w

HARVARD UNIVERSITY

«©,

LIBRARY-

OF THE

Museum of Comparative Zoology

BULLETIN

OK THE

MUSEUM OF COMPARATIVE ZOOLOGY

AT

HARVARD COLLEGE, IN CAMBRIDGE.

VOL. XIII.

CAMBRIDGE, MASS., U.S.A.
1886-1888.

Reprinted with the permission of the original publisher

KRAUS REPRINT CORPORATION

New York

1967

Printed in U.S.A.

CONTENTS.

Page
No. 1. — Report on the Results of Dredging by the United States Coast
Survey Steamer " Blake." XXX. Report on the Holothurioidea. By
Hjalmar Thekl. (1 Plate.) October, 1886 1

No. 2. — A Second Supplement to the Fifth Volume of the Terrestrial Air-
breathing Mollusks of the United States and adjacent Territories. By
W. G. BiNNET. (3 Plates.) December, 1886 23

No. 3. — Simple Eyes in Arthropods. By E. L. Mark. (5 Plates.)
February, 1887 49

No. 4. — Studies from the Newport Marine Laboratory. XVllI. On the
Development of the Calcareous Plates of Amphiura. By J. W. Fewkes.
(3 Plates.) May, 1887 107

No. 5. — Preliminary Account of the Fossil Mammals from the White River
Formation contained in the Museum of Comparative Zoology. By W. B.
Scott and H. F. Osborx. (2 Plates.) September, 1887 151

No. 6. — The Eyes in Scorpions. By G. H. Parker. (4 Plates.) Decem-
ber, 1887 173

No. 7. — Studies from the Newport Marine Laboratory. XIX. On certain
Medusae from New England. By J. W. Fewkes. (6 Plates.) February,
1888 209

No. 8. — On certain Vacuities or Deficiencies in the Crania of Mammals.
By D*. D. Slade. (2 Plates.) March, 1888 241

No. 9. — The Superior Incisors and Canine Teeth of Sheep. By Florence
Mayo. (2 Plates.) June, 1888 247

No. 10. — The Rattle of the Rattlesnake. By S. Gauman. (2 Plates.)
August, 1888 259

No. 1. — Reports on the Results of Dredging, under the Super-
vision of Alexander Agassiz, in the Gulf of Mexico (1877-
78), in the Caribbean Sea (1879-80), and along the Eastern
Coast of the United States during the Summer of 1880, by the
U. S. Coast Survey Steamer " Make," Lieut.-Commander C. D.
SiGSBEE, U. S. K, and Commander J. E. Bartlett, U. S. N./,
Coniiaanding.

(Published by Permission of Carlile P. Patterson and J. E. Hilgard,
Superintendents of the U. S. Coast and Geodetic Survey.)

XXX.

Eeport on the Holothurioidea, hy Hjalmar Theel. With one Plate.

The following list not only enumerates the deep-sea Holothurians
which were dredged during the Blake expeditions, but contains also
several other shallow-water forms brought home from different localities
of America, principally by the Hassler Expedition, and now in the
Museum of Comparative Zoology of Cambridge. Referring to my
report on the Challenger Holothurioidea, to which this list properly
may be considered as an Appendix, I have nothing of importance to add
with regard to general conclusions.

Deima Blakei, n. sp.

Fiffures 1, 2.

Three of the specimens present the greatest similarity with Deima validum,
while the remaining forms differ in a marked manner, having a certain degree
of variability and asymmetry in the number of pedicels and processes. The
three first-mentioned forms have eleven pedicels on each side of the ventral
surface, the posterior pair being very minute and placed behind the anus,
which is completely ventral in position. Immediately in front of the anus a
pair of minute pedicels run out from the odd ambulacrum, which is almost
naked or possesses one or two rudimentary almost inconspicuous appendages.
Along each side of the body, above the pedicels, a row of six large conical
processes is situated ; the dorsal surface bears, in addition, five or six pairs of
such processes.

VOL. XIII. — NO. 1. 1

2 BULLETIN OF THE

The other specimens, on the contrary, are not of such evident symmetry,
the number of processes and pedicels being more variable, and the processes
being much more flexible, almost like those in Oneirophanta mutabilis.

With regard to the deposits, all the specimens resemble the last-mentioned
species, to which they also bear a strong resemblance regarding the shape of
the genital tubes. According to the shape of the deposits, Deima Blakei has a
much thinner and more flexible integument than Deima validum. Considering
the obvious agreement with both Deima and Oneirophanta, I think the Blake
specimens properly may be regarded as transitional forms combining these two
genera. In external appearance, in the arrangement of the pedicels and pro-
cesses, in the shape of the tentacles, etc., they closely remind one of the genus
Deima.

Habitat. St. Vincent; depth, 573 fathoms ; six specimens. Lat. 17° 28'
30" N., Lon. 77° 30' W. (1880) ; depth, 610 fathoms ; one specimen.

Orphnurgus asper, Theel.
Habitat. Guadeloupe ; depth, 583 fathoms. A single specimen.

Euphronides depressa, var. minor, n.

All the specimens are greatly deformed. The largest attains only 150 mm.
in length. The azygos dorsal appendage is, as a rule, small.

Habitat. Lat. 39° 38' 20" N., Lon. 70° 56' W. ; depth, 1241 fathoms ;
numerous very badly macerated specimens. Lat. 24° 33' N., Lon. 84° 23'
W. ; depth 1920 fathoms ; several specimens. Lat. 41° 24' 45" N., Lon.
65° 35' 30" W. (1880) ; depth 1242 fathoms ; one specimen.

C?) Benthodytes typica, Theel.

All the specimens are badly macerated and deformed, and in such a state of
preservation as to render a closer examination impossible. As a rule, all the
P.sychropotidse change very considerably when preserved in alcohol, and, in
order to understand their organization and external appearance, it is quite
necessary to see them living.

Habitat. Martinique ; depth 1030 fathoms ; numerous specimens. Lat.
24° 33' N., Lon. 84° 23' W. ; depth 1920 fathoms ; numerous specimens.
Lat. 24° 30' N., Lon. 88° 58' W. ; depth 1568 fathoms ; several specimens.
Lat. 19° 7' N., Long. 74° 52' W. ; depth 1200 fathoms; two specimens.

Benthodytes assimilis, n. sp.

The species presents the greatest similarity with Benthodytes sanguinO'
lenta, and differs from it only in some minute features, which possibly may

MUSEUM OF COMPAKATIVE ZOOLOGY. 3

prove not to "be of specific value. But considering the differences whicli really
exist with regard to the outer appearance, and taking into consideration,
that the deposits were dissolved in the types brought home by the Chal-
lenger expedition, I propose to refer it, for the present at least, to a new
species.

The Blake specimen differs from Benthodytes sanguinolenta in being devoid
of the transverse ventral row of papillae situated immediately behind the
crown of tentacles ; the position of the anus is more ventral, and it carries
only a very few slender dorsal processes, which seem to be confined to the two
ambulacra alone. The madreporic canal appears to open exteriorly (?). The
integument is rather rough from numerous larger and smaller deposits, which
consist of four curved arms and a smooth central spine directed outwardly ;
each of the four arms generally bears a large process directed outwardly and a
few smaller ones. In the ventral perisome, the deposits are more irregularly
formed, and have the shape of unbranched rods and three- or four-armed bod-
ies. Thus the deposits of this species closely resemble those of Eaphmnides
depressa.

Habitat. Bequia ; depth 1591 fathoms. One specimen, 220 mm. long and
53 mm. broad.

Benthodytes sp. (?).

The very defective state of the specimens at my disposal renders a detailed
examination impossible. They seem to bear the closest resemblance to Bentho-
dytes abyssicola. There appear to be fifteen tentacles. The dorsal ambulacral
appendages are few and minute. The deposits present themselves as scattered,
very large and robust four-armed spicules with a long spinous central spine,
the extremity of which is usually split into two or three spinous tops, giving
to the surface of the skin a remarkable roughness. The central spines are
almost visible to the naked eye.

Habitat. Bequia j depth 1507 fathoms ; three very incomplete specimens.

Paelopatides Agassizii, n. sp.

One of the largest specimens has the following measurements: length
270 mm.; breadth 120 mm.; height varying between 5 and 10 mm. The
body is thus very depressed, almost flat, and very broad; its anterior and
posterior ends are obtusely rounded or truncated. The pedicels are only
present on the odd ambulacrum, where they form a thin double row over three
fourths of its length; the anterior fourth of the odd ambulacrum is naked.
The thin wide brim, which surrounds the body and reaches a breadth of about
40 mm., is pierced by a number of canals which branch off from the two
ventral lateral ambulacra, cross the brim, and run out in very minute papillae
situated in the margin of the brim. These papillae form a simple row in

4 BULLETIN OF THE

the margin of the brim round the body, and are scarcely visible to the naked
eye. The dorsal papilla3 are minute, few in number, and probably confined to
the ambulacra alone. The mouth is ventral in position, and the anus dorsal.
There are twenty (?) tentacles. The color is bluish violet.

The deposits are scattered, and consist of very regularly formed three-armed
bodies, with smooth nearly straight arms forming equal angles with one another
and having the ends slightly enlarged and pierced with one or several holes; a
long central simple column directed outwardly runs out from the centre of the
body and terminates in some minute spines. The calcareous ring is evidently
absent or dissolved. Two Polian vesicles 50 mm. long are present. Each of
the longitudinal muscular bands is divided into two. The respiratory trees are
long and more developed. A bundle of long slender genital tubes is situated
on each side of the dorsal mesentery.

Habitat. Lat. 39° 43' N., Lon. 10° 55' 25" VV. (1880); depth 1002 fathoms ;
two specimens. Lat. 38° 16' 45" N., Lon. 73° 10' 30" W. (1880); depth 1186
fathoms; one specimen. Lat. 39° 38' 20" N., Lon. 70° 56' W. (1880); depth
1241 fathoms; two specimens.

Stichopus Pourtalesii, n. sp.

On account of the very defective state of the specimens, it is almost impossi-
ble to get an exact idea of their true shape. So far as I can observe, they
resemble in all respects Stichopus natans of Sars, except that the ventral sur-
face appears to have two kinds of pedicels: small ones, like those of Stichopus
natans ; and very wide, wart-like ones, which seem to be placed along the
sides of the body. By means of these warts the animals adhere firmly to
rocks and stones, so that it seems almost impossible to obtain a perfect exam-
ple. The deposits resemble those of Stichopus natans, Sars, but possibly the
spire bears longer, more numerous spines on the four vertical rods. Consider-
ing the very incomplete state of all the specimens, it is probable that other
differences also exist between this species and that of Sars, but for the pres-
ent I cannot find any other than the large remarkable wart-like feet which
Stichopus Pourtalesii possesses.

Habitat. St. Kitts (1878-79) ; depth 208 fathoms; fragments of several
specimens, Grenada (1878-79); depth 291 fathoms ; fragmentary specimens.
Guadeloupe (1878-79); depth 734 fathoms; fragments. (Barbados 1878-79);
depth 209 fatlioms ; fragments. Lat. 18° 20' 30" N., Lon. 87° 16' 40" W.
(Bartlett, 1880); depth 600 fixthoms ; one specimen.

Stichopus Johnsoni, n. sp.

In a contracted state, the animal attains a length of 150 ram. The color
is yellowish brown. There are twenty tentacles of the same size and shape.
The ventral pedicels are not crowded, and they do not seem to form any well-

MUSEUM OF COMPARATIVE ZOOLOGY. 5

marked longitudinal series. The dorsal papillae are scattered, and of two
kinds : partly situated on rather large conical warts, and partly running out
directly from the surface of the skin. The papillae situated on warts form
a simple row along each side of the body, about six in each row, and are
besides found scattered irregularly over the rest of the back, though they
appear to belong principally to the ambulacia. Scattered among these warts,
the small papillae are visible. A single Polian vesicle, 20 mm. long, is present.
A thin bundle of long, slender genital tubes is situated on each side of the
dorsal mesentery.

The deposits consist of tables and buttons. The disks of the tables are
rather large, with a smooth or uneven margin, and are, as a rule, pierced with
numerous holes, which form several peripheric circles. The disks of the
ventral tables are smaller, and provided with fewer holes, which often form
only a simple peripheric circle. The spire is built up of four rods and one
transverse beam, and terminates in several teeth; usually some teeth are placed
also on the rods themselves and the transverse beam, so that a side view often
presents two crowns of teeth. The upper quadrangular opening of the spire
is often closed by a complete or incomplete cross. The buttons are smooth,
elongate, often asymmetrical or incomplete, and they are always pierced with
more than three pairs of holes; usually one side of the buttons is more devel-
oped than the other.

Habitat. Five miles south of Santa Barbara (Cal.); depth 22 fathoms; a
single specimen.

(^) Stichopus natans, Sars.

Habitat. St. Kitts (1878-79); depth 208 fathoms; some very imperfect
specimens.

C?) stichopus fuscus, Ludwlg.

The specimen seems to agree in all respects with the description of Ludvvig,
with the exception of the dorsal papillae, which have not been satisfactorily
mentioned by Ludwig. In the specimen from San Diego all the papillae are
placed on low, wide warts, which are scattered over the dorsal ambulacra as
well as interambulacra, so that they do not present an arrangement in rows,
except along each side of the body, where they form a simple row. The
C-shaped deposits appear to be thinly distributed, and the tables are small and
terminate in 20 to 28 teeth; the margin of the disk of the tables is smooth,
and perforated with a complete or incomplete circle of peripheric holes. The
short spire is composed of four rods and one transverse beam.

Habitat. San Diego, California (Hassler Exp.). One specimen, 170 mm.
long.

BULLETIN OF THE

Holothuria Verrilli, n. sp.

The following description applies to the specimen dredged at St. Vincent.
The body is ovate. The tentacles, probably twenty, are drawn inside the
body. The anibulacral appendages consist of small pedicels, scattered over
the body ; they are rather distant on the greater part of the ventral middle
line, and more closely packed along the lateral ventral ambulacra, and espe-
cially on the posterior portion of the ventral surface. They are not arranged
in rows. The integument is very rough from numerous crowded tables,
which are of varying size, some being very solid and robust, others of a more
delicate structure. The rounded or angular disks of the tables are always
pierced with a large central hole, surrounded by a single or several crowns of
peripheral holes. The spire is, as a rule, built up of four rods and one or two
transverse beams, and terminates usually in four rather long teeth, each pro-
vided with spines of considerable size ; the spire is rarely built up of more
than four rods. The specimen is whitish. The interior structure does not
present any differences from that usual in other species of this genus.

The variations with regard to the tables appear to be considerable. In two
of the specimens from Dominica, the spire often, but not always, terminates in
four smooth teeth ; in others, for instance those from Barbados and Grenada,
the top of the spire has a very irregular aspect, from numerous longer or shorter
teeth, which are placed not only round the opening of the top itself, but also
on a cross-like rod which covers this opening.

Habitat. St. Vincent (1878-79) ; depth 464 fathoms; one specimen 110
mm. long. Dominica (1878-79); depth 611 fathoms; one gigantic specimen,
230 mm. long. Dominica (1878-79) ; depth 982 fathoms ; two specimens.
Lat. 17° 30' N., Lon. 79° 14' W. (1880) ; depth 555 fathoms. Lat. 18° 20'
30" N., Lon. 87° 16' 40" W. (1880) ; depth 600 fathoms; two specimens, 230
mm. long. Barbados (1878-79) ; depth 399 fathoms; one specimen. Grenada
(1878-79); depth 416 fathoms; one specimen. Grenada (1878-79); depth
955 fathoms ; one specimen.

Holothuria Murrayi, Theel.
Habitat. Guadeloupe (1878-79); depth 769 fathoms; two specimens.

Holothuria lactea, Theel.

Habitat. Lat. 41° 33' 15" N., Lon. 65° 51' 25" W.; depth 810 fathoms;
r.umerous specimens, which differ from those brought home by the " Chal-
lenger " only in the fact that the spire of the table often terminates in a simple
long spine. Lat. 39° 43' N., Lon. 70° 55' 25" W. (1880) ; depth 1002 fathoms;
numerous specimens. Lat. 38° 18' 40" N., Lon. 73° 18' 10" W. (1880) ; depth

MUSEUM OF COMPARA.TIVE ZOOLOGY. 7

922 fathoms; one typical specimen. Lat. 41° 29' 45" N., Lon. 65° 47' 10" W.
(1880); depth 980 fathoms; one specimen. Lat. 18° 20' 30" N., Lon. 87° 16'
40" W. (1880); depth 600 fathoms; one specimen.

Holothuria arenicola, Semper.

Habitat. Charles Island, Gallapagos Archipelago (Hassler Exp., 1872).
Five specimens.

Holothuria lubrica, Selenka.

Habitat. Mazatlan. Two specimens, agreeing in all respects with the descrip-
tion of Selenka. The ventral cj'lindrical pedicels are slightly more crowded
than the small dorsal, conical papillae. The curved rods of the integument are
strongly spinous, especially towards the extremities.

Holothuria impatiens, Forskaal.

Habitat. Charles Island and James Island, Gallapagos Archipelago (Hass-
ler Exp.). Four specimens.

Holothuria imitans, Ludwig.

One specimen i.s cylindrical, and measures 90 mm. in length and 12 to 14
mm. in breadth; the other two are more contracted, of an oval form, and have
a length of 70 nmi. and a breadth of 25 mm. The color is dark grayish or
reddish brown on the back, and lighter on the ventral surface; the pedicels
and papillae are light. The anus is surrounded with five small groups of
minute papillae. In one of the specimens the ventral pedicels are distinctly
arranged in four series, one along each side and two along the odd ambulacrum,
each series containing about four pedicels in breadth. The dorsal papillae are
minute, smaller than the pedicels, and scattered without order. There are
twenty tentacles.

The tables closely resemble those described by Ludwig, but he has drawn
them with the upper part undermost, as I suggested in my report on the
Challenger Holothurioidea. Thus, the tables are completely devoid of disks,
and their spire carries at its outward end four double teeth. The rounded or
truncate inward end of the spire also bears some spines. No other deposits
are to be found in the body-wall itself, but the ambulacral appendages are
supported by large, slightly flattened rods, which carry a series of prominences
along each side ; these prominences are often united with their ends, so that
the rods themselves appear to have a series of holes along each side, just as is
found in the rods of Holothuria surinamensis, Ludwig.

Habitat. Panama (Hassler Exp., 1872) ; three specimens.

8 BULLETIN OF THE

Holothuria Marenzelleri, Ludwig (var. ?).

Although there exist some differences between our specimens and those
described by Ludwig, still I refer them to the above species on account of the
great similarity which I find to exist in several essential structural points. All
the specimens are of a dark brown color, and the largest reaches a length of
110 mm. in a contracted state. There are twenty tentacles. The anus is round.
Contrary to what seems to be the case in the typic Holothuria Marenzelleri, the
pedicels do not run out from warts, at least not the ventral ones; in some more
contracted specimens, however, the dorsal pedicels give the impression of do-
ing so. The dorsal pedicels do not seem to be true pedicels, but papillae of a
conical form, while the ventral whitish ones are longer, cylindrical, and pro-
vided with distinct light brown sucking disks. The ventral pedicels are pos-
sibly slightly more numerous than the dorsal papillae. I have observed a low
furrow along each side of the body, marking out the transition between the
dorsal and ventral surfaces. The calcareous ring is of usual shape. Three
larger and some smaller Polian vesicles are present. A single madreporic
canal is to be found. The genital organ consists of a single bundle of slender,
slightly branched tubes situated on the left side of the dorsal mesentery. The
ampullae of the dorsal and ventral appendages are distinctly visible on the
inner surface of the skin.

The deposits consist of short rods, which, however, very seldom remain
simple, but have the ends slightly dichotomously branched so that they have
the aspect of an X ; very often the branches of these deposits are united, the
rods themselves thus becoming transformed into perforated plates or jjlate-like
rods. A great part of the deposits also have the shape of small, very irregular,
smooth plates, perforated with a few (two to ten) holes, and spinous in the
uneven margin.

For my own part I must confess that most of those so-called species of Holo-
thuria which are characterized by having calcareous rods or small plates in the
skin resemble each other very closely, and that a revision of them is highly
desirable. Thus, the specimens from the Galapagos Archipelago also bear a
striking resemblance to Holothuria lubrica, Selenka.

Habitat. Charles Island and James Island, Galapagos Archipelago (Hass-
ler Exp., 1872). Numerous large and small specimens.

Cucumaria californica, Semper.

A detailed examination of the specimens shows several differences from the
type, but considering that Semper's specimen only attained half the size of
the specimens at my disposal, and that they are dredged at the same locality, I
must suppose that they represent the same species.

The body is ovate, and possesses ten nearly equal tentacles. The large
pedicels form a double row along each ambulacrum ; the interambulacra are

MUSEUM OF COMPAKATIVE ZOOLOGY. 9

naked. The color is darker or lighter violet or brown; the pedicels are yel-
lowish and the tentacles blackish. Probably the animal is dark in living state.
The calcareous ring is devoid of posterior prolongations, and in a low state of
development. The deposits consist of numerous thick, roundish, oval or elon-
gate, irregular perforated plates, which, contrary to the figure drawn by Semper,
often present uneven surfaces from the presence of low elevations or knobs.
However, the plates not unfrequently seem to be quite smooth. The number
of perforations is variable. The pedicels are supported by elongate simple or
three-armed perforated spicules or rod-like plates, and possess a very fragmen-
tary terminal plate. In one of the specimens the exterior layer of the perisome
contains small, scattered, irregularly formed perforated spicules, which are either
simple or irregularly three- or four-armed. These spicules, which are of much
finer construction than the underlying plates, are probably dissolved in the
remaining specimens. The specimen from Magdalena Bay appears to possess
anal teeth (?).

Habitat. Mazatlan ; three specimens. Magdalena Bay ; one specimen.

Cucumaria dubiosa, Semper (var. 1).

The specimens agree in all respects with the type described by Semper,
except that no interradial pedicels are to be distinguished. Considering, how-
ever, the very striking similarity in every other respect, I can only refer
them to the species of Semper. There is no doubt that Cucumaria miniata
also bears the greatest resemblance to this species ; a revision of all such forms
which are characterized by possessing the same kind of deposits is highly
desirable.

Habitat. Eden Harbor in the Strait of Magellan (Hassler Exp.) ; several
specimens. Mayne Harbor in the Strait of Magellan (Hassler Exp.) ; one
specimen. Lat. 37° 42' S., Lon. 56° 20' W. (Hassler Exp.) ; depth 44 fath-
oms ; two specimens.

Echinocucumis typica, Sars.

Figrare 3.

Some of the specimens, especially those brought home from Barbados and
St. Kitts, are remarkable in having an almost completely spherical body with
a highly reduced bivium, so that the oral and anal apertures closely approach
each other. The specimens obtained at Barbados reach 15 mm. in diameter,
and their whole appearance reminds one most strikingly of an Ascidian ; the
trivium is enormously developed ; the mouth and anus are each situated in a
small conical prominence on the upper part of the sphere. Otherwise they
seem to resemble the Norwegian Echinocucumis typica in almost every detail.
However, in the West Indian forms the pedicels seem, as a rule, to be smaller

10 BULLETIN OF THE

and more scattered on the ambulacra, excepting towards the mouth and anus,
where they appear to be much more crowded ; two of the tentacles are very
long, resembling in their retracted state long slender tubular sacs strengthened
with crowded transverse calcareous spicules, and they appear to be almost
unbranched. The close-lying plates render the body-wall very hard, rough,
and brittle, and closely resemble those in the type described by Sars.

With regard to the shape of the body, the specimens from Barbados form a
transition between the Dendrochirotse and Rhopalodinidae.

Habitat. Grenada (1878-79); depth 576 fathoms; one typical specimen.
Off Morro Light (1878-79); depth 250-400 fathoms; one typical specimen.
St. Vincent (1878-79) ; depth 464 .fathoms; one specimen. St. Kitts (1878-
79); depth 270 fathoms; four specimens. Lat. 24° 8' N., Lon. 82° 51' W.
(1877-78) ; depth 339 fathoms; eight specimens. Barbados (1878-79); depth
209 fathoms ; two specimens.

Bchinocucumis asperrima, n. sp.

The body, like that of Echinocucumis typica, is curved ; the ventral surface is
considerably more developed and more convex than the dorsal. The body
tapers strongly both towards the anterior and posterior extremity ; the caudal
portion is long, narrow, and tail-like. In the largest specimen, the body itself
measures about 25 mm. in length and 17 mm. in thickness; the retracted
anterior portion of the animal is 10 mm. long, and the tail 18 mm., so that the
whole length becomes about 53 mm. When fully extended the length is
probably considerably greater. The anus seems to be fringed by cylindrical
papillae and teeth (?). The hard, brittle glassy integument is filled up with
large reticulate scales, which are visible to the naked eye, each scale being
provided with a long, more or less eccentric spine, which gives to the skin
an almost spinous aspect. A closer examination reveals that each scale is
irregularly oval or elongate, and composed of several superposed layers of
calcareous network ; the spine, or rather spire, which is situated more or
less near the margin of the scales, presents traces of having been composed of a
network like that in Echinocucumis typica, but the perforations have dis-
appeared, and the whole forms a more or less irregular cone; at the base of
the spine some perforations are often found.

So far as I can see, the tentacles are like those of Echinocucumis typica.
The calcareous ring is very minute and devoid of posterior prolongations. A
single madreporic canal and one Polian vesicle are present.

The pedicels are very minute, so that it is difficult to detect them among the
large spines of the deposits. They appear to be more scantily distributed than
in Echinocucumis typica, but belong evidently to the ambulacra alone ; towards
the extremities of the body, the pedicels are more easily distinguished. They
are supported by curved transverse rods.

Habitat. Lat. 17° 55' N., Lon. 76° 41' 20" W. (1878-79); depth 150

MUSEUM OF COMPARATIVE ZOOLOGY. 11

fathoms; one specimen. Lat. 22° 9' 30" N., Lon. 82° 23' W. (1877-78);
depth 158 fathoms ; one specimen. Frederikstad (1878-79) ; depth 180 fathoms;
one epecimen.

Thy one scabra, Verrill.

The length of the larger specimen in the retracted state is about 90 mm.
The anus possesses fine calcareous teeth. The pedicels are cylindrical, slender,
rigid, and present in great number ; they attain a length of about 2 mm. The
calcareous ring closely resembles that in Thyone fusus. A single Polian vesicle
and one madreporic canal are present. The calcareous tables of the perisome
remind us slightly of those in the above-mentioned species, but the disks are
much more irregular, and pierced with a greater number of holes (sometimes as
many as twenty) of nearly equal size. The species undoubtedly bears a strik-
ing resemblance to Thyone fusus, but differs in having a strongly curved body,
and in that the posterior portion of the body is long and tapering; the tables
are also different.

Habitat. Lat. 40° 1' N., Lon. 70° 58' W. (1880) ; depth 129 fathoms;
several specimens. Lat. 38° 21' 50" N., Lon. 73° 32' W. (1880) ; depth 197
fathoms ; one specimen.

Thyone spectabilis, Ludwig.

Habitat. Patagonia (Hassler Exp.); numerous specimens. Off Bermeja
Head, Lat. 41° 17' S., Lon. 63° W. ; depth 17 fathoms; several specimens.

Thyone Hassleri, n. sp.

The body in a contracted state is nearly cylindrical, slightly more tapering
towards the posterior extremity, and measures about 120 mm. in length. The
color is brownish, except the ends of the pedicels, which are whitish. The two
ventral tentacles are much smaller than the remaining eight. The body-wall
is rather thin, but hard in consequence of the close-lying deposits. In the
three specimens at my disposal, the ambulacra are marked by a low, longitudi-
nal furrow. The pedicels, which seem to be slightly larger and more closely
placed on the ventral surface, and very sparsely scattered in the anterior por-
tion of the body, are present on the ambulacra as well as the interambulacra ;
but they are possibly absent on a very narrow space along each interambula-
crum. The deposits are very closely crowded, and consist principally of two
kinds : small, rounded, discoidal, highly transparent bodies in several layers ;
and minute, scattered, perforated cups. The discoidal bodies, which are larger
in the interior layer, resemble at first sight agglomerations of drops of oil ;
generally, they are not perforated, though they not unfrequently have one, two,
or four holes. Those in the inner layer of the perisome are usually without

12 BULLETIN OF THE

holes. The cups are often irregular and not very well developed, occurring in
several stages of growth. A complete cup is built up of a cruciform rod with
the curved arms united by a rim provided with several knobs. Sometimes
the cups almost form spheres.

At the posterior end of the body, the skin is filled up with irregular large
plates, perforated with numerous holes ; these plates are partly simple, partly
composed of several superposed layers, so that each plate has the aspect of a
thick irregular network. The posterior end of the body also feels very rough
and hard to the touch. The anus is devoid of teeth.

The pedicels have a small, more or less reduced terminal plate, but are
devoid of true supporting rods. The strong retractors are attached slightly in
front of the middle of the body. A single Polian vesicle and one madreporic
canal are present. Each genital bundle is very well developed, and consists of
numerous unbranched slender tubes. The calcareous ring is composed of ten
simple pieces, devoid of posterior prolongations.

This species certainly bears a strong resemblance to Thyone (TJiyonidium ?)
lechleri, Lampert, but differs mainly in the shape of the deposits and the
calcareous ring.

Habitat. Sandy Point, Strait of Magellan (Hassler Exp.); three specimens.

Thyonidium moUe, Selenka.

The tentacles vary greatly in number and size. The radial pieces of the
calcareous ring are slightly prolonged and bifurcate posteriorly.
Habitat. Payta, Peru (Hassler Exp.). Several specimens.

Psolus operculatus, PouRXALfes.

Figrure 4.

In addition to the description of Pourtales, the following may be men-
tioned. As a rule the odd ambulacrum is naked, except at the anterior and
posterior extremities where a few pedicels are to be found ; but in two speci-
mens one or more pedicels are also placed at about the middle of that ambu-
lacrum. The sole is strengthened by numerous close-lying deposits of a more
or less marked symmetrical shape ; they consist of solid oval or roundish
slightly concave plates or cups, which usually are perforated with four holes,
and have the margin more or less deeply undulated from low outwardl}^ di-
rected knobs. In addition to the symmetrical cups, others are present more
or less developed and pierced with a varying number of holes.

The largest complete specimen in the collection measures 37 mm. in length,
24 mm. in breadth, and about 11 mm. in height. The smallest has only a
length of 15 mm. In all the specimens I have seen, the mouth has five large
triangular scales, which, however, do not cover the opening completely, but

MUSEUM OF COMPAKATIVE ZOOLOGY. 13

leave a central space free ; in consequence of the scales being obtusely rounded
at their free angle, the naked central space of the mouth has an almost stellate
shape; and in each angle of this space, which alternates with the free obtuse
ends of the scales, a tooth-shaped free pointed end of an underlying scale be-
comes visible. These "teeth" are easily distinguishable in the smallest, as
well as largest specimens. The anus is surrounded by small overlapping scales
in such a manner that no true valves become visible. The scales are covered
with minute rounded granules. The number of scales between the mouth and
anus varies; in the largest specimen they are about ten. In all specimens the
pedicels form a double row round the sole, those in the exterior row piercing
the margin of the body.

One of the largest specimens from Barbados has the following measure-
ments: length 38 mm., breadth 32 mm., and height 25 mm. Consequently,
it is not depressed, but almost hemispheric, and is covered with numerous
grains placed upon the scales on the dorsal surface. These grains resemble
very complicated tables, and consist of a concave perforated disk supporting
an irregular elongate network with numerous small teeth in the free end. In
addition to the grains, the exterior layer of the dorsal integument contains
small, concave perforated cups, which carry numerous obtuse spines in the
rim. I have not been able to observe such cups in the other specimens at my
disposal, but they probably have been destroyed, together with the exterior
layer of the integument. The sole of the above-mentioned large individual
bears deposits which are often larger and more irregular than is the case in
the typical specimen.

Among the small typical specimens obtained at Sand Key, three are remark-
able in having anal and oral valves arranged j ust as in Psolus tuherculosus, and
in possessing only about three scales between the oral and anal valves. It
seems very probable that these specimens belong to another species.

Habitat. Sand Key; depth 110 to 150 fathoms; numerous typical speci-
mens. Barbados (1878-79); depth 82 to 103 fathoms; three small specimens,
about 15 mm. long, and one lauger specimen, 38 mm. long and 32 mm. broad.

Psolus tuberculosus, n. sp.

Figrure 5.

As is seen from the figures, the exterior appearance of this species is very char-
acteristic. The specimens dredged at Sand Key are the largest, and may be
considered as types. They measure 30 mm. in length, 16 mm. in breadth, and
14 mm. in height. When the animals are fully extended, these measurements
become slightly different. The mouth is closed by five large triangular valves,
which form together a very regular pentagonal shield ; the anus is also closed
by five small valves, which have the free angle rounded, and which form to-
gether a small, more rounded pentagon, or anal shield. The dorsal surface is
very hard and rough from large scales, which appear to be placed side by side

14 BULLETIN OF THE

and to overlap very little ; the marginal plates are. as usual, of minute size.
The scales bear numerous rounded granules, and, in addition, a very large cen-
tral process or tubercle of conical form with rounded top. The valves and
the marginal plates appear to be devoid of such tubercles. The largest tuber-
cles attain a length of nearly 3 mm., and are placed one in each angle of the
oval pentagonal shield. The anal pentagon has a rather prominent tubercle
at each angle. The ventral sole is surrounded by a double row of pedicels,
those in the exterior row perforating the margin of the body. Anteriorly,
where the body is more contracted, the inner row appears to be double, but
this evidently depends upon the contraction. The sole is strengthened by
crowded large irregular plates of various size, perforated by numerous holes
(the largest plates have as many as fifty holes or more) and provided with
numerous rounded knobs ; the ends of the knobs are sometimes united,
thus constituting an irregular network on the exterior surface of the plates
themselves. All the remaining forms are comparatively small, the smallest
only 7 mm. long; as a rule, all the small specimens I have seen have more
numerous and densely crowded tubercles, which generally resemble rather
long spines, while the small rounded granules, on the contrary, are not so
abundant, or may be even absent.

Habitat. Off Sand Key (1877-78); depth 50 fathoms; one slightly con-
tracted specimen. Barbados (1878-79), depth 103 fathoms, two small, con-
tracted specimens; depth 84 to 125 fathoms, one small specimen; depth 73
fathoms, - three small specimens; depth 94 fathoms, two minute specimens
7 mm. long. Barbados (Hassler Exp.), depth 100 fathoms; several small
specimens. Dominica (1878-79), depth 118 fathoms; one specimen, 15 mm.
long. Lat. 25° 33' N., Lon. 84° 21' W. (1877-78); depth 101 fathoms; one
specimen, 15 mm. long, 13 mm. broad, 8 mm. high. (?) Lat. 23° 62' N.,
Lon. 88° 5' W.; depth 95 fathoms; two specimens which possibly do not
belong to this species.

Psolus Pourtalesi, n. sp. (?).

Figure 6.

All the specitaens, which are of about the same size (30 mm. long, 20 mm.
broad, and 6 mm. high at the mouth), are remarkable in being very depressed
and flattened. With regard to the arrangement of the scales, and their size,
they evidently resemble Psolus incertus of Theel and Psolus peronii of Bell, but
they differ from these two species in several respects, especially in the shape
of the body. As will be understood from the figures, Psolus Pourtalesi has
numerous small, almost smooth scales, and is totally devoid of any oral and
anal valves. The pedicels form a double row round the sole, those in the
exterior row perforating the margin of the body. The odd ambulacrum is
naked, or possesses a few pedicels in its anterior and posterior parts. The sole
is strengthened with thinly scattered cruciform bodies, the arms of which often

MUSEUM OF COMPAKATIVE ZOOLOGY. 15

are dichotomously branched and united with one another, so as to give origin
to small, smooth perforated plates. There is no doubt that Psolus Fourtalesi
is nearly allied to Psolus squamatus.

Habitat. Lat. 41° 24' 45" N., Lon. 65° 35' 30" W. (1880) ; depth 1242
fathoms ; ten specimens.

Psolus braziliensis, n. sp.

Figrure 7.

The body is like that in Psolus phantapus. The length, including the ex-
tended mouth, is 32 mm. The color is whitish. Two ventral tentacles are
always much smaller than the eight remaining. The ventral rectangular sole
carries three series of pedicels, the two lateral composed of about four rows,
the middle of only two. Anteriorly and posteriorly the series run together.
The exterior row of each lateral series is placed in the margin of the body.
The dorsal body-wall is rather soft and covered with scales, which overlap
very little. The mouth is not closed by valves, but by a series of elongate
triangular scales with a very acute free angle; the anus is closed by similar
smaller and more irregular scales. Outside of the scales, the dorsal perisome
contains minute conical cup-like tables, and large, elongate conical table-like
deposits made up of a more or less irregular network with the free end spinous.
The sole is strengthened by small, scattered, smooth plates with an uneven
margin and perforated by four or more holes.

Scattered among the dorsal deposits small, highly reduced "pedicels" are
found, which are strengthened by a small but very well marked perforated
terminal plate, and by well-developed irregular plates. There is no doubt
that these are true pedicels, and thus it is a very interesting fact, that some
species of Psolus have retained the dorsal pedicels, though in a very rudi-
mentary state. The scales seem to present some larger pores, through which
the pedicels communicate with the ambulacral system (?).

Habitat. Porto Seguro; two specimens.

Psolus, sp. (?).

The body, which has a length of 12 mm., is very flattened and covered with
scales on the dorsal surface ; these decrease considerably in size towards the
oral and anal openings, which consequently are completely devoid of valves.
The general appearance of the body closely resembles that of Psoitis Pourtalesi.
The pedicels form a double row round the sole, the exterior row being placed
in the margin of the body. The odd ambulacrum is naked. The sole is
strengthened with small plates of a more or less symmetrical appearance ; the
most symmetrical are oval, with four holes, and twelve knobs or rounded
prominences arranged in the margin; in addition, the surface itself of the

16 BULLETIN OF THE

plates bears a few knobs. The plates themselves are, however, rarely so
symmetrical ; they mostly have more or fewer holes and knobs.

The most characteristic feature of this animal is that each dorsal scale bears
one or several slender flexible cylindrical appendages, which are supported
by a peculiar calcareous skeleton, composed of small crowded perforated plates
or cups. Unfortunately, the material is too scanty to allow any detailed ex-
amination, or to decide whether these appendages have any communication with
the water-vascular system. '-'

Habitat. Lat. 25° 35' N., Lon. 84° 21' W. (1877-78); depth 101 fathoms;
one very defective specimen.

Trochostoma Blakei, n. sp.

Fignire 8.

The body is ovate, the anterior extremity truncated and the posterior suddenly
tapering into a narrow tail or caudal portion. There are fifteen (?) tentacles.
The anus is devoid of anal teeth (?). The color is whitish or grayish. The
length of the body itself is about 68 mm., and that of the tail 7 mm. The
tail is doubtless longer when fully extended. The integument is thin, almost
transparent, but rough from numerous close-lying tables, which have a peculiar
shape. They consist of a small disk, which as a rule is pierced with three
comparatively large holes and has a more or less marked trilobate rim. The
disk supports a very long simple and slender column, which at the base
appears as composed of three rods. The end of the column is usually divided
into three obtuse slightly curved teeth, or it is slightly enlarged and sur-
rounded by a circlet of small hooks directed downward. The disks of the
tables rarely have more than three holes; but when that is the case, three of
the holes are always larger. In the tail, the tables have an elongate fusiform
disk, which has about four holes in the enlarged centre and cari'ies a spire made
up of three rods and terminating in several spines. No other deposits are to
be observed. The species is ^lo.^rly related to Marenzeller's Trochostoma
ardicum.

Habitat. Grenada (1878-79); depth 955 fathoms; one specimen.

Trochostoma antarcticum, Theel.

The specimens agree most fully with the Challenger specimens. The
deposits consist only of tables, characterized by their long spire, which as a
rule is composed of three parallel rods united by numerous transverse beams;
the ends of the three rods are bipartite or tripartite. No true wine-colored
deposits are visible, but several of the tables themselves have begun to change
in color, so that they in some places present a yellowish brown aspect ; imme-
diately in the neighborhood of tl^ese yellowish portions of the tables, some

MUSEUM OF COMPARATIVE ZOOLOGY. 17

small colored grains are visible, but these grains are never found except in
connection with such deformed tables. In Ankyroderma Marenzelleri, Theel,
the deposits also seem to undergo similar changes in color. I am much in-
clined to think that the presence or absence of wine-colored bodies cannot be
accepted as specific characters.

Habitat. Lat. 24° 8' N., Lon. 82° 51' W. (1877-78); depth 339 fathoms;
three specimens.

Trochostoma arcticum, Marenzeller, var. parva, n.

This form evidently bears the greatest resemblance to Trochostoma arcticum,
but some minor differences exist, in consequence of which I propose to con-
consider it as a variety. The fifteen tentacles have only a single short branch
on each side. The body- wall is very thin, but rough from the scattered tables.
The tail of the animal is destroyed, but the remaining portion of the body-
measures about 60 mm. The color is yellowish gray. The calcareous ring
possesses five bipartite posterior prolongations. The scattered tables have an
irregular disk, which is pierced with a varying number of large holes (usually
few in number) and provided with prolongations or processes running out
from the circumference of the disk. The disk supports, a spire, which is
irregularly spinous especially towards the free end, and composed of three rods,
which are transversely united at several points.

I have examined two other specimens dredged at the same station, the
largest of which attains a length of only 30 mm. Among the usual tables
I have found some minute ones resembling those of Trochostoma antarcticum,
Theel. This variety probably combines the extremes living in the arctic and
antarctic seas.

Habitat. Grenada (1878-79) ; depth 416 fathoms ; one specimen.

Trochostoma arcticum, Marenzeller, var. coeruleum, n.

This variety is distinguished from the northern form only by the abundance
of pigment in the skin, which gives to the animal a bluish-violet color. Pos-
sibly also the disks of the tables are larger and more regularly formed. The
tentacles have only a single pair of short branches near the top.

Habitat. Grenada (1878-79) ; depth 553 fathoms ; one specimen, about
80 mm. long.

Caudina arenata, Gould, var. armata, n.

So far as I can observe, the specimens agree in all respects with those
described by Selenka, Semper, and Marenzeller, except in the shape of the
deposits. The body itself of the largest specimen measures about 50 mm. in
length, and the narrow caudal portion is 35 mm. long. The fifteen tentacles

VOL. XIII. — NO. 1. 2

18 BULLETIN OF THE

have each two pairs of minute branches or digits. The calcareous ring has
five bipartite prolongations.

The very crowded deposits consist of irregularly formed tables, which devi-
ate from those described by Semper, etc. in having much larger disks and a
spire made up of only three rods, in consequence of which I propose to refer
the Blake specimens to a variety. In general, the disks of the tables are large,
smooth, of an irregular shape with uneven margin, and pierced with numerous
holes. They often have an irregular triangular or quadrangular form, with
twenty or more holes. The spire is composed of tliree irregularly spinous
rods, united by a few (two or three '?) transverse beams. So far as I can
understand from the descriptions hitherto made, the spire in the typical
specimens shoidd be composed of four rods.

Habitat. Lat. 35° 44' 40" N., Lon. 74° 40' 20" W. (1880); depth 898
fathoms ; three specimens. Lat. 41° 24' 45" N., Lon. 65° 35' 30" W. (1880);
depth 1242 fathoms ; two specimens.

Ankyroderma affine, Danielssen & Koren (van).

In the specimen dredged at St. Vincent, a few light wine-colored bodies are
present. On the contrary, I have not been able to detect a single one of those
colorless bodies which have been figured and described by Danielssen and
Koren (compare Figs. 26 and 27 in their report), and I must confess that these
bodies appear to me to be nothing else than artificial products owing to preser-
vation in alcohol.

Among the " tables " I have observed a few very scattered, minute perforated
plates supporting a very long spine, which carries at the top a crown of hooks,
like those found by me in Trochostoma antarcticum. The anchors always
have a discoidal, perforated base. Contrary to what is observed in Ankyro-
derma Jeffreijsii (var.), I never found the fusiform bodies except at the extrem-
ities of the body.

Habitat. St. Vincent (18 78-79); depth 464 fathoms; one specimen, 35
mm. long. Dominica (1878-79) ; depth 391 fathoms; one specimen.

Ankyroderma Jefireysii, Danielssen & Koren (var.).

Some of the specimens have a marked violet color from more or less crowded
wine-colored bodies, while others are almost colorless and devoid of such
bodies. The anchors have a discoidal perforated base, just as I have found in
Ankyroderma Danielsseni, which possibly may prove to be only a variety of
Ankyroderma Jeffrey sii.

Habitat. Lat. 41° 33' 15" N., Lon. 65° 51' 25" W. (1880); depth 810
fathoms; two specimens. Lat. 34° 39' 40" N., Lon. 75° 14' 40" W. (1880);
depth 603 fathoms; one specimen. Lat. 38° 20' 8" N., Lon. 73° 23' 20" W.

MUSEUM OF COMPARATIVE ZOOLOGY. 19

o

(1880); depth 740 fathoms; one specimen. Lat. 33° 35' 20" N., Lon. 76
(1880); depth 647 fathoms; one specimen. Grenada (1878-79); depth 553
fathoms ; two specimens.

Ankyroderma Agassizii, n. sp.

What especially distinguish this form from all hitherto known ones are the
deposits, which form several superposed layers, so that the thin body-wall be-
comes rough and brittle. In the interior a continuous layer of large, smooth,
irregularly rounded plates is to be found ; these plates overlap each other by
the edges, have a smooth but uneven margin, and are perforated with numerous
holes, as many as sixty or seventy; the central are larger than the peripheral
ones. Outside of these true plates we find other deposits, which, however,
are not closely packed, but much scattered; they resemble the tables which are
found in other forms of Ankyroderma, and consist of a rather large, irregular
disk, perforated with a varying number of large holes and carrying a simple
central spine. Here and there much smaller delicate tables may be found,
which have a trilobate disk pierced with only three holes and resemble those
found in Trochostoma Blakei. Scattered among these tables are situated the
stellate bodies characteristic of the genus. They consist of three to six long
spoonlike rods, arranged with the enlarged perforated end towards a common
centre; the enlarged, slightly concave end is pierced with numerous holes,
twenty-five to thirty or more. The anchors which are connected with these
stellate bodies have the usual shape, their base being discoidal and perforated,
and their symmetrical flukes slightly serrated.

The caudal portion of the body is strengthened by a thick layer of transverse
fusiform rods, with the enlarged centre pierced by a few holes.

Otherwise, the body has the shape characteristic of the Molpodids.

The body itself is nearly cylindrical, about 60 mm. long, wider posteriorly,
and decreasing slightly towards the anterior truncated end ; at the posterior
extremity it suddenly tapers into a narrow tail, which has a length of about
20 mm., so that the whole animal attains a length of about 80 mm. The
tentacles are drawn within the body, their true shape and number being un-
known. The color is light grayish inclining to violet. The radial pieces of the
small calcareous ring bear a bifurcate posterior prolongation.

Another specimen was obtained at a depth of 1058 fathoms (from an un-
known locality), which doubtless belongs to the same species. It has 15
minute tentacles and some small anal papillae.

Habitat. Bequia (1878-79) ; depth 1507 fathoms ; one specimen.

Synapta, sp. (?).

Habitat. Woman Key. One defective specimen, which probably is nearly
related to Semper's Synapta reticulata.

20 BULLETIN OF THE

Synapta, sp. (?).

From the defective state, ca close examination is impossible. The handle
of the symmetric anchors is dentate and the flukes serrated. The anchor-
plates are rather large, rounded or oval, perforated with numerous holes, and
at the slightly narrower truncate end, where the anchors are attached, resem-
ble an irregular network. The margin of the plates is uneven from the pres-
ence of processes or spines, and spines are also present on the surface of the
plates at the margin of the holes. Possibly the species is identical with
Synapta abyssicola, Theel.

Habitat. Lat. 39° 25' 30" N., Lon. 70° 58' 40" W., depth 1394 fathoms ;
one incomplete specimen.

Chirodota rotifera PouRTALi:s.

The largest specimen, which measures about 75 mm. in length, has fifteen
digits in each of the twelve tentacles (Ludwig only counted twelve digits).
The wheel papillae are principally placed on the interambulacra, but a few
also occur on the ambulacra, and they are less numerous on the ventral sur-
face than on the three dorsal interambulacra.

Habitat. Pcto Seguro (Thayer Exp.) ; several specimens.

Chirodota contorta Ludwig.

Habitat. P^rt Gallant, Patagonia; numerous specimens.

MUSEUM OF COMPARATIVE ZOOLOGY. 21

List op Holothurids in such an imperfect Condition that their
Examination is not possible.

Hab. Guadeloupe, depth 769 fathoms; one specimen.
" depth 734 fathoms; fragments.

" depth 878 fathoms; two fragments of an Aspidochirote.

" depth 734 fathoms; a Molpodid.

Dominica, depth 824 fathoms; fragments.
" depth 982 fathoms; fragments.
Martinique, depth 1030 fathoms; fragments.
St. Vincent, depth 573 fathoms; one defective specimen, related to

Holothura Verrilli.
Bequia, depth 1591 fathoms; one specimen.

" depth 1507 fathoms; fragments, probably of a Psychropotide.
Ham's BluflF, depth 2376 fathoms; fragments of a Psychropotide.
Grenada, depth 553 fathoms; fragments.
Montserrat, depth 303 fathoms ; fragmentary specimens.
Off Havana, depth 100 fathoms; fragments probably of an Echinocu-

cumis.
St. Lucia, depth 116 fathoms; fragments of an Echinocucumis.
Lat. 40° 1' N., Lon. 70° 58' W. (1880); depth 129 fathoms; an incom-
plete Chirodota.
Lat. 24° 1' N., Lon. 88° 58' W. (1877-78) ; depth 1568 fathoms ;

fragments.
Lat. 16° 42' N., Lon. 83° 1' W. (1878-79); depth 961 fathoms; frag-
ments.
Lat. 18° 51' N., Lon. 83° 7' W. (1880) ; depth 903 fathoms ; fragments.

EXPLANATION OF THE PLATE.

Fig. 1. Deima Blakei, Theel, from above.

" 2. The same, from below.

" 3. Echinocucumis typica, Sara.

" 4. Prolus operculatus, Pourt.

" 6. Prolus tuberculosus, Theel.

" 6. Prolus Pourtalesii, Theel.

" 7. Prolus brasiliensis, Theel.

•' 8. Trochostoma Blakei, Theel.

Blake' Holotmiiriaks

> •»

*•-

^

A

No. 2. — A Second Supplement to the Fifth Volume of the Terres-
trial Air-Breathing Mollusks of tJie United States and Adjacent
Territories. By W. G. Binney.

The following pages contain u list of the Locally Introduced Species,
the Universally Distributed Species, and the Central and Pacihc Province
Species, with such additional information relating to them as I have ob-
tained since the publication in this Bulletin (Vol. XI. No. 8) of the first
Supplement.

In a future Supplement, I propose to follow with the species of the
Eastern Province.

Thus in this revision of the subject the species will be arranged geo-
graphically, not systematically.

LOCALLY INTRODUCED SPECIES.

Zonites cellarius, Mull.
Also found hving in Portland, Oregon (Dore), and St. Louia.

Limax maximus, Lin.
Also, New Bedford and Cambridge, Mass., and New Haven, Conn.

Limax flavus, Lin. Stenogjrra decollata, Lin.

agrestis, Lin.

Arion fuscus, Mull.
Also, New Bedford, Mass. (Thomson).

Pruticicola hispida, Lin.
Also, Gay Head, Martha's Vineyard, Mass. (Thomson).

Fruticicola rufescens, Pennant.
Also, Nanshon, Buzzard's Bay, Mass. (Thomson).

Fruticicola Cantiana, Montagu.

Plate I. Fig. 13.

Quebec, Canada (F. R. Latchford).

I am indebted to the discoverer for specimens preserved in spirits which fur-
nished the following notes.

VOL. XIII. — NO. 2. 2

24 BULLETIN OF THE

Genital system complicated with accessory organs in the form of vagifial
prostates, one long, narrow, flagellate, tapering at apex, four short, cylindri-
cal, bluntly terminating. Genital bladder very large, oval, on a narrow duct.
Penis sac stout, tapering above into a flagellate extension, at the commence-
ment of which the vas deferens enters.

Jaw low, wide, ends attenuated, blunt : over twelve flat, broad, crowded ribs,
whose ends denticulate either margin.

Lingual membrane with 40-1-40 teeth. Centrals tricuspid ; laterals bicus-
pid ; marginals also bicuspid without the inner cutting point being bifid.

Turricula terrestris, Chemn,
Tachea hortensis, Mull.

Pomatia aspersa, Mull
Also, San Jose, Cal.

Besides the above, that have more or less firmly established themselves here,
various species have from time to time been noticed living, but the individual
or colony has died out. Some of these are : —

Zonites cultellatus See Vol. V. p. 135

alliarius " * "135

Stenogyra octona " " 196

Bulimulua obscurus " " 212

Pupa marginata . " "213

Helix depicta " "256

Pisana " "256

arbustorum " "256

lactea " "257

variabiUs " "257

Bulimus acutus " "399

Succinea putris " " 430

amphibia " "430

UNIVERSALLY DISTRIBUTED SPECIES.

For all of these see Vol. V.
Patula striatella, Anthony. Zonites arboreus, Say.

Microphysa pygmaea, Drap.* indentatus, SAY.t

Helicodiscus lineatus, Say. minusculus, Binn.

Vallonia pulchella, Mull. viridulus, Mke.

Pupa muscorum, Lin. milium, Morse.

Zonites nitidus, Mull. fulvus, Drap.

* See below, page 35.

t See Supplement I. for Zonites subrupicola.

MUSEUM OF COMPARA.TIVE ZOOLOGY. 25

CENTRAL PROVINCE SPECIES.

Macrocyclis Vanconverenssis, Lea.

A species of the Pacific Province, confined to the vicinity of the coast range
in California. Above Lat. 49° it passes the Cascade Mountains, reduced in
size, and ranges southeasterly into Idaho and Montana. I have actually re-
ceived it from the Coeur d'Alene Mountains, Idaho : Umatilla Co., E. Oregon :
Walla Walla, E. Washington Territory *

Macrocyclis HemphiUi, W. G. Binn.
Weston, Umatilla Co., E. Oregon. A species of the Oregon region.

Limax montanus, Ingersoll.
Also near Salt Lake City, Utah (H. Hemphill).

Zonites Whitneyi, Newcomb.
Also Emigrant Canon, near Salt Lake City, Utah (Hemphill).

Zonites nitidus, Mull.
Near Santa Fe, New Mexico. A universally distributed species.

Zonites arboreus, Sat.

A universally distributed species. Actually found also at Franklin, White
Bird Creek, Idaho : White Pine, Austin, Nevada : near Salt Lake City, Provo,
Weber Canon, Utah. (Hemphill.)

Zonites viridulus, Menke.
A universally distributed species. Found also in Utah (Hemphill).

Zonites indentatus, Sat.
A universally distributed species.

* It must be borne in mind that changes are constantly being made in the boun-
daries of the newer States and Territories. I use the names as now accepted, 1886.

26 BULLETIN OF THE

Zonites minusculus, Binnet.
Universally distributed.

Zonites milium, Morse.

Not actually received from the Central Province, but no doubt existing there,
as it has been found over the Eastern and Californian Provinces. Probably a
universally distributed species.

Zonites fulvus, Dkap.

A universally distributed species, received from numerous localities in Utah,
Nevada, and Colorado.

Vitrina Pfeifferi, Newc.

•

A species of the California Province. I have received it also from Logan
Canon, Weber Cknon, St. George, and Salt Lake City, Utah ; Austin and
White Pine, Nevada : White Bird Creek, Idaho. (Hemphill.)

Patula solitaria, Say.

Plate I. Fig. 10.

A species of the interior region of the Eastern Province. I have received
it also from White Bird Creek, Idaho ; Walla Walla, Washington Territory ;
Weston, Oregon (Hemphill) ; in addition to the localities given in Vol. V.
These last two points are about twenty-five miles apart, at the foot of the Blue
Mountains, one hundred and fifty miles from the Dalles.

The specimen figured, which is unusually elevated, is from Salmon River
Mountains, Idaho (Hemphill). A uniformly brown specimen with narrow
white band was also found.

One of the most unlocked for and interesting facts in the geographical distri-
bution of our land shells is the westward range of P. solitaria, reaching through
the Central Province into the Pacific Province to within a few miles of the
Pacific Ocean. (See extracts from Mr. Hemphill's letter on pp. 27, 28.)

Patula strigosa, Gould.

Plate II.

This is the most variable species found in North America. The original
specimen (see PI. XXVT. a), found on or near the Pacific Coast at Puget Sound
by the naturalists of the Wilkes Exploring Expedition, is large, almost discoidal,
with widely open umbilicus. It could not possibly occur to me that there were
any relations between it and the small, globose, narrowly umbilicated, highly

MUSEUM OF COMPAKATIVE ZOOLOGY. 27

elevated shell whicli I described from what was then Nebraska as Helix Cooperi.
(See Vol. IV. PI. LXXVII. Fig. 11.) Equally confident was Dr. Newcomb that
the small, carinated, lenticular shell described by him from Nevada as Helix
HemjJiilli was new to science. Subsequently, Dr. Gabb described as Helix
Haydeni what appeared to be a distinct species with heavy revolving ribs.
More recently authors less acquainted with the group have added to the sy-
nonymy by describing under the names of H. militaris and H. Bruneri what
appeared to them to be new species. When the researches of Mr. HemphiU
and others had brought large numbers of specimens from many localities in the
Central Province, it became evident that what had appeared distinct species
were connected by intermediate forms, and therefore should be considered va-
rieties only. Even Helix Idahoensis also seemed to be but an aberrant form of
the same protean species. Then came the explorations of Mr. Hemphill in
Utah, bringing to light several more well-marked varieties, constant in their
respective localities, several of which would be recognized by most naturalists
as good species. Mr. Hemphill ^as distributed these as var. IFasatchensis,
Oquirrhensis, Newcomhi, Gouldi, Binneyi, alhofasciata, castanea, Utahensis, Gab-
biana, muUicostata, — names printed in his catalogue, though as yet unaccom-
panied by descriptions or figures.

I here propose treating separately each of these marked varieties. It must
be borne in mind that in each form there is found considerable variation in
size, in elevation of spire, and breadth of umbilicus.

The geographical range of the group is very great. Though Idahoensis, Hay-
deni, and most of Mr. Hemphill's varieties are restricted to narrow Limits, the
forms usually referred to strigosa and Cooperi have been found from the Lake
of the Woods to the Rocky Mountains in the British Possessions on the north,
to numerous localities in New Mexico and Arizona on the south. The eastern
boundary is the main range of the Rocky Mountains, but in Wyoming and
Dakota (as now constituted) it is found more easterly, even in the Black Hills
at longitude 104° in the southwestern corner of Dakota, the original locality of
Cooperi. It was not, however, found by Mr. Hemphill at Helena, Montana,
nor nearer to it than a point two hundred miles south on the road to Salt Lake
City. On the west, it ranges to the Sierra Nevada and Cascade Mountains,
and passes the latter evpn to the Pacific Ocean, though the specimens collected
from time to time west of the Cascades in Washington Territory and Oregon
may have been individuals brought down by the Columbia River from the
regions east of the Cascades, or colonies descended from such. I doubt the
species being really an inhabitant of the Pacific Region.

It was Mr. Hemphill who called my attention to this explanation of the
presence in the Pacific Province of Central Province species. I cannot do
better than quote his words : " I have no evidence of Patula strigosa having
crossed the summit of the main range of the Sierra Nevada to the westward
and entered the Pacific Province. The Cascade range of mountains in Ore-
gon is, as you are aware, a continuation of the Sierra Nevada. It crosses the

28 BULLETIN OF THE

Columbia River between the Dalles and Portland, and continues its northerly-
course on the west side of the Columbia. Numerous spurs, however, break off
from the main range, and pass north through East Oregon into Utah and Idaho.
One of these spurs, called the Blue Mountains, shoots off the Cascades near
Mt. Hood, and runs nearly parallel with the Columbia, forming the eastern
boundary of its valley, and is about forty miles from the river, and terminates
about abreast of the mouth of Salmon River, Idaho, and on the south side of
Snake River. On the north side of Snake River these mountains have local
names, but are known by the general name of Bitter Root Mountains. They
include Salmon River Mountains, etc. By tracing the course of Snake River
and its tributaries you will see it drains the northern part of the great central
basin, and when it cut its way through these mountains it very likely drained
the great system of lakes that once covered a great part of this central basin.
Now the mountain ranges in this portion, northeast, are the metropolis of
strigosa so far as we know at present ; and it is not improbable that many indi-
viduals, and qu/te likely whole colonies, of that species are sometimes carried
into the streams by rains and floods, and are borne away on the waters towards
the Pacific Coast. Occasionally some of the specimens must find or make a
lodgement along the banks of the streams, and if the conditions are favorable
a colony will spring up and perhaps spread over the neighborhood. The banks
of the Columbia between the Dalles and the mouth of Snake River, a distance
of one hundred and fifty miles, are destitute of timber, and are covered for sev-
eral miles back with loose drifting sand, quite unfavorable to the existence and
spread of land shells. The locality where I found the variety castaneus was
on the bank of the Columbia near Celilo, about fifteen miles above the Dalles,
on the east side of the Cascades, but on the west side of the Blue Mountains.
This colony must have sprung from specimens brought down the stream by
floods. At a subsequent visit it had disappeared. It may be possible some
colonies will yet be found on the banks of the river below the Cascades. Very
likely the original strigosa may have come from some colony planted in this
way."

These same remarks will apply to Patula solitaria, the group of Triodopsis
Mullani, and Mesodon ptychophorus. In treating each separate form of the
species, I propose to follow the suggestion of Mr. Hemphill, as he has had so
much better opportunities than any one else to appreciate their variations. He
suggests arranging the group, whether considered as varieties or as distinct spe-
cies, in three series according to the modifications of the sculpture of the shells :
A. Shell transversely ribbed. B. Shell smooth or with rough striae. C. Shell
longitudinally ribbed.

MUSi!-UM OF COMPAKATIVE ZOOLOGY. 29

A. SHELL TRANSVERSELY RIBBED.
Var. Idaho ensis, Newcomb.

Plate II. Fig. 13.

In the comparison of the various forms here given, I call this a variety. I
am, however, convinced of its specific weight.

The transverse ribs in this are few, separated, and stout. There are twenty-
four upon the body whorl of one individual. It has as yet been found only in
Idaho. I give a new figure of a Salmon River Mountain specimen.

Var. Binneyi, Hemphill.
Plate II. Fig. 13.

Box Elder County, Utah (H. Hemphill). (See p. 31.)

This variety has strong rough wrinkles rather than decided ribs, about fifty
on the fir>?t whorl of one individual. Some individuals have a decided, erect
tubercle within the peristome near its junction with the parietal wall of the
aperture. There are no revolving bands of color.

This is the first of a remarkable series of varieties or species lound by Mr.
Henry Hemphill in the region of Great Salt Lake, Utah. I will here give his
own description of the habitat of these forms : —

" I commenced collecting at or near Ogden, Utah, and almost the first shell
1 picked up was the variety I call JVasatchensis. (See p. 34.) This pretty
and interesting shell I found living among quartzite boulders, in crevices sufti-
cientl}'' large to aff"ord cool and moist retreats during the active summer season,
and safe places for hibernating during the cold winter months. This shell
seems to be confined in its range to a very limited area, for I did not find a
single specimen either dead or living outside of a little plat containing an acre
of ground. I have often admired this shell, and think it one of the most inter-
esting varieties I found in Utah, as it combines the characters of Idahoensis,
Haydeni, and Hemphilli, as well as of Gooperi. Not only on this account is it
interesting, but because it is found living on or near the dividing line between
the Idahoensis group and the Haydeni group.* North of Ogden you will see I
found all the transverse-ribbed varieties, and south of Ogden all the longitu-
dinal ribbed varieties were found, with the exception of the variety of strigosa,
just assuming the Haydeni sculpturing (near Logan). Not a single transverse-
ribbed specimen occurred south of Ogden. AVhether this is merely accidental,
or whether there are some local causes on either side of this line which influ-
ence this change in sculpturing, I cannot say. I only point to the fact, and
that it seems a little strange that Wasatchensis should be found just on this
line.

" In the gulches near Ogden, and also on the mountain slopes among rocks
and leaves, I found the typical strigosa and Coo-peri, as well as a number of
small shells.

* That is, the transversely ribbed and longitudinally ribbed groups.

30 BULLETIN OF THE

" From Ogden I went to Salt Lake City, and thoroughly explored all the
canons, gulches, and other favorable places which I could reach in a day's walk.
This only resulted in the finding of the typical strigosa and Cooperi, both large
and small.

" I next went to Provo, Utah, fifty miles soiith on the same range of moun-
tains, and there also I found only the typical strigosa and Cooperi, large and
small.

" I then returned to Salt Lake City, and crossed the valley to the west, camp-
ing on the west side of a range called the Oquirrh Mountains. Here com-
menced a series of finds that was quite exciting and very interesting to me.
At the foot of the mountain my attention was attracted to a pile of detached
rock, usually a good place for snails. After a few moments' work among these
stones I was rewarded by finding quite a number of specimens of the variety I
call Utahensis. (See p. 33.) This has the form of Hemphilli, but is destitute
of the revolving ridges of Haydeni. The specimens were all constant in sculp-
turing, but varied very much in size and somewhat in form. I next went up
the side of the mountain a short distance to another pile of stones (limestone),
and here I found the variety I call Oquirrhensis. (See p. 34.) This has quite
prondnent revolving rib.s, more developed than in the typical Hemjyhilli from
White Pine, Nevada. This colony was also constant in sculpturing, but varied
very much in size, and also in form. I next went along the mountain side, and
crossed a little ravine, and commenced raking among the leaves and brush on
the steep slope of the mountain. Here I found a colony of the typical Haydeni,
constant in sculpturing, but as in the case of the other colonies, variable in size
and form. Following up this ravine to near the summit of the mountain,
I found a few isolated specimens of Haydeni under stones. Near the summit I
found two specimens of Cooperi. I then returned to the bushes where I found
Haydeni, and after some further work there passed along the side of the moun-
tain a very short distance to another ravine with low bushes covering its sides.
Here among the leaves I found a colony of the variety I call Gahhiana. (See
p. 34.) This is a coarse, rough Haydeni, with the revolving ribs nearly or
quite obsolete. This variety also maintained its peculiar sculpturing, but va-
ried again in size and form. Continuing my course along the mountain side, I
came to another ravine which I followed up a short distance to a perpendicular
precipice about fifty feet high, barring farther progress. At the foot of this
limestone wall I found another colony of one of the smaller forms, elevated like
Cooperi, with the revolving ribs nearly obsolete. Here, then, were five colonies
of the same species, apparentlj^, living on the same mountain slope, within a
short distance one of the other, each colony maintaining its peculiar sculptur-
ing, but varying in size and form.

" In due time I returned to Salt Lake City, where I remained a few days to
prepare my specimens.

" Eeturning to Ogden, I explored the mountains farther to the north than on
my first visit, which resulted in finding the variety I have called Newcomhi.
(See p. 32.) This colony I found living among bushes on the steep sides of a
gulch facing the north, a spot of continual shade. The specimens, both banded
and plain, were quite numerous ; but beyond the space of about fifty yards not
an individual could be found either above or below. I also found on a rocky
point two or three specimens of Haydeni, nearer Ogden, on the north side of
the city.

" From Ogden 1 went to Brigham City, and quite thoroughly explored all
that vicinity. Here I found a colony of the small albino strigosa, with and with-
out the tooth on the peristome. This colony occupied a pile of rocks at the
foot of the mountain, shaded by bushes, dead leaves, and the debris washed
down the mountain. I did not find this variety elsewhere, nor was a single

MUSEUM OF COMPARATIVE ZOOLOGY. 31

banded specimen found among them. The typical and also albinos of strigosa
and Cooperi occurred in this vicinity.

" I continued my course northward from Brigham City, pitching my tent on
the banks of Bear River. The valley here was considerably broken by the
mountain spurs, through one of which the river had cut its way, leaving high
rocky cliffs on either side, with scattered clumps of bushes along the river and
on the edges of the bluffs. Everything seemed favorable here to the existence
of snails. My first find was near the edge of the bluff, in cattle tracks and
small shady holes in the ground, of the white variety I call Binneyi. (See
p. 29.) These were all plain white. They were quite plentiful just on the
brow of the bluff and the slope towards the river. The next I found was in a
clump of bushes among leaves and brush. These I have called variety alho-
fasciata. (See p. 32.) The body of the shell is clouded, with the broad, re-
volving white band at the periphery. Some of this variety are beautifully
clouded beneath. None in these bushes were white.

" I next went up to the rocky cliffs about three miles from my camp, and
here among bushes I found the plain white varieties, Binneyi, with and with-
out the denticle on the peristome. I w^orked my way among the bushes and
rocks to the foot of the cliffs, and here on a mossy, grassy slope, directly at the
foot of a high cliff, I found a colony of the ribbed variety castaneus. (See
p. 32.) This spot is continually shaded by the tall cliff, the sun never shining
on it. Most of this colony are faintly marked with the broad white band of
albofasciata, but a few are plain chestnut-colored. I next crossed a small ra-
vine to another cliff, where a small patch of wild rye was growing very luxu-
riantly. It was about fifty feet square, directly beneath a little gully in the
cliff above, where the melting snows of spring and heavy summer rain formed
a little rivulet, pouring over the cliff and irrigating the rye. In this patch I
found a very prolific colony of the small interesting variety 1 have called
Gouldi. (See p. 32.) So plentiful were they, that I picked up by actual count
one thousand in about two hours. No large specimens were associated with
them, while the little fellows strayed but a short distance from the rye. No
typical strigosa were found in this vicinity ; all were ribbed.

" From here I went to Logan, Utah, where I found the variety with micro-
scopic revolving ribs, beginning of Haydeni, among stones at the head of a
gulch quite high on the mountains. The typical strigosa and Cooperi were
found here also.

" I next went to Franklin, just across the Utah line in Idaho, where I found
the thin, frail, iron-stained variety of strigosa, among red sandstones.

" You will see by this account that nearly all of these colonies were sepa-
rated, though some of them were but a few yards apart. While the typical stri-
gosa and Cooperi, large and small, seem to range over the whole region where I
collected, Ogden seems to be the dividing line between the transverse-ribbed
vafieties and the longitudinal-ribbed varieties. No transversely ribbed speci-
mens were found south of Ogden ; but a few Haydeni and the Logan variety
(beginning of Haydeni) are all that belong to the Haydeni group that I found
north of it, excepting a keeled variety found on the mountains of Salmon River,
Idaho. Whether there is any meaning in this I cannot say. The field is so
large,* many years will be required to work it up thoroughly. I have no
doubt other varieties will be found."

* In another of Mr. Hemphill's letters he writes: "The little spot in Utah
where I found my Utah serie.s is probably the only one that we may say is worked
up in the whole of the great basin of Utah, Nevada, Montana, and Idaho. The field
is very large, and there are many ranges of mountains passing through it that must
yield some nice tilings, and no doubt many more varieties of strigosa are just waiting
for the catcher."

32 BULLETIN OF THE

Var. Newcombi, Hemphill.

Plate II. Fig. 8.

Near Ogden, UtaJi (H. Hemphill). (See ante, p. 30.)

This variety has numerous separated, rough, heavy, transverse ribs (forty-
four on the first whorl of one individual), and two widely separated, revolving
bands of color. It varies, as usual in the group, in size and globoseness. Some
want the revolving band.

Var. multicostata, Hemphill
Plate II. Fig. 6.

Box Elder County, Utah (H. Hemphill).

On one specimen I counted over seventy coarse rib-like striae to the first
whorl. There are two revolving bands of chestnut on all the individuals re-
ceived from Mr. Hemphill. Two have the denticle on the peristome.

Var. Gouldi, Hemphill.
Plate II. Figs. 5, 16.

Banks of BearKiver, north of Brigham City, Utah (H. Hemphill). (See p. 31.)
One individual has sixty-two rough wrinkles on the first whorl. There are
two revolving bands of color. The specimen figured (Fig. 16) is the largest sent
me by Mr. Hemphill, others being smaller by one half, and some being very
much depressed (Fig. 5). Among the thousand specimens collected, none were
large.

Var. albofasciata, Hemphill.
Plate II. Figs. 3, 4.

Same vicinity as the last. (See p. 31.)

The body of the whorl is clouded, with a broad, revolving white band at the
periphery, and white around the umbilicus. Some individuals are white with
two revolving bands of color. On one there are about seventy rough wrinkles
to the first whorl. Some have a toothlike process on the peristome (Fig. 4).
The variety differs, as usual in the group, in the elevation of the spire and in
size.

Var. castaneus, Hemphill.

Plate II. Figs. 11, 14.

Box Elder County, Utah (see p. 31) : also Celilo, 15 miles from the Dalles,
Oregon.* (Hemphill.)

* Probably a colony brought down by the Columbia. It was not found on a
subsequent visit.

MUSEUM OF COMPARATIVE ZOOLOGY. 33

This variety differs somewhat in the sculpturing. The wrinkles are usually
less developed than in the previously mentioned varieties, but on a few indi-
viduals are coarser. Those from Eastern Oregon are almost smooth. The
principal characteristic of the variety is its color, which is uniform chestnut,
excepting around the umbilicus. A few Like the one figured have a double
revolving white band.

This closes the series of transversely ribbed varieties.

B. SHELL SMOOTH OR STRIATE.

In this section Mr. Hemphill suggests including the typical Mrigosa (see
PI. XXVL*), a large, flattened, widelj^ umbilicated, almost discoidal form, and
the typical Cooperi (Vol. IV. PI. LXXVII. Fig. 11), a small, elevated, globose,
narrowly umbilicated shell, as well as the innumerable varieties of size and
form and coloring which exist, some of which I have figured in Vol. IV. In
none of these variable forms do we find either transverse or revolving ribs.

Some individuals are of a dirty white, but usually two revolving chestnut
bands are present : others, retaining the bands, are mottled with light or dark
horn-color, or more or less completely banded or uniformly colored with light
or dark chestnut. Within the peristome on some is a decided denticle, such as
I have already described above for other varieties of the group. (PI. II. Fig. 4.)

One colony from Eastern Oregon is peculiar in form. (PL II. Fig. 10.)

This restricted form of strigosa, including Cooperi, is found over all the wide
region indicated for the species on p. 27. The Arizona localities from which I
have received it are Logan, near Phoenix : Pine Creek, below Natural Bridge :
Huachuca Mountains.

Var. Utahensis, Hemphill.

For locality, see ante, p. 30. This is a rough, coarse, carinated strigosa, fig-
ured in Terr. Moll., V. p. 158, Fig. 66. The peristome is sometimes continuous
by a heavy raised callus connecting its terminations. It is sometimes smaller
and more elevated.

C. SHELL LONGITUDINALLY RIBBED.
Var. Hemphilli, Newcomb.

Plate II. Fig. 15.

This form seems widely distributed. It was originally found by Mr. Hemp-
hill at White Pine, Hamilton, Nevada. Mr. Hemphill believes it will be found
all through the mountains bordering on both sides of the Snake River Valley,
Salmon River Mountains, Idaho. He also found it at various points in Utah

VOL. XIII. — NO. 2. 3

34 BULLETIN OF THE

and Colorado. The original specimen figured in Vol. V. being immature, I
here give (PI. II. Fig. 15) one of a mature individual. Above (p. 31), are
noticed specimens from Logan, Utah, showing the gradual change from strigosa
to Hemphilli.

