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BULLETIN

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VOL. XXII.

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CONTENTS.

No. 1.— Contributions from the Zodlogical Laboratory. XXVIII. Observa-
tions on Budding in Paludicella and some other Bryozoa. By C. B.
Davenport. (12 Plates.) December, 1891

No. 2. — Contributions from the Zodlogical Laboratory. XXIX. The Gas-
trulation of Aurelia flavidula, Pér. & Les. By Franx Smitu. (2 Plates.)
December, 1891

No. 3.— Contributions from the Zodlogical Laboratory. XXX. Amitosis in
the Embryonal Envelopes of the Scorpion. By H. P. Jonnson. (8 Plates.)
January, 1892

No. 4.— A Fourth Supplement to the Fifth Volume of the Terrestrial Air-
Breathing Mollusks of the United States and Adjacent Territories. By
W. G. Binney. (4 Plates.) January, 1892

PAGE

115

127

163

Bulletin of the Museum of Comparative Zodlogy
AT HARVARD COLLEGE.
Vor x XT E Nout.

OBSERVATIONS ON BUDDING IN PALUDICELLA
AND SOME OTHER BRYOZOA.

By C. B. Davenport.

With TWELVE PLATES.

CAMBRIDGE, U.S.A:
PRINTED FOR THE MUSEUM.

DecemsBer, 1891.

Bulletin of the Museum of Comparative Zodlogy
AT HARVARD COLLEGE.
Von 2X. Now ft.

OBSERVATIONS ON BUDDING IN PALUDICELLA
AND SOME OTHER BRYOZOA.

By C. B. Davenport.

With TWELVE PLATES.

CAMBRIDGE, U.S. A:
PRINTED FOR THE MUSEUM.

DrEcEMBER, 1891.

No. 1.— Observations on Budding in Paludicella and some other

Bryozoa. By C. B. Davenport.’
ConTENTS.
PaaE PAGE
A. SprcraL Part. III. Budding in Marine Gymno-
LI quot lemata . 40
ee 1. Architecture of sre ‘Stock 40
II. Budding in Paludicella.
: 2. Origin and Development of
1. Architecture of the Stock 2
2. Histol 6 thos Buddin the Individual . 3 53
eee OF ene 5 3. Regeneration of the Poly pide 64
Region ‘ 4
IV. Origin of the Gemmiparous
See oF the Poly pide a Tissue in Phylactolemata 66
the Terminal Bud sole VU y
4. Origin and Development of B. GENERAL CONSIDERATIONS.
. suena Bee aoe. |) ie Eawalos Hunding iia
peer cop ment of the vady: II. Relation of the Observations on
Wall 12 lal
Budding in Bryozoa to the
6. Development of tite Eolunide 18
Germ Layer Theory . 88
7. Origin of the Muscles 27 sas
Sore III. On some Characteristics of
8. Formation of the Neck and ; :
Gemmiparous Tissue 98
Atrial Opening 31 : Q
SoA evel eh ior IV. Relationships of Endoprocta
eeu opment: «on the; Com: and Ectoprocta . . 102
munication Plate 32
10. Role of the Mesodermal Summary . 106
Vacuolated Cells 34 | Literature cited Og

A. SPECIAL PART.

I. Introduction.

THE somewhat heterogeneous studies here brought together have been
prosecuted at different times and in different places, as opportunity for
getting light on the problem of non-sexual reproduction as exhibited in
the group of Bryozoa has presented itself.

While studies on the fresh water species were pursued chiefly here at
Cambridge, those on marine Bryozoa were made while occupying one of
the tables of the Museum at the United States Fish Commission Labora-

1 Contributions from the Zodlogical Laboratory of the Museum of Comparative
Zoology, under the direction of E. L. Mark, No. XXVIII.

VOL XXII. —wNo. 1.

1

%

2 BULLETIN OF THE

tory at Wood’s Holl, Mass., during the summer of 1889, and while at
Mr Agassiz’s Newport Laboratory during the summer of 1890. To my
instructor, Dr. E. L. Mark, for many valuable suggestions during the
progress of my work and the writing of this paper, to Mr. Alexander
Agassiz, for the kind hospitality accorded me at his Newport Laboratory>
and to Hon. Marshall McDonald, United States Commissioner of Fish
and Fisheries, and Dr. H. V. Wilson, Assistant at Wood’s Holl, for fa-
vors shown me while at the Wood’s Holl Laboratory, I make grateful
acknowledgment of my indebtedness.

A word as to localities. The marine Bryozoa were found especially
abundant at Newport on floating eel-grass in the cove and on the piles
of the wharf. The embryos of Cristatella and Plumatella were found in
colonies which literally covered the bottom of some parts of the south
or shady side of Trinity Lake, Pound Ridge, New York. They occur
especially in densely shaded and fairly deep water near the shore.

The Gymnolemata present many difficulties to finer technique. They
possess a chitinous covering, often very thick, and frequently, in addition,
a calcarous skeleton. When the latter is present, picro-nitric acid mixed
with sea water is a fairly good fixing reagent ; when it is absent, hot cor-
rosive sublimate was most serviceable. The objects must be transferred
through the grades of alcohol with extreme caution, to prevent the col-
lapse of the ectocyst. I used the chloroform-paraffin method of em-
bedding in order to make transfers more gradual at this stage. Some
difficulty was experienced in staining such small objects on the slide, since
the tissues are very loosely associated ; and on the other hand 7 toto
staining is unsatisfactory in some cases, owing to impenetrability of the
ectocyst. Often it was necessary to open the body cavity of each indi-
vidual by means of a sharp knife or needle. The best results were
obtained with alcoholic dyes like Kleinenberg’s hematoxylin and
Mayer’s cochineal; although Ehrlich’s hematoxylin was often used
with success.

II. Budding in Paludicella.

1. ARCHITECTURE OF THE STOCK-

Paludicella, as is well known, occurs in quiet streams and forms
stocks on the under surfaces of stones and other objects. Seen with the
naked eye these stocks appear as a fine lacework, composed of constantly
branching lines of individuals. Some of the stocks which I have meas-
ured are over 25 mm. in length along their greatest diameter.

MUSEUM OF COMPARATIVE ZOOLOGY. 3

When the stock is studied more carefully, it is seen that the individ-
uals which compose it are arranged one in front of the other, forming
lines: (Figs. 1, 2, 2%.) We may distinguish (1) a single primary branch,
which formsa continuous line from the oldest individual, which has been
derived directly from the egg, to the terminal one; and (2) secondary
branches, which arise from the individuals of the primary branch and at
right angles to theiraxes. Typically, a secondary branch arises from both.
the right and left sides of each adult member of the primary branch. but
in some cases the secondary branch of only one side appears to be formed.
The secondary branches are composed, like the primary, of a continuous
line of individuals placed end to end. These in turn give rise to ter-
tiary branches, which run out at right angles to the right and to the
left of the secondary ones, and hence parallel to the primary branches.
Quaternary branches may occur in like manner, but I have never seen
branches of a higher order than the fourth. All of these branches may
lie in one plane, but frequently some of the lateral buds are so placed
that they give origin to secondary branches which rise above the plane of
the object upon which the stock lies. A study of Figure 1 and the cor-
responding diagram, Figure 2, reveals some additional facts. The two
lateral buds of an individual do not arise at the same time, and there is
a tendency for the first, and therefore oldest and most developed, sec-
ondary branches to arise alternately on opposite sides of the primary
branch. This last rule has many exceptions, however.

The long axis of the individual coincides with that of its branch ; the
sagittal plane lies in that axis, and at right angles to the substratum.
The atrial opening is near the distal end of the individual in the sagit-
tal plane, and is turned away from the substratum. The anal aspect of
the polypide is placed nearer the tip of the branch, —hence distad ;
the mouth, on the contrary, proximad.

A very casual observation shows that not all branches nor all individ-
uals are of the same size. The shortest and therefore youngest branches
are placed most distally, and are seen as small buds. The terminal indi-
viduals of the branches are also evidently less well developed than the
more proximal ones. The adult individuals measure from 1.5 to 2.0 mm.
in length and from 0.30 to 0.35 mm. in width. The younger individ-
uals differ from the older in form also. The outline of the adult branch,
looked at from the side, and disregarding the atrial opening, is formed by
a series of beautiful sigmoid curves (Fig.9). The concave and convex
points of the upper and lower sides of an individual are not placed exactly
opposite each other, and the lower (abatrial) side approximates more

4 BULLETIN OF THE

nearly to a straight line. The point at which the upper and lower
curves most nearly approach each other is where the separation of two
individuals takes place; that at which they are farthest apart is the
middle of the zocecium, occupied by the polypide and sexual organs.
The outlines of the young zowcia are straighter, and their breadth is
considerably less than that of the adult.

From what we have already seen, the method of growth of the stock is
perfectly evident: it is by the formation of new median buds at the tips
of existing branches, and of new branches from lateral buds. In order
to understand the origin of the individuals of the primary branches, to
which subject we will first turn our attention, we must study the tips
of the branches.

