for preparations of the later stages. A few
observations have also been made on the cleavage of Hydvozdes
dianthus and Sthenolais picta, both of which resemble Podarke
in their mode of cleavage. I have not as yet carried the
development of these forms far enough to justify a detailed
account of the process, but enough has been seen to show
as I pointed out in a preliminary paper (No. 29, a) that bilateral
No. 3.] PODARKE OBSCURA VERRILEL. 437
symmetry appears at practically the same time here as in
Podarke, and that there is as much differentiation in the ovum
as in any annelid with the unequal type of segmentation. The
theoretical bearings of this fact I shall discuss later.
Table of Cleavages.
I have followed all divisions up to about 140 cells ; later
than this only especial groups were followed. All of these
divisions are indicated in the accompanying tables. The well-
marked stages of the earlier cleavages are denoted by the num-
bers at the top of the column, but after eighty cells these
numbers must be regarded as only approximate. Each table
gives the divisions of a single quadrant and begins with the
4-cell stage. The direction of each division is indicated by
the straight line / inclined to the right for a dexiotropic, to the
left for a leiotropic, vertical for a meridional, and horizontal
for a horizontal cleavage. If it be remembered that the line
always has the direction of the boundary plane between the
two cells, I think the table will be readily understood. When
the products of a division are equal, that is indicated by the
sign of equality. If unequal, by the sign of inequality, placed
across the direction line. A plus (+) sign after a cell number
indicates that it has been seen to divide again, but its divisions
were not followed.
In all cases the daughter-cells resulting from a division are
put in the column indicating the number of cells in the whole
embryo immediately after the division of these cells. Thus,
at the 16-cell stage, 2A divides dexiotropically and unequally,
the larger cell lying below. At the completion of this divi-
sion the whole embryo contains twenty-four cells. The smaller
cell, 3a, does not divide again, until about forty cells, and
when this division is completed the whole embryo contains
fifty-six cells, etc.
438 TREADWELL. [Vo. XVII.
Part II. GENERAL CONSIDERATIONS.
Axtal Relations.
The axial relations of the first cleavage planes have been
described above (p. 405). Those of the trochophore agree with
Amphitrite. The mesoblast bands occupy from the first their
definitive position at right angles to the prototroch. Although
the X-cells, as in Nereis, occupy a final position much farther
from the prototroch than they were at first, the cells between
them and the prototroch have a very different origin from the
cells in a similar position in Nereis, and I have seen no evi-
dence for a shifting of the neural axis, such as has been
described by Wilson (No. 34, @). The descendants of the
X3.2 group form a row of large cells across the body which
look like teloblasts, but I have no evidence that they really
have that function. (See p. 423.) I donot think that all of the
ventral ectoderm of the trochophore arises from the X-cells.
All the evidence indicates that some of the other second, and
probably to a limited extent the third, quartette cells have this
fate. (See Pl. XXXIX, Fig? 46)
Types of Cleavage.
In Podarke, as in other annelids, and in gasteropods and
lamellibranchs, two types of cleavage, the radial and the bilat-
eral, have been distinguished, the former appearing first, and
being gradually displaced by the latter as development proceeds.
The subject has been thoroughly discussed by Wilson (No.
34, @), Mead (No. 22), and Conklin (Nos. 5, a and 5, 4), and I
need not go over the ground again. As I have said in another
place (see p. 470), the most reasonable explanation of these
cleavages to my mind is that they were primarily mechanical,
and that morphogenetic processes have been secondarily moulded
upon the primitive forms. The first of these causes leads to
the radial or spiral divisions which appear first, and the second
to the bilateral divisions which have a direct reference to
the bilaterality of the future body. I agree perfectly with
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554 FOOT AND STROBELL.
PLATE XLV.
Reproduction of figures of various authors referred to in text. See p. 532.
PI. XLV.
The Hopkins Co., N. Y., Engravers.
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Journal of Morphology, Vol. XVII.
Photographs by Foot & Strobel.
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