The variety Hemphilli is characterized by minute revolving striae, and is
decidedly carinated.

Var. Oquirrhensis, Hemphill.

Plate II. Fig. 12.

Oquirrh Mountains, Utah (H. Hemphill). (See p. 30.)

This form has qiute prominent, revolving ribs, more developed than in the
typical Huydeni. The aperture is oblique, the ends of the peristome approached
and joined by a heavy callus. There is a strongly developed carina. Albino
individuals were found.

H. Bruneri, Ancey, is a synonym of Oquirrhensis.

Var. Gabbiana, Hemphill.
Plate II. Fig. 9.

Near Salt Lake City (H. Hemphill). (See p. 30.)

As described by Mr. Hemphill above, this variety is a coarse, rough Haydeni,
with the revolving ribs nearly or quite obsolete. Like all the other varieties,
it varies in size and shape. The ends of the peristome are nearly approached,
and often continuous.

Var. Haydeni, Gabb.

Utah (H. Hemphill). (See p. 30.)

This well-known form has the revolving ribs most developed of all. For
figure see Terr. Moll., V. p. 159.

Var. Wasatchensis, Hemphill.
Plate II. Fig. 7.

Wasatch Mountains, Utah (H. Hemphill). (See p. 29.)
This is the most peculiar variety, with coarse revolving striae and ribs (some-
times wanting), rough transverse wrinkles, decided carina crenellating the su-
tures, ends of peristome approached : the umbilicus is very narrow : the shell
is elevated, often pyramidal : apex acute. Albino individuals were also found.
With its peculiar pyramidal spire and small umbilicus it combines the sculp-
turing peculiar to several of the other varieties. (See p. 29.)

MUSEUM OF COMPARATIVE ZOOLOGY. 35

Patula striatella, Anthony.

This species, including Cronkhitei, has also been found in Wyoming and at
Ogden Canon, Utah : Nevada : Colorado. (Hemphill.)

Patiila Horni, Gabb.

Also Logan, Arizona.

Microphysa IngersoUi, Bland.

Plate III. Fig. 5.

A better figure than that in Vol. V. is here given.

Also found by Mr. Hemphill at Weston, Umatilla Co., Oregon : Mount Nebo,
Wasatch Mountains, Logan Canon, Utah. Also found by Mr. Ernest Ingersoll
near Lawrence, Kansas, on the banks of the Kaw.

Microphysa pygmaea, Drap.

Admitted as a universally distributed species (see p. 24), though not actually
as yet received from the Central Province. Sharing the peculiarity of jaw
with all our species of Microfhysa, I have placed it in that genus.

Microphysa conspecta, Bland.

Plate III. Figs. 4, 6.

Living specimens received from Dr. J. G. Cooper have enabled me to ascer-
tain that this species has the jaw characteristic of Microphysa. My figure,
drawn by camera lucida, gives the sixteen plates as they became actually dis-
arranged under pressure, showing them to be separated and not forming one solid
piece as in most of the genera. The central plates are not imbricated, and ap-
pear lightly connected. The other plates appear to overlap laterally on their
outer sides. The jaw is low, wide, slightly arched, the ends scarcely attenu-
ated, blunt.

There are 12-1-12 teeth on the lingual membrane. Centrals with long and
narrow base of attachment : reflection small, with three cusps, the middle one
much the largest,'all bearing short cutting points. Laterals same, but bicuspid.
Marginals low, wide, with two broad cusps, each bearing a broad, bifid cutting
point. The centrals and laterals are quite like those of Pupa.

A species of the Pacific Province also.

Helicodiscus lineatus, Sat.

A universally distributed species, found over the Central Province, as stated
in Vol. V. Specimens collected at Oakland, California, and in Idaho by Mr.
Hemphill, quite want the revolving lines.

36 BULLETIN OF THE

Polygyrella polygyrella, Bland.

Plate I. Figs. 6, 7 ; Plate VI. Fig. 8.

Also in Deer Lodge Valley, Montana (Hemphill).

The genital system (PI. III. Fig. 8), as would be anticipated, is characterized
by the length of all the organs. The penis sac (p. s.) is long, narrow, cylin-
drical, receiving the vas deferens at its blunt apex, and bearing the retractor
muscle just below. The genital bladder (g. b.) is long, narrow, pointed above
and below ; its duct is long and narrow. The testicle and ovary are long and
narrow.

Triodopsis Levettei, Bland.

Plate I. Fig. 16.

See Supplement to Vol. V. p. 154.

Also seventy miles southeast of Tucson, in the Huachuca Mountains, Arizona.
A species of the Central Province rather than of the Texas Region, as suggested
in " Manual of American Land Shells."

Triodopsis Mullani, Bland

I am convinced by larger suites of specimens that I was wrong in referring
(Vol. V. p. 333) this species to Mesodon devius. The group is very puzzling,
and some confusion has resulted from my treatment of it. It must, therefore,
be considered that Triodopsis Mullani, Bland, as described and figured by him
is a distinct species confined to the regions east of the Cascades in Northern
Idaho. It is very globose, with a decidedly tridentate aperture. (See Vol. V.
p. 338, Fig. 222, and Man. Amer. Land Shells, p. 119, Fig. 87, for a copy of
Bland's original description.) Tlie shell I describe below as T. Sanhiirni is
somewhat nearly related to Mullani, but has its aperture much more contracted
by the teeth on the peristome and the more developed parietal tooth. T. Har-
fordiana is the form which in Terr. Moll., V. (309, Fig. 203) I mistook for Poly-
gyra Harfordiana (see Suppl. p. 151). It is a small shining shell, flattened,
with larger umbilicus and less developed teeth. Triodopsis Hemphilli is a
nuich larger, coarser, russet-colored shell, scarcely umbilicated, with a small
parietal tooth, and a slight approach only to the lamellar dilatation of the inner
edge of the peristome so characteristic of the typical devius; no denticle on the
outer edge of the peristome. All these forms show the scars on the epidermis,
though no hairs were present in my fresh specimens. Besides these well-marked
forms are found individuals, not associating with them, which seem to connect
Harfordiana with Mullani (see Terr. Moll., V. Fig. 221, and the following, PI. I.
Figs. 6, V). The typical Mesodon devius is confined to the Pacific Province.
See Terr. Moll, IV. PI. LXXIX. Fig. 13 ; V. Fig. 220. It is a very di^^tinct
species, as yet not noticed in the Central Province.

MUSEUM OF COMPARATIVE ZOOLOGY. 37

Triodopsis Sanburni.

Plate I. Fig. 9 ; Plate III. Fig. 3.

Shell narrowly umbiiicated, globose, depressed, thin, sparsely hirsute, with
distant, scarcely perceptible wrinkles of growth, yellowish horn-colored ; whorls
five and one half, slightly convex, the last hardly descending, beneath convex ;
aperture oblique, lunate, trilobed, with a heavy, prominent, blunt parietal tooth ;
peristome white, broad, reilected, almost covering the umbilicus, thickened,
bearing on its right margin a large squarely truncated denticle, on its basal
margin a stout, bluntly pointed denticle, the two denticles separated by a small,
rounded sinus. Greater diameter, 1 1 mm. ; lesser, 1 0 mm. ; height, 5 mm.

Kingston, Northern Idaho (J. Rand Sanburn).

Lingual membrane as usual in the genus. Teeth 26-1-26, with about eight
laterals on either side, the ninth tooth having its cutting point split, the eleventh
in another membrane : centrals with slightly developed side cusps and decided
cutting points : laterals like the centrals, but bicuspid : marginals long, low,
with two very wide, blunt cusps, the inner much the larger, both bearing long,
oblique, irregularly bifid or trifid cutting points. (PI. III. Fig. 3.)

Genital system with no accessory organs. Penis sac long, cylindrical, some-
what attenuated at its apex, where it receives the vas deferens and retractor
muscle : genital bladder long, narrow, suboval : duct to genital bladder stout
below, gradually tapering above. The same arrangement is found in the geni-
talia of the typical devius.

This shell, found in quantities living by Mr. Sanburn, shows no variation
excepting slightly in size. There are no individuals showing a transition to
forms of Mullani. It is nearly allied to that species as described by Mr. Bland.
It is, however, much less globose, and has its aperture very much more con-
tracted by teeth. The parietal tooth is not long and curving, but erect and of
equal width to its bluntly truncated top. The upper tooth on the peristome,
opposite, not above, the parietal tooth, is also erect and bluntly truncated. The
lower peristome tooth is bluntly triangular. The sinus between the two pa-
rietal teeth is small and rounded.

I have described the shell as hirsute, though no hairs were found on the scars
which surely bore them.

The general appearance of the shell is that of T. Hopetonensis.

Triodopsis Harfordiana.

Plate I. Figs. 6, 7-

Shell umbiiicated, depressed, thin, shining, sparsely hirsute, greenish horn-
colored, wrinkles of growth not prominent; whorls four and a half, hardly
convex, the last scarcely descending, deeply grooved l)ehind the peristome,
hardly convex beneath ; aperture very oblique, lunate, trilobed, with a small

38 BULLETIN OF THE

l^arietal tooth ; peristome narrow, scarcely reflected, bearing two distant,
slightly developed denticles. Greater diameter, 8^ mm. ; lesser, 8 mm. ; height,
3 mm.

Triodopsis Harfordiana, W. G. Binney, not of J. G. Cooper, Terr. Moll., V. 309,

figure only, not description : PI. VIIL Fig. R, lingual dentition.
Mcsodon devius, var., W. G. Binn., Man. Amer. Land Shells, 118, Fig. 88.

Salmon River, Idaho (H. Hemphill).

Genitalia unobserved.

Lingual dentition (under erroneous name of Triodopsis Harfordiana) . See
TeiT. Moll, V. 1. c.

This is the shell formerly mistaken by me for Polycjyra Harfordiana. It is
a small, very much dejiressed, shining shell, with open umbilicus and slightly
developed teeth. Its surface is scarred as if it had been hirsute. Though
much more depressed, it has the general appearance of a tiny T. tridentata.

Triodopsis Hemphilli.

Plate I. Fig. 17.

Shell imperforate, globosely depressed, coarse, slightly wrinkled, russet-
colored, sparsely hirsute ; whorls five and a half, convex, the last globose,
slightly descending ; aperture very oblique, lunate, with a short, narrow,
slightly curving parietal tooth ; peristome white, broad, thickened, revolute,
usually quite concealing the umbilicus, bearing on its basal margin an elon-
gated, lamellar toothlike process. Greater diameter, 17 mm. ; lesser, 14 mm. ;
height, 7 mm.

Kingston, Northern Idaho (J. Rand Sanburii).

The surface is scarred as if hirsute when quite fresh.

The shell, by its coarser texture, closed imibilicus, and lamellar peristome
denticle, is more nearly allied to the typical Mcsodon devius than to Mullani,
Harfordiana, or Sanburni. Though common at the locality given above, it is
not variable, nor have I received it from other points.

Lingual membrane of the same character as in T. Sanburni.

Genitalia as in the last-named species.

Mesodon ptychophorus, A. D. Brown.

Plate I. Figs. 3, 16.

Shell with umbilicus almost concealed, globose, with coarse, distant striae of
growth, thick, of a dull russet-color ; spire elevated, apex acute ; whorls five, con-
vex, the last swollen below, rapidly descending ; aperture oblique, subcircular,
parietal waU with light callus ; peristome white, thick, narrow, reflected, with
a thickening scarcely approaching a tooth-like process on its basal margin, its

MUSEUM OF COMPARATIVE ZOOLOGY. 39

termination almost entirely conceaung the small umbilicus. Greater diam-
eter, 19 mm. ; lesser, 15 mm. ; height, 11 mm.

Var. MAJOR. Six full whorls, umbilicus less concealed. Greater diameter,
22 mm. (Fig. 3.)

Helix ptychophora, A. D. Brown. See Vol. V. p. 355.

Arionta Townsendiana, var., W. G. Binn. 1. c. Suppl., PI. IV. Figs. E, F. —
Man. Amer. Land Shells, p. 128, Figs. 101, 102.

Deer Lodge Valley, Montana : the large variety was found by Mr. Hemphill
along Salmon Eiver, Idaho : Bitter Root Mountains, Umatilla Co., Oregon :
Weston, Oregon, to the DaUes. The range westwardly through the Cascades
has been already explained above (see p. 28).

Formerly I was disposed to believe this to be a variety of Arionta Town-
sendiana, but the larger number of specimens received from various localities
has convinced me oT its being distinct. It is a true Mesodon, very much like
M. clausus. It is a smaller shell than Townsendiana, more globose, less widely
umbilicated, with more circular aperture ; the sculpturing lacks the transverse
striae and malleations of the Ariontce.

For genitalia, jaw, and lingual dentition, see Terr. Moll., V.

To my knowledge, Arionta Townsendiana has not been found east of the
Cascade Mountains.

Mesodon Columbianus, Lea.

Plate I. Fig. 5.

A species of the Pacific Province as well as the Central Province. Also re-
ceived from Coeur d'Alene Mountains, Idaho : Deer Lodge Valley, Montana.
(H. HemphiU.)

One Cceur d'Alene Mountain specimen with parietal tooth is figured.

The form found at these Central Province localities is the variety called lahi-
osa by Gould. It is more globose than the type, has a more circular aperture,
without the horizontal basal margin or toothlike thickening to the peristome.
The latter is extremely broad, grooved, not flattened. It must be remembered
that this toothed form is not the armigerus, Ancey, which will be treated under
the Pacific Province species.

Vallonia pulchella, Mull.
A universally distributed species. Also at various points in Utah (Hemphill).

Pupa muscorum, Lin.

Plate III. Fig. 11.

Universally distributed.

The shell figured, which appears to me identical with this species, was sent
to me by Mr. Ancey as P. sublubrica, from White Pine, Nevada.

40 BULLETIN OF THE

Pupa Blandi, Morse.

A northern region of Eastern Province species. Also found at Ogden and in
the Wasatch Mountains, Utah (Hemphill).

Pupa corpulenta. Morse.
Ogden Canon, Utah, with two parietal teeth (Hemphill).

Pupa Arizonensis, Gabb.

Plate III. Fig. 10.

I give^a figure of Pwpa hehes, Ancey, drawn from a specimen sent me by Mr.
Ancey. To me it seems identical with Arizonensis.

Pupa hordeacea, Gabb.
Pupa alticola, Ingersoll.

Plate III. Fig. 9

A better figure of an authentic specimen is given here. Wasatch Mountains,
Utah (Hemphill) : Ouray, Colorado (Ingersoll).

Vertigo ovata, Sat.
A universally distributed species.

Ferussacia subcylindrica, Lin.

Also from various points of Utah, Idaho, and Nevada.
A species also of the northern region of Eastern Province.

Succinea Haydeni, W. G. Binn.
Also, Salt Lake City, Utah. A species of northern region.

Succinea Sillimani, Blakd.

Succinea lineata, W. G. Binn.

Also in Idaho. A northern region species. As S. chrysis it is also described
from Alaska. (See Man. Amer. Land Shells, p. 473, Fig. 515 ; and below, p. 46.)

MUSEUM OF COMPAKATIVE ZOOLOGY. 41

fciuccinea Stretchiana, Bland.
Also at Elko, Nevada

Succinea avara, Say.

A northern region species. (See Vol. V. p. 420.)

PACIFIC PROVINCE SPECIES.

I have not included the species from the extreme northern regions, which
more properly belong to the fauna of Asia. Such are : —

Pupa arctica Wall. Pupa edentula, Drap.

columella, Benson. signata.

Succinea turgida, West. muscorum, var. Lundstromi.

annexa, West. columella, var. Gredleri.

Vallonia asiatica, Nevill. Krausseana, Reinh.

See Man. Amer. Land Shells, pp. 473, 474.

Macrocyclis Vancouverensis, Lea.
A. dark reddish variety was found in Alaska by Mr. Dall.

Macrocyclis sportella, Gld.

Macrocyclis Voyana, Newc.

A variety simplicilabris has been noticed bj Ancey (Le Naturaliste, IV.
pp. 110, 111).

Macrocyclis Hemphilli, W. G. B.

See also p. 25. Found also at Freeport, W. Terr.

Macrocyclis Duranti, Newc.

ffaplotrema has been suggested as a subgeneric name for this species (Ancey,
1. c.) on account of its simple peristome.

Zonites Whitneyi, Mewc.
See also p. 25.

Zonites nitidus, Mull.
Zonites arboreus, Sat.
Zonites cellarius, Mull.
See p. 23.

42 BULLETIN OF THE

Zonites indentatus, Say.
Zonites viridulus, Mke.

Portland, Oregon (Hemphill) : Victoria, British Columbia (Rev. G. W.
Taylor).

Zonites milium, Morse.
Zonites chersinellus, Dall.

See Supplement I.

Zonites fulvus. Mull.
Vitrina Pfeifferi, Newc.
See page 26.

Limax campestris, Binn.
Limax Hewstoni, J. G. Coop.
Limax hyperboreus, Westerlund.

See Man. Amer. Land Shells, p. 473.

A species collected in Arctic America by the " Vega." I am indebted to Mr.
Dall for a specimen from Commander Island, Siberia.

Jaw arched, smooth, with median projection. Lingual membrane with about
42-1-42 teeth. Centrals tricuspid : laterals bicuspid, twelve in number on
each side: marginals about thirty in number on both sides, aculeate, simple,
without bifurcation or side spur. Fig. 516 of Man. Amer. Land Shells shows
a central tooth with its adjacent lateral and three extreme marginals of Mr.
Ball's specimen.

From Seattle, Washington Territory, I have received a small Limax similar
in outward appearance to hyperboreus, and with similar dentition.

See Westerlund, Sibirien Land och Sotvatten MoUusker, p. 21.

Prophysaon Hemphilli, Bl. & Binn.
Prophysaon Andersoni, J. G. C.

It is a true Prophysaon, though described originally as an Avion.

The lingual membrane has 30-1-30 teeth, with about 12 perfect laterals.
Centrals tricuspid : laterals -bicuspid : marginals with one long, stout, oblique
inner cutting point, and one outer, short, blunt, sometimes bifid cutting point.
Resembling that of P. Hemphilli.

Jaw low, arcuate, ends blunt ; with numerous (over 15) irregularly devel-
oped, broad, stout ribs, denticulating either margin.

Animal small, long, and slender, dirty white with dark reticulations : an in-
distinct dark-colored circle around the mantle near its edge, and a dark band
running longitudinally from the rear of the mantle to the tail on each sidp of
the centre of the back.

Reticulations foliated as in Prophysaon Hemphilli and in the figure of Arion
Joliolatus. The mantle covered with minute tubercles, not foliated. -

MUSEUM OF COMPARATIVE ZOOLOGY. 43

The animal extends itself into a long cylindrical worm-like body, with ob-
tuse ends. Length wTien fully extended, 60 mm.
The synonymy of this species is as foUows : —

Arion Andersoni, J. G. Coop., formerly Prophysaon Bemphilli, var., W. G. B.,

T. M. V.
Prophysaon Andersoni, J. G. C, in letters.

Ariolimax Columbianus, Gould.
Ariolimax Californicus, J. G. Coop.
Ariolimax niger, J. G. Coop.
Ariolimax Hemphilli, W. G. B.

Ariolimax Andersoni, W. G. B.

Formerlj'- I supposed this species to be Arion Andersoni, of Dr. Cooper.
Learning that Dr. Cooper's sjjecies is a Prophysaon, I still retain for this the
specific name Andersoni, W. G. B.

Arion foliolatus, Gld.

Still a doubtful species, known only by the original figure and description.

Binneya notabilis, J. G. Coop.

Also found by Mr. Orcutt fifty miles from St. Quentin Bay, Lower
California.

Hemphillia glandulosa, Bl. & Binn.

Patula striatella, Anth.
Mariposa, California.

Patula pauper, Mor.

Patula asteriscus, Morse.
Tacoma, W. Territory.

Patula solitaria, Sat.

Plate I. Fig. 10.

This can hardly be considered a species of the Pacific Province, though colo-
nies have been found west of the Cascades. (See pp. 27, 28.)

The specimen figured was found by Mr. Hemphill at Wliite Bird Creek,
Salmon River, Idaho.

Microphysa Lansingi, Bland.

Microphysa pygmsea, Drap.
See p. 35.

44 BULLETIN OF THE

Microphysa conspectt . Bi.,
See p. 35,

Microphysa Stearnsi, Bl.

See Supplement I. p. 147. Found also in iUaska.

Helicodiscus lineatus, Say.
Vallonia pulchella, Mull.
San Diego, California.

Gonostoma Yatesi, J. G. Coop.
Polygyra Harfordiana, J. G. Coop
TrioHopsis loricata, Gld.
Stenotrema germanum, Gld.

Mesodon Columbianus, Lea.

The true M. Columbianus is correctly described and figured in Terr. Moll,. II.
and III. It is very readily distinguished by its peristome, the basal margin of
which is horizontal in its direction, with a slight thickening or projection before
it reaches the base of the shell. It does not appear to range as far southerly as
California. Northerly it has been found to 59° latitude.

The form called labiosa by Dr. Gould (see Vol. II.) is recognized by its very
circular aperture, its widely reflected, sinuous peristome, sharp on its outer edge,
not flattened on its face. Its ujiper surface is elevated as in Columbianus. It is
sometimes toothed. Originally found iii the region of Astoria, Mr. Hemphill
has collected it at Kalama on the Columbia River, forty miles below Portland,
a|nd also from Deer Lodge Valley, Montana, and in the Coeur d'Alene Moun-
tains, Idaho. (See p. 39.)

My Figs. 4, 5 of Plate I. show the toothed variety from Idaho and an enlarged
view of the epidermis. It is less hirsute than armigerus.

The form called armigerus by Aiicey (Le Naturaliste) is the one common in
California, ranging as far south as 37° 20'. I have figured it on PI. I. Fig. 12,
as well as an enlarged view of the epidermis. It is the most densely hirsute of
the group. It is a more globo.?e shell below than the typical form. The peris-
tome is narrow, much less develojjcd ; the 'parietal tooth is long and narrow,
sometimes wanting. It has much the appearance below of a large Stenotrema
germanum, with which species I have confounded it rather than with Colum-
bianus. I have no doubt it will eventually be considered a distinct species.

Mesodon devius, Gld.

As restricted (see p. 36), this species seems to be confined to the Oregon

Aglaja fidelis, Gray. Aglaja Hillebrandi, Newc.

infumata Gld. ArioD'--a arrosa, Gld.

MUSEUM OF COMPARATIVE ZOOLOGY. 45

Arionta Townsendiana, Lea.

As restricted (see p. 39), this species seems confined to the Oregon region.

Arionta exarata, Pfb.

Arionta Californiensis, Lea.

As proposed in Man. Amer. Land Shells, 1 unite under this specific name the
various forms described as —

Helix vinda, Val. (See Vol. IV. for a facsimile of figure.)
Nickliniana, Lea. (See Vol. III. PI. VI. Fig. a.)
arhoretorum, Val. (See Vol. IV. PI. LXXXVI. Fig. 13.)
nemoraviga, Val. (See saine, PI. LXXIX. Fig. 11.)
anachoreta, W. G. B. (See same, PI. LXXVI. Fig. 5.)
ravientosa, Gld. (See Vol. V.)
Parkeri, Tryon.
reticulata, Pfu. (See Vol. V.)
Bridgesi, Newc. (See Vol. V.)

I have figured, in Man. Amer. Land Shells, Fig. 109, a large umbilicated
form, probably very^ near to Newcomb's type of H. Bridgesi, a small umlaili-
cated form (Fig. 168), a larger imperforate form (Fig. Ill), and a figure of a
^hell received under the name of Diabloensis from Dr. Cooper (Fig. 113).

Arionta intercisa, W. G. Binn.

I am now convinced that redimita is a variety of this species.

Arionta Ayersiana, Newc. Arionta Traski, Newc.

tudiculata, Binn. Carpenteri, Newc.

Mormonum, Per. Dupetithouarsi, Desh.

Arionta sequoicola, J- G. C.

An enlarged view of the sculpturing of this species is given in Man. Amer.
Land Shells (Fig. 127)

Arionta ruficincta, Newc. Arionta Kelletti, Forbes.

Gabbi, Newc. Stearnsiana, Gabb.

Euparypha Tryoni, Newc.

The allied species E. Levis, Pfr., recently collected by Mr. Orcutt in Lower
California, has a genital system (PI. IIL Fig. 2) very near that of E. Tryoni
(see Vol. V. PI. XIV. Fig. c). I did not detect the organ 2 in levis. The

46 BULLETIN OF THE

jaw is high, arched, with blunt ends : six ribs on the anterior surface, denticu-
lating either margin. The lingual membrane (PI. III. Fig. 1) is long and
narrow : teeth 38-1-38, with about nine laterals on either side, the tenth tooth
having the inner cutting point bifid : centrals and first laterals without side
cusps and cutting points : marginals low, wide, with two distinct cusps, each
furnished with bifid cutting points.

Pomatia aspersa, Mull.
See p. 24.

Glyptostoma Newberryanum, W. G. B.

Perussacia subcylindrica, Lin.
Received also from Washington Territory.

Pupa Rowelli, Newc. Pupa Californica, Newc.

Pupa muscorum, Lin.
A variety Lundstromi, Westerlund, has been described from Alaska.

Succinea Sillimani, Bl. Succinea rusticana, Gld.

Stretchiana, Bl. Nuttalliana, Lea.

Hawkinsi, Baikd.

Succinea chrysis, Westerlund.

Alaska. This is the well-known yellowish variety of S. lineata, often found
at far northern points. An authentic specimen is figured on p. 473 of Man.
Amer. Land Shells.

Succinea Oregonensis, Lea.

Succinea avara, Sat.
Received also from California.

Veronicella olivacea, Stearns.
Onchidella borealis, Ball.
Onchidella Carpenter!, W. G. B.

MUSEUM OF COMPARATIVE ZOOLOGY. 47

EXPLANATION OF THE PLATES.

PLATE L

ig. 1.

Mesodon armigerus.

" 2.

Same : epidermis enlarged.

" 3.

Mesodon ptychophorus, var. maj

" 4.

Mesodon labiosus.

" 5.

Same : epidermis enlarged.

" 6,

7. Triodopsis Harfordiana.

" 8.

Mesodoji armigerus.

" 9.

Triodopsis Sanburni.

" 10.

Patula solitaria.

" 11.

Triodopsis Mullani.

*' 12.

Polygyrella polygyrella.

" 13.

Fruticicola Cantiana.

" 14.

Polygyrella polygyrella.

" 15.

Triodopsis Levettei.

" 16.

Mesodon ptycliophorus.

" 17.

Triodopsis Hemphilli.

PLATE II.

Fig. 1, 2. Patula Idahoensis.

" 3. Patula strigosa, var. albofasciata.

" 4. Patula strigosa, vavi albofasciata : toothed.

" 5. Patula strigosa, var. Gouldi.

" 6. Patula strigosa, var. multicostata.

" 7. Patula strigosa, var. Wasatchensis.

" 8. Patula strigosa, iJar. NewcombL

" 9. Patula strigosa, var. Gabbiana.

" 10. Patula strigosa, var.

" 11. Patula strigosa, var. castanea.

" 12. Patula strigosa, var. Oquirrhensis.

" 13. Patula strigosa, ■rar. Binneyi.

" 14. Patula strigosa, var. castanea.

" 15. Patula strigosa, var. Hemphilli.

" 16. Patula strigosa, var. Gouldi.

48 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY.

PLATE III.

Fig. 1 . Lingual dentition of Euparypha levis.
*' 2. Genital system of same.

a. genital bladder.

b. penis sac.

c. vas deferens.

d. vaginal prostate.

Fig. 3, Lingual dentition of Triodopsis Sanburni.
' ' 4 Jaw of Micropbysa conspecta.
" 5. Micropbysa Ingersolli.
'* 6. Lingual membrane of Micropbysa conspecta.
*' 7. Same of Fruticicola Cantiana.
" 8. Genital system of Polygyrella polygyrella.

a. genitalTsladder.

b. penis sac.

c. vas deferens.

d. retractor muscle.
Fig. 9. Pupa alticola.

" 10. Pupa Arizonensis.
" 11. Pupa sublubrica.
" 12. Pupabebes.

Bium Z^c^iuDijl.Jr^late

%,^

2 M^%M

4 |,.. <^./

■•^1^

2 €^;-

>^h)^

^ %^

■i3'Bl^

^■gSj

II

12 i«.->:;:A

13

(Ad

■'^*%,

i4 I

€!

,^^%

15

16 \:;:;i^¥T5i^.

wm^

i^

17

~ZvX!

No. 3. — Simple Eyes in Arthropods. By E. L. Mark*

That portion of Mr. Locy's paper on the development of the spider f
which deals with the formation of the eye appears to possess importance
outside the objects of his special study. The discussion of the bearings
of his discoveries on the simple or monomeniscous eyes of Arthropods in
general, is the object of the present paper.

Two irreconcilable views have been held of late with regard to the
origin of the retina in the simple eyes of Arthropods. The writers upon
the subject have been pretty evenly divided in opinion. Grenadier,
Lankester and Bourne, and Carriere have all claimed, more or less dis-
tinctly, that the retina was derived from the "hypodermis ;" while Gra-
ber, Lowne, and Schimkewitsch have clearly inclined to the opinion that
it was an outgrowth from the cephalic ganglia. It has been impossible
for either party to establish its views beyond debate, on account of the
absence of the proper embryological information.

Grenacher ('79, p. 158) claims the ectodermic (hypodermal) origin of
the retina as duly established for certain cases, but admits that, although
highly probable, a similar origin has not been proved for eyes of the type
to which those of the spiders belong. He says : " Der zweite Punkt auf
den es wesentlich ankommt, betrifft die Herkunft des Retinaelementes.
Was diese anbelangt, so haben wir auch einige Beispiele kennen gelernt,
die uns in einer "Weise, wie kaum etwas zu wiinschen iibrig lasst, diese
Abstammung klarlegen ; nur schade, dass sich so wenige andere anfugen
lassen. Mit den ersteren meine ich die Augen der Qchwimmkaferlarven
(Figg. 1-10, Taf. I), die uns so evident als moglich nicht nur die Ab-
hangigkeit des Retinaelementes, sondern auch aller iibrigen Augentheile
von dem Integument, der Hypodermis mit Cuticula, erkennen lassen.
Damit ist aber fiir diese Thiere auch zugleich die Abstammung des Eeti-
naelementes vom ersten, ausseren embryonalen Keimblatt, dem Ectoderm,
gegeben.

" Nicht so gunstig steht es mit den iibrigen Formen von Larvenaugen,
sowie den einfachen Augen der Spinnen und Insectenimagines. Wenn

* Contributions from the Zoological Laboratory of the Museum of Comparative
Zoology at Harvard CoHege. No. XI.

t Wm. A. Locy, Observations on the Development of Agelena ncevia, Bull. Mus.
Comp. ZooL, Vol. XII, No. 3, pp. 63-103, 12 pi., Jan., 1886.

VOL. XIII. — NO. 3. 4

50 BULLETIN OF THE

auch viber die Herkunft eimelner Augentheile, iiber die Abstammung der-
selben von der Hypodermis, namentlich bei den erstgenannten beiden
Catagorieii, kein Zweifel obwalten kann, so ist doch hier die Retina in
den von mir untersuchten Zustanden ausser aller Continuitat mit ihr
nnd jenen Augentbeilen, und der erforderliche strenge jSTachvveis dieses
jedenfalls hochst wahrscheinlichen urspriinglichen Zusammenhanges ist
erst noch zu fiihren."

In his last paper on this subject Grenadier ('80, p. 430) reiterates his
inabihty to solve the problem, when he says : *' The genesis of the two-
layer 'Stemma' out of the hypodermis, to which the conclusions from
analogy point, is still entirely obscure to me also, and is only to be made
out by direct observation."

Lankester and Bourne ('83) have expressed their opinion on the
origin of the retina either in an incidental way or with a certain amount
of reserve. I have not hesitated to class them on this side of the ques-
tion, however, since they evidently incline in this direction. Of the lat-
eral eyes in scorpions they say (p. 182): "Both nerve-end cells and
indifferent cells of the lateral ommateum * apparently belong to the epi-
blastic layer, and are shut off together with the layer of hypodermis cells
from the -subjacent connective tissue bj' a well-marked 'basement mem-
brane,' which in the region of the ommateum may be called the eye-cap-
sule, or, better, the ' ommateal capsule.' " In this connection it should
be borne in mind that these lateral eyes are claimed by them to be
»io?iostichous.t They believe (p. 211), however, that "a few examples
clearly transitional between the monostichous and the diplostichous con-
dition have been described by Grenacher (among Myriapods)." There-
fore by inference their supposed diplostichous (in reality triplostichous)
condition must likewise have had both its layers derived from the hypo-
dermis. The difficulties in the way of this transition from monostichous
to so-called diplostichous eyes do not seem to have impressed themselves
so forcibly upon these observers as they did upon Grenacher, who, not-
withstanding his familiarity with the facts, confessed, as we have seen,
that the double-layer condition presented a still unsolved problem.

Finally, they have expressed J more precisely, although incidentally,
the conviction that the retina in the central (" diplostichous ") eyes of
the scorpions is of hypodermic origin ; but they have nowhere offered an

* "All the soft tissues of an arthropod eye, as distinguished from the cuticular
lens," they call "ommateum."

t " An ommateum consisting of a single layer of cells."
t See pp. 56, 57.

MUSEUM OF COMPARATIVE ZOOLOGY. 51

explanation of the method of its formation other than that implied in the
allusion to Grenacher's researches on Myriapoda.

Carriere ('85, p. 178), basing his conclusions principally upon the ap-
pearances presented by the ' stemma ' in the pupa of an ant, believes that
it is derived from the hypodermis by, — first, a lenticular thickening of
the hypodermis produced by an elongation of the hypodermis cells ; and,
secondly, by the rearrangement of the latter into two layers, one above
the other, of which the outer remains in continuity vfith the permanent
hypodermis and constitutes the " vitreous body," while the inner is trans-
formed into the retina. The method by which this rearrangement is ac-
complished is to be learned a little farther on (p. 189), where he says :
" According to my interpretation, therefore, the simple eye (Napfauge)
and the compound eye (Facherauge) of the Arthropoda are organs which
arise out of like components in a similar manner (through splitting of the
hypodermis into two layers), but in their further development diverge
from each other in two opposite directions."

While the authors just quoted agree in believing the retina to be an
immediate derivative from the liypodermis, those cited below are at least
so far in agreement ,as to hold that the retina is 7iot developed directly
from that layer.

Graber's objection to the view that the retina is derived from the
hypodermis was based principally upon its total separation from the
hypodermis and its derivatives (pigment-cells and " vitreous body ") by
means of the so-called pre-retinal septum or lamella * discovered by him.
Combating Grenacher's conclusions, Graber ('79, p. 66) says : If really
the pigment-cells were directly continuous vidth the retinal cells, as
Grenacher's Fig. 31 (Vespa) makes them, then there would be an unin-
terrupted transition from retina to hypodermis, and consequently the
typical two-layer " stemma " could be considered as only a modification
of the apparently one-layer eye of the Dytiscus larva. " Fine solche
directe Verbindung der Retina," he adds, " mit den das Auge umsaumen-
den Integumentzellen existirt aber nicht ; Hypodermis, Pigment- und
Krystallkorperzellen einerseits und Retina anderseits bilden vielmehr je
ein geschlossenes Gauzes fiir sich, indem sich eben zwischen beiden
Straten unser praretinales Septum durch und durch zieht, und so vielleicJit
auch fur die Zuldssigkeit der Grenadier' schen Theorie heziiglich des hypo-
dermalen (wir sagen nicht ectodermatischen) Ursprimgs der Arthropoden-
Retina eine schwer za uberivindeude Schraiike bildet." In his resume
of the principal results of his paper Graber (p. 88) gives as the second
result : " Die Retina des Stemma ist in ihrer ganzen Ausdehnung durch

* I shall in the future refer to this structure as the "pre-retinal membraiie."

52 BULLETIN OF THE

eine besondere cuticulare mit der Sclera zusammenhangende Zwischenla-
melle (praretinales Septum) vom integumentaleu Epithel (Hypodermis,
" Pigment-" und " Glaskorper-" zellen) abgesondert. — Dies spricht (vom
rein topographischen Standpuuct aus) fiir die Ausschliessung derselben
von der Hypodermis."

Graber's belief in the derivation of the retina from the nervous system
rather than from the hypodermis is still more emphatically expressed in
his subsequent paper on the eyes of Chsetopoda (Graber, 79**, pp. 280 and
310), where he says of the retina of Alciope : " Dieser [axis] Fad en
spricht aber auch am meisten dafiir, dass die primaren Eetinazellen, resp.
deren mehrkeriiige Differenzirungsgebilde, oder die secundaren Retina-
pallisaden, nicht direct von der ausseren (integumentalen) Zelllage, son-
dern aus der inneren (secundaren) Anlage des Nervensystems sich
ausbildet." Concerning the eyes of Chsetopods in general, he adds
(p. 310): "Der Augapfel als Ganzes besitzt keine eigne Umhiillung
(Sclerotica im Sinne der Wirbelthiere und Cephalopoden), wohl aber
kommt eine solche dem Retinabecher zu, der als ein selbststandiger
Abschuitt vom allgemeinen oder integumentaleu Theile abgelost vs^erden
kann. Diese Retina-Hiille ist eine diinne Cr^icula und erweist sich topo-
graphisch als ein gestielter blasenartiger Anhang der Hirnkapsel." He
says further (p. 312) : " Die Retina ist in ihrer gesammten Ausdehnung
nichts Anderes als die Endausbreitung des Sehnervs," etc.

In the first published abstract of his paper on the structure and func-
tions of the eyes of Arthropoda, Lowne ('83, p. 142) claims that his
" Dioptrcn " of the compound eye apparently corresponds to the cornea,
the vitreous, and the fibrous membrane (Graber's preretinal lamella) of
the simple ocellus. By implication the "Neuron" in the compound eye
and that in the simple eye are therefore also homologous. Concerning
the origin of these two parts he says (p. 142) : " All the structures of the
Dioptron are developed from the cellular Hypoderm, whilst all the struc-
tures of the Neuron are formed from a solid papilla, or from a number
of papillfE which are outgrowths from the Cephalic Ganglia, so that in
this respect there is ground for a morphological comparison of the Dioptron
with the dioptric structures, and of the Neuron with the nervous structures
of the eye of a Vertebrate."

In the paper as ultimately published by Lowne ('84), it is evident that
his conclusions relative to the origin of the " Neuron " from the cephalic
ganglia are based, so far as his own observations go, upon the develop-
ment of the compound eyes ; so that he only leaves it to be inferred that,
in his opinion, it has in the simple eyes the same ongm. It is in tliat

MUSEUM OF COMPARATIVE ZOOLOGY. 53

sense, at least, that I understand the tenor of his criticism (p. 415) of
Grenacher's belief : " At present the origin of the retina of the simple eye
cannot be said to have been determined ; I have sought in vain for any-
reliable indications as to its origin. Dr. Grenacher believes it to arise
by a modification of the cells of the hypoderm. His arguments in favor
of this origin are very unsatisfactory, and apparently indicate that the
vitreous, and not the retinal elements, arise from this layer."

The conclusions reached by Schimkewitsch ('84) place him also with
those who regard the retina as an outgrowth of the cephalic ganglia. He
says (p. 10) : "According to my observations, the eye of Epeira and of
other spiders may be divided into two quite distinct parts : one part we
call epithelial, the other part retinal or neural. The first embraces a lens
and a vitreous body, and is separated from the second by a pre-retinal
membrane. The retinal part is formed by a collection of terminations of
the fibres of the optic nerve ; each termination is formed by an enlarge-
ment of the fibre, which supports, in the case of Epeira, a double bacillus
and nuclei. The two parts [epithelial and retinal] are enveloped by a
membrane — a prolongation of the neurilemma of the optic nerve — which
merges into (se covfond) the subcutaneous connective layer and the pre-
retinal membrane {lame)." At p. 14 of the same paper he adds : " The
existence of a pre-retinal membrane is an argument — and such is also
the opinion of Graber — in favor of the development of the retina at the
expense of a neural rudiment, and not at the expense of an epithelial
reduplicature, as Grenacher supposes.* Besides that, we have the very
important observations of Bobretzky, who shows that the retina of the
compound eyes of the crayfish is certainly developed at the expense of the
neural rudiment." His general conclusion on this matter is summarized
in the following words : " Les couches epitheliales et mesodermiques
prennent aussi part a la formation des yeux, comme cela a lieu chez les
Vertebres."

In his more recent paper on the embryology of spiders, Schimkewitsch
('84*; does not deal with the origin of the eyes.

The answers to the questions concerning the source of the retina and
the method of its formation, now furnished by Locy, seem adequate to

* A part of the argument implied in the above quotations from Schimkewitsch
does not appear directly from the quotations themselves, but rests upon his interpre-
tation of "the membrane which merges with the pre-retinal membi'ane and with the
so-called subcutaneous layer." These three structures are, in his opinion, connective
tissue, and therefore of mesodermic origin.

Further along in the preseut paper this view will be discussed, and an explana-
tion will be offered of what seems to be the cause of the author's apparent error.

54 BULLETIN OF THE

settle these conflicting views, — so far, at least, as regards the eyes of the
spider-like type. While the fornaation of the retina from the epiblast,
independently of the cephalic ganglia, determines the controversy in favor
of those who have maintained its hypodermal origin, the method by
which it is formed shows that none of his predecessors have in the least
foreseen the true course of events.

He has discovered that in both typos of retina exhibited by spiders
the retinal part of the eye is formed by an infolding. In the anterior
median eyes of Agelena* — and probably the same is true in all spiders'
eyes which fall under the class called by Graber ^os^bacillar, — this in-
folding gives rise to a pocket which is ultimately detached t from the
hypodermis. The two walls of the pocket soon come into contact, so
that this infolded, detached portion of the eye is composed of two layers.
The layers are of unequal thickness ; and while one of them — the thinner
and deeper — remains normal, the other, by the process of infolding, be-
comes inverted. The cells of the thick, inverted layer are developed into
retinal cells. The bacilli are formed at what were originally the deep
ends of the ectoderm cells (Figs. 1, 8, 10, 20-22. Compare Locy, I. c.
PI. X.), and therefore in the inverted condition of the layer are in front
of the retinal nuclei. | In the course of the involution the outer or thick
wall of the pocket becomes applied directi}'' to the deep surface of that
portion of the ectoderm which lies immediately behind the infolding.
This region of the ectoderm is meantime being converted into a so-called
vitreous body.

The inversion of the retina proper is a fact of broader significance than
would at first appear, and it atfords a satisfactory explanation of some
of the points in the anatomy and histology of simple eyes which have
been so earnestly discussed during the past few years.

After Grenacher ('79) it is especially Lankester and Bourne ('83) who
have emphasized the differences between what the latter authors have
named monostichous and diplostichous ommatea ; but how far they still
were from a full appreciation of the real differences is to be gathered both
from the name employed — diplo?,i\chon?> for an omraateum composed of
at least three originally distinct layers — and from the statement that
Grenacher had shown in Myriapoda stages intermediate between mono-
stichous and (their so-called) diplostichous conditions. From the latter

* The conditions in the remaining eyes of Agelena are described and discussed on
pp. 75 and 94.

t Compare footnote, p. 66.

t It seems to me more appropriate to refer the position of the bacilli to that of
the nuclei, rather than vice versa ; and I shall therefore speak of the two types of eyes
as pre- and post-nuclear, instead of post- and pre-bacillar as Oraber has done.

MUSEUM OF COMPARATIVE ZOOLOGY. 65

we must infer, it seems to me, that their explanation is equivalent to say-
ing that the " diplostichous " condition has arisen by a gradual sinking
down of the retinal area, and a subsequent closing in of the adjacent
epiblast to constitute the outer layer of the ommateum. The funda-
mental diflference between such a method and that shown by Locy to
exist in spiders is, that, according to the former assumption, there is no
inversion of the retinal area, whereas in spiders there is a complete inver-
sion of the more superficial of the two infolded layers.

It must be left to future observers to ascertain whether any of the
monomeniscous eyes of Arthropods are, as seems possible, actually formed
in the manner suggested by the condition in the Myriapods ; i. e., without
the inversion of the retinal area. Meanwhile one examines with fresh
interest the conditions hitherto described in order to ascertain, if may
be, the probable outcome of future studies.

Next in importance to the presence of two distinct cell-layers,* the
presence or absence of Graber's pre-retinal membrane will be significant.
In all cases where there is an obvious pre-retinal membrane, and when
the " vitreous " is composed of a layer of cells which abut directly (per-
pendicularly) upon it, I believe there can be little doubt that the retina
has been formed by a process of inversion. Such I think is the case in
the eyes of all the Arachnoids hitherto carefully studied.

The cases among Arachnoids which will at first sight present the
greatest obstacle to the acceptance of this view are those of the scor-
pions ; it is therefore to these that most attention will be given.

Graber has given figures and descriptions of the median eyes in scor-
pions, which have been reviewed both by Grenacher ('80, pp. 421-425)
and by Lankester and Bourne ('83, pp. 191-193). Their criticisms deal
especially with the nuclear conditions of Graber's " Eetinaschlauche."
His " parietal pigment- and matrix-zone of the retina " was not reviewed
by Grenacher, but is considered at some length by his later critics, under
the head of " Intrusive pigmentary connective tissue."

* The presence of the third or posterior layer is unquestionably of the greatest im-
portance as a test of an invagination with inversion ; but I believe that it may be so
reduced in thickness in the adult that the negative evidence of its not having been
hitlierto found in any particular case should not weigh too heavily in the interpre-
tation. I find, for example, in the case of some adults (Tegeneria, Theridium,
Thomisus) that the posterior layer is indicated only by the presence of very thin,
flattened nuclei, sometimes so densely enveloped in pigment-granules as to be
almost unrecognizable, but occurring at such regular intervals as to leave little doubt
about their real nature.

56 BULLETIN OF THE

Graber ('79, pp. 84, 85, Figg. 13, 14) found that in the median eyes
of Buthus there was left, after the action of caustic potash had made
the central portions of the sections paler, a rose-colored granular rim or
marginal zone, and that in this zone were to be seen a few, mostly in-
distinct, nuclei and markings perpendicular to the sclera, which together
might serve at first sight to suggest the presence of a tall cylindrical
epithelial sclera-matrix. This view Graber definitely puts aside, how-
ever, and concludes that the appearance is due to the oblique direction
of the section, the apparent epithelium being only the cut-ofi" (anterior)
ends of " Retinaschlauche." But inasmuch as there are no other sub-
cuticular (subscleral) structures, these " retinal sacs " have assumed, in
his opinion, notv/ithstanding their other functions, the rote of matrix-
cells.

Even without our present knowledge of the manner in which similar
eyes arise, this interpretation would be unsatisfactory, because the mar-
ginal zone is most sharply marked off from the retina in the posterior half
of the ball of the eye, and it would be difficult to imagine the course of
retinal cells which in this region could be so cut as to give rise to the
appearance figured. But I do not doubt the accuracy of the figure in
question (Graber's Fig. 14), and believe that its interpretation becomes
easy when considered iii connection with the probable origin of the re-
tina. If the median eye in Buthus was formed by an involution with
inversion of the retina, Graber's " Matrixzone " would be the posterior
layer of that infolding, and its gradually merging into the retinal layer
in the anterior half of the ball of the eye would be entirely parallel to
what occurs in the formation of the " pre-nuclear " eyes in spiders.

Lankester and Bourne ('83) have also had under consideration this
pigment- and matrix-zone of Graber, and have arrived at conclusions
which are entirely new. It will be most satisfactory to quote their own
words upon what they call " intrusive pigmentary connective tissue : "
" The structures which we consider as intrusive connective tissue in the
central eyes of the Scorpion may be compared to the interneural cells
of the lateral eyes. Like these, they are pigmentiferous, and serve
to fill up the spaces between the several nerve-end cells and between
these and the ommateal capsule. But whilst we regard the interneural
cells as ectodermal in origin, . . . we find reasons for considering the
intracapsular pigmentary connective tissue of the central eyes of Scor-
pions as derived from mesoblast, and of the nature of connective tissue.

" We have not embryological evidence for this conclusion, and depend
entirely upon the branching, inosculating character of the pigmentary

MUSEUM OF COMPARATIVE ZOOLOGY. 57

cells, and upon the analogy of the pigment -cells surrounding the reti-
nulse of the polymeniscous eyes of Insects and Crustacea, which are
very generally held to be of the nature of connective tissue, as also upon
that of the ' packing-tissue ' to be described below in the central eye of
Limulus.

" We are by no means anxious to maintain that the more epithelium-
like cells amongst what we are about to describe as ' intrusive intracap-
sular connective tissue ' may not be of distinct origin from other portions
of this pigmentiferous framework, and referable to interneural cells of
ectodermal nature ; but any such distinctions must be based upon em-
bryological facts which we do not possess. In the present state of
knowledge it seems most convenient and justifiable to hold that in the
central eyes of the Scorpions there are no interneural cells of ectodermal
origin, as there are in the lateral eyes, and that their place is taken by
intrusive connective tissue" (pp. 191, 192).

I believe the authors will agree with me that Locy has now furnished
the embryological facts which, by a fair use of reasoning from analogy,
will allow us to affirm with considerable certainty that at least their
" epithelium-like cells " (or, as they have in another place called them,
" intracapsular pavement " cells) are not intrusive, but are derived from
the ectoderm, — not, it is true, in so simple a manner as one might have
imagined by merely comparing them with the conditions (interneural cells)
which they have found in the lateral eyes. There is this fundamental
diff"erence between their conceptions and those which are now presented
to us : in their view the " intracapsular pavement " cells, even if shown
by embryology to be derived from the ectoderm, would still be essen-
tially interneural cells ; i. e., such as were originally interspersed among the
retinal cells (compare their explanation to Fig. 7). But in the present
aspect of the case that is not probable ; they are distinctly not comparable
with the interneural cells of the lateral eyes, — assuming that the latter
are " monostichous," * — but belong to an extra-retinal region of the
ectoderm.

What they are functionally, is to be inferred from their pigmented con-
dition. Their position indicates that they are, in addition, the matrix for
that portion of the basement membrane which has received the name
" sclera."

Whether the " intracapsular epithelium " represents the xohole of the
posterior layer of the infolding, is a question which is intimately con-

* Whether Lankester and Bourne are right in claiming the lateral eyes of scorpions
to be "monostichous," is quite another question, which will be discussed presently.

58 BULLETIN OF THE

nected with the author's theory of an intrusive (mesoblastic) connective
tissue.

At least three possibihties may be suggested to explain the inter-reti-
nular pigment-cells discovered by Lankester and Bourne in the central
eyes of scorpions : (1) They may be developed from indifferent hypo-
dermal cells practically in situ ; (2) they may be cells which have been
detached from the posterior layer of a retinal involution, and have grown
in between the retintd^e from behind ; or (3) they may be, as claimed
by the authors, intrusive mesodermal cells.

If the lateral eyes are really '•' monostichous," that would seem to afford
an argument in favor of the first possibility, the interneural cells of the
lateral eyes being really pigment-cells developed in situ ; and in that
case the " inter-retinular pigment-cells " of the central eyes would cor-
respond to the interneural cells of the lateral eyes.

The above-quoted arguments (pp. 56, 57) in favor of the third possi-
bility do not seem to me to outweigh the fact that it is the hypodermis
and its derivatives which have in Arthropods the greatest tendency to
the pigmented condition.

Finally, the intimate connection between the other pigmented cells
and the " intracapsular epithelium " would be favorable to the second
view, — at least I cannot regard the intrusion between the retinal ele-
ments of pigment-cells from this source (posterior layer of the involution)
as any less probable than their migration through the " ommateal cap-
sule " and the intracapsular epithelium.*

No one, however, will think of arriving at a conclusive answer lo
this question by other means tlian a careful histogenetic study of the
developing eyes of some of the scorpions.

So far, then, as regards the median (central) eyes of scorpions, they do
not present conditions sufficiently di^Terent from those of spiders to pre-
vent a similar interpretation of their parts. With the lateral eyes, how-
ever, the case is quite different. If the recent researches of Lankester

* There are otlier indications, besides that of a triplostichous condition, which
point to the probability of an involution of hypodermis as a source for all the post-
vitreous portions of the ommateum. In the scorpions, as well as in the spiders, the
emergence of the optic-nerve fibres is so eccentric (especially in Androctonus) that
one might almost venture to predict even the jilace and the direction of the invagina-
tion. (See theoretical considerati(ms, below, pp. 91, 92.)

Perhaps Metschnikoff ('71, p. 22.'J, Taf. 16, Figg. 10, 11) was very near to discover-
ing the true relation of the eyes to the hypodermis when he explained that they
appeared as thickenings of the dermal fold which forms an overgrowth over the
cephalic ganglia.

MUSEUM OF COMPARATIVE ZOOLOGY. 59

and Bourne are to be accepted, it would appear that the lateral eyes pre-
sent a much simpler type than the median eyes, — so far, at least, as
regards the relation of the retinal layer to the hypodermis, the point upon
which the interpretation essentially turns.

It is of importance in tlie consideration of this question that in neither of
their figures (Lankester and Bourne, Figs. 2, 3, 4) are the " interneural "
cells represented as reaching to the cuticular lens. They form a layer,
— uninterrupted except by the narrow nerve-fibre prolongations of the
retinal cells, — the individual elements of which are wedged in between
the posterior ends only of the cells composing the retina. Nothing in this
relation stands in the way of these interneural cells being directly com-
pared with the posterior layer of the retinal infolding in spiders' eyes.
The only serious obstacle to a direct comparison with triplostichous eyes
is the absence of a true " vitreous."

The authors afiirm with great positiveness the entire absence of the
vitreous layer. There are two considerations which make it appear to rae
possible that Graber in figuring that layer may not have been so grossly
in error as they claim. There are great differences in the thickness of the
" vitreous " in the adult eyes of different Arthropods. (Compare Gren-
acher, '79, Figg. 28 and 31.) It is possible either that a very thin layer
of cells may have been overlooked by Lankester and Bourne, or that,
after secreting the substance of the cuticular lens, the " vitreous " cells
are in the adult crowded to the margin or completely obliterated.

If, then, it should happen from any cause whatever (e. g. the extreme
thinness of the layer, or its prompt degeneration and disappearance after
secreting the lens) that the " vitreous body " had escaped the attention
of these authors, as suggested by Lowne ('84, p. 416), then one might
readily conceive that the lateral eyes of scorpions were formed on practi-
cally the same plan as the median eyes of the scorpion and the pre-
nuclear eyes of spiders. In that event the cells called by Lankester
and Bourne " interneural " Avould doubtless represent the posterior of
the infolded layers.*

Although Graber ('79, Fig. 4) has given a figure of the lateral eye
(Scorpio europa3us) which in some respects is much less satisfactory than

* If this were the case (comjiare Lankester and Bonrne, op. cit., "Explanation of
the small italics in all figures " and explanations of Figs. 7 and 8), the question
raised by the authors — ■ whether the " pignientiferous cells " (pp) witliin the retinal
capsule of the central eye were erjnivaleut to the " interneural epithelial cells" {cjq)
of the lateral eyes, or were "intracapsular (intrusive) connective tissue" — would
be answered in favor of the former of the two possibilities.

60 BULLETIN OF THE

those of Lankester and Bourne, and although he has given no definite
description of a sclera-matrix in these eyes, yet one may fairly infer
(cf. I. c, p. 77) his belief in such a matrix, and can find in his figure
(left side) indications of nuclear structures which easily admit of such an
interpretation. These (sclera-matrix 1) cells I consider to be, in any
event, the equivalent of what Lankester and Bourne have described as
" interneural epithelial cells," the nature of which, it will be observed
from their figures (Figs. 2, 3) and descriptions, differs considerably in
Euscorpius and Androctonus.

But in addition to the considerations presented by Lankester and
Bourne, there is another objection to the interpretation here proposed,
Avhich at present I am not able to explain. The direct and apparently
primitive manner in which the retinal cells are continued into the nerve
fibres seems to point to a normal rather than an inverted condition of
the retina.

In either event, tlie nature of the lateral eyes in scorpions is deserving
of further study ; and it will not be surprising if it is found that they
arise by a process of infolding accompanied by inversion of the retina.

Grenacher ('78) has given a figure of an ocellus in one of the Phalan-
gidce which indicates the presence of a distinct layer of cells (" vitreous")
in front of the retina ; and although he has not seen anything of a layer
behind the retina, these eyes present no more serious obstacle to an origin
by involution than do most of the hitherto published figures of the eyes
of spiders.

The conditions in the eyes of Myriapoda leave more room for doubt.
Graber, Grenacher, and Sograff are the only authors who have recently
given them any considerable attention.

The eyes in Myriapods — aside from Scutigera, in which they are of
a conspicuously different type — are apparently either monostichous
(Chilognatha) or so-called diplostichous (Chilopoda). The latter evi-
dently approach more nearly the conditions found in Arachnoidea, and
will be considered first.

Graber ('79, p. 59) claimed their substantial agreement with the ocelli
of the Arachnoids and Hexapods. While Greiiacher's subsequent work
has made much of Graber's description appear illusory, there are still
sonm points in which it is probable that Graber has given reliable presen-
tations of the histological structure. There is, at least, one thing in
which T believe his observations deserving of more attention than they

MUSEUM OF COMPAKATIVE ZOOLOGY. 61

have hitherto received. He has especially defended the cuticular inter-
pretation of the " sclera," and in connection therewith has urged the ex-
istence of a cuticular matrix. The nuclei of this matrix he has very
distinctly, and I am inclined to think very truthfully, figured (Fig. 18, k)
and described (pp. 64, 84) for Scolopendra. Even Grenacher ('80, p. 441)
has granted a conditional assent to their presence, although maintaining
that he did not feel entirely convinced.*

To anticipate a conclusion, the grounds of which will be presented
later, — in connection with a discussion of the nature of the pre-retinal
membrane, — I may say here that the existence of a distinct cell-layer
posterior to the retina, and inside the cuticular " sclera," appears to me a
strong argument in ftivor of the view that the retina in the Scolopendridse
has been formed by an involution with inversion. If Graber had realized
the probable identity of these posterior cell-layers in Myriapods and
scorpions, it is possible he might have been saved the expression of his
sixth conclusion : " The ends of the retinal sacs [cells] appear to form,
at least in part, the matrix of the sclera."

There is a very palpable difference between the figures of the " vitre-
ous" by Graber, and the figures and descriptions by Grenacher ('80,
p. 434) ; nor is there any room to doubt that Grenadier's work is, in
most particulars, incomparably the more satisfactory and reliable. But
Grenacher finds, if not a layer of uniformly fashioned cells, at least in
some individuals of one species (Branchiostoma) a vitreous composed
of an uninterrupted layer of cells, which differ from the vitreous cells
of spiders, for example, only in the more central position of their nuclei,
and the inclination of their axes towards (deep ends away from) the axis
of the eye. This exceptional condition of the vitreous — found only in
a few individuals — Grenacher brings into relation with the fact that the
lens in these cases Avas only partially developed, and deduces the con-
clusion that these animals had recently suffered a moulting, and that the
increased thickness of the hypodermis and vitreous is simply evidence of
increased functional activity. He recognizes the difficulty in the way of

* According to Grenacher ('80, Fig. 8) the pigment-cells which invest the eye
have the character of a continuous epithelium such as the posterior layer of the re-
tinal infolding in spiders does at an early stage ; but their relation to the thick strati-
fied cuticula (viz. outside the latter) forbids a comparison. If Grenacher's account is
correct, the ilyriapods stand quite alone in having such a continuous mesodernuc
investment of the eyes.

Compare also Sograff ('80), PI. Ill, fig. 17, where a nearly continuous layer of
cells is represented outside the thick cuticula of the eye, but inside only isolated
nuclei scattered among the nerve-fibres which occupy the space between the cuti-
cula and the basal ends of the retinal cells.

62 BULLETIN OF THE

reconciling this condition of affairs with the tj'^pical one-layer condition
of the ommateum ; he seems to consider it, however, as only a phase in
the process of formation, which is insufficient to decide whether the eye
is to be regarded as a one-layer or a two-layer structure ; for he says :
" Which of these two conditions, which are alternately realized in the
various phases of the life of the individual, shall we assume as the pri-
mary, in order to refer to it the other condition (a thing which presents
in itself no difficulty) 1 Here, I believe, the observation of the first rudi-
ment of the development can alone give a reliable answer; I at least feel
incapable of deciding solely upon the hitherto accumulated facts."

It might have been unwise for Grenadier, and it may be even now
rash for one to hazard a conjecture as to which was the primary condi-
tion ; but in view of what is now known about spiders' eyes, I think the
evidence favors the conclusion that the exceptional cases present the
more primitive condition. One or the other of two things is likely to
have taken place, — either the retina was formed by an involution which
allowed the " vitreous " to be from the first a continuous laell-area, or the
retina resulted from a depression of the hypodermis, followed by a ring-
like ingrowth of vitreous cells from the margins of tlie depression. The
obliquity of the axes of the vitreous cells, as seen in the finished eye,
might suggest the probability of simple ingrowth ; but in these excep-
tional growing eyes, the continuity of the layer, its nearly uniform thick-
ness, and the very slight oliquity of the central cells, while not absolutely
incompatible with such an origin, appear to me more favorable to the
supposition of a primitively uninterrupted vitreous layer. There is still
a wide difference between the one-layer condition figured by Grenadier
for Dytiscus larvae, and the completed eye of Scolopendra. If, as seems
probable, Grenacher is right in supposing the exceptional individuals of
Branchiostoma to have been engaged at the time of capture in the con-
struction of lenses, the lateral displacement of the vitreous cells had
probably only just begun; but even when completed, the "vitreous"
and retina still continue to form two essentially distinct cell-layers.

Graber has claimed the existence of a pre-retinal membrane in Myria-
pods; but Grenacher asserts that he assigned to it an impossible position.
It is true Grabor has not carefully described, nor very precisely repre-
sented it ; but I fail to understand how it was possible fur Grenadier to
speak of it as located in an impossible place. However inaccurately
Graber may have described the cell-layers which constitute " vitreous "
and retina, they certainly are in contact, even according to Grenadier's
own description ; and it is along this region of contact that I understand
Graber to have located the pre-retinal membrane. Even Grenacher's

MUSEUM OF COMPARATIVE ZOOLOGY. 63

own figures [l. c, Taf. XX, Figg. 2-4) seem to me favorable to the presence
of a cuticular partition between the two cell-layers under consideration.

If there are some features of the eye in Chilopoda which seem to favor
a method of formation similar to that traced in spiders, there are almost
none in the case of the Chilognatha, provided the figures by Graber are
to be superseded by the account given by Grenadier. Neither Graber
nor Grenacher has figured anything that could be compared to the pos-
terior layer of a retinal involution ; and Grenacher denies, in addition,
the existence of a "vitreous." In brief, according to the latter author,
the whole eye is composed of a single continuous layer of cells formed
into a cup-like depression ; all, except the cells at the margin of the cup,
are bacilli-producing elements. "Whether all the cells of the depressed
region, or only the marginal ones, are engaged in the production of the
lens, the author does not suggest. Apparently, the only chance of there
having been a distinct " vitreous " in this case, would rest upon the pos-
sibility that these marginal cells at first meet in front of the retina, and
afterwards suffer a complete centrifugal displacement ; but of this there
is as yet no direct evidence.

The apparent improbability of an involution with inversion in the case
of the Chilognatha is not without weight in considering the nature of the
eyes in Chilopoda, since the arrangement of the retinal cells is so strik-
ingly similar in the two groups as to render a fundamental difference
between them highly improbable. Further, the almost strictly sym-
metrical (radial) arrangement of the parts in all Myriapoda stands in
contrast to a very common obliquity in the eyes of spiders. So, not-
withstanding the several arguments which I have presented in the case
of the Scolopendridse favorable to an involution with inversion, I am not
entirely certain that such has reall.y taken place. While the evidence
strongly inclines me to a belief in a process of inversion for Chilopoda, I
agree with Grenacher that nothing short of a study of the development
of the eyes is likely to afford an absolutely satisfactory answer.

I am not able to read Sograff's paper ('80), published in Russian ; but
in his preliminary paper ('79) he does not seem to have recognized any
difference between the structure of the eyes of coleopterous larvae and of
spiders.*

In the case of Hexapoda the simple eyes of the larvfe and the ocelli
of the adult are sufficiently different to require separate consider-

* "The eyes of the Lithobidae and Scolopendridfe are exactly like the eyes of the
larvfe of Acilius and other Coleoptera, as well as those of the spiders " (Sograff, '79,
p. 17).

64 BULLETIN OF THE

ation.* There are no satisfactory observations on the course of events
during development in either of these cases.

The simple eyes of the larvce of Dytiscus and Acilius have figured as
types of the one-layer condition since the time of Grenadier's masterly
work ; and indeed there seems at first sight little or no opportunity for
any other interpretation, even though Graber ('80) at first suggested, and
then (in a footnote, I. c, p. 67) definitely claimed the existence of a
pre-retinal membrane in the case of Dytiscus. But the direct and evi-
dent continuity of the " vitreous " cells with the retinal cells, especially
the uniformity in the positions of the nuclei in the two regions, makes
an inversion of the retinal layer extremely improbable. Even in the
larger dorsal eyes of Acilius, where there is a perceptible difference in
the size of the nuclei in the " vitreous " and the retina, the continuity
appears from Grenacher's figure (/. c. Fig. 4) absolutely uninterrupted.
There is a striking similarity between this eye and the anterior median
eye of Salticus ; but the presence of (even a few) nuclei just in front of
the anterior face of the retina in the latter case (compare Grenacher, '79,
Fig. 28) is sufficient evidence of an interruption in the continuity be-
tween " vitreous " and retina in Salticus, and makes a substantial differ-
ence between the two at least possible. However improbable a like
interruption in the continuity of these cell-layers may be in Acilius, it
is not to be overlooked that a complete separation of retina from
" vitreous " even here could easily have been followed by conditions
like those figured by Grenacher ; for to accomplish this it would only
have required a subsequent displacement of the basal ends of the " vit-
reous " cells containing pre-retinal nuclei to the margin of the pigmented
cylinder. That such a displacement — accompanied, perhaps, with
partial obliteration — has really taken place in the case of Salticus,
seems probable from the paucity of the pre-retinal nuclei figured,t and
their entire absence from the funnel-shaped depression in the middle
of the retina.

Finally, in iheventral eye of Acilius figured by Grenacher ('79, Fig. 10),
the appearance of the vitreous is certainly not more favorable to a mono-
stichous than to a so-called diplostichous condition. While in the dorsal
eyes the basal (nucleated) ends of the vitreous cells abut upon the peri-
phery of the cylindrical ocular mass, in the ventral eyes they appear to
end directlj'' in front of the retina, to the surface of which they are
almost perpendicular. They consequently appear in the figure to form

* Tlie "compound ocelli " are not so directly comparable with the types of eyes
witli which the present paper is concerned.

t I can confirm the fact from my own observations.

MUSEUM OF COMPAKATIVE ZOOLOGY. 65

a continuous cell-layer in front of and concentric with the retina. The
critical region — where the pigmented hypodermis passes into the layers
behind the lens — is not satisfactorily portrayed in the figure. On one
side (the right) the hypodermis seems to be directly continuous with the
retinal layer ; upon tlie other side it is continuous with the layer form-
ing the vitreous body, the retina being on this side more detached from
it. Not finding nuclei in the vitreous layer, Grenacher admits that they
may have entirely disappeared ; but he is more inclined to the opinion
that they are grouped with nuclei of the ring-shaped pigmented zone at
the anterior border of the retina, — where the nuclei are too numerous
to be supposed to belong exclusively to the pigment zone, — and that
the finely attenuated posterior ends of the cells, bent outward towards
the nuclei, escaped direct observation.

If the nuclei of the " vitreous " have completely disappeared, it is diffi-
cult to see how this could be regarded as a monostichous eye. There is
nothing, it is true, in the second assumption which precludes the idea
that the ommateum consists of a single layer of cells ; but it is equally
clear that it does not preclude the possibility that the nuclei of the
" vitreous " have been displaced towards the margin of the lens ; and this
would be compatible with a true involution of the retinal cells. I think
that such a displacement of the nuclei from the central portion of the
" vitreous " — in a manner analogous to that which Grenacher believes to
have taken place with the retinal nuclei in the case of Salticus (Grenacher,
'79, Fig. 25 K) — is more probable than either their total disappearance
or their having primitively held a marginal position.

In all these cases there is the opposing argument that no third layer of
cells was discovered.

The ocelli of the imagines also seem from previous descriptions to be
destitute of a third layer, — at least no one, so far as I am aware, has
claimed it. From one of Grenacher's figures (that of Crabro, I. c, Fig. 34)
I infer that a third layer may nevertheless exist as a thin sheet of cells,
forming, as in spiders, the matrix of the so-called sclera.*

The only observations on the development of the simple ocelli of the
imago are those of Carriere already alluded to. They are too incomplete
to serve as a safe guide. I am, moreover, persuaded, from the examina-

* Grenacher (79, p. 60) speaks of the nuclei as belonging to this fine cuticula, and
in the copy of his paper whicli I have, the (bhie) nuclei lie on the inner side of the
cuticula. Since the "registering" appears to be very accurate for the "vitreous"
cells, I have no doubt that tlie nuclei of the sclera are printed as Grenacher intended,
although no mention of their position in relation to the c'uticular membrane
("sclera") occurs in the text.

VOL. XIII. — NO. 3. 6

66 BULLETIN OF THE

tion of some of the early stages in the formation of the ocelli of Vespa,
which Mr. F. A. Houghton is investigating, that a process of involution
takes place ; and I believe that here also it will be shown that there is an
inversion of the retinal area.*

If the presence of a distinct and continuous layer of " vitreous " cells in
front of the retina possesses any weight in favor of an involution after the
type of spiders' -eyes, then the simple ocelli of adult Hexapods are likely
to have followed the same plan of development as the eyes of Arachnoids.
That the cells of the vitreous layer are usually so flat and thin that they
have sometimes been overlooked, does not in the least diminish their im-
portance as an index to the manner in which the retina was produced.
Indeed Carri^re ('85, p. 178) has shown conclusively that the cells com-
posing the thin layer which represents the " vitreous " in the completed eye
of Vespa, are much reduced in size as compared with their condition dur-
ing the formation of the lens. The figure which he has given (Fig. 142)
of the eye of the wasp during this stage is very instructive, for it shows
that, however obvious the continuity of hypodermis and retina may ap-
pear in the finished state of the eye (compare Grenadier, '79, Fig. 31),
they are separated during this earlier condition by a wide interval, and
that consequently the supposed continuity can have no such importance
as might otherwise be attributed to it. Although Grenadier has not fig-
ured anytliing which may be fairly taken to represent Graber's pre-retinal
membrane, it is evident from Carriere's figure of the earlier condition that
retina and "vitreous" are sharply separated by a line which seems to be a
continuation of the inner cuticula of the hypodermis, much as in the eyes
of spiders ; and Grenacher himself, criticising Leydig's views, has insisted
upon the sharp separation of the two cell-layers.

* Since the above was written, Carriere ('86) has published an article in the
Zoolog. Anzeiger (Jahrg. 9, no. 217, pp. 141-147), in which he has reverted to the
histological conditions of the ocelli in the Diptera and Orthoptera ; but he has not
given any further evidence concerning their development.

Postscript. — Under date of June 1, Prof. Carriere writes me that he has arrived
(independently) at the conclusion that the ocelli in Hymenoptera and Diptera are
formed by a process of involution, but that the infolded region does not become
detached from the hypodermis.

It is possible that this difference of opinion is more formal than real, since there
is probably no period in the formation of the ocellus, after the earliest stages of
involution, during which the involuted portion is not in contact with the hypodermis
in the region of the "vitreous ;" but the ultimate intervention of the pre-retinal
membrane is to me sufHcient evidence of an interruption in the original continuity
of the cell-layers. That is all I should wish to claim by saying the infolded portion
of the hypodermis became " detached " from the permanent hypodermis.

MUSEUM OF COMPARATIVE ZOOLOG\. 67

I have referred especially to the ocelli of Hymenoptera because of the
evidence of a third layer, and the certainty of there being a " vitreous "
which undergoes a great reduction during the development of the eye.
Even if a " vitreous " should in some instances appear to be wanting in
the adult, the condition could be fairly explained as a result of ultimate
atrophy. The evidence for the existence of a third layer is in most cases
still wanting. "When Grenadier (79, p. 57) claimed a substantial agree-
ment in the morphology of the ocelli of insects and the eyes of spiders,
he based his conclusion on the presence of two distinct cell-layers, — a
vitreous and retina. With the present knowledge of the development in
the case of spiders, it again becomes an open question whether the mor-
phological change in insects follows the same fundamental plan. It "S not
impossible that there are among insects two methods of development for
the ocelli, — one with, the other without, retinal inversion. A conspicu-
ously reduced " vitreous," and the probable existence of a distinct post-
retinal layer of cells in Hymenoptera, inclines me to the opinion that in
some cases, at least, there is an inversion.

One of the questions which is most intimately connected with that of
the origin of the retina concerns the nature and significance of the pre-
retinal membrane. In connection with this I shall consider the inner
cuticala or basement-membrane of the hypodermis and the " sclera."

Graber ('79, pp.64-67) was the first to call attention to the existence of
a homogeneous cuticula-like membrane (" prseretinale Zwischenlamelle ")
between the " vitreous body " and the retina, and, as we have seen, to lay
stress upon its existence as an argument against Grenadier's supposition
that the retina was derived from the hypodermis. The question in his
mind turned upon the direct cordinuity of the hypodermis (pigment) cells
with the cell-layer forming the retina. Such a continuity being precluded
by the presence of his pre-retinal membrane, the inference of a hypoder-
mal origin for the retina became for him untenable.

Grenacher subsequently ('80, pp. 429, 430) conceded the existence of
such a structure in the case of scorpions and spiders, but was unwilling
to follow Graber in his generalization that all " Stemmata " possess this
membrane. Unable to disprove Graber's claims in the case of Dytiscus by
a re-examination of the subject, he was still unwilling to give them any
weight, because Graber " claimed with equal certainty the existence of
such a cuticular membrane for Myriapods, but assigned to it an entirely
impossible location." But the problem of reconciling a pre-retinal mem-
brane with the supposed hypodermal origin of the retina, was not attempted
by Grenacher.

68 BULLETIN OF THE

While the existence of a pre-retinal membrane, as claimed by Graber,
is corroborated for eyes of the " pre-nuclear " type, and its presence made
readily comprehensible by the observations of Locy, the conclusions drawn
by Graber from this anatomical fact have received the reverse of con-
firmation. Whether eyes of the post-nuclear type exhibit this membrane,
is not so easily determined ; but the question will be considered in a
subsequent part of the present paper.

Lankester and Bourne ('83, p. 182) apply the name " ommateal cap-
sule " to that portion of the " basement-membrane " (inner cuticula) which
lies in the region of the ommateum * of the lateral eyes of scorpions, and
then extend the use of the term | to " diplostichous " eyes, so as to cover
what has been called by the earlier writers "sclera." Denying the existence
of the separate " vitreous " claimed by Graber for the lateral eyes, they
of course find in these eyes nothing equivalent to Graber's pre-retinal
membrane. In the central eyes, however, it exists as " a strong lami-
nated membrane," forming a septum which divides the vitreous body
from the rest of the ommateum. The ommateal capsule, of which the sep-
tum, they say, forms a part, is " finely laminated and devoid of nuclei."