2. HistoLtoGy oF THE BuppInG REGION.

Figures 7-9 will serve to show more in detail the method of formation
of new terminal individuals. We find in these cases one polypide already
pretty well developed and attached to the body wall by means of the kamp-
toderm at about the point at which the pyramidal muscles (mu. pyr.)
are seen to be forming. That portion of the animal which extends from
about the region of formation of the muscles to a point a little proxi-
mad of the tip represents the region which will go to form the new in-
dividual. The tip itself, for reasons which will presently appear, is not
to be included in the terminal individual. The tip of the branch is to
be regarded as homologous with the margin of the corm in corm-building
genera of Gymnolemata. Figures 7-9 (gn.) also show the position of
the bud whichis to produce the polypide. By consulting first Figure 9,
in which the polypide bud is apparent, the significance of the swellings
of the body wall in Figures 8 and 7 becomes clear.

Figure 14 (Plate II.) represents a stage in the development of the
polypide bud, somewhat later than that shownin Figure 9, and this may
serve us as a starting point in our study of the origin of a new individual,
and, first of all, of the new polypide. The whole of Figure 14, from the
tip down to the neck of the older polypide (cev. pyd.), may be divided, for
convenience, into three zones: first, that distad of the young bud, which
may be called the ¢t7p of the branch (Fig. 14, a to 8) ; secondly, the region
of the bud itself, which may be called the gemmiparous zone (6 to y) ; and
thirdly, the region between this last zone and the neck of the older poly-
pide, which, for want of a better name, may be called the proaimal zone
(y to 8). In the formation of a new polypide between a and f, that
region will in turn become divisible into the three zones just named,

MUSEUM OF COMPARATIVE ZOOLOGY. 5

exactly as the region a to 8 represented the ¢¢p of the branch when the
older polypide, whose neck is shown at cev. pyd., was of the age that the
younger bud is now. It will be necessary first of all to study carefully
each of these three regions before treating of their origin and fate.

The tip of the branch consists of the two layers of cells which are found
in other parts of the body wall, —the ectoderm and the mesoderm, as the
ccelomic epithelium may, for brevity’s sake, be called. The cells of the
ectoderm at the extreme tip (Plate I. Fig. 6) are greatly elongated, form-
ing a columnar epithelium. There are about 25 or 30 of the larger cells.
They have a length of 28 » to 32 p, and a diameter of about 4. They
possess an ovoid nucleus averaging 5.7 p by 2.6 p, which lies in the middle
of the cell but slightly nearer the coelomic epithelium than the cuticula.
It possesses a large nucleolus over 1 » in diameter, which often appears
stellate owing to the threads of plasma surrounding and proceeding from
it and forming a nuclear network. As the figure shows, the plasma of
the cell is filled with large, apparently deeply stained granules, some of
the largest being over 0.6 » in diameter. The coarser granules lie chiefly
in the immediate vicinity of the nucleus, but are also found arranged in
long lines at right angles to the surface throughout the greater part of the
cell, becoming finer the farther they lie from the nucleus. A fine network
can sometimes be made out between the large granules, but this appear-
ance is more evident at the peripheral portion of the cell, where there are
no large granules. At the outer and inner ends of the cells one finds large
vacuoles, the largest of which are of about the same size as the nucleus ;
these become smaller the nearer they lie to the nucleus. In many cases
the larger vacuoles are each seen to be partly filled by a body which stains
slightly, and, as focusing determines, is more highly refractive than the
plasma. Similar highly refracting, slightly staining granules are found
in, and in fact often composing, the smaller “‘ vacuoles.” Owing to the
fact that the deeply staining granules lie near the nuclei, and that the
vacuolated and finely granular plasma lies more remote, there is a very
marked deeply staining band occupying the middle of the ectodermal
layer, and having about four tenths the thickness of the whole layer.

At the outer ends of the cells, and doubtless secreted by them, there is
a cuticula about 1» thick. Its inner surface is sharply marked off from
the underlying plasma; its outer surface is less sharp, and there are
usually very minute particles of dirt attached to it (not represented in the
figure). The whole cuticula forms in section a continuous band of
substance, which stains deeply in Ehrlich’s hematoxylin (but not at all
in alum cochineal), and covers nearly the whole tip. Looked at from

6 BULLETIN OF THE

the surface after staining in hematoxylin, it appears uniformly dark.
The mesoderm of the tip is highly modified, and a description of it
will be more instructive after I shall have described the normal ccelomic
epithelium, as I shall do later.

Passing from the extreme tip towards B (Fig. 14), one finds the ecto-
dermal cells gradually changing in form, size, and structure, and becoming
slightly broader, and very much shorter. Their nuclei lie near the inner
ends of the cells, possess a thick ‘nuclear membrane,” and are more
nearly spherical than those of the columnar cells, but of about the same
size. They each possess one very large, centrally placed nucleolus, whose
diameter equals and sometimes exceeds one third that of the nucleus, and
whose outline is often somewhat stellate. Outside of the nucleus in the
cell body there are fewer and fewer vacuoles as we pass from the tip, but —
the plasma is still coarsely granular, and here, as before, these stained
granules surround the nucleus. It is now the regions between cells
rather than those at the inner and outer ends which remain unstained,
so that the cells are separated from one another by light spaces.

The mesodermal layer becomes somewhat thinner than at the tip, that
is to say, its cells are flattened. The nuclei are elongated in the axis of
the branch, and average about 4p by 2.24. They possess one spheri-
cal nucleolus, whose diameter is about two thirds of the minor axis of
the nucleus. Small, clear vacuoles often with highly refractive spherical
bodies are abundant in the cell protoplasm, which stains as a whole less
deeply than does the ectoderm. Such highly vacuolated elements will
be called reticulated cells.

If we study the gemmiparous zone at a stage considerably earlier than
that shown in Figure 14, in fact at a stage in which a polypide is about to
arise, we find an appearance of the layers represented by Plate I. Fig. 3.
In such a region the ectoderm consists of cuboid cells about 7p high by
6.5 w broad. The nuclei are large, nearly spherical, and vary in size from
3.52to 6.0. The largest nuclei are those in the region from which a bud
is about to arise (ex.). One in this region (to the right of ex.) is 6.5 p
by 6.0 » in diameter, with a nearly spherical, eccentrically placed nucleo-
lus of about 3.0 in diameter. This nucleus is the largest which I have
found in the whole tissue of Paludicella, and the same is true of the nucle-
olus. From the examination of many regions from which buds are about
to arise, I can assert that such regions always, in Paludicella, possess large
nuclei and large deeply staining nucleoli.) I shall have occasion to de-
scribe similar conditions elsewhere, and to point out the probable signifi-
cance of these facts. The cell body possesses a highly granular, deeply

MUSEUM OF COMPARATIVE ZOOLOGY. 7

staining plasma; the inner ends of the cells, however, do not stain so
deeply as the middle or peripheral portions.

The cuticula (omitted from Fig. 3, see Fig. 5) is usually somewhat
different in appearance from that at the extreme tip. In section we can
distinguish two layers: an outer, thicker, deeply staining layer, which is
_not continuous but appears broken into larger or smaller bits; and an
| inner, thin, non-stainable and highly refractive portion, from which the
first layer is often slightly separated. This second layer is closely applied
to the underlying cells, which doubtless secrete it. Looked at from the
surface (Fig. 10, a.) the deeply stainable layer is seen to be broken into
irregular polygonal pieces ranging from 2 » to 17 » in diameter and sepa-
rated from one another by spaces ranging from 0 to 6 up.

The mesoderm forms a loose epithelium, whose average width is less
than that of the ectoderm (Fig. 3, ms’drm.). As a whole, moreover, it
stains less deeply. In a portion of the gemmiparous zone, which lies
about 180° from the budding region, the mesoderm has become so delicate
‘a layer, if it exists at all, as not to beeasily distinguishable. In the vicin-
ity of the bud its cells have irregular outlines and extend out into the
celom as though possessed of the power of amceboid movement. The
nuclei are spherical or ovoid, smaller than those of the ectoderm, and on
the whole have smaller nucleoli. The cell body is highly vacuolated.
The vacuoles are not large and clear in outline, but whole regions of the
cell body seem to be reduced to a non-stainable condition, and in some of
these regions a finenetwork may still be observed.

The proximal zone (Fig. 14, y to 6) is distinguished, soon after the:
first rudiment of the bud appears, by the diminished thickness of the
ectoderm. ‘The cells have become transformed from a columnar to a
pavement epithelium. The nuclei are smaller, the nucleoli less prom-
inent, and the cell body stains much less deeply. The cuticula is of
two kinds, as before, but with this difference: the deeply staining outer
part is less conspicuous, and the pieces are smaller and more widely sep-
arated. Looked at from the surface, we find an appearance like Figure:
10, c., in which the dark bodies represent the deeply staining cuticula.
These pieces are much smaller than those of the gemmiparous zone,
ranging from 0.6 » to 9.5 w in diameter, and separated from each other
by spaces ranging from 0 to 13 p.

3. ORIGIN OF THE POLYPIDE IN THE TERMINAL Bup.

Observation having shown that budding in Paludicella follows definite
laws, we ought to be able to discover the place and time at which buds

8 BULLETIN OF THE

will arise ; and it is necessary to do this in order to study the origin of
the gemmiparous cells, and the changes which they undergo preparatory
to an actual involution.

The study of tips of branches shows that the necks of the polypides of
any branch all lie in one plane, and that this plane also includes the
youngest polypide ; also that the youngest polypides always arise distad of
the next older. Knowing these facts, our observations may be confined to
a short line running from the neck of the youngest apparent buds to the
tips of the branches studied. The time at which to search for incipient
buds and the place in the line where they will be found is illustrated by
Figure 7 (Plate I.). The youngest developed bud is one the axes of whose
tentacles are approximately parallel to the axis of the branch, and whose
brain cavity, gn., is not yet constricted off from that of the esophagus.
The place of origin is near the tip, immediately beyond the point at which
the ectoderm changes rapidly from a columnar to a pavement epithelium.

Figure 3 is from a section across the branch in the region of an incip-
ient bud. I have already described the conditions of the cells of this
region. Those near ex. are larger than the surrounding ones, and show
signs of cell division both in the ectoderm and mesoderm. In both cases
shown in the figure, the direction of division is such as will tend to
increase the superficial area of the layer in which it occurs. The ecto-
derm seems to be the most important layer of the two in the process of
invagination which is about to take place. I think one is led to this
conclusion if one considers a folding of an epithelium to be due to an
increase in the area of the epithelium within a certain circumference
without a correspondingly great increase in the circumference itself.
Such a conception implies, first of all, mutual pressure of the cells of
the invaginating epithelium. The cells of the mesodermal layer do not
seem to be under mutual pressure; in some cases they are barely in
contact. The cells of the ectoderm are evidently closely applied, and
probably, therefore, under mutual pressure.

The one case of cell division which is occurring in the ectoderm is at
the inner end of the cell. In fact, the centre of the nuclear plate is much
nearer the deep end than are the centres of the adjacent nuclei. The
effect of this division is to increase the area on the inner surface of the
ectoderm more than that on the outer, as appears from a study of the
sections shown in Figures 4 and 5. In Figure 4 certain cells lie already
below the niveau of the surrounding ones, very much as though they had
moved downward on account of this being the direction of least resist-
ance. <A later stage of this process is shown in Figure 5. Here the

MUSEUM OF COMPARATIVE ZOOLOGY. 9

nuclei are already arranged in a deep saucer-shaped layer. The transi-
tion to the U-shaped arrangement of Figure 37 (Plate IV.), in which
the invagination of the inner layer of the bud is completed, is not a diffi-
cult one to understand. It is to be observed, however, that the folding
is of such character that it can hardly be termed a typical invagination.
Comparing Figures 4, 5, and 37, it appears rather to be of a type some-
what intermediate between typical invagination and typical ingression.
The cavity of the bud first arises through a rearrangement and reshap-
ing of the cells of the inner layer of the bud. At this stage the nuclei
of the invaginated region stain very deeply, and have large nucleoli.
Figure 21 (Plate III.) shows the condition of the bud at this stage as
seen in longitudinal section. The proliferation which gave rise to the
rudiment of the bud is shown, by a comparison of Figures 37 and 21,
not to have been confined to one point, but to have occurred along a line,
so that the resulting bud is boat-shaped, and not cup-shaped. The whole
mass is therefore bilaterally symmetrical. Even at this early stage one
can distinguish a difference in the form of the bud at the anal and oral
ends. At the oral end (Or.) the bud passes more abruptly into the body
wall than at the anal end. Later, this feature becomes more marked.
This is an indication of a fact for which later stages will bring better
evidence: that the formation of the bud proceeds from the oral towards
the anal end, and that the increased length of the bud that one finds in
the stage represented by Figure 22 is due to growth at the anal end.

4. ORIGIN AND DEVELOPMENT OF THE LATERAL BRANCHES.

The first lateral branch appears as a prominent protrusion of the lat-
eral walls of an individual of the primary branch when the ganglion of
that individual has already nearly closed, and when the bud of the next
younger individual has attained a stage somewhat later than that shown
in Figure 37. The zone in which the lateral buds arise Jies about mid-
way between the neck of the median polypide and the tips of its tenta-
cles at this stage. The place of appearance in this zone is approximately
90° to the right or left of the neck of the polypide of the median indi-
vidual. In one case measured, however, that shown in Figure 20 (Plate
II.), the centres of the two lateral buds seemed to be unequally distant
from the neck of the polypide, and each over 90° from it (approximately
100° and 110° respectively. (Compare page 3.)

A cross section of the branch through the region in which the lateral
bud is arising shows that the condition of the body wall at. the bud is
quite different from that of the rest of its extent. Figure 19 represents

10 BULLETIN OF THE

a longitudinal section of a portion of the body wall passing through the
non-budding region. The wall seems to consist of one layer only of cells,
and a fine, non-stainable cuticula. This layer of cells is the ectoderm,
for it can be traced directly into the outer layer of the tip. The meso-
dermal layer is not represented in the region from which the figure
was drawn, but I believe it is not entirely absent from this part of the
individual, for occasionally extremely flattened cells, spindle-shaped in
section, may be seen lying inside of the ectodermal layer, quite sharply
marked off from it by a distinct line. Further evidence of the existence
of two layers is found in the fact that one occasionally sees in the flat-
tened body wall two nuclei lying together, one nearer the ceelom than
the other. The cells of the ectoderm are seen to be very much flattened
(average 2.5 »), and their nuclei are widely separated (35 p). The nuclei
are oval, and rather smaller than those near the tip. They possess a
single, rather large nucleolus, which does not stain intensely. ‘The cell |
protoplasm stains very little. The cuticula is about 0.5 p thick.

If we study the body wall in the budding region, when the latter is
first indicated on the surface by a marked protrusion of the outline of
the zocecium (Plate II. Fig. 15), we find that this protrusion is due to
an elongation of cells. There are about twenty-two cells in this section,
which are more or less thickened. Since the section figured passes
through the centre of the circular thickening, and is about one sixteenth
the diameter of the circle in thickness, it follows that there are over 250
cells of the ectoderm which have already at this stage become somewhat
enlarged previous to evagination. The highest of these cells are the
central ones, of which the largest is 22 high. The largest nuclei are
4p by 6.3 p, which approximates the size of those in the gemmiparous
region (page 6). They are placed nearer the coelomic epithelium than
the exterior, are nearly spherical, and each possesses one large nucleolus
and a quite apparent network with deeply stainable nodal points. The
cell body is stained as a whole rather deeply by Ehrlich’s hematoxylin,
but particularly around the nuclei. The outer parts of the central cells,
however, are stained very little, and the deep ends of some of the lateral
cuboid cells not at all. The network of plasma contains only fine
granules, and these seem to lie in rows parallel to the long axis of the
cell. The structure of the outer-layer cells, at a somewhat earlier stage,
is shown in Figure 18, under a higher magnification. The network is
very apparent in these large spherical nuclei, and the plasma of the cell
is seen to contain coarse granules, which lie near the nuclei and stain
deeply.

MUSEUM OF COMPARATIVE ZOOLOGY. ig |

While the cuticula of Figure 18 is seen to be that of the normal body
wall in this region, that shown in Figures 15 and 16 appears under the
microscope after staining in hematoxylin to be of two distinct kinds :
(1) that outside of the central region, which is highly refractive and not
at all stained; and (2) that which lies immediately over the central elon-
gated cells of the bud, which is also highly refractive but stains deeply.
In fact, the central cuticula resembles in every way that already described
for the tip of the branch, and shown in Plate I. Fig.6. | Moreover, it
has other points of resemblance to the latter. It does not stain at all
in alum cochineal; the outer boundary of the branch is often uneven
at this place (Fig. 16) ; and particles of dirt are often found adhering to
it, while the rest of the cuticula is comparatively free. The difference in
staining properties of the central and lateral cuticulas indicates that the
' former undergoes with age a change in its chemical properties ; the irreg-
ular outer boundary and the adhesion of dirt particles seem to indicate
that the newly formed cuticula is viscid. The mesoderm of the stage of
Figure 15 consists of a single loose layer of subspherical cells of the two
kinds already noticed, reticulated and non-reticulated. The series of
Figures 18, 15, and 16 shows the behavior of columnar cells in the forma-
tion of a typical outfolding as distinguished from the slipping in of cells
to form the polypide (Figs. 3, 4, and 5).

In stages later than that of Figure 16, the tip of the branch becomes
further removed from the body wall of the median branch. The cells at
the tip always retain their elongated columnar condition. A polypide
is soon formed on the upper part of the body wall immediately behind
the tip, exactly as in the case of the median branch. A septum is
very early formed, cutting off the lateral from the median individual,
and the lateral secondary branch becomes the median primary one of
new individuals (Plate VI. Fig. 58).

We have already traced out the origin of the polypide of the median
branch from the mass of cuboidal cells near the tip ; it remains to de-
termine whether the cells which give rise to the lateral branch can be
traced directly back to the cuboidal cells of the tip, or whether they have
arisen from the flattened epithelium of the general body wall and sec-
ondarily acquired their plump “ embryonic” character.