The " ommateal capsule " in the lateral eyes of Limulus (I. c, p. 203),
" whilst well marked in every other region, is deficient immediately below
the retinula, where the group of optic-nerve filaments passes out of or into
the capsule." The authors regard this deficiency of the capsule as related
to the intrusion of connective tissue into the eye ; for it is around the
optic nerve that the intrusion appears to take place.

In the central eyes of Limulus they " could not define an ommateal
capsule," the intrusive connective tissue being much more abundant than
in the lateral eyes ; but a vitreous body composed of short cells is sepa-
rated from the retinal body behind it by " firm membrane," not very
clearly indicated in their figures, but apparently continuous with the
basement-membrane of the hypodermis.

It seems to me possible that the great difficulties attending the investi-
gation of these eyes account for the fact that the authors have not dis-
covered a post-retinal capsule.

* Compare the quotation in the footnote, p. 50.

t However appropriate this terminology may be for monostichous eyes, it evi-
dently is not sufficiently distinctive in the case of " diplostichous " eyes. It would
doubtless be better to adopt a terminology which should express the topographical
relation of the basement-membrane to the retina. The wJiole capsule might then be
called the ^^ retinal capsule." In diplostichous eyes the "sclera" could then be
called the peri-retinal (or better, perhaps, the post-retinal) membrane, in contradis-
tinction to the remaining portion, already appropriately named by Graber " pre-
retinal membrane."

MUSEUM OF COMPARATIVE ZOOLOGY. 69

The views held by Schimkewitsch ('84, pp. 8, 9, 12) are widely at
variance with those of all tlie other writers. He is without doubt right
in bringing the " inner cuticula," the so-called "sclera," and the pre-retihal
membrane into a single category ; but misled, as I think, by appearances
of the sclera that can readily be explained in another manner, he has
concluded that all these structures are cellular.*

Schimkewitsch finds that at the point of insertion of the dorso-ventral
muscles of the abdomen this " inner cuticula " is continuous with the
sarcolemma of the muscular bundles. Reasoning from Froriep's ('78)
conclusion that the sarcolemma of the striate muscles in vertebrates is to
be. regarded as connective tissue, he maintains that this internal cuticula
in Arthropods must also be regarded as a connective [-tissue] formation.
He reaffirms the fact stated by Graber ; viz., that this same cuticula is
prolonged in the form of a pre-retinal layer, and that it merges with the
envelope of the eye ("sclera"), — "although it tends to prove the chiti-
nous nature of this envelope ; hut,'" he adds, " nuclei are readily visible in
its thickness.'''' f Finally, in Lycosa saccata during development there
lies beneath the integument, directly under the chitinogeuous layer and
outside the future subcutaneous muscular layer, a series of very flat
cells ; and they represent, so he claims, the future " internal cuticula " of
Graber.

Neither the nuclei in the thickness of the internal cuticula, nor the
conditions observed in the development of Lycosa, are figured, so that it
would be very difficult to judge of the value of Schimkewitsch's conclu-
sions, were it not that he has figured the same conditions, which recur
in the envelope of the eye (sclera). " I have already shown," he says

* MacLeod ('80, pp. 31-34), it is true, has urged a similar proposition respecting
the so-called membrana externa, or m. propria of the tracheal tubes, as well as the
basement-membrane of the integument ; but his conclusion is based upon theoretical
considerations rather than upon satisfactory direct evidence. Until the demonstra-
tion in this membrane of nuclei distinct from those of the epithelial cells (chiti-
nogenous matrix) is possible, the question cannot be considered as settled in favor of
the connective-tissue nature of the membrana propria of the integument.

Grenacher ('80, p. 26) has also spoken incidentally of the fact that the thin, inner
cuticula of the hypodermal cells in the larv* of Dytiscus are " stellenweise kerntra-
gende ;" but I do not understand that he directly commits himself to' the opinion
that these nuclei belong to cells which have served as the matrix of what he calls
*' Cuticula," much less to the opinion that this membrane is a cellular structure.

t " La meme cuticule interne se prolonge en forme de lame preretinenne dans les
yeux et se confond avec I'enveloppe de I'ceil, comme I'a demontre Graber, et je puis
afifirmer le fait, bien qu'il tende h. prouver la nature chitineuse de cette enveloppe ;
mais des noyaux dans son epaisseur sont bien visibles" (p. 9).

70 BULLETIN OF THE

(p. 12), "that Graber's cuticula ought to be considered as a connective
[-tissue] layer, and in the envelope of the eyes I have been able to estab-
lish oval nuclei (PI. II, Fig. 4, nrk) ; and I claim that the pre-retinal layer,
which is merged with these membranes, is also of connective nature."

The conditions of the eye-envelope are somewhat difierently repre-
sented in each of Schimkewitsch's three figures illustrating its cellular
composition. In one figure (Fig. 4, PI. II) the nuclei appear to lie on
the outer surface of the homogeneous membrane; in another (PI. Ill,
Fig. 4) they are distinctly on the inner surface ; while in the third (PI.
Ill, Fig. 11) they are less definitely related to the membrane, a portion
of the nuclei appearing simply as thickenings in it. Figure 4, PL III,
is evidently drawn to the largest scale, and also, I believe, represents
more truthfully than the others the relations of the nuclei to the mem-
brane ; they are simply tangent to the inner surface of the double-contoured
membrane. I believe they are without the least doiibt the nuclei of the cells
which constitute the posterior of the two layers resulting from the involution
of the hypodermis to form the retina.

"With this explanation of the nuclei supposed to lie in the " sclera,"
the theory of the connective-tissue nature of the " internal cuticula " is
deprived of an apparently valuable support, and now seems to rest on
quite as unsatisfactory evidence as ever before.

Lowne ('84, p. 415) believes that "the columnar cells immediately be-
neath the cornea (Grenacher's vitreous) represent the dioptron." " They
are separated from the retina by a fibrous membrane which apparently
corresponds to the membrana basilaris of tlie compound eye." This
basilar membrane the author has previously defined as a cuticular struct-
ure. But it is evident from the context that the author rests his conclu-
sions on the peculiar fibrous pre-baciUar layer which is found in Salticus,
and which Grenacher ('78, p. 51) considered to be composed of fibres
from the anterior ends of the retinal cells. Lowne, it is true, denies the
direct connection (claimed by Grenacher) of these fibres with the marginal
ring of nuclei ; and adds : " In some of these sections the fibrous mem-
brane has completely separated from the bacilla, just as the membrana
basilaris separates from the retina in the compound eye." It should be
remembered, however, that Grenacher also found nuclei in this fibrous
layer, and that Lowne's statement in no way affects the validity of that
observation,* nor does he (Lowne) attempt any explanation of the fact.

* From the examination of sections of the eyes of an adult Salticus made by Mr.
Locy, and of those of Theiidium tepiilariorum, C. Koch, by Mr. G. H. Parker, I am
able to confirm Grenacher's observation.

MUSEUM or COMPARATIVE ZOOLOGY. 71

I think it is sufficiently evident that this " fihrous membrane " in Salticus
cannot be considered the morphological equivalent of the pre-retinal mem-
brane originally described by Graber ; for if it were, it would be the only
known case in which the pre-retinal membrane was composed of inter-
laciyig fibres (compare Greuacher, '78, Figs. 25, 27), to say nothing of the
occasional presence of nuclei within it. Hence, while I agree with the
implied conclusion of Lowne that the vitreous layer and the retina are
separated by a cuticular structure, I regard his reasons as altogether
uncritical, and such as would lead, if logically pursued, to an entirely
different conclusion.

Carri^re ('85, p. 187), considering it probable that the two layers of the
monostichous eyes have originated by a process of delamination, as in the
compound eyes, finds it in no way remarkable — even though the sepa-
ration is much more distinct than in the latter case — that the outer
layer of the monostichous eye (a genuine epithelium) develops a " Basal-
membran " after the manner of the ordinary epithelium of Arthropods.
" But this membrane not only separates, it also joins the upper with the
lower layer ; at least I have never met a case in which the two layers
had become separated from each other." Although not precisely stated,
there can be no doubt that Carriere regards his " Basalmembran " as the
equivalent of Graber's pre-retinal membrane, and as a cuticular structure.

Locy's observations and the conclusions Avhich directly result from
them not only place the retina in a more satisfactory relation to the hypo-
dermis, but also afford at the same time a fair explanation of the condi-
tion and mutual relations of sclera, pre-retinal membrane, and the internal
cuticula of the hypodermis. It now becomes probable — unless in spe-
cial cases the reverse is proved by direct observation — in all those
instances where a pre-retinal membrane is demonstrable in the adult
" stemma," first, that the retina has been produced by an involution of
the ectoderm (hypodermis), which has inverted the more superficial of the
two infolded cell-layers ; and consequently, secondly, that the eye is not
simply two-layered, as supposed by Grenacher as well as all subsequent
observers, but is really three-layered {triplostichous).

In the light of this process of involution the deep cuticular layer
(" Birmen- Cuticula,^' Graber) appears in readily appreciable relations.
Whether as an " inner cuticula " to the permanent hypodermis and the
pigment-cells, as the so-called sclera which invests the retinal bulb, or as
a pre-retinal membrane, it is really one and the same thing. These three
structures have a like origin, — they are the continuous product of the
basal ends of ectoderm cells ; and the pre-retinal membrane alone requires

72 BULLETIN OF THE

the further modifying statement that it may be double, whereas the oth-
ers are the result of the activity of only a single layer of cells. Grabers'
conception of the " Zwischenlamelle " — as a direct prolongation of the
iutegumental " Binnen-Cuticula," from which the sclera proper branches
off on the inner or deep side towards the nervus opticus — is to be so far
amended as to make both sclera and cuticula to branch from the " Zwi-
schenlamelle," rather than the sclera and " Zwischenlamelle " to branch
from the cuticula. Either conception is to that extent faulty that there
is no such thing as a branching off or a splitting, but quite the contrary,
— a fusion. It is possible that some of the lines seen by Graber within
the " Zwischenlamelle " (and explained by him as the result of the ordi-
nary stratification of cuticular membranes) are indications of the plane
along which the fusion between the component layers of this pre-retinal
membrane took place.

The brilliancy of the eyes of many spiders, to which Duges ('36,
p. 177) was the first to call attention, was investigated by Leydig, but it
has received little or no attention from recent writers.

Leydig ('55, p. 439 ; '57, p. 254 ; '64, p. 48) describes the structure
which is the cause of this brilliancy as a tapetum, M'hich is either con-
tinuous, lining completely the fundus of the eye, or, in some species
(Clubonia claustraria, Hahn, and Theridium sp. ?), interrupted by a band
of black pigment which traverses its middle in wavy lines.*

In Phalangium the tapetum is not continuous, but consists of isolated
scales ("Flitterchen"). In still other cases (Lycosa saccata, and several
species of Epeira) it forms a narrow band at the anterior rim of the eye-
pigment, but becomes visible (as radial streaks lodged in the dark pigment)
only after the eyes are dissected out. The tapetum usually consists of
scales of the same kind as those which are met with in the tapetum of the
fish's eye. They are minute, iridescent plates, which lie close together,
and are separable only when subjected to strong pressure. In other
cases (Phalangium, Micryphantes) the tapetum is composed of spherules
larger than the pigment-granules.

Graber's ('79) account of the tapetum in Tegenaria domestica
(" Scheitelauge") is limited to the description of his Figs. 27 and 30.
In the former, the " bliiulich griin schimmerndes Tapetum" is repre-
sented as composed of numerous minute plates, forming a stratum on
both sides of the pre-retinal memhrane (!), the long axes of most of the

* In Clubonia claustraria this Mack wavy line corresponds, according to Leydig,
with the major axis of the oval eye.

MUSEUM OF COMPARATIVE ZOOLOGY. 73

plates being perpendicular (!) to the membrane. In Fig. 30 the "kry-
stalloide Plattchen " of the tapetum appear as irregular, angular, more or
less lozenge-shaped bodies, composed of a granular central mass and a
broad rim of uniform thickness, in the substance of which is located the
pigment which gives the "Plattchen" their peculiar color.

Graber has apparently fallen into an error both as regards the location
and the direction of the elements which compose the tapetal layer. It is
not likely that the tapetum in Tegenaria differs so fundamentally from
that of Agelena. It is probable that Graber has mistaken the posterior
ends of the retinal cells for the corresponding ends of the so-called
vitreous cells.*

Grenacher ('79, p. 55) omitted a consideration of the tapetum for two
reasons, — because (1) it presents nothii^g of importance for the compre-
hension of the simple eyes and their relation to the compound eyes ; and
(2) the method of examination would of necessity have been different,
since the employment of nitric acid to depigment the eye destroys the
tapetum in a very short time, without leaving a trace of it.

Without entering into a discussion of tlie nature of the tapetum, or its
prevalence in the eyes of spiders, I wish to call attention to a few facts
"vj'hich appear to me of deep interest, and possibly of fundamental impor-
tance, in any attempt to appreciate the morphological bearings and the
functional capabilities of such eyes.

No one, I believe, has hitherto called attention to the distribution of
tapeti further than to indicate, as Leydig has done, that certain spiders
do, and others do not, possess this structure. My examinations have not
been sufficiently numerous to allow a very trustworthy conclusion to be
drawn from them ; but I have been impressed by the fact that, in the
few cases examined, the tapetum, when present, was limited to the lat-
eral anterior and to the posterior eyes ; that the anterior median pair
does not possess such a layer. When it is remembered that a division
of the eyes into two groups is necessitated by the different types of
bacillar development,t and that, so far as at present observed, the groups

* Postscript. — An examination of sections of the posterior median eyes (Scheitelau-
gen) of Tegenaria dpmestica, which Mr. Parker made at my suggestion soon after his
return to Cambridge in August, has confirmed my opinion that this species does not
differ essentially from Agelena in the position of the tapetum. It is certain that
it lies beneath the retinal layer, and is in no sense adjacent to the pre-retinal
membrane.

+ For convenience of reference I shall call the group embracing only the anterior
median pair in Agelena the group with pre-nuclear bacilli, or, briefly, pre-nuclear
group (Graber's post-bacillar); the remaining six eyes in Agelena will then consti-

74 BULLETIN OF THE

founded on the position of the bacilli, and those based on the presence
or absence of a tapetum, correspond,* one can hardly avoid the cotivic-
tion that these two features are in some way connected, and that the
dimorphism first pointed out by Grenacher is emphasized in other matters
than those to which his attention was directed.

The origin of the tapetum and the exact method of its formation are
not yet sufi&ciently clear to me ; but I hope to be able before long to
acquire more information upon the obscure points. In connection with
the development of the eyes of the "post-nuclear" group, Locy ('86,
p. 89) has mentioned a structure which separates the two layers of the
retinal infolding, and he has described it as a " much-folded chitinous
layer, probably homologous with the cuticular covering of the body, with
which, in the earlier stages, it appears to be continuous."

After renewed examinations of his preparations, and others of a simi-
lar nature from other spiders, I have arrived at the conclusion that this
layer is without any doubt the tapetum, and that there is no certainty of
its having been at first continuous with the external cuticula of the body.
As understood by Locy, it was a natural inference, with regard to its
formation, that it resulted, like the cuticula, from the secretive activity
of the ends of the cells composing one or both the layers of the retinal
infolding. This view seems at first to receive confirmation from the
early appearance of the tapetum, its apparent continuity (in many cases)
with the external cuticula, its greenish-yellow color, and the peculiar
shape of the separate elements which ultimately make up this layer. I
find also that in Theridium f it is composed of tolerably regular, elon-
gated, hexagonal plates (PL III, Fig. 17), neatly fitting edge to edge (as
though secreted by a pavement-epithelium) ; and in one instance I have
noticed distinct perpendicular markings in some of the scale-like plates
when seen edgewise. If the plates were really comparable with the
cuticula, these markings might be the equivalents of " pore canals." I
should add, however, that they were so strong as to suggest rather the
composition of the plates out of numerous perpendicular rods of uniform
size.

But notwithstanding all this, the tapetum may be the result of a cell-

tute the post-nuclear (Graber's pre-bacillar) group. If the relation suggested above
should be realized, " pre-nuclear " eyes might with equal propriety be designated as
non-tapetal, and "post-nuclear" as tapetal.

* In Thomisus vulgaris, Hentz, I have not been able to find any evidence of the
existence of a tapetum either upon sagittal or transverse sections. However, the
only sections at my disposal are such as have not been depigmented.

t Theridium tepidarioruin, C. Koch.

MUSEUM OF COMPAKA.TIVE ZOOLOGY. 75

metamorphosis rather than a simple secretion. Of one thing, at least, I
am convinced, — the tapetum owes its origin to a limited number of cells,
the nuclei of which become very much elongated during the process of
involution. How this takes place can best be shown in connection with
a general account of the changes accompanying the formation of the eyes
which possess a tapetum.

The hypodermal infolding in the eyes of the "post-nuclear" group was
not studied in detail by Locy ; it appears to be considerably more com-
plicated than in the case of the anterior median pair. This I have been
able to make out from the specimens which Mr. Locy has kindly placed
at my disposal.* Most of the figures on the accompanying plates are
intended to illustrate these co]iditions. The first seven figures (PI. I)
present the median faces of successive sagittal sections from the left half
of the head of an individual about four days after hatching. The first
section is the one nearest the median plane. The directions of the in-
foldings are such that sagittal sections are more favorable for the study
of the posterior median and anterior lateral eyes than for the posterior
lateral. The nature of the infolding-process is most readily understood
by the aid of sagittal sections of the posterior median eye ; and hence I
begin the description with that eye.

Of all the sections studied, those which are represented in Figures
8 and 9 (PI. I) are in some respects the most satisfactory, hut in other
respects they are possibly misleading. There is a considerable thickening
of the hypodermis in two regions, and these two thickened tracts appear
to be connected by a continuous row of nuclei (tap.) so arranged as to
suggest that an S-shaped folding of the hypodermis has taken place. The
principal difference between this condition and that described by Locy
appears at first sight to be due to the relative thickness of the three com-
ponents of the ** S." In the anterior median eye the middle part is from
the beginning the thickest ; in the present case it is the thinnest. In one

* This paper was begun in the belief that there was no important difference
in the method by which the pre-bacillar and the post-bacillar types of ocelli are de-
veloped. After a large portion of the paper was already written, the author received
(March, 1886) from Mr! Locy for re-examination the preparations which had served
as the basis of his paper. The results of the re-investigation of his material, al-
though not sufficiently complete to form an entirely satisfactory presentation of the
subject, are incorporated here because they are deemed of importance, and because to
have waited until the questions to which they give rise could have been more ex-
haustively studied would have necessitated both an extension of the paper beyond
the original plan and an undesirable delay in its publication.

76 BULLETIN OF THE

of these figures, however (Fig. 9), there is some evidence that the row of
nuclei {tap.) is not single, but double, and that it is the result of an out-
folding of cells [tap.) lying between the regions pr. and r. This conclu-
sion is strengthened by the condition of the anterior lateral eye as shown
in Fig. 4, tap. It is almost certain, from the shape and direction of the
nuclei, that the equivalent region in this case is a fold, open helow. If
this middle region really represents a double rather than a single layer
of hypodermal cells, then the S-shaped appearance is deceptive ; and one
must suppose that half of the fold has become merged in one of the
thickenings (or otherwise obscured), while the other half remains as the
only apparent means of connection between the two thickenings. It is
further evident that this ow^folded middle region must be in the nature
of a re-entrant fold from the apex * of an original evolution, of which
the two thickenings constitute the walls.

The condition and connections of this middle region are of great im-
portance in deciding upon the morphological relations of the retina, and
it is therefore to be regretted that the evidence as to its real nature is not
more conclusive.

In the tract nearest the anterior median eye (Fig. 8, jo r.) the thickening
results simply from a displacement and a slight elongation of the cells
and their nuclei, the latter overlapping each other like so many tiles. But
the posterior thickening is more complicated ; it consists of two parts.
The anterior part is composed of cells, the nuclei of which have their
long axes nearly parallel with the surface of the head ; they collectively
form a broad band (r.) nearly perpendicular to the surface of the head ;
the nuclei are wedged between each other so as to form two or three
irregular rows. Behind this, and more or less in continuity with it, is a
region [pr r.) which gradually diminishes from a thickness nearly equal-
ling the length of the " perpendicular band," to the thickness of the or-
dinary hypodermis. The nuclei in this triangular region are, in the main,
perpendicular to the surface of the head, although showing a tendency to
radiate from a point near the deep end of the " band." There are, then,
four more or less distinct tracts already recognizable. These may be
named /ro»i behind forward, pre-^-etinal (pr r.), retinal (r.), tapetal (tap.),
BJid post-retinal (p r.), respectively. The same regions may also readily

* It is possible that the re-entrant fold was not confined to the bottom (apex)
of the eye-pocket, but extended along its margins, and that the " fissure " in the
tapetum, subsequently referred to, is to be explained as resulting from the failure of
these two lateral ingrowths into the pocket to unite along the axis of the latter.

MUSEUM OF COMPARATIVE ZOOLOGY. 77

be traced in Fig. 2, although in this section the nuclei of the " band "
(r.) are more regularly polygonal.

The further changes and the ultimate fate of each of these four tracts
seem fairly evident from a simple comparison of this figure (Fig. 2) with
Fig. 12, which shows a corresponding view of the same eyes (but from
the right side of the head) of an individual killed eight days after hatch-
ing. (Consult also Figs. 11, 16, 20-24, and the explanations of the
figures.) The relative positions of the parts have become slightly changed
in the later stage, owing to a continuation of the process of folding and
the closer approximation to each other of the three anterior regions.

Numbering from behind forwards, it will be seen that the fourth or
last tract {p r. Fig. 12) has grown backward untU it now lies underneath
nearly the whole of the other three regions, and that the first tract
{pr r.) has grown forward in a corresponding manner, and thus intervenes
between the cuticula and the greater portion of the rest of the ocellus.
In the place of the third tract (tap.) the ** tapetum " now appears, with
here and there a greatly elongated nucleus, and in the second tract (r.)
the ends of the cells, which were previously directed forwards, and are
now directed downwards, — *'. e., toward the tapetum, — have developed
the bacilli (hac.) characteristic of retinal cells.

From this stage onward, the significance of each of the four layers is
evident, and the determination of the homologies with the three layers
of the other type is to a certain extent possible.

The first or posterior tract {pr r.) becomes the most superficial layer
and secretes the lens (Figs. 12, 22) ; it is the equivalent of the so-called
" vitreous body." * The cell-boundaries in this, as in the other layers, are
not made readily distinguishable by the process of preparation employed ;
but the shape and direction of the well-stained nuclei show that they are
quite oblique to the surface of the lens, and that some of them are

* This layer of cells, which I have hitherto called " vitreous body " or " vitreous,"
in conformity to the prevalent nomenclature, deserves a designation more in keeping
with its primitive function, — the secretion of a cuticular lens. Any designation
intended to replace so simple a word as "vitreous" must be equally brief in order to
be acceptable. I propose the name lentigen as a substitute for " vitreous body."
I believe this substitution is the more desirable since, according to the best present
information, there are probably some cases (c. g. Dytiscus) in ^fhich " lentigen " and
" vitreous body " would not be strictly identical. According to Grenacher's descrip-
tion, certain of the pre-retinal cells in Dytiscus do not abut upon the lens, and their
participation in its production may therefore be questioned. They do intervene
between the lens and the sensitive surface, however, and may appropriately retain
the title "vitreous" cells.

78 BULLETIN OF THE

slightly S-shaped, The line of demarcation between this and the second
tract, or next deeper layer, is not always sufficiently distinct to allow one
to claim with certainty the presence of an internal cuticula (basement-
membrane) equivalent to the pre-retinal membrane of Graber. In some
cases (Fig. 24) I have seen a sharp limiting membrane between the pre-
retinal and retinal layers ; but in other cases (Figs. 20-22) it has been
impossible to find the least indication of such a membrane. The form
and relation of these two tracts indicate a gradual slipping of the first
upon the second, rather than a typical folding ; but this is probably to
be considered as simply a modification of what originally was a true fold-
ing at the retino-lentigen margin of the retinal pocket. The overgrowth
of the lentigenous cells finally results in the same relation between the
two tracts as was originally produced by the ingrowth (infolding) of the
retinal layer. In the original method the retinal layer formed one wall
of a free pocket (compare Locy, '86, PI. X, Fig. 64) ; in the modified
process it is from the beginning in contact with the lentigen. The pos-
terior region of the latter is finally extended (Figs. 11, 12) so as partially
to envelop the posterior margin of the retina.

The relations of the second tract (r.) are not equally clear upon all the
sections. If Figs. 8 and 9 were taken to represent the original unmodi-
fied condition of the hypodermal foldings, the conclusion might be that
there had been an outfolding having the second tract for its wall on one
side, and the third tract on the other. If this were the typical method,
there could be no doubt but that that face of the second layer which at
this stage is directed forwards, and in which are developed the bacilli,
would correspond to the originally deep surface of the hypodermis. The
bacilli would therefore be developed here, as in the anterior median eyes,
at that end of the cells which in the original position of the hypodermis
must have been turned away from the light. But of the justice of this
conclusion I am not convinced; for in other cases (Fig. 4) the out-
folding, as stated above, appears to involve only the second tract, and in
still others there is not sufficient evidence of a true folding of any kind.
In Figs. 2 and 16, for example, the conditions are such as might have
been produced by a detachment (delamination*) of the cells of the third
tract (tap.^ from those of one of the adjacent layers, without the forma-
tion of any ow^folding. If either of the latter suppositions represents
the true state of the case, then the anterior face of the retinal tract (r.)

♦ The delamination might possibly have resulted from an abbreviation in the
process of forming the tapetum, which originally took place exclusively by means
of an tutfolding of the tapetal cella.

MUSEUM OF COMPARATIVE ZOOLOGY. 79

corresponds to the superficial ends of the component hypodermal cells,
and the bacilli accordingly occupy the ends of the cells which were
originally directed towards the light.

Upon either supposition there is a difficulty in instituting a comparison
with the eyes of the "pre-nuclear " group. Upon the first assumption,
while the bacilli would occupy the originally deep ends of the cells, as in
the other type, the retinal layer as a whole would have been only par-
tially and temporarily inverted, — not permanently, as in that type, — and
therefore a strict homology could not be claimed. But upon the second
assumption, while the infolding would result in an inversion of the
retinal layer, as in the simpler type, the bacilli would occupy the
originally superficial ends of the cells, and this would also present a
serious obstacle to a satisfactory comparison.

I have not, perhaps, a sufficient number of successive stages to place
the matter beyond question, but believe that the evidence from the ma-
terial which I have, and also certain theoretical considerations, point
towards the second assumption — that the retinal layer is inverted — as
the more pi»obable.

In the later stages (Figs. 11, 12, 21-24) it is not always easy t9 dis-
tinguish at once between the nuclei of the first and second layers ; but
careful attention to the shape and inclination of the nuclei, as well as to
the intensity of their staining, allows one to determine fairly well the
extent, if not the exact boundaries, of each layer. In Figure 22, for
example, the nuclei of the " lentigen " were excessively flattened and
apparently degenerating ; those of the retinal layer were much paler, less
broken, and less granular.

The origin of the third tract {tap.) is involved in the question just
considered ; but whatever this origin, — whether it arise by delamination,
or by an outfolding which affects only its own cells, or whether it result
from an outfolding one wall of which is the retinal layer, — the ultimate
condition of this tract can scarcely be called in question ; it produces the
tapetum. Its nuclei (compare also Figs. 18-22) often undergo a remark-
able elongation, and conform in shape to the curved direction of the layer.

In all the eyes of the " post-nuclear " group in Agelena the tapetum
has the form of a short canoe, the cavity of which is directed towards
the retina. Its greatest length corresponds with the direction of the ecto-
dermic infolding. The end corresponding with the bottom of the pocket
of involution is narrower than the opposite end, and does not approach so
near to the surface of the head as the latter. The variations in the curva-
ture from end to end are often considerable, amounting in some cases to

80 BULLETIN OF THE

a sharp bend in the middle (Fig. 24), and the inclination of the sides to
each other may also vary several degrees. The tapetum does not carpet
the whole fundus of the eye, being, even in its broadest part, much nar-
rower than the latter (Figs. 13, 14, PI. Ill) ; but it appears to be as exten-
sive as the layer of bacilli developed in front of it. Corresponding in
position to the keel of the canoe, is a narrow interruption, or fissure, which
extends through the whole length of this layer. It is sometimes slightly
curved, S-shaped, and its edges are not always clear cut. It is probable
that the appearance which Leydig described as "a band of black pigment
traversing the middle of the tapetum " was due to the presence of a
similar fissure. In some instances the broad outer end of the tapetum
appears to abut directly upon the inner surface of the external cuticula ;
but even in such cases I have not found in its vicinity any modifications
of the cuticula, neither an infolding, nor any marked interference with
its regular course. In no case have I been able to trace a direct con-
tinuity of cuticular and tapetal substances. Often the tapetum cannot
be followed up to the external cuticula ; but where the conditions of
the sections were favorable for its study, I have never failed to find that
the narrow, deep end of the tapetum reaches to, and is apparently con-
tinuous with, the internal cuticula, or basement-membrane. This con-
dition seems to afford confirmation of the opinion that the tapetum
results from an 02<^folding of cells which previously occupied a position
at the bottom of an early hypodermal infolding, involving the " retinal "
and *' post-retinal " tracts. For if the tapetal cells originally grew into
the cavity of the hypodermal pocket from its deepest end, they would
naturally retain a direct connection with that portion of the basement-
membrane where they were at first situated. The region of this ingrowth
into the cavity of the original pocket may have extended along the two
margins of the pocket for a greater or less distance, and the interrup-
tion in the tapetum (" fissure ") may possibly have resulted from the
failure of these two regions of ingrowth to meet along the axis of the
original pocket. The absence of a direct connection with the external
cuticula is in itself a strong argument against considering the tapetum
homologous with that layer ; this is further strengthened by a consid-
eration of the chemical differences between the two, referred to by
Grenacher.

The tapetum in Agelena consists of small, thin, slightly curved, scale-
like, iridescent structures which are superposed and closely packed.
The whole layer has a considerable thickness, and when viewed in lon-
gitudinal section, a peculiar wavy, fibrous appearance. If tliese scales

MUSEUM OF COMPAKATIVE ZOOLOGY. 81

were the product of a cuticular secretion on the part of the cells of the
tapetal layer, one would rightly expect the nuclei of the cells to retain
some constant relation to the scales. They should all be located on one
or both surfaces of the scale-like layer, or they should all lie in the
middle between two sheets of such structures. But I have been unable
to find any such constancy of relation, the few nuclei being distributed
through the layer apparently without any regard to their distance from
either surface of the tapetum (Figs. 15, 18-22, tap.). For these reasons
I believe it must be admitted that the tapetal scales are formed by a
metamorphosis of the cell-substance of the cells forming what I have
called the third, or tapetal tract, and not by a process of cuticular secre-
tion. I have not traced the development of the separate scales within
the body of a cell, but from the small number of nuclei present it is
evident that each cell must give rise to a large number of the scale-like
elements.

The fourth or deepest layer apparently corresponds with the deepest or
third layer in the eyes which present the simpler structure, — the pre-
nuclear ocelli. There is no doubt that it owes its formation here, as well
as there, to a process of hypodermal infolding (Figs. 2, 5-9, 16, 18, 19),
and it retains, even after the formation of the tapetum, an evident con-
tinuity with the indifferent hypodermis immediately in front of it. Like
the deep layer in the eyes of the " pre-nuclear " group, it also becomes
the seat of an early and intense pigmentation. That it subserves the
ordinary functions of a pigment-layer to the retina can scarcely be
doubted ; but instead of progressively diminishing in thickness and indi-
viduality, as in the pre-nuclear eyes, it here seems to increase in thick-
ness, and may perhaps fulfil important functional relations not shared
by the corresponding layer in the simpler ocelli. In the more advanced
stages (Figs. 20-24) this layer is considerably augmented in bulk as com-
pared with earlier stages and in comparison with the mass of nuclear
material. Its anterior border overlaps the anterior margin of the other
layers (Fig. 22), much as the superficial layer {pr r.) at an earlier stage
(Fig. 12) envelops the posterior margin of the layers underlying it.
From its connection with the optic nerve it has acquired a somewhat
conical shape (Figs. 23, 24). A portion of the nuclei still forms a more
or less continuous layer near the surface (Fig. 20) ; others (Fig. 22) lie
near its axis. Throughout the whole of its substance very fine striations
are now distinguishable. The direction of the striations makes it evi-
dent that they are due to the radiation of the fibres of the optic nerve,
towards which they all tend. But I am not yet entirely certain about

VOL. XTII. — NO. 3. 6

82 BULLETIN OF THE

the method of the distribution of the nerve-fibres to the retinal layer.
It will require a more careful study of maceration-preparations in con-
nection with sections in different planes to settle this important question.
It seems to me improbable that the nerve-fibres pass directly through the
tapetura. From what I have seen, I think that most of them pass
around the margins of that layer to join the anterior ends of the retinal
•"•-ells, though I have reason to think that some of them reach the retina
through the fissure in the tapetum.

The position of the other eyes is not quite so favorable for study by
means of sagittal sections ; and yet an examination of Figs. 4-6 is suffi-
cient to show that the infolding does not take place in the same direc-
tion in both of the lateral eyes. In the anterior laterals the retinal mass
lies in front of the infolding, whereas in the posterior laterals the retinal
mass lies, as in the posterior median eyes, behind the infolding.

In the anterior lateral eye (Figs. 4, 5) the four tracts are readily dis-
tinguishable ; and it is necessary only to compare Figs. 4 and 5 with the
later stage in Fig. 15, and the still older one of Figs. 18 and 19, in order
to learn that the fate of each is the same as in the eye already described ;
a further description is therefore unnecessary.

That all the layers — especially that producing the tapetum — are not
seen with the same distinctness in the posterior lateral eye, is, without
question, due to the direction of the axis of that eye. The sections are
cut in a plane which makes a considerable angle with the main axis of
the eye and of the infolding, and the figures therefore give a more ob-
lique view of the cells of the tapetal layer, which consequently are not
so readily distinguishable from those of the retina. The earlier sections
(Figs. 4, 5) pass through the fundus, — the last (Fig. 7) through the
margin of the infolding, where the first and the fourth layers begin to
merge into one another. (Compare Explanation of Figures.)

It can be seen from the figures of a later stage (Figs. 13-15) that the
axis of this ocellus continues to be nearly perpendicular to the sagittal
plane. Of the three sections, that which is nearest the surface of the
head (Fig. 13) shows the greater portion of the tapetum,* with its
median fissure, nearly en face; there are also shown, between the ob-
server and the tapetum, faintly expressed markings nearly perpendicular
to the fissure. I could not discover that they were continuous across
the region of the fissure. They are undoubtedly due to the difierentia-

* A part of the posterior end of this structure was cut away with the preceding
section.

MUSEUM OF COMPARATIVE ZOOLOGY. 83

tion of bacilli, — the intervals between the markings corresponding very-
well with the intervals shown when the plane of sectioning is nearly
parallel with the direction of the fissure (compare Fig. 19), — but I am
uncertain whether it is to be concluded from this that the bacilli have
the shape of broad plates, or whether these plate-like structures are really
composed of row& of rods, which the method of preparation and mount-
ing (Canada balsam) has made incapable of optical resolution. There
is a suggestive resemblance between these plate-like markings and the
sinuous figure formed by the peculiar arrangement of the bacilli in the
posterior eye of Lycosa as given by Grenacher (78, Taf. Ill, Fig. 24) ;
but I was not able to satisfy myself that these plates presented the
folded-back-and-forth arrangement shown in Grenacher's figure. From
what is known of the form of the bacilli in other simple eyes, it seems
most reasonable to suppose, however, that the plates are composed of
rows of bacilli.

The second section (Fig. 14) shows the remaining portion of the tape-
tum, belonging principally to the anterior end of that structure ; if there
were portions of the bacilli present upon this section, they were too faint
to be discerned.

Finally, the third (deepest) section (Fig. 15) passes entirely below the
tapetum, cutting through the post-retinal layer.

The presence or absence of a pre-retinal membrane in the eyes of the
present type is of some interest, and yet it may not be of radical impor-
tance. Whether the change in the relative positions of the retinal and
pre-retinal tracts during development is due to a true folding, or to a
slipping of one layer over the other, may depend simply upon how faith-
fully the original method of transposition (folding) is adhered to. With
the gradual substitution of a slipping for a folding, the opportunity
for the formation of a pre-retinal membrane may have gradually disap-
peared ; nevertheless, I am of opinion that evidence of such a membrane
will usually be found during some stage in the formation of the ocellus.

In some spiders (Tegenaria, Theridium) the development of the re-
tinal infolding and the secretion of the lens are accompanied by a grad-
ual displacement of the deep ends of the " lentigenous " cells towards
the margin of the eye, so that in the adult the pre-retinal membrane is
almost in contact with the posteric)r surface of the lens, especially near
the margin opposite that towards which the nuclei of the "lentigen" are
displaced. This of course increases the difficulty of discerning the
membrane.

84 BULLETIN OF THE

The method of connection between retinal cells and optic-nerve fibres
is a fact upon which Grenacher has placed great importance, since upon
it depends largely, in his opinion, the interpretation given to the func-
tional value of the individual elements of the retina. According to
Grenacher's investigations (79 and '80) the posterior (deep) end of each
cell of the retina (in the " Stemma ") is prolonged into a single nerve-
fibre, the optic nerve being composed of a bundle of such fibres, pre-
sumably as numerous as the retinal elements. This condition — espe-
cially well marked in Dytiscus, in the posterior dorsal eyes of Epeira
(Grenacher, '79, Figs. 1, 18, 20), in Lithobius, lulus, and Glomeris
(Grenacher, '80, Figs. 9, 11, 13) — has also been confirmed by Lan-
kester and Bourne ('83, Figs. 2, 4, 7, 11) for Scorpionidse and other
Arthropods.

"Without being prepared to question the accuracy of the observations
of these authors in the cases cited, I am of opinion that there are suffi-
cient reasons for not accepting as universal this mode of union between
retinal cells and optic-nerve filaments. I do not wish to be understood
as opposing the idea of the independent communication of the elements
of the retina with the nerve-centre, but only as claiming that generali-
zations as to the manner of -union between retinal elements and optic-
nerve fibres cannot be as quickly and safely drawn as might be inferred
from previous writers.

The nature of the optic-nerve connection in the anterior eye of Epeira as
described and figured by Grenacher ('79, p. 44, Fig. 18, A) is in itself suffi-
cient to raise doubts concerning the universality of the method claimed
by him ; viz., a direct prolongation of the (ultimately) posterior ends of
the retinal cells. Grenacher says that the peripheral fibres of the optic
nerve are continued without sharp limitation directly into the neighbor-
ing (" herantretenden ") retina-cells ; but the inner [axial] fibres enter
into the interior of the retina, where they divide into two bundles, — a
smaller dorsal, and a larger ventral, — which then spread out in single
fibres, which in turn join the ends of the corresponding [retinal] cells.
That which seems to me unwarranted in his conclusions is, that the axial
fibres are joined to the ends of the retinal cells. It is not quite clear
from the figure cited how this union could be easily effected. The same
feature, but in a more marked degree, is also shown in Mr. Locy's sec-
tions of the anterior median eyes of Agelena a few days after hatching
(PI. II, Figs. 10, 11, and PI. V, Figs. 23, 24), and in the adult eyes (an-
terior median) of Theridium tepidariorum, C.K., which I have examined,

Grenacher himself called attention to a want of symmetry in the eyes

MUSEUM OF COMPARATIVE ZOOLOGY. 85

in question (Epeira), the entrance of the optic nerve being slightly dor-
sal ; but the significance of this fact was not perceived by him.

The same peculiarity is also noticeable in the figure of Epeira diadema
given by Schimkewitsch ('84, PI. II, Fig. 4), where, besides, the radiating
fibres of the two bundles described by Grenacher are also figured. They
are, however, erroneously assumed by the author to be muscle fibres.*

In these cases (and doubtless similar conditions prevail in many others)
the optic nerve leaves the bulb of the eye not directly opposite the lens,
and not always at the point which corresponds to the shortest distance
between the eye and the brain. It is noticeable that the place of emer-
gence is in some instances (Figs. 10, 11, 20, 23, 24, n. opt.) very near to
the superficial border of the retina. If the opinion held by Grenacher
were to be substantiated in these cases, we should expect to find the major
part of the optic-nerve ramifications bending abruptly backward as soon
as they had entered the cuticula of the bulb, and forming behind the
bulb a kind of nerve-fibre sheath, which would gradually become thinner

* Schimkewitsch (p. 14) finds in these nerve-fibres the sphincter described by
Leydig. "But," he adds, "I have never seen that this sphincter takes its origin
from the integument, ias claimed by Grenacher. . . . The action of the muscle as a
constrictor has been observed by Leydig ; but I am not able to understand how the
muscle would be able to change the visual axis, [even] if it were attached to the in-
tegument, as Grenacher supposes, since the cornea-lens is quite immovable."

Leaving aside the question as to the accuracy of Grenacher's conclusions about a
change in the direction of the visual axis, it must be sufficiently evident upon com-
paring the figures given by the two authors (Grenacher, '79, Fig. 18, M, M') that the
structures in question have nothing in common. Whatever may be the effect of its
contraction, the muscle figured by Grenacher encircles the eye, lying, as he expressly
states (/. c, p. 46), outside the cuticula which invests the eye ; whereas that to which
Schimkewitsch attributes the function of a sphincter lies wholly within the cuticular
envelope.

Leydig ('58, p. 441) observed powerful, jerking contractions of the pigmented
layer in the eyes of several living spiders. It is a long step that Schimkewitsch
has to take when he says Leydig has observed the action of his supposed sphincter
muscle. It is the more surprising that he should have adopted such an interpreta-
tion of the fibres, when a much more natural one had already been given, as above
quoted, by Grenacher. He adduces no argument to prove the contractile nature of
the fibres, and, it would seem, must have arrived at his conclusion rather hastily,
and without the remembrance of Grenacher's description of the optic nerve.

If it were tiecessary to strengthen with special arguments the natural interpreta-
tion given by Grenacher, one might insist — in addition to the observed direct
continuation of the fibres with the optic nerve — upon the absence of transverse
striations, and a susceptibility to staining reagents like that of nerve-fibres rather
than that of more deeply staining muscle-fibres.

86 BULLETIN OF THE

towards the side opposite the place of entrance, as the* fibres one after
another effected a union witli the basal ends of the retinal cells. But
nothing of the kind seems to exist in either of the cases cited or in those
which have come under my own observation. The fibres, instead of
following the surface of the bulb beneath the post-retinal membrane
(" sclera "), traverse directly the retinal layer in several groups.* Their
connection with the retinal cells, however, is not — as one Avould fairly
infer from Grenadier's account — at the posterior (originally free) ends, but
rather with the anterior parts of the cells, f — at least it may be designated
as certainly pre-nudear. + The evidence of this rests partly upon the
position and general direction of the nerve-strands in a region behind
the forming bacilli and in front of the nuclei, and partly on the modifi-
cation of form which many of the retinal cells and their nuclei exhibit
in consequence of this relation. The elongation of the anterior ends of
the nuclei § is so evidently a result of the peculiar position and connec-
tions of the nerve-filaments (PL V, Figs. 23, 24) that I cannot for a
moment think it attributable to any other cause.

There is also reason to believe that a similar condition exists in the
eyes of the " post-nuclear " type, and that the nerve-fibres which appear
to emerge from the deep surface of the retinal layer really pass around
the margins of the tapetum (somewhat as in Pecten), to join the now super-
ficial ends of the retinal cells This in turn increases the probability of
the inversion of the retina in " post-nuclear" eyes. (Compare Explanation
of Figures.)

I shall return to a consideration of the manner in whicli this interest-
ing connection is brought about in the pre-nuclear eyes, and of the prob-

* Since the groups do not necessarily lie in the plane of the section, they are not
all seen in one section ; but I am satisfied, from the examination of several cases, that
such a division of the fibres usually takes place.

t That such a method of nerve-connection with sensory cells is not wholly with-
out parallel, will be evident upon comparing tlie conditions here described with the
account of the termination of the radial nerve of the cochlea in mammals as given
by Lavdowsky (76, pp. 529, 530, Taf. 35, Figg. 10 A, 10 C).

X The connection here (after inversion) called "pre-nuclear" is of course equiva-
lent to a post-nuclear connection before inversion. The nerve-fibre, which I believe
I'eaches the nucleus itself, therefore retains as nearly as possible its original method
of connection with the retinal cells ; i. e., it approaches the nucleus from what was
originally the deep end of the hypodermal cell.

§ The nuclei present no such modification of form in the earlier stages of tlie
formation of the eye, before the appearance of the optic nerve, but are sinalarlv
rounded at both ends.

MUSEUM OF COMPARATIVE ZOOLOG\. 87

able cause of its existence, in the followiag portion of the paper, devoted
to theoretical considerations.

What have been the causes, and what is the real significance, of the
hypodermal infolding accompanying the formation of ocelli ]

The following speculations are an attempt at the solution of these prob-
lems. It is not supposed that they offer a complete explanation of the
phenomena, but it is hoped that they may stimulate criticism on the part
of future observers, which will ultimately lead to a satisfactory elucidation
of the conditions.

The case of ocelli with pre-nuclear bacilli, in which there has been an
involution with inversion of the retinal layer, will be considered first.
One meets here a problem similar to that which is encountered in
endeavoring to explain the origin of the retina in vertebrates. If the
retina in the ancestors of vertebrates was a patch of ectoderm in its
normal position, then there are two questions to be settled in explain-
incr the present condition. One is. What could have been the advantage
in the assumption of the inverted position of the retinal cells in rela-
tion to the direction of the Avaves of the light-stimulus 1 The other,
How could the retina have remained functional during the whole of
the involution-process which accompanied the formation of the neural
tubel

Here, in the " pre-nuclear eyes," the same questions arise : If the retina,
which is formed by a process of inversion, was once a normally located
portion of the " hypodermis," how could it have remained functional
during the process of inversion, and what could have been the motive
which led to the inversion 1

The question of the immediate cause may perhaps be more readily
answered in the case of vertebrates than here ; for in vertebrates the ulti-
mate inversion of the retinal cells is only a necessary consequence of a
much more fundamental change, — the involution of the central nervous
system, — which may find its adequate explanation in something (e. g. the
protection of the nervous system) very remotely, if at all, connected with
the functions of the eye. But in the case of spiders' eyes it is different.
The retina is formed comparatively late in embryonic life, end, so far
as is yet known, independently of any such neural infolding. Unless,
then, the retinal inversion can be connected with the formation of the
cephalic portion of the central nervous system, the cause of this remark-
able complication must be sought in some advantage secured to the eye
itself. It is not necessary that the motive be one that is constantly oper-

88 BULLETIN OF THE

ating to produce the original result ; it is only necessary to show how this
influence once operated to bring about the end achieved.

Protection to the retina may have been one of the objects gained ; but
it is not easy to see how that is better accomplished by an inversion than
by a simple depression of the retinal area.

The influence of the light itself, especially the direction of the rays
which gain access to the retinal cells, may have been more important.
Either a gradual shifting in the position of the original lenticular thicken-
ing of the cuticula, or the development of a new lenticular region, may
have been the means by which this new and transforming influence was
brought to bear on an already existing retina; for unless the involu-
tion can be connected with the formation of the central nervous system,
this complicated ocellus must be imagined to have been developed from
a more simple functional eye.

It is assumable that this primitive eye was composed of a single layer
of modified hypodermal cells occupying the normal position (perpendicu-
lar) in relation to the surface of "the head,* that the proximal (deep)
ends of the sensory cells were in connection with the nervous centre by
means of nerve-fibres, and that it was in the distal (free) ends of the
cells that the bacilli were formed.t

* Either these cells at first all shared in the secretion of the corneal lens, or else
this function was confined to a portion of the cells, evenly distributed over the sensi-
tive area, only isolated cells being modified into sensory elements. The latter con-
dition is at present realized in the eyes of many of the invertebrates, and one might
at first be inclined to regard it as the result of a differentiation accomplished in the
cells of the sensitive area during its development as an organ of special sense. If
that were the most reasonable assumption, it would become very doubtful whether
the ocelli of Arthropods have ever passed through any such stage of differentiation,
unless the lateral eyes of scorpions prove to be truly monostichous, as claimed by
Lankester and Bounie. But the results of modem inquiries into the origin of sen-
sory organs have made it more and more probable that this differentiation of epithe-
lium into sensory cells and indifferent cells (" Stutzzellen ") is to be carried back to a
period which antedates the formation of all special-sense organs. In the light of this
important generalization a sensitive area, composed exclusively of sensory cells,' must
be looked upon as a highly modified condition resulting from the atrophy or dis-
placement of the indifferent cells, or, possibly, their gradual conversion into sensory
elements.

t There is notning to favor the supposition that these ocelli were developed from
retinal cells which contained bacilli at their deep ends before the process of inversion
began, for there is not a single case among the invertebrates in which such a condi-
tion exists, where other complications do not make it probable that there has been an
inversion. The principal cases of "post-nuclear" bacilli are found in the dorsal
eyes of Onchydium, and the eyes at the margin of the mantle in certain Lamellibranchs

MUSEUM OF COMPARATiyE ZOOLOGY. 89

I know of no example among Arthropods in which this condition is
strictly realized, provided the still problematic development of the lateral
eyes of scorpions is not taken into consideration. Even the simplest are
considerably modified.

It is not certain along what line of modifications the eye with inverted
retina has been developed. Not all triplostichous eyes are necessarily
like the pre-nuclear type in spiders. A triplostichous condition might
be produced by a simple depression of the retinal area and a subsequent
closing together of the surrounding hypodermis, ultimately giving rise to
an inner and an outer corneal layer, as in many of the mollusks. The
condition of the eye in Peripatus suggests such a method of formation in
this primitive Tracheate.

It is not unreasonable to suppose, however, that all the triplostichous
eyes have passed through a condition of simple sac-like depression, in
which originally the retinal cells are not inverted, and that from this
simple condition two others have originated, — (1) By a closing together
and fusion of the lips of the original depression a more or less volu-
minous cavity (filled with a so-called lens) is formed in front of the still
uninverted retina and behind a double layer of hypodermis, — a triplos-
tichous condition such as is realized in Peripatus (Carriere, '85, p. 124 ;
Kennel, '86, p. 32, Taf. Ill, Fig. 34). (2) By an approximation of the
walls of the depression its cavity is reduced to an axial fissure ; the cells
corresponding to the " outer cornea " in the first case become the " lenti-
gen ; " those corresponding to the " inner cornea " become a " vitreous ; "
the retina still remains uninverted, — a monostichous (potentially tri-

(Pecten, Spondylus, etc.). It seems to me there is little doubt but that in both
these cases there has been at some time an inversion of the retinal area. The pecuHar
course of the optic-nerve fibres and their method of joining the sensory cells (at their
anti-bacillar ends), as well as the position of the bacilli, point to this conclusion.
They are not, it will be observed, in any sense monostichous eyes.

The eyes of Planaiians, also, may possibly be interpreted as having bacilli of the
"post-nuclear" type; but here, too, the course of the nerve-fibres points to an in-
version of the retina, and, in addition, it is doubtful if the eye is monostichous.

Postscript. — Although Dr. Patten informs me that there is no inversion of the
retina in the case of Pecten, I believe that an inversion at some time during the
phylogeny of the eyes of Pecten has been the cause of their present condition. But
whether there is an inversion during the ontogeny of Pecten or not, the question im-
mediately before us is little affected by it ; for eyes like those of Pecten are already
too complicated to have served as the primitive condition of the triplostichous ocelli
of Arthropods. It may therefore still be safely assumed that the cells of the primitive
ocelli had ^re-nuclear bacilli.

90 BULLETIN OF THE

plostichous) condition such as is realized in Dytiscus as described by
Grenacher.

The triplostichous eye with inverted retina may have begun, like that
with the normal retina, in the sac-like depression ; but it has probably
passed through a stage in which there was an early obliteration of the
original cavity, as in the second case above. Perhaps the eye in Dytis-
cus or in some of the Myriapods is the nearest approach — in the hith-
erto described ocelli of Arthropods — to this earlier condition. Here, at
any rate, none of the cells in the retinal area retain the function of se-
creting cuticula, and the area is therefore relieved from the necessity of a
fixed topographical relation to the lens, — an important consideration in
the development of the theoretical views which follow

Of the two possible ways suggested, in which a change due to the ac-
tion of the light may have been brought about, I will first consider that
which assumes, — (1) that light gained access to some portion of the
periphery of the eye-bulb through other parts of the cuticula than that
which originally served for the transmission of light ; and (2) that this
light from a new direction operated to develop a practically new eye out
of a portion of the already existing retinal cells.

To make this hypothesis more intelligible, one may begin with the con-
crete case of the anterior median eye in spiders. (Compare Figs. 25, 26,
30-32.) It may be assumed that the eye from which this " pre-nuclear "
type was produced had the form and position * indicated in Fig. 30 ;
that the light which hitherto affected the retina entered through the cuti-
cularlens {Ins.), in the direction indicated by the arrow, A ; but that, after
the development of the eye up to a certain stage, light also gained access
in the direction of the arrow P through another region of the cuticula. The
same influences which originally tended to the production of an eye un-
derneath the cuticular region (Ins.) may now have operated on that por-
tion of the cells of the already formed retina xuhich were directed towards
the new lens; and in time these retinal cells may have developed the
characteristic bacillar structures at the ends of the cells nearest to this
new lens {Ins'. Fig. 31).

* This primitive eye has been assumed to have occupied the angle of the forehead,
as at present (Fig. 11), and to have had its axis inclined to the horizon at an angle
of 45°. It might have been parallel with the horizon, or even more nearly perpen-
dicular to it, without having materially affected the problem. If, however, it had
been perpendicular, the newly admitted light would have been in front, and the new
lens in front of, instead of behind, the original lens, and as a consequence the
involution would have been directed forward instead of backward.

MUSEUM OF COMPARATIVE ZOOLOGY. 91

The advantages of vision in the new direction may have been due to
the more favorable relation of the cells to the direction of the newly ad-
mitted light as compared with that which came along the original course,
inasmuch as the latter was nearly perpendicular to the axes "of the retinal
cells (and therefore not favorable, upon Grenacher's theory, to the per-
ception of distinct images), whereas the former would be parallel to the
axes of some of the retinal cells, and therefore competent to furnish (upon
the development of the lens) a more distinct image.

Any advantage of this nature Avould gradually lead to an extension of
the favorably located portion of the retina, and even to any modification
of the form of the layer as a whole whereby it should be brought into
still more favorable optical relations to the newly admitted light. This
might be accompanied by a gradual regressive modification of parts of the
retina not so situated as to be capable of profiting by light entering from
the new direction. In this way the originally symmetrical condition
would be replaced by conditions more and more unsymmetrical.*

Thus in time a new lens might be formed and the old one atrophy ;
one region of the original retina might become converted into a new retina
with new bacilli at the deep ends of the cells, and the cells of the remaining
regions sink from their function of percipient elements to that of simple
pigment-cells. The disappearance of the original bacilli in the persist-
ently functional area of the original retina might be complete, or only
partial,

A strong indication that the anterior median eye in Agelena previously
existed in the condition of a functional monostichous eye, the deep ends
of whose retinal cells were directly continuous with the optic-nerve fibres,
is found in the relation of the optic nerve to the present eye, and espe-
cially in its relation at diff"erent stages of its growth. Without some such
assumption the peculiar connection of the optic nerve with the retina
would remain apparently inexplicable ; but upon this assumption the
conditions appear as a natural consequence of the changes accompanying
involution. In the earliest stage in which the connection of the optic
nerve with the retina has been figured, before the appearance of the
bacilli (Figs. 1, 2), the nerve-fibres emerge from tlie outer and posterior

* Grenadier has shown tliat there is an unsjTnnietrical condition of the retinal
cells and their bacilli in the anterior median eyes of Lycosa. (See Grenadier, 78,
Taf. III. Fig. 22 A, and text, p. 48.) This must doubtless be regarded as a secondary
differentiation, — i. c. as evolved after the infolding and from a more symmetrical
triplostichous condition ; but it is instructive as indicating the possibility of
regressive changes due to the altered functional requirements imposed on the retina.

92 BULLETIN OF THE

border of the retinal infolding iinmediately tinder neath the " lentigen.'^
Upon the development of the bacilli the fibres emerge farther and farther
back from the surface of the head, until finally a considerable interval
separates the nerve from the lentigenous cells (Figs. 10, 23, 24, 20).
This is exactly what might have been expected if the eye had been de-
veloped phylogenetically by the inversion of a layer of cells which were
already in functional activity before the process of inversion began, and the
deep ends of which were connected with the optic nerve* It is also consist-
ent tvith the formation at the deep ends of the retinal cells of secondary
bacilli, which may be regarded as the physical cause of a recession (onto-
genetic) of the 2^lO'Ce where the op)tic nerve emerges.

If the fibres of the optic nerve were originally joined to the proximal
ends of the sensory cells, it is natural that they should have retained
this connection for a longer or shorter period after the beginning of the
involution which finally inverted the retina. The nerve-fibres are ulti-
mately connected to post-bacillar parts of the retinal cells. There can
be no doubt that the formation of the bacilli is a progressive process ;
they are not begun throughout their whole extent at the same time, but,
beginning at the originally deep ends of the retinal cells, they increase
in length by successive additions to the ends of the rods ivhich are di-
rected toivards the nuclei. It is equally evident that there is a gradual
shiftin" in the reorion to which the nerve-fibres are distributed, so that
this region is always post-bacillar. Nothing seems more reasonable, in
view of these facts, than that the secondary condition of the nerve-fibre
distribution results from the gradual development of bacilli in the region
of the original distribution, whereby the nerve-fibres are excluded from
their primitive mode of connection witli the sensory cells. If this is tlie
true explanation of the cause of the shifting of the nerve-fibres, it off'ers
a valid argument in favor of the secondary (i. e. recent) origin of the pre-
nuclear bacilli.

But if these bacilli are not the original rods, what has become of the
latter 1 Were it not for this marked influence of the developing bacilli
on the course of tlie optic-nerve fibres, one might have assumed that tlie
new bacilli were not absolutely new structures, but only the original
bacilli migrated from one end of the retinal cells to the other, pari passu
with the process of retinal inversion, being therefore new only in the
sense that they occupy new positions. Such a view seems, for the rea-

* Til is explanation of the peculiar position of the optic nerve as it emerges from
the eye was first suggested to me by Dr. Whitman.

MUSEUM OF COMPARATIVE ZOOLOGY. 93

son assigned, untenable. It is more likely that the primitive baciUi
have, with loss of function, atrophied, and that consequently the pre-
nuclear bacilli of inverted retinse are not homologous with the pre-nuclear
bacilli of unin verted retinse.

It is possible that the primitive bacilli do not in all cases completely
atrophy. There are at least certain problematic bodies in the retina of
scorpions which may find an explanation in connection with this hy-
pothesis. I have in mind the structures which Graber described for
Audroctonus as " posterior nuclei," — subsequently claimed by Grenacher
('80, pp. 423, 424) to be only peculiar, highly refractive bodies, — and
the structures which Lankester and Bourne ('83, pp. 185, 193) have
seen in the central eyes of Euscorpius Italicus, and have described under
the name of " phaospheres."

It may be an obstacle that the " phaospheres " are also sometimes
found in front of the nuclei, and further, that the rhabdomeres are not
formed within, but at the surface of the retinal cells. The variability in
the relation of the phaospheres to the nuclei may be regarded as an ab-
erration rendered possible by the loss of function, rudimentary structures
being more liable to vary than such as are at the height of their func-
tional activity. (Compare Darwin, Origin of Species, chap, v.) The
second obstacle is probably not of great importance, since it still remains
to be shown that intra-cellular and extra-cellular rod-like structures are
essentially different. Besides, it is conceivable tlaat the primary bacilli
may have been intra-cellular, while the secondary bacilli are extra-
cellular.

A more serious obstacle arises from the fact that similar structures
(phaospheres) also exist in the lateral eyes of Euscorpius Italicus (Lankes-
ter and Bourne, '83, p. 185), in the case of which, evidences of an in-
folding and inversion are not so satisfactory as with the median eyes. If
the lateral eyes do not result from an infolding and inversion of the re-
tinal layer, this explanation of the " phaospheres " would go for little or
nothing, since their presence in the lateral eyes could not be explained
on the same hypothesis. I have endeavored, however, to show (p. 59)
the great probability of an inversion of the retina in these lateral eyes,
and must await a satisfactory disproval of that opinion before allowing
this possibility to outweigh the considerations in favor of the explanation
of phaospheres which is here attempted.

In the above hypothesis regarding the origin of "pre-nuclear" ocelli,
tlie two points demanding explanation have been kept in view, — the
continuance of functional activity, maintained by means of the simul-

94 BULLETIN OF THE

taneous operation of light from two directions, and the ad^'antage to
vision secured through the more favorable relation of the retina to the
direction of the newly admitted light ; and there are, in addition, some
hitherto unexplained anatomical features which gain by this hypothesis a
reasonable explanation.

Changes similar to those imagined above might possibly have accom-
panied a gradual shifting in the position of the original lens (compare
Figs. 25-29), rather than the substitution of a new lens. Such a shift-
ing, from whatever cause, might have concentrated the light upon one
portion of the retina at the expense of remaining parts. The less-favored
parts might have been degraded in functional importance, and might
have atrophied. So far not much difficulty would be encountered in
appreciating the assumed conditions ; but how the light, acting through
the original, though shifted, lens, could have afforded any advantage
which would have been competent to initiate an inversion, or' to carry
forward such a process when once begun, is not so easy to comprehend.

In considering the development of " post-nuclear " eyes, however, it
will be possible to show how such a migration on the part of the lens
may have been an important factor in the process of inversion.

The structure of ocelli with "post-nuclear " bacilli, both in the adult
condition and in such stages of development as are at present known, is
only conditionally referable to what has been assumed above as the
primitive state of the eye, and the development is not so easily explained
as that of eyes with pre-nuclear bacilli.

The difficulty depends partly upon the uncertainty as to the exact
changes through which the eye passes in its ontogeny. Further study
will unquestionably soon determine this in a more satisfactory way.
But even when it has been definitely established that the retinal layer
either does or does not become inverted, it will not even then follow that
the relations of the two types to each other, and to a primitive antece-
dent condition, will at once become evident. One naturally looks for a
development of both types from a common origin, and, for a time at
least, along a common line.

If the retina is inverted, a general comparison with the retina of "pre-
nuclear" eyes becomes possible ; but the bacilli cannot be strictly homol-
ogous, since they do not occupy equivalent ends of the retinal cells.

If the existence of an inversion were established, a common line of
development could be fairly maintained; the "post-nuclear" type must
then be considered less modified, as far as regards the retina, than the

MUSEUM OF COMPARATIVE ZOOLOGY. 95

" pre-iiuclear " type : the " post- nuclear " eye without tapetum (if such
exist) would, to a certain extent, represent a common antecedent of both
types, one of which might have been produced by the substitution of
new (pre-nuclear) for old (now become post-nuclear) bacilli, and the other
by the addition of a tapetum without change in the bacilli.*

On theoretical grounds this seems to be the more probable phylo-
genetic course ; but upon this assumption — that there is an inversion of
■,he retina — the explanation of the motive to the infolding offered above
for " pre-nuclear" eyes could not be simply extended to eyes of the post-
nuclear type, since the cause of the development of new bacilli in one
case, and their non-development m the other, would then be left
unexplained.

There are grounds for supposing that the retention of the original bacilli
in "post-nuclear " eyes is due to the development of a tapetum, — a subject
to which I shall return directly.

If the retina is not inverted, even a general comparison with the retina
of " pre-nuclear " eyes becomes difficult ; for the involution in that event
affects only the tapetal and post-retinal layers, not the retina itself. In
that case, too, the primitive condition of the eye must be assumed to
have been unlike any primitive conditions at present known ; viz., with
bacilli at the deep ends of the hypodermal (sensory) cells. f

If there has been no inversion of the retina, the obstacles to an expla-
nation of the development are considerable. What can have been the
cause of an infolding which involves only the tapetal and post-retinal
layers, or of the peculiar outfolding between retinal and tapetal layers 1
I have been unable to form any idea of how this condition could have
been produced from a primitively monostichous retina with post-uucleixr
bacilli, consistently with the retention of the functional activity of the
eye during all the changes. Neither has it been possible to comprehend,
upon the same assumption, how the optic nerve came to emerge from the
post-retinal layer.

* But if the retention of the original bacilli in the inverted retina was at first
directly dependent on the existence of a tapetum, this " common antecedent " con-
dition (without tapetum) would not have been realized, except as the result of a re-
gressive modification of the "post-nuclear" eyes, involving the disappearance of the
tapetum.

+ It is not entirely impossible that eyes may have arisen which in the primitive,
uninverted condition possessed post-nuclear bacilli ; but it is very in)probable that
such was the case, because we have not at present, in any animal, a single instance
of monostichous eyes in which that condition obtains. (Compare the footnote to
pp. 88, 89.)

96 BULLETIN OF THE

On the other hand, if it be assumed that there has been an inversion,
some of the steps in the process appear more easily explainable. Figures
25-29 have been drawn to indicate a possible line of development by
inversion, having two stages (Figs. 25, 26) common to this and the "pre-
nuclear " type. The direct cause of the beginning of the inversion has
been assumed in this instance to be a gradual shifting in the position
of the original lens, rather than the appearance of a second lens bring-
ing light from a different direction. The shifting — so one may reason
— is accompanied by a gradual atrophy of one side of the retina, the
simultaneous development of a tapetum, and a peculiar modiiication in
the course of the fibres of the optic nerve which arise from the persistent
portion of the retina,

A lens changing in its relation to the retina, as indicated in the
figures, might easily allow a part of the eye to remain functional during
the process of inversion ; but alone it would aff'ord no explanation of the
cause of the inversion, since it would not begin to have an influence
(similar to that ascribed to the new lens in " pre-nuclear " eyes) until
the change in the direction of the axis of the retinal depression (the
thing to be explained) had become sufficient to make some of the retinal
cells parallel to the axis of the lens. It must be admitted, then, that,
alone, this shifting of the lens is not an adequate explanation. It may
be, however, that the formation of a tapetum is the cause, in con-
nection with the shifting of the lens, both for the atrophy of one side
of the retina, and the inversion of the other side.

If the formation of a reflecting structure (tapetum) were accompanied,
by a slight shifting on the part of the lens, the tapetum would practi-
cally cut off the light from one face of the retina and reflect it to the
sensitive elements of the opposite face. That would result in an atrophy
of the part robbed of light, and an increased development of that on
which additional (reflected) light fell.

The direction of the reflected rays may, in addition, have influenced
the shape of the retina : if the tapetum were at first a straight band
parallel with the original axis of the optic depression (compare Fig. 26),
the light falling upon it would be reflected at nearly equal but very
oblique angles, no matter upon \^at portion of the band it fell. If, how-
ever, the deep portion of the band became slightly curved (concave towards
the persistent portion of the retina), — as would be altogether natural
with an increase in the thickness of the retinal layer on one (functional)
side, and a corresponding decrease in thickness on the other (atrophied)
side, — the rays reflected from the curved portion of the tapetum would

MUSEUM OF COMPARATIVE ZOOLOGY. 97

fall upon the sensitive surface more nearly perjjendicular to it than they
would have done without such a curvature. The advantage of this, even
if an increase in the intensity of the light were the only end achieved,
is evident ; but, in addition to the increased illumination afforded by this
part of the tapetum, it is probable that the rays of reflected light would
take directions more nearly parallel with the axes of the corresponding
retinal cells (Fig. 27), and that thus conditions favorable for more distinct
vision — perhaps even for the perception of images — would be realized.*
Such an advantage once secured at the deep end of the tapetum, it is
easy to appreciate how an increase in the extent of the curved portion of
the band would enlarge the more successfully reflecting area, thus en-
hancing the total effect of the light, and possibly affording a more -exten-
sive (reflected) image. Once begun, this process would not cease until
it had involved the entire eye.

This, it seems to me, would be sufficient to explain the curvature
actually found in the adult eyes, where the retinal cells are all perpen-
dicular to the tapetum, and would besides afford an exjilanation of the
retention of the original bacilli at the (primitively) free ends of the cells.

It is no longer probable that the iridescent scales of the tapetum are
referable to the cuticular secretions of the hypodermis. It is more likely
that the tapetum is formed from cells which grow from the apex of the
original retinal involution into the cavity formed by that involution, and
that they take the form of an outfolding. Whether the tapetal cells,
phylogenetically considered, originally constituted a distinct portion of the
hypodermis embracing the area corresponding to the apex of the subse-
quent involution, it is at present impossible to decide ; but it seems less
probable than that they should have been gradually differentiated from
a portion of the retina after the involution (but not the inversion) had
begun. It may even be imagined that the tapetal scales in some way
represent the metamorphosed bacillar elements of the cells from which
they are developed, although I know of no direct evidence of it. Unless
they are formed from cells which have previously possessed the function
of retinal elements, their source and the cause of their appearance will be
still more problematical.

There is reason to suppose that the course of the optic-nerve fibres
through the post-tapetal layer is a secondary condition. If — as is prob-

* That this curvature finall}' became so great that the light was reflected outwaid
through the lens, and thus served to help in tlie illumination of outside objects,
does not necessarily interfere with this assumed primitive function of the tapetum.

VOL XIII. NO. 3. 7

98 BULLETIN OF THE

able from previously presented arguments — these post-nuclear eyes were
developed from fanctional monostichous eyes, the deep ends of whose reti-
nal cells were directly connected to the nerve-fibres, the fibres should
retain t'heir connection with the deep ends of the cells, and should ex-
hibit, even in advanced stages, a course similar to that pursued by the
nerve in " pre-nuclear " eyes at an early stage (Fig. 1 ). Instead of that
they traverse the post-retinal layer, which may have acquired the func-
tions of an optic ganglion in addition to its duties as a pigment-layer.
The narrowness of the tapetal band makes it probable that most of the
nerve-fibres pass around its margins in making their way from the retina
to the post-retinal layer. Although this is a modification of, it is not
fundamentally different from, the condition in pre-nuclear eyes. In the
latter the fibres are collected into a single bundle at the deep end of the
pocket, and therefore emerge at the posterior harder of the eye only ; in
the post-nuclear type the fibres pass over the lateral margins of the pocket
(and the outer edges of the tapetum) as well as its deep end (compare
Figs. 28, 29) before they are joined into a single trunk. The only real
difference between the two is in the share which the " post-retinal " layer
appears to take in the formation of eyes of the "post-nuclear" type. It
is conceivable that this condition may have been brought about gradually
during the stages of inversion, — that the nerve-fibres of the aborted half
of the eye, instead of undergoing complete atrophy, acquired relations
with the persistently functional parts of the retina and their nerve-fibres,
and thus influenced the course of the latter.

Cambridge, June 22, 1886.

MUSEUM OF COMPARATIVE ZOOLOGY. 99

BIBLIOGRAPHY.

Carridre, J.

'85, Die Sehorgane der Thiere vergleichend-anatomisch dargestellt. Miinchen
u. Leipzig: R. Oldenbourg. 1885. 6 + 205 pp. 147 Abbildg. u. 1 Taf.
'86. Kurze Mittheilungen aus fortgesetzten Untersucliungen iiber die Sehor-
gane (1-4). Zool. Anzeiger, Jalirg. 9, No. 217, pp. 141-147. 8 March,
1886.
Dug6s, A.

'36. Observations sur les Araneides. Ann. des Sci. nat., 2^ ser., Zool, Tom.
VI, pp. 159-218. 1836.
Froriep, A.

'78. Ueber das Sarcolemm und die Muskelkerne. Arch. f. Anat. u. Physiol.,
Jahrg. 1878, Anat. Abth., pp. 416-428, Taf. 15. 1878.
Graber, V.

'79. Ueber das unicorneale Tracheaten- und speciell das Arachnoideen- und
MyriapodenAuge. Arch. f. mikr. Anat., Bd. XVII, Heft 1, pp. 58-93,
Taf. 5-7. 1879.
'79*. Morphologische Untersuchungen iiber die Augen der freilebenden ma-
rinen Borstenwiirmer. Arch. f. mikr. Anat., Bd. XVII, Heft 3, pp. 243-
323, Taf. 18-20. 6 Dec. 1879.
Grenacher, H.

'79. Untersuchungen iiber das Sehorgan der Arthropoden, insbesondere
der Spinnen, Insecten und Crustaceen. Gottingen. Vandenhock und
Euprecht. 1879. 8 + 188 pp., 11 Taf.
'80. Ueber die Augen einigen Myriapoden. Zugleich eine Entgegnung an
Herrn Prof. Dr. V. Graber in Cernowitz. Arch. f. mikr. Anat., Bd.
XVIII, Heft 4, pp. 415-467, Taf. 20, 21. 9 Oct. 1880.
Kennel, J.

'86. Entwicklungsgeschichte von Peripatus Edwardsii Blanch, und Peripa-
tus torquatus n. sp. II. Theil. Arbeiten a. d. zool.-zoot. Institut Wiirz-
burg, Bd. VIII, Heft 1, pp. 1-128, Taf. 1-7. 1886.
Lankester, E. R., and A. G. Bourne.

'83. The minute structure of the lateral and the central eyes of Scorpiu and
of Limulus. Quart. Jour, of Micr. Sci., Vol. XXIII, n. ser., pp. 177-212,
Pis. 10-12. Jan. 1883.
Lavdowsky, M.

'76. Untersuchungen iiber den akustischen Endapparat der Siiugetliiere.
Arch. f. mikr Anat., Bd. XIII, pp. 497-557, Taf. 32-35. 20 Oct. 1876.

100 BULLETIN OF THE

Leydig, F.

'55. Zum feineren Bau der Artliropoden. Arch. f. Anat., Physiol, u. wiss.

Med., Jahrg. 1855, pp. 376-480, Taf. 15-18. 1885.
'57. Lelirbuch der Histologie des Measchen uiid der Thiere. Frankfurt a.
M. : Meidiugeu, Sohn und Co. 12 -f 551 pp., 271 Holzschu. 1857.
Locy, W. A.

'86. Observations on the development of Ageleua nsevia. Bull. Mus." CoTup.
Zool. at Harvard Coll., Vol. XII, No. 3, pp. 63-103, 12 pi. Jan. 1886.
Lowne, B. T.

'83. On the structure and function of the eyes of Arthropoda. Proc. Roy.

Soc, London, Vol. XXXV, No. 225, pp. 140-U7. 12 Apr. 1883.
'84. On the compound vision and the morphology of the eye in insects.
Trans. Linn. Soc, London, 2 ser., Zool., Vol. 11, Pt. 2, pp. 389-420, Pis.
40-43. Dec. 1884.
MacLeod, J.

'80. La structure des trachees et la circulation peritracheenne. Memoire
couronne. Bruxelles: H. Manceau. 1880. 72 pp., 4 pi. 8°.
Metschnikoff, E.

'71. Embryologie des Scorpions. Zeitschr. f. wiss. Zool., Bd. XXI, Heft 2,
pp. 204-232, Taf. 14-17. 15 June, 1871.
Schimkewitsch, W.

'84. Etude sur I'anatomie de I'epeire. Ann. des Sci. nat., 6* ser. Zool.,

Tom. XVII, Art. No. 1. 94 pp., 8 pi. Jan. 1884.
'84". Zur Entwicklungsgeschichte der Araueeu. Zool. Anzeiger, Jahrg. 7,
No. 174, pp. 451-453. 18 Aug. 1884.
Sograff, N.

'79. Vorlauflge Mittheilungen iiber die Organisation der Myriapoden. Zool.