Figure 18 ( Plate IT.), to the cellular conditions of which I have already
referred, shows an early stage of the lateral branch, and Figure 20, gm. 1.,
shows on a smaller scale the different cellular conditions in the body wall
in the region of two lateral buds which are yet far from showing ex-
ternal signs of evagination. The cells are cuboid and much higher than

12 BULLETIN OF THE

those of the adjacent body wall. Have they been so ever since they were
derived from the tip, or have they secondarily become so ? I believe
that these cells have never been flattened pavement epithelial cells, for
the following reason. All ectodermal cells of the body wall near the tip
are cuboidal; if these cells have only secondarily acquired this form,
they must have passed through a stage in which they were flattened epi-
thelium. Now, if these cells could be distinguished by greater thickness
from the cells of the surrounding body wall, at a time at which the lat-
ter cells had only just begun to emerge from the cuboidal condition to
become differentiated into the pavement epithelium of the body wall, it
would follow that, even though they had secondarily increased in size as
a result of an impulse preparatory to evagination, and even though they
would have been at a stage only a very little earlier indistinguishable
from the other cells of the body wall, yet they would never have passed
in this case through a flattened condition, because at a stage only a very:
little earlier the whole body wall was composed of cuboid cells.

The conditions which I have set as the criterion of our problem are
fairly realized in Figure 17, which represents a portion of the body wall
of a median branch which extends from the gemmiparous region above to
the thickened body wall of the nascent lateral bud below (gm./.). It will
be seen, by a comparison of the body wall of this region with that shown
in Figure 19, which is taken from the same individual farther from the
tip, that even the most differentiated part of the body wall of Figure 17
is in a relatively indifferent condition as compared with the pavement
epithelium of the ectoderm of Figure 19, in which the mesoderm, indeed,
has become so thin and insignificant as scarcely to be visible. We may,
therefore, maintain that the ectodermic cells of the body wall have only
just begun to lose their cuboidal condition to become pavement epi-
thelium, and therefore conclude, in accordance with the argument just
presented, that the cells of the lateral bud (gm./.) have never passed
through a stage in which they were flattened epithelium. It is evi-
dent, also, that the Anlage of the second lateral bud is also derived
from near the tip, because, as in Figure 20, we find two lateral regions of
cuboidal cells.

5. DEVELOPMENT OF THE Bopy WALL.

It is, of course, almost impossible to gain direct evidence upon the
place of origin and method of development of the body wal], and one is
therefore forced to the collection and weighing of circumstantial evi-
dence. Braem (’90, pp. 127, 128, 131) believes that the body wall (the

MUSEUM OF COMPARATIVE ZOOLOGY. 13

cystid, in Nitsche’s sense) has a double origin in Paludicella: “ Ein
Theil des Cystids zwar vor dem Polypid, ein anderer aber erst spiter
angelegt und zwar aus der polypoiden Knospe selbst entwickelt wird.”
The part developed from the bud of the polypide is the elliptical region
of the body wall, whose main axis lies in the sagittal plane and which
has the neck of the polypide at the distal focus and the attached ends
of the retractor muscles and the parietovaginal (or pyramidal) muscles
lying in the proximal circumference,—the greatest part of the ellipse
thus lying oral of the atrial opening. The evidence for this conclusion
Braem finds in the following facts, which my own observations confirm:
“The great retractor first appears in the angle between the oral part of
the polypide bud and the cystid wall (cf. Figs. 23, 24, el. mu. ret.]; then
its cells gradually become elongated, and as its point of origin retreats
' farther and farther from the polypide, it finally appears as a bundle
which joins a point lying between the mouth of the polypide [neck of
the polypide] and the inferior septum with the pharynx, and, as I be-
lieve, also with the cardial part of the stomach” (p. 125). Compare
the muscles at the left end of Plate I. Fig. 8. Further on he says:
“Die Parietovaginalmuskeln [pyramidal muscles] erscheinen an der
Knospe zuerst in Form zweier seitlichen Leisten, in welchen die einzel-
nen jugendlichen Fasern senkrecht zur Langsaxe verlaufen. Indem sich
alsdann lateral von der Knospe das Cystid durch Neubildungen erweitert,
werden die Fasern verlaingert und die beiden Biindel treten in Fliigelform
deutlicher zur Rechten und Linken der Miindung hervor. Ihr Ursprung
an der Cystidwand riickt nun von der Miindung immer weiter ab und
gelangt schliesslich auf die gegeniiberliegende Seite, wo er anal und late-
ral seinen definitiven Platz findet.” Compare Plate I. Figs. 7-9, mu. pyr.,
and Plate VI. Fig. 63, mu. pyr. From these observations Braem (’90,
pp. 127, 128) concludes: “ So scheint es sicher, dass auch hier ein grosser
Theil des definitiven Cystids, das ja zum anderen Theil schon vor der
polypiden Knospenanlage entwickelt war, aus dem Material dieser letz-
teren hervorgeht. Das folgt namentlich aus der Art und Weise, wie
sich die Muskeln bilden. . . . Auch hier wiirde, wie bei den Phylac-
tolemen, oral vor der Knospe nach dem Retractor hin, ein grdsseres
Gebiet der Leibeswand der Knospenanlage entstammen, als seitwiirts
und hinten.”

An analysis of the facts has led me to conclusions differing somewhat
from those of Braem ; namely, that all or nearly all of the cells of the body
wall (cystid) are derived from the tip of the branch or from the immedi-
ate descendants of cells so derived. The number of cells contributed to

14 BULLETIN OF THE

the formation of the body wall by the neck of the polypide is much
smaller than Braem has suggested, and probably insignificant in amount.
The retreat of the points of origin of the retractor and parietovaginal (py-
ramidal) muscles may be in part accounted for by the normal growth in
area of the body wall, and in part by the actual movement of the point
of origin with reference to the cells of the body wall. These conclusions
rest upon the following circumstantial evidence.

Owing to the small number of cells in the body wall at the tip, and
the comparatively slow growth of the cystid, karyokinetic figures are
much less frequent than in the polypide. Quite a long search has there-
fore not afforded cases enough to enable me to draw any perfectly satis-
factory conclusions as to just where, and where only, growth was taking
place. I have, however, seen nuclear division occurring in the elongated
cells of the extreme tip, rather more abundantly in the cuboidal cells
between the extreme tip and the gemmiparous zone, and most abun-
dantly in the gemmiparous zone, but here evidently having to do with
the origin of the polypide, muscle cells, etc. Proximal to the gemmipa-
rous zone, I have noted few cases of nuclear division excepting about
the neck of the polypide. It seems probable that the cells of the tip
of the branch are not to be regarded as forming a differentiated organ
whose elements rarely divide, but as quite capable of adding new cells to
the body wall. On the other hand, there is by no means a Schevtel in the
botanical sense, but the cells added to the body wall continue for a time
to divide vigorously, and finaily give rise to the polypide, to the Anlage
of the lateral branches, and to the body wall. The cells belonging to
the proper cystid then cease to divide rapidly.

I have already shown how the cells of the tip secrete a cuticula, which
becomes gradually replaced by a second cuticula secreted beneath it as
the body wall attains its adult dimensions. It appears as though the
first cuticula were secreted by the cells of the tip only. This being so,
since the area of the body wall increases, this first cuticula must either
stretch to cover the enlarged area, or else it will fail to cover it and
appear as isolated patches upon the body wall, and these isolated patches
will become more and more widely separated as the area of the body
wall increases. This latter condition seems to be the one realized in this
case. The presence of the old cuticula is easy to demonstrate, since it
stains deeply in hematoxylin ; and it may be easily distinguished from
that formed later, for with the same reagent this stains not at.all. Figures
6, 11, 12, and 13 show different appearances of the cuticula at different
parts of the body wall. At the extreme tip (Fig. 6) there is a continu-

MUSEUM OF COMPARATIVE ZOOLOGY. 15

ous deeply stained band of cuticula. In Figure 11 it no longer appears
quite homogeneous, but is darker at some places than at others. The
ectoderm is here composed of cuboidal cells. At a later stage of devel-
opment the ectodermal cells have become very much flattened. A thin,
unstainable, more deeply lying cuticula has already begun to form, and
the outer deeply stainable cuticula is seen to be broken up into bits.
Figure 13 is from the adult body wall. The ectoderm is flattened. The
inner cuticula has attained a great thickness, and the outer cuticula is
represented by only a few deeply staining patches. One attains a simi-
lar result by studying the surface of a stained individual. Figure 10
shows the condition of the outer cuticula at intervals along the same
branch from the gemmiparous region a to a nearly adult region, d. The
bits of cuticula become more and more widely separated and smaller, as
T have already described in detail on page 7. Here, then, we have not
merely an interesting case of replacement of one cuticula by another to
meet the needs of the enlarged body wall by a method which has no par-
allel, so far as I know, in any other group of animals, but for the specific
purposes of our problem a criterion of growth of the body wall quite as
satisfactory as karyokinesis, and much easier of application.

Let us apply this criterion in our attempt to answer the question, Is
that portion of the body wall lying between the neck of the polypide
and the points of origin of the pyramidal muscles (Plate VI. Fig. 63,
b-a, b-c) derived wholly from the neck, or is it merely the result of
interstitial growth of that part of the original cystid which was pre-
formed in the neck region? If the first condition is true, we should
expect to find no indications of the outer cuticula secreted by the tip of
the branch; if the second, we should éxpect to find the outer cuticula
broken into bits, and underlaid by the inner lately formed cuticula.
Figure 63 shows clearly the deeply stained outer cuticula here sep-
arated into bits, and, to my mind, thereby proves that this part of the
eystid has had an origin similar to that of the rest of the body wall.
Moreover, a comparison of the portion of the section figured with the
remainder (and this comparison has been made on many sections from
several individuals) shows that the parts of the cuticula about the neck
are indeed rather smaller and farther removed from each other than at
the opposite side of the branch; but the difference in this respect is not
very marked, and may well only signify that there is a more rapid
growth of the body wall in the vicinity of the neck of the polypide than
at the opposite side.

But how then do the points of origin of the pyramidal muscles come

16 BULLETIN OF THE

gradually to move away from the neck of the polypide at which they
arose, in order finally to lie so that the muscle fibres are nearly parallel ?
If the points of origin remain fixed with reference to the surrounding
cells, they can hardly come to lie absolutely closer together, but only
relatively so by growth of the body wall between these points and the
neck. If, however, we find that in older individuals the points of origin
are not only relatively but absolutely closer together, we are driven to
the conclusion that these points move relatively to the surrounding cells.
To decide whether the points of origin come to lie closer together behind
the neck absolutely or only relatively, I measured cross sections of four
individuals through the region of the neck in which the muscle fibres
showed evident differences of length, and therefore of age. I may
preface a table of these measurements with the statement that the mus-
cles first appear plainly differentiated at a stage when the polypide is
well formed (Fig. 7, mu. pyr.), and that the growth of the body wall in
circumference is not very considerable after this time. The numbers
indicate measurements in micra : —

Distance on periphery between ea of mus- 80.1 ONS

cles, atrial side ... . . A ee GUY 154 187 260
Distance on periphery pened origins of mus-

cles, abatrial side .. . 5, Oak oe ge Los peal 286 264 220

Total length of neuipliess ie ee ican ee) aay. 440 451 480

The distance on the “atrial side” signifies the distance measured over
a, 6, c, Figure 63 (Plate VI.). The length of the remainder of the sec-
tion is the distance on the “ abatrial side.”

From these measurements it appears that the “ origins” of the py-
ramidal muscles approach each other absolutely, —a condition which
Braem’s hypothesis cannot explain, and which can be reasonably inter-
preted, it seems to me, only by assuming, however unique and difficult
of conception such a condition may be, Rick the points of origin move
relatively to the surrounding cells of the body wall. (Compare also
the movement of parietal muscles referred to on page 29.)

It is not necessary to assume that the increase in extent of the body
wall after the polypide is first formed is due to the addition of cells from

1 Professor Mark has called my attention to a discussion of the movement of
the fixation-point of a muscle in Mollusks by Tullberg (’82, pp. 26, 27, 44). This —
author says that he has undertaken no special investigation of the method of i
migration, but concludes that this motion must result from the absorption of the
inner muscle fihyes as new ones are formed on the outside. I do not find any
evidence of such a process in Paludicella.

MUSEUM OF COMPARATIVE ZOOLOGY. aly

the neck. The change in form of the ectodermic cells from a columnar
to a pavement epithelium must alone cause a great increase in the ex-
tent of that layer. Some measurements that I have made seem to me
to prove that the area of the body wall does increase greatly, even out-
side the region whose growth Braem attributed to the addition of cells
from the neck of the polypide. Thus, in one case, the distance from the
distal end of the polypide bud, which becomes the neck of the adult,
to the point of origin of the young retractor muscle was 0.17 mm.; from
the same point to the septum separating the young individual from the
next older was 0.27 mm. In the next older individual, from the neck to
the origin of the retractor muscle was 0.72 mm.; from the neck to the
septum was 2.0mm. Thus assuming that the older individual passed
through a stage exactly equivalent to that in which we find the younger,
the distance from the neck to the origin of the retractors has increased
0.55 mm., and from the origin of the retractors to the septum 1.18 mm.
The first distance is that in which Braem has assumed the body wall to
grow by additions from the neck of the polypide, and this assumption was
apparently made to account for the increase in extent of this region ; but
the area between the origin of the retractors and the septum, which is
outside the region to which additions such as Braem contemplates could
have been made, has grown in this case very considerably more in extent.
This case is not a typical one, however, for we rarely find the distance
from the origin of the retractor to the septum to be so great. In gen-
eral, from observation of a number of cases, I should say that in the
adult the distance between the neck of the polypide and the origin of the
retractors, is to the distance between the latter and the septum about as
5:4, and that therefore the growth of the first region is slightly greater
than that of the second. From the fact, however, that the cells around
the neck of the polypide for a long time retain a somewhat embryonic
character, and may quite frequently be seen in division, this was to have
been expected. The conclusion which I draw from this last series of
conditions is, then, that it is unnecessary to suppose the addition of cells
from the neck of the polypide to account for the fact that the origin of
the retractors is carried backward from the polypide. Normal growth of
the body wall, such as occurs elsewhere, is quite sufficient to account

for it.
To recapitulate. That portion of the cystid lying in the vicinity of

the neck can hardly be derived from the neck alone, for the cells still

show adhering to them the cuticula which they derived from the tip of

the branch. It is not necessary, in order to account for the movement
VOL. XXII. — NO. l. 2

18 BULLETIN OF THE
of the origins of the muscles away from the neck, to suppose that the
circumcervical region is derived in that way; for (1) the origins of the
pyramidal muscles actively migrate away from the neck to a certain
extent, and (2) the normal growth of the body wall is sufficient to ac-
count for the carrying backward of the origin of the retractors.
From the facts already gained it seems clear that the ectocyst (cuticula)
is first formed at the tip, and then, to meet the wants of the growing
colony, this is replaced later by a cuticula of different chemical compo-
sition, which becomes thicker as the body wall grows older. At a late
stage we find a separation of the thick cuticula itself into two layers, of
which the outer one is much the more highly refractive.1 (Plate II.
Fig. 13; Plate III. Figs. 26, 29.)

6. DEVELOPMENT OF THE POLYPIDE.

We have already (pages 8, 9, Figs. 5, 14, 37) seen how the foundations
of the polypide are laid by the ingression of cells of the outer layer of
the body wall pushing before them the mesoderm, and how, finally, those
cells arrange themselves in a boat-shaped mass to form the inner layer
of the bud (Plate III. Fig. 21), which possesses no actual cavity, and
is constantly separated from the external world by the ectoderm which
remains behind to form the neck of the polypide. Even when a cavity
is formed later, it does not communicate with the exterior until the
permanent atrial opening has arisen. The earliest differentiation in the
bud is, as mentioned by Allmann (’56, p. 36), the formation of a cavity
which is to become that of the atrium. This cavity is first formed
at an early stage as an extremely slight fissure in the midst of the inner
layer. Figure 22 shows a longitudinal section of this stage. Cell di-
vision is taking place throughout the whole mass, but especially at the
neck of the polypide, cev. pyd. The position of the cavity is represented
by the central non-nucleated space, and this gives rise, as the later his-
tory of development shows, to the atrium and the pharynx..

Figure 23 represents a stage which is doubtless of short duration, for
I have found it only twice. The bud is much more developed at the

1 Such a two-layered condition of the cuticula was long ago described by Reichert
(’70, pp. 265, 266) for Zoébotryon. He distinguished “ eine dussere, festere, starker
lichtbrechende und sprodere Schicht und die innere weichere.” Realizing that the
“ectocyst” or cuticula undergoes many changes in form, — formation of lateral
buds, of septe or communication plates, and increase in size of the stolon, — he
suggested, without having observed the process, that probably during these
changes the more rigid outer layer disappeared and was replaced by the inner
softer one.