Anzeiger, Jahrg. 2, No. 18, pp. 16-18. 13 Jan. 1879.
'80. Anatomy of Lithobius forficatus. (Russian.) Works pubHshed by the
Laboratory of the Zool. Museum, Univ. of Moscow, Vol. I, No. 2. 34 pp ,
3 pi. 1880.

MUSEUM OF COMPAKATIVE ZOOLOGY. 101

EXPLANATION OF FIGUEES.

LETTERS.

A. = Anterior.

mu.

bac. = Bacillus.

mu'.

C71C. = Brain.

n. op

Jis. tap. = Tapetal fissure.

P.

gl. = Poison gland.

pr.

Ing. = "Lentigen,"=" Vitreous "

pr r.

(auct. ).

r.

Ins. = Cuticular lens.

tap.

The following letters are used to designate respectively : —

= iluscle.

r^ Muscle, cut cross-wise.
= Optic nerve.
= Posterior.

= Post-retinal cell-layer of the eye.
= Pre-retinal cell-layer.
= Retina.
= Tapetum.

Figures 1-24 were all drawn, with the aid of the Oberhauser camera, to the same
scale (X 515 diam.) from halsam-mounted sections cut from objects stained in alco-
holic borax carmine (Grenacher's) and imbedded in paraffine. Figures 1-16 and
18-24 relate to Agclena noivia; fig. 17 to Thcridium tcpidariorum, C. K. Figures
1-16, 18, 19, 23, 24 are from preparations by Mr. W. A. Locy; figs. 17, 20-22 from
preparations by Mr. G. H. Parker.

PLATE L

Figs. 1-7. Median faces of successive sagittal sections from the left half of the
head of a young Agclena ncevia, about four days after hatching. The position of the
portion of the brain nearest to the eyes is indicated at en c.

Fig. 1. The plane of the nearer surface of the section passes through the middle of
the anterior median eye, cutting its optic nerve obliquely. The latter emerges from
the retina immediately heneath. the " lentigen." The distal ends of the elongated
nuclei in the "lentigen " are scarcely discernible, not being sharply marked off from
the surrounding substance, nor so deeply stained as at their proximal ends. Behind
the anterior eye, and beyond its optic nerve, are the muscles which separate the pos-
terior median eyes, and then pass obliquely forward and downward, in part beneath
the anterior median eye, in part between it and the anterior lateraf eye (compare
Figs. 2 and 3). Beyond these muscles, and partly obscured by them, is the layer of
cells composing the median wall of the posterior median eye. The muscle-cells are
traceable through the " hypodermis " to the cuticula at the surface of the head.

Fig. 2. This section embraces a large portion of the lateral wall of the anterior
median eye, and the middle region of the posterior median eye. In the latter there
are four well-marked regions, — post-retinal, tapetal, retinal, and pre-retinal.

Fig. 3. The lateral wall of the posterior median eye is embraced in this section, so

102 BULLETIN OF THE

that the four regions are not as distinctly shown as in Fig. 2. In the post-retinal
region (anterior margin of the eye) there is a single cell which differs from the ordi-
nary hypodermal cells and resembles the cells with spherical nuclei found through-
out the body-cavity. I am unable to say whether it is a hypodermal cell preparatory
to division, or an intrusive element of different origin. The region in front of this eye
embraces three successive layers, — nearest the median plane a portion of the lateral
■wall of the anterior median eye; beyond this, a portion of the muscles above de-
scribed, distinguishable by the direction of their very large (seen flat-wise ?) nuclei;
and finally beyond the latter the median wall of the anterior lateral eye. The nuclei
of the latter are reproduced in

Fig. 3a, to show more accurately the arrangement of the cells. The four smaller
nuclei near the middle of the group correspond in position with the faintly stained
nuclei of the tapetum in the following figure, and undoubtedly belong to the tapetal
layer.

Fig. 4. This section embraces the middle portion of the anterior lateral eye, the
muscular bands which pass between the post, median and post, lateral eyes, and a por-
tion of the median wall of the latter (post-retinal tract). The nuclei of the tapetal
region are arranged as though resulting from an outfolding between retinal and post-
retinal layers. Most of the nuclei in the anterior layer of this fold are less deeply
stained than those of the posterior layer. In this and the three following figures the
position of the poison-glands is shown at gl.

Fig. 5. The region of tangency between the lateral eyes and their mutual flatten-
ing is shown. The post-retinal tracts of both eyes are in contact. The tapetal cells
and the post-retinal tract of the anterior eye are separated by the space of the original
infolding. The distinction between the different tracts of the posterior eye is not
readily to be made out, since the section embraces a part of its median wall; but some
of the nuclei near the middle probably are tapetal. In the next section.

Fig. 6, the posterior lateral eye is cut nearly through the middle. The axis of the
eye being nearly perpendicular to the plane of the section, the latter embraces in the
centre only retinal cells flanked by a few tipetal cells, the latter being separated by a
narrow interval from the post-tapetal tract. The lateral region of the anterior eye,
which appears in this section, is composed principally of pre-retinal cells.

Fig. 7 shows the extreme lateral margin of the anterior (lateral) eye, and a section
of the posterior eye near its lateral margin. In the latter are to be seen in the centre
the nuclei of the retinal cells; to the left and beyond them, those of the pre-retinal
cells ; and to the right the post-retinal cells, separated from the retinal elements
by a clear space.

Fig. 8. Lateral face of a sagittal section through the anterior and posterior median
eyes of the left side. The tapetal tract appears to be represented by a single row of
nuclei. Consult the text, pp. 75-83.

Fig. 9. Median face of a sagittal section through the posterior median eye of the
right side. A single faintly-stained nucleus in front of the retinal nuclei apparently
belongs to a tapetal cell, and thus suggests the existence of a fold in the tapetal
layer. This opinion is strengthened by the prolongation of the other tapetal cells
towards the region of the supposed outfolding. The tapering ends of the tapetal
nuclei jroint to the same region, but the lines representing the cell-boundaries have
not been printed with sufficient distinctness. Consult the text, pp. 75-83.

MUSEUM OF COMPARATIVE ZOOLOGY. 103

PLATE n.

Fig. 10. Median face of a sagittal section through the anterior median eye of the
left side, several days after hatching. The bacilli have begun to appear, and the
fibres of the optic nerve are seen to be distributed to the retinal cells near their
nuclei, — between them and the forming bacilli. The flattened nuclei of the post-
retinal tract still indicate the presence of a distinct layer of cells behind the retina.
The distance between the place where the optic nerve emerges and the " lentigen " is
greater than at first. (Compare Fig. 1.)

Figs. 11, 12. Two successive sagittal sections of the anterior and post, median eyes
of the left side (median face) and of the same age as the preceding. The tapetum
of the posterior eyes is already formed.

Fig. 11. The optic nerve of the post, eye communicates with the middle of the
post-retinal layer. A large portion of the median half of the tapetum removed with
this section. The optic-nerve fibres of the anterior eye (not drawn) were distributed,
as in Fig. 10.

Fig. 12. The general direction of the original infolding is still evident in the pos-
terior eye. The post-retinal layer is contmuous with the hj'podermis in front of the
eye, and the pre-retinal behind. The bacilli at the anterior edge of the eye are partly
obscured by an overlying portion of the tapetum, in which are to be seen the elon-
gated nuclei. Beneath the outline of the anterior eye the optic nerve of the anterior
lateral eye of the same side is cut obliquely.

PLATE IIL

Figs. 13-15. Lateral faces of three successive sagittal sections, through the lateral
eyes of the right side. From the same spider as Figs. 11 and 12.

Fig. 13. Beyond the plate-like bacilli (consult the text, pp. 82, 83) is the tapetum
with its longitudinal, uneven fissure, flanked on either side by the nuclei of the reti-
nal cells, which are scanty immediately in front of the tapetum.

Fig. 14. Section through the bottom of tlie canoe-shaped tapetum of the post, eye,
showing the fissure and some of the nuclei of the flanking retinal cells, as well as
some of the narrower marginal nuclei of the post-retinal layer. In the anterior eye
are to be seen the post-retinal layer and some of the cells of the retina.

Fig. 15. Only the nuclei of the post-retinal layer indicate tlie posterior eye. The
tapetum of the anterior eye is cut lengthwise near its middle. All four layers are
distinguishable, the bacilli being alreadj'^ developed.

Fig. 16. Lateral face of a sagittal section through the posterior and anterior median
eyes (the latter in outline) from the left side of a specimen one day after hatching,
showing the four tracts of the posterior eye before the appearance of tapetum or
bacilli.

Fig. 17. Theridiiim tepidariorum, C. K., adult. Portion of a sagittal section —
lateral face — passing though the tapetum of the posterior lateral eye of the right side.
The outer border of the tapetum is obscured b}' pigment-granules of the post-tapetal
layer, extending outward to the oval outline. The tapetal plates are large and quite
regularly arranged; the tapetal fissure is broad and irregular in outline.

104 BULLETIN OF THE

Figs. 18, 19. Two successive sagittal sections of the anterior lateral eye of the left
side. . Agelena ncevia, eight days after hatching. The tapetum does not reach the
external cuticula.

Fig. 18. The distant surface of the section nearly coincides with the plane of the
tapetal fissure, only a small portion of its left half being shown, near the muscle-fibres,
mu'. The greater portion of the tapetum is seen from behind, and nearly perpendicu-
lar to its surface. It obscures the bacilli in front of it. There are five greatly elon-
gated tapetal nuclei stUl visible.

Fig. 19. The nuclei of the "post-retinal" layer are large and closely packed.
Three tapetal nuclei are visible at the edges of the tapetum, which is viewed more
nearly edgewise than in Fig. 18. The bacilli are perpendicular to the corresponding
parts of the tapetum, and therefore do not all point to a common imaginary centre.

PLATE IV.

Figs. 20-22. Median faces of three successive sagittal sections through the right an-
terior and posterior median eyes, after the formation of pigment-granules has begun.

Fig. 20. The position of the optic nerve of the anterior eye is sketched in from
the two preceding sections. It will be seen that its place of emergence is still farther
from the " lentigen " than in Fig. 10. The near edge of the tapetum in the posterior
eye shows two elongated tapetal nuclei. The pre-retinal (lentigenous) nuclei are dis-
tinguishable from the retinal nuclei by their deeper color, greater flatness, and more
granular appearance.

Fig. 21. In the posterior eye five tapetal nuclei are visible, and in the "post-
retinal " layer the radiating branches of the optic nerve. The near edge of the bacil-
lar layer is cut; the nuclei of retina and " lentigen " appear as in the previous section.

Fig. 22. In the anterior eye the post-retinal layer has apparently joined the retinal
layer. (Compare Fig. 20.) Many of the retinal nuclei present a peculiar vacuolated
appearance at their outward ends. The bacilli have attained a greater length than
in Fig. 10, their deep ends being covered by pigment-granules. The anterior eye is
joined by a muscular (?) band — inserted near the emergence of the optic nerve — to
the anterior margin of the posterior eye. In the latter the tapetum reaches the in-
ternal cuticula, but not the external cuticula; it contains four tapetal nuclei. Many
of the retinal nuclei are elongated, and taper at one end (compare the retinal nuclei
of the anterior- eye in Figs. 23, 24), probably indicating the region of their connec-
tion with a fibre of the optic nerve. The bacilli are evidently more numerous than
the retinal nuclei.

PLATE V.

Fig. 23. Median face of a sagittal section ; anterior and posterior median eyes.
The course of the optic nerve to the posterior eye sketched in from the preceding
sections. In the anterior eye the fibres of the optic nerve can be traced to the elon-
gated anterior ends of the retinal nuclei, which exhibit shapes dependent on this
union.

Fig. 24. Lateral face of a sagittal section through the anterior and posterior
median eyes of the right side of the same specimen as the last figure. The distribu-

MUSEUM OF COMPARATIVE ZOOLOGY. 105

tion of the fibres of the optic nerve in the anterior eye as in Fig. 23. The post-retinal
nuclei still distinguishable, although considerably flattened. In the posterior eye the
retinal cells are separated from the "lentigen" by a distinct pre-retinal membrane.
Bacilli already well developed iu the anterior half of the eye. The tapetum reaches
to the external cuticula as well as to the internal cuticula, and contains several tape-
tal nuclei. The optic nerve and its radiating fibi'es are shown in the " post-retinal "
layer.

Figs. 25-32. Diagrammatic figures to show a possible course of development of
the several layers of the simple eyes from the hypodermis. Consult the text, pp.
87-98.

Figs. 25, 26, 30-32. To illustrate the development of eyes of the " pre-nuclear "
type. The primary bacilli, at the distal ends of the hypodermal cells, are colored yel-
low ; the secondary bacilli, at the (originally) deep ends of the cells, red. Optic-
nerve fibres are yellow ; they should have been continued up to the nuclei. Arrows
in Figs. 30, 31, indicate the directions of the light from two different sources. (The
letters.^, and P. were accidentally omitted.)

Figs. 25-29. To illustrate the development of eyes of the "post-nuclear" type.
The primary bacilli (yellow) retained on one side of the eye ; replaced on the other
side by the tapetum (here assumed to have been developed from the remaining half
of the original retina). Optic-nerve fibres, red; they should have been continued
up to the nuclei on the side away from the bacilli.

CONTENTS.

I. Source and Relations of Retina. p^c,

1. Historical Summary 49

2. Discussion of the Conditions in —

a. Arachnoids 55

i. Myriapods 60

c. Insects 63

II. Pre-retinal Membrane and "Sclera" 67

III. Tapetum 72

IV, Development of "Post-Nuclear" Eyes in Agelena.

1. Posterior Median Eye 75

2. Lateral Eyes 82

V. Optic-Nerve Termination 84

VI. Theoretical: Causes of Inversion in Eyes with —

1. Pre-Nuclear Bacilli 87

2. Post-Nuclear Bacilli 94

VII. Bibliography 99

VIII. Explanation of Figures 101

/,

■Mt

Mark - Simple

..'«-..-5'^ *^*

■€::.■

i'

"J ff -^T. ^-^

■^':><-

n op-

..• •*■?!:■<:■■

I.a.-

■ " ff

. -•C^^- 'facyn..

20.

21.

22.

tap.

A> '"H

Vt. •'

16.

X

~)

JB.

\

19.

'^.

tap.

Ma r k - S implk Eye h

.'■•' o

I.

pr r. y

/

''^'■^^

w

"' ■-'■' ■% ,iia

'•"'^ji^^ist. _>*'*

■'f-:«Sf-.^a'

~N-

vi^' /

lf..L.Mark-,del.

/

B.Mii^ci.i'"'

Mark - Simple Eyes

Pr.. V

23.

:.-:< '<*.>>•>

■^

25.

t»p

/"■

2e

'".</

=/■'

24. ■

/r.«.

30.

31.

33

27

26

23

1 Marl:

B ^fe^;»l ;,..h

No. 4. — Studies from the Newport Marine Zoological Laboratory.
Communicated hy Alexander Agassiz.

XVIII.

On the Deoelopment of the Calcareous Plates of Amphiura.
By J. Walter Fewkes.

In a paper published in March, 1886,* it was shown that the egg of
Ophiopholis develops into a pluteus-like larva in which the two lateral
arms with calcareous rods are well developed. In the month of July
of the past summer a similar larva was traced into an adult pluteus.
This adult pluteus of Ophiopholis is the same as that doubtfully referred
by A. Agassiz to Amphiura squamata, thus confirming the statements f
made in the paper above quoted. While however it was possible to
determine the general anatomy of the adult pluteus of Ophiopholis, cir-
cumstances rendered it impossible for me to follow the growth of the
calcareous plates and skeleton in the body of the young Ophiopholis
forming in this pluteus. It was more convenient to complete my studies
of this part of the subject on another genus. For this work the well-
known viviparous Ophiuran, Amphiura squamata, Sars, was chosen.

This species is well suited for the study. It is common near the New-
port Marine Laboratory, and easily collected. It is viviparous, and the
young are found in the parents through the months of August and Sep-
tember, when the Laboratory is open for work. Whatever disadvan-
tages come from the possible retardation or acceleration in the sequence
of the development of the plates brought about by the abbreviated
development, is certainly offset by the ease with which material can be

* Preliminary Observations on the Development of Ophiopholis and Echina-
rachnius, Bull. Mus. Comp. Zobl., Vol. XIL No. 4, pp. 105-119. In this paper it was
first shown that Ophiopholis has a nomadic pluteus.

t On p. 119 (op. cit.) it is said, " Ophiopholis aculeata has a developnient with
metamorphosis, passing through a larval stage called the pluteus," and on p. 106,
note, " The pluteus referred to Amphiura squamata in the ' Embryology of the Echi-
noderms,' and doubtfully to Amphiura in ' Embryological Monographs,' may be a
pluteus of Ophiopholis." The embryology of A. squamata is partially traced in the
following pages.

VOL. XIII. — NO. 4.

108 BULLETIN OF THE

procured. My attention in the following observations was chiefly di-
rected to the growth of the hard parts of the body, often called the
skeleton, while observations on the bilateral larva are simply introduced
as they are thought to throw light on some of the many obscure ques-
tions in relation to this part of the subject.

I. GENERAL OBSERVATIONS.

Many observers have called attention to the fact that A. squamata is
viviparous. No one, so far as the literature has been studied, has seen
the young in the American shallow-water Amphiura, although Lyman
and others have shown its undoubted identity with the European,
A. squamata. Of the other species of Amphiura which live in our waters
no one has studied the development.

Metschnikoff * has shown that A. squamata is hermaphrodite. This
observation has been verified by Apostolides,t and I have found the
male genital glands in the Newport specimens in the same position as
figured by Metschnikoff t in the European. Almost every specimen of
Amphiura which was collected in August and September was found to
contain young, while some had the male glands with lively sperm and
young in various stages of growth in the same individual. This fact
may look like self-fertilization. It remains to be seen, however, whether
the sperm from one individual can impregnate its own ova, or whether
this product from another specimen is required for this function. I am
not aware that any one has yet succeeded in artificially impregnating an
Amphiura with its own sperm. Self-fertilization may take place, but no
one has yet recorded it.

My specimens of the adults were found in crevices of the cliffs just
below low-water mark. We found good collecting-grounds on the south
end of Castle Hill, at Price's Neck, and near Horse's Head, Conanicut
Island. The adults prefer a bottom composed of broken Mytilus shells
and small stones. Lyman § has already spoken of their preference for
a bottom of broken shells. With a long-handled dip-net a few handfuls
of this bottom can be scraped up from the crevices, and the adults can be
easily picked out of the fragments of shells with pincers.

* Studien iibcr die Entwickelung der Echinodermen und Nemertinen, Mem.
de VAcad. Imp. des Sci. de St. Petersb., [7] XIV. 8, pp. 13, 14 (separate copy).

t 1* These. Anatonne et Developpeiueiit des Ophiures, Arch, dc Zool. Exp. et
(?e,>.., X. p. 204.

X Op. cit., PL III. Fig. 1, B. Our Amphiura squamata is also hermaphrodite.

§ Ophiuridae and Astrophytidae, III. Cat. Mus. Comp. Zool., No. 1.

MUSEUM OF COMPARATIVE ZOOLOGY. 109

The young were taken from the adult by cutting off the disk, leaving
the arms intact. By removing the disk in this way it was found that
the young remained in it, and when left for a short time in pure
water the older specimens crawled into view. Lyman * has recorded
that adults found near Bordeaux often in confinement voluntarily cast
their disk, from which the orange-colored y^ung emerge. The older
forms of the young can voluntarily escape from the disk through the
genital slits. Those which have an umbilical attachment, particularly
the bilateral larvae, must be teased from the ovarian attachment by
means of needles or small scalpels when required for study. A deli-
cate dissection is necessary to separate the larva from the inner wall of
the body without harm to the attached young.

The larvse were studied alive. Many were killed in weak alcohol,
hardened in 93° alcohol, placed in chloroform for three minutes, and
then mounted in Canada balsam. The treatment with chloroform
brought out the plates with success. Staining in borax carmine showed
the water-tubes, but obscured the plates.

Young Amphiurse were found from the first of August until the end
of September, with little reduction in numbers except in the last week.
The number of young from diflerent adults varied. Ordinarily a gravid
adult would have from ten to fifteen (generally ten) free young, and
possibly several bilateral larvae at the same time. The older young live
free in the body cavity, generally with the arms coiled up, but often
with an arm extended through the genital slit. Parturition is moder-
ately slow, sometimes rapid. The young when born are orange-colored
on the disk, with Avhitish-colored arms, and with plates less firmly
articulated than in the adult. When once born, young were not seen, to
return to the pouches, nor were they cared for by the adult. They did
not cling to the mother after birth. Especial attention was directed to
this observation, for I was familiar with the figures given by Thomson f of
young Ophiurans of-another genus clinging to the disk of the adult.

The young Amphiur£e which voluntarily left the parent were of course

* Op. cit., p. 123.

t Notice of some Peculiarities in the Mode of Propagation of certain Echino-
derms of the South Sea, Journ. Linn. Soc, XIII. Dr. W. Stimpson {Proc. Bost.
Soc. Nat. Hist., IV. p. 2'26) found in Charleston, S. C, small Ojjhiurans clinging
to the arms of Hemipholis cordata, Lym. {Ophiolepis elongata, Say). He regarded
them as the young of the animal to which they were clinging, and thought that they
"correspond" to the genus " Ophionyx, M. T."

Lyman (Challenger Ophiuroidea, p. 157) describes and figures two stages of the
young Hemipholis which he finds clinging to the arms and disk, and "suspects"
that the genus is viviparous.

110 BULLETIN OF THE

in confinement in glass aquaria, which condition must be given its proper
significance, and may have deterred them from clinging to the parents.
In this connection let me mention an observation which has been
repeatedly observed in dredging our common " basket-fish." The egg
and early development of this animal (Gorgonocephalus Agassizii) is
unknown, but the young with arms with a single bifurcation have
repeatedly been brought up from the bottom clinging to the disk of an
old adult. It is very necessary to find out whether or not the basket-
fish is viviparous, as this would possibly indicate.

The young Amphiurse are born at intervals, in a continuous series,
not all at the same time. There are well-developed young of different
sizes in the same parent. It was not possible to teU from the size, in all
cases, whether the mother or adult had young in the body. Swollen
specimens were ordinarily gravid, but many large specimens were without
young.

When the disk of many swollen specimens was looked at from above
(abactinal region), one or more of the interradial regions was observed to
have a reddish color and to be more swollen than the remaining. On
dissecting these specimens to learn the cause of the color and apparent
abnormal condition, they were found to harbor in their bodies bundles
of claret-colored ova. The development of these ova in the Amphiura
was traced by opening several specimens. Eggs were found in all con-
ditions of cleavage and larval growth, from very young specimens to an
adult Crustacean (Copepod V). They are parasitic in nature, and pass
their 3arly life in the body of the Ophiuran. In several instances
the ova of Amphiura were found with the ova of the parasite, but in
most cases an amorphous reddish mass indicated the possible position of
the ovarian gland of the host. The ova of the Ophiuran and those of
the parasitic Crustacean can be readily distinguished by a difference in
color which is well marked. The eggs of the Crustacean are found in
bright red or pink clusters. Those of the Amphiura are red and ora^i^e,
and not in free packets.

The ova of the Crustacean are unattached to the parent. They are
often found without parent Crustacean. The development of the parasite
will be treated in a special paper. None of the many attempts to produce
artificially two Amphiurans by cutting the disk in halves led to positive
success, although a six-armed Amphiuran cut in such a way that three
arms were left in each half of the body lived as two individuals for a
considerable time. They were not observed, however, to bud off new
arms, as it was hoped they would do. Embryos with four and six arms
were repeatedly found. Adults with six arips were cowpion,

MUSEUM OF COMPARATIVE ZOOLOGY. Ill

The disk in several instances was removed from its connection with
the arms, and the tive remaining connected arms lived for three days after
the mutilation.

I had some difficulty in identifying the adult Amphiura, from the fact
that in some of the best descriptions of A. sqaamata the color of the live
animal is not given, while in others it is recorded as white.* None of the
adults of A. squamata studied were white, but all were brown or choco-
late colored when alive. Variation of color is great among specimens of
the same genus, and in some localities this species may be while; bu!^
the specimens which were studied were not. white.

II. THE BILATERALLY SYMMETRICAL LARVA.

August Krohn t and Max Schultze J first found out tliat Amphiura
(Ophtolepis) squamata, Sars, is viviparous ; and that discovery has been
established without possibility of doubt by Sars,§ Lyman, || Metschni-
koff,ir Apostolides,** Ludwig,tt and others. Its viviparous life falls into
the following divisions: (1) The development of the bilateral larva;

* Packard states (Zoology, p. Ill) : "A. squamata, Sars, has long slender arms
and is white." In Agassiz's "Sea-Side Studies," p. 115, A, squamata is spoken of
as the "white Amphiura."

The adults were identified by comparison with specimens in the Museum of Comp.
Zoology identified by Mr. Lyman, and by reference to published descriptions. Prof.
Verrill has also examined my specimens of the adults, and verifies my identification.

+ Ueber die Entwickelung einer lebendig gebarenden Ophiure, Arch. f. Anat.
Physiol, u. Wiss. Med., 1851. Krohn first showed that Amphiura (Ophiolepis)
squamata is viviparous.

The first naturalist to describe the young oi Amphiura {Ophiolepis) squamata was
Joh. MiiUer {Arch. f. Anat. Physiol, u. Wiss. Med., 1851, p. 1 et scq.). He errone-
ously ascribed to Ophiolepis in this place a pluteus form. Following Krohn's paper
(op. cit., p. 353), where Ophiolepis (Amphiura) squamata is shown to be viviparous,
it is acknowledged that the young described by Miiller is of some other Ophiuran,
and not Ophiolepis squamata.

t Ueber die Entwickelung von Ophiolepis squamata, einer lebendig gebarenden
Ophiure, Arch. f. Anat. Physiol, u. JFiss. Med., 1852.

§ Jahresbericht of Leuckart, 1865, p. 86.

II OphiuridEe and Astrophytidse, III. Cat. Mas. Comp. Zool., No. 1.

H Oj}. cit., p. 13.

** Op. cit.

tt Zur Entwickelungsgeschichte des Ophiurenskelettes, Zeit. f. Wiss. Zool.,
XXXVI.

112 BULLETIN OF THE

and (2) The development of the pentagonal or stellate young, free in the
body uf the parent.

The youngest embryo of Amphiura which was observed by me is a
blastosphere.

Blasto&phere. — The blastosphere (Pi. 11. Fig. 1) was found free in the
body of a dissected adult, and had probably ruptured its connection
with the parent. It closely resembles the blastosphere of some other
Echinoderms, anil is of about the same age as that of Amphiura figured
by Metschnikolf * and by Apostolides.f

The few blastospheres of Amphiura which were ftnind were unat-
tached to the body walls or to each other. In later stages, as in the bi-
symmetrical larvae, the young Amphiura) are attached l)y a structure
called the umbilicus. Sir W. Thompson has spoken of the free young
of certain viviparous Echinoderms in the body cavity of adults, in his
" Notice of Peculiarities in the j\Iode of Propagation of certain Echino-
derms of the Southern Sea," X as not appearing to have in any case an
organic connection with the parent. It seems natural to suppose, if
the bisymmetrical larva is attached, that the younger stages are not
free ; but I have no proof of this. It is supposed, not proven by
observation, that the blastosphere is broken from its attachment.

The cells of the blastosj)here are surrounded by two envelopes (??i^, m^).
I am unable to prove that either of these envelopes is " chitinartig," as
Metschnikolf describes the apparently homologous outer envelope. The
inner envelope resembles somewhat the cortical laj^er which I have de-
scribed in the ovum of Ophiopholis where it is believed to be homologous
to the zona radiata of other Echinoderms. Both envelopes are transpar-
ent. Diameter, .13 mm. The blastodermic cells arc spherical, red in
color. There is no ciliation on the outer surface of tlie blastodermic
cells. Nucleus of each cell well seen. There is a segmentation cavity
(cav) as in other Echinoderms.

Gastrula. — There is no free nomadic gastrula in Amphiura, but the
blastosphere is followed by a larval condition (PI. II. Fig. 3), in which
we recognize certain characters of a gastrula. According to Metschni-
koff,§ directly after the blastosphere stage there appears in the pro-
tojilasm of the blastodermic cells two layers of cells, " von denen die

* Op. cif.., PL in. Fig. 3. The "cavity" is lettered v (no explanation) in PI. III.
Fig. .5 ; cs in Fig. 4 (cs, Fig. 4, is the segmentation cavity),
t Op. cit., PL XII. Fig. 9.
} Jonrn. Lin v. Snc, XII.
§ Op. cit., !>. 14.

MUSEUM OF COMPARATIVE ZOOLOGY. llo

untere kcirnig iind roth die obere dagegen glassartig iind homogen er-
scheint." A stage similar to his is figured in PI. II. Fig. 3. The mode
of formation of the cavity is not made evident in either ApostoHdes' or
Metschnikoff's account. The inner layer of cells, or the red cells, is sup-
posed to be the mesoblast ; the outer, the epiblast ; and the walls of the
cavity, or hypoblast, are concealed by the mesoblast. It is possible that
hypoblast and mesoblast have as yet not differentiated themselves in the
red cells. The blastosphere unquestionably has a true segmentation cav-
ity, but by the concentration of the pigmented cells near its interior, by
which concentration the superficial layer (epiblast) of transparent cells
appears to be separated, renders the interior of the egg so opaque that ob-
servation of the contents is almost impossible without cutting sections.
As only one blastosphere and not more than four gastrula^ were found,
my material was limited. The transparent outer layer {ep) is probably
the epiblast, and the masses of reddish cells in the interior of the body of
the embryo may be the same as the so-called amojboid or mesoblastic cells
in other Echinoderm embryos. The true hypoblast either is not sepa-
rated from the red cells or is differentiated from them and hidden by
these opaque cells. There is what appears to be an external opening (a)
passing into the opaque region of the ovum, which fact would seem to
indicate the existence of a cavity. Unfortunately, however, I am not sure
that such an opening exists. ApostoHdes, however, has described and
figured this opening, and there is no reason to doubt its presence. It is
necessary to have new observations on the existence of this primitive
opening and the way it is formed. It disappears early in larval life.
The mode of formation of the hypoblastic wall of the cavity of the gastrula
of Amphiura has been interpreted in two ways. The first, and that
which would seem the true one from what we know of other Echino-
derms, is the embolic method; the second by delamination, unknown
elsewhere in the group, is very exceptional and peculiar. ApostoHdes *
supposes that in Amphiura the hypoblast is formed by a delamination of
the blastodermic cells and not by invagination. Metschnikoff f says that
it is formed by invagination. It is probable that the true blastopore was
not observed by this naturalist, and the invagination which he observed
was that of the mouth and possibly the oesophagus. This, however, does

* Op. cit., pp. 25, 192.

t Op. cit., p. 14, PI. III. Fig. 6. A cavity with hypoblastic walls between it and
the cutis (c) must have existed, as he speaks in the text of such a cavity (*' Darman-
lage "). His figures do not well represent the hypoblast.

VOL. XIII. — NO. 4. 8

114 BULLETIN OF THK

not prevent our accepting the theory that the cavity of the gastrula is
formed as Metschnikoflf supposes.

In Ophiopholis it has already elsewhere been shown that the archen-
teron is formed by embole, and the known law of development in other
Echinoderms would point to the same method in Amphiura. If there is
an invagination of the blastoderm to form an archenteron in Amphiura, it
is more masked than in Ophiopholis, and at present it is not possible for
me to say whether Apostolides' or Metschnikoff's view of the mode of
formation of the archenteron is the correct one. It looks very much as
if the epiblast is separated from the reddish layer by a delamination, but
it must be remembered that Amphiura is a viviparous genus, and possibly
has a highly abbreviated * development in its early history. We may
consequently suppose that more or less modification or concealment in the
embolic mode in which the archenteron is generally formed in Echino-
derms has resulted. It must also be remembered that the majority of
gastrulaj of Echinoderms are embolic. My observations support in part
Apostolides' statement that the primitive cavity, not however the seg-
mentation cavity, of the gastrula is the intestine (" anus embryonnaire ")
of the future pluteus. Probably the stomach should have been included
with the intestine. The external opening, if such exists, is early closed,
and if it is lost, as it may be, from the attached life of the young Am-
phiura, is probably always functionless. We have the following state-
ment in regard to the anus of the young Amphiura. Apostolides states :t
" Dans le stade suivant, ou I'ebauche du tube digestif est completement
dessinee, on distingue bien au sommet de I'estomac, au milieu d'un bourre-
let, I'oritice anal." This would seem to show that there is an anal open-
ing, bui how it is formed cannot be answered so far as observation goes
at present.

In his first paper Metschnikoff recognizes an opening into the cavity
of the larva, and considered it as formed by an infolding of the blasto-
derm. He was probably mistaken in supposing this opening to be the
primary opening, or blastopore. He is believed to have missed altogether

* The abbreviation in development which leads to the reduction in the arms of
the pluteus stage in Amphiura is not believed to cause any great modification or va-
riation in the development of the primary plates of the test and arms. One or two
writers have brought to their aid, in speaking of the apparent discrepancy in the time
of the development of these plates in Amphiura and an Ophiuran with a pluteus, the
possibility of modification by abbreviation in the former genus. The argument is
deceptive, and should not be given too great weight.

t Op. cit., p. 208.

MUSEUM OF COMPARATIVE ZOOLOGY. 115

the blastopore, and the gastrula cavity or future intestine, as be confesses
practically in a later paper.*

The following quotation from Apostolides leads me to suspect that this
author did not clearly distinguish the mesoblastic cells in his young Am-
phiura with a single cavity (intestine) and single opening (anus). Possibly
he confounded them with the hypoblast. He says :t "Dans I'ectoderme
on commence a apercevoir quelques points oranges premiers indices
de calcification." If these calcifications are really formed in the ecto-
derm or epiblast, it is exceptional among larval Echinoderms, where they
are regularly formed in the mesoblastic cells. Metschnikoff;}: rightly in-
terprets the orange cells of the young Amphiura as mesoblastic or "cutis"
cells. There is nothing in Apostolides' account either of Ophiothrix or
of Amphiura to show that he recognized these cells which play such an
important part in the growth of certain parts of the larval Echinoderm.

A study of Metschnikoff" 's Fig. 6. PI. III.^ is an instructive one. In
this figure the epiblast (ep) is well formed, and the opening (an opening
not figured, § but described in the text) on the lower pole is identified with
the mouth opening of the older larvae, which assume a bilaterally sym-
metrical contour. The young Amphiura is already bilaterally symmetrical,
for on each side of the "opening" can be seen the beginning of the
vaso-peritoneal vesicles, or water-tubes (v). At the pole opposite the
supposed mouth there are trifid bodies (cc), identified as the provisional
spines of the pluteus.

The homology of the parts of the larva mentioned has given me much
trouble ; for if we regard the SQ-called mouth as the original opening or
future anus, the positions of the water-tubes and spines as compared with
the same stage in other Echinoderms are wrong. If the opening in ques-
tion (mv) is a mouth or second infolding of the epiblast, where are the intes-
tine and the anus 1 In his admission * that Apostolides is right in his
interpretation of the homology of intestine and anus Metschnikoff" must
have abandoned the idea that the interpretation of this figure is a correct
one so far as the opening mv is concerned. I have found a larva similai-
to the figure quoted (Fig. 6), vnth the two transparent bodies (v) which

* Zeit. f. Wiss. Zool, XXXVII. p. 307.

+ Op. ciL, p. 210.

X Studieii iiber die Entwickelung der Echinodermen und Nemertinen, Mirfi.
de I' Acad. Imp. dcs Sci. de St. Petersb., VIP ser. XIV. 8.

§ There is a mistake in letteriug and in de3cription. On p. 15 mv is spoken of
as mouth, mv in the explanation of Figs. 3, 4, 5, is the vitelline membrane ("Dot-
terhaut").

116 BULLETIN OF THE

he has interpreted as water-tubes, and I am led to regard it as admitting
another interpretation from his. It shows that what he regards as mouth
may be in reaUty the anus. I am not wholly settled in mind, however,
in this conviction, especially if the two transparent bodies (v) are, as he
interprets them, water-tubes, the right and left vaso-peritoneal vesicles.
Their position would lead to the belief that Metschnikoff's interpreta-
tion is correct, for in all Echinoderms these bodies are found one on each
side of the plutean or brachiolarian mouth. Subsequent larvae, which
are here figured, show that the provisional plutean appendages are not
necessarily first formed at the anal pole, as these are situated in the larva
he figures.

Mouth, (Esophagus. — The mouth (or) of Araphiura is formed by invag-
ination, I was in doubt when I wrote my preliminary account of the
development of Ophiopholis whether the primitive gastrula opening be-
came mouth or anus of the pluteus. My figures* seem to indicate that
the gastrula mouth becomes the plutean mouth ; and if that is true, Ophi-
opholis is certainly exceptional. I find the same difficulty in the study of
the development of Amphiura, although it seems as if the general law *
of Echinoderm development ought to hold here as in Strongylocentrotus
and others. In a bisymmetrical larva of Amphiura (PI, II, Fig. 4) we have
oesophagus, stomach, and intestine well developed. If there is in this

♦ Op. cit., PI. L The law referred to is that the first opening, blastopore, is the
future anus, and a second opening is found to develop into the pluteus mouth. This
law has been found to hold in several genera of Echinoids, but has not been supported
by observations of the Ophiurans. The supposition has been that in Ophiurans the
law is the same as in Echinoids. Observations are now wanting to prove that such
is the case. In my paper on the development of Ophiopholis it was not possible for
me to prove that the gastrula mouth, blastopore, becomes the vent of the pluteus.
The lettering gni (PI, IV., Bull. Mus. Comp. Zobl., "Vol. XII. No. 4) of the gastrulae
of Echinarachnius is a typogi-aphical error, as a reference to my text will show. In
some other Echinoids the blastopore becomes the vent of the pluteus, according to
most authorities. I have not observed the fate of the blastopore in Echinarachnius,
and this erroneous lettering might imply that I was sure that the blastopore becomes
the pluteus mouth. The candid reader of my text {pp, 128, 129) will I hope acquit
me of holding that the blastopore becomes the pluteus mouth in Echinarachnius, Of
the origin of the mouth of the pluteus it is said (p. 128) : " The walls of this infold-
ing" (second invagination) "break away and form the future anus {v) of the stages
immediately following the gastrula, and probably the mouth of the pluteus," Of the
fate of the blastopore in Echinarachnius I have no observations, and "nothing to
show that there is any difference in this genus from what is recorded in Strongylo-
centrotus and other Echinoids " (p. 129),

MUSEUM OF COMPARATIVE ZOOLOGY, 117

larva an anal opening into the intestine, that opening would be function-
ally useless, for it is closed by the sac in which the embryo hangs. Be-
fore the young sever their attachment to the parent, anus and intestine
are atrophied or higlily modified so as to lose all semblance to these or-
gans in other Echinoderm larvae. The mouth also in very early stages,
as can be observed by an examination of Figs. 5, 7, is closed by the sac in
which the larva is suspended. It would not seem strange if, in the pos-
sibly abbreviated development which is found in Amphiura, a true anal
opening never forms, and that the primitive gastrula cavity is formed not
by invagination but by delamination. The intestine and anus in stages
corresponding to Fig. 4 are not figured by Metsclmikoff.

For a considerable time, and almost through the whole course of the
development of the bilateral embryo, a conspicuous cluster of orange pig-
ment is found at the anal pole of the larva near the intestine.

There are some difficulties in a comparison of the bilateral larvoe (Figs.
4-11) with others which have been figured by other observers. In the
papers by Apostolides and Metsclmikoff" the position of figures of the same
larva is diff"erent, and Metschnikoff" does not follow in his figures the ori-
entation given in the text. He says:* "Wenn man sich den Embryo
mit dem Esophagus nach oben, den Magen nach unten liegend denkt, so
wird sich die Wassergefusssystem Anlage auf der linken Seite befinden."
This is a position exactly opposite that in which he has placed his fig-
ures. As the mouth on a median line is a convenient point for reference,
its position ought to be mentioned when speaking of the position of the
larva. When the mouth is turned to the observer and the anal end of
the larva is above, the right water-tube (right-hand side of larva) is that
which divides into five divisions. When the mouth is turned from the
observer and the anal pole placed above, the left water-tube is that which
divides to form the water-vascular system.

Umbilicus. — The connection of the bilateral larva with the ovary is by
means of a structure which may be called the umbilicus, or "ISTabelschnur"
(«). It is at first, in young larval stages, broad and thick, and later
becomes reduced in size to a simple string-like structure. Its existence
prior to the pentagon-shaped larva is not indicated by Apostolides and
Metschnikoff", although represented by Max Schultze. Metschnikoff" t
says: "Erst auf solchen Stadien (Fig. 17) konnte ich deutlich den
von Krohn und Max Schultze bereits gesehenen Strang beobachten
welcher sich dem das provisorische Skelet tragenden Kcirpertheile des
Embryo inserirt." In the early conditions (Figs. 5, 8, 9) of the bisynimet-
* Op. cit., p. 16. t Op. cit., p. 18.

118 BULLETIN OF THE

rical larva it is present, but has been ruptured in the young larvae which
he has figured prior to that represented in Fig. 1 7, and will be seen figured
in my plate in some of these or corresponding stages.

Of the ultimate fate of the " Nabelschnur " (u) Metschnikoff says:*
"Daer iiber schliesslich (ebenso wie das provisoriche Kalkskelet) ver-
schwindert, ohne in den Kdrper des sich bildenden Sternes direct Uberzu-
gehen, so muss man seine Riickbildung durch Atropie annehmen." That
a part of the umbilicus and the whole of the provisional skeleton of the
pluteus is absorbed seems to me true, as traces of the provisional skeleton
(ps) are found in the pentagonal larva even when free from the mother.
Of the freedom of the oldest stage when the remnant of the plutean skel-
eton was observed there may be doubt ; but there can be little question
that this skeleton enters into the formation of the future starfish, al-
though possibly not directly into the formation of any special organ.

It is thought that all the "hunchback" partf of the larva figured in
Fig. 7 passes by absorption into the embryo.

As to what part of the bisyrametrical larva is the homologue of the
pluteus of Ophiopholis it may be said that the Amphiura young is a
pluteus without arms, although the calcareous framework of the lateral
arms is present. The larva (Fig. 7) is a pluteus with aborted arms.

Water-tubes and " Lateral Scheiben.'" — In the early stages of growth
up to the pentagonal larva the water-tubes (Hydrocoelen) and the lateral
bodies (Enteroccelen) were seen, but nothing new added to our knowledge
of these structures. In one larva the right-hand water-tube is present
after the left has begun to push out the five extensions which form the
terminal tentacles. This tube was thought to open externally, and near
its opening a trifid calcification was observed. It is known that mon-
strosities so called in the development of the tubes are said sometimes to
give us a larva with even a pentamerous right water-tube, and it may be
that this development belongs in this category. It does not seem reason-
able that the right-water vesicle disappears, as stated by Metschnikoff. %
We must wait in answer to the question of the fate of tlie right vesicle
until we know the origin of the right " Scheibe," or enterocoel.

Observations upon the origin of the water-tubes of the Ophiurans are
very much needed in the present state of science, and we can hardly put

• Op. ciL, p. 18.

t The protuberance on the right-hand upper corner of the figure imparts to the
larva a hunchbacked appearance. All of this protuberauQe is absorbed in the growth
of the young Amphiura,

J Op. cit., p. 16.

MUSEUM OF COMPARATIVE ZOOLOGY. 119

great confidence in some of the speculations which have been indulged in
until we know whether the Enterocoelen, and the Hydrocoelen or water-
tubes, originate in Ophiuraus as paired structures or not, and whether the
right Enterocoel is the same as the right "Lateral Scheibe" of Metscli-
nikofF or not. The question also of the connection of the water " tubes "
with the oral plate or madreporite is also imperfectly answered. It may
be supposed that the Hydrocceleu form from the Enterocoeleu, which are
themselves diverticula of the first invagination, and which persist in the
form of the " Lateral Scheiben."

Provisional Spines of the Pluteits. — Max Schultze * first made the in-
teresting discovery that the embryo of the viviparous Amphiura squamata
is furnished with a provisional calcareous skeleton which is comparable
Avith the spines of the arms of a pluteus. This important discovery has
been verified by several observers. It presents us with a most interesting
case of the retention of structures useful to free larva in an embryo where
they can have no use, or if they have any use it must be a somewhat dif-
ferent function from that which they have in the free pluteus.

The provisional spines of the pluteus have a maximum development in
the bisymmetrical larva (Fig. 8), but are not wanting in the younger
stages of the pentagonal embryo, where they are very much reduced in
size. The number, mode of origin, and position of the provisional spines
of the pluteus seem to diff"er in difi"erent specimens. They are not always
double or bisymmetrically arranged in reference to a plane passing through
the mouth of the symmetrical larva and the umbilical connection with
the parent. In the majority of instances the spine on the side opposite
that in which lies the "left water-tube " is well developed, while that on
the same side as the left water-tube is stunted (see Figs. 6, 7).

The provisional spines generally originate near the anal pole, but are
found in some larvae in the vicinity of the stomach and on one side of the
body (Fig. 4, ps). In older stages of the bilateral larva the provisional
spines form by reticulation a calcareous network (Fig. 10) similar to
what we find in the anal lobe of Echinarachnius. This reticulation is
hardly distinguishable from the permanent radial plates which form in
the same position on the larva. The provisional calcareous rods are ulti-
mately absorbed in the developing embiyo, but do not wholly disappear
until after the young Amphiura has passed into the pentagonal form (Fig.
13). When last observed they were noticed just under the region of the

* Oj\ ciL, pp. 44, 45 ; PI. I. Figs. 2, 3, 4, 5 a. Krolui was not able to find a trace
of the pluteus (op. cit., p. 340).

120 BULLETIN OF THE

body where the umbilicus is joined to the edge of the disk (Fig. 12).
Metschnikoff has figured them in the same position in Fig. 17 of his
Plate IV. Tliere seems abundant evidence that they are absorbed into the
body of the forming Ophiuran, as in Ophiothrix and Ophiopholis.

III. THE PENTAGONAL EMBEYO.

There are two forms or conditions in which the pentagonal embryo is
found. The one (Fig. 12) of these follows in age close upon the bilateral
larva, and is still attached to the mother ; and the latter is represented
by those larval stages when the young Amphiura has severed its connec-
tion with the parent and is leading an independent life (Fig. 13). The
exact time at which the umbilicus is broken was not observed, but the
rupture takes place certainly a relatively long time before the young
leaves the parent. The young larva then seems for some time to live free
in the parent without umbilical connection.

It becomes an interesting physiological question to determine the mode
of alimentation of a young Amphiura in the body of the parent, and with
no real connection with the adult. It would seem as if in older stages at
least the young might be nourished by foreign matter taken into the open
mouth. The genital slits of the parent would furnish an easy entrance
for foreign bodies or small animals into the sacs, and the young Aniphiurae
while free in the body of the parents probably use these bodies as food.

A. THE DISK.
1. Plates of the Abactinal Eegion of the Disk.

Dorsocentral and Radials. — The aboral integument of the disk has
embedded in it in young stages of growth six reticulated calcareous
plates. These plates consist of a single central, dorsocentral {dc), and
five radials, the primary radials or radialia {rp). These plates have been
observed, figured, or described by Krohn,* Schultze,t Lyman,:]: A. Agas-

* Op. cit., p. 34L Krohn figures (PL XIV. Fig. 1) a cross-shaped dorsocentral
surrounded by a continuous calcareous ring with no separate radials. This " einzigen
Stiicke bestehende Kalknetz " gives rise to " fiinf Schuppen." The radials, accord-
ing to a note on this page, are isolated from the beginning.

t Op. cit., p. 41.

::: OphiuridiE and Astrophytidse, Old and New, Bull. Mus. Comp. ZooL, Vol. III.
No. 10, p. 264.

MUSEUM OF COMPARATIVE ZOOLOGY. 121

siz,* MetschnikofF,t and Ludwig.J The dorsocentral early takes its per-
manent place, and remains near the centre of the abactinal region of the
disk ; the radialia are subsequently to formation pushed nearer the peri-
phery by the interposition of new plates between them and the dorsocen-
tral. They are never, however, in Amphiura pressed to the very periphery
of the body, and consequently never extend out on the arms. In early
stages the dorsocentral § is not formed, the five radialia originating first.

The dorsocentral in the young Amphiura (Fig. 1 3) occupies the centre
of the abactinal surface of the body, and is irregularly pentagonal. Its
origin was not traced, but there is no reason to question the observations
of Ludwigt and Schultze|| that the radials appear before the dorsocentral.
In the youngest pentagonal embryo which was studied (Fig. 12) in which
the umbilicus {u) was still unbroken, the five radialia (rp) were well
formed and of comparatively large size, while the dorsocentral (dc) was
small, indicating apparently a later formation. Ludwig t says, " Ganz
unterdriick aber wird die Entwickelung eines Centrale niemals." The
radialia or primary radials are among the first plates to form, and origi-
nate while yet the Amphiura is in a bilaterally symmetrical condition.
It is extremely difficult to distinguish them in earliest conditions from
the network at the anal end of the provisional pluteus rods (Fig. 8), but
they are among the first plates of the Amphiura to form. The question
of whether they antedate in formation any of the plates of the actinal
region of the disk will probably be correctly answered in the affirmative.
They probably appear before the first pair of adambulacral (q. v.) plates
and undoubtedly before the terminalia (q. v.).

A. Agassiz states :1[ " We have the most positive proof of the origin of
the dorsocentral plate of starfishes and Ophiurans as a single Y-shaped rod
appearing simultaneously with the five basals." Ludwig, on the other
hand, states : " Diese sechste Platte, das Centrale tritt bei Amphiura squa-
mata in der Eegel spater auf als die fiinf Eadialia." Ludwig holds **

* Embryology of Echinoderms, Mem. Amer. Acad. Arts and Sci., III. 1856.

t Op. ciL, p. 18 ; PI. IV. Fig. 17.

t Op. ciL,-p. 195.

§ The reader is referred in this connection to Fig. 16, PI. VII., in my paperon the
development of Echinarachnius {Bull. Mus. Comp. Znol., XII. 4). In this figure,
which is of a young sea-urchin, the calcareous network of the dorsocentral plate {c pi)
has not begun to form, although that of the ring of plates surrounding it is well
marked.

II Op. ciL, PL I. Fig. 4.

IF Report on the Echini, Mem. Mus. Comp. Zool., Vol. X. No. 1.
** Page 187.

122 BULLETIN OF THE

that the terminals appear at the same time as the radials, but could not
determine whetlier their origin is earlier or later in time. He considers
it probable that the terminals appear earlier. It is suggested that they
appear in Amphiura * later, as their comparative sizes (shown in my
figures) indicate. It is believed that Ludwig is right in his statement
that the centrale (dorsocentral) appears later than the five primary radials
in Amphiura.

It is interesting to see how far this order of late development of the
dorsocentral is repeated in plates of the Asteroidea and Echinoidea sup-
posed to correspond with the dorsocentral, radials, and terminals. Our
knowledge of the sequence of the development of these plates is hardly
accurate enough to make definite statements, but there seems to be some
resemblance in these three groups in this particular.

According to A. Agassiz,t the abactinal system of the young Echinoid
" consists of a single large plate, . . . and the new plates are added in a
spiral manner round the anal plate." This large abactinal plate is figured
in Fig. 28 1 and in several figures by Loven. It would appear from
this that they regard | the suranal plate as formed in sea-urchins of
this age before the oculars and genitals. A. Agassiz finds in Salenia an
adult genus with this plate, as in the young of some other genera ; and ac-
cording to Loven, § in this genus (Salenia) this plate is retained through
life, and instead of being a temporary is a permanent structure. A. Agas-
siz II has examined specimens of young Saleniee to obtain information in
regard to the suranal plate and its homology with the " single large anal
plate of the early stages of young Echini belonging to other families;" but
he finds that "the arrangement of the plates of the abactinal system does
not diflTer from that of the older specimens, the suranal being only pro-

* Sladen (op. cit., p. 27) judrjea from the figures of larval Ophiurans which pass
through a pluteus stage, given by Agassiz, Metschnikoff, and Miiller, that it is more
probable that traces of the terminal plates appear before the first radials. In the
case of the Amphiura studied and figured by Metschnikoff, and possibly from the
figures of Miiller, he finds the reverse seems to occur. My observations on A. squa-
viata show that the radials are well formed before the terminals attain any great size,
or that the radials are of considerable size before the terminals have grown from a
simple spicular form.

t Embryology of Echinoderms, Mem. Amer. Acad., IX. 1864, p. 12, Fig. 28.

t Revision of the Echini, Mem. Mus. Covip. Zool., p. 280, PI. IX. Figs. 3, 6, 7, 8 ;
PI. X. Fig. 2.

§ Lltudes sur les !6chinoidees, Kovgl. Svenska Vetenskaps Handlingar, Bandet 11,
No. 7.

II Report on the Echini, Menu Mus. Comp. Zool., Vol. X. No. 1.

MUSEUM OF COMPARATIVE ZOOLOGY. 123

portionally smaller." This fact has possibly a meaning in the comparative
time when the suranal (dorsocentral) is formed, as compared with the
ocular and genital, as will be spoken of directly.

In regard to Neumayr's statement that in the young " Glyphostomes "
the anal plate is first formed, and that the plates of the genital ring are
later detached from it, A. Agassiz* states that undoubtedly the anal
plate in young Echinoids is the first plate to appear, and that genital
and ocular plates are independently formed around it.

Our interest in the study of the dorsocentral plate of Amphiura is
connected intimately with the origin of the suranal plate of the Echinoids.
In Echinoids of some genera, according to the authority mentioned, the
abactinal region is covered by a large single plate, suranal, which is pos-
sibly the dorsocentral, while in Amphiura a plate believed to be homo-
logous, dorsocentral (d), is very small in young stages, and is thought to
be developed after the radials. While opinions may be divided as to the
homology of the primary radials in Amphiura with ocular and genitals
of sea-urchins, it would seem as if a uniformity of opinion might be
arrived at in regard to the dorsocentral. If, however, in Echinoids this
plate forms before the ocular and genitals, and in Amphiura after the
same, one is tempted to ask whether they are homologous. One might,
of course, avoid the difficulty by the truism that the relative time of de-
velopment is of little consequence, and that the appearance of the plate
in Amphiura is simply retarded. Such an escape from the difficulty does
not give much satisfaction, even if we remember the abbreviated devel-
opment of Amphiura. The theory that the dorsocentral of Amphiura is
homologous to the suranal of sea-urchins is believed to be true. As far
as any objection based upon the different time of appearance of this struct-
ure is concerned, it is first necessary to examine the observations adduced
in its support. t While the evidence seems to be against the late forma-
tion of the dorsocentral in Echinoids, the author is confident that in one
genus of Echinoids, viz., Echinarachnius, no single plate centrally placed,
which represents the suranal, is developed before plates regarded as homo-
logous to the oculars and genitals. He believes that the suranal, which

* Report on the Echini, Mem. Mus. Comp. Zool., Vol. X. No. 1, p. 33.

t It is believed that the difference in relative time of the appearance of the dorso-
central, and the ten plates around it, in Stvongylocentrotus and Amphiura cannot be
satisfactorily studied except from stages of the former genus much younger than
those figured by Loven for this purpose (op. cit., PI. XXI.). There is a call for a
study of the young sea-urchin, between these and the pluteus, before we can defi-
nitely state whether dorsocentral or the ten surrounding plates first appear, or
whether they appear simultaneously or not.

124 BULLETIN OF THE

is here regarded as the dorsocentral, is developed after the oculars or
genitals,* and that the dorsocentral is formed axially to the same. In
Toxopneustes, according to authority mentioned, the facts seem to be
diametrically opposite those mentioned for Echinarachnius, while the
last-mentioned genus resembles Amphiura so far as the time of the devel-
opment of the dorsocentral is concerned.

The dorsocentral of the starfish, Asteracanthion, is apparently formed
in some cases after the radials (oculars) and genitals. In Asterina the
dorsocentral seems to coexist with the other ten plates from the first, as
shown in Lud wig's figures, although he does not say whether the dorso-
central appears before or after the other ten. Loven's figure of the young
A. glacialis (op. cit.) is not young enough to answer our question. In
A. Agassiz's Embryology of Asteracanthion it is shown that the ten cal-
careous rods are the first to form, and attain a considerable size before the
dorsocentral is represented. Metschnikoff gives very instructive stages +
of the young of an unknown Asterid ; but his description is so short, and
the arrangement of plates in it so remarkable, that it would be out of
place to interpret them here. This stage and those preceding it give no
answer to the question when the dorsocentral is formed. The question
which plates in the young Amphiura correspond to the oculars of sea-
urchins assumes a new phase in the light of what we know of the perma-
nent retention of the radials in the abactinal hemisome of the body of Am-
phiura, and the relation of the terminals to the primitive tentacle. Now
that we know that the primary radials of Amphiura are not pushed out to
the extremity of the rays, but always remain in the disk, and that another

* Consult PI. Vn. Fig. 16, Bull. Mus. Comp. Zool., Vol. XII. No. 4. This
figure is thought to show the truth of the belief stated. No limestone rods were
observed in C2)l, which occupies the position of the suranal or dorsocentraL

+ The figures alluded to are found on PI. XII. Figs. 1 and 2 (Studien liber die
Entwickelung der Echinodernien und Nemertinen). Fig. 1 is an abactinal view,
with five large peripheral, spiniferous plates, and a madreporic plate (JIfy). Within
this ring of jseripheral plates are seven smaller, non-spiniferous plates, one of which
is centrally placed. Metschnikoff was unable to determine the genus to which this
starfish belongs. He found the absence of the anus to recall Astropecten, Luidia, or
Ctenodiscus, but supposes that the character of the spines does not belong to these
genera. With this objection, so far as the size and general arrangement of these
huge spines are concerned, I cannot agree with him. I have studied the young of
our C. crispatus, and find the five peripheral plates which he figures, each with
three large conical spines, a median and two lateral, on each plate. Between each
pair of these peripheral plates, which are regarded as the terminals, there are three
adambulacial plates in each interradius, while in the stage figured by Metschnikoff
there is but the single madreporite in this position.

MUSEUM OF COMPARATIVE ZOOLOGY. 125

set of plates (termiuals) do suffer the change, we have this difficulty in a
comparison of the young Echinoid with the young Amphiura. The ter-
minals of Amphiura are independent centres of calcification from the
radials. If terminals and radials in Amphiura lie in the same radius,
how can the one or the other, especially the former, be the same as the
oculars of the sea-urchin 1 If we compare the apical region of a sea-
urchin and the abactinal hemisome of the young Amphiura, we have iu
Amphiura the terminals, plates which are supposed to be the same as
oculars of the sea-urchins. If that is so, what plates in sea-urchins can
be found to represent the radials of Amphiura, plates which are separate
calcifications in both Ophiurans (Amphiura) and Asterina between termi-
nals and dorsocentral 1 None exist. If, on the other hand, we say the
oculars of sea-urchins are the homologues of the radials of Amphiura,
they are not the same as another definite calcification, the terminals situ-
ated at the tip of the arm. Is it not more logical, from embryological
grounds, if we compare the apical system of young Echinoids with the
abactinal hemisome of Amphiura, not to suppose the first-formed plate in
an ambulacral radius is an ocular homologous to a terminal, but an oc-
ular homologous to a radial ; provided, of course, we compare the radial
series of Amphiura with tlie radial series of Echinoids 1* Is it possible
that what we call the ocular of the sea-urchin is in reality a consolida-
tion of the radial and the terminal, or that a plate homologous to the
radial is never developed 1 Either of these conditions would be a pos-
sibility, and more probable than that the eye-plate of the sea-urchin

* By the. " radial .series " of plates in Amphiura the author means the series which
lies in the radius extending from the centre of the dorsocentral through the middle
of the primary radials and terminals. By the radial series of the sea-urchins, the
author means those plates which lie in ?. radius extending from the centre of the dor-
socentral through the ocular. The above remarks in relation to radials and oculars
of Ophiurans and sea-urchins apply to those who compare the terminals of starfishes
and brittle stars without pluteus, with the ocular plates of the sea-urchin. Those, on
the other hand, who compare the terminals and radials (primary) of Amphiura are
believed to have this dilhculty. If the terminal of Amphiura is compared with the
genital of a sea-urchin, the madreporic opening of the Echinoid, which lies in the
same interradius as a genital, ought to lie in the same radius as a terminal in Am-
phiura. The same objection would hold in a comparison of the radialia of Amphiura
and the genitals of sea-urchins ; the madreporic body, which in the young Am-
phiura is found iu a plate called the oral, in the interradius would be found in the
radius. This, of course, supposes the fact that the genitals and the madreporic
body, since they lie in interradii, are comparable, and waives tlie homology of the
so-called ambulacral plates, which Ludwig does not find in sea-urchins except in the
auriculsB,

126 BULLETIN OF THE

is homologous at the same time to the radials and the terminals which
originate in both Amphiura and Asterina in two separate calcifications.

A comparison of the young sea-urchin with the young Ampliiura reveals
the following fact. The radials {rp) of Amphiura occupy a position, as
regards the dorsocentral, similar to that which the ocular plates of the
young sea-urchin hold to its anal plate, which is regarded as the dorso-
central. In the sea-i;rchin the ocular plate is perforated for the eye-spot.
The eye has not been found in the radials of any Ophiuran. In one
case the plate is an ocular, or eye-plate ; in the other it has no eye. Nor
is the eye known in the terminal in the Amphiura. Is a plate with an
eye homologous to one without an eye] This of course opens the ques-
tion whether the " eye " of the starfish and the " eye " of the Echinus are
homologous. I believe an answer to this question can only be given by
a histological study of the eye and its relation to the water-tube in
Echinoids. A. Agassiz has shown the relationship of the eye-spot to
the unpaired tentacle of Asteracanthion, and it remains to be seen
whether in Echinoids the eye-spot is similarly formed. When it has
been shown that the eye-spot of Echinoids is homologous to the eye-spot
at the end of the arm of the starfish, it may be asserted that the termi-
nal plate of the starfish is homologous to the ocular of the urchin.
The adult form of the starfish and of Amphiura would imply that the ter-
minal plate or the plate over the eye-spot of the starfish is homologous
to the terminal plate of Amphiura, notwithstanding an eye-spot has not
been described in any of the Ophiurans. If an association of the eye-spot
with a plate means homology of those plates, the oculars of the urchins
and the terminals of the starfishes (Ophiurans) are homologous ; but if
homologous, what plate in the young sea-urchin corresponds with the
radial (rp) of Amphiura ?

From a comparison of the young Amphiura with the young Echinoid
it would seem as if a non-ocular (without pigment-spot) plate {rj)) in
the former occupies the same relative position to the dorsocentral as an
oculated plate in the latter. Are they not then homologous ? From a
study of the adult Amphiura and the adult starfish it would seem that
the plates {tp) at the tip of the ray adjacent in the latter to an eye-spot
are homologous. If the terminal plate of the starfish with the eye-spot
is homologous to the terminal of an Amphiura, and the plate with the
eye-spot is homologous in starfishes and urchins, we are led to suppose
the radials of Amphiura to be plates unrepresented in urchins. It
seems more natural to compare radials in Amphiura with oculars in sea-
urchins, notwithstanding the position of the eye-spot.

MUSEUM OF COMPARATIVE ZOOLOGY. 127

According to Balfour,* the central calcareous plate appears after the
five radials and the five iuterradials. From this reference and the others
already mentioned, it would appear that in the starfishes, as far as ob-
served, the dorsocentral forms after radials and interradials. On account
of a discrepancy in the observations of Thomson and Gotte it is difficult
to compare the centrodorsal of Crinoids with the dorsocentral of the
Ophiuran, It would seem from Thomson's account as if the centrodorsal
was a single plate originating after the basals, but Gotte holds that the
centrodorsal is formed of a number of at first independent rods which
arise simultaneously with the basals.

The shape of each of the five radialia may be seen by a consultation of
Figs. 13, 14. In the early condition of the plates the calcareous network
consists of a somewhat coarse, open reticulation, over which grows a finer
network connecting portions of the larger reticulation, and finely knitting
the whole together. This second kind of network does not appear in
figures of the primary radials and dorsocentral which have been given
by others.

The primary radials, as shown by Ludwig, are not pushed out to the
end of the rays, as is believed by many naturalists. They always remain
on the abactinal hemisome of the body. It is therefore necessary to
modify what Balfour says on page 564,* of the formation of the plates of
Ophiurans, that " the original five radial plates remain as terminal seg-
ments of the adult rays." The original five radial plates are believed to
be the primary radials of the abactinal hemisome in Amphiura, and are
recognized in late stages on the body of the Ophiuran.

Oral Plates. — There are certain plates (Fig. 18 6) situated in the inter-
radii, peripherally to the dorsal plates, or radialia at the very rim of
the disk, which, although belonging to the actinal hemisome, must be
mentioned here. They in point of fact originate on the abactinal hemi-
some, and by subsequent growth are carried to the actinal hemisome,
forming the oral shields. Their position of origin only will be spoken
of here, as a description of them will be given in an account of the plates
of the month {q. v.).

The oral plates originate on the abactinal hemisome in the interradii
on the outer margin of the disk. The first, or one of the first, of these
to appear is perforated (Fig. 17 o), and according to Ludwig,t is a Tuadre-
porite or oral plate bearing the madreporic opening (see oral plates).

Intermediate Plates. — Certain plates which are next to form on the

* Comparative Embryology (Second Edition), p. 559.
t Op. cil., pp. 196, 197.

128 BULLETIN OF THE

abactinal hemisome after the primary radials and dorsocentral, were
given by Ludwig the name of intermediate plates. These plates immedi-
ately following the primary radials form in the interradii, and may there-
fore be called interradials or basals. In the line of the radii also there are
new plates beginning to form, among which may be mentioned underbasals
and radial shields. We shall first consider the basals and interradials.

Basals. — The first interradial plates form on the periphery of the
abactinal hemisome on interradii between contiguous radialia. They are
triangular in shape, and occupy a triangular interspace between adjoining
primary radials. These plates are commonly confounded with the orals,
which are forced to the actinal surface of the disk before the interradials
arise. The first set of interradial plates may be known as the abaxial
basals or first interradials. The next plates to form on tlie abactinal
hemisome after the abaxial interradials are also interradials, and arise in
the corners left between the dorsocentral and contiguous radialia. They
arise as trifid or quadrifid calcareous spicules, and are five in number.
They are not, however, synchronous in origin. Even in this stage,
although two rings of interradials are formed, the radialia are not sepa-
rated from the dorsocentral, and the surface of the abactinal hemisome
is mostly made up of the " primary rosette " of plates, the dorsocentral
and the radialia. As the growth of the new interradial plates proceeds,
the increase in size of the radialia and dorsocentral is not the same as
that of the interradials, and the original rosette is more or less contorted
in its form. Almost simultaneously with this contortion appear a number
of plates, among which may be mentioned a new ring of interradials,
five radial plates between the dorsocentral and the radialia, and the
radial shields. In the formation of new rings of interradials, at least in
the next set of plates, the newly formed seem to lie adaxially to those
already developed. The next ring of interradials arises between the last-
formed interradials and the periphery of the dorsocentral.

In the case of the radial series of plates, however, the next plates to
form after the radialia are the radial shields. These plates are remark-
able in more than one way. Anatomically they can be recognized in all
genera of Ophiurans, and their mode of development in pairs is exceptional
among radial plates of the disk. All abaxial plates thus far formed on
the abactinal hemisome have originated singly, one in each interradius,
and are five in number. The primary radials and basals follow the same
law as far as the number five goes. The radial shields are the first in
the abactinal hemisome to originate in pairs. On the actinal side we
shall find all plates originate in pairs except the tori, or jaw-plates ; but on

MUSEUM OF COMPARATIVE ZOOLOGY. 129

the abactinal side of the disk the plates which ultimately form radial
shields are the first bodies to arise in this way. The radial shields lie
just abaxially to the radialia, one on each side of a radius. In one in-
stance, and that in the preparation figured, a median radial plate abax-
ially placed to the radialia had formed before tlie radial shields began
to appear. In other specimens that was not observed to be the normal
method of formation. I have figured this specimen from its similarity to
a larva figured by Lyman,* about which more will be said later when
considering the homology of the radial shields. It is not until the radial
shields have reached some size that a radial plate is formed between each
of the radialia and the dorsocentral on the lines of the radii. This last-
mentioned plate, the underbasal,t tends to separate the primary radialia
and dorsocentral, and from the first their edges do not join each other.

The interpolation of new plates in the abactinal hemisome now be-
comes more or less irregular. If any law for the formation of these plates
exists, the modification in size of the plates renders it extremely difficult
to trace it in their formation at this time.

The nomenclature of the intermediate plates on the abactinal hemi-
some is similar to that given by P. H. Carpenter in his discussion of
Crinoidal and Ophiuran morphology.^ It seems to me, however, that it
would have been better, in considering the relationship of the basals in
the young Amphiura and their homologues in the projection of the calyx
of an Antedon larva, for Carpenter to have introduced, instead of his Fig.
II. (a copy of one of Lud wig's figures), a copy of another (Fig. 25) of the
same author. In this figure (Fig. 25) there is but one circle of interradial,
intermediate plates and no " underbasals," while the intermediate plates
of Ludwig's Fig. 25 and Carpenter's diagram of the Antedon (Fig. III.)
numerically correspond. The additional intermediate plates, both radial
("underbasals") and interradial ("basals"), in the figure by Ludwig,
which he (Carpenter) has chosen for Fig. II., lead to a difficulty in one
particular in a comparison of the young Amphiura and Antedon. It is an
important thing to know whether the intermediate plates of Ludwig's Fig.
25 are the same as the Plates 3 of Carpenter's diagram {loc. cit., Fig. IL).

* Challenger Ophiuroidea, PI. XL. Fig. 11, p. 157.

+ Notes on Echinoderm Morphology, No. V. On the Homology of the Apical
System, with some Remarks upon the Blood-vessels. Quart. Jourti. Micros. Sci., Vol.
XXIL The homology of this plate with the Crinoidal underbasal is recognized by
Carpenter.

X Notes on Echinoderm Morphology, No. V. pp. 10, 11. Quart. Journ. Micros.
Sci., Vol. XX.

VOL. XIII. — NO. 4. 9

130 BULLETIN OF THE

This question can be answered in part by a knowledge of whether the
ring of interradials just abaxially or outside of the so-called basals (3) are
earlier or later in formation than the basals (3). They appear to be later,
for in Lud wig's Fig. 21 we have a single interradial plate just beginning
to form between an abaxial and an adaxial interradial (the abaxial is prob-
ably the oral). Moreover, this seems to be the mode of formation referred
to by Ludwig in the words, " Es scheiben Uberall im Bereiche des dorsalen
Scheibenperisoms neue Interraediarplatten zwischen und neben den ein-
mal gebildeten sich anlegen zu konnen." If the intermediate plates are
formed later, the Plate 3 in Carpenter's Fig. II. would be the same as
one of the ring of interradials in Ludwig's Fig. 25, which exactly corre-
sponds with the basals (3) of the projection of the Antedon larva.

The determination of the relative length of the arm when the under-
basals and basals appear may be made by considering the relative devel-
opment and number of pairs of the adambulacral plates. Carpenter
states:* "The radials of the young Amphiura do not long remain in
contact with the dorsocentral ; for by the time that two adambulacral
plates have appeared between them and the terminals they are separated
from the dorsocentral by the rudimentary basal plates, while underbasals
are developed shortly after." In the figure quoted (PI. I. Fig. 12) by
Carpenter in this connection, which is probably a little older than one
necessary to illustrate the above statement, three pairs of side arm-plates
(adambulacral) are figured between the terminal {T) and the primary ra-
dials (4). Two pairs of lateral arm-plates at least are developed before the
plates which Carpenter calls basals appear. It is taken for granted that
the lateral arm-plates are considered adambulacral by Carpenter, — a ho-
mology of which there is little doubt, — and must be the ones referred to
by him, since they are the only plates, in the figure quoted by him (PI. I.
Fig. 12), between the terminals {T) and radialia (4).t

The homology of the radial shields of the Amphiura with the first bra-
chials of the Crinoid would seem not unreasonable. J The only paired
plates of the arms with which they could be compared are the adambula-
cral. With these, however, they have little resemblance save in their
double origin.

*D

* On the Apical System of the Ophiurids, Quart. Journ. Micros. Sci., Vol. XXIV.,
Jan., 1884, p. 6.

t The first and second adambulacrals lie on the oral side of the disk, and cannot be
those referred to by Carpenter as appearing between the terminals and radials.

t This suggestion is believed to be original, although it is a direct sequence of the
adoption of the theory that the radials of Amphiura and of the Crinoids are homolo-
gous, as shown above (adopted from Carpenter and others).

MUSEUM OF COMPAEATIVE ZOOLOGY. 131

Lyman * gives two very instructive figures of the young Hemipholis
cordifera, from which he draws the following conclusion : " It thus ap-
pears that radial shields so nearly universal among Ophiurans are not
special plates, but entirely homologous with other disk-scales, and by no
means the first to appear." In the younger of these two stages of the
young Hemipholis there is a dorsocentral surrounded by five radial plates
and an outer circle of five interradial, while there are ten arm-joints.
The development of the basal plates must be very much more retarded
in this genus than in Amphiura ; for in the latter, with half the number
of arm-joints and many more interradial plates, the radial shields and
some other plates have appeared. The second figure (Fig. 11, op. cit.)
of a young Hemipholis older than the last is very interesting. In it
there is a dorsocentral surrounded by five radials. In each of the inter-
radii there are three interradial plates. There is a second radial beyond,
abaxiaUy to the primary radial. Peripherally placed to the second radial
are radial shields, one on each side of the radius. The condition here
is about the same as that which we find in an Amphiura in which the
development of the arms is very much less (Fig. 19) than in Hemipholis.
Every observation would probably agree with the above-quoted statement
of Lyman, that the radial shields are not the first to appear ; and it
is thought that they are the same in mode of origin as the dorso-
central, radialia, or interradial plates. The radial shields arise before
the underbasals, which are the only other plates in the radii in this
early condition. They are the first of the radial series to arise abaxiaUy
to the radialia.

2. Plates op the Actinal Region op the Disk.

The plates of the mouth originate early in the development of the
young Amphiura. The so-called V-shaped plates {ad}, ad^), described
below as the first and second pair of adambulacral, are among the first
to form, and can be seen as trifid calcareous bodies in the bilaterally
symmetrical embryo (Figs. 7, 8, 10). Although I have not directly fol-

* Report on Challenger Ophiuroidea, PI. XL. Figs. IT, 12, p. 157. As stated
elsewhere, the young Ophiurans clinging to the arms of Hemipholis (Ophiolepis)
were observed by Stimpson many years ago.

The younger stages in the formation of the plates in the young Hemipholis would
offer an interesting subject for investigation for those naturalists who work in locali-
ties where it is found, as from a comparison of Lyman's figures of the young with
those here given of Amphiura it is suspected that there is considerable variation in
the two genera in this particular.

132 BULLETIN OF THE

lowed them back to this larva, from a study of my figures and a com-
parison with Metschnikoff's Fig. 16, there seems abundant evidence
that they precede all other plates of the actinal region of the disk.
There is also evidence that they antedate the formation of the terminals,
although they are probably formed after the radialia or primary radials.

Metschnikoff,* in speaking of the plates of the actinal region, says that
the five parts of the skeleton on the ventral surface of the embryo repre-
sent the future jaws. Apostolides t also describes five V-shaped plates.
Tliere are really five pairs of these plates in early stages, and ten pairs in
later conditions when both pairs of adambulacral plates are developed.

The following plates will be considered in our discussion of the mouth
skeleton :

1. Adambulacral ; first and second pairs, ad} and ad"^.

2. " Ambulacral ; " spoon-shaped plates, os, spl.