x,

MUSEUM OF COMPARATIVE ZOOLOGY. 19

anal end than in the last stage, and there is a second cavity below the
atrium, from which it is separated by a line of nuclei. This is plainly
an early stage in the formation of the alimentary tract, which thus first
appears at the anal side of the bud, as in Phylactolzemata, and is progres-
sively formed towards the oral end. An appearance similar to the one
figured would be given by a slightly oblique section of a later stage; but
this section is strictly sagittal, and no trace of the lumen appears in adja-
cent sections. I have found a similar condition in a series of longitu-
dinal sections at right angles to the sagittal plane of the bud (Plate IV.
Figs. 39 and 40). Figure 39 shows that the atrio-pharyngeal cavity is
first developed at the anal end, and in Figure 40, which is three sections
(about 15 ».) below Figure 39, the anal end only of the alimentary tract
_is formed. It is worthy of notice that the cells of the mesodermic layer
of the bud are often greatly vacuolated at this stage, as in Figures 39 and
40, vac. Braem (90, p. 126) says of this stage: ‘Die der Resorption
dienenden Darmabschnitte, Magen und Enddarm, werden gemeinsam an-
gelegt, indem auf jeder Seite der Knospe eine Liingsfalte die Wandungen
nach innen und gegen einander zu einbiegt, worauf die benachbarten
Theile des inneren Blattes verschmelzen und so durch eine Art Abschniir-
ung das primaire Knospenlumen in den vorderen Atrialraum und die
hintere Darmhohle getrennt wird.” While I thoroughly agree with this
statement, the additional fact of the formation of the tract progressing
from the anal towards the oral end is interesting, in that it shows that the
process of formation of the organ in Paludicella is fundamentally similar
tc, although differing slightly in detail from, that of the Phylactolemata.
Figure 24 shows in sagittal section a still later stage in the development
of the alimentary tract. A cross section of this stage is seen in Figure
30 (Plate IV.), in which the separation of atrial and gastric cavities is
demonstrated. The inner layer of the bud is here seen to be separated
from the ectoderm by a distinct line, and, to a certain extent, even by
the mesoderm. The distal (oral) part of the cavity of the alimentary
tract next becomes considerably enlarged to form the stomach (Fig. 25).
The outer layer of the bud, ms’drm., penetrates between the stomach
and the atrium, and a depression is formed at the bottom of the atrial
chamber which will give rise to the cesophagus. Even at this stage the
cesophagus is not in communication with the stomach, but their cavities
are separated by two layers of cells of the inner layer of the bud. These
two layers become those of the cardiac valve (Plate IV. Fig. 36, vlv. cr.).
By a further comparison of Figures 25 and 36 it will be noticed that,
whereas in the earlier stage, as in Endoprocta, there is no ccecum to the

20 BULLETIN OF THE

alimentary tract, in the later stage the ccecum has already begun to form,
as in Phylactolemata, by an outpocketing of nearly the whole of the
lower wall of the stomach. (Compare also Plate I. Figs. 7, 8, and 9.)

Very soon after the establishment of the alimentary tract, and between
the stages shown in Figures 24 and 25 in sagittal section, there begin
to appear organs which have a very considerable phylogenetic signifi-
cance; namely, the lophophoric ridges, ring canal, and tentacles.

The lophophorie ridge is a fold which surrounds the mouth, and from
which at intervals tentacles arise. The ridge, however, arises before the
tentacles. The general position of the ridge, as well as its method of ori-
gin, may be learned from an inspection of a series of sections of the age
of those shown in Figures 31-34. In a section lying near the oral
end of the bud (Fig. 33), one finds two spaces, — a lower, whjch is that
of the stomach, and an upper, the esophagus and atrium. This upper

space is broader above than below, and the cell layer which lines it is:

thick below, but above, or nearer to the body wall of the budding
individual, it is thinner. The transition from one condition to the
other is quite abrupt, and is marked by a salient curve (/oph.). Ina
section near the anal end of the bud (Fig. 31), it will be seen that here
too the inner layer is thick below and thin above. The characters men-
tioned are still more strikingly shown in the median section, Figure 32.
That the differences in thickness of different parts of the inner layer are
recently acquired modifications of an earlier simpler condition is indi-
cated by comparing Figure 32 with Figure 30, which is from a younger
bud. The series of points (Joph.) of transition from thick to thin epi-
thelium forms on the reconstructed polypide a curved line, convex above.
This line is the ridge of the young lophophore (compare Fig. 25, loph.).
I have said that the lophophoric ridge arises before the tentacles. The
evidence for this assertion is found in a series like that referred to above,
where, although the ridge exists along the entire side of the atrium,
one finds nascent tentacles in the middle region only (Figure 32, left
hand).

As Figure 25, of a later stage than Figures 31-33, shows, ‘the lopho-
phore curves downwards rapidly at the anal end, so that it here lies at

right angles to the axis of the rectum, but does not extend at all beyond’

the anus. Orally, there is in the median plane only the slightest trace
of the lophophoric ridge. By the formation of this ridge in the wall on
each side of the atrial chamber, the original atrio-pharyngeal cavity has
become separated into two regions. The space lying within or below the
ridge forms the pharynx and the intertentacular space ; that lying with-

MUSEUM OF COMPARATIVE ZOOLOGY. 21

out and above, the atrium of the adult. (Plate III. Fig. 25; Plate IV.
Fig. 32, atr.) Since the lophophore curves rapidly downward to the
anus and does not extend behind it, the act of cutting off the lower part
of the atrio-pharyngeal cavity from the upper (atrium proper) does not
continue behind the anus, which therefore opens directly into a part of
the atrium. This part has the form of a compressed funnel, and is
bounded behind and laterally by the kamptoderm, and orally by the
hinder ends of the lophophoric ridges, and also, since the latter do not
meet in the median plane, by the pharyngeal cavity. Thus it has come
about that the anus, which at first opened into the common atrio-pha-
ryngeal cavity of the bud, has now, in the separation of the two regions,
come to lie near their point of division posteriorly, but to open distinctly
“into the atrial cavity. The more pronounced separation of the part of
the atrial cavity into which the anus directly opens from the remainder
of the atrium takes place much later, and will be described further on.
In Figure 33, the ring canal (can. crc.) is seen to be already formed. At
this stage it is found on one side only, the left, if one looks at the poly-
pide from the tip of the branch. It occurs in only four sections (each 5 p
thick), being found on the next section behind Figure 33, and on two sec-
tions nearer the oral end. At its oral extremity, it terminates blindly
as a thickening of the outer layer of the bud; at its anal end, one sees
cells of the outer layer extending out partly over the canal, but failing
to enclose it ; in the next section the mesoderm is undisturbed. In sim-
ilar sections of an older polypide (corresponding in age approximately to
Plate IV. Fig. 35), the canal is found on both sides, and near to the oral
end, but at about the middle of the series (cf. Fig. 35) it is found to
open again into the body cavity. I therefore conclude that the ring
canal makes its first appearance at the base of the lophophore in a
region just oral of the middle of the polypide. Exactly how it arises,
whether by a growing together of the lips of a shallow furrow formed
from the mesodermal layer, or by the formation of a pocket, which, elon-
gating, penetrates between the inner and outer layers of the polypide at
the base of the nascent lophophore, I have not been able to determine.
Two facts induce me to believe that the later formation of the canal
oralwards results from the penetration of a sac-like mass of mesodermal
cells between the two layers of the polypide at the base of the nascent
lophophore. One usually finds, (1) as in Figure 33, can. erc., a double
mesodermal wall between the lumen of the canal and the cclom, and
one layer between the former and the inner layer of the bud; and
(2) at the oral blind end of the ring canal a number of loose cells

22 BULLETIN OF THE

(occasionally dividing) representing the blind end of the pocket and
lying between the inner and outer layers, both of which are intact.

Braem (’90, p. 50) describes the formation of the ring canal in Phylac-
toleamata as taking place in the manner just suggested for Paludicella.
His studies were made, he says, preferably on statoblast animals. Nitsche
(’75, p. 358) concluded that in Phylactolemata the ring canal was first
a furrow, whose lips fused, and my own study (’90, p. 129) has led me to
the same conclusion. Since reading Braem’s account I have looked over
some of my own sections of Cristatella again. Certainly the process is
not so clear in the buds of the adult colony as in the statoblast embryo
which Braem figures. Nevertheless the series of sections (90, Plate IV.
Figs. 33-38) given as evidence of my statement still seem to me capable
only of the conclusion I drew from them. Perhaps the processes may
be different in detail in the two cases; certainly the two explanations
are not fundamentally dissimilar.

The ring canal being established in the oral part of the polypide, it
grows forward, as I have said, and, secondarily, the canals of both
sides meet in the median oral line and their lumina become confluent
(Plate VI. Fig. 52, can. crc.). From what has already been said, it is
clear that the lateral parts of the ring canal are not now continuous
with each other behind. They become so only after the formation of
the tentacles.

The tentacles arise upon the lophophoric ridge at a stage a little later
than that represented in Plate IV. Figure 32. At the stage represented
by Figure 35, however, the tentacles have begun to form, as indicated by
the fact that in the series from which this figure was taken the fold into
the upper part of the atrium appears now deep, now shallow, according
as the section passes through the length of a young tentacle, or only
through the lophophoric ridge between the tentacles. The position of
the section (Fig. 35) is about the middle of the series, corresponding
to Figure 32.

By a comparison of facie 35 with Figure 32 in respect to the tenta-
cles, it will be apparent, first of all, that the lophophoric ridge itself has
been heightened and that this heightening has been effected, not by a
deepening of the fold existing in Figure 32, the lips of the fold remain-
ing quiescent, but by a movement downwards of the outer lip (*) of the
groove which is to form the ring canal. The movement is of course ac-
companied by an increase in the length of the kamptoderm, kmp. drm.
This growth of the lophophoric ridge naturally does not result in making
the tentacles project farther above the ridge. Their elongation must

MUSEUM OF COMPARATIVE ZOOLOGY. 22

take place quite independently of the former’s. The lophophoric ridges
have now become elongated folds lying upon the right and left of the
polypide, which at this stage has a very compressed appearance (Plate LV.
Fig. 41). The folds occupy the position of the ridges, and therefore do
not lie throughout their whole extent in one plane, but oralwards are
nearly parallel to the body wall (Plate III. Fig. 25), analwards trend
nearly at right angles to it. It results from this fact, that one cannot
see the anal tentacles when looking at the polypide from the side of
the body wall to which it is attached. Figure 41 (Plate 1V.) shows also
that no tentacles have yet made their appearance at the oral ends of the
two lophophoric ridges.1_ The tentacles are here seen to be arising in
two long rows, and so that those of one row are placed opposite the in-

tertentacular spaces of the other. There are six tentacles in each row.
- The rows are not continuous with each other oralwards or analwards.

The separation of the atrial and oral cavities, begun by the first
formation of the lophophore, is, now that the tentacles have arisen, much
more pronounced. Other changes now occur in this region, which pro-
duce an extensive modification in the form of the polypide.

One of the first of these changes is the close approximation and
finally fusion of the anal extremities of the lophophoric ridges oralward
of the anus. A stage in this is shown in Figures 43 and 44 (Plate V.),
which are sections in the position of the lines 43, 44, of Figure 25
(Plate LII.), but through a slightly older polypide than that represented
by Figure 25. The section shown in Figure 43 passes across the rec-
tum, grazes the outer lip of the ring groove of the anal tentacles, and
finally cuts, nearly longitudinally, one of the middle tentacles of the
row. The two lophophores are not yet completely fused in front of the
rectum. In Figure 44 (compare Plate III. Fig. 25, 44) this break in
the continuity of the lophophore is more prominent.

By the completion of the union of the lophophores in front of the
anus, the rectum is quite cut off from communication with the inter-
tacular space. It now opens only into the thin-walled, funnel-shaped
depression of the atrial cavity.

Pari passu with this operation the stomach and rectum are being
more completely separated from the pharyngeal cavity by the penetra-
tion of a double layer of mesoderm between these regions from each side,
and a fusion of the corresponding layers of the two sides. Finally, the

1 Compare Plate IX. Figure 77, which is a superficial view of the young lopho-

phore from Flustrella, in which the process is similar to that in Paludicella, only
the down curving of the anal tentacles occurs later than in the latter case.

24 BULLETIN OF THE

walls of the stomach and pharynx become separated from each other by
a part of the ccelomic cavity, as in Plate IV. Figure 36. This process
of separation of the alimentary tract proceeds analwards, and finally the
rectum is far removed from the oesophagus.

The anus thus comes to lie farther outside of the anal tentacles.
Finally, the ring canal, which is formed progressively farther and farther
analwards, follows the fusion of the anal ends of the lophophores, and
thus completes the canal behind the cesophagus. (Plate IV. Fig. 36 ;
Plate VI. Fig. 53, can. ere.)

The anal part of the ring canal is doubtless not merely a groove,
but a tube; but the ring canal is not closed at this, and probably not
at any stage throughout its entire extent, for in Plate VI. Figure 52,
two sections below Figure 53, an opening is shown to exist on each
side (at can. erc.), putting the cavities of the ring canals and the |
celom into communication with each other. These openings lie at
the sides of and slightly above the ganglion (gz., Fig. 52); a position
exactly comparable with that of the openings in the ring canal of Phy-
lactolemata, which leads from the ccelom into the lophophoric arms on
the one hand, and into the circumoral part of the ring canal on the
other.

By a comparison of Figure 41 (Plate IV.) with the sections shown in
Figures 60-62, it will be seen that the row of tentacles has undergone
a change of form: from being laterally compressed, it has become cir-
cular. This change of form has not resulted from an increase in the
number of the tentacles, for at the stage of Figure 41 there are six ten-
tacles on each side already formed (the sixth not visible), and there
are in front of the mouth spaces already reserved for the two additional
tentacles. There are also, probably, two nascent tentacles at the anus,
although these are little developed, making a total of 16. In Fignre 61
there are only 15 tentacles ; moreover, the actual diameter of the ten-
tacular corona in the sagittal plane is less than at the earlier stage
of Figure 41. This change of form is perfectly normal, all young
polypides having tentacles arranged in two parallel rows, and adult
polypides having a circular lophophore.

These changes in the form of the tentacular corona are correlated
with important changes in the direction of the axes of other organs.
These changes may be understood by comparison of Figures 25 and 36,
together with the assistance of Figures 7-9, all of which are oriented
in the same manner. In Figure 25 the points fixed by the cardiac valve
(vlv. cr.) and anus (an.) lie in a line which is approximately parallel to

“MUSEUM OF COMPARATIVE ZOOLOGY. 25

the body wall. In Figure 36 the line passing through the same points
makes an evident, but not very large, angle with the body wall. This
line has undergone, then, a slight change of position only. The axiy
of the anal tentacles lies in both cases nearly parallel to the body wall,
and so does the neural wall of the pharynx. The oral tentacles, on the
contrary, whose axes in the earlier stage are directed perpendicularly
to the body wall, lie in the later stage with their axes parallel to the
wall; and the base of the lophophore, which in the earlier stage trended
at its oral end parallel, at its anal perpendicular to the body wall, in
the later lies throughout its whole extent in one plane perpendicular
to the body wall. The axes of the oral tentacles have rotated through
an angle of nearly 90° relatively to most of the other organs of the poly-
pide. The canse of this rotation must evidently be sought in unequal
growth in different parts of the polypide. A comparison of the length
of the kamptoderm on the anal side in Figures 25 and 7 indicates
that it has grown more in length than on the oral side. This excessive
growth would tend to rotate the line wv. cr. — an. to a position perpen-
dicular to the body wall. Since this rotation has not occurred to so
great an extent as was to have been expected, we must look for a com-
pensating growth on the oral side of the polypide, between vlv. cr. and
the neck of the polypide, which shall be nearly equal to the excessive
growth of the anal kamptoderm, and which must be outside of the oral
kamptodem. These conditions of location are fulfilled only by the
oral wall of the cesophagus, and it is by change of position and growth
of this wall that the extension of the anal kamptoderm is nearly com-
pensated for on the oral side of the polypide. By this growth in the
wall of the cesophagus the oral part of the ring canal has been brought
to lie over the anal part, the sagittal diameter of the tentacular corona
has been reduced, and the compressed lophophore has been transformed
into a circular one.

Concerning the number of tentacles, Dumortier et van Beneden (50,
p- 46) observe that in the adult there are ordinarily 16, although
individuals with 18 tentacles occur not infrequently, an observation
which Kraepelin (’87, pp. 98, 99) confirms. In addition to these num-
bers, I have found 15 and 17. The growth of the odd tentacle is quite
interesting. The sections reproduced in Figures 60-62 (Plate VI.) will
serve to illustrate a condition which I have quite frequently found in
a polypide with 17 tentacles. In this particular series there are only
15 tentacles. The successive sections abundantly demonstrate that
the odd tentacle (*) is anal in position, and that it is younger than any

26 BULLETIN OF THE

of the others; thus in Figure 61 its tip is cut, in Figure 60 there are
only 14 tentacles visible, and these are found in the two following sec-
tions. Since there are six sections which pass through the tentacles,
and the odd tentacle is found in only three of these, it follows that it
is only about one half as long as the others.

The nervous system arises, as in Phylactolemata, by a depression in
the floor of the common atrio-pharyngeal cavity, in the region which later
becomes the anal surface of the pharynx. As in Phylactolemata, we
first see a shallow pit (Fig. 25, gn.).. This appears to become deeper,
sinking downward and somewhat toward the cardiac valve (Fig. 78, gn.).
Finally it becomes constricted off from the wall of the esophagus, and
then appears as a cellular mass closely attached to it and surrounded
exteriorly only by mesoderm. (Plate I. Fig. 8; Plate VI. Figs. 52,
53, gn.) Even before the closure of the ganglionic pocket is completed, -
the formation of the circumcesophageal nerve, first described by Krae-
pelin (’87, pp. 62, 63) in the adult, begins.

Figure 52 (Plate VI.) shows a transverse section of a young polypide
in which the ganglion is solid, and not provided with a large cavity as
in Phylactolemata. There is a small cavity in the upper part of the
ganglion, and this is not yet wholly closed from the esophagus. The
ganglion is continuous with a pair of hornlike processes (”.) which
partly enclose the cesophagus, and at a later stage do so wholly
(Plate IV. Fig. 36,2.) The cells of these horns are found dividing in
unusual abundance. The horns lie next to the digestive epithelium,
and between it and the mesodermal lining of the ring canal. From the
method of growth, and from the sharp line of separation between the
tips of the horns and the surrounding tissue, there can be little doubt
that the circumesophageal nerve of Paludicella, like the lophophoric
nerves of Phylactolemata, arises as an outgrowth of the brain.