3. Oral ; mouth-shield ; madreporite, o.

4. Torus angularis ; jaw-plates, to.

5. Teeth, t.

Adambidacral Plates. — There are two pairs of adambulacral to be
considered in this connection, known after Ludwig as the first {ad^) and
second {ad"^) pairs. They are both regarded as homologous to the side
plates (Ip) of the arms, which will be later described. The adambulacrals
originate in pairs, five in number. The first pair [ad^) support the torus
(to). Both pairs are early formed in the development of the actinal
hemisome.

First Fair of Adambulacral Flates. — The double origin of the
"V-shaped" plates has been shown by Ludwig, and is evident from
the figures of Max Schultze (Figs. 5, G) and Metschnikofi". Apostolides t
writes : " Les premieres grandes plaques calcaires qui apparaissent avant
meme que le bras soit a peine ebauche sont les cinq pieces fourchues
de I'adulte ; il est facile de se convaincre de leur apparition primitive,
grace a leur forme en V et la disposition des tentacules buccaux que

* 0}}. cit., p. 18. The lettering cc, in Metschnikoffs Figs. 11, 12, 13, 16, and 17,
PI. IV., does not refer to the same structures as cc in Fig. 6, PI. III. cc in Fig. 16
is an adambuhicral plate ; in Figs. 11, 12, 13, and 17, it is a terminal, and in Fig. 6,
PI. III., it is one of the provisional pluteus plates. The rods cc, in MetschnikofTs
PI. IV. Fig. 16, are probably the first and second adambulacral. The following cor-
rections may be made in " Selections from Embryological Monographs, Echinoder-
mata" (Mem. Mus. Camp. Zoo!., Vol. IX. No. 3, PI. III.): cc, Figs. 9, 10, 11, and U
are probably terminals ; in Fig. 13, cc are adambulacral, and not provisional lime-
stone rods homologues of the pluteus rods.

+ Op. cit., p. 213.

MUSEUM OF COMPARATIVE ZOOLOGY. 133

nous avons mentionnee." On page 132 he writes: "On admet que
ces pieces fuurchues sout formees par la division d'un ossicule discoide
sur la ligne mediane, et la deviation de chacune des deux moities,
jusqu'a la rencontre de la moitie correspondante du disque voisin h.
laquelle elle se soude." In these descriptions it seems probable that
Apostolides refers to the fii'st pair of adambulacral and possibly the
second pair also. It can hardly be supposed that he refers to the first
pair of ambulacral, which are later described by me as the spoon-shaped
plates after Ludwig, since these never have a V-shape. Whether he
refers in his description to the first ambulacral or the first adambulacral
(with the second), it may be borne in mind that neither has been formed
by a division of a " discoid " ossicle, nor are they ever five in number.
The members of the five pai7-s of adambulacral as well as of ambulacral
originate as ten separate calcifications. In the youngest condition (a
stage a little younger than Fig. 1 7) of the growth in which they were
observed the first pair of adambulacral plates were formed although the
terminals were very small. I am therefore led to suppose that the first
pair of adambulacrals appear before the terminals. In this embryo
(Fig. 17) the pentagonal form is but obscurely indicated. The first pair
of adambulacral are portions of the "maxillae" of MetschnikoflTs figure
(PI. IV. Fig. 18, cc).

The first adambulacral plates originate in pairs about the mouth (Fig.
15). In early conditions they lie more in those axes which later become
the interradials, although they arise before the young has passed into
conditions in which either radii or interradii can be definitely recog-
nized. In Ludwig's Fig. 23 they are smaller than the terminals, but in
some of my preparations they are larger.

In a later stage (Fig. 17), in which the rays have begun to push out,
the first pair of adambulacrals assume a more or less irregular crescentic
form, with concave edges turned to the radii. By a continued growth the
adradial edge of these plates begins to approximate so that plates of
adjacent pairs approach each other. This approximation is confined to
about half their interradial border. The adradial half of the rude cres-
cent extends to thfe mouth opening. By the approach of two of these
first adambulacral plates (ad^) which lie in different pairs, a V-shape is
given to the combination. The plates however are free along the line
of the interradii. The double network of these plates anpears as in the
radialia (Fig. 18, rp).

Of the homology of these plates with the adambulacral there seems no
doubt. I believe also that Ludwig's comparison of them to the side

134 BULLETIN OF THE

plates of the arms is a correct one, and borne out by their mode of for-
mation as compared with the first ventral plate of the arms, as will be
explained in a subsequent explanation of the formation of the ventral
plates.

Second Pair of Adambulacral Plates. — The second pair of adambu-
lacrals [ad^) arise after the first pair, aborally to the same, and are situated
more on the interradius than the first pair. These plates also differ from
the first pair in the possession of appendages in the form of club-sliaped
spines. These spines are free at one extremity. The fact that the second
pair of adambulacral plates as well as the side plates of the arms have
spines would incline one to believe that they are homologous to each
other. Tlie second adambulacral plates are ten in number, in five pairs,
and with the first adambulacral are among the earliest plates to form.

In Fig. 1 7 there will be seen between each pair of terminal plates (tp),
on the periphery of the disk, two knob-like structures which extend be-
yond the edge of the disk. These did not escape the attention of Max
Schultze,* who described them as extending beyond the disk as "keulen-
formige Fortsatze." Ludwigt has also described these bodies, and rec-
ognized their resemblance to spines. They were purposely omitted by
him from his figures. I think this omission is unfortunate, as they con-
firm a theory of the relationship of the second adambulacral plates
which Ludwig supports, that these plates are homologous to the side
plates of the arms. He says : % " Beziiglich der Homologie der Seiten-
platten am Arme der Ophiuren mit den Adambulacralstiicken der See-
sterne kann ich auf meine frilheren Ausfiihrungen verweisen und brauche
wohl kaum zu bemerken, dass diese Homologie auch in den eben erwahlen
entwickelungsgeschichtlichen Thatsachen eine Stiitze findet." The posi-
tion of the second pair of adambulacrals so called, and the club-shaped
appendage seem to refer these plates to the same category as the side
plates of the arms, and make them homologous with adambulacral plates
elsewhere among stellate Echinoderms.

The club-shaped appendages lose their relatively large size as the
growth of the arm goes on, and it is only when the terminals are just
beginning to be pressed out from under the radialia that their projection
beyond the edge of the disk is noticed. These club-shaped spines can
be seen by looking at the young Amphiura from the abactinal as well as
the actinal regions.

Ambulacral Plates. — Of the plates which have been referred to the

* Op. cit., PI. L Fig. 5 c, Fig. Qd, p. 43. t 0}\ cit., p. 194.

X Op. cit., p. 189.

MUSEUM OF COMPARATIVE ZOOLOGY. 135

ambulacral series, there are two pairs which may be considered in the
account of the plates of the actinal region of the disk of the young Am-
phiura. The former of these, or the adoral pair, are known as the spoon-
formed plates {spl) ; while the second, partially concealed from view in
some of my figures, form the ossicles which complete the calcareous ring
of the mouth. The spoon-shaped plates may be known (following Ludwig)
as the first pair of ambulacral ; the second as the second pair of ambula-
cral. The former are superficial in their position ; the latter more pro-
found. Both resemble each other in their paired origin.

Spoon-shaped Plates. — If we study a young Amphiura in which the
pentagonal form has been donned (Fig. 15), there will be noticed in the
radius near the mouth opening and between adjacent pairs of first adam-
bulacral plates two elongated reticulated plates placed side by side. These
plates are commonly pointed on the adoral ends, more spatulate at the
other extremities. They originate early in the growth of the embryo,
and in young stages are equal in size to the first pair of adambulacral.
The increase by growth of the first pair of adambulacral plates leaves,
however, the spoon-shaped plates smaller than the adambulacral. Their
position leads to the theory that they belong to the ambulacral series, and
their mode of origin does not disprove what their position teaches ; but it
may be doubted from their want of connection with the first pair of
adambulacral plates in early conditions {vide infra) whether they are
"ambulacral plates."

Second Pair of Amhidacral Plates. — The aboral radial ends of the first
pair of adambulacral plates of adjacent pairs of these structures are knit
together by two plates which are classed as the second pair of ambulacral
plates. These plates form the radial part of the circumoral calcareous
ring, and occupy the same position as regards the first pair of adam-
bulacral plates as the arm-joints do to the side plates of the arms.

That the second pair of ambulacral plates are ambulacral in their
homology is not doubted, but the fact of their union with the first pair
of adambulacral has led me to doubt whether they were not the first
pair of ambulacral instead of the second. There seems much to support
this theory, for it brings all the ambulacral plates whether of the disk or
arms into harmony ; viz., an ambulacral plate is joined to a correspond-
ing adambulacral. The spoon-shaped plates not only show an exception
in their superficial position, but also in early condition are not joined to
the first pair of adambulacrals. Although for convenience they are in
this paper designated as the second pair of ambulacral plates, it is not
wholly clear to me that they are not in reality the first pair, and that

136 BULLETIN OF THE

the spoon-shaped plates are not amhulacral. If the spoon-shaped plates
are ambulacral, they are highly modified.

The manner of growth of the ambulacral plates has been carefully de-
scribed and figured by Ludwig, and I have little to add to his account.

They originate in pairs one on each side of the median line of the arm
in a deeper region of tlie arm on the ventral side. In their earliest form
they appear as tritid spicules or small parallel bars. These two members
of a single joint unite over the median line, forming by coalescence the
solid arm-joint. The union of the separate calcifications has been well
figured by Ludwig. The union takes place at first on the adoral and
aboral ends, so that in a half-formed arm-joint a median unclosed opening
remains after the junction of the two ends. The body thus formed is at
first much longer than broad ; later it becomes discoid, when the consoli-
dation is complete.

The distinction between ambulacral and lateral arm-plates is recogniz-
able from very early conditions, and the former are well consolidated
before union with the lateral plates is effected.

That the ambulacral plates of Ophiurans are spurs of the side plates
was questioned by Lyman,* from his study of certain lower genera of
deep-sea Ophiurans, Ophiothelia and Ophiohelus. The separation of the
two members which compose one of these " arm-bones " even close to the
tip of the arm affords a difficulty in accepting the theory of some natural-
ists that they originally formed as spurs from the small lateral plates.
The development of the plates in Amphiura shows that the arm-joints,
" ambulacra," and lateral arm-plates not only originate in two separate
calcifications, but also that they have great similarity to the permanent
plates in such a genus as Ophiohelus. Attention has been called by
Ludwig to the resemblance of the unconsolidated ambulacral plates of
Amphiura and the same plates of the deep-sea Ophiuran Ophiohelus.'
Lyman first suggested the embryonic nature of the unjoined arm-joints
of Ophiohelus and other genera.

Orals, or Oral Shields. — The position of the first-formed orals (o) is
an interesting one ; and a morphological interpretation of their relationship
to plates in other Echinoderms is beset with many difficulties, which others
have discussed. t

* A Structural Feature hitherto Unknown among Echinodermata, Ann. Mem.
Bost. Soc. Nat. Hist., 1880, pp. 3-7, PL I. Fig. 12. Report on the Ophiuroidea
dredged by H. M. S. Challenger during the years 1873-76, Zoology, Vol. V. pp. 237,
238, PI. XXVin. Fig. 6.

t Ludwig, Ueber den priinaren feteinkanal der Crinoideen, nebst vergleichend-

MUSEUM OF COMPARATIVE ZOOLOGY. 137

The orals originate near the margin of the pentagonal larva, and have a
part of their extent at least on the abactinal side. A single oral which
is pierced by an opening is larger than the rest, and is one of the first to
form. This is supposed to he the same as the madreporic plate. It is
larger than the remaining orals, and like them, by the increase of the
plates in the interradii between them and the dorsocentral, is forced in
the growth of the disk to the actinal side of the body. In their young-
est condition the orals resemble other plates in their spicule-like shape.

The literature written by those who have observed the development of
the plates of Amphiura does not agree with Sladen when he says : *
"The orals and some of the accompanying plates of the actinal hemi-
some next appear [after radials and terminals] before any trace of the
dorsocentral plate is present." If he means that all the orals appear be-
fore the dorsocentral, it cannot have been knowledge derived from what
has been published on the development of Amphiura ; for Ludwig has
said nothing to support such a statement, nor does his figure show more
than one oral before the formation of the dorsocentral. On the other
hand, Krohn in 1851 and Metschnikoflf f eighteen years after figure a
well-developed dorsocentral plate before any sign of an oral. It will not
be claimed that the figures of the last-mentioned naturalists are perfectly
accurate in this particular, for it is believed that the madreporic plate
ought to have been represented by them in figures showing the imma-
ture dorsocentral, but one cannot suppose that they support Sladen's
statement. In Ludwig's Figs. 17, 23, in which no dorsocentral exists,
the madreporic plate is formed, but there is no other oral represented. In
his Fig. 19, where the dorsocentral is well developed, one of the orals is
little more than a three-pronged spicule. Evidently here the dorsocentral
has antedated in formation one of the orals. My preparations teach me
that the dorsocentral is of considerable size before some of the orals. J

anatomischen Bemerkungen iiber die Echinodermen iiberhaupt, Zeit. f. Wiss.
ZooL, XXXIV. pp. 318-322. Neue Beitrage zur Anatomie der Ophiuren, Zeit. f.
Wiss. ZooL, XXXIV. p. 342. Entwickelungsgeschichte der Asterina gibbosa, Zeit.
f. Wiss. ZooL, XXXVII. Carpenter, Quart. Joumi. Micros. Sci. XX. {ns).

* Op. ciL, p. 29. t Op. cU., PI. III. Fig. 17.

X What is said above is on the supposition that Sladen calls the orals the plates
(5, PI. I. Fig. 13), and no others. I think I am just in this supposition. If however
he includes among orals the spoon-shaped plates and the adambulacral, as might
be done, my criticism above would be unjust, and I gladly withdraw it.

Sladen's paper on the "Primary Larval Plates of Brachiate Echinodenns" devotes
some space to the homologies of the odontophore of the starfish. As he does not
consider in this discussion the first pair of adambulacral and the spoon-shaped plates

138 BULLETIN QTi' THE

Torus angularis and Teeth. — These structures arise later than the first
pair of adambulacral plates, but develop quite early in the growth of the
young Amphiura. They form as independent calcifications. The torus
is at first an elongated plate or bar, which later becomes semicircular. In
Fig. 20 this plate is represented as perforated and reticulated. It ap-
pears that the teeth are not separate centres of calcification, but grow out
directly from the adoral region of the torus. The calcareous deposit
which enters into their formation has the form at first of a reticulated
perforated triangular plate.

B. PLATES OF THE AEMS.

The plates of the arms are the following : —

1. Terminals, tp.

2. Side plates, Ip.

3. Ventrals, v.

4. Dorsals, d.

Terminals. — The terminal plates (tp) which lie at the aboral extrem-
ity of the arms have been described by many observers. These plates
have been confounded by many writers with the radials. Ludwig * first
distinguished them from what are already described as the radialia or
primary radials. The fact that certain plates early formed in the
young Ophiurau were pushed out by a growth of new plates was known,
hut in all cases these plates were regarded as " primary " plates and were
in some instances morphologically misinterpreted. In Amphiura Krohnf
has figured the terminal plate, but gives it no special description. Max
Schultze X recognized the fact that the terminals belong to the arm proper,
and correctly designates them as the " erste Anlage der Arme." A.
Agassiz § observed the terminal plates in an Ophiupan, probably Ophi-
opholis, which he referred to Amphiura. He regards them as the first

of Amphiura, it might be supposed that he does not consider these early formed
plates as primary plates of the test. In strict language they are mouth-plates, but
are so early formed in the larva that they may be regarded as primary plates. As a
question of opinion I think they ought to be mentioned in a discussion of the homol-
ogy of the odontophore.

♦ Op. cit., p. 187.

t Op. cit., PI. XIV. Fig. 1, J ; p. 342.

t Op. cit., PI. I. Figs. 4, 5, c. In Fig. 6 they are lettered /. He does not seem
to have connected Plate c. Figs. 4, 5, with /, Fig. 6.

^ Op. cit. , p. 20, Fig. 32, y.

MUSEUM OF COMPARATIVE ZOOLOGY. 139

developed dorsal shields (primary radials?). Ludwig* regards this inter-
pretation as incorrect. A. Agassiz has shown that this plate is forced out
by growth of the arm to its distal extremity. Metschnikofl't correctly
figures the terminalia, and regards them as the " ersten Anlage der Wir-
belstiicke." The true arm-joints or ambulacral plates, which are regarded
the same as the " Wirbelstucke," are formed as a rule in pairs, not medi-
ally and unpaired. Ludwig J gives an accurate account of the growth of
the terminal plates, and shows that they form early in the career of the
young Amphiura. He is doubtful whether they originate before or after
the radialia, and regards it as probable that they are formed before the ra-
dialia or primary radials. Carpenter and Sladen § have discussed the
homologies of the terminalia, adding no new facts, but drawing for illus-
tration from the excellent paper of Ludwig so far as the development
in this genus Amphiura is concerned. Sladen § says : " The primitive
structure and mode of formation of the terminal plate is different from
that of the first radial." It seems to me that the difference in primitive
structure, if any, ought to have been more fully pointed out, and it is
doubted whether there is any great difference in these particulars. I
find nothing in Ludwig's account to justify the above statement of
Sladen, and my own observations show that both the terminal plate
and the first radial have many points of resemblance in " primitive struc-
ture " and " mode of formation." It is not intended to be denied that
the form of the terminals and first radials may differ from the very first,
or that they cannot be distinguished one from the other.

The terminals originate after the primary radials. This statement,
hardly in accord with that of Ludwig, is supported by the figures of
Krohn, Schultze, and Metschnikoff,t in which the terminals are much
smaller than the radials, and in which the indications are that the latter
are just forming. My own observations support the statement. I have
never, however, recognized a young Amphiura with radials and without
terminals. The terminal plate originates on the abactinal side of the
water-tube, or " feeler," and by a growth of the arm is pushed out to the
very end of the ray (Fig. 12). According to Lyman,|| the terminal plate
is a hollow tube ; and according to Ludwig,* it grows from the abactinal
side around the feeler on both sides, joining on the actinal side. The

* Op. ciL, p. 187. t Op. ciL, PI. IV. Fig. 17.

t Op. cit., pp. 187, 188.
§ Op. cit., pp. 29, 30.

II Ophiuridae and Astrophytidse, Old and New, Bull. Mus. Comp. ZoQl., Vol. III.
No. 10, p. 258, PI. V. Figs. 1, 2, 3, 4.

140 BULLETIN OF THE

end of the water-tube is said by him to pass through the tube thus
formed.

The significance of the terminal plate has played an important part in
discussions of Echinoderm morphology, and is by many thought to be the
same as the ocular plate of the starfish. This opinion seems well sup-
ported ; but whether the terminal or the radial is the homologue of the
ocular of the sea-urchin is open to discussion.

As to the exact relationship of the terminal plate to other plates of the
arm, it may be well to inquire whether it cannot be homologized with
the so-called dorsal plate of the first or second adambulacral plates of the
actinal region of the disk. That question Avill be considered, not answered,
in our discussion of the dorsal plates of the arms.

When the arm is broken, a new terminal is formed by being pressed
out by the growth of new plates, just as in the originally formed ter-
minal plate. In the very instructive figures of the young of Asterias
glacialis, Linn., by Loven,* we have (Fig. 257) in the radial plate (/?) a
structure which may be considered the primary radial. If, however, we
regard p as homologous to the radial plate, rp, of the Amphiura young,
as its position on the radius would seem to indicate, its time of develop-
ment, as compared with the interradials, h, is much retarded. It seems,
indeed, not improbable that p, Fig. 257 (Loven, o]). cit.), is one of the
series of plates along the middle aboral line of the ray, three of Avhich
are shown in Fig. 259. Possibly these plates are homologous with the
dorsals of Amphiura and other Ophiurans. Loven's figures (Figs. 256,
258) are interesting in another way. In the former of these, which is a
view from the actinal side, in each interradius, there are two plates which
in Fig. 258 bear spines. What are these plates 1 No one seems to
have asked the question, as it is perhaps thought to be self-evident that
they are adambulacral. As compared with the young Amphiura they
have similarities with the second pair of adambulacral (arf^). As in
Amphiura these plates, although homologous to the lateral plates, are
somewhat modified, so in the young A. glacialis they are somewhat dif-
ferent from other adambulacral plates. Among all the plates of the
arm the terminal offers this peculiarity. It is the only plate which ori-
ginates on the dorsal side of the water-tube and grows around it to the
ventral. It therefore originates like a dorsal, and when grown occupies
also the position of both laterals and possibly the ventral. Is it homo-

* Etudes sur les Echinoidees, Kongl. Svenska Vetenskaps Handlingar, Bandet
11, No. 7. The plate p, according to Loven, is a plate of the " systeme periso-
matique." In the very young there is a single median series in this species.

MUSEUM OF COMPARATIVE ZOOLOGY. 141

logons to the other plates of the arms, and if so, to which, — dorsals or
laterals or ventrals ? In its mode of origin it is very much like a dorsal.
It arises in the median dorsal line ; it is single. It grows on the sides
of the vessel as a lateral. With the ventral it has no resemblance. If
it were possible to carry the homology of plates so far that every pair of
adambulacral plates should have corresponding dorsals, it would be neces-
sary to regard the primary radials as the dorsals of the first pair of radials,
and then the terminals might be regarded as the dorsals of the second pair
of adambulacrals. The third pair of adambulacrals would then be rep-
resented by true lateral plates, with a dorsal in the arm itself. This sup-
position and all similar theories seem to be overthrown by the fact that
the terminal in the growth of the arm is pushed to its tip, far away from
the plates with which it occupies relationships in early life. Whether it
will be found that the terminal is a modified dorsal or lateral plate, or
a plate unrepresented in other regions of the arm and disk, its fate in
the formation of the arm is unique. While its early structure as a
spicular calcification on the median radius resembles the radialia and
the dorsal plates, its form in the adult is very different from these
structures, and its relations to the water-vessel such as no other plate of
disk or arms has.

Side Plates. — The side plates (Ijj) of the arms are regarded as adam-
bulacral in their homology. They originate laterally and in pairs, grow-
ing dorsally and ventrally until they approximate dorsals and ventrals.
The oldest side plates are adoral, and new side plates form between those
already present and the terminals. The first pair of side plates originate
after i\\Q first ventral {V), Siudi before the arm has begun to push out.
They therefore appear when first formed in the wall of the disk. Spines
arise from the aboral edge of the side plates, those on the first pair of
side plates being well formed before the fourth pair of side plates have
appeared (Fig. 20). The time of the appearance of the side plates as
compared with the first ventral will be seen, by a comparison of the above
statement with that of Ludwig, to be contradictory. Ludwig says : *
" Es entstehen aber die zu einem Armgliede gehorigen Seiten- Dorsal- und
Ventralplatten nicht etwa auf einmal sondern zuerst sich nur die Seiten-
platten an." While both V and V^ (PI. XI. Fig. 18, op. cit.) are regarded
by him as ventral, especial attention is turned by Ludwig to V^ as the
first ventral, in his reference to the sequence of the formation of the side
plates and ventrals. I believe that the contradiction pointed out between
Ludwig's account of the sequence of these plates and my own is apparent

* Op. cit., lip. 188, 189.

142 BULLETIN OF THE

rather than real ; for the ventral plate V belongs to the first pair of
adambulacral plates {ad'^}, which are themselves homologous with side
plates. Although the first ventral (F) is formed before the first side
plates, it appears after the first adambulacral pair to which it belongs.
Considering these facts, the law pointed out by Ludwig,* that the side
plates precede the ventral in time of formation, holds likewise for the
first adambulacral, and is true of the side plates if we give them their
true interpretation as adambulacral plates.

Ventral Plates. — The ventral arm-plate or under arm-plate is early
developed in the young Amphiura. The first ventral (V) is already well
formed when the terminal plate has just begun to push its way axially
from the periphery of the disk. The first ventral plate (Figs. 16, 17) is
formed before the first side plates of the arm, but after the first adam-
bulacral. Ludwig * states : " Erst nachdem die Seitenplatten sich an-
gelegt haben, beginnen auch die Dorsal- und Ventralplatten aufzutreten
und zwar sind wenigstens bei Amphiura squamata die Ventralplatten
den Dorsalplatten immer ein wenig voraus." I have already spoken of
this sequence in my account of the side plates. It is here for the first
time suggested that the plate Vv is the ventral plate of the first or second
pair of adambulacrals. If it (F) is a ventral plate of the true side
plates, it is more rapid in its growth, as compared with the true side
plates, than the other aiid subsequently formed ventrals.

The ventrals originate on the median ventral line, and are unpaired.
They first appear as a trifid spicule (Fig. 20, v), one prong of which is
adoral, the others aboral and lateral. In early formation they are free,
and do not arise from the lateral arm-plates. They precede, in time of
formation, the corresponding dorsal of the same joint ; and while in most
particulars the growth of the new plates resembles the growth of those of
a repaired arm of an Ophiuran as described by Lymau,t the sequence of
dorsals and ventrals does not seem to agree with the descriptions by the
last-mentioned author, who says that in a repaired arm the upper (dorsal)
plate is first formed.

Ventrals never arise by coalescence ot plates on either side of th6
middle line of the arm.

♦ Op. dt., p. 189.

t Ophiuridse and Astrophytidse, Old and New, Bidl. Mus. Comp. Zool., p. 258.
" Then appear on the central point of juncture, above, clusters of grains which in
time grow into upper arm-plates, and a similar process follows for the lower arm-
plates." The fact that the dorsal arm-plate in Amphiura originates as a single
spicule after the ventral has a meaning as compared with certain embryonic genera.
(Seep. 145.)

MUSEUM OF COMPARATIVE ZOOLOGY. 143

In a discussion of the relationship of the genus Brisinga to the Ophi-
urans, A. Agassiz * has sought to show that it is an intermediate genus,
connecting starfishes and Ophiurans. He finds the homologues of the
ventral plates of the Opliiuran in the fusion of the interambulacral plates
along the median line of the arm. He says : " In the case of the Ophi-
urans . . . the lower arm-plate is formed by the junction of opposing
spurs of the interambulacral plates, as can readily be imagined from a
comparison with Brisinga, where we find a spur from the interambulacral
plates extending nearly two thirds across the arms." That there are
anatomical, perhaps embryological, grounds .upon which Brisinga may be
regarded as reducing the " gap hitherto unfilled between starfishes and
Ophiurans," is not doubted ; but it may well be questioned whether the
ventral plate of Amphiura, originating as it does on the median line and
later than the corresponding lateral plates, is homologous to any part of
the interambulacral plates of Brisinga.

A. Agassiz t states that "a row of limestone cells extending along the
median line separates the base of the suckers," and that the embryo
starfish has no trace of any interambulacral system. He calls attention
(p. 53) to the absence of a well-defined interambulacral system of plates
in a young starfish (PI. VIII. Fig. 9), in which the rays are well devel-
oped, and considers the young starfish as still eminently Ophiuroid in
most important embryonic features. He shows a distinct row of " me-
dian ambulacral spines (u^) " on the abactinal side of the arras. These
plates witli spines are those supposed from A. Agassiz's description to
be formed as follows : The radial plates of the abactinal system of the
" dorsal part of the arms gradually extend towards the edge of and
down on to the actinal side, enclosing the water-system little by little,
and finally, as has been described, covering the ambulacral tube," etc.
The median plates are later, according to A. Agassiz,:}: absorbed along the
median line in Asteracanthion. It would appear then that from the
unabsorbed end of these plates, homologous with the adambulacral
plates, grow the ambulacral plates above, or on the abactinal side of
the water-system into the position which they eventually have in the
adult. In the Ophiurans the median plate of the starfish before absorp-
tion of the plate is represented, according to him, by the lower arm-
plates (ventrals). The Ophiurans are regarded as remaining in an
embryonic condition so far as these plates are concerned.

Aside from the fi\ct already commented upon, that in Amphiura the

* Mem. Mils. Comp. Zool, Vol. VI. p. 102.

t Embryology of Starfish, p. 47. J 0/^. cU., p. 92.

144 BULLETIN OF THE

ventral plate is a median actinal deposit, and not, as in the starfish, joined
by the growth of plates to the median line to form the embryonic
median plate, the author finds this difficulty in the homology indicated
above. It would seem from the description that both ambulacral and
adambulacral were derived from the same calcification in Asteracanthion,
a calcification beginning on the abactinal and growing down on each side
to the actinal median coalescence. In Amphiura ambulacral and adam-
bulacral plates are from the first separate and distinct calcifications.

In the abbreviated development of Asterina as given by Ludwig there
seems to be a wide diff"erence in the growth of the plates from that of
Asteracanthion recorded by A. Agassiz. Adambulacral and ambulacral
plates are recorded by the former from the very first, and in the oldest
stage figured no embryonic median actinal row of spiniferous plates is
figured in the arm. Asterias glacialis seems also, according to Loven's
figures, to differ from Asteracanthion in this particular. The plates which
appear to correspond with the lateral ambulacra of A. Agassiz's account
seem to be separated along the median line of the arm on the actinal
side, and median plates below the water-vessel or its position are not
figured. Perhaps no genus of starfishes can better serve to explain these
discrepancies than Pteraster. The embryology of this starfish is very
much needed, and from the interesting fact that the young is carried in
a pouch on the abactinal surface of the body, and is therefore probably
without a brachiolaria, we may expect interesting revelations from its
study.

If one cannot accept the theory that the ventrals of Amphiura are
homologous with the embryonic median plates of the young starfish,
Asteracanthion, and cannot regard them as formed from the adambulacral
plates by coalescence along the median line, it may be asked, What are
they, and to what plates in the starfish are they homologous 1 In answer
to this question we might ask another, Why is it necessary to suppose
that they are represented in the starfish ] We know that there are plates
on the dorsal hemisome of Amphiura which seem not to be represented
in the starfish. Why not suppose that the ventrals are unrepresented 1
Perhaps they belong neither to ambulacral nor interambulacral systems,
but are special plates for the protection of the nerve and water system of
the arms. Perhaps also similar coverings of the Echinoid are also not
referable to either ambulacral * or interambulacral systems, as we under-

* Ludwig regards the ambulacral plates of the starfish as unrepresented in the
sea-urchin, or highly modified into the auricles. This homology of what are com-
monly called the ambulacrals in the sea-urchin with the adambulacral of starfishes

MUSEUM OF COMPARA.TIVE ZOOLOGY. 145

stand it, but to special plates not represented in the starfishes, Asteracan-
thion, or Asterina, young or old.

Dorsal Plates. — The dorsal or upper plates of the arm (Fig. 19, d)
originate in the median dorsal line as simple trifid spicules, and form in
series from the adoral to the terminal, the adoral being the oldest. The
last formed is nearest the terminal. In their first condition they resem-
ble the ventrals, and the subsequent growth is similar. The dorsal ap-
pears after the corresponding ventral. This fact is an interesting one in
comparative anatomy. Many genera of Ophiuridse (Ophiohelus, Ophi-
ambyx, and others from deep seas) and all the Astrophytidae are destitute
of dorsals. In these Ophiuridae the ventrals are present, and in the
Astrophytidae the first ventral is developed while others are wanting.
The dorsals disappear before the ventrals, if the want of dorsals in these
low genera is due to degradation, or the genera have not progressed
through embryonic stages in which dorsals appear, if, as is probably
the case, dorsals have never appeared. In the growth of Amphiura the
ventrals form first, and those genera with a single ventral and no dorsal
may be compared with my Fig. 17, PI. III.

I am led to suppose that the dorsals have been inadvertently omitted
in certain of the figures of a young Amphiura by Ludwig (PI. XL Figs.
21, 25), for he has not represented these plates in a young specimen in
which three pairs of side arm-plates are represented (PI. XI. Fig. 21, ad^,
ad*, ad^). In a young Amphiura of about the same age (PI. III. Fig. 19)
at least one dorsal plate is formed, and in another as old as that repre-
sented in his Fig. 25 (same plate) the dorsals have increased in number.
In none of Lud wig's figures are dorsals represented, although in Figs. 21,
25, they must have been already formed.

The dorsal originates adaxially to its side plates on the median line, as
shown in my figures.

would explain the position of the water-vessel in the former group. We must look
with interest to the method of growth of these plates in sea-urchins much younger
than any yet studied for a solution of this question.

As the viviparous Amphiura and the Asterina with the direct development have
thus far furnished the best information in regard to the method of formation of the
plates in Ophiurans and starfishes, perhaps the growth of the plates in Echinoids
can best be revealed by the life history of the Hemiaster of the South Sea, with
young in pouches in the ambulacra! zones. Although the young Hemiaster has
been well described by A. Agassiz, Thomson, and others, the growth of the young
plates is as yet not well enough known for comparison.

VOL. XIII. — NO. 4. 10

146 BULLETIN OF THE

The following summary may be made of the preceding observations : —

1. The intestine of the bisymmetrical larva is early developed, and
later in development becomes atrophied and is lost.

2. The mouth and oesophagus (1) of the bilateral larva is formed by an
invagination of the epiblast while yet the larva is enclosed in its sac and
attached to the parent.

3. The provisional skeleton of the bilateral larva is not always sym-
metrical, and sometimes develops on one side. The first-formed rod is
not always a trifid calcification.

4. An umbilical connection exists in all later stages of growth until
the pentagonal form is assumed. The relation of the umbilicus to the
mouth, stomach, and intestine is described.

5. The first calcareous plates to form on the abactinal hemisome are
five first radials, and a little later a dorsocentral. The radials antedate the
terminals.

6. The first plates to form on the actinal hemisome are the first adam-
bulacral.

7. The second pair of adambulacral plates bear club-shaped spines.
These last structures are homologous to the spines of the lateral plates of
the arms.

8. The first ventral plate to form belongs to the first pair of adam-
bulacral plates, and not to side plates of the arms. This first ventral,
although not belonging to the portion of the arm free from the disk, is
homologous to the other ventral arm-plates.

9. The radial shields originate before a plate called the " underbasal "
forms between the dorsocentral and the primary radials, and while there
are but two intermediate plates in each of the interradii.

10. The homology of certain plates of the young Amphiura to the ba-
sals, as suggested by Carpenter, is discussed, and doubts advanced whether
the individual plates mentioned by him are basals in preference to other
interradial plates.

11. The ambulacral plates do not always originate as trifid spicules,
but sometimes first appear as parallel unbranched rods.

12. A. squamata is infested by a parasitic Crustacean, which, although
in adult form closely allied to a Copepod, lays eggs in packets in the
host. These ova were found in conditions of cleavage, in a nauplius
stage and in intermediate conditions. The adult is also found in the
Amphiura. Eggs not attached to adult.

MUSEUM OF COMPARATIVE ZOOLOGY. 147

The following summary may be made of new figures, or new anatomi-
cal details first figured : —

1. Figures (PI. I. Figs. 1, 2) of plutei of Ophiopholis older than that
figured in Bull. Mus. Comp. Zo'OL, XI. 4, Fig. 23, and younger than
adult. Figure (PI. I. Fig. 3) of an adult pluteus of Ophiopholis.

2. Figures (PI. II. Figs. 5, 7, 8) of the umbilical connection of the bi-
laterally symmetrical young with its parent. These differ from those of
Max Schultze in showing the relation of this structure to internal organs.
In Apostolides' and Metschnikoff's figures of the bisymmetrical larva
this structure is not represented. Figure (PI. II. Fig. 4) of a larva with a
single asymmetrical pluteus spine. Figures (PI. II. Figs. 13, 14) of the
actinal and abactinal hemisome of a young Amphiura of an age between
that figured by Ludwig on PL XI. Figs. 17, 23, and PI. XI. Fig. 19.

3. Figure (PI. III. Fig. 20) of the actinal hemisome of a young
Amphiura older than Ludwig's PI. XI. Fig. 18. This figure shows struc-
tures purposely omitted in all Ludwig's figures, viz. spines and club-
shaped bodies, appendages of the second pair of adambulacral. Figure
(PI. III. Fig. 17) older than Ludwig's PI. XL Fig. 19 and younger than
his PI. XL Fig. 18, illustrating the formation of the first side plates
of the arms. Figure (PI. III. Fig. 19) illustrating the relative situation of
the dorsals. Dorsals are omitted in all Ludwig's figures of the arm from
the abactinal side. My figure is younger than his PI. XL Fig. 21, in
which a dorsal ought to be represented. Figure (PI. III. Fig. 15) show-
ing the arm-joints or ambulacral plates of the arms in situ and before
coalescence.

Cambridge, January, 1887.

148 BULLETIN OF THE

EXPLANATION OF THE PLATES.

LETTERING.

a.

Opening into the supposed cavity of the blastosphere, blastopore ?

ad>.

First pair of adambulacral plates.

adP.

Second pair of adambulacral plates.

al.

Anal lobe.

air.

Anterolateral rod.

ar.

Anterior rod.

c.

Infolded epiblast.

cav.

Cavity, segmentation cavity.

cr.

Calcareous trifid spicules.

d.

Dorsal plate, upper arm-plate.

dc.

Dorsocentral plate.

eb.

Epiblast.

/.

Feeler, leg, paired feeler.

ga.

Stomach.

i.

Intestine.

ir.

Interradial plate.

Ip.

Lateral arm -plates, adambulacral, side-plates.

Ir.

Lateral rod.

Is.

Lateral "Scheibe," enterocoel on left side.

Iw.

Left-water tube or hydrocoel.

m.

Madreporic opening.

m}.

Inner layer or envelope of the segmentation spheres.

m2.

Outer layer or envelope.

rrib.

Mesoblast.

mhc.

Mesoblastic cells }■ " Mesenchyme ? "

0.

Oral plate.

OS.

Ambulacral plates, "ossicles," "arm bones."

oe.

(Esopiiagus.

or.

Mouth.

pig.

Pigment.

pr.

Posterior rod.

ps.

Pluteus spine.

rp.

Radial plate, first radial.

rp'^.
rp^.

> Plates of disk formed after the first radials.

rs.

Radial shield.

MUSEUM OF COMPAKATIVE ZOOLOGY. 149

TV). Right water- vessel, hydrocoel.

sp. Spine of ami.

spl. Spoon-shaped plate.

t. Teeth.

tf. Unpaired or terminal feeler. See wt.

to. Torus angularis, jaw-plate.

tp. Terminal plate, terminal.

u. Connection of pentagonal larva with parent. In stages earlier than

pentagonal larva also found.

V. Ventral plate, lower arm-plate.

wt. Terminal end of water- vessel of the arm.

PLATE L

Figures drawn with Camera lucida, Obj. BB.

Fig. 1. Pluteus of OphiophoUs aculeata, Gray, in a little older condition than that
figured in Fig. 23, PI. L, Bull. Mus. Comp. ZooL, Vol. XIL No. 4.
" 2. The same somewhat older. Seen from side on which mouth opens.
" 3. Adult pluteus of 0. aculeata before young Ophiuran has begun to form.

The drawings from which these figures were made are from plutei taken at Frye's
Island, New Brunswick. This island bears the name of CailifiTs Island on the Admi-
ralty Chart.

The same plutei are common at Eastport, Maine.

PLATE II.
Figures drawn with Cainera, Objs. BB, DD, Zeiss. All except Fig. 1 with Obj. BB.

Fig. 1. Blastosphere of ^mp^mra sg-wamate. Diameter, .15 mm.
" 2. Same, younger.
" 3. Gastrula.

" 4. Ventral view of a bisymmetrical larva, unattached.
" 5. The same, lateral view, attached.
" 6. Somewhat older larva than tlip last, showing +he vasoperitoneal sacs or

water-tubes.
" 7. The last, lateral view, unattached. The remnant of the attachment in the

upper right-hand comer.
" 8. An older larva than the last, attached. Dorsal view.
" 9. The same, older.
"10. The same, still older.
"11. Somewhat older larva.
"12. A pentagonal attached larva with well-formed radial, dorsocentral, and

terminal plates. Abactinal view. Attachment at u.
"13. Youngest free Amphiura, unattached to parent. Found free in mother.

Abactinal view. The great prominence of two of the terminal plates, tp,

is due to the position which the specimen had when drawn.

150 BULLETIN OF THE MUSEUM OF COMPAKATIVE ZOOLOGY.

Fig. 14. An older larva from the body of parent. Abactinal view. The club-shaped
bodies ad^ are spines of the second pair of adambulacrals, which in this
stage project beyond the periphery of the disk.

PLATE III.

Fig. 15. View of the calcareous plates of the actinal side of the disk of Amphiura in

a pentagonal larva younger than PL II. Fig. 13.
" 16. One fifth of the actinal hemisome of an older pentagonal larva than last.

This figure has, in addition to plates of Fig. 15, the ventrals v, and orals o.
" 17. Pentagonal larva, actinal view, older than last, showing the origin of the

lateral plates Ip.
" 18. Abactinal view of an older larva in which the arms have increased in length,

the terminal plate being pushed outward by the formation of the lateral

and ventral plates. One arm is shaded, two adjacent arms drawn in

outline, and two arms not represented.
" 19. The arm and portion of the abactinal hemisome of an older Amphiura.

Three pairs of lateral arm-plates are represented, and two dorsals are

shown. Abactinal view.
" 20. An arm and portion of the actinal hemisome of a larva about the same age

or slightly older than the last.

Fkw k f; s , Am p h uj ra

J.V/F del

H Meiselliih

;• !-;v, K'-; M an: •■•u ;■!> A

6.

"•* u

X.

12 .

(/(■

/

jwK ati

1^;

i^

'f..>'

X

5.

/

/

/ 1/,.::

"r :..!^:!,iai^\

■ -v

.MU

^'

/ Is

xric-

-^

iic^

.-.•ix

ij«c

Si,'- f •

■^>:=^'

V,'

';<

. -^-

15.

16.

M;UD-rt,,.

r

'/»

^^

'■ '.r

,!^/.

18

'I'

Vv^v^^f^^:

,//

,'V:

1

17.

/

,u1'

sp/

t-^^r^U:

r r .

'/<

i< Mpi.= p1 ith

No. 5. — Preliminary Account of the Fossil Mammals from the
White River Formation contained in the Museum- of Comparative
Zoology. By W. B. Scott and Henry F. Osborn.

This paper is a brief abstract of a memoir upon the Cambridge col-
lection of Miocene Mammals, which is now in preparation. This
collection was made by Mr. Samuel Garman in Nebraska and Dakota,
and has been very kindly placed in our hands by Professor Agassiz for
preparation and description. The work of excavating, cleaning, and
mounting the fossils has been for the most part performed jy Dr.
Franklin C. Hill, Curator of the Geological Museum at Princeton, and
to him our best thanks are due. The drawings were all executed by Mr.
R. Weber.

Geological Museum, Princeton, N. J., July 9, 1887.

RODENTIA.

Palaeolagus Haydeni, Leidy. Several specimens of jaws and teeth repre-
sent this species in the collection, but add nothing to our previous knowledge.
Ischyromys typus, Leidy. Isolated teeth.

OREODONTA.

Hyaenodon horridus, Leidy. A most valuable and indeed unique speci-
men of this species, belonging to the Cambridge collection, has already been
described by one of us elsewhere.* Here it will suffice to recapitulate some of
the more important facts established by it. The posterior dorsal and lumbar
vertebrae show the characteristically creodont feature of involuted zygapophy-
ses, such as are not found in any known carnivore. The scaphoid and lunar
bones are separate, and a distinct central is found; the manus is plantigrade
and pentadactjd, and the ungual phalanges are deeply cleft. This specimen
renders it perfectly certain that Hyctnodon was a typical creodont, and that it
was in all probability an aquatic form. It also shows that Hycenodon is not at
all allied to Mesonyx, as has been supposed, but rather to Pterodon, Protopsalis,
and Oxycena.

* Scott, Jouin. Acad. Nat. Sci, Phil., Ser. 2, Vol. IX. No. 2.

VOL. XIII. — NO. 5.

152

BULLETIN OF THE

Hyaenodon leptocephalus, Scott.* This species is peculiar for the long,
narrow cranium, and for the position of tlie posterior nares, which are roofed in
by the entire length of the palatines and by the pterygoid plates of the alis-
phenoid. In size it slightly exceeds the H. crucians of Leidy. This species
was established upon two fine skulls in the Cambridge collection.

Figure 1. — Skull of ITycenodon leptocephalus, from below upon the under surface.

CARNIVORA.

CANID^.

Cynodictis (Amphicyon) gracilis, Leidy. With the possible exception
of some specimens from the Uinta eocene, the genus Amphicyon has not been
found in America. Galecynus, as has been lately shown, f cannot be separated

* Lnc. cit.

+ Huxley, P. Z. S., 1880, p. 280 ; Lydekker, Brit. Mus. Cat. Foss. Mam., Vol. I.

MUSEUM OF COMPARATIVE ZOOLOGY. 153

from Canis. The American species whicL have been referred to Amphicyov
and Galecynus in reality belong to Cynodidis, which has the same dental
formula as Canis, but differs in the construction of the teeth.

CRYPTOPROCTIDuE.

Diaictis felina, Leidy. This genus has usually been placed in the same
family with Hoplophoneus ; but the materials now at command show that it is
quite distinct, and more nearly allied to the recent Madagascar form Crypto-
procta. There are several cranial and skeletal fragments in this collection
which are of much interest. The radius has the same shape as in Hoplopho-
neus, with a concave disk-shaped he^ad and expanded distal end. The tibia
has a very much flattened astragalar facet, and the astragalus has not such a
deeply grooved trochlea as in Hop)lophoneus ; the phalanges of the second row
have an excavation on the outer side, showing that the claws were retractile.
A very fine specimen in the Princeton Museum, of which an account will
shortly be published, brings out the resemblance to Cryptoproda very clearly ;
as in that animal, the foot is pentadactyl and completely plantigrade, and the
ungual phalanges were simple, compressed, and without bony hoods.

NIMRAVID^.*

Hoplophoneus (Drepanodon) primaevus, Leidy. Numbers of fine spe-
cimens of this species are preserved in the collection, which with some of the
Princeton material enable us to give a restoration of this very interesting type.
The vertebrae are for the most part like those of the true cats, but with some re-
semblances to Cryptoproda. The scapula has a prominent spine, with acromion
and metacromion. The humerus is remarkable for the great prominence of
the deltoid ridge ; there is a very prominent internal condyle and large epicon-
dylar foramen ; the trochlea is like that of the true cats. The ulna and radius
are essentially feline, and need no especial description. The carpus is also
feline, but has a small vertical diameter; the scaphoid and lunar have coalesced
(the first case reported from the White River formation), though the line of
junction is still clearly visible. The metacarpals are five in number, the
poUex very much reduced, and the other digits small and slender. The un-
gual phalanges show an unexpected degree of specialization ; they are com-
pressed, curved, and have a large lamina of bone reflected over their base as in
the higher -FelidcE, and a strong process for the tendon appears below the ar-
ticular facet. These phalanges are very diff"erent from those of Cryptoproda,
Dinidis, and Procelurus. The pelvis is in general like that of the Cryptoproc-

"' If Cope's definition of this family (Tert. Vert., p. 948) be accepted, Hoplo-
phoneus cannot be included in it. "We do not consider, however, that the absence of
the hallux is a good family character, while the foot structure of Hoplophoneus shows
that it should be placed in a separate family from Dinidis, for which the name
Nimravidce may be retained.

154

BULLETIN OF THE

tidcB. The femur is rather long and slender, and has a distinct third trochanter,
which is also to be seen in Crijptoprocta, Dinidis, Frocelurus, and Amphicyon,
and is probably an inheritance from their creodont ancestry. In. appear-
ance the femur of Hoplophoneus closely resembles
that of Procelurus as figured by Filhol.* The tibia
is stout, laterally compressed, and curved forward ;
the distal end is broad, and not very deeply grooved,
and witli heavy malleolus. The fibula has a slen-
der shaft and expanded distal end. The tarsus is
feline, but with some differences ; the astragalus is
more flattened than in the true cats, and the calca-
neum has the arctoid character of a conical process
on the outer sfde near the distal end (found also in
Amphicyon, Procelurus, and Dinidis). The meta-
tarsals, five in number, are slender and weak ; the
three external ones are strongly interlocked, as in
the cats.

Restoration (see Plate I.). — This animal had a
very striking appearance, with its short rounded head
and exceedingly long and trenchant canine tusks ;
the neck is long, the trunk, especially the lumbar
region, is short as compared with Cryptoproda ; the
tail is very long, as in nearly all of the early flesh-
eaters ; the limbs were stout, the feet on the con-
trary very weak, as in the creodonts. The struc-
ture of the foot renders it all but certain that this
animal was digitigrade, though some features of its
plantigrade ancestry, as the articulation of the as-
tragalus with the cuboid, are retained. H. primce-
vus was a small animal, standing hardly more than

Figure 2. — Left hind foot
of Hoplophoneus, viewed
from in front.

18 inches high and about 33 inches long, exclusive
of the tail.

Hoplophoneus occidentalis, Leidy. This is a larger species, equalling
the puma in size, and with a more robust skeleton.

ARTIODACTYLA.
OREODONTID^.

Oreodon Culbertsoni, Leidy. This very common and well-known species
is represented by numerous skulls and parts of the skeleton.

Oreodon gracilis, Leidy. Little has hitherto been known as to the
* Soc. So. Ph. et Nat. Tours, 1880, PI. V. fig. 3.

MUSEUM OF COMPAKATIVE ZOOLOGY. 155

skeleton of this species ; it is relatively lighter and more slender than in the
larger species, but otherwise not different from it. Most important is a speci-
men containing all the metacarpals and phalanges in undisturbed position, and
this shows most distinctly the presence of the pollex, as one of us* had pre-
viously shown to be true in the case of 0. Culbertsoni. This correspondence
between the two species removes all suspicion that the pollex in the specimen
first described might be a case of abnormal polydactylism. The discovery of
a five-toed artiodactyl is of the utmost importance, as it furnishes the demon-
stration of what has long been surmised, that the ungulates of both odd and
even-toed series have been derived from pentadactyl forms.

Eucrotaphus (Oreodon) major, Leidy (Eporeodon major, Marsh). This
genus differs from Oreodon in the presence of large inflated tympanic bullae, and
also {fide Marsh t) in the absence of a pollex. The dentition and char?cter of
the skull are identical in the two genera.

Agriochoerus latifrons, Leidy. Isolated jaws and teeth.

SUID^.

Hyotherium (?) americanum, sp. nov. There is in the Princeton Museum
a suilline skull from the White River formation, which cannot be corre-
lated with any of Dr. Leidy's genera. It agrees very closely and is probably
identical with the Hyotherium of Europe, and will be provisionally referred to
that genus. In the Cambridge collection there is a suilline hind foot, which
may be referred to the same species. The astragalus is very oblique, the
external condyle greatly exceeding the internal in size ; the neck is short and
the distal end broad ; the calcaneal facets are confluent. The cuboid is low,
broad, and deep (antero-posteriorly). The metatarsals are very suilline in
character, the median pair short and massive, the laterals shorter and espe-
cially more slender ; the proximal ends are all on the same transverse line, and
the articular faces nearly plane ; the trochlear ridges on the distal ends are
confined to the posterior aspect, thus differing from Sus, Dicohjles, and other
recent genera. The phalanges of the median digits are heavier but not much
longer than those of the lateral digits.

Measurements.

M.

Astragalus, length (outer side) 032

" width trochlea 019

Cuboid, length 016

width 015

Metatarsal II., length 048

III. " 063

* Scott, Proc. Am. Ass. Adv. Sci., 1884, p. 493.
t Dinocerata, p. 187, fig. 162.

156 BULLETIN OF THE

Metatarsal IV., length 068

" V. " 055

Proximal phalanx, digit IV., length 025

" " " IV., width proximal end 013

« « " v., length 022

" " " v., width proximal end Oil

Entelodon (Elbtherium) Mortoni, Leidy. Eepresented by several skulls
in good preservation, one of which is particularly interesting as showing the
milk dentition. This wiU be fully described in our final paper.

HYOPOTAMID^.

HyopotamuB americanus, Leidy. Represented by fragments of lower
jaws with molar teeth.

CAMELID^.

Poebrotherium Wilsoni, Leidy. Two skulls, one of which exhibits the
milk dentition, represents this species.

TRAGULID^.

Leptomeryx Evansi, Leidy. Riitimeyer* has recently questioned the
propriety of referring this genus to the chevrotains, and considers it more
allied to the Camelidce. In consequence of this opinion from such a distin-
tinguished source, we have carefully examined the dentition and skeleton of the
genus, and are now in position to give a nearly complete account of it, which
will be done in the final paper. Here we need only record the conclusion
reached, that Leptomeryx, though exhibiting several points of divergence from
the modern genera of the family, is nevertheless a true traguline. We thus
reach a different conclusion from Riitimeyer on this subject, and agree with
Schlosser.t

GENUS INCERT^ SEDIS.

Hypisodus minimus, Cope. This minute ruminant is the earliest known
hypsodont form found in America. Professor Cope gives the dental formula
as I. ^, C. ^, Pni. ^, M. f ; and states that "in the mandibular series the six
incisors, two canines, and two first premolars form an uninterrupted series of
ten subequal teeth, and are followed by a long diastema." X The genus has
hitherto been known only from the dentition, but there is fortunately in this

Abh. d. schweiz. pal. Gesell., Bd. X. p. 98.
t Morph. Jahrb., Bd. XH. p. 75.
t U. S. Geol. and Geogr. Surv. Terr., 1873, p. 501.

MUSEUM OF COMPARATIVE ZOOLOGY. 157

collection the well-preserved facial part of a skull, together with ihe lower
jaws ; hardlj' enough, however, to make the systematic position of the animal
entirely clear. The orbits are very large and deep-set, as in the tragulines,
and separated by a mere septum ; the lachrymals have a considerable extent
vertically, but extend little on the side of the face, and do not reach the nasals;
the maxillaries are proportionately higher than in Leptorneryx ; the nasals are
much contracted ; the palate is well arched from side to side, and the palatines
seem to be shaped much as in Tragulus ; the mandible is very slender.

The last upper premolar is composed of an external and internal crescent,
enclosing a valley between them ; the third and second are very small and
apparently secant, without internal cusps ; the first, if present at all, was evi-
dently separated from the second by a considerable diastema.

PERISSODAOTYLA.

MBNODONTID^.

MENODU9, PoMEL.

Syn. Titanotherium, Leidy. Megacerops, Leidy. Brontotherium, Marsh. (1 Si/m-

borodon, Cope.) Diconodon, Marsh.

Generic Characters. — Dentition : I. | (variable), C. \, Pm. |^, M. f. The
incisors are small and variable in number. The upper and lower median in-
cisors are usually wanting. Molars and premolars alike, resembling those of
Chalicotherium in pattern. A stout pair of transversely placed horns devel-
oped from the frontals and nasals.

There are three skulls in this collection and the horns of several others, rep-
resenting four or five species which may readily be distinguished. The chief
difficulty is in deciding where to draw the generic lines, which is increased by
the fact that the mandibles are seldom found associated with the skulls. As
in Uintatherium, the variability in the various portions of the skull, especially
in the region of the horns, is so extreme, that no two skulls are found which
are exactly alike. But the dentition, which is constant among the Dinocerata,
here greatly complicates the problems of classification. The premolars vary in
number, and the incisors, always of relatively small size, and fairly constant
in number in the upper jaw, vary from three to none in the lower jaw.* In
all the lower jaws found in Professor Cope's collection of Menodontidce from
Northern Colorado there are no incisors, and the mandibular symphysis is
extremely narrow. In the lower jaws of the Cambridge and Princeton collec-
tions, which are all from the Nebraska and Dakota exposures, the symphysis
is broad, and the incisors where preserved are two in number, while in one of
the Cambridge specimens no less than three incisor alveoli may be counted
upon one side of the symphysis.

• One of the Cambridge skulls has but a single upper incisor, M. color adensis.

158 BULLETIN OF THE

We might infer from this that Symhorodon can be clearly separated from
Menodus by the absence of the lower incisors, accompanied by a narrowing of
the symphysis ; but Professor Cope has recently described a new species, M.
angustigenis, from the Swift Current Creek region,* which combines the nar-
row type of symphysis with the presence of two incisors. The separation of
these genera is rendered still more improbable by the parallelism which exists
between the skulls from the Nebraska and Colorado localities, especially in
respect to the conformation of the nasal bones and the horns. The genus
Symhorodon is however provisionally adopted at present to include the species
•with a narrow mandibular symphysis and no lower incisors.

The genus Brontotherium, Marsh, cannot be distinguished from Menodus. It

rests in part upon the premolar formula, , in the synopsis given by Pro-

o — o

fessor Marsh.t as distinguished from Menodus with ? Pm. . One of the

" ° 4_4

lower jaws of the Princeton collection, however, has the premolar formula 3 — 4 ,
demonstrating that the first lower premolar is a variable tooth, and cannot in
this case be used in classili cation. The same rule applies to the second cone
upon the last upper molar, the supposed generic character of Diconodon,
Marsh. This is found in different species in all degrees of development, from
a small prominence upon the basal cingulum to a well-developed cone {M.
Proutii).

Such characters as the invariable absence of lower incisors may subsequently
be found to separate one genus of the Menodontidce from another; but our
present evidence goes to show that they cimply characterize the extremes of a
closely related series of animals, from the same horizon, of which the interme-
diate forms are represented by numerous species. The safest basis of specific
determination seems to be the correlation between the development and pro-
portion of the horns and of the nasals, the rule being that where the horns
are long the nasals are short, and conversely. The number of the teeth
does not at present seem to be absolutely constant, even within the limits of
the species.

The following determination of the species in the Cambridge collection is,
for the above iind other obvious reasons, provisional. The classification can
be finally settled only when the lower jaws and skulls are found in associa-
tion. If, for example, a large number of forms of the M. coloradensis type of
skull are found with but a single upper incisor, they will undoubtedly repre-
sent a species distinct from both S. trigonoceras, Cope, and M. ingens, Marsh.

M. coloradensis, Leidt, 1870. Syn. M. ingens, Marsh, Am. Journ. Sci.

and Arts, 1874. S. trigonoceras, Cope, Synopsis New Vert. Col., 1873, p. 13.

The type of this species, a snout with horns and nasals, was figured by Pro-

* The Ve.rtebrata of the Swift Current Creek Region of the Cypress Hills. Geol.
and Nat. Hist. Sizrv. of Canada, 1886, p. 81 c.
t Am. Joum. Sci. and Arts, Cd Ser., XI. 339.

MUSEUM OF COMPARATIVE ZOOLOGY.

159

fessor Leidy * in 1873, and agrees closelj' with the corresponding portions of
the smallest skull in the Cambridge collection, both in form and measurement.
The skull is entire, and enables us to fully define this species.

Dentition : I. L?L?> C. ^, Pm. ^, M. ^. No diastema behind the canine.
Second upper incisor sometimes wanting. First upper premolar small. Last
upper molar without distinct second cone. Upper premolars with a strong
internal cingulum. Anterior nares transversely broad and shallow vertically.
Nasals long and broad. Horns short and stout, obliquely compressed at the
base so that their faces point in three directions, erect and slightly recurved
when viewed from the side. The greatest diameter at the base is fore and aft.
Orbits large, and widely open. Superciliary ridge not prominent. Zygomatic
arches broad and powerful, but without flanges, Post-glenoid and post-tym-
panic processes separate or not broadly united.

Figure 3. — Anterior portion of the skull of three species of Menodus, showing; the rela-
tions of the nasals to the horns in side view. 1. M. coloradensis. 2. M. tichoceras.
3. M. dolichoceras.

The skull of this individual is considerably smaller than the type of M.
ingens, measuring only 27^ inches from the occipital condyles to the tips of
the nasals. The superciliary ridges expand into small postorbital- processes,
which are wanting in the above type. The post-glenoid processes do not
touch the post- tympanic. The M. ingens skull has two incisors, while this
specimen has but one. It is possible that one or more of the above differences
may prove to be of permanent specific value, but in the conformation of the
nasals and of the horns, as well as in all other details of proportion, these
skulls are apparently closely similar.

In comparison with the type of S. trigonoceras, Cope, the horns and nasals
have somewhat similar proportions, but are less distinctly triquetrous at the
base. The skull also resembles that of M. angustigenis, Cope.

M. tichoceras, sp. nov. This species may prove identical with S. altirostris,
Cope. Dentition : I. f , C. \, Pm. ^, M. S.t No diastema behind the canine.

* Extinct Vertebrate Fauna, etc., U. S. Geol. Surv., Vol. I. Plate I.
t The number of lower incisors is inferred from the distinctly worn tips of the
upper incisors.

160 BULLETIN OF THE

Second cone on last upper molar united with the cingulum. Probably two
lower incisoi-s. Upper premolars with a faint or no internal cingulum. Nasal
bones intermediate in length and narrowing anteriorly. Horns elbngate, sub-
cylindrical in section at the base, and in side view inclined obliquely forward,
so as to partly overhang the snout. Anterior nares transversely narrow and
vertically deep, so that the snout is very elevated. Superciliary ridge promi-
nent, rugose, and overhanging the temporal fossae. Orbits rather small and
enclosed. A post-orbital process. Z^'^gomatic arches wide and partly flanged.
Post-glenoid and post-tympanic processes widely united.

Description of Skull. — The type of this species is a single large skull, with
the dentition complete, and lacking the upper part of the horns and the crest
of the occiput. The total length is 29 inches, while Professor Cope's type of
S. altirostris measures but 25^ inches. The separation from the latter species
depends upon the number of lower incisors. Apart from size, the chief dis-
tinction from M. Coloradensis is in the narrow and elevated terminal portion
of the skull, giving a widely different appearance in front view. The zygo-
matic arch is very massive, and presents a bulge in the posterior half, which
however is much less prominent than in S. bucco, Cope.

It is also distinct froni M. Proutii, Leidy. In the Princeton collection is a
large skull which has been referred to this species. It differs from M. ticho-
ceras in the presence of a diastema behind the superior canine, as well as in the
presence of a distinct second cone upon the last upper molar, aud of a strong
internal cingulum upon the premolars.

M. dolichoceraa, sp. nov. This species may prove identical with S. acer.
Cope. Dentition: I. ?, C. ^, Pm. ^, M ^. Upper premolars with a faint in-
ternal cingulum. Nasal bones extremely short and obtuse. Horns extremely
long and powerful, directed obliquely forwards and outwards, projecting beyond
the nasals in side view. The section is sub-oval at the base, with the long axis
obliquely transverse. Cranium very broad and saddle-shaped above the orbits,
narrowing somewhat posteriorly. A prominent and overhanging superciliary
ridge. Post-glenoid and post- tympanic processes united for a short distance.
The skull which we have made the type of this species" is much larger and
more powerful than Professor Cope's type of S. acer. The horns are longer
and more widely divergent at the base. The angle of inclination of the horns
and the diminutive proportions of the nasals, as well as the form of the top of
the cranium, all bring this specimen near S. acer, and separate it from other
known species. Unlike S. acer, the horns are not united by a ridge. The
specimen is incomplete in the supra-occipital region, the zygomatic arch is
fragmentary, and the maxillary, palatine and basi-occipital regions are much
distorted,

M. platyceras, sp. nov. The type of this species is a pair of horns with
the nasal bones attached. All other portions of the skull are wanting.

The dentition is unknown. Nasal bones extremely short and obtuse, as in

MUSEUM OF COMPARATIVE ZOOLOGY.

61

M. dolichoceius and M. acer. The inner contour of the uorns is concave ; they
are greatly flattened antero-posteriorly with a ridge-like outer margin, and
connected by a well-raised median ridge. The posterior face is nearly plane,

Figure 4. — Horns of M.platyceras. 4. Viewed from in front and in section.

4«. Viewed from the side.

the anterior is convex, so that the section of the horn is plano-convex from
base to tip. In side view the horns completely overhang the nasals, and are
slightly recurved. The long axis of the horn section is directly transverse.

Measurements.

2

•5.1
•3 d

i

22
»•- 2

Distance between tips
of horns, outside
measurement.

Length of horns meas-
ured from tins to
median fronto asal
suture.

Antero-posterior di-
ameter of the molar-
premolar series.

Free portion

of

nasals.

Approximate

diameter of

anterior nares.

Length.

Breadth.

Verti-
cal.

Trans-
Terse.

M, coloradensis
. f. tichoceras
M. dolichoceras
M. plaiycera
M. Proutii

M.

.70

.80?
.74

M.
.16

.13

.09

M.
.33

.58

.42

M.
.16

.32

.25
.20

M.
.31

.34

.37

M.

.08

.06
.04

M.
.12

.13

.09

M.
.075

.11

.075

M.
.135

.09

.075

.911

....

The above measurements bring out very clearly tne decrease in the propor-
tions of the nasals pari passu with the gradual elongation of the horns. An-
other very interesting fact is brought out by the comparison of the transverse
and longitudinal diameters of the horns at the base. As we pass from the
short to the long horned types, through M. coloradensis, tichoceras, dolichoceras,
and platyceras, there is a gradual rotation of the- longer axis of the horn-section
from a fore and aft to a transverse plane ; the species last named representing
the extreme of the transverse type.

VOL. XIIT. 11

162

BULLETIN OF THE

The accompanying figures show the four t5^es of skull as seen in the fronto-
nasal region. The first type, with long nasals and short erect horns, is repre-
sented by M. coloradensia and characterizes also M. ingens and M. angustigenis.
The second type, with medium nasals and short obliquely placed horns, is

MUSEUM OF COMPAEATIVE ZOOLOGY, 163

represented by M. tichoceras, and characterizes M. Proutii and M. altirostris.
The third, with short obtuse nasals and long horns, is represented by M. doli-
choceras, M. acer, and M. platyceras.

There are doubtless other species of Menodus in this collection, but the fore-
going are the only fully defined types. The lower jaw with three lower incisors
probably belongs to a new species. There is also a pair of diminutive horns,
resembling those of S. heloceras, Cope. Another pair of horns presents a smaU
knob upon the antero-interior surface, about half-way to the tip, which gives
the horn quite a different aspect from those above described.

Restoration op M. Proutii.

The accompanying restoration of Menodus (see Plate II.) is from materials
in this collection, in the E. M. Museum of Princeton, and in the collections
of Professor Cope, as follows : Mus. Comp. Zool., the fore and hind limbs
and fore feet. E. M. Museum, the pelvis, hind feet, anterior dorsal verte-
brae, the cervical vertebrae, the anterior ribs, and skull. The scapula and
outlines of the processes of the cervical vertebrae and spines of the first and
second dorsal vertebrae are from the Cope collection. The outlines of the pha-
langes of the fore foot are from specimens in the Cambridge collection, and
from Professor Marsh's drawings. AU the structures which are wholly or in
part conjectural, such as the sternum, the outline of the scapula, the lumbar
vertebrae, and sacrum, are drawn in plain or dotted lines without shading. On
the other hand, several of the ribs which are known from the Princeton col-
lection are not shaded, for the sake of uniformity. Several of the posterior
dorsal vertebral centra are shaded for the relief eflFect. The proportions of the
neck, back, and pelvis, with those of the skull, are known from the fact that
these parts in the Princeton collection belong together, i. e. to one individual.
The larger bones of the fore and hind limbs are also, for the most part
from a single individual ; and a number of vertebrae found with the head
of a radius of another individual enable us to determine the proportion be-
tween the fore limb and the centra of the dorsal vertebrae. The size of the
scapula, which belonged to an isolated series, was fixed by the proportions
which obtain between this bone and the humerus in the Proboscidia, Rhino-
ceridce, and Dinocerata ; viz. that the scapula varies from ^ to f the length of
the humerus. We have given it |- the humerus length.

The animal is placed in an erect standing position, the right leg being drawn
slightly back. The fore limb is placed nearly at the maximum of extension ;
the angle of this limb, as indicated by the articular facets of the head and
trochlea of the humerus, being intermediate between that of the elephant and
rhinoceros. It was capable of being flexed to a much greater degree than
is here represented, so as to bring the animal nearer the ground.

The skull and neck, to which the trunk and limbs are proportional, proba-
bly belong to M. Proutii, a species of about the medium size attained by these
animals ; for, judging by the measurements of the skuUs which are known.

164 BULLETIN OF THE

there were other species both smaller and larger. This animal was about
eight feet high at the shoulder, and over twelve feet long. The height is
greatly increased by the extraordinary development of the spines of the
anterior dorsal vertebrae. These are well preserved, and in two cases com-
plete to the tip, in the materials at our disposal. They are broad and flattened
nearly to the tip, so as to fit closely together. The neck is longer than that
of Uintatherium, but shorter than that of the rhinoceros. With the power of
flexing the elbow, the head could readily be lowered to the ground in feeding.
The arm, fore-arm, and shoulder-blade are decidedly rhinocerotic in character,
although showing a greater proportional length and less flexion capacity.
The thigh and lower leg, on the other hand, are rather elephantine in their
shape and proportions, and indicate much less play at the knee-joint than in
the rhinoceros. The limb bones are relatively shorter than in Uintatherium,
but the metacarpals and tarsals are much longer and less spreading, thus
adding considerably to the height. These segments, combined with the elonga-
tion of the dorsal spines, gave Menodus as great a height as was attained by the
eocene genus, with its longer Hmbs.

AMYNODONTID^.

Ehinoceros-like animals, as far as yet known, extending from the Middle
and Upper Eocene (Bridger Beds) to the White River Miocene Beds ; horn-
less ; canines and incisors present in the typical number in both jaws ; pattern
of the premolar transitional to that of the molars ; first upper premolars rudi-
mentary or wanting; pattern of true molars like that of the rhinoceros, but
with the transverse crests simple; skull with a powerful sagittal crest.

AMYNODON,* Mar.sh.

Probable syn. Orthocynodon, Scott anrl O.sborn.t

Dentition : I. f, C. \, Pm. |, M. |. Upper caninr:, obliquely placed; lower
canines erect and placed immediately in front r,f the upper when jaw is closed.
The third and fourth upper premolars only approacn the molar pattern by
the development of double transverse crests. First upper premolar small and
single fangec' . Post-glenoid and post-tympanic processes separate.

* This Eocene genus, owing to the imperfect condition of the type skull in Pro-
fessor Marsh's coUectiou at the time of description, was incorrectly defined, (Am,
Journ. Sci. and Arts, 3d Ser., Vol. XIV. p. 251,) and the present writers, after a
personal examination, were led to believe that the type specimen of 0. antiquiis
represented a distinct genus. It now proves to be the same, as far as we know at
present.

t E. M. Museum Bulletin, No. 3, May, 1883.

MUSEUM OF COMPARATIVE ZOOLOGY.

165

Dentition

I. f, C.

METAM JTNODON, gen. nov.

\, Pra. f , M. |. Upper and lower canines obliquely
placed, the latter fitting somewhat internal to the former when the jaw is
closed. The first upper premolar wanting; the second, third, and fourth pre-
molars are of the molar pattern. Post-glenoid and post-tympanic processes
widely united.

Figure 7. — Skull of Metamynodon planifrons, in side view, about one sixth natural size.

Metamynodon planifrons, sp. nov Specific characters. First upper molar
with an incomplete internal cingulum. Lower median incisors small. The
molars greatly exceeding the premolars in size.

This genus is represented by a single skull in fine preservation, and the
anterior portion of the left mandibular ramus. The latter specimen was found
some little distance from the skull, but for many reasons may be safely placed
with it. The canine-incisor formula is the same, and the diameters of the
canine fangs are similar. There is one less premolar, but the molar-premolar
series as a whole has the same antero-posterior length.

Metamijnodon is evidently a highly modified .successor of Amynodon, of about
double its size and strength. The dentition is reduced by the loss of one upper
and two lower premolars. The pattern of the premolars presents a slight pro-
gression in the complication of the transverse crests of pm^ ; but as a series
they show a decided retardation of growth as compared with the molars which
assume very large proportions. The mandibular symphysis is relatively
much narrower. The sagittal crest is still more powerful. The skull is modi-
fied by the unusual shortening of the facial region, and the flattening of the
cranium and broadening of the zygomatic arches, but without the develop-

166

BULLETIN OF THE

ment of horns or other protective structures. It equalled in size the largest
of the modern rhinoceroses, and belongs to a line which is quite distinct from
that of either Uyracodon, Aceratherium, or Diceratherium. The great reduc-
tion of the premolar series separates it from the first, while the retention of
the fuU canine-incisor series separates it from the last two lines of descent.

The skull is remarkably broad and flat, with powerful and widely extended
zygomatic arches, and a long flattened cranium, surmounted by a strong sagit-
tal crest. The antorbital or facial region is considerably less than one third
the entire length of the skull, instead of one half the length, as in Amynodon
and the modern rhinoceroses. The occiput is low, and projects considerably
behind the condyle. The small proportions of the facial region and great
development of the area of attachment for the muscles of the lower^ jaw are
respectively in direct relation to the unusual reduction of the premolar series
and the great size of the molar and canine-incisor series. With these numerous
peculiarities, the skull still retains a rhinocerotic character and has unmis-
takable resemblances to that of Amynodon.

TTtC

Figure 8. — Skull of Metamynodon. Front view.

The premaxillaries are broad and flattened above, and, bulging forwards, con-
verge into the broad rounded alveolar border. They are quite distinct in the
median line. The anterior nares, as viewed from in front, are triangular,
bounded above by the short, flattened obtuse nasals which overlap the inner
faces of the converging premaxillaries. The nasals viewed from above are
smooth, short, and broad. The maxillaries form a wide union with the fron-
tals, and are deeply excavated behind the canines to the large infra-orbital
foramina. The sutures of the lachrymals cannot be distinguished; they proba-
bly had a short exposure upon the face. The lachrymal foramen is within the
orbit. The frontals are very long, extending from the interorbital space to the
middle line of the cranium. There are no post-orbital processes, but rugose
supra-orbital processes widely overhanging the orbits, which they completely
conceal from above. They are separated by a notch from the prominent ant-
orbital rugosity. The orbits are thus small and deeply enclosed. The malars
have a faint postorbital process. Their greatest diameter is vertical, but the
zygomatic processes of the squamosals are twisted, so that they unite with the

MUSEUM OF COMPARATIVE ZOOLOGY. 167

skull with the greatest cliaineter horizontal (Fig. 7). The squamosals are
low and widely united with the parietals. The articular facets for the mandi-
ble and post-glenoid processes resemble those in the rhinoceros, on a larger
scale. The parietals are rather short, a considerable portion of the cranium
being formed by the supra-occipitals. The occiput is low and broad, with
poTverful condyles, which are much extended transversely. The space between
the condyles and post-glenoid processes is rather short. The paroccipital and
post-tympanic processes are on a level and closely united. The latter forms a
wide union with the post-glenoid, completely enclosing the external auditory
meatus inferiorly. The basi-occipitals and sphenoids form a prominent ridge,
which is not overlapped anteriorly by the pterygoids. These bones are rather
short and obtuse. This region of the skull i?, upon the whole, very similar to
that of the rhinoceros. The relations of the bones composing the hard palate
are also rhinocerotic, except that the incisive alveolus is much shorter.

Dentition.

Lower Jaw. The crowns of the entire mandibular series are wanting. There
were three lower incisors, which, so far as we can judge from the alveoli, were
smaller than the upper, and much crowded by the large canines. The lateral
incisor was the largest, the series decreasing towards the middle line. The
canine fang is completely preserved, and indicates a large, semi-procumbent,
laterally compressed tooth, measuring 1^ inches in transverse diameter. It is
followed by a diastema of two inches. The first and second premolars are want-
ing; the third has two fangs, and has about half the antero-posterior diameter
of the first molar. The fourth premolar is two thirds the diameter of the first
molar. The three molars increase rapidly in size, covering a space equal to
that occupied by the upper molars, and three times that occupied by the
premolars. The last molar is the largest, and was apparently trilobed.

Upper Jaw. The maxillary series are better preserved, the inner faces of
the molar crowns showing on one side or the other in all except the first and
last of the series. The incisors were placed in a uniform curvature, the lateral
incisor being separated from the canine by a narrow diastema. The median
alveolus is the largest, and the series apparently decrea.sed in size laterally,
reversing the relations of size shown in the mandibular series. The canines
were subequal in size, and inclined forwards like those in the mandible. A
narrow diastema separates this tooth from the small two-fanged second pre-
molar, the first premolar having entirelj^ disappeared. The tliird and fourth
premolars have a broad, swollen, anterior transverse crest, and somewhat nar-
rower and much more slender posterior crests. The fourth premolar has a
faintly developed combing crest, as in the third premolar of Amynodon. The
molars show a sudden and remarkable increase in size, occupying a space three
times as great as that taken by the premolars. The crown of the first molar is
transversely oblong, measuring 2| by 2 inches ; the second is subquadrate;
the third is antero-posteriorly oblong. As in the premolars, the anterior crest
in ml and m^ is the largest, and without distinct " anti-crochet," but the pos-

168

BULLETIN OF THE

tenor crest is also strongly developed. In its great inward extension m} has
lost the internal cingulum, which is well developed in m^ and m^, as well as in
the premolars. The broken outer contour of the molars indicates that the
outline was similar to that observed iu the Amynodon molars.

Figure 9. — Base of skull of Metamynodon. ppf, post-pa1atine toramen. fov, foramen
ovale. Jim, foramen lacerura medium. Jlp, foramen lacerum posterius. As, alisphe-
noid canal.

Measurem.
Skull.

M.

Length of the skull from the incisor alveolus to the occipital condyles . .550

Transverse measurement, outside of the zygomatic arches 365

Height of the occiput 165

Breadth " " 190

Length of face, front of orbit to premaxillaries, anterior border . . . .170
Length of cranium, front of orbit to occiput 385

MUSEUM OF COMPARATIVE ZOOLOGY. 169

Upper Teeth.

M.
Antero-posterior diameter of mo]ar-premolar series (pm. .065, m. .160), .225

Measurement of the canines, outside 130

" " " inside 056

Diameter of first molar, antero-posterior .047 ; trans 068

" third molar, " .060 " 064

« fourth premolar, " .025 " 045

« canine, « .035 " 035

Lower Jaw.

Length of sj'mpliysis, 130

Breadth of jaw opposite canines ' 075

Diastema behind the canines 050

Depth of jaw below first molar 096

Antero-posterior diameter of molar-premolar series 210

Measurement outside of the canines 060

Transverse diameter of the canines 030

Antero-posterior diameter of the canines 037

RHINOCERID^.

Aceratherium (Rhinoceros) occidentale, Leidy. This species is abun-
dantly represented in the collection by skulls, teeth, and portions of the skele-
ton. Little more than the skull has been described as yet, but it is now
possible to give a nearly complete account of the osteology of this species, as
will be done in the final paper. The American species of Aceratherium are
lighter, more slender, and retain more evidence of lophiodont ancestry than
the European species, or any of the recent forms. The scaphoid does not
cover the magnum so extensively as, and the lunar has a greater contact with
the magnum than, in any of the modern genera, nor does the lunar rest so
completely upon the unciform as in the latter. The metacarpals are heavier
than in Hyrachyus, more slender than in the recent types ; there were plainly
four digits in the manus. The phalanges have about the same proportions as
in the Sumatran rhinoceros. In the hind foot, compared with that of living
species, we find that the tarsus is higher and narrower, the astragalus more
deeply grooved, with longer neck and smaller cuboidal facet ; the calcaneum is
not so heavy ; the metatarsals, especially the lateral ones, more slender.

In the limb bones the processes for muscular attachment, such as the deltoid
hook of the humerus and third trochanter of the femur, are much less mas-
sively developed than in recent species.

HYRACODONTID^.

Hyracodon nebrascense, Leidy. This species is very abundantly repre-
sented. Its osteology has already been partially described in another place,*

• E. M. Bull., No. 3, p. 17.

170 BULLETIN OF THE

and it is therefore unnecessary to dwell npon it here further than to remark
its very close resemblance in many important respects to the the eocene genus
Hyrachyus. In general there are also certain analogies with the horse, in the
delicate head, long neck, and elongated and narrow I'eet.

Hyracodon major, sp. nov. The type of this species is a fairly complete
skeleton in the Princeton Museum, and in the Camljridge collection it is rep-
resented by a beautifully preserved fore-foot. Of this the carpus is high and
narrow ; the scaphoid is less produced laterally than in Aceratherium, the facet
for the trapezium is very small and infero-lateral in position, those for the
trapezoid and magnum much larger, and nearly equal in size. The lunar is
contracted and anteriorly rests only upon the unciform, touching the magnum
laterally, while in H. nebrascense there is apparently no anterior contact be-
tween the lunar and magnum. The cuneiform is high and much compressed,
and the pisiform is short, compressed, and much expanded at the free end.
The trapezium is a very small bone ; it is pushed to the posterior side of the
trapezoid so as not to be visible from the front, and has no contact with meta-
carpal II. The trapezoid is well developed, though relatively smaller than in
the rhinoceros. The magnum is very large, in accordance with the develop-
ment of the third digit, and is especially elongated in the vertical direction.
The unciform is very high and narrow, and descends much below the level of
the other carpals ; owing to this compression the facet for metacarpal III. is
entirely lateral instead of distal ; there is an unusually extensive contact be-
tween the unciform and the magnum.

The lateral metacarpals are slender, narrow, and curved, the median one
considerably longer and much heavier. Metacarpal 11. abuts against the mag-
num by a considerable facet, while in H. nebrascense the facet is very small.
Metacarpal V. is represented by a minute nodular bone, which is attached to
the unciform and to the ulnar side of metacarpal IV.

Measurements. H. nebrascense. H. major.

M. M.

Carpus, breadth 040 .060

" height (median line) 033 .050

Unciform; width 020 .023

" height 021 .033

Metacarpal II., length — .115

" III., " — .128

« IV., " — .105

« v., " 010 —

Hyracodon (?) planiceps, sp. nov. This large species is distinguished
from H. nebrascense by its extremely low and broad cranium, which is flattened
upon the upper surface and entirely lacks the sagittal crest, which is repre-
sented by two ridges diverging from the supra-occipital border. This flat-
tening alters the proportions of the occiput and temporal fossa. Comparing

MUSEUM OF COMPARATIVE ZOOLOGY. 171

this skull with that of H. nehrascense, we find about the same relative
height as between the skulls of Metamynodon and Amynodon. The antero-
external column is less sharply folded than in H. nehrascense ; the first molar
has a small conical tubercle at the entrance of the valley ; the outer wall of
the last molar extends beyond the posterior crest much more than in the
other species of the genus, as in Amynodon and the Lophiodontidce. The
transverse crests are subequal and extend obliquely across the crown, thus dif-
fering from JI. arcidens, Cope, in which the anterior crest is the longer and
curves around the posterior.

The skull, which was that of a young animal, lacks most of the facial por-
tion. The extreme breadth across the zygomatic arches is 6^ inches, while
the height of the occiput is 2^ inches ; in a young specimen of H. nehrascense
these measurements are 4| and 3 inches, a great difference of proportions.
The periotic is exposed on the surface of the skull ; the parietals are short ;
the post-glenoid and post-tympanic processes are separated below ; the lachry-
mals extend considerably on the face.

Measurements. K planiceps. H. nebrascense.

M. M.

Upper molar series, length 103 .070

First molar, width 035 .026

Second " " 036 .028

Third " " 037 .026

Second molar, length 035 .027

Third " " , 040 —

The proportions of the teeth thus differ considerably in the two species. In
H. planiceps they increase in size from m. 1 to m. 3, while in the srnaller ani-
mal m. 2 is the largest. In the former species the molars closely resemble
those of Amynodon, but differ widely from the proportions found in Metamy-
nodon. In fact, this animal may turn out to belong to a genus very different
from Hyracodon, but at present we prefer to retain it provisionally in that
group.

ANCHITHERID^.

Mesohippus (Anchitherium) Bairdi, Leidy. The genus Mesohippus,
Marsh, differs from Anchitherium in the structure of the incisor teeth, which
have no enamel pit. The Cambridge collection contains an excellent skull
and brain cast, the description of which is reserved for the memoir.

PLATE II.

Restoration of Menodus Proutii.
One sixteenth natural bize.

P4

p

i>

^

^

M

a

m

CO

0^

t>

N

C£

'v:

ir.

"cS

o

£

W

p^

ts

o

c

►4

^

o

J3

hri

^

HH

05

fb

c

o

o

!2i

o

M

H

^

03

o

H

cc

H

(i^

No. 6. The Eyes in Scorpions. By G. H. Parker*

The subject discussed in the following pages has already attracted the
attention of able investigators, and were it not that the authors of the
later papers have pointed out questions only partially answered, a recon-
sideration of the subject might appear presumptuous. It is hoped that,
in discussing these questions from an embryological as well as histological
standpoint, the additional evidence obtained may throw some light on
their solution.

The study of the eyes in Arthropods requires so much technical skill
that until very recently satisfactory work in this field has been almost
impossible. Aside from papers mainly of historical interest, the most
comprehensive publication for the student to-day is Grenacher's " Unter-
suchungen iiber das Sehorgan der Arthropoden." This appeared in 1879,
and contained an admirable study of the eyes in spiders ; it did not,
however, touch upon the organs of sight in scorpions. The same year,
Graber, in his paper entitled " Ueber das unicorneale Tracheaten-
Auge," severely criticised Grenacher's conclusions. Grenacher, in order
to answer his critic, turned his attention to the eyes in scorpions, and, in
his paper on the eyes in Myriapods, published in 1880, he included a
reply to Graber. Three years later a comparison of the eyes in the scor-
pion and king-crab was published by Lankester and Bourne. The sub-
stance of these four papers, when viewed in the light of newly discovered
embryological facts, has recently been fully discussed by Mark. Previous
to the appearance of Mark's paper, Patten, after having made a compara-
tive study of the eyes in certain mollusks and arthropods, included in his
general description an account of the histology of the eyes in scorpions.
The five papers quoted, namely, those of Graber ('79), Grenacher ('80),
Lankester and Bourne ('83), Patten ('86), and Mark ('87), are the only
ones in which the histology of the eyes in scorpions is considered.

The publications on the development of the eyes are even less exten-
sive than those on the histology. MetschnikofF ('71, p. 225), in his

• Contributions from the Embryological Laboratory of the Museum of Compara-
tive Zoology at Harvard College, under the Direction of E. L. Mark. — No. XII.
A Thesis presented for the Degree of S. B.

VOL. XIII. — NO. 6. U

174 BULLETIN OF THE

paper on the development of the scorpion, barely alludes to the eyes.
Their probable method of development is described by Patten ('86, p.
672). His conclusions as far as they touch upon the eyes in scorpions
are based upon inferences drawn from the method of development in
other forms, not from actual observations. In a preliminary communica-
tion by Kowalevsky and Schulgin ('86, pp. 530-532) the method of
development for the median eyes is described at some length. On ac-
count of incompleteness in their studies, these authors were forced to
omit a description of the lateral eyes. Later in this paper, the substance
of their communication will be considered.

The species of scorpions previously studied have been numerous.
Graber ('79, p. 71) examined the eyes in Scorpio eurojiteus, Schr., and
Buthus afer, L. Grenacher's investigations ('80, p. 42) were made upon
Buthus afer, Ischnurus caudicula, and Lychas americanus. Androctonus
funestus, var. citrinus, Ehr., Euscorpius italicus, Roess. and E. carpathi-
cus, were the species studied by Lankester and Bourne ('83, p. 180).
The embryological researches of Kowalevsky and Schulgin were made
upon Androctonus ornatus.

The species which I have studied belongs to the genus Centrums.*
In July and August, 1886, through Mr. C. W. Johnson, gravid females
were obtained from Florida. At intervals during the following winter
Mr. Johnson and Mr. F. S. Schaupp of Texas supplied me with fresh
material. I am also indebted to Dr. H. A. Hagen for some alcoholic
specimens from Arkansas.

In preparing the eyes for study by means of sections, the two chief
difficulties encountered were the presence of chitinous lenses and dense
pigment. It is difficult to cut the lens, and often this structure is in
part torn away, thus destroying the surrounding tissue. In the median
eyes, by careful dissection, the soft parts may be separated from the lens
and cuticula, and cut without the interference of these hard structures.
The separation is best accomplished after the tissues have been hardened.
The method of dissection cannot be applied to the lateral eyes, for they
are almost completely surrounded by chitine. In these eyes the best
results were obtained by trimming otf the chitine around the eyes, and
cutting the retina and the lens after the removal of as much chitine as

e.
Tlie pigment is so abundant and so dense that even the thinnest sec-

* I am unable to state what species tins is. I have not succeeded in finding
it described anywhere. Specimelis in the collection of the Museum marked bj'
Simon as "Centrurus sp. incog." are of the same species as those here described.

MUSEUM OF COMPARATIVE ZOOLOGY. 175

tions cannot be studied to advantage until they have been depigmented.
For this purpose I know of only two classes of successful reagents, acids
and strong alkalis. Grenacher has generally employed the first, Graber
the second.

Of the acid reagents strong solutions are required. Lankester and
Bourne ('83, p. 180) employed 5 or 10^ solutions of nitric acid. In
the eyes which I have studied, this mixture did not remove the pigment,
even after the lapse of a week ; and I was forced to use stronger and
stronger grades, till 50% was reached. This mixture gives fair results,
but must be made and used with much caution. A given volume of acid
should be poured slowly into an equal measure of alcohol, never the re-
verse, and the mixture should be kept cool, otherwise the acid may attack
the alcohol. In such an event the solution is rendered worthless, and,
should the specimens be in it at the time, the heat generated by the
reaction gives the acid such additional dissolving power that the sections
are at once destroyed. A more efficient acid reagent is a mixture of
equal parts hydrochloric and nitric acids. A 35 % solution of this mix-
ture in strong alcohol gives better results than the pure nitric acid at
50%, and does laot so readily attack the alcohol.

Of the alkalis, weak ammonia, sodic hydrate, and potassic hydrate
are most serviceable. The solids are to be preferred to the ammonia,
since from them solutions of a definite strength can more easily be made.
An aqueous solution of J or ^% potassic hydrate has given the most
satisfactory results.

The method of using the depigmenting fluid is as follows. Unstained
material is cut in paraffine ; the ribbons are mounted on a slide with
Schallibaum's fixative ; when the sections are fixed, the paraffine is re-
moved with turpentine ; the slide with the sections is then successively
washed with alcohol of 98%, 90%, 70%, and so on, till a grade homo-
geneous with the depigmenting fluid is reached. Into a shallow white
dish filled with the depigmenting fluid the slide is now gently lowered.
In z^few seconds the pigment, dissolving, will be seen as a reddish cloud.
The process is usually completed in less than a minute, and the slide is
promptly transferred to a dish of clean water or alcohol and there gently
rinsed. The sections are next stained by exposure to the dye in a shal-
low dish. After being sufficiently stained, they may be washed and
mounted in glycerine, or, after the proper steps in dehydrating and clari-
fying, mounted in benzol-balsam or other mounting medium.

The dyes which have been found the most serviceable are some of the
carmines and haematoxylin. The aniline dyes have almost invariably

176 BULLETIN OF THE

given poor results. For general purposes Grenacher's alcoholic borax-
carmine is excellent. In both embryonic and adult material Czoker's
alum-cochineal gave fine nuclear outlines. In the adult eyes, the rhab-
domes and the cell boundaries were most distinctly shown by Kleinen-
berg's haematoxylin. A very faint coloration with this dye gave the best
results for nerve-fibres.

For the isolation of the retinal elements two maceration fluids were
used. A weak solution of chromic acid, as employed by Patten ('86, pp.
736, 737), gave good results ; but since the mycelium of a fungus is often
developed in very dilute solutions of this reagent, it can be used only
when it is carefully watched and its results are controlled by another
method. It was employed in the following manner. The retina, after
the removal of the lens and surrounding tissue, was placed for five or ten
minutes in a ^% solution. After this treatment, which slightly hardened
the tissues, the first solution was replaced by a second of 5^0%- I" ^^is
the retina remained for three or four days, at the end of which time the
retinal cells were easily separable. The most satisfactory method of iso-
lating the cells is to place on a slide in dilute glycerine a small portion of
the macerated retina, and, having protected it with a cover-glass raised
on wax feet, to gently tap the cover-glass till the cells are separated.
One part of 0.2% solution of acetic acid in sea-water mixed with an
equal volume of 0.04% osmic acid in sea- water, although only partially
successful as a maceration fluid for the retina in scorpions, is a reliable
check for the results obtained from chromic acid.

After the cells have been isolated, the abundance of pigment which
they contain so obscures their contents that scarcely more than their out-
lines can be studied. The removal of the pigment is on the whole more
successfully accomplished before than after isolation. For this process,
as for simple isolation, the retina should be subjected to the action of
^% chromic acid for five or ten minutes, and then transferred to a solu-
tion of ^% potassic hydrate. In this the pigment dissolves, forming a
reddish cloud. After about a minute the retina should be removed to
distilled water, rinsed, and transferred to Grenacher's alcoholic borax-
carmine. This reagent performs both the office of a maceration fluid and
a dye. In from twelve to twenty-four hours the retinal cells can be iso-
lated, and present in difl'erent regions of the retina three principal condi-
tions. First, those from the exterior of the retina are seriously altered
by the continued action of the potash ; second, those from the centre of
the retina remain almost unchanged, still retaining most of their pig-
ment; third, those from an intermediate position, without being other-

MUSEUM OF COMPARATIVE ZOOLOGY. 177

wise much alterea, lose most of their pigment. It is from ihese last
that the hest results were obtained.

X no eyes in scorpions are situated on the prosomatic shield. According
to their position they may be classed into two natural groups, the median
and the lateral eyes. As their name implies, the median eyes are situated
close to the sagittal plane. They are a little in advance of the centre of
the shield, two in number, and always symmetrically placed. The lateral
eyes form two isolated groups, one on either side, at the edge of the shield
where its anterior border meets its lateral margin. In different genera,
the number of eyes in each group varies from two to seven. Two kinds
of lateral eyes have been distinguished ; the larger or " principal," and
the smaller or " accessory " eyes. As will be shown later, no essential
difference exists between these two groups ; the smaller and larger eyes
are constructed on the same plan.

On account of the marked dissimilarity in the structure of the median
and lateral eyes, they will be described separately.

The Median Byes.

xrenacher ('79, p. 40) first pointed out tnat the vitreous and retinal
layers in the eyes of spiders were separate. Graber in the same year con-
firmed this discovery, and showed that the median eyes of scorpions had
a similar structure. These two-layered eyes were designated by Lan-
kester and Bourne ('83, p. 195) as diplostichous, and among them were
included the median eyes in scorpions. Up to this time all authors
agreed that the median eyes of scorpions were two-layered.

One of the results of Locy's work ('86, p. 85), as Mark has indicatea
('87, p. 71), is that in spiders the so-called diplostichous eyes are in
reality three-layered, or triplostichous. The embryological facts on which
this statement -is based will be referred to later. For the present it is
sufiicient to note that an interesting question presents itself, namely, if
the so-called diplostichous eyes in spiders have been shown to be triplo-
stichous, may we not look for a similar condition in the median eyes
of scorpions 1 Some of the reasons for believing this have already been
stated by Mark ('87, pp. 55-58), but the final settlement of the question
can only be reached through embryological means. It was my principal
object in beginning these studies to reach a satisfactory conclusion in
this matter.

Patten ('86, p. DV2j had alreaay ciaimea taai; the median eyes in

VOL. XIII. — NO. 6. 12

178 BULLETIN OF THE

scorpions were three-layered, and that they were probably formed from
a cup-like involution of ectoderm. The closure of the cup produced an
optic vesicle, the deeper half of which became retina, while the more
superficial half was probably represented by a structure to be described
hereafter, the preretinal membrane. The details of this method of de-
velopment, as will be seen later, are not confirmed by my observations ;
but nevertheless it remains to Patten's credit that he was the first to
insist that the eyes in scorpions were three-layered, and not two-layered
as had been previously held.

Metschnikoff ('71, p. 225), in his paper on the development of the scor-
pion, did not discuss the formation of the eye further than to claim for
it a hypodermal origin. His evidence on this point can scarcely be consid-
ered as conclusive, for his studies were made from superficial views only.

The youngest material at my disposal was already somewhat advanced;
but the eyes were still sufficiently undifferentiated to give adequate evi-
dence as to their origin, and thus to afford a trustworthy basis for the
interpretation of structures in the adult.

In the earliest stage examined, the eyes appear on surface view as a
pair of oval, slightly pigmented areas. They are situated at the anterior
end of the head, one on either side of the median line, and somewhat
above the mouth. In a slightly older stage a sagittal section a little at
one side of the median plane shows the region of the pigmented areas to
be already composed of three layers of hypodermis (PI. III. fig. 12, prr.,
r., and j) r.). The hypodermis of the prosomatic shield {pr r.) extends
downward toward the mouth, and preserves its indifferent condition ;
before reaching that opening, it is folded upon itself, the deeper arm (r.)
of the fold passing dorsally in contact with, the deep face of the external
portion. The ventral third of the infolded layer is as thin as the ex-
ternal layer of hypodermis, but the remaining two thirds are considerably
thickened and contain much pigment. This thickened layer, becoming
rapidly thinner at its dorsal end, is also folded upon itself to form a
third layer (/> r.), which passes ventrally next the deep face of the thick-
ened portion, and at the point of first folding becomes continuous with
the external hypodermis as it proceeds in the direction of the mouth.

This condition is practically an involution of the hypodermis. The
infolded layers take the form of a flattened sac, or pocket, the open end
of which is situated in the median plane between the mouth and the
previously described pigmented areas. From its opening the pocket
extends vertically upward, and its anterior face is closely applied to the
deep surface of the permanent hypodermis.

MUSEUM OF COMPARATIVE ZOOLOGY. 179

At the stage represented in Fig. 1 2, the cavity of the pocket is scarcely
noticeable. It should appear, of course, between the second (r.) and
third (p r.) layers, and at the deep end of the infolding a trace of it is
visible {cav.). The second and third layers, however, are quite distinct,
and show no indications of fusion. The cavity of the pocket is oblit-
erated only by its opposite walls coming in contact, so that even in
Fig. 12 a pocket may be spoken of without inconsistency. In stages
earlier than that given in Fig. 12, the cavity of the pocket is very no-
ticeable, and from its external opening to its deep end it is a continuous
open space.

In a horizontal section of the earliest stage examined, the region just
above the external opening of the pocket presents the appearance of a
slightly irregular tube cut crosswise (PL III. fig. 13). The wall of the
tube is made up of a single layer of hypodermis, whose deep surface
is covered with a delicate basement membrane (fig. 13, mh.). The cavity
of the tube is continuous with the pocket of the infolding (fig. 13, cav.).
At about half the distance from its opening to its deep end, the pocket is
divided in the median plane into a right and left compartment (PI. III.
figs. 14, 15). Each compartment has the form of a sac flattened from
before backwards. The sacs extend dorsally on either side of the median
plane, and end blindly.

One can distinguish, then, in the invagination a common neck, and
two symmetrically placed sacs which arise Trom it. In the sagittal sec-
tion (PI. III. fig. 12) already described, the thin ventral third of the
infolded hypodermis corresponds to the neck, and the thickened dorsal
two thirds to the anterior wall of the sac. The position of the sacs is
indicated externally by the areas of pigment already alluded to ; the sacs
are destined to become the retinas. The neck soon disappears, but some
time before this takes place the outer wall of each sac is thickened still
more and becomes more deeply pigmented. The thickened faces form
the essential part of the retina, with which, after the closure of the pocket,
the posterior thinner layer fuses.

The three hypodermal layers which enter into the composition of the
eye, have received special names. That portion of the permanent hypo-
dermis which is directly external to the optic sac, constitutes the first
layer. At a later stage it produces the lens, and consequently has been
termed by Mark ('87, p. 77) the " lentigen." By other authors it has
been generally designated as the " vitreous." Directly under the lentigen,
and forming the thick external wall of the optic sac, is the second or
retinal layer. Behind this layer the thin internal wall of the sac forms

180 BULLETIN OF THE

the third or post-retinal layer. At the sides and blind end of the sac,
the two deeper layers, the retina and post-retina, are continuous.

Granting the optic sacs to have arisen by involution, it is important to
notice that of the three layers described the retinal layer is inverted ; i. e.
that face which before involution is external becomes after involution
internal. A similar inversion in the retinas of the anterior median eyes
of Agelena has- already been demonstrated by Locy ('86, p. 87). In
fact, at this early stage, the only striking difference between the eyes in
Agelena and Centrurus is, that in the scorpion the two sacs are united
by a common neck, whereas in the spider they are independent involu-
tions. It seems scarcely possible that this is an essential difference, and
I therefore believe that the median eyes of scorpions, like the eyes of
spiders, arise from hypodermal involutions not immediately connected
with the formation of other organs.

Since the above conclusion was arrived at, Kowalevsky and Schulgin
('86, pp. 530-532), who have studied the development of Androctonus,
have published in a preliminary communication the results of their work.
In their description of the nervous system the development of the eye
occupies several paragraphs. On account of the absence of figures their
necessarily brief account is somewhat difficult to follow, and in one place
I am not sure of their meaning.

Their statements on the median eyes are substantially as follows. A
pair of semicircular depressions occur in the cephalic plate. From the
anterior margin of each depression a fold grows down toward the mouth.
The closure of each depression by its fold gives rise to a right and left
cephalic vesicle. From the region at which the mouth of each vesicle
has just closed, a new fold develops. Each of the new folds opens
toward the animal's mouth, and takes on the form of a pocket. The right
and left pockets thus formed are the first traces of the median eyes. The
authors then describe the connection of the two pockets by a common
neck, and the thickening of the retinal layer, in the ventral part of which
pigment is deposited.

As will be noticed, the description summarized has to do with the
earliest condition in the formation of the eye. The youngest stage of
my material is too advanced to permit me to make positive statements
on this subject. The point about which I have had difficulty relates to
the description of the brain and eye folds. In describing the formation
of the brain vesicles the authors speak of an accessory fold (eine acces-
sorische Falte, p. 530). When the development of the median eyes is
described, they speak of a new fold (eine neue Falte, p. 531). Finally,

MUSEUM OF COMPARATIVE ZOOLOGY. 181

in the paragraph especially devoted to the median eye (p. 531), the
following occurs : " Die Mittelaugeu werden von det' gleichen Falte *
gebildet, welche am Baue der Kopflappen Antheil nimmt, nur mit dem
Unterschiede, dass fiir den Bau des Hirns die tiofen Theile der Falte
verwendet werden, wahrend die Augen Derivate der peripherischen Theile
derselben Falte* sind." After speaking of an accessory fold and a new
fold in connections already alluded to, the statement that the cephalic
lobe and median eye are derived from the same fold seems to me
contradictory.

The involution of t.he optic sacs in spiders, as Locy has shown ('86,
PI. .XI. fig. 70), takes place at a much later period than the formation of
the cephalic ganglia, and to all appearances independently of the latter.
Whether in scorpions the growth of these two structures is connected or
not, is a question for the determination of which I have not yet secured
the requisite material. Besides the statements of Kowalevsky and Schul-
gin, which are somewhat obscure, there remains as a guide only the
analogous case in spiders ; the fact that the later stages in the eyes of
spiders are essentially the same as those of tlie scorpion, lends support to
the view that the eyes in scorpions, as in spiders, arise from folds inde-
pendently of those concerned in the formation of the brain.

The most noticeable changes which the pair of sacs undergoes in the
further development of the eyes are, first, an obliteration of their cavities,
and, second, a considerable change in position. The closure of the sacs
is first effected in the region where they unite with the common neck.
From this point the fusion of the retinal and post-retinal layers proceeds
toward the blind end of each sac, and the neck, becoming detached from
the sacs, is slowly withdrawn to form a part of the permanent hypodermis
(PI. II. fig. 11, col.). The line of demarcation between the retina and
post-retina at the deep end of the sac is the last trace of the already ob-
literated cavities (PI. II. fig. 10, cav.).

The change in position undergone by the eyes is correlated with a
change in the form of the animal's body. In the embryo the region of
the prosomatic shield occupies the anterior face of the animal, and there-
fore lies in a plane approximately perpendicular to the long axis. The
optic sacs are situated near the centre of this region, the plane of their
flattening being nearly vertical, and the lines corresponding to the future
axes of the eyes being horizontal. As the animal develops, the shield
assumes a position more nearly horizontal, till at length it becomes en-
tirely so. The axes of the eyes, having shifted through an arc of 90°,

• The Italics are not in the original

182 BULLETIN OF THE

then have a vertical direction. The only planes which in both the adult
and embryo cut the eyes similarly are those parallel with the sagittal
plane. In a horizontal section of a young embryo the eye shows the
same relation of parts as one sees in a transverse section of an adult.

As previously stated, the eye in the embryo consists of three cell layers,
lentigen, retina, and post-retina. Tliese three layers are recognizable
in the adult eye, and in considering the histology of this structure the
three layers will be treated in the order named.

The lentigen, as Grenacher (79, p. 40) first clearly demonstrated in
spiders, is distiuct from the retina, and is directly continuous v/ith the
hypodermis. Graber (79, p. 61) established the existence of a similar
condition in the median eyes of scorpions.

The lentigen results from a modification of the hypodermis directly
external to each optic sac. For some time after involution this hypo-
dermis consists of undifferentiated cells, whose positions are indicated by
their spherical nuclei. About the time when pigment is deposited in
the retina, the hypodermis in front of each pigmented area thickens, and
the outlines of its cells become visible (PI. III. fig. \b,pr v.). Tins is the
first modification in the formation of the lentigen. The thickening of
the lentigen increases, and each cell assumes the form of a long pyramid,
whose base rests upon a membrane between retina and lentigen, and
whose slightly truncated apex reaches the forming lens (PI. II. figs. 9
and 10). In immature eyes the sides of the lentigenous cells are perpen-
dicular to the surface on which they rest. In a transverse section of the
head of an adult (PI. I. fig. 2), the cells are curved. About three fourths
of the lentigen, extending from the median toward the lateral margin of
the eye, has its cells convex toward the sagittal plane ; in the lateral
fourth, the cells are concave toward the sagittal plane, and in the small
intermediate region they are straight (compare Lankester and Bourne,
'83, pi. X. fig. 8). In a longitudinal section of an adult head (PI. I.
fig. .1), the lentigenous cells all appear perpendicular to the surface on
which they rest.

The nuclei of the lentigen cells, at the first indications of a thickening
in the lentigenous region, keep to its deeper parts, and form in the
adult eye a continuous line close to the deeper face of the lentigen (PI. I.
fig. 2, nl. pr r.).

The lentigen as a whole is of glassy transparency. In young stages
the hypodermis at the edge of the lens nearest the median plane shows a
deposit of pigment. This pigmented region in time extends around the

MUSEUM OF COMPARATIVE ZOOLOGY. 183

edge of the lens, and, as Graber has indicated (79, p. 62), forms in the
adult a complete circle, — the iris. In the iris proper the whole of each
cell contains pigment granules, while in the adjoining hypodermis the
granules are scattered in small groups through the cells, and are especially-
abundant at their outer ends.

The lens owes its origin exclusively to the activity of the lentigen. As
is well known, it consists of a thickening of the external cuticula. The
lentigen bears the same relation to the lens as the hypodermis does to
the indifferent cuticula.

In Centrurus the cuticula at most points on the body consists of three
layers. The outermost, first recognized as distinct by Graber (79, p. 59),
is a thin, homogeneous, colorless layer (PL I. fig. 2, U). Under this is a
second layer of abou.t equal thickness with the first, but usually of a deep
yellow color (PI. I. fig. 2, II'). These two layers together form about
one fourth the whole thickness of the cuticula. The third layer (PI, I.
fig. 2, II"), embracing the remaining three fourths, is distinctly laminated.
The deepest lamella of this third layer readily takes up borax-carmine.
The remaining lamellse are distinguishable from the second layer chiefly
by their want of color. The cuticula is very commonly penetrated by two
sets of pore-canals (PL I. fig. 2, can. po. and can. po.'), fine and coarse.

As the indifferent cuticula passes into the region of the lens, the fol-
lowing conditions are noticeable. The external hyaline layer passes un-
changed either in thickness or texture over the front of the lens. The
second or colored layer becomes perfectly colorless, and by its increased
hickness adds to the convexity of the lens. The bulk of the lens, how-
ever, is produced by a thickening of the third layer.

Whereas in the indifferent cuticula only its deepest lamella is colored
with borax-carmine, in the lens all parts below the outer homogeneous
layer readily take up this dye. A similar condition has been observed
in several other local thickenings in the general cuticula, especially on
the ventral side of the animal. The conclusion to be drawn from these
observations is, that the lens in its composition is more closely related to
the last-formed cuticular lamella than it is to the older lamellse.

The coarse pore-canals never occur in the lens. Grenacher (79, p. 90)
was unable to find fine pore-canals in the lens of Phalangium, although
Leydig had previously claimed them to be found in such lenses. Graber
stated (79, p. 60) that all arthropod lenses which he had examined con-
tained fine pore-canals. In Centrurus, notwithstanding that many sec-
tions of lenses have been examined, fine pores, have never been visible,
although in the adjoining cuticula they are plainly evident.

184 BULLETIN OF THE

Graber ('79, p. 59) raised the question whether the lens consists of
only the normal cuticular layers thickened, or contains additional layers.
This is a question upon which evidence is not easily obtainable, for
it deals with layers which in the lens naay be of considerable thickness
and yet remain so thin as to be almost imperceptible in the indifferent
cuticula. The condition of the lens in young individuals offers some
evidence. About the time a young scorpion leaves the mother's back, the
indifferent cuticula appears to consist conclusively of what in later stages
corresponds to the external hyaline layer. Careful search has failed to
show any subjacent cuticula, and yet in the region of the lens a very per-
ceptible layer of stainable cuticula is visible. This seems to indicate
that the lentigen has the power of producing cuticula independently of
that produced by the indifferent hypoderrais. Admitting this, it seems
probable that of the many lamellae in the lens some may be peculiar to
the lens itself and unrepresented in the adjacent cuticula.

The separation of the retina and lentigen, as discovered by Grenacher,
was further emphasized by Graber's discovery ('79, pp. 64-67) of a
limiting membrane (" praeretinale Zwischenlamella ") between them.
This preretinal membrane, as Graber showed, is continuous with the
" sclera " and the basement membrane of the hypodermis. The explana-
tion of these structures which is offered by the formation of the eye from
a hypoderraal sac, has already been discussed by Mark ('87, p. 71). He
has claimed that the sclera is the basement membrane of the post-retinal
layer, and that the preretinal membrane is the fused basement membranes
of the lentigen and retina. The explanation given in the case of the
infolded eyes of spiders applies equally well to the median eyes in
scorpions.

As to the nature of the basement membrane, especially in the region of
the sclera and preretinal membrane, two opposing theories have been
advanced. Graber ('79, pp. 63, 64) maintains that the basement mem-
brane including the sclera is cuticular, not cellular, and as its matrix he
claims cells whose nuclei were found both by Grenacher ('79, p. 60, fig.
34) and himself ('79, p. 64, fig. 18). For the preretinal membrane
Graber ('79, pp. 64, 65) also claims a cuticular nature and states that it
contains no nuclei. Lankester and Bourne ('83, p. 189) describe the
omraateal capsule or sclera as laminate and devoid of nuclei. Mark ('87,
p. 71) believes that the basement membrane with its modifications is a
cuticula derived from the basal ends of the hypodermal cells.

Opposed to these views Schirakewitsch ('84, pp. 8, 9, 11, 12) main-
tains that the basement membrane and its modifications are connective

MUSEUM OF COMPAKATIVE ZOOLOGY. 185

tissue, and consequently cellular. His' first argument is for the basement
membrane of the unmodified hypodermis. He shows that this membrane
passes off from the hypodermis and invests muscles. Arguing by analogy
from Froriep's conclusion that the sarcolemma of striate muscles in ver-
tebrates is connective tissue, he maintains that the investment of the
muscles in spiders and the continuous basement membrane are connective
tissue. This argument of itself is scarcely convincing, for we do not
know that the sarcolemma in vertebrates and arthropods has necessarily
the same structure. Schimkewitsch used a second argument, which was
more weighty, namely, that in the envelope of the eye (sclera) nuclei had
been found. But the figures which illustrate this point are, as Mark
('87, p. 70) has stated, open to criticism.

In the developing eye in Centrurus, the basement membrane appears
as a thin sharply defined structure bounding the deep ends of the hypo-
dermal cells. It is continuous over the optic nerve, and unites with the
membrane investing the brain (PI. III. fig. 16, mb.). In the region of
the preretinal membrane it is double, one layer limiting the lentigen, the
other the retina (PL II. fig. 9, mb.). This confirms Mark's theoretic con-
clusion. In the earliest stages studied, mesodermic nuclei occur at inter-
vals between the two membranes, except directly over the centre of the
eye, where the two membranes are in contact (PI. III. figs. 14, 15, nl.
ms d.). Although mesodermic nuclei occur between the two retinas, and
also between the retina and the brain, tliey are never found within the
basement membrane of the eye region, as they are within the envelope of
the brain. As the two layers of the preretinal membrane unite, the
mesodermic cells, instead of being included between them, migrate toward
the margins of the eye, and leave the preretinal membrane when com-
pleted destitute of cellular elements. In the region of the sclera, how-
ever, mesodermic nuclei, often very much flattened and always closely
applied to the outside of the membrane, are distinguishable almost up to
the adult state (PI. III. fig. 15, PL II. fig. 9, nl. ms d.). It is, therefore,
nearly certain that some of the substance of this mesodermic covering
enters into the formation of what is known as the " sclera." In the
adult sclera, however, no nuclei are visible, and besides it is by no means
certain that these mesodermic cells form a continuous investment over
the basement membrane, — perhaps nothing more than a network.

The nuclei in the eye on the right of Schimkewitsch's Figure 11
(PL III.) are almost identical in appearance with those found in the
young eyes of Centrurus, where they appear to occupy the middle of the
membrane ; they are in reality outside it, as can be readily demonstrated

186 BULLETIN OF THE

when, as sometimes occurs, one finds a place where the niesodermie ele-
ment with its nucleus has been loosened from the sclera, and both nucleus
and sclera remain uninjured.

The nuclei which Schimkewitsch has drawn in Fig. 4 (PI. II.) and
Fig. 11 (PI. III.) are undoubtedly mesodermic, and represent a thin
tissue on the outside of the sclera.* Those in his diagramatic figure
(PI. III. fig. 4),- if they are, as Schimkewitsch says, identical with those
of the other two figures, are mesodermic nuclei drawn on the wrong side
of the sclera ; if, on the other hand, their position is correct, they are not
the same nuclei as those in Figs. 4 and 11, but, as Mark ('87, p. 70)
maintains, the imclei of the post-retinal layer.

From what has been said it will be inferred that in the adult neither
the sclera nor preretinal membrane contains nuclei. It is conceivable
that in some cases mesodermic nuclei might be surrounded in either of
these structures. Such, of course, would be exceptional. Of the twenty
preretinal membranes studied in section only one has shown nuclei ; but,
strange as it may seem, half t of this one contained no less than fourteen.
They were uniformly distributed, and always elongated parallel to the
striations of the membrane. In position they were appreciably nearer
the retiiia than the lentigen (PI. II. fig. 8, nl. ms d.). This instance
shows that the preretinal membrane may at least have a central layer of
mesodermic tissue, although the greater part of it is ectodermic cuticula.

The great thickness of the preretinal membrane in scorpions has al-
ready been noticed by Graber ('79, p. 67). In Centrurus, as in others, it
presents a fibrous laminate appearance, and in specimens treated with
potassic hydrate it is slightly swollen and vacuolated.

At the edge of the preretinal membrane, where its two constituents
separate, the one which passes around the retina is much thinner than
the one which continues under the hypodermis. This is an indication
of the relative amount of substance contributed respectively by the retina
and the lentigen in the formation of the membrane. The line which
would separate the lentigenous from the retinal part must be drawn
somewhat nearer the retina than the lentigen. It is on this line, more-

* This limitation of the meaniiifj of the word "sclera" seems desirable in view
of the possibility that a mesodermic covering may be altogether wanting, but it is
not intended as a criticism of Schimkewitsch's statement that the sclera contains
nuclei; for the "sclera" as previously understood may evidently be in part meso-
dermic, and therefore cellular, as Schimkewitsch has claimed.

+ The remaining half of this membrane was mounted on a second slide, and
treated by a method which did not make its nuclei distinguishable.

MUSEUM OF COMPARATIVE ZOOLOGY. 187

over, that one would expect to find mesodermic elements if any were
present, and naturally enough it is in this region that the exceptional
nuclei previously referred to occur (PI. II. fig. 8).

The fact that mesodermic tissue is incorporated in the preretinal mem-
brane makes it highly probable that the mesodermic cells noticed on the
sclera really contribute to that layer, and that the sclera is in part meso-
dermic and in part ectodermic. To summarize, then, the preretinal
membrane, like all parts of the basement membrane, appears first as an
ectodermic cuticula. Mesodermic elements may be included between its
two layers, but this is the exception. The most of the membrane is in
any event cuticula, of which the greater part is produced by the lentigen,
the lesser by the retina.

The retinal and post-retinal layers. — The intimate connection into
which these two layers enter in forming the retina is a sufficient reason
for considering them together. Grenacher's ('79, pp. 39-57) researches
on the eyes of arachnids led him to believe that the retina consisted of
a number of similar elements, each of which contained a rod-like body, or
bacillus, and a nucleus. Each element was, therefore, to be considered a
single cell. He also discovered that there were two different types in
the disposition of the nucleus and bacillus. Either, as in the anterior
median eyes of Epeira ('79, pp. 43-45, fig. 18 A), the bacilli were in
front of the nuclei, or, as in the posterior median eye (fig. 18 B), they
were behind the nuclei. In the structure of the eye this interesting
dimorphism, as Grenacher has termed it, has proved to be a feature of
common, if not universal, occurrence with spiders.

Graber, who based his conclusions on the study of the retina in scor-
pions as well as spiders, opposed Grenacher's views, and claimed to have
found in the median eye of Buthus ('79, pp. 71, 72) at least two nuclei
to each element, — a large, basal, ganglionic nucleus, and, near the outer
end of the element, a smaller apical one. The equivalent of Grenacher's
bacillus lay between these. In the case of the lateral eyes * of Buthus
(PI. V. fig. 5), as well as in the anterior and posterior median eyes of
Epeira (PI. VII. figs. 25, 26), Graber figured a third small nucleus
directly behind the bacillus.

This discovery, if corroborated, would invalidate Grenacher's view of
dimorphism in the eyes of spiders, and one would be forced to admit
that the retinal elements are multinuclear, and therefore not single cells.
Grenacher's ('80, pp. 415-430) reply to Graber, at least so far as the

* When the discussion of the lateral eyes is reached, the subject of their nuclei
will be considered more at lengtli.

188 BULLETIN OF THE

retina in scorpions is concerned, is based on a study of the median eyes
only. He ('80, pp. 422-425) shows conchisively that for a ganglionic
nucleuij Graber has described and figured a body which is not a nucleus.
Grenacher, after a careful search for Graber's middle and anterior nuclei,
positively denies their existence. This, as Grenacher says, leaves the
retinal elements in scorpions devoid of nuclei ; he then proceeds to show
that in the region of Graber's so-called ganglionic nucleus there exists a
true nucleus essentially unlike the latter. Therefore, according to Grena-
cher, the retinal elements in scorpions are to be placed in the category
to which the anterior median eyes of Epeira belong.*

Lankester and Bourne ('83, p. 188) agree with Grenacher that each
retinal cell contains a single nucleus ; but they also maintain that
Graber's anterior and middle nuclei are to be found in the retina.
These nuclei, however, do not belong to the retinal elements proper, but
to small intrusive pigment cells.

The composition of the adult retina in Centrums has been studied by
means of sections and maceration preparations. A horizontal section
of an adult retina (PI. I. fig. 1) presents a concavo-convex outline; a
portion of the convex face occupies the median plane of the body, and is
fused to the corresponding part of the opposite retina. The concave face
is limited by the preretinal membrane. The concave region is composed
of a series of deeply pigmented club-shaped masses, which taper off into
the lighter middle region. Behind the lighter area, which occupies fully
half of the thickness of the retina, many of the bands and lines of pig-
ment become thickened into irregular dark blotches, which make up a
poorly defined mottled area. This soon merges in the median plane into
the retina of the opposite side, and elsewhere into a densely pigmented
zone limited behind by the sclera. This pigmented zone can be traced
around the side of the retina till at the edge of the latter it becomes
confluent with the pigmented area first mentioned.

After removing the pigment and staining the section in Grenacher's
alcoholic borax-carmine, the outermost pigmented region (PI. I. fig. 2) is
seen to consist of a very granular substance, in which cell-walls can be
traced from the preretinal membrane backward to the pointed, rod-like
structures, or rhabdomes. The latter cause the lightness of the large

* Graber ('79, p. 69) designated those elements in which the nuclei were behind
the bacillus as " postbacillar " ; those in wiiicli tlie nucleus was in front of the bacil-
lus, "prebacillar." Mark ('87, p. 73) has proposed for these terms pre- and post-
nuclear, respectively. Since these present advantages over the older terms, they
will be adopted in the following pages.

MUSEUM OF COMPARATIVE ZOOLOGY. 189

middle area. This granular substance (PL II. -fig. 4) extends down
between the rhabdomes, and merges with a less regularly granular sub-
stance behind. The rhabdomes at their deep ends merge imperceptibly
into this irregularly granular substance. In the region where the deep
ends of the rhabdomes disappear, large slightly granular nuclei occur
(Fig. 4, 111. r.). All the nuclei in the retina of Centrurus are found in
what has been described in the pigmented eye as the mottled area. The
nuclei nearest the concave surface of the retina are the largest, and, as
has been previously mentioned, are slightly granular. Behind these, in
the middle of the nuclear region, smaller oval nuclei (Fig. 4, nl. pig.)
occur. Here also nerve fibres are abundant, and those curious bodies
mistaken by Graber for nuclei and designated by Lankester and Bourne
under the name of phaospheres (Fig. 4, pha sp.). The deepest nuclei
(Fig. 4, 111. p r.) in the retina are flattened, and more deeply colored than
the rest. They lie upon the internal surface of the densely pigmented
zone, previously mentioned, and form a line of separation between that
zone and the coarsely granular substance in front. The substance of the
deepest zone is almost identical in character witli that of the outer portion
of the retina, and its granular appearance, like that of the external layer,
is largely due to the colorless remains of pigment granules. The smaller
anterior and median nuclei of Graber do not exist in Centrurus, either
in the retinal cells or between them, as claimed by Lankester and Bourne
('83, pp. 192, 193). The latter authors state ('83, p. 192) that the
reason Grenacher overlooked these nuclei was that the acid which he
used to remove the pigment destroyed them. In the case of Centrurus
sections depigmented with the 35% mixture of nitric and hydrochloric
acids, with ^-% solution of potassic hydrate, or unaffected by depigmenting
reagents, but colored with borax-carmine and cut three micromillimeters
thick, show no trace whatever of anterior or middle nuclei. The exami-
nation of fresh material and of maceration preparations has given the
same results. Moreover, since the nuclei in the brain after treatment
with J% potassic hydrate are not to be distinguished from those in the
same organ unaffected by that reagent, it seems scarcely possible that the
same reagent could destroy nuclei in the retina. It is therefore safe to
conclude that at least in the retina of Centrums no nuclei exist external
to the band of larger nuclei already described.

Having shown that the retinal nuclei are limited to the deeper region
of the retina, and that these nuclei are "of "three principal types, we are
now prepared to inquire into the cellular composition of the retina.
This is best done by means of isolation preparations. In the retina

190 BULLETIN OF THE

there are at least three kinds of cells. Two can be readily isolated ; the
third has been studied only in sections.

The retina extending from the line of deepest flattened nuclei to its
outer margin breaks up into two very distinct forms of cells, — retinal or
nerve-end cells, as Lankester and Bourne ('83, p. 182) have called them,
and pigment cells. The retinal cells (PI. II. fig. 5) are elongated and
rounded at their outer ends ; they terminate below in nerve fibres. From
the rounded external end the calibre is uniform till the region of the
rhabdomeres is reached. Here the cells increase in diameter, and then
continue for some distance uniform in size. Finally, each cell, enlarging
slightly at its deep end, rapidly tapers into a nerve fibre. Throughout
its whole extent the retinal cell contains pigment, which is principally
concentrated, however, at its rounded outer end.

The pigment cells (PI. II. fig. 6) at their anterior ends, like the pig-
mented tops of the retinal cells, abut against the preretinal membrane.
From this they pass backward, and in the region of the rhabdome, where
the retinal cells enlarge, they contract to thin fibres, which, after the
rhabdome has been passed, again expand into irregular pigment sacs at
the deep part of the retina. When isolated, they present the appearance
(PI. II. figs. 6, 7) of two sacs of pigment connected by a slender rigid
fibre.

The large round or slightly oval nuclei have been identified as be-
longing to the retinal cells (PI. II. fig. 7), and the smaller oval nuclei
occupy the deep swollen ends of the pigment cells. It is possible
that some of the pigment cells may not be prolonged in front of the
rhabdomes, and therefore not possess anterior sacs ; but I have never
been able to discover such. The filamentous middle portion connecting
the two extremities of the long pigment cells is so constant and char-
acteristic in maceration preparations, that pigment cells which do not
extend to the front of the retina must form the exception, if in fact they
exist at all.

Another method employed in studying the cells of the retina, and one
especially instructive for the region of the anterior zone, was by the aid
of sections perpendicular to the retinal cells. The retina has the form of
a shallow bowl ; consequently in sections perpendicular to its axis the
deeper portions of the retina will lie at the periphery of the section, and
its centre will be the region nearest the preretinal membrane.

Figure 3 represents a portion of a retinal section whose centre, and con-
sequently highest portion, is toward the right, and whose periphery or
deeper portion is toward the left. The relatively higher portion of the

MUSEUM OF COMPARATIVE ZOOLOGY. 191

section is at that point below the preretinal membrane where the rhab-
domeres diminish into simple cell boundaries, and the five cells which
make a single group are here easily distinguishable. To the left the
rhabdomes are much larger, and have assumed their usual outlines. The
rhabdomes have increased in size at the expense of the cells. It will be
noticed that each of the cells present belongs to some group of rhab-
domeres, and consequently all are retinal cells.

The section (Fig. 3, a) which w^as the next external to the one just de-
scribed shows practically the same condition, except that, being slightly
nearer the front of the retina, the rhabdomes are not quite so distinct,
especially in the extreme right, where in one or two groups scarcely any
trace of the rhabdomeres can be seen. Nevertheless, all the cells of the
former section can be identified, and moreover between the groups in the
upper right hand corner an additional cell is noticeable. This cell, which
by a comparison of the two sections is seen to be a supernumerary element,
is not a retinal (nerve-end) cell ; but since in maceration preparations the
outer expanded ends of the pigment cells were always found near the
preretinal membrane, there is every reason for considering this such a
cell. Moreover, when sections nearer and nearer the preretinal membrane
are examined, these additional cells become more numerous, until finally
they are with difficulty distinguished from the retinal cells. The anterior
sacs of the pigment cells, then, can be demonstrated on sections as well
aa by maceration.

The rhabdomes never reach the anterior face of the retina, but fall
short of it by the thickness of several sections. This space between the
rhabdomes and preretinal membrane corresponds to the anterior zone of
deep pigmentation seen in longitudinal sections. The pigment in this
region is so dense that the outlines of the cells can be traced only with
difficulty.

The phaospheres, as Lankester and Bourne ('83, pp. 185, 186) have
called the curious bodies mistaken by Graber for nuclei, are abundant in
the nuclear zone of the retina (PI. II. fig. 4, pha sp.). They are as small
as the oval nuclei around them, and often smaller, but differ from these
in containing usually one, and sometimes two, three, or even four highly
refractive dots. Lankester and Bourne state that they are usually behind
the nucleus of the retinal cell. In isolated cells I have never succeeded
in satisfactorily identifying them, therefore in Centrurus I cannot feel sure
of their position. In one section only has a phaosphere occurred in a
prenuclear position ; in all others they have been strictly behind the
neighboring nuclei.

192 BULLETIN OF THE

As to their nature two suggestions have been maae. juankester and
Bourne ('83, pp. 185, 186) imply that they are of the nature of rhab-
domes; in this light they are further discussed by Mark ('87, p. 93).
Patten ('86, p. 684) is inclined to look upon them as degenerate nuclei.
In Centrurus the phaospheres, being of nearly the same size as the nuclei,
present less favorable opportunities for study than in those scorpions
where they are much larger. Those in Centrurus stain in much the
same way that the surrounding nuclei do, and in fact are to be distin-
guished from these mainly through their highly refractive dots. In many
cases, however, these dots are not well marked, and it is then difficult
to determine whether a given body is a nucleus or a phaosphere. The
nuclei are constantly oval in form; the phaospheres are more or less
irregular in outline. This irregularity, however, is only noted in phao-
spheres which have very refractive dots, and never in those which seem
to be transitional in form between nucleus and phaosphere.

The third type of cell occurs as a single layer of pavement-like ele-
ments at the back of the retina (PI. II. fig. 4). It has been correctly
stated by Graber ('79, p. 84) that this pavement layer is the matrix of
the sclera. Lankester and Bourne ('83, p. 192, pi. X. fig. 8, />) have
also observed it in Androctonus, where the cells are relatively much
smaller than in Centrurus. In sections of Centrurus the outlines of
these cells are visible, though faint ; in form they are broadly columnar.
Their nuclei, as previously stated, take a deep color, are flattened, and
are always located at the end of the cell farthest from the sclera.

This deep layer of cells envelops the convex face of the retina, passing
up on its sides till it reaches the edge of the retinal cup (Lankester and
Bourne, '83, pi. X. fig. 8, p). Here, as Graber has shown ('79, PI. V.
fig. 14), it becomes continuous with the retinal layer. Only in the re-
gion where the retinas of the two median eyes fuse does this basement
layer fail to cover the deep surface of the retina proper.

The principal histological changes which take place during the devel-
opment of the eye relate to nuclei, the pigment, and the optic nerve.
The formation of the optic sacs, the disappearance of their common neck,
and the fusion of the post- retinal with the retinal layer has already been
described.

While tiie eye is yet an ectodermic pocket (PI. III. figs. 12-15), the
nuclei are distributed through the whole of the thickened retinal layer ;
in the post-retina they form a single row. At this stage the nuclei of
the different cells are indistinguishable. Their outlines are round or

MUSEUM OF COMPAKATIVE ZOOLOGY. 193

slightly oval ; their contents, except for a few sharply marked granules,
are very transparent. Somewhat later, but before the optic sacs have
closed, they are less abundant near the front face of the retina, but other-
wise no special arrangement is as yet evident.

The rhabdomeres play an important part in the future distribution of
the nuclei. They first appear as light streaks, which, beginning close to
the preretinal membrane, gradually extend backward. With the exten-
sion of the rhabdomeres, the nuclei recede to the deeper parts of the
eye, and with very few exceptions * never occupy a place in front of the
rhabdomeres.

At about the time the young scorpion is born,_ the cavity of the optic
sac having disappeared, the nuclei of the retinal layer are found to have
arranged themselves in two groups. In axial sections of the eye (PI. II.
fig. 9) one group forms an irregular line at the base of the rhabdomeres,
the other a broad band in the deeper part of the eye. The space sepa-
I'ating these two groups is considerable, and contains only a few scattered
nuclei. The deeper nuclei in the broad band, i. e. those nearer the sclera,
are to be referred to the post-retinal layer.

At this stage the nuclei are still undifferentiated, and even after the
young scorpion has left the mother's back it is some time before one can
recognize differences between them. It is only in the fuUy developed
adult that a marked differentiation is reached. By this time the nuclei
of the retinal cells have become slightly more homogeneous (PI. II. fig.
4, 7il. r.) and somewhat reduced in size. The nuclei of the post-retinal
cells have become much flattened and stain more deeply. These, as
well as the nuclei of the pigment cells, are reduced in size, and have
become more homogeneous. The columnar " matrix " cells previously
described, and to which these flattened nuclei belong, constitute the
post-retina ; and their transition at the rim of the optic cup into the reti-
nal layer is only a preservation of the relation they have sustained to that
layer from the time of the original involution. This interpretation of
the "matrix" cells has already been maintained by Mark ('87, p. 56).

The phaospheres appear at a very late date. In young scorpions
which have left the mother's back no trace of phaospheres was discover-
able, and it was only in those eyes in which the three forms of nuclei
were already distinguishable that the structures were noticed. The time
of their appearance — a period of nuclear differentiation — is evidence
in favor of their nuclear origin.

* In only one instance out of the many in which developing eves have been
examined has a nucleus remained in a prebacillar position
VOL. xiii. — '■'o. 6. 13

194 BULLETIN OF THE

That the retinal cells and the post-retinal cells, as well as the pigment
cells, contain pigment, has already been stated. Lankester and Bourne
('83, p, 194) were somewhat in doubt whether the retinal cells in the
median eyes of scorpions contained any pigment. Patten ('86, p. 728)
believes that they do not contain pigment. The evidence furnished by
sections perpendicular to the length of the cells CPl. II. fig. 3, gra. pig.)
is, I think, conclusive.

Under the head of "intrusive pigmentary connective tissue," Lankes-
ter and Bourne ('83, p. 191) include the pigment cells in Androctonus,
and, with less confidence, their so-called intracapsular pavement. The
pigment cells proper are considered by them as of mesodermic origin.
This they defend by several arguments, but admit that their reasons
cannot be regarded as offering a sufficient basis for a final conclusion.

During early stages in the development of Centrurus, mesodermic
tissue is often seen making its way into the substance of the brain, and
its appearance is characteristic. It penetrates into the nervous system
as thin continuous sheets of cells, which in cross-section appear as lines.
During the development of the eye no such appearances have been en-
countered, and it is fair to conclude that mesodermic tissue has not
gained access to the eye by the same means that it has to the brain.

Lankester and Bourne suggest that it may have entered the eye
capsule at the opening for the optic nerve ; but the capsule (sclera) is
reflected on to the optic nerve, and, even admitting that mesodermic
tissue did gain access here or from the brain, where it undoubtedly exists,
one would naturally expect the pigment to appear first in the region of
the optic nerve. Contrary to this, as Kowalevsky and Schulgin ('86,
p. 531) have shown, — and my own observations confirm theirs, — pig-
ment first appears in the front of the retina on its ventral — afterward
becoming its anterior — edge, at a point farthest from that where the optic
nerve joins the retina. Taking all the evidence into account, it seems
that the nerve-end cells, the intracapsular pavement cells (post-retina),
and the pigment cells are alike ectodermic, and that the retina contains
no tissue that can be referred to a mesodermic source.

The optic nerve in the adult scorpion joins the eye at a point on the
under side of the eye capsule. From this point bundles of fibres pass
anteriorly through the base of the retina in front of the post-retinal
layer, and from small secondary bundles are given off single fibres which
join the bases of the retinal cells.

In the youngest stages studied, the optic nerve was already formed, and
its fibres (PI. III. fig. 17, n.fbr.) passed over the front of the retina,

MUSEUM OF COMPARATIVE ZOOLOGY. 195

apparently connecting with the external ends of the retinal cells. kX
least the fihres disappear here, and cannot be traced into the retina. The
optic nerve (PI. III. fig. 16, n. opt.) at this stage emerges from the retina
by passing over the rim of the optic cup in a region corresponding to the
outer edge of the pocket. The region extends from the dorsal margin
half-way down toward the ventral margin of the cup.

During the further development there is but little change in the
point of exit for the optic nerve. It simply shifts from its posterior
lateral position in the embryo, to a posterior ventral one in the adult.
The change in the course of the intracapsular fibres is much more sig-
nificant.

There is reason to believe that in the embryo the nerve fibres are at-
tached to the external ends of the retinal cells (Figs. 14-17). In the adult
they certainly emerge from the deep ends of these cells. The steps which
connect the earliest with the final condition consist of a migration of the
point of attachment for the nerve fibre from the external end of the cell
to the deep end. The migration of the fibres takes place at the same
time that the nuclei recede into the deeper parts of the eye, and seems to
be controlled by the same influence, namely, the growth of the rhabdo-
meres. An analogous condition in the eyes of Agelena has been described
by Mark ('87, pp. 84-87). There is, however, a difference ; the nerve
fibres in Agelena never come to have a post-nuclear attachment to the
retinal cell, whereas in the figures of Graber and those of Lankester and
Bourne, and certainly in the retina of Centrurus, the nerve fibres emerge
from the cell behind the nucleus. Mark ('87, pp. 91, 92) has claimed
for thsse facts an important significance, and concludes that they point
to a functional condition of the retina before involution. The bearing of
this will be further considered under the head of theoretic conclusions.

The Lateral Eyes.

The lateral eyes in scorpions, although in some respects more inter-
esting than the median eyes, have on the whole received less attention.
Grenacher in his two papers previously quoted makes no mention of
them ; for our present knowledge of their structure we are indebted to
the researches of Graber ('79) and of Lankester and Bourne ('83). The
results of these inquiries are in so far unsatisfactory that in several es-
sential points they are directly opposed to each other. The points upon
which there is a conflict of opinion are (1) the origin of the retina,
and (2) the presence or absence of a lentigen.

196 BULLETIN OF THE

On the question of the origin of the retina in arthropods, two un-
reconcilable opinions have been held. Some authors have maintained
that the retina was an outgrowth from the brain, and others that it was
a modification of the hypodermis. Graber may be taken as a represent-
ative of the former school, Grenacher of the latter. The evidence upon
which they based their opinions was derived in the two cases from quite
different kinds of eyes. Grenacher believed, since he had found in
eyes like those of the larval Dytiscus a retina which was continuous
with the hypodermis, that therefore the retina in the more complex
eyes was derived from the same hypodermal source. Graber, arguing
from those eyes in which the retina is separated from the hypodermis by
a preretinal membrane, maintained that the retina is an outgrowth from
the brain, and not derived from the hypodermis. Such an eye as the
larval eye of Dytiscus would, even in the absence of other evidence,
seriously weaken the force of Graber's argument. As an explanation of
such structures, Graber is inclined to think that the larval eye of Dy-
tiscus really possesses a preretinal membrane, with hypodermis in front
of it ; but that, on account of the thinness of this structure, Grenacher
has overlooked it. In other words, Graber considers the arthropod
ocellus as a two-layered structure, the outer layer of which is hypoder-
mal, and the inner layer, or retina, neural in its origin.

In Graber's figures and description of the lateral eye in scorpions, the
two essential parts of the median eyes, the lentigen and retina, are rep-
resented ; but the lentigen, unlike that of the median eyes, is reduced
to a very thin layer of cells. This is perfectly consistent with Graber's
theory ; but whether it represents the actual structure of the eye or not
is questionable, since Lank ester and Bourne ('83, pp. 182 and 187) ex-
pressly state that the lateral eye of Androctonus is composed of a single
layer of cells, — a thickening of the superficial hypodermis, — and claim
that Graber is incorrect in describing a separate layer concerned in the
formation of the lens.

Since the publication of these papers, Locy's discoveiy ui the method
of development in spiders' eyes has firmly established the hypodermal
origin of the retina. It has also offered a perfectly rational explanation
for the presence of Graber's preretinal membrane. Thus the hypothesis
of the neural origin of the retina is no longer tenable.

The presence or absence of a lentigen and preretinal membrane is, as
Mark ('87, p. 55) has stated, important in determining whether a given
eye has been formed by involution with inversion or not. Although the
hypodermal nature of the retidas in both the lateral and median eyes of

MUSEUM OF COMPARATIVE ZOOLOGY. 197

scorpions is unquestionable, yet whether the lateral eyes, like the me-
dian, have been formed by an involution vs^ith inversion, or whether
their formation is accompanied simply by a thickening and more or
less extensive depression in the hypodermis, is still an open question.
Graber's figure ('79, PI. V. fig. 4), with its preretinal membrane and
lentigen, would indicate that the eye arose by involution. Lankester and
Bourne's figures ('83, PI. X. figs. 2, 3, and 4), in which these structures
are absent, would favoi* ^he explanation that the eye is only a hypodermal
thickening.

The position of the lateral eyes in scorpions has already been described.
In the adult Centrums each group consists of four eyes, three of which
are large and are designated by systematists as " principal " eyes, and
the fourth is small and known as an " accessory " eye. The larger eyes
are arranged in a horizontal line at the antero-lateral angle of the shield ;
the small eye is above a point midwav between the posterior and middle
larger eyes.

A vertical section through the axis of one of the larger eyes (PI. III.
fig. 18) shows at the surface a strongly convex lens (Ins.) beneath which
a relatively small retina (r.) appears. The outline of the latter is marked
by the basement membrane (mb.), and on its dorsal and ventral edges it
is seen to be continuous with the hypodermis [hd.). In an eye from
which the pigment has not yet been removed, the whole retina is
intensely black. The pigment extends up to the margin of the lens, as
figured by Lankester and Bourne ('83, PI. X. fig, 1), and spreads out
above and below into the adjacent hypodermis. It is hr more abundant
in the dorsal hypodermis than in the ventral.

The lens in the adult eye consists of essentially the same parts as in
the median eye, and contains no pore-canals. Its substance except the
front hyaline layer is stained throughout by alcoholic borax-carmine. In
young individuals (PI. III. fig. 21) the lenses of the lateral eyes, even
better than those of the median eyes, show a formation of stainable
cuticula (II"') under the hyaline layer (Jl) before a similar secretion has
taken place from the general hypodermis.

In the adult eye not the least appearance of a lentigen or preretinal
membrane is to be found, even after careful depigmentation. Tlie fact
that the pigmentiferous tissue extends up to the lens is of itself sug-
gestive of the absence of a lentigen, for in ocelli generally this layer is
remarkable for its transparency. When to this is added the fact, that no
nuclei exist in the front part of the eye, and that in no place does the
basement membrane extend as a preretinal membrane across the front of

198 BULLETIN OF THE

the eye, the evidence against the presence of a lentigen is apparently
complete.

The composition of the retina in the lateral eyes is much more diffi-
cult to study than in the median eyes. This is due in part to the small
size of the lateral retinas, and in part to their almost complete chitinous
investment. To- make isolation preparations is wellnigh impossible, by
far the best results being obtained from the study of sections.

Graber ('79, PI. V. fig. 5), believing that the composition of the
median and lateral retinas was essentially the same, has figured in the lat-
eral eyes of Scorpio retinal elements with three nuclei. Moreover, the
retinal elements are grouped, as in the the median eyes, in fives (PI. V.
fig. 8).

Lankester and Bourne ('83, pp. 181-187) claim that the retina con-
sists of unicellular elements, or nerve-end cells, as they call them, and of
indifferent cells. The indiiferent cells occur both between the nerve-end or
retinal cells, as "interneural cells," and around the edge of the retina, as
"perineural cells." The indifferent cells all contain pigment, the retinal
cells, in their opinion, are probably pigmented on their peripheries.

In Centrurus the nuclei (PI. III. fig. 18, nl. r. and nL pi n.), as in
the median retinas, are limited to the deeper portion and to the periphery
of the eye, and Graber's anterior and median nuclei are not present. The
nuclei {nl. r.) belonging to the deep portion of the retina are slightly
larger than those (nl. pi n.) on the periphery, and very uniform in size.
The fact that in this part of the retina there is onlj' one form of nucleus
leads to the conclusion that the retina in Centrurus is composed of only
one kind of cells, and that here the interneural cells described by Lan-
kester and Bourne do not exist.

Sections perpendicular to the axis of this retina show immediately
under the lens the sharp outlines of cells which deeper in the retina have
their walls thickened into rhabdomeres. No additional cells, like those
in the median eyes, appear in the outermost sections of the retina, end
therefore the interneural cells, if present, must be limited to the deeper
portion of the retina. The fact that there is no difference in the nuclei
of this region leads me to believe that interneural cells are entirely
wanting. In Centrurus the retinal cells (PI. III. fig. 19) show no
tendency to be arranged in groups of five, and the rhabdomeric thicken-
ing {rhb m.) takes place on all sides of the cell. This is particularly
noticeable in examining the region nearest the lens. In the outermost
sections the cells are sharply outlined and their walls are very thin.
In the second or third section from the lens, the walls suddenly become

MUSEUM OF COMPARATIVE ZOOLOGY. 199

thicker around the whole circumference of the cell, and take on a lus-
trous appearance. With Kleinenberg's hsematoxylin the substance of
the rhabdomeres can be colored, and the line of demarcation between
products of the separate cells can be distinguished. This structural con-
dition can be traced to the deeper part of the retina, where the cell
outlines become indistinct, the rhabdomeres incasing each retinal cell
for a half or two thirds of its length.

Pigment (PI. III. fig. 19, gra. pig.) is uniformly distributed through
the retinal cells, as well as the perineural cells to be described later. This
is best seen in sections perpendicular to the axis of the eye. Phao-
spheres, although present in the median eyes, do not occur in the lateral
eyes. The optic nerve (PL III. fig. 18, n. opt.) emerges from the deep
end of the retina, and its course is so oblique to the axis of the eye that
a section which shows the retina well seldom shows much of the optic
nerve.

The perineural cells surround the depressed retinal area, and their
attenuated ends, especially on the ventral side of the eye, often reach
out, even in the adult condition, in front of the retinal cells themselves
(PI. III. fig. 18). The positions that the nuclei occupy in the ventral
portion of the perineural ring suggest that these cells may at one time
have extended far enough to have completely covered the retina, and the
fact that in young individuals (PI. III. fig. 21) the retina is largely cov-
ered by the perineural cells indicates that in all probability the lens is the
product of these cells. In that event the perineural cells are the physio-
logical equivalent of the lentigen. The peripheral margin of this lentige-
nous ring passes by insensible gradations into the surrounding hypodermis.

The development of the lateral eyes is referred to by Kowalevsky and
Schulgin ('86, p. 531) as follows: "Die Seitenaugen entwickeln sich
unabhangig von den Mittelaugen, und bei ihrer Ausbildung nimmt die
Vertiefung der obern Schicht der Kopfplatte Antheil. Die Einzelheiten
dieses Vorganges sind von uns noch nicht bearbeitet." This is the only
reference which they or other students have made to the development of
the lateral eyes.

The " ocular areas," as Lankester and Bourne designate the regions
occupied by the lateral eyes, appear in Centrums as pigmented tracts of
hypodermis on either side of the head and a little below and behind the
median optic sacs. Horizontal sections of the embryo cut these areas in
tlie most advantageous way for a general study ; they show that the
whole ocular area is produced by a thickening of tiie hypodermis.

200 BULLETIN OF THE

The horizontal sections shown in Figs. 22-27 (PI. IV.) are arranged
to represent the characteristic features of the ocular area of the left side
of the head, as one would observe it in passing from a dorsal to a more
ventral position. Calling that of Fig. 22 the first section, they are the
1st, 3d, 6th, 13th, 16tli, and 21st sections in a series from a single
animal. Fig. 22 represents the hypodermis directly above the eyes and
at the edge of the ocular area. The extent of this area is indicated by
the thickened region. Two sections below this (Fig. 23) the ocular area
is more extended, and shows a single simple depression (No. 1). It will
be observed that the band of nuclei indicates a more marked depression
even than the outline of the hypodermis itself. This simple depression
in the hypodermis indicates the position of a lateral eye. The cells
which compose the wall of the cup are wedge-shaped ; their nuclei are
below the middle of the cells, and those cells which occupy the central
portion of tlie depression are so attenuated at their free ends as scarcely
to reach the surface. The basement membrane (mb.) closely invests the
deep face of this structure, as it does any ordinary hypodermal thicken-
ing. The sixth section, Fig. 24, exhibits a region in which the ocular
area is greatly thickened, but it shows no depressions, and the nuclei
extend very near to the surface. Fig. 25, seven sections deeper than
Fig. 24, presents four cup-shaped depressions (Nos. 2, 3, 4, 5), each essen-
tially like the depression previously described. The two central depres-
sions (Nos. 3, 4) are the largest ; next in size is the anterior one (No. 2),
and smallest of all is the posterior one (No. 5). As in the case of depres-
sion No. 1 (Fig. 23) the band of nuclei in the region of each depression
forms a much deeper cup than the outer surface of the hypodermis. Tlie
basement membrane {mb.), as in Fig. 23, invests only the deep surface of
each hypodermal cup. From this plane ventrally the hypodermis gradu-
ally becomes thinner, and at the extreme edge of the dorsal shield the
indifferent hypodermis is reached. (Compare Figs. 18,20.)

The five depressions just described are early stages in the development
of the lateral eyes. In the adult Centrurus only four eyes are present.
Of the five depressions seen in the embryo the most posterior (No. 5)
of the ventral four disappears, and three remaining form the " princi-
pal " lateral eyes. The fourth or " accessory " eye arises from the dorsal
depression (No. 1), which, even in the embryo, occupies a position above
the space between the second and third depressions (Nos. 3 and 4) of
the lower row. The presence in the embryo of a rudimentary fifth eye
is interesting, in view of the fact tliat there are five eyes in the adult of
Androctonus, as has been shown by Lankester and Bourne. It is proba-

MUSEUM OF COMPARATIVE ZOOLOGY. 201

ble that one of these five eyes in Androctonns is represented by the rudi-
mentary eye in Centmrus, although this can be definitely settled only by
a careful comparison.

In the embryo the fibres of the optic nerve (n. opt.) emerge from the
base of the retina (PI. IV. fig. 25). This, moreover, is their position
throughout the life of the scorpion (PI. III. fig. 18).

The further changes which affect the form of the optic depressions
before they become matured eyes are unessential modifications of the
already established plan. At the time of the production of a lens (PI.
III. fig. 21) the lentigenous (perineural) cells stretch over from all sides
and overtop the retina. The external ends of the lentigenous cells con-
tain no pigment (PI. III. fig. 20).

The basement membrane, from the time wnen the depressions are
formed till the eye is completed, covers the modified hypodermis as it
covers a simple hypodermal thickening. There is never any indication
of a preretinal membrane, nor, from the structure of the eye, should we
expect to find one. In aU stages the basement membrane presents the
appearance of a single delicate lamella, and at no time is there an addi-
tional sheet of mesodermic tissue, as in the median eyei.

The evidence derived from the anatomy of the adult eye, the auiso^^^o
of a preretinal membrane and permanent lentigen, and the continuity of
the retina with the hypodermis, together with the facts derived from a
study of the development of the eye, show conclusively that in scorpions
the retina of the lateral eye is what Lankester and Bourne have called
monostichous, and that this retina, unlike that of the median eyes, ia
normal, not inverted.

Theoretic Conclusions.

The striking similarity in the structure and development of the median
eyes in scorpions and the anterior median eyes in spiders has already been
indicated. In both cases the retina by a process of involution has be-
come inverted. The question whether the retina was functional during
the phylogenetic involution of the eye is, as Mark has maintained, an-
swered in the affirmative by the phases noted in the development of the
optic nerve. At least, the fact that the fibres of the optic nerve are at
first attached to the morphologically deep ends of the retinal cells, and
only at a later date come to emerge from the opposite end, is most easily
explainable on the supposition that the retina was functional before invo-
lution. The primitive eye would, then, consist of a single layer of retin"'

202 BULLETIN OF THE

cells from the deep ends of which the nerve fibres emerge. Admitting
that in the ancestral eye the rhabdomeres were in their usual positioni
namely, at the outer end of each retinal cell, an inversion of this retina,
would not only place the optic fibres on the front face of the retina, but
the rhabdomeres would come to occupy the deep ends of the cells. The
prenuclear rhabdomeres of a normal retina would, therefore, be homolo-
gous with the postnuclear rhabdomeres of an inverted retina. The
prenuclear rhabdomeres of the median eyes in scorpions must, then, be
secondary structures, developed in such a way as to replace functionally
the older postnuclear structures.*

The phaospheres, as Mark ('87, p. 93) has already suggested, may rep-
resent the remains of postnuclear rhabdomeres. These are to be regarded,
then, in the nature of disappearing organs, and the fact that in some
species of scorpions they are present, while in others they are absent,
would favor this view. As Mark has stated, the phaospheres, if they
represent postnuclear rhabdomeres, should be found only in eyes with
inverted retinas. Lankester and Bourne, as previously mentioned, have
described them in the lateral eyes of Euscorpius. Mark hesitated, in the
case of the lateral eyes, as to whether he should follow Graber's observa-
tions and consider them triplostichous, with inverted retinas, or whether
he should follow Lankester and Bourne and consider them monostichous.
In the former case the phaosphere might readily represent postnuclear
rhabdomeres ; in the latter, this interpretation would be out of the ques-
tion. In Centrurus the structure and development of the lateral eyes show
conclusively that they are monostichous, and there seems to be small room
to doubt that the same is the case with the lateral eyes in Enscorpius.
In these eyes, however, Lankester and Bourne claim the presence of phao-
spheres. I have had no material from Euscorpius to examine ; but since
in Centrurus the median eyes contain phaospheres, while the lateral eyes
are devoid of them, it is a matter of interest to see whether, upon further
investigation, the presence of phaospheres in the lateral eyes of Euscor-
pius is confirmed, or whether that genus, like Centrurus, has phaospheres
in the median eyes only. If they should not be found in the lateral
eyes, there would still be reason for considering them the remnants of
rhabdomeres ; but if they should be found there, this view would be no
longer reasonable.

The possible relation of the median to the lateral eyes in scorpions
has already suggest ,d itself, for in pointing out the probable nature of

* This relation of the structures of the normal and inverted retina has been fully
discussed by Mark ('87, pp. 87-94),

MUSEUM OF COMPARATIVE ZOOLOGY. 203

the phylogenetic antecedent of the median eyes, a condition has been
implied which agrees with the essential features of the lateral eyes. Of
all the eyes in spiders and scorpions, the lateral eyes in scorpions are un-
doubtedly the least complicated, and they may be looked upon as deviat-
ing least from the probable ancestral type.

Summary of Results.
No9. 2-11 refer to the median eyes ; No8. 12-17 refer to the lateral eyes.

1. The retinas of the median and lateral eyes are strictly hypodermal in

their origin.

2. The median eye is triplostichous, and is formed by an involution of

hypodermis accompanied with an inversion of the middle layer,
which forms the retina proper.

3. The first layer or leiitigen, is modified hypodermis immediately ex-

ternal to the pocket of involution, and, in addition to secreting
the lens, serves a purpose which gave to it its earlier name of
■'vitreous."

4. The lens is the specialized cuticula produced by the lentigen. it

differs from ordinary cuticula in containing no pore-canals, a^id,
excepting the external hyaline layer, in being stainable through-
out.

5. The lentigen can produce cuticula independently of the general

hypodermis.

6. The second layer, or retina, is inverted, and consists of +wo kinds of

cells, — retinal (nerve-end) cells and pigmftnt cells. It contains
phaospheres.

7. The retinal (nei've-end) cells contain pigment ; their walls are thick-

ened into prenuclear rhabdomeres, and a nerve fibre emerges from
their deep ends. They are so arranged in groups of five, that five
rhabdomeres are united to form one rhabdome.

8. Each of the pigment cells is reduced to two sacs, connected by a stiff

fibre. The external sac contains pigment ; the internal, the
nucleus and pigment.

9. The third or post-retinal layer is the " sclera matrix " of Graber.

It becomes intimately fused with the retina.
10. The fibres of the optic nerve in the embryo emerge from the external
ends of the inverted retinal cells ; in the adult, from the opposite
ends.

204 BULLETIN OF THE

11. The basement membrane is a cuticula produced by the inner ends of

the hypodermal cells. The preretinal membrane is the united
basement membranes of the lentigen and retina. It may or may
not contain mesodermic elements. The sclera is the basement
membrane of the post-retina. It is usually overlaid with a deli-
cate mesodermic tissue.

12. The lateral eyes are monostichous, and arise from a simple thickening

and depression of the hypodermis.

13. A ring of "perineural" cells, forming the margin of the depression,

secretes the lens, and therefore constitutes the lentigen. Since,
owing to subsequent recession, they do not remain interposed
between the lens and retina, they have not the double function
of lentigen and " vitreous " which the outer layer of the median
eye has.

14. The lens has the same structure as in the median eye.

15. The retinal cells occupy only the deeper portion of the depression.

There are no interneural cells. Along the external portion of
each retinal cell its lateral walls are thickened into rhabdomeres.
The nucleus is near the deep end of the cell, and from this end
the nerve-fibre emerges. Phaospheres are not present.

16. The basement membrane (sclera) contains no mesodermic elements.

There is no preretinal membrane.

17. The lateral eyes may be fairly taken to represent the ancestral type

of the median eyes.

Cambbidob, July 1, 1887.

MUSEUM OF COMPARATIVE ZOOT.OGY, 205

BIBLIOGRAPHY.

Graber, V.

'79. Ueber das unicorneale Tracheaten- und speciell das Arachnoideen- und
Myriapoden-Auge. Arch. f. mikr. Anat., Bd. XVII. Heft 1, pp. 58-93,
Taf. 5-7. 1879.
Grenacher, H.

'79. Untersuchungen iiber das Seborgan der Arthropoden, insbesondere
der Spinnen, Insecten und Crustaceen. Gottingen : Vandenhock und
Ruprecht. 1879. 8 + 188 pp., 11 Taf.
'80. Ueber die Augen einigen Myriapoden. Zugleich eiue Entgegnung an
Herrn Prof. Dr. V. Graber in Cernowitz. Arcb. f. mikr. Anat., Bd.
XVIII. Heft 4, pp 415-467, Taf. 20, 21. 9 Oct., 1880.
Kowalevsky, A., and M. Schulgin.

'86. Zur Entwicklungsgescliichte des Skorpion (Androctonus ornatus).
Biologisches Centralblatt. Bd. VI. Nr. 17, pp. 525-532. 1 Nov., 1886.
Lankester, E. R., and A. G. Bourne.

'83. The minute Structure of the Lateral and the Central Eyes of Scorpio
and of Limulus. Quart. Jour, of Micr. Sci., Vol. XXIII. , n. ser., pp. 177-
212, Pis. 10-12. Jan., 1883.
Locy, W. A.

'86. Observations on the Development of Agelena neevia. Bull. Mus. Comp.
Zool. at Harvard Coll., Vol. XII. No. 3, pp. 63-103, 12 pis. Jan., 1886.
Mark, E. L.

'87. Simple Eyes in Arthropods. Bull. Mus. Comp. Zool. at Harvard Coll.,
Vol. XIII. No. 3, pp. 49-105, 5 pis. Feb., 1887.
Metschnikoff, E.

'71. Embryologie des Scorpions. Zeitschr. f. wiss. Zool., Bd. XXI. Heft 2,
pp. 204-232, Taf. 14-17. 15 June, 1871.
Patten, W.

'86. Eyes of Molluscs and Arthropods. Miltheilungen a. d. zool. Station
zu Neapel, Bd. VI. Heft 4, pp. 542-756, Pis. 28-32. 1886.
Schimkewitsch, W.

'84. litude sur I'Anatomie de I'l^peire. Ann. des Sci. Nat., 6" s^r., Zool.,
Tom. XVII. Art,. No. 1. 94 pp., 8 pi. Jan., 1884.

206

BULLETIN OF THE

EXPLANATION OF FIGURES.

ABBREVIATIONS.

a.

Anterior.

n.fbr.

Nerve fibre.

can. po.

Fine pore-canals.

n. opt.

Optic nerve.

can. po.'

Coarse pore-canals.

nl. ms d.

Nucleus of mesodermic

cav.

Cavity of infolding.

nl. pig.

" pigment

cl. pig.

Pigment cell.

nl. pi n.

" perineural

col.

Neck of invagination.

nl. p r.

" postrctiual

enc.

Brain.

nl. pr r.

" lentigen

env. em.

Embryonic envelop.

nl.r.

" retinal

gra. pig.

Pigment granule.

P-

Posterior.

hd.

Hypodermis.

pha sp.

Phaospliere

ir.

Iris.

pr.

Post-retina.

11.

Outer hyaline layer of cuticula.

pr-

T.entigen.

W.

Middle

r.

Retina.

11".

Deep

rhb.

Rhabdome.

Ins.

Lens.

rhb in.

Rhabdomere.

mh.

Basement membrane.

srl.

Sclera.

mh. pr r

. Preretinal "

1,2.3 4 5.

Lateral eyes.

mu.

Muscle.

cell.

\11 the figures were drawn with the aid of an Abbe' camera. Except where
otherwise specified, all the preparations were examined in benzol-balsam.

Figures 1 to 18 represent the structure of the median eyes. Figures 1 to 9
illustrate the adult eye.

PLATE I.

Fig. 1. A horizontal section of the retinas of the two median eyes seen from the
dorsal side. The tissue has been simply hardened and cut, the pigment
remaining intact, and no dye being employed. X 195.

Fig. 2. A transverse section of the retina r>^ the right median eye seen from the
posterior face. The pigment has been removed by potassic hydrate
and the tissue stained in Grenacher's alcoholic borax-carmine X 195.

PLATE II.

Fig. 3. The outer face of a frontal section through the retina of a median eye.
The portion of the figure nearer the right side is close to the centre of
the retina, that to the left is nearer the periphery. Colored with Klei-

MUSEUM OF COMPARATIVE ZOOLOGY 207

nenberg's haematoxylin. The outline figure on thin paper (Fig. 3a) h
taken from the section directly external to the one just described. X 475.

Fig. 4. Posterior face of a part of a transverse section of the retina described in
Fig. 2. X475.

Fig. 5. A retinal cell isolated in ■^^% solution of chromic acid, and examined in a
mixture composed of equal parts of water and glycerine. X 475.

Fig. 6. A pigment cell isolated and examined in the same manner as that shown
in Fig. 5. X475.

Fig. 7. A retinal cell with an attached pigment cell. The pigment was removed
with a solution of potassic hydrate, and the cell was isolated and stained
in Grenacher s alcoholic borax-carmine. Examined in a mixture of
glycerine and water. X 475

Fig. 8. Tlie posterior lateral portion of a horizontal section of a retina seen from
the dorsal side. Partially depigmented with a solution of potassic hy-
drate, and subsequently stained with Czoker's cochineal. In several
places the lentigen has been artificially ruptured. X 475.

Figs, y to 17 represent the structure of the median eyes in young scorpions.

Fig. 9. The posterior face of a transverse section of the right retina in a young
scorpion about the age at which it leaves the mother's back. Depig-
mented with potassic hydrate ; stained in Czoker's cochineal. X 195.

Fig. 10. The left face of a section through the right eye parallel to the sagittal
plane. Pigment unchanged; stained in Grenacher's alcoholic borax-
carmine. This specimen was taken about the time of birth. X 195.

Fig. 11. Right face of a section from the sagittal plane of an individual somewhat
younger than that seen in Fig. 10. In this section the neck of the in-
vagination (col.) is seen to reach almost to the retina. In the sections
on either side of this the neck appears much reduced, and at no point
does it unite with the retina. X 195.

PLATE III.

Fig. 12. The right face of a section almost in the sagittal plane of an embryo. The
lower part of this section was exactly in the median plane. The upper
part was somewhat to the right of that plane. Pigment unaffected ;
stained in Grenacher's alcoholic borax-carmine. X 195.

Figs. 13 to 17 represent the dorsal faces of a series of horizontal sections in the re-
gion of the median ej-es. In all the pigment is unchanged, and all have
been stained with Grenacher's alcoholic borax-carmine. The region of
the eye extends through forty-four sections. X 195. Beginning with the
most ventrally situated and passing dorsally, Fig. 13 represents the
seventh. It will be noted that the sections are not strictly horizontal,
but that they dip slightly to the left ; consequently in Fig. 13 the wall
of the pocket is cut on the right in the thickened or retinal region, but
on the left nearer the orifice of the pocket.

Fig. 14, the fourteenth section, shows the cavity of involution just before it is
divided into a right and left compartment.

Fig. 16, the twenty-third section, shows the cavity divided.

Fig. 16, the thirty-first section, shows the right compartment reduced in size.

208 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY.

Fig. 17, the forty-first section, represents the wall of the deep (dorsal) end of the

pocket cut tangentially.
Figs. 18 to 27 inclusive relate to the structure of the lateral eyes. Figs. 18 and 19

are from preparations of adult eyes.
Fig. 18. The anterior face of a vertical a.xial section of the riglit eye (No. 2) ;

compare PI. IV". Depigmented with a solution of potassic hydrate;

stained with Grenadier's alcoholic borax-carmine. X 325.
Fig. 19. Anterior face of a frontal section. Partially depigmented with potassic

hydrate ; stained with Kleinenberg's haematoxylin. X 475.
Figs. 20 to 27 inclusive give the structure of the eyes in young scorpions. Figs. 20

and 21 are from material of the same age as Fig. 9.
Fig. 20. Anterior face of a vertical axial section of left eye (No. 3). The pigment

is unafEected.^and no dye has been used. The edge of eye No. I is seen

above. X 325.
Fig. 21. Anterior face of a vertical axial section of left eye depigmented in potassic

hydrate and stained with Grenadier's alcoholic borax-carmine. X 325.

PLATE IV.

Figs. 22 to 27 inclusive are taken from the dorsal faces of a set of sections of the
youngest embryos at hand (of the same age as those from which Figs. 13
to 17 are taken). The sections have been depigmented with a solution
of potassic hydrate and stained in Grenadier's alcoholic borax-carmine.
X 325. The figures represent the left cluster of lateral eyes. Begin-
ning dorsally and proceeding ventrally, Fig. 22 is the first section, Fig.
23 the third, Fig. 24 tlie sixth. Fig. 25 the thirteenth, Fig. 26 the six-
teenth, and Fig. 27 the twenty -first.

Parkkr - Kyf:s ;\ Scorpion?.

Pi. ]

iti prr

- \

7/^r.

/

canpo.

If
ll~

B.Nfpise!. liUi

Parker- Eyes in Scorpions.

Pl !!;

JP'f^.ptft

K

rhh.

•■'■■■prr. A 0

«„

- #^

,*»*« *

#«» '9

'nl tug (/

4»*. A.

_ •• •

%

'v.v»»,.

f ^(4y

s"-:a*.

-•Si,

^

• '^1

. **/•!;

'/?'/:-

' »

%

GHP .Isl

n./hr

pArlr\KH -

r^\r.

PL.iir

fi/.fujte/

//'• r.

«^

\ A

1^

* * • * *

;r/, lu* d

n

)X

12.

«4

16.

y/-« c'v

nt,.

■» .4

X9.

*»*^''^*»*S5* ** * *

rA4.

<n-il^^

ya puj

'» .»

n^^t

V*

- i

•»K

B.Meisel. iith

PAP.KKR-EYES iK SCOHJTONS

PL.!\r

25

'/ opt .

• »
- *'*«*V

""/" /S

tnh.. ^ 9^

'#

% »

#

*!*-

*^'

>\

-«•

« .

\% r

V

S i»

I***::

6„

- T • c v

\ H Si ^

6

\ V

\ a.

ft

»'((
'.''?/

■ I /

rt/.i'iS'

26.

27.

tn*.

»*«:"«. .

z^^.

\-. .IV

«l^

i j .«*.

^~ Oi t>

^
o

/'

6
0

«i)

/

// ■

"©.,•

GH-P del.

B.Mfis-l. lilh

No. 7. — Studies from the Newport Marine Zoological Laboratory.
Communicated hy Alexander Agassiz.

XIX.

Oil Certain Medusa from New England. By J, Walter Fewkes.

The following paper is intended as a contribution to our knowledge of
New England jelly-fishes. It deals for the most part with animals of
this group from the northern Avaters of the coast of Maine, and from
Grand Manan.* During a vacation visit of a month's time at the latter
locality, in the summer of 1886, the author collected several new and
highly interesting medusae, t Incidentally, in studies of animals of
other groups in the summer of 1885, some observations were made on
Eastport medusse.

* "While the waters of the Gulf Stream justly attract the attention of natural-
ists interested in the study of our pelagic fauna, there is niucli yet ^o be done with
the dip-net in the cold waters of the Bay of Fundy and the coasts of Nova Scotia
and New Brunswick.

t Mention is made in these pages of those medusae only which were collected
by the author, and no attempt is made to include all tliose mentioned by others.

It is next to impossible to make out a complete faunal list of the medusae of any
locality, except after years of study. From the nature of their life, stragglers and
sporadic swarms of rare medusae appear in localities where the medusan fauna
has been well studied. For ten years I have kept watch of tlie medusae which
appear in Narragansett Bay in summer months, and a season rarely passes in
which some jelly-fish new to the known fauna is not observed. Sometimes
specimens of some new genus will appear in such abundance that it seems im-
possible that we could have missed seeing them if they had appeared in other
summers. In some years the water near the Newport Laboratory is filled with
Pleurobracliiae, wliile in others stragglers only appear. In the past summer the
most common acaleph in Narragansett Bay was Dautylometra, hundreds of speci-
mens of which were seen, and yet in former summers we rarely have observed
more than a half-dozen in the course of a summer.

In tlie light of these facts it seems preposterous to attempt a monograph of the
medusae of the Bay of Fundy witii the limited material collected on the short
visits which I have been able to make to these waters.

VOL. XIII. — NO. 7. 14

210 BULLETIN OF THE

I have had in mind since that time a new visit to these localities to
gather materials for the publication of a monographic paper on the
medusae of the Bay of Fundy, but have been unable to make the ne-
cessary collecting trips for its completion. It is now thought best to
publish some of the more interesting observations which have already
been made, as aids to those who may make a more exhaustive local
study of these animals, or as a preliminary to a more extensive exami-
nation of animals of this group from these localities.

While the majority of the medusae here mentioned are from Eastport,
Maine, and Grand Manan, New Brunswick, a description of a new genus,
Hydrichthys, from Newport, R. I., is added.* This 'strange genus is
parasitic in its hydroid stage on the sides of an osseous fish, and besides
the unique parasitism presents us the anomalous condition of an at-
tached hydroid closely related to the well-known Velella and Porpita.
The form of Nanomia, the anatomy of Callinema, and the peculiarities of
tlie various other medusae here mentioned from the vicinity of Grand
Manan, show how characteristically boreal this medusan fauna is, and
how much it differs from that of Narragansett Bay. They show how
rich the field is for an extended research in this region in this kind of
marine study, f

The short visit which was made to Grand Manan, and the collecting
trips to Eastport in 1885 and 1886, have shown me that th'i medusan
fauna of the Bay of Fundy and Passamaquoddy Bay, near these places, is
very characteristic. It differs markedly from that of Newport, and is
distinctly boreal in its affinities. While this paper was in preparation the
author has had occasion to study the medusan fauna of the Arctic Ocean,
and to publish notices of jelly-fishes collected by Lieutenant Ptay and
General Greely in high latitudes. It has been noticed in carrying on
this work simultaneously that there is a marked similarity in the fauna
of the Arctic and that of the Bay of Fundy, and it may be said that the

* This curiously modified hydroid was cap*^ured during the summer session
(1887) of the Newport Marine Laboratory.

t The author would here add a notice of his own experience to that of others as
to the advantages of Grand Manan for marine zoological work. Wliile many, per-
liaps a majority, of tliose who have studied zoology in this place, have spoken of
its many advantages for dredging and shore collecting, few have tried surface
fishing in tliese waters. 1 had been led to suppose from certain sources, that
revelations with the Miiller net would be small in these localities, but I find
Grand Manan and Eastport among the best localities which I have visited on the
New England coast for the collection of pelagic and " surface animals " with the
dip-net.

MUSEUM OF COMPARATIVE ZOOLOGY. 211

relationship is closer between the jelly-fishes of these distant localities than
between those of Xarragausett Bay and the Bay of Fundy. The cause
of this similarity may readily suggest itself to one who examines the
direction of the currents of water which bathe the Kew England coast.
The cold currents setting down from the Arctic have brought with them
an assemblage of mednsan genera of a facies in marked contrast with
that of those brought into Narragansett Bay by warmer waters. This
assemblage partakes of the characters of the Arctic, where the current
has its birth. While it is true that some of the northern and boreal
genera of medusse occasionally round Cape Cod and appear even in num-
bers in the bays to the south of this headland, they show by their rarity^
and their dependence upon the prevailing winds at the time, that thew
home is to the north.*

Among familiar examples we "might mention the well-known Cyanea
arctica and Aurelia Jlavidula. Hardly a summer passes in which both
of these genera are not found in Narragansett Bay near the Newport Lab-
oratory, and sometimes the former are in great numbers. I have, how-
ever, never seen them at Newport so large or so numerous as those which
were taken almost every day at Eastport. Sporadic examples of Turris,
Melicertum, and Staurophora are constantly taken in our surface fishing
at Newport, but a few* days at Eastport showed me a wealth of indi-
viduals of these genera which was unknown to me before. This difier-
ence in fauna exists also in the Physophores. Nanomia never ventures
into Newport waters, and the magnificent Agalma seems to have its
habitat on our coast limited to the southward of Cape Cod.

If it were the purpose of this paper to contrast the pelagic medusan
faunae of the Bay of Fundy and Narragansett Bay, many other instances
might be mentioned to show how different the jelly-fishes of the two

* While there are many boreal medusae which straggle into Narragansett Bay,
a still larger number of those whose home is in the tropics make their way into
our Southern New England waters through the agency of the Gulf Stream. The
surface waters of the Gulf Stream are often blown nearer sliore than is commonly
supposed. I have noticed in the water near the Laboratory a rise in tempeiature
of over ten degrees in a single flood of the tide. The higher temperature of the
water is a good sign that we are to expect oceanic animals in our dip-nets, and we
are seldom disappointed. The cause of the elevation in temperature is thought to
be directly connected with the prevailing wind from the southeast, where the Gulf
Stream lies

It is believed that the fact that the differences in the temperature of the water
— now warmed by the Gulf Stream, now cooled by other currents — is what gives
such a great variety to the marine fauna from Ca[)e Cod southward-

212 BULLETIN OF THE

regions really are.* It can hardly be supposed that different physical
conditions and environment, as far as the coast line itself is concerned,
could have brought about such a great difference and such a restriction
in these floating pelagic animals. The great influence in t-heir limitation
must be the temperature of the water, and its difference in the two
localities.

As strictly related to this line of inquiry is a suggestion in regard to
the possible medusan fauna of a region contiguous to the Bay of Fundy.
It is a well-known fact tliat the southern part of the Gulf of St. Law-
rence, near Prince Edward's Island, presents us an assemblage of south-
ern genera of Mollusca, surrounded by strictly boreal forms. It would
be very interesting to discover what the character of the hydroid and
medusan life of this warm area is, and to see if we have, as in the case
of the Mollusca, a colony of southern genera protected in their northern
home by the higher temperature of the water. I liave been unable to
visit this locality for study, but I commend the problem to those who
engage in marine work on this coast. Unfortunately we know next
to nothing of the acalephian fauna of this region of the Gulf of St.
Lawrence.

CTENOPHORA.

Mertensia ovum, Morch.

The common tentaculated Ctenophore at Grand Manan resembles M. ovum.
It is not rare near Eastport, where I found it in the summer of 1885 iu con-
siderable numbers. It was taken in some abundance at Grand Menau in
1886.t

* Tabular lists of medusEe from the Bay of Funrly region and from that of
Narragansett Bay are given by A. Agassiz in the " North American AcalepliEe."
The well-marked contrast which one can easily see in these lists appears even
more ^.triking when we add to those of the Bay of Fundy some of the charac-
teristic boreal genera here mentioned.

t Ova of a Ctenophore were found in great abundance at Grand Manan in July
and August, 1886. These were traced into young Mertensiae, and are possibly of
this species. They look unlike the eggs of Plcurobrachia found at Newport. The
fact that Pleurohrachia rhndodadyla, recorded by other observers from Eastport,
was not seen by me does not mean that it is not thought to exist there. I have
only spoken of jelly-fishes observed, and do not wish this paper to be regarded as
a list of medusae which live iu the Bay of Fundy.

MUSEUM OF COMPARATIVE ZOOLOGY. 213

Bolina alata, Ag.

This beautiful specimen of Cteuophores was found once, but there is reason
to believe that it is common in the Bay of Fundy.

In the few specimens which were seen there were no parasitic Actinians in
the body, as is found in the related Mnemiopsis from Newport. Of course,
negative evidence of this kind may not mean much, for early in the season at
Newport none of the specimens of Mnemiopsis have specimens of Actinians *
in their chymiferous tubes or stomachs.

Beroe roseola (Ac).
Several specimens were found at Grand Manan.

SIPHONOPHORA.
Nanomia cara, A. Ao.

Plates I,, II., III.

The only Physophore which was captured at Grand Manan is the interesting
medusa called by A. Agassiz f Nanomia cara. This jelly-fish, described many
years ago, has been repeatedly mentioned in text-books and general works on
zoology, but since its discovery nothing has been added from direct observa-
tion to our knowledge of its anatomy and somewhat exceptional embryology %
as made known by A. Agassiz. It was therefore with much enthusiasm that
I first saw from the wharf back of the Dominion House at North Head, Grand
Manan, many specimens of this beautiful animal swimming in the water. As
is well known, many interesting and doubtful details of anatomy remain yet to
be made out in regard to this animal, and it was with keen pleasure that the
medusa was captured in abundance and placed in aquaria for study.

* It is, however, an interesting fact that I went directly from Eastport and
Grand Manan to Newport, and on my arrival tliere, not more than five days after
leaving the nortliern localities, plenty of Actinians in Mnemiopsis were found.
The yearly record of the time of the appearance of this parasite at Newport
shows it much earlier in otlier years than at the time I was at Eastport.

t Proc. Bost. Soc. Nat. Hist., IX. 181 ; Nortli American Acalephae, Illiist. Cat.
Mas. Comp. Zool., II. 200-213; Seaside Studies in Natural History, pp. 76-8o.

X Although nothing has been added to a knowledge of its anatomy and devel-
opment, the possibility that a closely allied Physopliore occurs in the Arctic is
commented upon by Moss and by the author. So little is known of the generic
characters of the Physophore supposed to be Nanomia from Robeson's Channel
and Lady Franklin Bay, tliat we cannot definitely say they are the same. There
seems no good reason to doubt their identity.

214 BULLETIN OF THE

As the only figures which we have of Nanomia are of the young, my first
care was to obtain a figure (Plate I.) of the adult animal.

The method by which a drawing of the outline of this large Nanomia was
made may have an interest to those engaged in the study of the Siphono-
phores. The outlines of Plate I. were drawn in the following way.

The animal was placed in an upright glass jar, with flat sides, similar to
those of glass vessels used for the bath in photography. This glass receptacle
was placed in the bright sunlight, on a table between the observer and the
window, or some source of light. It was so placed that a well-defined shadow
of it was projected on the paper held a few inches back of the animal, on the
side of the glass opposite the window. The paper was tacked to a board held
upright and firm by simple means, which any one can devise. The shadow of
the Nanomia was so clearly defined that even the fainte.st lines of outline were
seen projected on the paper. There are times when a Siphonophore floating
in the water keeps almost perfectly quiet for some minutes. This is a good
opportunity to trace on the paper the lines of the shadow with a pencil.
Although I could not make the whole contour before a new movement of the
medusa, it was easy to draw the nectocalyces and sections of the polyp-stem
before the animal changed its attitude.

The only trustworthy account which we have of Nanomia is the original
description by A. Agassiz.* This observer not only described the first long-
stemmed Physophore from American waters, but he also gave the first series
of recorded observations on the development of the young of any genus of
Siphonophores.

From my own studies of Nanomia I am convinced that the adult of Nano-
mia has never been figured or described. The reasons for this belief will, I
hope, appear as I go on in my account. The description by A. Agassiz was
pioneer work in a field where later observations have been extensively made ;
yet for over fifteen years Nanomia was the only long-stemmed Physophore
known from the waters of the United States. His description has been
repeatedly copied, and his figure is widely used in general accounts of these
animals. It is found necessary to diff'er from one or two statements made in
the original description in i-egard to Nanomia. These diff'erences are specially
noted, and a redescription is not made of those points of anatomy where in the
main my account agrees with that already published. The fact that Nanomia
more than any other Siphonophore is used in text-books and general descrip-
tions of marine animals published in America to illustrate the general charac-
ter of the group, would seem an inducement to publish an}'' contributions
which might be made in regard to its embryology and anatomy.

It may be well, at the very threshold of my description, to mention the

* Tlie best account of the anatomy and embryolonry of Nanomia is in " North
American Acnleplire." Tliere are other notices of tlie same animal by tlie same
author, one of the best known of which is in " Seaside Studies," by Mrs. E. C. and
A. Agassiz.

MUSEUM OF COMPARATIVE ZOOLOGY. 215

reasons which led me to regard the published figures of the adult as the
young, and not the adult Nanomia.* One of the most important reasons
which have influenced me is the small size and the small number of nectoca-
lyces. While the specimen figured is barely six inches long, specimens of
Nanomia were often found at Grand Manan four and five feet in length.
While A. Agassiz never found more than four pairs of fully developed nec-
tocalyces, many of the adults had fifteen pairs of these structures.

A more important fact, however, which would seem to indicate that the
figure is that of a young animal, is the following. The great number of em-
bryonic tentacular knobs,t or those described on the " first set of polyps,"
show immaturity ; for these knobs are always confined to young or larval
forms in related genera, like Agalma, Halistemma, and Stephanomia. The
adult permanent knobs, or "corkscrew-shaped tentacles," are aU immature.
The adult form of these knobs is not attained in any of those of Nanomia yet
figured.

In order to facilitate the reader in a comparison of my description with that
in the " North American Acalephae," the following table is introduced. The
terms in the first column are from the published account, those in the second
are made use of in the present description .

First set of polyps Embryonic polypite with embryonic ten-
tacular knobs.

Second kind of polyps ..... Undeveloped permanent polypites with

undeveloped permanent knobs.

Third kind of polyps Hydrocyst, taster.

Fourth kind of appendage (p. 206) Undeveloped hydrocyst, taster.

The largest specimen captured measured, when extended, over four feet;
when retracted, its length was three feet. The specimen which is figured, ot
life size (Plate I.), was one of the most convenient for study, but not one of
the largest. It may safely be said that hundreds of specimens of the size
represented were taken just off the wharf near the Dominion House at
North Head, Grand Manan.

The adult animals, as they float extended in the water, can readily be dis-
tinguished by a practised eye from the southern Physophore, Agalma elegans.
The whole external appearance of the two genera is different. The tentacles
of Nanomia are carried in a different way from those of Agalma, and are not
drawn to the polypites in the same clumps, while the tentacle itself is more
often thrown into festoon-like folds, as shown in the figure. It is needless

* North American Acalephae, Illust. Cat. Mus. Comp. Zool., No. 2, p. 201,
Fig. 332.

t On many of the small specimens of Nanomia from Grand Manan, embryonic
knobs (Plate II. Fig. 8) were found. These closely resemble the knobs figured by
A. Agassiz. They were not found in adults as far as observed.

216 BULLETIN OF THE

to say that Nanomia is no less graceful than the beautiful " sea necklace,"
Agalma, iu all the motions of tentacles and tentaculai" knobs.

Axis. — The axis of Nanomia is long, highly flexible, muscular, dotted with
reddish pigment spots. It is divided into two regions, which may be known
as the nectostem (ns) and the polyp-stem (ps). The length of the latter
is several times that of the former. The polyp-stem appears to be more easily
bent than the nectostem, but this appearance is brought about by the rigidity
imparted to the latter by the close approximation and form of the nectocalyces.
It is needless to say that the axis, as in all Physophores, is hollow throughout,
and that from it most of the appendages ot the colony have arisen.

Float. — The float (/) resembles that of other Physophores. It is a small
sac enclosed in an enlargement of the axis, and has reddish pigment in its
outer walls. The contents seem to be a bubble of air or gas, as in other
Siphonophores. The longer axis of the float does not coincide with that of
the axis of the Nanomia, but is bent at a small angle.

Nectocalyces. — The nectocalyces (no) are biserial in their arrangement,
with bell openings pointing in opposite directions. Their close approximation
imparts to the stem (nectostem) a rigid character, which however disappears
when their connection with it is once broken. The rows of nectocalyces are
transparent, gelatinous, almost invisible as the animal swims in the water.
Near the float there is a small cluster of undeveloped bells, the full grown
being more distant from the float than the less developed. The specimen
figured has thirteen pairs of well developed nectocalyces. Each nectocalyx is
bell-shaped, fastened to the axis at the apex, and has two lateral horns or
spurs, shown in the figure in profile, which interlock with corresponding spurs
from the opposite side of the axis.

The structure of the bell and its tubes is well described by A. Agassiz.
The bell is rounded, with small circular orifice, slightly closed by a thin
velum. The bell cavity is spacious. The chynjiferous tubes are four in num-
ber, in addition to a marginal vessel and a single tube communicating, through
the point of union of the bell and stem, with the cavity of the axis of the
animal.

The fact that the nectocalyx is slightly flattened on the upper and lower
sides, and the existence of a corresponding bulge on the remaining sides has
brought it about that, while the radial tubes of the nectocalyx of the former
spheromeres is regular and straight, passing from common junction directly to
bell rim, those of the two lateral spheromeres are tortuous, forming a single
loop, as shown in the figure (Plate III. Fig. 2). This character is by no means
peculiar to Nanomia, but is an interesting fact in the asymmetrical develop-
ment of the bell.

ffydrophyllia. — The bracts, covering scales, or hydrophyllia (hph) are
colorless, transparent bodies, covering the bases of the appendages to the
polyp-stem. Each hydrophyllium is irregularly rectangular to triangular in
shape. Two adjacent sides of the rectangle are so elongated that a triangular

MUSEUM OF COMPAKATIVE ZOOLOGY. 217

shape is given to these bodies. The free and distal angle diagonally opposite
the angle of attachment is rounded and very obtuse ; the angle of attachment
is more acute.

A tube extends from the point of attachment diagonally to the opposite
angle of the covering scale, where it ends blindly. This tube is undivided,
unbranched, with entire edges.

Folypites. — The polypites (p) are flask-shaped bodies, attached by a short
peduncle to the polyp-stem. Their free end is open, forming a mouth. The
rim of this orifice, or the lips, are without appendages. The basal peduncle
is short, and of somewhat smaller diameter than the polypite itself. Near
the base the polypite bears a " Wiraperwiilst," or ferule-like thickening of
the walls.* At that point reddish pigment is found, and buds which are im-
mature tentacular knobs arise. The tentacles also originate at that point.
The polypites are regularly distributed along the polyp-stem, dividing the
stem into sections or regions, which may be known as inter-polyp regions.
The oral extremity of the polypite, except when it is retracted, extends be-
yond the hydrophyllia. The opening of the mouth sometimes expands, by
which the lips become trumpet-shaped. The rim of the mouth is entire.
Fragments of food were seen inside the polypite. Rows of large cellular
bodies, in parallel lines, extend along the inner wall of the polypite. These
are possibly hepatic in function.

Tentacles. — The tentacles (to) are long, filamentous bodies, arising from the
base of the polypite. They are highly contractile, and generally, when the
animal is at rest, extended. Each polypite has a single tentacle. There are
two kinds of tentacles, one of which bears tentacular knobs, the other being
destitute of the same.f The former, which are the tentacles proper, are those
which arise from the polypites ; the latter, the filaments of the hydrocyst,
which have no tentacular appendages.

The peculiar festoon-like way in which the tentacles are often carried, is
noticed by A. Agassiz. This habit is marked in the genus, and is more
common in Nanomia than in the southern genus Agalma. Although I have
studied all the Mediterranean species of Physophores alive, I recall none
where this habit is so well marked as in Nanomia.

Tentacular Knobs. — The adult tentacular knobs (Plate II. Fig. 9) of Nano-
mia resemble those of Agalmopsis, Fewkes.J The various parts which enter

* This increase in size of the polypite at the " Wimperwiilst " is largely owing
to the increased development of the middle layer of the body.

t The tentacles which are destitute of tentacular knobs do not arise from
polypites, but from the hydrocysts.

In the growth of the tentacles the tentacles do not first form, and then the
tentacular knobs bud from it, but the knobs first form on the " Wimperwiilst," and
then the tentacle is pushed out, bearing these bodies, already imperfectly formed.

X One form of Agalmopsis, Sars, Stephanomia pictum, Metsch., Halistemma te.r-
gestinnm, Claus, Agalmcpsis fragile, Fewkes. These various aliases of Agalmopsia
are mentioned, lest confusion be introduced by the above statement.

218 BULLETIN OF THE

into the formation of the tentacular knob are the peduncle, the involucrum ,
the sacculus, and the terminal filament.

The terminal filament {ft) is long, thread-like, single, arising from the
distal end of the sacculus. In its walls are imbedded many lasso-cells, or
uematocysts. The sacculus is closely coiled in several turns. It is a large
reddish body, armed with batteries of lasso-cells, and crossed by prominent
lines.

The involucrum {inv) forms a cap over the sacculus.* It is bell-shaped,
with entire edges, the sacculus {sac) arising from the inner central point.
The whole tentacular knot hangs from the tentacle by the peduncle.

Tasters.] — Among the most interesting and it would seem exceptional struc-
tures in the genus Nanomia are those organs which are known as tasters (lit').
The most marked peculiarity in their anatomy is the existence of an "oil
globule " (og) near their base.

The tasters hang from the polyp-stem midway between the polypites. A
single adult and many half-developed tasters occur between each pair of polyp-
ites. Individual tasters are small, slender, flask-shaped bodies, resembling
immature polypites. They arise directly from the stem' and are destitute of
a basal peduncle. The distal extremity is closed.

Each taster bears near its attachment a prominent red body of spherical
shape, known as the " oil globule." The taster has a single long tentacle Qi ta),
destitute of lateral appendages. In the water in which Nanomia was kept
alive, several tasters which had separated from the main stem were found
floating about near the surface. These were not seen to grow into colonies of
Nanomiae, but gradually became opaque and decayed, never in those studied
growing into new colonies.

tronophores. — A. Agassiz supposea uuai. sepai aie male or female colonies of
Nanomia were found. He considered that some colonies of this genus are all
males, while others are all females. My observations diff"er in this respect
from his. The adult Nanomia, like the genus Agalma, has male and female
bells on one and the same colony.

The sexual bells (g) of Nanomia are found near the oase of the tasters,
where they form botryoidal clusters. These clusters occur on all parts of the
polyp-stem wherever hydrocysts are found. The interior of the male bells in
many cases has a milk-white color, while the female bells are always trans-
parent. Each male gonophore is bell-shaped and fastened to the base of the
cluster by a short flexible peduncle. The walls of the bell are thin, with four-
radial tubp« joined to a marginal canal. The peduncle is penetrated by a

* The name sacculus has been given to the coiled red structure which forms
the larger part of the knob by otliers. It seems more natural simply to inter-
change the ternas, so that what is now called the involucura may be known as the
sacculus, and vice versa.

t The term " taster," used to designate these structures, is open to some objec-
tions, but is regarded as one of the best which has been suggested to apply to these
peculiar organs in the Physophores*'

MUSEUM OF COMPARATIVE ZOOLOGY. 219

vessel which connects this radial system of tubes with the cavity of the axis of
the colony. The bell margin has a marked velum and is destitute of tentacles.
The sperm is found in the inflated proboscis, which fills almost the whole bell-
cavity. This receptacle is in older male bells, and in those especially which
are found near the extremity of the polyp-stem, of a milk-white color. The
spermatozoa have a rounded head and small vibratile tail. The clusters of
female bells which occur with the male have a similar attachment, and are also
campanulate, resembling those of Agalma. Each bell carries a single ovum.
Individual eggs and bells voluntarily separate from the attachment to the
colony, and the latter live for some time free in the water. The ova of Nano-
mia can easily be seen by the unaided eye, as they float about in the water in
which a parent Nanomia is captive.

A method of collecting the ova is to allow the Nanomia to remain quiet for
some time m a glass jar. This jar contained about three gallons of water, and
was so placed on a table that one could see through its sides, the window
or source of light being on the opposite side of the jar. In this way the
ova could readily be distinguished in the water, and after a few hours they
rise to the surface. When they are seen floating at diff'erent depths in the
water, it is possible to pick them out one by one with a pipette. When the
ova rise to the surface it is more convenient to skim them off by means of
a watch-crystal, or some similar shallow receptacle. (

Development. — The development of the older larvae of Nanomia, after the)
formation of the float, has been well described by A. Agassiz in his account
of the animal, to which reference has already been made. He considers that
there are two methods of development, one from the egg, and the other by
budding from the parent colony His figures are mostly from stages which he
regards as formed by the latter method, and are of larvae after the float has
already formed.

It is certainly an exceptional method of growth of new colonies of Siphono-
phores to find the young budding from the parent, and new observations - are
desirable to determine the details of such growth. There is no known genus i
which resembles Nanomia in this respect, and all other 'genera, whose embry-
ology is at present known, reproduce new colonies by ovulation alone. The
following observations have a bearing on the origin of the larva of Nanomia,
although they leave the important question in doubt.

A minute comparison of the float of the parent colony with the " oil glob-
ule " of one of the tasters was made, in order to detect differences and resem-
blances, if any, between them. While it was found that there are marked
differences in these two structures, I could not say ^hat the differences would
prevent the one being a development of the other. Still, I have not been able
to persuade myself that such is the case. I have repeatedly found the tasters
with their oil globules detached from the parent axis, but all attempts to raise
these into older stages similar to those figured by A. Agassiz have failed.
There is one point in which there is a great difference in the tasters which I

220 BULLETIN OF THE

have studied and the youngest larva he figures. They diflfer from the stages
which he figures in the presence of the tentacle which always characterizes the
taster. A failure to raise one of these tasters separated from the colony into a
new colony, it might be said, does not prove that under other conditions better
results may have been reached. As a question of opinion, it is regarded as
highly doubtful that the colony of Nanomia reproduces by budding, and that
the new colony is ever formed from a taster. Nanomia, however, us shown by
Agassiz, has an egg development, and passes directly from a planula-like young
into stages similar to the youngest which he figures. It is therefore thought
that the embryo, without exception, is derived from an egg. The segmenta-
tion of the egg was observed, and, as nothing has ever been published on the
egg of Nanomia, a few stages in the segmentation are here represented.

The egg of Nanomia, like that of Agalma and other genera, is transparent,
colorless, almost invisible in the water. The interior is penetrated by and
almost wholly made up of a spongy mass of protoplasm, forming a network
filling the contents of the egg. A thin covering of protoplasm surrounds the
egg. Metschnikoff * describes in the egg of Epibulia a similar network, and
the author! has devoted some space to a consideration of the same in Agalma.

The first change (Plate II. Figs. 1, 2) in the external contour of the Nano-
mia egg is the formation of a primary cleavage-furrow. This furrow was formed
by the bending in of the outer wall of the egg at one pole. This infolding of
the primary furrow leads to well-marked folds on the outer wall of the egg,
which recall the phenomenon of " Faltenkranz " in some other animals. In
about an hour's time after the first appearance of the infolding to form the
primary furrow, a 2-celled cleavage stage was formed, and the first cleavage
plane (1 cZ) is well developed. About another hour elapses before the sec-
ond cleavage plane is formed and a well marked 4-cell stage (Figs. 4, 5) is
developed.

In his paper on the development of Agalma the author points out the pecu-
liar warping of the first cleavage plane by the formation of the second. It
was there shown, that by the growth of the second cleavage furrow at right
angles to the first, it was brought about that the plane of the first cleavage
was broken near the equator of the egg. In the same way "and by an analogous
process in the development of the Nanomia egg the second cleavage plane is
60 formed that the continuity of the first plane is likewise broken. Figure 4 of
Plate II. illustrates this broken condition of the plane in Nanomia. Whether
this modification is of any morphological importance, or has any influence in
subsequent development of the cells, cannot be at present determined. The
8-cell stage is produced by the formation of two new furrows (Fig. 6) bending
in on one side of those cells already formed in a way analogous to that already
described in Agalma.

* Studien iiber die Entwickelung der Medusen und Siphonophoren. Zeit. f.
Wiss. Zo6\., Bd. XXIV.

t On the Development of Agalma, Bull. Mas. Comp. Zool., Vol. XI. No. 11.

MUSEUM OF COMPARATIVE ZOOLOGY. 221

The egg of Nanomia in the eight-cell stage is the oldest which has been
studied. There seems to be nothing peculiar in the method of segmentation
as compared with that of Agalma. Among other medusae it has some like-
nesses with that of the Ctenophora and certain Trachymedusse.

Between the eight-cell stage and the youngest as figured by A. Agassiz
there is a considerable gap, which I am not able to fiU by new observations.
This interval is, however, in part bridged by observations on an allied genus
found in the Mediterranean, already published by Metschnikoflf. This ob-
server * has studied a Siphonophore, which is closely allied to Nanomia, and
seems to resemble in mode of growth, as far as known, that which has been
already described and figured by A. Agassiz.

Older larvae, which he supposes to belong to the same genus, Metschnikoflf
has raised from planulae which are a little younger than the youngest Nano-
mia figured by A. Agassiz. He has shown that in these larvae no " primitive
hydrophyllium " t is formed, and that the first structure to develop is the
float. He regards his genus as the same as Nanomia.

A few years ago I was inclined to regard the genus referred to by Metschni-
koft* as the same as Nanomia. The adult tentacular knobs described for the
first time m- this paper confirm me in that opinion, but there is one thing
which leads me to doubt their identity. The existence of the large oil glob-
ules in the bases of the tasters is very exceptional among Physophores. I
have studied the animal, Stephanomia pictum, referred to by Metschnikoff,
and was one of the first to describe it,t but I do not remember seemg struc-
tures similar to the " oil globules " of the tasters of Nanomia. In the
published descriptions of this animal there are no similar structures. The
question then arises whether the presence of this structure is sufiicient to sep-

* Op. cit.

t The term "primitive hydrophyllium" was suggested in my paper on the
development of Agalma to designate the cap-shaped covering scale which forms
such an important organ in determining the form of the larva. The designation
" primitive larva," used to distinguish the stage in which this organ is most de-
veloped, was suggested in the same paper. The primitive larva is supposed to
be an ancestral form of Calycophores and Physophores, and to be closely allied
to the ancestral form of other Hydromedusae.

X Contributions to a Knowledge of the Tubular Jelly-fishes, Bull. Mus. Comp.
Zool., Vol. VI. No. 7, pp. 136, 137, Plate II. Neither in Metschnikofrs figure of
Stephanomia, nor in Claus's figure of Hnlistemma tergestinum, which all seem to re-
gard the same, the relative size of the hydrophyllia seems to be smaller than in
Nanomia. The same is true of my Agalmopsis from Florida. Claus's figure of the
taster of his Halistemma, Plate II. Fig. 4, shows what maj- be a small " oil glob-
ule" near the base of this organ, and the structure in the same figure lettered mg,
"male sexual bell," has some resemblance to the "oil globule" of Nanomia.
Still from his description it does not seem that tiie " oil globule " has the predom-
inance in size which it has in Nanomia. It must also be said that \i mg (Plate II.
Fig. 4) is a male sexual bell, it is very different from the same bodies in Nanomia.

222 BULLETIN OF THE

arate Nanomia from the allied Stephanomia, auct., Halistemma, Claus, and
Agalmopsis, Fewkes. We have on. the Florida coast an Agalmopsis, A. fragile,
Fewkes, which has the same knot as Nanomia, and in other particulars is very
near it. They are not the sanie species, although generically they seem to be
very close. For the present I adopt Agassiz's name, Nanomia, not because it
differs from other Siphonophores in the way some have thought, but on new
grounds, or because of the marked character of the " oil globule " in the taster
of Nanomia. In all other respects Nanomia is like Agalmopsis, Fewkes, from
the Mediterranea"n and Floridan Seas.

It is predicted that the egg of Nanc_.na will be found to develop at first a
float, and then an embryonic tentacle with embryonic knobs ; that there is
never developed a primitive hydrophyllium ; and that an Athorybia-like cov-
ering scale does not form. The type of development, as compared with that of
Agalma, is more abbreviated, and consequently more direct in Agalmopsis
than in Nanomia.

The facts which lead to this conclusion may be seen from what is said below.
The state of our present knowledge of the development or growth of the lar-
val stages of Nanomia may be shown in the following historical summary : —

1. The larva in which the float is fully formed is traced from older larvse
into the genus Nanomia. This series of observations was made by A. Agassiz,
the discoverer of Nanomia, who considers that the youngest stage (with float
only) develops from a bud, and also from the egg. The earliest stage
which he figures he regards as identical, whether formed by either method of
development.

2. Metschnikoff obtained younger stages, or those before the float is devel-
oped, of an allied Physophore. The youngest stage which he figures is a
planula.

3. The author here describes the segmentation of the egg of Nanomia into
the eight-cell stage.

The only break now in a consecutive series of obsei .ations is between two
and three, or the eight-cell stage and the planula. Judging from what we
know of other Siphonophores, no embryonic structures appear in this gap, and
we are justified in supposing that no primitive hydrophyllium, or covering
scale, appears before the float in Nanomia.

The fact that in Nanomia no primitive hydrophyllium, such as is found in
Agalma, exists, does not prevent our recognizing in the youngest larva with a
float, and a tentacle with embryonic knobs, all the parts of the stage called
the primitive larva. Metschnikoff" has shown that a Siphonophore float is
homologous to a bell,* and I have no hesitation in accepting the theory that
the float of Physophores is homologous with one of the nectocalyces of the

* The primitive larva, or, as I have elsewhere called it, the primitive medusa,
from which all the Siphonophores liave phylouenetically arisen, would seem to be
somewhat like older stajres on Plate IIL of my " Development of Agalma," Bull.
Mus. Comp. Zool., Vol. XI. No. U.

MUSEUM OF COMPARATIVE ZOOLOGY. 223

Calycophores. In 1883 the float was compared with the anterior nectoealyx
of Uipliyes. I regard the first nectoealyx of Monophyes as the same as the
primitive hydrophyllium of Agalma.*

In the phylogeny of the Siphonophores, both Physophores and Calycophores
have a stage called the primitive larva in common, and it is possible their an-
cestor was not unlike the so-called primitive larva stage of Agalma, with a
single cap-shaped hydrophyllium, one polypite, and a knob similar to that
which I have called the embryonic knob (Plate II. Fig. 8). The Calyco-
phores retain certain organs which characterize this form, as the primitive
hydrophyllium and the embryonic tentacular knob. In the Physophores,
however, a specialized float, a modified bell, is developed, the embryonic knob
gives place to other kinds of knobs, characteristic of the diff"erent genera of
Physophores.

The primitive larva preserves the Medusa form, and may be supposed to
approach more closely the ancestral form of the Siphonophores among other
Hydromedusee than any other medusiform larva. The name primitive larva
appears to me to be a good one, and can well be accepted as a help in studies
of the phylogeny of the Siphonophores.

I have already elsewhere devoted some space to showing that the primitive
larva finds its nearest homologue among Hydromedusse, in certain Tubularian
medusiform gonophores. I chose Lizzia for my comparisons. It was perhaps
premature for me to take any one genus for such a comparison, and it might
have been better to have chosen the Trachymedusse instead of the Tubularians
for such an homology. From the character of the egg cleavage, and the fact
that the development, as far as known, is similar in the Siphonophores and
genera of Trachymedusse, it is possible that the young stage of the former,
which I have named the primitive larva, is more closely related to certain
medusiform larvae among the Trachymedusse than to genera like Lizzia. The
close homology between a medusiform gonophore and a simple hydroid, how-
ever, is such that I think we are justified in regarding the young of Nanomia
with a float and no primitive hydrophyllium as homologous with the prim-
itive larva of Agalma. I believe the ancestral form of all Hydromedusse, as
well as of all the Siphonophora, will be found to be similar to the primitive
larva of Agalma in its younger stages. It had the form of a ciliated planula,
with an enlargement at one end and a mouth at the opposite. The enlarge-
ment at one end was formed of three layers, is bell-shaped or gelatinous, and
forms the bell of the Medusa, the float of Nanomia, and the i^rimitive hydro-
phyllium of Agalma. In the fi.xed hydroid it becomes a base of attachment,
in Pihizophysa or Nanomia a float, and in Agalma a covering scale. It is
well to have some name to designate this prototype, and no one has suggested
any better one than the " primitive medusa." f

* Embryological Monographs, No. III. Plate VII., Mem. Mus. Comp. Zool.,
Vol. IX. No. 3.

f It would be interesting to trace the resemblance of this primitive larva or

224 BULLETIN OF THE

HYDROIDA.

Sarsia mirabilis. Ag.

Many specimens of Sarsia were seen at Grand Manan on a single excursion.
Later they disappeared, and were not again collected. The hydroid Coryne *
was also found.

Hydrichthys mirus, gen. et sp. nov.

Plates IV., V.

During the month of August of the past summer (1887), in the surface
fishing carried on at the Newport Marine Laboratory, I captured a most inter-
esting genus of parasitic hydroid. This genus and its peculiar life are un-
described as far as known. The mode of parasitic life is most extraordinary,
and the modification of its structure of an anomalous character.

A small fish of the genus Seriola (S. zonata, Cuv.) was taken in the dip-
net at a time when the sea was quiet.f Upon the side of the body (Plate IV.

primitive medusa, the ancestral form of the medusae, with the prototype ("Pili-
dium-like larva ") of the six groups of marine larvse described by Balfour. It is
thought that such a resemblance not only exists, but also has an important phylo-
genetic meaning. It is not in place to discuss this question in this paper.

It may be asked whether the primitive larva of Agalma, with its huge primitive
covering scale, or the primitive larva of Nanomia, where that scale is replaced by
a float, is nearest the primary or ancestral larva of Hydromedusae. The youngest
forms of the primitive covering scale and the float closelj' resemble each other,
and the departure from that form seems greater in Agalma than in Nanomia. A
nectocalyx seems more highly organized than a pneumatophore ; still, between a
primitive hydrophyllium, such as exists in Agalma, and a float like that of Nano-
mia, it is hard to tell which is more highly specialized. It cannot be said that the
adult Nanomia is less highly specialized than the adult Agalma. Although the float
of Nanomia is first formed, it follows the primitive hydrophyllium in Agalma.
While this fact might seem to indicate want of homology of the float in the adults
of the two genera, it does not seem to prevent our considering the primitive larva
to be represented by the young Nanomia with a float and no covering scale.

* Although it was not my intention to speak of the hydroids collected in tne
Bay of Fundy, I must mention beautiful specimens of Corymorpha dredged in
shallow water not far from Eastport. The medusae were just ready to drop from
the hydroids, and as they were almost mature in July probably in later months
they are found in abundance free swimming in the sea. I was of course on the
look-out for the so-called free liydroid Acaulis, Stimpson, and other similar hy-
droids, but was unable to collect any of these animals. The broken heads of tlie
liydroid Pennaria, which somewhat resemble Acaulis, were found.

t The Seriola was in company with two others. Neither of its companions,
however, were afHicted with the paVasites mentioned below.

MUSEUM OF COMPARATIVE ZOOLOGY. , 225

Fig. 1) and near the anal opening of this fish a patch of reddish-colored bodies
was noticed. This patch was at first supposed to be a fungoid growth from a
wound or abrasion of the body. A laore careful examination of the supposed
fungus showed me my error, and revealed the fact that it was an attached ani-
mal with true hydroid aifinities. The fish with the attached hydroid was
kept alive in an aquarium for some time, and from the hydroid many me-
dusae (Plate V. Figs. 1-3) of interesting relationship developed. Thousands
of these medusae were raised, and the general characters of their structure and
external anatomy studied. They seem to be hardy in their younger stages,
but it is doubtful whether I have raised them into adults.* The form of the
medusa is quite different from that of any known genus thus far found at
Newport, but not unlike in general affinities certain well-known tubularian
genera commonly found there in surface fishing, f

The exceptional, and it is believed unique, condition in Hydrichthys is the
character of the hydroid, and the imusual feature its attachment to the sides of
the body of the fish as a parasite or commensalist-J The polymorphic structure
of the hydroid is quite different from that of any known hydrozoon.

The modifications in the anatomy of the hydroid are believed to have been
in part due to its attachment' to its host. This supposition, if it is well
founded, and the additional fact that Hydrichthys has never been foimd in
any other habitat or attached anywhere else than to the body of an osseous
fish, may mean that we have in this genus a case of parasitism, or possibly
commensalism, and that this condition has rendered functionally useless or
modified the form of certain structures commonly present in other hydroids,
while it has increased in relative size and possibly importance other organs,
especially those concerned in reproduction and the dissemination of the young.
Hydrichthys, looked at in this light, presents us with one of the most interest-
ing conditions of hydroid life which has yet been recorded.

It was impossible to determine how much nourishment the hydroid Hy-
drichthys draws from the fish upon which it lives through the network of
tubes from which the gonosomes and filiform bodies arise. The absence of
tentacles, or organs the function of which is the capture of food, would seem to
deprive Hydrichthys of those means of capturing and drawing food to the
mouth which are almost universal among fixed hydroids. Possibly in its
parasitic life the hydroid obtains its sustenance from the fish on the sides of
which it lives.

The question whether the fish ultimately succumbs to the parasite is an
interesting one, but one which cannot be definitely answered at present. The
only specimen of Seriola captured which was infested by the hydroid appeared
to be well and healthy, and lived for a considerable time without exhibiting

* The oldest medusa raised from the parasitic Hydrichthys has four tentacles,
t Sarsia mirahiUs and Ectopleura ochracca.

X From my limited knowledge of Hydrichthys v^e are not justified in consider-
ing it a commensalist.

vor,. XIII. — NO. 7. 16

226 BULLETIN OF THE

any inconvenience from the attached parasite. The muscles of the fish, how-
ever, under the " basal plate " of the hydroid were somewhat wasted ; and after
the fish was killed, the shrinkage in its body walls seemed to indicate that the
fish had not wholly enjoyed his strange companion.

Hydroid. — The hydroid colony of Hydrichthys forms a cluster of reddish
and orange-colored bodies attached to the sides and circumanal region of
Seriola zonata.

The base of the whole colony Is about three fourths of an inch in lateral
extent. The base of attachment to the fish is a flat thin plate with ramifying
tubes, by means of which the colony is fastened to the fish, and upon it separate
clusters of sexual bodies (gonosomes) and filiform structures (hydranths ?) are
united together. The structure of the flat plate is not peculiar to Hydrich-
thys, but resembles that of many other hydroids attached to submarine objects,
as Perigonimus and Hydractinia. The walls of the basal plate are leathery,
or coreaceous, rather than calcareous. This basal plate is destitute of promi-
nent projections such as exist in Hydractinia, but is smooth both above and
below.*

In studying the character of the basal plate of Hydrichthys I was reminded
of the anastomosing tubes on the under side of the float of Velella.

Each gonosome (Plate IV. Fig. 2) is botryoidal, consisting of an axis and
lateral branches with medusse in all stages of growth. The axis of the gono-
some arises by a single trunk from the basal plate, and tapers uniformly from
attachment to apex, opening t at the free end into the surrounding water.
This axis resembles in its histological structure the stalk which bears the
medusiform gonophores or Chrysomitrae in the genus Velella. It is sensitive,
highly contractile when touched, transparent, or but slightly colored.

The side branches are similar in structure to the stem. They are generally
simple, but sometimes subdivided or branched. The lateral branches near the
base of attachment are longer than those near the free end of the stem. The
side branches are of uniform diameter, and arise irregularly from the main
stem. Like the main stalk, they have a cavity within, which communicates
freely with that of the main stem.

In specimens preserved in alcohol the lateral branches are short and con-
tracted, but in live specimens both the main stalk and its lateral branches are
long and extended. There is no chitinous sheath about the axis or branches.
Each lateral branch or supplementary division bears at its free extremity,
which is closed, a cluster of medusa buds in all stac^es of growth from a simple
spherical enlargement or expansion of the axis to a medusiform body with two

* The attachment of the basal plate to tlie wall of the fish is so firm that it is
with (lifTicully broken away. I was obliijed to cut it off. and with the hydroid
thus dissected portions of tlie body of the ho.«t were also n ptured.

t There appears to be an opening at the free end /i tlie gonosome. I could
not determine to my satisfaction that the supposed opening really exists. I could
not observe that it was functional.

MUSEUM OF COMPARATIVE ZOOLOGY. 227

stumpy tentacles at its free extremity. Small lateral branches without me-
dusa buds are not rare, especially near the free extremity of the main stem.
They are small, however, and project but little from the main stem.

The free extremity of the gonosome, or of the main stem of the same, is
destitute of medusa buds, and, as has been said above, is without appendage.
There are no tentacles about this terminal opening, and its rim is entire.

Whether the terminal opening of the main stem serves as a mouth or not
it is impossible for me to say. No food was found in the cavity of the stem,
and it is supposed that the whole structure is dependent upon the tubes of the
basal plate for its nutrition. The main stalk is not supposed to take in food
from the surrounding water through the terminal orifice.

The cluster of buds at the extremity of the lateral branches of the gonosome
are the structures which give the color to the colony. They resemble the
medusiform buds found in other Tubularian hydroids in their mode of attach-
ment, their general structure, and their mode of growth.

In addition to the botryoidal clusters of gonosomes there also arise from
the basal plate by which the colony is fastened to the fish long flask-shaped
bodies, recalling in their external form the tasters of the Siphonophores.
These bodies (Plate IV. Figs. 3, 5), like the gonosomes, arise from the upper
walls of the basal plate of tubes attached to the body of the fish. Like the
gonosomes they are numerous in the hydroid colony. The filiform bodies are
elongated flask-shaped structures, of about unifor-m size throughout, arising
from different points of attachment at the base from the gonosomes. They
are, like the gonosomes, destitute of appendages, but they probably have an
opening at the free extremity. The walls of the filiform bodies are composed
of an outer thin and an inner thickened layer. There is a cavity within.
The walls are dotted with pigment spots, which are especially numerous
around the free extremity. In one of these filiform bodies there is a spherical
mass, which resembles half-digested food. It is doubtful whether this mass
is food. The free end of the filiform bodies is sometimes trumpet-shaped,
but ordinarily rounded, the opening being concealed by the contraction of the
lips. The bodies of the filiform structures move backwards and forwards on
their attachments, and are sometimes spirally coiled in a single turn. They
recall in general appearance the spiral zooids of Hydractinia and the tasters ot
Siphonophora, but, unlike either of these structures, have an orifice at their
free end. They are thought to have close likenesses to the "central polyp"
of Velella.

Medusa. — At the extremity of each lateral branch or its subordinate divis-
ion there is found a small cluster of buds, which is composed of medusae in
all stages of growth. While attached to the branch, and before separation
from it, these bodies take on all conditions of growth, from a simple hernia-
like spherical bulb to a cylindrical body with two stumpy tentacles. No
more than two tentacles are developed in the oldest attached medusa go-
nophore which was studied. The course of the growth of the medusa of
Hydrichthys from a hernia-like bud to a small medusa is in no respect

228 BULLETIN OF THE

peculiar, but follows the laws of growth so often described in these structures
in related genera.

The cluster of medusa buds is confined to the terminal end of the lateral
branches. Near the base of attachment of each bud there is a patch of red
pigment. As the medusa grows in size and the proboscis begins to be formed,
the shape of the bud gets elongated, cylindrical, and at the same time two
opposite tentacles push out on its free margin. The proboscis has a yellow
and orange color. The reddish patches of pigment near the base of attach-
ment of the immature bell persist even after the medusa has detached itself
from its connection with the lateral branches.

The different layers of the body of the medusa bell (Plate IV. Fig. 4) can
be readily seen through its transparent walls. Of these the epiblast, hypo-
blast, and intermediate layer can be easily recognized. The origin and growth
of the radial tubes, and the subsequent formation of the circular or marginal
canal, was traced. This growth does not differ from what has alread}'^ been
described in Syncoryne (Sarssia) and several other genera.

The fish (Seriola) was kept alive in an aquarium for several days, and from
the attached hydroid many free medusiform gonophores were raised. On the
morning following the day when the fish was captured, many medusae were
found in the aquaria, and every day after its capture many specimens ripened
from the undeveloped buds, and one by one detached themselves from their
union with the gonosome. There is no possibility of a doubt that the free
medusa, as here described, has detached itself from the gonosome attached
to the body of the fish.

The free medusa (Plate V. Fig. 1), when it breaks its connection with the
gonosome, has two short tentacles situated opposite each other on the bell
margin. The medusa bell long before detachment had begun the peculiar ex-
pansion and contraction which precede separation, and when once free moves
gaily about in the surrounding water. Shortly after its detachment, the me-
dusa with two tentacles resembles a young Stomatoca.* The structure of the
Hydrichthys medusa just escaped from its attachment to the gonosome is as
follows.

The bell is oval, without apical projection, and recalls in outline that of
Sarsia. The onter surface is dotted with numerous nematocysts.f Bell walla
colorless and transparent. There are four broad radial vessels and a marginal
tube. The tentacular bulbs are reddish, without ocellus. Two tentacles arise
from tentacular bulbs diametrically opposite on the bell margin. No otocysts
on the bell margin. The proboscis is cylindrical, of an orange and yellow
color. There are patches of red pigment near its attachment. The mouth is
simple, with entire margin destitute of appendages.

* The fact that Stomatoca ie a medusa of Perigonimus was pointed out by
Haeckel, Allman, Hincks, and others.

t These nematocysts are most prominent in younger stages in the growth of
the medusa. Tliey are well marked even before the medusa form is attained.

MUSEUM OF COMPARATIVE ZOOLOGY. 229

The medusa with two opposite tentacles was raised into one with four
(Plate V. Fig. 2), passing out of the stage resembling Stomatoca into one like
Sarsia.

The form of the bell and the arrangement of tubes is unchanged in the
passage from the medusa with two tentacles into one with four. The new
tentacles form on the bell margin, half-way between those already formed.
They arise near the junction of the radial and marginal canals. All the tenta-
cles now grow to a great length, and the medusa, once very active, sinks to
the bottom of the aquarium. Its motion is from now on more sluggish than
before, either from exhaustion or habit. I was unable to raise them into
medusae with more than four tentacles.

The affinities of Hydrichthys would not be difficult to make out if we were
to deal with the medusa alone. So close are the resemblances with such gen-
era as Sarsia, Ectopleura, and other allied Tubularians, that there would have
been no doubt in my mind, if I had the medusa alone to deal with, that Hy-
drichthys is a close ally of these genera. It is the form of the hydroid which
complicates the problem in regard to the affinities of the parasite, for, so far as
the hydroids of the Tubularians allied to Sarsia are concerned, there are none
which have any resemblance to the hydroid of Hydrichthys.

11" we approach the study of Hydrichthys from the hydroid side, remember-
ing the undoubted affinities of the medusa, it seems to me that we must regard
the modifications in its structure and its polymorphism as due to the attach-
ment to the walls of its host, the fish. We know, of course, too little of the
other possible habitats of this strange hydroid to -declare that it is never found
in any other place, but the general structure of its body would seem to point
to a special modification of its structure brought about by its parasitic life.

The peculiarities of structure which separate Hydrichthys from other allied
Tubularian hydroids are the total absence of tentacles, combined with a poly-
morphism in which there are two kinds of individuals already described,
viz. botryoidal gonosomes and filiform hydranths (?)•*

In all Tubularian hydroids there are tentacles of some kind or other near a
mouth opening. In Tubularia, for instance, we have circles of tentacles ar-
ranged about a mouth, and from the intertentacular regions or intervals on the
head hang down grape-like clusters of gonophores. Suppose, for purposes of
comparison with Hydrichthys, that in Tubularia the chitinous sheath of the
single hydroid is absent, the tentacles reduced to nothing or absent, and the

* It might be supposed that the second of these are simply the main stem of
the gonosomes, stripped of lateral branches with medusa buds. The differences
in the structure of the two show the error of such a supposition. It might be
objected to my interpretation that there are two kinds of individuals in Hydrich-
thys, on the ground that the filiform bodies are undeveloped gonosomes. That
objection is also believed to be poorly supported, for young gonosomes differ
even as markedly as the adults from the filiform bodies. The designation of the
filiform bodies as hydranths is simply conjectural.

230 BULLETIN OF THE

whole head modified into the form of an elongated axis or stem. By these
changes the clusters of grape-like organs would appear as lateral branches of a
main stem ; and if we suppose the clusters of gonophores pushed out to their
tips, we should have an exact resemblance to the condition of the gonosomes *
of Hydrichthys, where they are simply botryoidal clusters of immature medusae
mounted on peduncles which arise from a common stalk. How is it with the
filiform bodies of Hydrichthys ? In reply, it may be said these do not occur
in Tubularia. Morphologically, they may be supposed to be the single simple
hydroid, stripped of tentacles, gonophores, and enveloping sheath, so that the
axis alone, with its terminal opening, is about all that remains. By this
reduction we have one of the simplest forms of hydroids. Such an individual
is certainly as low in organization as the Protohydra, Microhydra, and similar
low genera which are destitute of tentacles.

This reduction in the form^of the hydranth by the disappearance of the ten-
tacles in Hydrichthys is believed to be a degeneration brought about by its
life, and not, as in Protohydra, due to the low zoological position of the hy-
droid.f The character of the medusa of Hydrichthys and its resemblance to

* As this comparison is only in general external outlines, no account of the
fact that the gonophores of Tubularia take the form of actinulae, while those of
Hydrichthys appear as medusae, is considered. En passant, however, it might be
said that morphologically the actinula and the medusa are thought to be homolo-
gous, as several naturalists have already shown. I regard both medusa and hy-
droid as a modification in different directions of an ancestral form which is most
closely adhered to in a stage of the Siphonophores to which I have given the name
"primitive larva," or " primitive medusa." Morphologically considered, a medusa
and a simple hydroid are homologous, as shown by a study of Stephanoscyphus
( Allman), Cunina, the young of Agalma as compared with the young Nanomia, and
other genera. This identity, in a morphological way, of medusa and hydroid has
long been recognized, and was pointed out many years ago by Claus and others.

The egg in its development may pass into one or the other of these homologous
stages. It may become fixed to a submarine object, and become a fixed hydroid;
it may pass into a free medusa or medusiform condition homologous to a hydroid,
as in Glossocodon or in Agalma ; or it may be developed into a parasitic Hydrich-
thys. It seems probable that, as I have already elsewhere shown, the attached form
of the medusa or the hydroid is a secondary condition, and that the primary con-
dition is a direct development from the egg to the adult medusa. I would regard
the ancestral form of metagenesis to be the development of the " primitive me-
dusa," from an organism with both hydroid and medusan affinities, directly from the
egg without attachment. From that medusa, — which I would call and have else-
where named the primitive medusa, — in some instances, free medusiform gono-
phores bud, as in Agalma; in other cases, the primitive medusa becomes attached,
and is modified into a hydroid from which free gonophores separate ; while in still
other cases, Nanomia, the primitive medusa is neither medusiform nor attached
hydroid-like, but planula-like, with a float. The primitive medusa is homologous
in all these changed forms.

t There is no reason to suppose that non-tentaculated genera allied to Hydra

MUSEUM OF COMPARATIVE ZOOLOGY. 231

Sarsia shows that the affinities of the genus are higher than its hydroid would
seem to indicate. There is a pretty close likeness between most of the hy-
droids of the medusae to which the Hydrichthys medusa is allied. This radical
departure in Hydrichthys in the form of the hydroid itself may have a mean-
ing, and the exceptional' anatomy is thought to be due, at least in part, to its
parasitic life, especially as the medusa is so closely allied to other tubularian
medusii'orm gonophores. In the development of the egg of Hydrichthys, it is
supposed that the planula, instead of fastening itself to some submarine oVjject,
becomes attached to the fish. The necessities for the development of tentacles
would be reduced from the fact that the fish (Seriola) carries the hydroid
about, and perhaps furnishes sustenance for the parasite from its own body.
As a result, the hydroid sufi'ers a degeneration, or remains in a degraded
condition.

The needs of procreation, however, still remain, and the necessity for the
locomotion of the sexual zooid and the organs for the development of new
individuals is in no way diminished by the parasitic life of the hydroid. In-
stead of being reduced in size, they are, if anything, enlarged in number ; and
as the medusiform gunophoi'e separated from the gonosome is placed under
exactly the same conditions as that of any fixed hydroid, it retains characters
of its near relatives.*

Hydrichthys has certain features in the anatomy which recall the floating
hydroid, Velella. The gonosomes resemble in several particulars the sexual
bodies of Velella, and the free medusa is not very diff'erent from Chrysomitra,
the medusa of Velella. The flat basal disk also of Hydrichthys has points of
resemblance to the basal plate and the ramifying tubes on the under side of
the float in the well-known V. spirans. In the polymorphism of the two there
is some likeness. In Velella we have a single non-tentaculated "central
polyp," or pojypite, surrounded by many sexual bodies, or gonosomes. We
have in Velella, moreover, two kinds of individuals, which is perhaps the
simplest kind of polymorphism anywhere known among Siphonophores,
except in the kindred genus Porpita. In Hydrichthys we also have two

ever have a free medusiform gonophore. They probably have a development
like Hydra, and are destitute of special locomotive zooids.

It is, of course, an open question whether Hydra and Protohydra are nearer the
ancestral type than other hydroids. It is not unlikely that they are degenerate
forms, and not ancestral. The peculiarities of their habitat in fresh water might
have led to their low zoological position. As a question of opinion, the author
regards them as phylogenetically low, and nearer the ancestral form of hydroids
than Syneoryne and others.

* Those who have studied the Hydromedusae have for the most part based
their classifications either on the form of the hydroid, or the form of the medusi-
form gonophore. Both are in error if they rely upon either hydroid or medusa
alone as a basis of classification. Hydrichtliys certainly sliows that this is true ;
for, if known from the hydroid alone, it might he placed in a zoological position
very far from that which its medusa would indicate as its true one.

232 BULLETIN OF THE

kinds of individuals : the gonosonaes, which are similar to the sexual indi-
vidual of Velella, and the " filiform bodies," which closely resemble the cen-
tral polypite of Velella and Porpita. If this likeness between the parasitic
Hydrichthys and the free-swimming Velella is a morphological one, it may
throw new light on the relationship of the hydroids and Siphonophores. The
parasitic nature of the life of Hydrichthys leads us to compare it with the
strange Coelentrate organism, Polypodium hydriforme, also parasitic, described
by P. Owsjannikow,* and later by O. Grimm,f in the ova of Acipenser. The
resemblances between the two are, however, of a most distant kind, and the
affinities of the two are slight.

The only stage in the life history of Polypodium which can be homologized
with Hydrichthys is the hydroid stage, the cylindrical hollow tube covered
by buds. This is the spirally twisted tube with numerous lateral append-
ages, figured by Ussow % in Figs. 1-5. If we suppose the hydroid of Hy-
drichthys to have the lateral branches reduced in size, the buds brought to
the side of the main axis, and the main axis itself closed at either end, flexi-
ble, and motile, we should have something similar to what exists in the first
stage of Polypodium, found in the egg of the sturgeon. I cannot, however,
believe that the likeness is very close between them, although the form of both
is undoubtedly due, in part at least, to their parasitic life on the animals with,
which they are associated.

When we come to compare the organism formed from Polypodium by the
breaking up of or budding from the stem, and the relatively highly organized
Sarsia-like organism (medusa) derived from Hydrichthys, we find little like-
ness between them, judging from the figures of Polypodium given by Ussow,
and my own. I am therefore convinced that the affinities of Hydrichthys and
Polypodium are very remote, and that parasitism has affected them in very
difterent ways,§ so far as the modifications in their anatomy are concerned.

Turris episcopalis, Fewkes.

This beautiful medusa was found in great abundance at JNorth Head, Grand
Manan. The few specimens of this genus which have been found at New-

* Arbeiten der dritten russischen Naturforscherversammlung in Kiew. Refer-
ence : Zeit. Wiss. Znol., XXIL 292 ; Me'langes biologiques de I'Acad. dea Sci. de
St. Pe'tersbourg, 1871.

t Arbeiten der Naturforschergesellschaft zu Petersburg, 1873.

J Morpliologisches Jahrbucb, XII. 137-153; Ann. Mag. Nat. Hist., XVIII. 110-
124, PI. IV. It is of course not impossible that Hydrichthys may be a transition
form between true hydroids like Tubularia and Syncoryne on the one hand, and
the extremely modified genus Polypodium on the other. The author does not
deny this possibility, although the relation of the two is distant.

§ The amount of modification in tlie structure of Polypodium would naturally
be very much greater than in Hydrichthys, on account of its peculiar habitat
inside the fish.

MUSEUM OF COMPARATIVE ZOOLOGY. 233

port, R, I., from one of which the type was described, are evidently stragglers
from cold water, where they are abundant, and not from the warm waters of
the Gulf Stream, from which they have yet to be taken.

MelicertuEQ campanula, Esch.

This large and beautiful medusa is one of the most common at Grand
Manan.

Specimens of the young in all stages of growth were easily collected. These
are found to have been well described by Agassiz, and nothing of value was
added to his observations.

Nemopsis* bachei. Ao.

Staurophora laciniata, Ag.

This beautiful medusa is common at Grand Manan. It grows to a large
size, and is one of the most conspiciious genera in sheltered bays near the
north end of the island. I have also found several large specimens of Stau-
rophora at Frye's Island, New Brunsvvick.t

Halopsis ocellata, A. Ao.

Plate III. Fig 1.

The genus Halopsis was found quite abundantly near the wharfs at Grand
Manan. The specimens which were taken differ somewhat from the figures
and description of the type, but evidently belong to this species.

The bell, in several specimens, is from four to six inclies in diameter. Its
walls are thick, without apical prominence. The radial canals arise regularly,

* Sometimes erroneously written Mnemopsis. The derivation is vfjiua. tentacle,
and oi|/(y. The use of the wrong speUing is liable to lead to confusion with the
Ctenophore, Mnemiopsis.

t In the surfajCe fishing at Frye's Island, New Brunswick, several interesting
larvae were found with Staurophora. Among these were many specimens of the
singular worm ' rva, Mitraria. These larvae were taken in great abundance in
July, and were generally captured with tlie Miiller net in night fishing. In
Narragansett Bay, Mitraria is not found. Tiie problematical affinities of this
singular worm larva, and its abundance in Passamaquoddy Bay, would seem to
invite naturalists to observations upon its development.

Swarms of an Appendicularia different from tliat found at Newport were also
observed at Grand Manan and Easfport. The body of the Grand Manan Appen-
dicularia is larger than the Newport, and more dumb-bell-shaped, the tail arising
from the middle of the body.

234 bullp:tin of the

not in four groups,* from the stomach cavity. Sexual glands are situated or-
dinarily as described, but often have a bright pink color instead of white.

Otocysts large, compound, as already described in Halopsis by A. Agassiz.
This medusa is very abundant at Eastport, Me., as well as at Grand Manan,f
where it seems to occur during the whole summer. No subject would better
repay investigation than that of the histology of the " compound eyes." or
otocysts, of Halopsis.

Oceania languida (Ag.)4 A. Ag.

An Oceania similar to 0. languida was found in abundance near Eastport,
Me. A few specimens occurred at North Head, Grand Manan.

Obelia, sp. ?
An unidentified Obelia is common at Grand Manan.

DISCOPHORA.
Cyanea arctica. Per. et Les.

Nowhere on the Atlantic coast, except at Eastport, Me., have I seen such
magnificent specimens of this medusa as near the landing-place at North
Head, Grand Manan.

Aurelia flavidula, Per. et Les.

The Aurelia aurita described by Stimpson from Grand manan is evidently,
as already pointed out by A. Agassiz, the A. fiavidula, Per. et Les. Speci-
mens were found at North Head in considerable numbers, and of great size.

Callinema, Verrill,

Plate VI.

Since its discovery at Eastport by Prof. A. E. Verrill, the interesting genus
Callinema has not been studied, although Eastport has been repeatedly visited

• In this respect ray specimens differ from tlie type.

t This is thought to be the first mention of Halopsis from localities north of
Massachusetts Bay, on the New England or New Brunswick coasts.

X Name languida used by L. Agassiz in 1862 in " Contributions to the Natural
History of the United States." A special description of 0. languida, with figures,
is to be found in " North American Acalepha;," by A. Agassiz. The specimens
studied closely resemble the types.

MUSEUM OF COMPARATIVE ZOOLOGY. 235

by naturalists. No additions worth mentioning to our knowledge of this
extraordinary genus has been made since Verrill's original paper. Prof. Ver-
rill collected Callinema on two different occasions, and he records that he
found three specimens in all. In the sunmier of 1885, I also found this jelly-
fish among the Eastport wharves, and took a single specimen.

My specimen of Callinema was collected under most unfavorable circum-
stances. The water was very rough, and it was with great difficulty that I
succeeded in capturing the medusa and bringing it on shore. When the genus
was first seen it was mistaken for a Cyanea, and before its capture it was re-
garded as a new specimen of Zygodactyla. It was only later, when brought on
shore, that it was possible for me to detect its true relationship, and to estab-
lish its identity with the rare Callinema.

This genus is one of the most extraordinary found on the New England
coast. It is believed that an extended account of its anatomy is necessary,
not only to show how distinct it is from a Pacific Ocean relative, H. ambigua,
but also to afford a means of comparison and determination of the systematic
position of a Mediterranean ally, called by Haeckel Phacellophora sicula.

The original description* of Callinema by Prof. Verrill is concise, and
leaves no doubt as to the form of the more important organs of his genus.
Unfortunately, his account is unaccompanied by figures, so that some details
of structure need illustration to render his description clearer. Since my re-
discovery of Callinema, Prof. Verrill has sent me woodcuts representing por-
tions of the disk and tubes, and part of a tentacle, so that I can easily
follow his written description as far as these organs are concerned. There is,
however, still believed to be a call for the publication of figures of the medusa
as a whole, to show the relationship of the parts. In the present description
I have simply tried to emphasize certain details of structure, barely touched
upon in the original accounts, and to figure the outlines of the medusa as a
help to future investigators.

Callinema ornata, Verr.

Disk (Figs. 2, 3) flat, thick, with rounded apex, fourteei) inches in diam-
eter.f The margin of the bell hangs downwards when the medusa is in
motion. The external surface of the bell (Figs. 1, 2) is covered with small

* Description of a Remarkable New Jelly-fish, and two Actinians, from the Coast
of Maine. Am. Journ. Arts and Sci., Vol. XL VIII. pp. 116-118. See also Ann.
Mag. Nat. Hist., Vol. IV. p. 161.

Haeckel (System der Medusen Acraspeden, p. 643) prints a condensed notice
of Callinema, under the name Phacellophora, but does not mention Prof. Ver-
rill's original description in the American Journal. Verrill's description in the
" Annals and Magazine of Natural History," used by Haeckel, is, however, the
same as the original account.

t One of Verrill's specimens was eighteen inches in diameter and another ten.

236 BULLETIN OF THE

warts or papillae. Walls of the bell transparent, with conspicuous radiating
tubes.

The radial tubes (Fig. 3) are of two forms: those which lie in the radius of
the sense bodies, which are more or less anastomosing and branching ; while
those in intermediate sphaerosomes are unbranched, straight, and almost paral-
lel with each other. Tubes broad, slightly brown color, extending from the
stomach cavity to the marginal vessel. There are sixteen sets of anastomosing
tubes and the same number of unbranched vessels. The former lie in the radii
of the sense bodies of the bell margin. The marginal vessel is continuous,
obscurely sinuous, broad, without lobes.

There are sixteen hooded (Fig. 5, v) sense bodies on the bell margin. Each
marginal sense body (o) is pearl-white and conspicuous. The intimate structure
is like that of P. sicula, described by the Hertwigs.* The rim of the bell
between each pair of marginal sense bodies (Figs. 4, 5) is filled by a broad lobe
(rt, b), the margin of which is indented and incised or scalloped. The sixteen
marginal lobes are separated by deep incisions, at the deepest part of which lie
the marginal sense bodies. The marginal lobes are penetrated by blindly end-
ing vessels or tubes (cr), which arise from the circular tube (cl) between and
among the tentacles. These blind tubes of the marginal lappets are sometimes
slightly bifurcated at the end, and sometimes send off small lateral serrations.
They are never branched, nor anastomosing. The tube which arises from the
marginal circular vessel in the radius of the otocyst divides into three divisions
shortly after it leaves the point of origin. The median, or smallest of the
three divisions, extends into the cavity of the style of the otocyst (o). Tbe
two lateral divisions (ch) are somewhat bow-shaped and follow along the side
of the cleft in which the margin of the bell is incised for the otocyst. The
cavity of the two bow-shaped divisions (ch) is entire on the inner border, and
more or less serrated on the side turned toward the marginal cleft in which the
otocyst lies.

The tentacles (p) are numerous, and arise, not from the edges of the mar-
ginal lappets, but from the neighborhood of the circular marginal vessel {cl).
The tentacles vary very greatly in size, and are placed side by side (Figs. 3, 4)
along the circular tube into which, alternating with the marginal vessels, they
o])en. Each tentacle is long and somewhat flat, with a finely scalloped double
edge of white color. There are from eight to ten tentacles between each pair
of marginal sense bodies.

The mouth lobes (ga) resemble those of Cyanea, and consist of folded cur-
tains of yellow and brown color. The walls of the actinostome are more or
less extended outward (Fig. 1), and the lips are entire.

There are eif^ht large sexual bodies (sp) hanging at the base of the mouth
parts near their attachment. These structures are prominent and have a
brownish color. The sexual filaments are large and conspicuous.

No other species of Callinenia, or of the closely allied Phacellophora, has

* Nervensystera and Sinnesorganen der Medusen, pp. 113, 114.

MUSEUM OF COMPARATIVE ZOOLOGY. 237

been taken in the Atlantic or in the Mediterranean, with the exception of the
problematical P. sicula, Haeck., from Messina.

In his original description Prof. Verrill suggests that Callinema is allied to
Hecccedecomma ambiguum, Brandt, of the North Pacific, but finds that the
Eastport species differs from the Pacific in the shape and character of the ten-
tacles, the marginal lobes, and ovaries, and that the figures of the Pacific form
have much more complicated mouth-folds. I agree with Professor Verrill in
his conclusions in regard to the differences between the two medusae, and find
his medusa specifically dift'erent, not only from the published figures of the
Pacific Phacellophora, but also from specimens themselves, some of which were
collected on my recent visit to the Pacific coast. It is also believed to be
generically different from Heccaedecomma.

Haeckel* suggests that Callinema is a new species of Phacellophora There
are close likenesses between Callinema and Phacellophora, and also differ-
ences which seem great enough to give the name Callinema a generic worth.
Haeckel, however, regards these differences as specific only, and regards Calli-
nema as a new species of Phacellophora. In the same genus he places three
other species, camtschatica, Brandt, ambigua, Brandt, and sicula, Haeckel. I con-
sider, as stated above, that there is a generic difference between Callinema and
the first two species. Of the third species, from Messina, there are no special
lescriptions, and no figures of the medusa as a whole, and we are wholly in the
ilark in regard to the structure of the mouth parts. What is known from the
notices by the Hertwigs f — the figures are of a quadrant of the bell and an en-
larged sense body — would lead me to suppose that his medusa is very close to
Callinema. It would seem to be a species of Callinema allied to 0. ornata.
Until we know more of its general anatomy, we must remain in doubt whether
it is more closely allied to Phacellophora or Callinema. I can heartily agree
with Haeckel that an exact study of the structure of the medusa considered by
Hertwig is very desirable. The author believes that histological researches
lose some of their value if not preceded by an accurate specific identification
or specific description of the animal studied, if it is different from known
species.

*.Das System der Medusen. Acraspeden, p. 643.

t Nervensystem und Sinnesorganen der Medusen, pp. 113, 114, Taf. IX. Fig.
15, Taf. X. Fig. 16.

Cambridge, October, 1887.

238

BULLETIN OF THE

EXPLANATION OF THE PLATES.

PLATE L

View of Nanomia cara (life size).

f-

Float.

nc.

Nectocalyx,

7-

Sexual bell.

ns.

Nectostem.

hph.

Hydropliyllium.

og.

Oil globule.

ht.

Hydrocyst.

P-

Polypite.

h ta.

Tentacle of the hydrocyst.

ps.

Polyp stem.

k.

Retracted tentacular knob.
PLATE IL

ta.

Tentacle.

Nanomia cara, A. Ag.

c/. Stiff projections at the distal end

of the embryonic tentacles.
1 cl. )

} First and second cleavage planes.

Terminal filament of the adult
tentacular knob.
ht. Hydrocyst.
h ta. Tentacle of tlie hydrocyst.

2 c/

n.

tnv, Involucrura of adult knob.

Ic. Lateral nematocyst of the em Dry -

onic knob.

07. Oil globule.

ped. Peduncle of the tentacular knob.

pi. Protoplasmic elevation.

sac. Sacculus.

Fig. 1. Egg with the primitive furrow almost formed, showing superficial proto-
plasmic envelope and protoplasmic network.

Fig. 2. The same, a little younger.

Fig. 3. Two-cell stage.

Fig. 4. Four-cell stage.

Fig. 5. Four-cell stage turned in another plane.

Fig. 6. Beginnings of the furrows which form the eiglit-cell stage.

Fig. 7. Hydrocyst of Nanomia found detached from the parent stem.

Fig. 8. Embryonic tentacular knob.

Fig. 9. Adult tentacular knob.

MUSEUM OF COMPARATIVE ZOOLOGY. 239

PLATE in.

Fig. 1. Upper portion of a taster of Nanomia, showing the so-called oil globule
forming a protuberance on one side The tentacle is not represented

Fig. 2. Four nectocalyces of Nanomia, showing their mode of fitting together.
The stem is shown through the sides of the " horns," or gelatinous
extensions of the nectocalyx. The sinuous tubes are the lateral chym-
iferous vessels. The radial tubes, which pass directly, without a sinu-
ous course, from the tube wb>'-b joins the system to the stem, are not
shown.

Fig. 3. Ualopsis ocellata (side view).

PLATE IV.

Fig. 1. A fish {Seriola zonata) with Hydrichthys attached to its side and anal
region.

Fig. 2. Single cluster of gonophores separated from attachment to the basal plate
by which the whole colony is united to the fish. The attachment is at
the lower end. Medusa buds in various stages of development are
shown at the ends of the lateral branches. Each attached colony has
a large number of bodies like Fig. 2 scattered irregularly on the basal
plate. The structure represented in Fig. 2 is described as the gono-
some of Hydrichthys.

Fig. 3. Single filiform body of a Hydrichthys colony.

Fig. 4. Section (optical) of a medusa bud of Hydrichthys. The two projections
on the left are the opposite tentacles, which have an internal cavity
communicating with radial tubes, two of which are represented. The
two spurs from this cavity which arise near the bases of the tentacles
are the beginnings of the circular canal. The large cavity at the centre
of the bell is the cavity of the proboscis. The slit-like cavity separated
from the cavity of the proboscis by the thick layer and the thin layer
which lines the former, is the future bell cavity.

Fig. 5. Enlarged end of the filiform body of Hydrichthys, showing the orifice open
and a round mass (food ?) in its cavity.

PLATE V.

Fig. 1. Adult medusiform gonophore of Hydrichthys with four tentacles (side
view). This medusa was raised from the hydroid, and is supposed to
be not much younger than the adult.

Fig. 2. An immature medusa of Hydrichthys found in the aquarium on the morn-
ing after capture. Raised from the Hydrichthys in countless num-
bers. (Side view.)

Fig. 3. View of the last-mentioned from actinostomal region. This medusa is
a very little younger than Fig. 2, since the two stumpy tentacles have
not yet begun to appear.

240 BULLETIN OF THE MUSEUM OF COMPAKATIVE ZOOLOGY.

PLATE VI.

Callinema ornata, Verb.

a. Jfortion of the marginal lobe adjoining the marginal cleft in which the otocyst
lies. Tlie separation of this lobe from the remainder of the marginal lappet
is indicated by a slight depression in the margin or rim of the lappet

6. Intermediate portion of the marginal lappet between two indentations which
separate it from a.
Of the two regions of the margin of tne umbreiia, a may oe called the ocular
lappet and b the velar lappet.

ch. Vessel arising from the marginal tube and blindly ending in the ocular
lappet.

cr. Vessels of the same character as the last in the velar lappets.

cl. Marginal or circular chymiferous tube.

ga. Oral folds

0. Otocyst, or marginal sense body.

p. Tentacle.

sp. Sexual organs.

t*. Hood over the marginal sense body.

Fig. 1. Side view of Callinema, bell contracted.

Fig. 2. Same, bell more expanded. (The tentacles are cut off in Fig. 2 and more

or less retracted in Fig. 1. Half of the figure drawn in outline.)
Fig. 3. View of the anastomosing and unbranclied radial tubes, seen from above.

(Tubes drawn in a quadrant of the bell.)
Fig. 4. Section of the bell margin, including a velar (h) and an ocular lappet {a).

This fifjure shows also the relative position of the otocyst, tentacle, and

blind tubes of the marginal region.
Fig. 5. A section of the bell margin of the same specimen from which the last was

drawn (shown from a different spheromere).

All figures except Fig. 1, Plate IV., were drawn from nature by the author.
The pen and ink sketches of Plate III. Fig. 3, and of Plates IV. and V., were
made by Mr. S'. W. Denton. All the others are by the author.

"^^■"i^

1*'>^-^

^xr7^7*W-^'-

.,^-^

^H

\

r

KEWKi'.^; M ;•: 1 1 iJ n ,3c.

m^iJijjwfiTy^^^

\ \

'•^■..

\^-a.'*,;: . ..V

II- I'i

ITvVKL■.s,^l!"ln''^^..

Pl.IV.

S!lW»S™S

2.

Ti:\vus.MTDVs/^.

PlV.

.S^

^^0^

%■ ■ ■#

\L-^

// «

'\V=»

%.

V

y

\

'•-■-. K

V

^ f

/"

'V

^ *

l )

5.

., \

\

\

N

.y

y

V

ItoslMii ril,,|,n;i,,^ .,„ ( ',,

242 BULLETIN OF THE

These may be properly termed anterior and posterior tympanic vacu-
ities, or foramina, corresponding to the foramen lacerum medium and
foramen lacerum poster ius basis cranii of anatomists. Plate II. Figs. 9,
10, a.

2. " Orbito-nasal " includes the vertical plate of the palatine, and
the margins of the palatine, maxilla, alisphenoid, orbitosphenoid, and
frontal, at their lines of juncture, as also the combination of certain
foramina. Plate II. Fig. 7, a, b.

3. " Palatine " designates the anterior and posterior portions of the
palate, one or both. Plate I. Figs. 1, 2, a, b.

4. " Facial " includes the side wall of the face, the latero-nasal por-
tions of the maxilla, and the anterior root of the zygoma. Plate II.
Fig. 8, a. Plate I. Figs. 3, 5, a, b.

5. The " Occipito-squamosal " is the space comprehended between the
supraoccipital, exoccipital, and squamosal. Plate II. Fig. 11.

6. The " Squamosal " and " Parasquamosal " are indicated by the
terms used. Plate I. Fig. 4, b.

Ihe cranial vacuities in the various orders of the Mammalia occur
as follows.

MoNOTREMATA. — The skull of the Echidna presents no vacuities. In
the Ornithorynchus, there are relatively large anterior and posterior
deficiencies, the first representing the foramen ovale, and the second
the jugular and the prsecondyloid foramina combined. There are also
small ones in the basisphenoid.

Marsupialia. — Many of the Macropodidse have large posterior palatine
vacuities. These are present also in Phascolarctos (Plate I. Fig. I, a),
in the Dasyu^'dag (Plate I. Fig. 2, a, b), and in the Peramelidae. Pera-
meles lagotis has a large oval vacuity which extends from the second pre-
molar to the penult molar, and posterior to this are found several small
ones. In the Didelphidae there are large posterior palatine vacuities.

Edentata. — This order is singularly free from cranial deficiencies.
In the Dasypodidse the posterior tympanic vacuity, or foramen lacerum
posterius, is somewhat enlarged. Among the Sloths, Cholo?ptis hoffmanni
presents considerable deficiencies in the basi-sphenoidal region.

Chiroptera. — In a few genera, notably in Pteropus, the posterior
tympanic vacuities are large.

Insectivora. — In some of the Erinaceidae, the post-tympanic are
large, while there are also extensive post-palatine vacuities, especially in
Erinaceus europceus. In Sorex, large latero-basal ones are found, and
Tupaia has a large longitudinal 'central deficiency of the malar, in addition
to the palatal vacuities.

MUSEUM OF COMPARATIVE ZOOLOGY, 243

RoDENTiA. Lagomorplia. — In the Hare, at the posterior portion of
the inter-orbital septum, the foramen, which serves as a common outlet
of the optic nerves, is sufficiently enlarged to constitute a vacuity.
There are also large vacuities extending from each orbit into the
latero-nasal regions ; these being covered externally by the singularly
reticulated plate of the maxilla. (Plate I. Fig. 3, a, b.) Pre- and post-
palatine deficiencies reduce the palate itself to a mere narrow bridge
extending across between the premolars.

Sciuromorjiha. — In the Sciuridse, there is a small orbito-nasal defi-
ciency. In Castor fiber there are large anterior tympanic spaces.

Myomorpha. — The anterior root of the zygoma presents a vacuity
in very many of the Rodentia (Plate I. Fig. 4 a), and in the Rats gen-
erally this is vertical and dilated superiorly. In Fiber zibethicum^ the
malar vacuity is large, and there is also one in the posterior process of
the squamosal (Plate I. Fig, 4 b), which is also present in several of
the Muridae. In Lagostomus, a tliin bony plate separates the infra-
orbital foramen from the antorbital vacuity.

Hystric.omorpha. — In the Porcupines generally, and especially in
Erethison dorsatus, the infra-orbital as also the ante-tympanic vacuities
are large. In the Capybara, the former is immense. In Chinchilla a
large deficiency also occurs in the parasquamosal region between the
alisphenoid, parietal, and tympanic. (Plate I, Fig. 5, a.) In Paca, the
foramina, rotundum, and lacerum anterius combine to form a capa-
cious orbito-nasal vacuity,

Carnivora. Pinniped ia. Phocidce. — Large latero-posterior oasal de-
ficiencies occur in all, while in some, as in F. vitidina, P. groenlandica,
and F. fcetida, there is in addition to these a more or less extensive per-
foration in the basioccipital. (Plate I. Fig. 6, b.) In the orbito-nasal
region, not only is the spheno-palatine foramen much enlarged, but a
deficiency occurs at the juncture of the maxilla, palatine, and frontal,
often attaining a large size. (Plate II. Fig. 7, a.)

Otariidce. — The foramen lacerum posterius is miich enlarged, while
the orbito-nasal vacuities are extensive, in this family. In Zalophus
and Callirhinus, in addition to the above, there are large vacuities at
the juncture of the vertical plate of the palatine with the alisphenoid and
orbitosphenoid. (Plate II. Fig. 7, b.)

Rosmaridce. — In the Walruses there are large orbito-nasal and pos-
terior tympanic vacuities, while the anterior root of the zygoma is
largely dilated.

Fissipedia. — In this sub-order, with very few exceptions, no vacuities

244 BULLETIN OF THE

occur. In Enhydra (Sea Otter) the post-tympanic fissure is larg-? ;
there is also an orbito-nasal deficiency. The infra-orbital opening is
capacious.

Ungulata. Artiodactyla. — In many of the Ruminants, as in the Cer-
vidse, CamelidtTe, Antilocapridse, and in some of the Bovidse, as in Anti-
lopinae and Caprinse, a large facial vacuity exists at the juncture of the
frontal, lacrymal, malar, and nasal bones, which leads into the nasal
cavities. (Plate II. Fig. 8, a.) "Where the upper incisors are entirely
absent, the anterior palatine foramina assume large proportions, becom-
ing veritable deficiencies. In some of the Cervidae, as in Rangifer,
Alces, and in Antilocapridse, a more or less extensive orbitonasal vacuity
exists at the juncture of the vertical plate of the palatine, alisphenoid,
and lacrymal. In Suidse and Dicotylidse the foramen lacerum viedium
is large, and in Hippopotamidae both ante- and post-tympanic foramina
are capacious.

Perissodactyla. — In the Equidse, the anterior and posterior tympanic
foramina with the ovale combine to form an extensive deficiency in the
postero-lateral basal region. (Plate II. Fig. 9, a .) In the Rhinoce-
rotidse, the foramina, ovale, and lacerum medium are combined. There
is also a considerable orbito-nasal vacuity, as well as one formed by
the combination of the two anterior palatine foramina.

In Tapiridse, the anterior, posterior tympanic foramina, and the ovale
are joined, as also are the anterior palatine, as in the Rhinocerotidse.

SiRENiA. — In the two genera Manatus and Halicore, which consti-
tute the present order, the entire latero-posterior basal region, between
the occipital and alisphenoid, may be considered as a vacuity, so imper-
fectly is it filled by the tympanic and periotic. (Plate II. Fig. 10, a.)
In the later-ooccipital region, at the juncture of the squamosal with
the supraoccipital and exoccipital, a large vacuity also exists, very im-
perfectly filled by the periotic. (Plate II. Fig. 11, a, b.) The dilatation
of the supraorbital foramen is also large, and there are extensive ^orbito-
nasal openings.

Hyracoidea. — In Hyrax, the anterior tympanic deficiency is rela-
tively large.

Proboscidea. — In the Elephant, the tympanic deficiencies so uni-
formly present in the odd-toed Ungulates can scarcely be said to exist.

Cetacea. — In the Odontoceti, and notably in the Delphinoidse, large
irregular openings exist between the recess which holds the united
tympanic and periotic and the cranial cavity. The optic foramen, as
it passes out through the orbitosphenoid, is much enlarged, being

MUSEUM OF COMPARATIVE ZOOLOGY. 245

converted in some instances into a vacuity. Upon the latero-extemal
walls of the posterior uares large oval notches or deficiencies occur.

Primates. — The sphenoidal and sphenomaxillary fissures in man, as
also the foramen lacerum medium, which is often very large and irregular
in shape, come under the second category of vacuities. The same also
applies to the anterior tympanic of the higher Apes.

In studying the etiology of these cranial vacuities in the Mammalia.;
it would seem at first sight, especially if the imperfect osseous condition
of the skull in many of the lower Vertebrates be taken into consideration,
that their existence was due to phylogenetic degeneration, taken in
the widest acceptation of the term. A closer study of the conditions
presented, however, apparently limits this degeneration to one of en-
vironment. Take as an illustration the Pinnipedia, in which group
the economy of nature as regards the disposition of material is admira-
bly shown. These true Carnivora have become adapted to an exist-
ence in water. Consequent changes suited to this aquatic life have
been undergone. The thick skull of the Fissipedia is no longer neces-
sary ; consequently the cranial walls have become much thinned, and
several large and extraordinary vacuities in different regions, notably
in the basal, have been formed.

A reduction has taken place in the number and strength of the teeth,
and other characteristics of the order have been materially altered or
entirely lost. These changes have been foreshadowed in the Enhydra
(Sea Otter), as has already been noted.

So also any diminution in the strength of the cranial walls of the
ancient branch of the Ungulata, the Sirenia, due to large deficiencies,
is counterbalanced by the aquatic habits of the order.

In the Rodents, the alveolar border of the maxilla is pushed far back,
and thus the unoccupied space between the incisors and premolars is
relatively large. This absence of teeth necessitates only a small supply
of bony material in the immediate region, so that in the case of the
Hare, which feeds upon a succulent diet, little strength or resistance is
demanded, and consequently large vacuities are found in the latero-nasal
region. The nasal plate of the maxilla is rendered lighter by the
reticulation, which may be considered as a series of small vacuities,
while it still serves as a protection to the delicate structures beneath.
Again, the presence of the vacuity in the side-walls of the face in many
of the Ruminants, and in consequence the apparently weakened condition
of the parts, may be explained by the statement that cither the animal
is of so peaceful a nature that consolidated bones such as the frontals

246 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY.

of the Bovin^e are entirely unnecessary, or, being combative, provision
is made for purposes of offence and defence by the growth of antlers
or other horns.

Thus, without further illustration, it may be said, that while it is
difficult in the present state of our knowledge to account for the varied
character and position held by cranial vacuities, or to explain why these
should be more . frequently present in some orders than in others, and
in certain genera of an order and not in others, it may nevertheless be
safely affirmed that whenever osseous material can be set aside without
interference with the general economy, or without detriment to the
structure of the immediate parts, it is dispensed with. This general
law applies to all vacuities or deficiencies, wherever situated, in the
crania of the Mammalia.

Cambridge, January, 1888.

SLAOE. CRANIAi. VACUJTIKS

PLATE I.

1

^1

-O.

^y

iM

%lk

:r •■-U^

%^

.r

^v

i^ b

'^es'Sg,

i;..s

SL^DE. CRANIAL VACUITIBS.

PLATE i I.

^t^j^jjy^

«6»»^

id

No. 9. — The Superior Incisors and Canine Teeth of Sheep. By

Florence Mayo.*

In 1839 Goodsir (p. 83) stated that " the cow and sheep, and prob-
ably all the other ruminants, possess the germs of canines and superior
incisives at an early period of their embryonic existence."

This statement remained imdisputed until 1873, when Pietkewickz
(p. 509) denied the existence not only of the teeth germs, but also of
the so-called dental lamina. He says : " Dans une longne serie de
preparations faites sur des embryons de boeuf et de mouton, pris depuis
le moment le plus recule de la vie embryonnaire jusqu'a une longuer de
30 centimetres, non seulement je n'ai jamais constate la presence de
follicules, mais je n'ai meme jamais trouve trace de la lame epitheliale."

Legros and Magitot('73, p. 452) content themselves with simply quot-
ing the results attained by Pietkewickz, but add nothing of their own.

Somewhat later, Piana ('78, p. 222) asserts that the epithelial lamina
of the upper jaw extends to the region where the lateral incisors ought
to develop, and that the enamel germs of the canine teeth exist at a
certain stage of development, but soon abort.

Pouchet and Chabry ('84, p. 158), calling the canine tooth the fourth
incisor, admit the existence of a dental lamina in the region of the
upper jaw, which is directly over the second incisor of the lower jaw,
but claim that in front of this point it becomes gradually merged into
the crest of the plunging wall. They add : " Ainsi non seulement la
region incisive des ruminants ne presente aucun vestige de dents, con-
trairement a ce qu'on avait cru jL une certaine epoque, mais elle ne pos-
sede pas meme de lame dentaire differentiee, dans toute son ^tendue."

In view of these conflicting statements and the theoretical interest of
the questions involved, further studies upon the subject are desirable.
Therefore, at the suggestion of Prof. E. L. Mark, and under his direc-
tion, I have undertaken to re-examine the development of the teeth in
sheep embryos of different ages, hoping to be able to add something tc
what was already known. My observations are as follows : —

* Contributions from the Zoological Laboratory of the Museum of Comparative
Zoology at Harvard College, under the Direction of E. L. Mark. — No. XIII.

VOL. XIII. — NO. 9. 16

248 BULLETIN OF THE

The jaws of a sheep embryo whose length was 37 m.m. were sec-
tioned so that the plane of the first section was parallel to the median
plane of the jaw. After a small number of sections had been cut par-
allel to this plane, the object was slightly rotated, so as to keep the
plane of the sections nearly perpendicular to the outer margin of the
jaw. By thus frequently changing the plane of cutting, each section
of the series was a true cross-section of the part of the jaw from which
it was taken. This method of cutting must give more satisfactory
results than can be had by cutting either parallel or perpendicular to
the median plane of the jaw without any change in direction.

In the first of the sections of the upper jaw, in the region which
corresponds to the first incisor of the lower jaw (fig. 1), the dental la-
mina is not distinct from that portion of the buccal epithelium which
Pouchet and Chabry ('84, p. 152) have called the "mur plongeant."
But before the first incisor of the lower jaw has been passed, and in the
region of the second and third incisors (figs. 2, 3, and 5), the dental
lamina, although not sharply marked oft" from the " plunging wall," is
readily distinguishable from it. By comparing figs. 1 and 3, one finds
that the epithelial tissue in fig. 3 sinks deeper into the mesoderm than
in fig. 1 ; that the deep portion forms an angle of about 45° with the
axis of the plunging wall in fig. 1 ; and that the width of this deep
portion, that is, the distance from the base of the malpighian layer on
one side, to the base of the same layer on the other side, is less than
the width of the plunging wall in fig. 1. In fig. 3 the dotted line is
introduced to show where the boundary of the plunging wall, as it
appears in fig. 1, would fall if it were " projected " on to the plane of
this section. This deep portion beyond the dotted line, although con-
tinuous with the plunging wall, and not histologically different fi'om it,
I believe to be, both by reason of its size and its direction, the most
anterior indication of the dental lamina. In the sections through the
canine region of the same jaw (fig. 7) the conditions of the dental la-
mina and plunging wall are the same as in the incisor region.

Dursy ('69) gives drawings of several sections through the incisor
and canine regions of a sheep embryo at about the same stage as the
one just described. He says (1. c, p. 214) : " Taf. III. Fig. 1-8 zeigt
die Zahnfurche mit dem Schmelzkeim von einem Schafsfotus, dessen
Gaumen im Schliessungsprocess begriffen war ; auffallend daran ist die
Weite dor Furche und daher auch die Breite der hellen Kernmasse des
•Schmelzkeims an alien Schnitten, die somit an den zahnlosen Stellen
beim Schafe um diese spate zeit noch vorhanden ist." Dursy evidently

MUSEUM OF COMPAKATIVE ZOOLOGY. 249

disregards the existence of the dental lamina and calls it the enamel
germ, of which at this stage I find no trace. He also figures (Taf. III.
Fig. 1-9), as existing throughout the incisor and canine regions, an
area — or, as Tomes calls it, a "halo" — in the mesoderm which iu
his opinion always precedes the development of the dentine germ, and
is probably caused by a concentration of mesodermic nuclei. I have
been unable to find, in. any of the stages of development, this halo
existing in any region of the upper jaw farther forward than that of the
first premolar. The only indication of sxich a condition has been a
slightly increased concentration in the nuclei immediately surrounding
the epithelial germ, which, however, is hardly more pronounced than in
the mesoderm which abuts upon neighboring portions of the buccal
epithelium, and which is never sharply marked ofl;' on the deep side
from other concentrations of nuclei which presage the formation of
cartilage in the deeper mesoderm.

In an embryo 56 mm. long, cut in the same manner as the one just
mentioned, the dental lamina is present throughout the incisor region.
When studied with a low magnifying power (x 33), the sections through
a part of the region of the first incisor, as in the younger stage, show
no differentiation of a lamina from the plunging wall (figs. ll-H) ; but
when a higher power is used (x 175), the malpighian layer of that por-
tion of the plunging wall from which the lamina ought to proceed, is
found to present an irregular outline on the side toward the mesoderm
(fig. 30, I. big.). It is no longer a layer one cell deep, but is composed
of irregularly arranged cells, several deep. In the sections further
back, behind the middle of the first incisor, and throughout the remain-
ing incisor region (figs. 15-19), the dental lamina can be distinguished
from the plunging wall by its size and direction. Its malpighian layer
on the lingual side has undergone the same change as that just de-
scribed in the region of the first incisor. The histological condition of
the lamina in this region is identical with that which is presented at an
early stage of development by the lamina, in regions where teeth are
normally produced.*

* I find that the two walls of the dental lamina in the premolar region of tlie
upper jaw, and in the incisor, canine, and premolar regions of the lower jaw, are
histologically different. Pouchet and Chahry have mentioned this fact (pp. 154-
155), and have given the names "adamantine" and " abadamantine " to tiie two
walls of the lamina; but they do not state what the structural difference is. I
have found that the malpighian layer of the lingual wall of the lamina is several
cells deep. These cells are prismatic in form, and are compactly though irregularly

250 BULLETIN OF THE

The fact that the dental lamina in the region of the second and third
incisors is directly continuous with the differentiated portion of the
plunging wall in the region of the first incisor, and has the same histo-
logical characteristics as that portion, seems good reason for believing
that the latter is the representative of the dental lamina, which in this
region never becomes further developed ; whereas in the region of the
second and third incisors it has become prolonged, and has changed its
direction, owing to the multiplication of its undifferentiated cells.

In the canine region (fig. 20), the dental lamina at the place of its
connection with the plunging wall has become very narrow. Its width
at this jwint is very little more than the combined width of the two
malpighian layers which form its walls, the corneous layer of epithelium
being at this stage almost imperceptible. The deeper portion of the
lamina by its enlargement has given rise to an enamel germ, which,
although much smaller than the corresponding germ on the lower jaw,
has the same histological characteristics.

The next stage studied was that of an embryo 87 mm. long. The
lamina in the region of the first incisor (fig. 21) seems neither to have
advanced nor to have retrograded in development from the condition in
the embryo 56 mm. long. In the region of the remaining incisors
(figs. 22, 23) the walls of the dental lamina have become thicker, and
the corneous layer of epithelium forming its centre has undergone the
same change as in the centre of the canine enamel germ of the preced-
ing stage, — the cells are smaller and less regular in shape In the
region of the third incisor (fig. 31) the differentiated portion of the
dental lamina, together with some of the unmodified portion, has begun
to separate from the buccal epithelium ; the mesodermic tissue by its
ingrowth occupies for some extent the region which in earlier stages
was uninterrupted epithelium. Although in this condition the lamina
has a comparatively broad connection with the plunging wall, sections
through the posterior portion of the incisor region show it entirely

arranged. On account of this irregularity the layer is in some places broader than
in others, and presents an irregular outline on its mesodermic side. The labial
wall of the lamina is histologically unchanged from the malpighian layer of tiie
buccal epithelium. It is one cell deep, and has an even outline on the side toward
the mesoderm.

The lingual wall increases in extent as the result of cell multiplication and forms
the base of the enamel organ. Since the cells of the base of the enamel organ
surround the dentine germ and at length produce the enamel, it is obvious that
the lingual wall of the lamina produces, first, the enamel organ • and finally, the
enamel.

MUSEUM OF COMPARATIVE ZOOLOGY. 251

surrounded by mesoderm. Throughout the regions of the third incisor
and the canine tooth, small portions of the unchanged dental lamina
are becoming separated from the epithelium. The corneous cells form-
ing the centre of these small epithelial projections become vacuolated,
and probably disappear, leaving only the cells of the malpighian layer,
which, upon separating from the buccal epithelium, and becoming em-
bedded in the mesoderm, form insulated masses or knots, which at this
stage are very numerous. I have found an occasional knot of this kind
in other regions of both jaws ; but nowhere else have I seen so many as
in the regions just mentioned. Since similar knots or islands appear
during the degeneration of the neck of the enamel sac, I judge that
they are all produced by the active ingrowth of mesoderm ic tissue, and
are to a certain extent indications of a regressive development on the
part of the dental lamina.

Plana (p. 220) likewise believes that the disappearance of the dental
lamina in later stages is accomplished by its transformation into such
islands. Legros and Magitot (p. 469) also describe similar epithelial
knots, which are the remains of the dental lamina in the ordinary devel-
opment of teeth. Although the epithelial knots found in the anterior
portion of the upper jaw at this period are analogous to those found
.where the enamel organ is well developed, they differ from the latter,
since when first formed they consist of prismatic cells from the mal-
pighian layer. These cells gradually assume a more rounded shape,
and the knots finally become lost in the surrounding mesodermic tissue ;
whereas the knots described by Legros and Magitot, although buds from
the malpighian layer of the lamina, are claimed by them never to be
made up of prismatic cells, as is that layer, but of small polyhedral cells
which resemble those in the centre of the lamina at an early stage.
The difference in appearance of these two kinds of epithelial knots is
due, I believe, to the fact that those in the superior incisor and canine
regions are the result of the rapid breaking up of the dental lamina,
which quickly sets them free from the buccal epithelium ; whereas
those in the region of normally developing teeth are formed more
slowly, and probably as the result of a more active cell proliferation
on the part of the epithelium.

In the canine region also (fig. 32) the enamel germ is losing connec-
tion with the plunging wall, owing to the ingrowth of mesoderm, and
is slightly larger than the germ in the embryo 56 mm. long.

In an embryo 93 mm. long the dental lamina has increased in size
(figs. 34, 35), but, aside from a more marked difference between the

252 BULLETIN OF THE

labial and lingual walls, it is not histologically different from the condi-
tion in the embryo whose length was 87 mm. In the canine region
(fig. 33) the enamel germ has increased in size, and has sunk deeper
into the mesoderm. The epithelial islands now consist exclusively of
somewhat rounded cells from the malpighian layer, the corneous epithe-
lium having disappeared from them. These knots by their juxtaposi-
tion form an almost unbroken series between the enamel germ and the
epithelial plunging wall.

When the embryo has become 112 mm. long, the dental lamina in
the region of the first incisor cannot be distinguished from the plunging
wall. The cells of both the corneous and malpighian layers, which in
younger stages had become differentiated, have again attained the con-
dition of those of the plunging wall. In the region of the lateral
incisors (fig. 36) the dental lamina, though yet distinguishable, has
become much smaller and sinks less deeply into the mesoderm. Its
differentiated cells have decreased in size, — cells from the malpighian
and corneous layers closely resembling each other, — and its boundaries
are less easily discernible on account of the greater irregularity in the
arrangement of the malpighian cells. The enamel germ of the canine
tooth (fig. 37) has become at this stage much diminished in size, and
its cells are less specialized than in the preceding stages. Several of
its central cells appear vacuolated, and this suggests an explanation of
the manner in which it has suffered a reduction in size.

From the preceding account it is evident, (1) That in the embryo
sheep at a certain stage of development, the dental lamina exists
throughout the canine and incisor regions of the upper jaw. Its an-
terior portion, which is the last to develop and the first to abort, does
not attain so prominent a condition as its lateral portion. After ad-
vancing in development for a time, it retrogrades and finally disappears.
(2) That in the canine region the dental lamina gives rise to an enamel
germ which never reaches a stage of functional activity ; for neither are
its central cells transformed into a stellate reticulum, nor do those of
the malpighian layer ever produce enamel, and in later stages both
disappear.

In this region there is no trace of a dentine germ. The fact of the
existence in sheep of rudiments of such organs as usually result in the
formation of teeth, is of interest because it is one of those peculiar
structures for which it is difficult to account without the aid of the
theory of natural selection. From the observations here recorded, one

MUSEUM OF COMPARATIVE ZOOLOGY. 253

readily sees that the disappearance of the superior incisors and canines
is progressive. In the region of the incisors the evidences even of the
beginnings of tooth development have almost disappeared, the region of
the first incisor being the least differentiated portion of the tract, while
the canine region is represented by a moderately large, but functionless
enamel sac. Since in some ruminants destitute of incisors, small
rudimentary canine teeth are found on the upper jaw of the adult ani-
mal, it is a fair inference that the teeth are being lost from before back-
ward, and that the canine teeth, the last to disappear from the sheep,
are in f uch cases undergoing degeneration, although not wholly func-
tionless.

It it 18 admitted that the history of the development of the individual
reproduces, at least in part, the history of the ancestors of that indi-
vidual, and that the changes in development take place in the same
order as in the ancestors, then we have reason for believmg that the
progenitors of the rununants possessed incisors and canine teeth on the
upper jaw ; that these teeth becoming, perhaps by a change in environ-
ment, no longer necessarj'^ for obtaining food, have gradually ceased to
develop ; and that the disappearance of the teeth has been a progress-
ive process, beginning with the middle incisors and gradually involving
the teeth farther back.

Cambridge, September, 1887.

254 BULLETIN Oh THE

BIBLIOGRAPHY.

Dursy, EmiL

'69. Zur Entwicklungsgeschichte des Kopfes des Menschen und der hoheren
Wirbelthiere, Tubingen, 1869. 12 + 232 pp. mit eiuem Atlas von 9 Taf.

Goodsir, John.

'39. On the Follicular "Stage of Dentition in the Ruminants, with some
Remarks on that Process in the other Orders of Mammalia. Report of the
Britisli Association for the Advancement of Science for 1839. Notices and
abstracts of communications, pp. 82-83. London, 1840.

Kolliker, A.

'63. Gewebelelehre. Leipzig, 1863. pp. 406-424.

Legros, Ch., et E. Magitot.

'73. Origiue et Formation du Follicule Dentaire chez les Mammiferes. Jour-
nal de I'Anatomie et de la Physiologic. Tom. IX., 1873, pp. 449-503.
Pis. XV.-XX.

Owen, Richard.

'40-'45. Odontography. London, 1840-1845.

Piana, Gio. Pietro.

'78. Osservazioni intorno all' esistenza di rudimenti di denti canini ed incisivi
superiori negli embrioni bovini ed oviui. Memorie dell' Accademia delle
Scienza dell' Istnto di Bologna. Serie III., Tomo IX., Fasicolo 2, pp.
217-225. 1 Tav.

Pietkewickz, V.

'77. De la valeur de certams arguments de trasforraisme, empruntes a revo-
lution des foUicules dentaires chez les Ruminantes, Comptes rendus.
Paris, 1877. Tom. 84, No. 11, pp. 508-509.

Pouchet, G., et L. Chabry.

'84. Contribution a I'Odontologie des Mammiferes. Journal de I'Anatomie
et de la Physiologic. Tom. XX., 1884, pp. 149-192. Pis. V.-VII.

Tomes, Charles S.

'82. Manual of Dental Anatomy, Human and Comparative. Second edition.
London, 1882. 8 4- 440 pp.

Waldeyer, W.

'72. Structure and Development of the Teeth. Strieker's Manual of Histol-
ogy. New York, 1872, pp. 321-341.

MUSEUM OF COMPARATIVE ZOOLOGY.

255

EXPLANATION OF FIGURES.

The following abbreviations are used in the figures.

cnn.

Canine.

Ing.

Tongue.

crt. Mkl.

Meckel's Cartilage.

I. Ing.

Lingual side.

et.

Epithelium.

vid.

Lower jaw (and os mandi

g. de.

Dentine germ.

bularis).

g. cnn.

Enamel-organ gera

I of canine.

ms d.

Mesoderm.

g. en a.

Enamel-organ germ

1.

mur.

Plunging wall.

g. i'.

" " of first incisor.

mx.

Upper jaw (and os maxillaris)

g. i".

<< «

second "

n.

Nerve.

g. i'\

« <(

third "

0. en a.

Enamel organ.

g. pr, moi

1' (< «

first premolar.

pr. mol.

Premolar.

i.

Incisor.

St. con.

Stratum corneum.

la. de.

Dental lamina.

St. Mpg. Stratum Malpiglii.

I. lab.

Labial side.

The average thickness of the sections is about 7.5 fi, and the number of each
section in the series to which it belongs is indicated by the number in parenthesis
adjacent to the number of the figure.

PLATE I.

Figures 1-25 are magnified 17 diameters ; figures 26-29a, 11 diameters ; figures
30-37, 175 diameters. All were drawn with the aid of the Abbe camera.

Figures 1-10 are from sections of the left side of the jaws of an embryo sheep,
37 mm. long, preserved with picrosulphuric acid, stained by means of Czoker's
cochineal followed by alcoholic borax-carmine, imbedded in paraffine and mounted
in Canada balsam. The figures all show the anterior face of the sections, which
were so cut that the plane of the first section was parallel to the median plane of
the head, the object being gradually rotated so as to keep the plane of the sections
as nearly as possible perpendicular to the outer margin of the jaw.

Fig. 1 shows the plunging epitlielial wall of the upper jaw, and the centre of
the germ of the enamel organ of the first incisor on the lower jaw.

Fig. 2. On the lower jaw the section passes through the region between the
first and second incisors, where only the dental lamina is to be seen. On the
upper jaw the plunging wall is continued into the dental lamina without there

256 BULLETIN OF THE

being any well-marked division between the two. They have a slightly different
direction.

Fig. 3. A section through the middle of the region of the second incisor of
the lower jaw. On the upper jaw the dotted line shows approximately the
outline of the plunging wall of Fig. 1, as it would appear when projected on to
the plane of this section. The portion beyond the dotted line is the dental
lamina.

Fig. 4 is from a section about midway between the second and third incisors of
the lower jaw.

Fig. 5 passes through the middle of the third incisor of the lower jaw.
Fig. 6 is from the region between the third incisor and canine tooth.
Fig. 7 shows the enamel germ of the canine tooth on the lower jaw. On the
upper jaw the dental lamina can be distinguished from the plunging wall by its
size and direction, as in the preceding figures.

Fig. 8. This section passes through the region between the canine tooth and
the first premolar on the lower jaw. The dental lamina of the lower jaw no
longer appears as an outgrowth from the epithelium of the plunging wall. The
dental lamina of the upper jaw is much smaller than in the preceding sections.

Fig. 9 shows the middle of the enamel germ of the first premolar tooth of both
jaws. The asterisk marks the position of a longitudinal ridge of epithelium near
the base of the dental lamina.

Fig. 10. A section from the region between the first and second premolars.
The dental lamina is pear-shaped in section throughout this region. The lateral
ridges at the base of the dental laminae are also continued through the greater
part of the region.

Figs. 11-20 are sections througli the left side of both jaws of a sheep embryo
56 mm. long, which was treated in the same manner as tlie embryo of 37 mm.,
with the exception that it was stained in Grenadier's borax carmine only. The
sections were cut in the same manner as in the figures just described.

Figs. 11-15 are sections through the region of the first incisor of the lower jaw,
showing the enamel germ of the first incisor as it appears in different regions.
On the upper jaw the dental lamina and plunging wall are seen. Fig. 14 is
through the centre of the enamel organ of the incisor.

Fig. 16 passes between the first and second incisors on the lower jaw. The
dental lamina of the upper jaw has become broader, and its section therefore
appears more elongated.

Fig. 17 passes through the middle of the second incisor on the lower jaw.
Fig. 18 shows the dental lamina in the regions betweea the second and third
incisors.

Fig. 19. This section is taken through the centre of the enamel germ of the
third incisor of tlie lower jaw.

Fig. 20 is through the middle of the enamel germ of the canine tooth of
both jaws.

Figs. 21-25a are sections of the upper jaw of a sheep embryo 87 mm. long,
treated in the same manner as the embryo 37 mm. long. The figures show the
anterior faces of the sections through the upper jaw of the right side.

Fig. 21 shows the extent of the plunging wall and the dental lamina in a region
opposite the middle of the first incisor of the lower jaw.

MUSEUM OF COMPARATIVE ZOOLOGY. 257

Fig. 22. The same in the middle of the second incisor region.

Fig. 23. The same in tiie middle of the third incisor region.

Fig. 23a shows the appearance seven sections further back than Figure 23.

Fig. 24 is a section behind the centre of the third incisor, showing a part of
the dental lamina cut off from the buccal epithelium by the ingrowth of
mesoderm.

Fig. 25 is a section through the middle of the canine region behind the region
where there is a narrow connection of the enamel-organ germ with the buccal
epithelium.

Fig. 25a. The enamel germ is divided by the deepening of a constriction
shown in Figure 25 into two arms, the cross-sections of which appear in this
figure as two isolated patches of epithelium.

Figs. 26-29a are sections through the left half of the upper jaw of an embryo
sheep 112 mm. long, which was hardened in chromic acid and stained with
Czoker's cochineal, followed by borax carmine. The sections were made in the
same way as described in Figs. 1-10. They are magnified only 11 diameters.

Fig. 26 shows the condition of the plunging wall in the region opposite the first
incisor of the lower jaw.

Fig. 26a shows the dental lamina more sharply marked off from the plunging
■wall as seen a few (18) sections farther back than Fig. 26.

Fig. 27 is a section through the middle of the region opposite the second in-
cisor of the lower jaw, showing a small but well defined dental lamina.

Fig. 28 shows the dental lamina in the region of the third incisor.

Figs. 29, 29a, are sections through the canine region.

Fig. 29 shows the rudimentary lamina to be still continuous with the buccal
epithelium ; but four sections further back it is detached from the " wall."

Fig. 29a. Back of the canine region the lamina is continued as ajidge or fold
of epithelium, which soon changes from a horizontal to a vertical position.

PLATE IL

All figures of this plate are magnified 175 diameters.

Fig. 30. The deep portion of the dental lamina of Fig. 14. The change in
the thickness of the malpighian layer is to be seen here, also its irregularity of
outline.

Fig. 31 is a highly magnified view of the incisor region shown in Fig. 24.
The difierence between the differentiated and the undifferentiated portions of the
lamina, which are here both surrounded by mesoderm, is w.ell marked.

Fig. 32 gives a view of a portion of Fig. 25. The histological condition of the
canine germ is the same as that of the differentiated portion of the dental lamina
in Fig. 31.

Figs. 33-35 are from cross sections of the upper jaw of an embryo sheep
93 mm. long, which was treated with picrosulphuric acid and stained in borax-
carmine

Fig. 33 is a section through the germ of the canine tooth. That portion of the
neck of the germ which is nearest the buccal epithelium is resolved into a series
of epithelial knots or islands.

VOL. XIII. — NO. 9. 17

258 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY.

Fig. 34 shows the condition of the lamina eight sections behind that shown in
Fig. 36, still in the incisor region. The sections were 7.5 fi. thick.

Fig. 35 is the anterior face of a section through the incisor region, showing the
condition of the dental lamina in the upper jaw.

Fig. 36. The dental lamina of Fig. 28 as it appears when highly magnified.

Fig. 37. A portion of the section outlined in Fig. 29a. The central cells of
the germ have become vacuolated.

vt

,,i, ^ ^f^'tf^,-,

.^f'

^*"-

la.rf* ,,f(

t?'..-

^.. %..?

Mayo - Teeth.

PL. I

(IM)

F M (iei

ZT.

B Meisel, hth

]Sro. 10. — Tlie Rattle of the Rattlesnake. By Samuel Garman.

The habit of sloughing is common to all the serpents. A short time
before the removal takes place, the new epiderm makes its appearance
beneath the old. Its presence is easily detected by a whitish color
under the outer layer. The milky tint of the second layer extends over
the whole body ; on the eyeball it interferes greatly with the sight.
During the time of its formation, several weeks, while the vision is
affected, the snake prefers seclusion, and is disinclined to partake of
food. Some days before casting, about a week in the most recent case
followed, the milkiness vanishes, the skin resumes its ordinary aspect,
and the sight becomes again as keen as formerly. By rubbing the lips
the slough is loosened around the mouth, then it is pushed over the
head to the neck, whence it is taken back over the body. From the
neck backward it is, in some cases, removed by means of a coil or two of
the tail, the body being crowded through and the epiderm left behind.
A hole in the ground or between rocks, the sticks in a brush heap or
the stalks in the grass, answer the same purpose as the ring made by
the tail. Some manage to get the coat back until under the ventral
scales, when the latter are used somewhat as in gliding, their free
hinder edges catching and stripping off the slough as the body is moved
slowly forward. From the hinder part of the body the removal is an
easier matter : the loosened portion is caught around a stick or under a
stone, and with a pull the balance is taken off in an instant. The
slough comes away like damp paper; it is wet with a sticky mucus on
the inner side, turned outward in the operation. The mode of growth
and of removal is similar among the rattlesnakes. These snakes differ
in retaining a portion of each slough, that covering the tip of the tail,
to form one of the rings of the rattle. The attachment is purely me-
chanical ; the rings are merely the sloughs of the end of the tail.

On the majority of the snakes, both the venomous and the non-
venomous, the tail tapers more or less gradually to a point. At the
end it is protected by a sub-conical cap of the epiderm. Under the
latter lies the skin, and under it again the termination of the vertebral
column, — a bone formed of vertebrae that have coalesced and changed

VOL. XIII. — NO. 10.

260 BULLETIN OF THE

their shape until the outlines of the mass nearly resemble those of the
surface of the tip. This terminal bone is hard externally, and cellular
within ; it contains and protects the extremities of the cord and vessels
of the column in the positions occupied by them in the embryo before
the consolidation was effected. In the different species the number of
vertebrae included in this bone varies considerably ; sometimes, also, it
is seen to vary in individuals of the same species. Before the appear-
ance of the scale-like folds on the tail of the embryo, the skin of the ex-
tremity is smooth ; afterward, on some, the tip takes on the semblance
of being protected on the sides by scales, the distal portions of which
have blended with the cap, while their bases have remained distinct,
much as if the conical envelope were still undergoing process of enlarge-
ment. In such cases the line of demarcation between the scales and
the cap is irregular and indistinct. This condition obtains in species of
Tropidonotus, Eutsenia, Nerodia, and allies. The line of separation is
very decided and regular in Crotalus. As the tail develops more slowly,
the scales do not appear on it until after they are well formed on the
body. Up to the time of their formation, the story of the caudal devel-
opment of the rattlesnake is the same as that of any other serpent.
The general shapes and the numbers of vertebrae differ greatly in the
various kinds, but the history is similar in all. With the purpose of in-
dicating the manner of growth of the rattle, and, as far as may be, of
determining its origin, we shall have to follow it up through different
species, a complete series of any one of them not being at hand.

Sistrurus, Garm. Figs. 1-4.
Crotalophorus, Gray, not of Linne.

S. miliarius, Linn., is the only rattlesnake of which we have a good
series of the very early embryos. Some of these, alVeady three inches
in length, are not yet furnished with scales on the tail, though tlie
entire body is well provided. Outwardly, in these specimens, the tail
is short, thick, blunt, slightly compressed, and has no indication of the
characteristic feature so prominent after birth. The vertebrae are
separate.

Figures 1 and 2 of the diagrams are drawn from embryos of S. cate-
natus, Raf. (Crotabis tergeminus, Say), six and a quarter inches in length.
Their only promise of the rattle is to be noted in the shape and size of
the cap, or button. Upon the body the scales are perfect ; the button
evidently is incomplete, being little more than half of what it ultimately

MUSEUM OF COMPARATIVE ZOOLOGY. 261

becomes. If a button as it is at birth were to be cut through the con-
strictiou immediately behind the anterior swelling, the hinder portion
would correspond with the cap as seen in Figures 1 and 2. There is no
evidence of any fusion of scales with the button around its front border.
Except in case of the button, there is externally very little difference
between this stage and the next represented. Within the cap the ver-
tebrae are distinct, slightly smaller than those just in front of them,
like the latter surrounded by muscles, and the skin is thicker than else-
where. Between this stage and the following the anterior portion of
the cap appears to be added by backward growth at the front margin,
like that which la^.er in life displaces the older button to make way for
the new.

Figures 3 and 4 are drawn from young ones of the same species,
S. catenatus, Eaf , eight and a quarter inches in length, about a week after
birth. In them the button has been perfected, the cap having gained,
as compared with Fig. 2, all the portion anterior to the constriction.
On several of these specimens there is a tendency to fusion and irregu-
larity among the scales immediately in front of the button, but in no
case is there any disposition on the part of the scales to fuse with the
latter. A portion of the button corresponding to the externally visible
part of each ring has been acquired, while the entire length has in-
creased a couple of inches, in a short time just before birth. Inside of
the button the changes have been greater : the vertebrae, still plainly
outlined, have consolidated into a single elongate mass, the size of which
is being inci*eased by both lateral and terminal growth ; the vertical
processes have grown together ; and the muscles have been displaced by
the enlarging bone and the thickening skin. Muscular command of the
individual vertebrae within the button has been lost in the consolidation,
but the muscles of the tail retain a firm hold on the mass, and the loss
finds compensation in a better means of agitating the rattle. For later
stages we are compelled to turn to a closely allied genus.

Crotalus, Linne.
Crotahphorus, Linn. ; Caudisona, Laur.

Figures 5 and 6, from a Crotalus conjluentus, Say, fourteen inches in
length, show a considerable advance from the preceding. The specimen
was taken, with the third button about half grown, when the process of
pushing back the second ring was well under way. The first ring had

262 BULLETIN OF THE

been set free with the first slough, holding only by the collar ; and if
the snake had been allowed to live a little longer, the second sloughing
would have discovered the third button perfected, clasped by the sec-
ond ring, the latter pushed back and loosened from the balance of the
epiderm. Of the second ring the narrower posterior extension is quite
empty ; its anterior chambers are closely filled with the tumid skin,
the loss of the ring being prevented in this manner, while the outer
swelling of the new button is crowding it backward. A considerable
shrinkage of the skin takes place after the moult ; it is insufficient to
allow the ring to slip off, though admitting of great freedom of motion.
In front of the border of the second ring, Fig. 5, lies the fold, shrunken
by alcohol in the specimen, by which the ring was displaced, and which
was to become the largest chamber of the next succeeding. This fold is
usually hidden by the epiderm attached to the ring, as in Fig. 6, until
the operation of sloughing has been finished. The mass of bone oc-
cupies the place of eight or more of the vertebrae in this stage, the lines
of separation being still noticeable to some extent. By a longitudinal
section the cord and vessels are disclosed in their original positions, sur-
rounded now by spongy bone, in which the cavities radiate from the
centre toward the surfaces. On the upper and lower faces there is less
indication of the composition.

Figures 7 and 8 were taken from a large specimen of Crotalus hor-
ridus, Linn. In it the traces of the vertebraj in the terminal bone are
almost obliterated ; the bone has thickened, pushed forward at the edges,
and otherwise enlarged. Along with this there has been an excessive
development of the muscles of the tail. The rattle is entire, of eleven
rings and a button. The hinder seven of the rings belong to the period
of the snake's most rapid growth ; they form the "tapering rattle" com-
mon to the young individuals, formerly used in classification of the
species by some authors. Four of the rings and the button pertain to
a part of the creature's life in which the gain in size was much less
rapid ; they form the " parallelogramic rattle " of the same writers.
The mistaken use of these features in specific diagnoses no doubt arose
from study of incomplete rattles. The change from the taper to the
more nearly parallelogramic takes place about the seventh ring, — in
Sistrurus miliarius often with the sixth, with the larger species fre-
quently with the eighth, — and affords the means of obtaining an ap-
proximate idea of the comparative age of the owner of the series of
rings. The figures show the rattle as commonly held by the snake
when crawling. In a single series of rings there is much variation in

MUSEUM OF COMPARATIVE ZOOLOGY. 263

shapes, as in sizes, and there are also considerable differences in the
rattles within the species. In the case of the small snake Crotalus
exsul, Garm., from Cedros Island, Lower California, the large size of
the first ring is evidence of derivation from a larger species, probably
C. lucifer, B. & G., of the mainland. In this case, the change in button
has not kept pace with the reduction in size of body, or the changes in
squamation, etc. While the rings vary with rapidity of growth in the
body, from amount of food, it is unlikely that it makes an , difierence
in their number, or that of the sloughings.

More than seventy specimens have been looked over for evidence of
growth of a new button between the months of May and September ;
two, and a doubtful third, favor the conclusion that a ring is added in
the fall. One of these, as it was in September, is sketched in Figures
5 and 6. On the other hand, living specimens kept through the winter
prove that a new growth does take place toward spring, and that when
the epiderm is shed, on coming out of winter quarters, the animal is
possessed of an addition to the rattle.

The mechanism of the organ has been so often described and figured
that it is unnecessary to give a detailed description here. Among the
most accurate of the earlier writers is LacepMe, 1789 (Histoire des
Serpens, II. pp. 390-420, PI. XVIII.); and of the more recent, Czermak,
1857 (Ueber den schallerzeugenden Apparat von Crotalus, in Vol.
XIII. of the Zeitschrift fiir wissenschaftliche Zoologie, pp. 294-302,
PI. XII.). For comparison with what has been recorded above, a few
sentences are quoted from Lacepede (p. 404). Speaking of the mode of
growth, he says : " Quand une piec>3 est formee, il se produit au-dessous
une nouvelle piece entierement semblable a I'ancienne, et qui tend ^
la detacher de I'extremitc de la queue. L'ancienne pi^ce ne se separe
pas cependant tout-k-fait du corps du serpent ; elle est seulement re-
poussee en arriere ; elle laisse entre son bord et la peau de la queue, un
intervalle occup^ par le premier bourlet de la nouvelle piece ; mais elle
enveloppe tou jours le second et le troisieme bourlets de cette nouvelle
piece, et elle joue librement autour de ces bourlets qui la retiennent.
. . . Si les dernieres vertebres de la queue n'ont pas grossi pendent
que la sonnette s'est formee, chaque piece qui i'est moulee sur ces ver-
tebres a le memo diamctre ; et la sonnette paroit d'une ^gale largeur
jusqu'k la piece qui la termine ; si, au contraire, les vertebres ont pris
de I'accroissement pendant la formation de la sonnette, les bourlets de la
nouvelle piece sont plus grands que ceux de la piece plus aucienne, et le
diametre de la sonnette diminue vers la pointe."

264 BULLETIN OF THE

The anatomy of Crotalus was studied by Tyson in 1683 (Philo-
sophical Transactions, No. 144).

In regard to the use of the rattle there is not much to be said.
Mainly, it is used to warn off disturbers, and thus prevent useless ex-
penditure of venom. Success in capture of food depends on an ever ready
supply of poison. To secrete a new lot takes time. The rattle is used
also in breeding season, though it is doubtful if the dull-eared creatures
depend on sound, rather than scent, to find their mates. A theory ad-
vocated by some maintains that the organ is used in imitating insects, to
draw the birds. An objection to this is the fact that birds are somewhat
rarely found in stomachs of the Crotali. An observation appearing to
favor this theory was made on a Dakota snake, found braced up among
the branches of a sage bush in such a way that the head overlooked the
surrounding bushes, while the tail, within the mass of branchlets, was
free to keep up the rattling that attracted the attention of a party
more than fifty yards distant. But the approach of the troop may
have occasioned the creature's peculiar behavior.

Origin of the Rattle.

Many serpents besides those possessed of a crepitaculum are addicted
to making a rattling noise by vibrations of the end of the tail. It is
likely the modifications of the organ apparent in some or others of these
are consequences of this habit. In illustration of the extent to which
the tail has been modified in different cases, apparently for similar pur-
pose, attention is directed to Figures 9-14, from species allied to
the rattlesnakes.

Rhinocero'phis ammodytoides, Ley bold, Figs. 9, 10, from the Argen
tine Confederation, has its most prominent distinguishing features in a
prominence on the top of the snout, and, of more importance in this
writing, a peculiar termination of the tail. Fig. 9 outlines the caudal
surface. The terminal piece is sub-crescentic in longitudinal vertical
section, and sub-round in transverse. Externally it is covered by the
horny skin, internally it is bony. On the top, two of the dorsal scales
reach back more than a third of the length, and near their tips fuse
with each other and the skin about them. Fig. 10 shows the arrange-
ment after the skin and muscles have been removed. The outside of
the bone is hard, the inside not solid. It is penetrated by the canals of
the vertebrae, — indications of its origin. Inferiorly, it extends forward
below three of the vertebrae, firinly anchylosed to it and to each other,

MUSEUM OF COMPARATIVE ZOOLOGY 265

the anterior of the three being partly subtended. In front of it, the
column is normal. Each vertebra is long, low, rather broad, and verti-
cally crossed in the middle by a light line, as if two had joined end to
end. The neural spines are low, inclined backward, and, in the hinder
three or four, expanded laterally on the upper edge into a flange that in
the posterior unites with the terminal bone. Zygapophyses and para-
pophyses are feebly developed ; the hypapophyses are blade-like, thin,
and fragile. Appearances suggest that the tip is carried upon and
struck against the ground.

On Lachesis mutus, Linn., Fig. 11, from Brazil and Northern South
America, Vtie end of the tail is a long, slender, compressed, cultriform
blade. The scales in front of it are small and tubercular. This is es-
pecially the case with a dozen or more of the sub-caudals, that, as they
approach the end, are subdivided and spine-like. Within the cap the
bone is similar to those described above. The vertebrse preceding it are
slender, with weak processes. Near the extremity the tail is slender
and very flexible, a condition enhanced by the smallness of the scales.
It looks as if it were carried off the surface.

Halys acutus, Gth., Fig. 12, is a serpent recently described by Dr.
Gunther, 1888 (Ann. Mag. Nat. Hist., (6), I. 171, PI. XII.), from the
mountains north of Kiu Kiang, China. It is remarkable on account
of a flexible pointed lobe extended from the end of the snout, and for
the peculiar scutellation of its compressed - tail. Dr. Gunther says the
tail is not to be in any way taken as an initial step in the develop-
ment of the rattle of Crotalus, though the organ in this species may in
a much smaller degree exercise the same function as in the rattlesnake,
being an instrument by which vibrations and sound are produced.
From what we have seen above, it is not difficult to imagine a rattle
developed from the arrangement of scales and vertebrse present in this
snake. However, as Dr. Gunther remarks, and as illustrated below,
it is quite unnecessary to suppose the tail of Crotalus has gone through
such modification.'

Ancistrodon piscivorus, Holbr., Fig. 1 3, the Moccasin, from the South-
ern United States, is similar to Rhinocerophis in the structure of the
tip. The terminal bone is not so greatly developed. A greater number
of scales have fused with the cap.

On Ancistrodon contor-trix, Linn., Fig. 14, the Copperhead, of the United
States to Mexico, the tip differs a little from that of its congener, the
Moccasin ; it is directed downward as well as backward. Most often
the cap, or button, has one or two swellings in a degree resembling those

266 BULLETIN OF THE

on a ring of the rattle. A living specimen of this snake, kept for a year
or more, would take to rattling on the floor whenever he was irritated.
The sound was made by the terminal inch of the tail, this part being
swung from side to side in the segment of a circle, so that the tip
might strike downward. The result was a tolerable imitation of that
made by a small rattlesnake.

Both Copperhead and Moccasin bear evidence of union between cap
and scales. All the specimens have two scales fused above and two
below the button ; some show that more have joined the two above,
and that one or more of the laterals has been included on the sides.

The testimony of the embryo is to the effect that the rattlesnakes
were derived from forms in which the terminal vertebras were not
fused into a terminal bone. There seems to be no radical difference,
in the earlier stages of the end of the tail, between the above men-
tioned as well as other non-crotalophorus forms and Crotalus. So much
divergence in the number and shape of the caudal vertebrae occurs
in the various genera, that these features become matters of secon-
dary interest in a general comparison. In the later development the
rattlesnake goes farther than any of the others. The bone at the
end of the column is of the same nature throughout the Ophidia.
On Crotalus it eventually contains a greater number of vertebrae,
there is a greater enlargement of the mass, and in devoting it ex-
clusively to shaking the rattle, instead of striking upon objects, a difi'er-
ent use is made of it. In front of the rattle the neural spines incline
forward, possibly a consequence of the function of the tail. This in-
clination has little weight when compared with forms like Ancistrodon,
where the spine is so low. Similar leaning toward the head occurs in
the Hydrophidse and in Ogmophis, a Tertiary fossil of uncertain affinity.
So far as the vertebrae are concerned, they point to no special one of
the recent allies as representative of the stock from which the rattle-
snakes have sprung.

With the button there is but little more success. While it miaht
possibly have been formed or enlarged by fusion of scales with the cap,
there is really no reason to suppose scales were formed on the end of the
tail only to be lost again. In fact, embryonic data favor the conclu-
sion that it was formed by simple enlargement, or expansion of the cap
itself. A cap that by its shape would be mechanically held to its suc-
cessor might be produced by slight changes in that of any one of a num-
ber of species of the family, in addition to those figured. Shape is the
important feature in the retention of the series of caps. This, in the

MUSEUM OF COMPARATIVE ZOOLOGY. 267

rattlers, is obtained through that of the end bone, the thick skin cover-
ing the latter, and the mode of growth. Generally, on the pointed tip
there is no chance to retain the cap during and after the slough. With-
out the backward growth from the front border at the time of forming
the cap, again, the rattle would not exist, as each new cap would be
formed entirely within its predecessor. Ancistrodon coiitortrix, the Cop-
perhead, Fig. 1 4, gives a hint of the probable manner of origin of the
rattle, in the folds, or swellings, at the front border of the cap. The
presence of these folds apparently indicates that growth from the mar-
gin has taken place. If, as seems to be the case from the folds, the
necessary manner of growing already exists, but a slight increase in
it, increasing the amoimt of the swellings and constrictions, would be
needed to provide the Copperhead with a rattle. After the retention of
the displaced cap was secured, the change from the habit of striking
the tip upon the ground to simple shaking would be followed by loss of
flexibility in the tail itself, by rigidity of the column, — a condition,
with inclusion in the cap and the peculiar strain on the muscles, favor-
ing consolidation of the terminal vertebrae, and tending to draw the
spines forward. It appears very much as if the rattle originated in
some such way.

Though the Copperhead has been specially used as an illustration
here, it is not asserted that the rattlesnakes are directly derived from it.
Taking the general characteristics into consideration, it seems more
likely they took origin in several stocks; one of them, allied rather
closely to Ancistrodon, yielding the Sistruri (the small rattlesnakes
with large crown shields) ; another, nearer to Lachesis, giving rise to
Crotalus durissus and allies.

In summarizing, we may say the rattlesnakes have probably been de-
rived from members of the same family that had no rattle. The button
of the rattle was formed by enlargement of the terminal cap covering
the terminal bone, very likely without fusion with scales. The shape
of the button was determined by that of the bone and skin of the tip ;
it is modified in the second and following rings by the ring immedi-
ately preceding. The exterior or exposed part of each button after the
first, is formed in front of the ring with which it is in contact, and
pushes the latter back. As the button is displaced to become a ring,
it is prevented from passing entirely off by the swollen skin, com-
pletely filling its anterior chambers, behind the constrictions. The
development of the button and the rattle was accompanied by a consoli-
dation and compacting of a larger number of the vertebrae, with loss

268 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY.

of the muscles directly belonging to the reduced portion, and with
greater development of the muscles in front of it. And, finally, the
probability that the rattlesnakes represent at least two lines of descent
may be added ; one, that of Sistrurus, more closely connected with the
Copperheads ; another, that of Crotatus durissus and allies, connecting
with that of Lachesis mutus.

ApKiL 16, 1888.

LIST OF DIAGRAMS.

PLATE I.

Figs. 1, 2. Sistrurus catenatus. 4 times nat.

3, 4. Sistrurus catenatus. 3^ times nat.

6, 6. Crotalus confluentus. 2 times nat.

7. Crotalus horridus. Nat. size.

PLATE II

Fig. 8. Crotalus horridus. Nat. size.

9, 10. Rhinocerophis ammodytoides. 2^ times nat.

11. Lachesis mutus. 3 times nat.

12. Halys acutus. After Giinther.

13. Ancistrodon piscivorus. 2 times nat.

14. Ancistrodon contortrix. 2^ times nat.

Garman, Rattlesnake.

Plate, I

- mm '

^^^!>^^r^!>V\i'\i^

BMeisel.hih Boston .

Garman. Rattlesnake

Plate !I

^:

-21^

13

~<o^;

->>

y^m

V^

10

14.

"'^^M^^^4^"§'^?^^'

^■Z^-^/ V

12

Harvard MCZ Libra

3 2044 066 302 910

Date Due