Serial sections show that the ganglion suddenly diminishes in size
immediately below the point at which the circumoral nerves arise, but
one can trace a layer of cells continuous with the brain downwards for
ten or fifteen micra farther, to near the cardiac valve. At this point
one can still see nuclei of a third layer lying between the digestive epi-
thelium of the valve and the mesoderm. It seems to me, therefore,
that this may be regarded as a gastric nerve, which seems to originate
by a single root and later to give rise to two nerves, one of which lies
on either side of the cardiac valve.

MUSEUM OF COMPARATIVE ZOOLOGY. Darl

7. ORIGIN OF THE MUSCLES.

a. Retractor. — After its first formation the bud becomes elongated
in the direction of the axis of the branch. The derivation of this elon-
gated stage from the much shorter earlier one might be effected in one
of two ways: either, first, by the ingression of cells from the ectoderm
at points successively more and more remote from the point of primary
invagination, the additions to the length of the bud being made by a
continuation backwards of that process by which the first foundations
were laid; or secondly, by cell proliferation at the point of first invagi-
nation pushing the oral end of the buds farther and farther from the

neck of the polypide.

‘I think there can be little doubt that the second is the method
by which the bud becomes elongated; and for the following reasons.
(1) The oral end of the bud, on the supposition of continued invagina-
tion of the body wall, should become very gradually of less diameter, and
transverse sections at that end should exhibit the ingression (potential
invagination) of cells which were observed in the earliest stage; but
as a matter of fact the oral end is abrupt (Plate III. Fig. 22, 23, Or.),
and no stages of ingression are to be found there. (2) On the first
assumption, the inner layer of the bud should be at all points in equally
close relation to the ectoderm of the body wall; on the second, the
inner layer should be closely connected with the ectoderm at the neck
of the polypide (Plate III. Fig. 22, cev. pyd.), but elsewhere it should
be sharply separated from it. As a matter of fact, a sharp line can
be distinguished, in a sagittal section, separating the inner layer of the
bud from the overlying ectoderm at all points except at the neck (anal
part) of the polypide (Plate III. Figs. 22-25). Moreover, cross sections
of the anal part of the bud show the inner layer passing directly into
the ectoderm, and oralward the outer layer of the bud tends to pene-
trate more and more between the ectoderm and the inner layer.
Therefore I conclude that the inner layer of the bud is constantly
augmented by cell proliferation in its mass, and especially at the neck
of the polypide, and this explanation also accounts for the active cell
proliferation observed at the neck in Plate III. Figure 22, cev. pyd.

Since the polypide later becomes attached to the body wall by the
comparatively narrow “neck” only (Figs. 7, 9, cev. pyd.), a separation of
the oral part from the body wall has to take place. This process begins
at the oral end. In its earliest stages it is indicated by the sharp sep- .
aration of the inner bud-layer from the overlying ectoderm, and the

28 BULLETIN OF THE

partial penetration of the mesoderm on each side into the space between
these two layers (Plate IV. Fig. 30, ms’drm.). At a later stage the
mesoderm may be seen as a single cell layer lying between the ectoderm
and the inner layer of the bud midway between the oral and anal ends
(Plate IV. Fig. 32, ms’drm.), and as a double cell layer at the oral end of
the bud (Fig. 34, ms’drm.). It is from these cells at the oral end of the
bud that the retractor muscles are to arise (Plate III. Figs. 23-25, cl.
mu. ret.). As the oral end of the kamptoderm and cesophagus to which
their inner ends are attached moves away from the ectoderm, and as the
area of the latter itself increases, the two ends of the cells move farther
and farther apart, and the young muscle cells become drawn out into
spindle-shaped muscle fibres. (Plate ITI. Fig. 25, cl. mu. ret.; Plate IV.
Fig. 36, mu. ret.) The retractor thus arises unpaired and remains so
at its origin, but nearer its insertion in the ring canal and cesophagus .
one can distinguish a division into right and left masses. The adult
muscle fibres consist of two parts at least, the inner contractile portion
and an outer less modified protoplasmic portion, which can be traced
over the whole of the first part, but is most evident around the nucleus,
where it has a granular appearance.

b. Pyramidalis. — At about the stage of Figure 25 (Plate III.) one
finds, on cross sections of the branch which pass through the neck of the
polypide, that the mesoderm of the body wall on each side of the neck
is greatly thickened, and that its closely packed cells, which lie three
or four deep, have become somewhat elongated. Cell division is quite
common in the ectoderm of this region, and by it the area of the cireum-
cervical region is increased and the two ends of the muscle fibres are
carried farther apart, one end remaining attached to the neck of the
polypide and the other moving towards the abatrial surface. I have
given reasons above (page 16) for believing that the abatrial ends of the
muscles are not carried towards the abatrial side passively, and solely by
the growth of the body wall, but that the ends move relatively to the
cells of the body wall. A somewhat late stage in the development of
the pyramidalis is shown in Figure 63 (Plate VI.). Nearly the whole
of the mesoderm of the body wall has here been transformed into
muscle cells. The insertion of the muscles is in the mesoderm of the
neck of the polypide. (Plate VI. Fig. 63; Plate V. Fig. 45.)

c. Parietal muscles first make their appearance at about the stage
of the terminal individual of Plate II. Figure 14, immediately below
the bud and to the right and left, i. e. so that the muscles, which
usually arise paired, have their long axes parallel to the sagittal plane

MUSEUM OF COMPARATIVE ZOOLOGY. 29

and perpendicular to the long axis of the branch. They arise from cells
of the mesoderm, most of which in this region are filled with vacuoles,
and often project into the celom. But in my opinion the muscle cells
do not themselves arise from such vacuolated cells, for at even an earlier
stage (corresponding to Figure 21, Plate III.) one can distinguish thick-
ened patches of elongated cells in the mesoderm which are undoubtedly
the young muscle cells; but they do not show the slightest traces of
being vacuolated, and in fact are sharply distinguished from the adjacent
cells by their uniformly granular appearance and their deeper coloration.

Braem (90, pp. 124, 125) has already stated that the parietal muscles
arise in pairs, and come to traverse the ccelom, not remaining in the
body wall. The truth of this statement I can confirm in‘the case of
the parietal muscles first formed, which lie near the future septum.
Plate V. Fig. 42 shows the origin of the muscle fibres on both sides
of the branch. They have already migrated into the celom. As Braem
plainly states, the component parts of this pair of muscles, developed
from the mesoderm, migrate towards each other and finally fuse into
one unpaired mass, as we see in Plate III. Figure 26. It is perfectly
evident, in this case at least, that both ends of two muscles originating
far apart migrate in some manner towards each other so that the cor-
responding ends come to lie close together. Such a migration cannot
be accounted for merely by growth of the body wall. The ends of the
muscle fibres must move relatively to the body wall.

When the muscles have reached their permanent positions in a
diameter of the branch, we find their ends attached to the cuticula.
As the muscle fibres stain deeply in haematoxylin, they can be distinctly
traced through the vacuolated and poorly stained cells of the body wall
(Plate III. Fig. 26). Figure 29 shows a bit of the wall mechanically
separated from the cuticula, the end of the muscle fibre remaining in
place. Fine lines can be distinguished in the contractile, deeply stain-
ing portion of the fibre. The surface by which attachment is effected
appears very slightly crenulated on longitudinal sections of the muscle
fibre. I could not distinguish any structural peculiarity on the part
of the cuticula to which the muscle was attached, — nothing to indicate
how attachment is effected.

Freese (88, pp. 15, 22, Fig. 11) has described a similar method of
attachment of the muscles to the cuticula for Membranipora.

1 My friend, Dr. G. H. Parker, tells me that a similar method ot attachment of mus-
cle fibres to the cuticula occurs in Crustacea. According to Tullberg (’82, pp. 27, 44,

45), the adductor muscle fibres are in Mollusks attached to the cells of the ectoderm.
The same condition as in Mollusks seems to exist in Annelids (Eisig, ’87, pp. 25, 36).

30 BULLETIN OF THE

At a later stage smaller bundles of muscles arise successively toward
the neck. These muscles are free from the body wall at their middle
region. They do not usually pass through the colom in a diameter of
the branch, however, but rarely subtend as chords an are of more than
120°. As Braem supposed, such muscles, although arising later than
the most proximal pair, originate in a similar manner to them (Plate
VI. Fig. 55). The mesoderm is very thin at the region at which they
are first seen, and they are quickly discerned by their larger nuclei
and prominent cell body. At a later stage they have grown much
longer, and become freed from the body wall at their middle part.

As is well known, there are two fwniculi in Paludicella, called by
Allman respectively anterior (nearer the atrial opening) and_ posterior.
The origin of the funiculi of Paludicella was observed by Dumortier

et van Beneden as long ago as 1850. They say (p. 54), “La couche ©

muqueuse une fois formée s’etend rapidement dans Il’interieur et touche
bientét par son extrémité inférieure les parois opposées de la loge.
Les cellules muqueuses dont le tout est encore composé contractent de
l’adhérence dans cet endroit, et c’est ce qui donne naissance au muscle
rétracteur de l’estomac [= funiculi].” Allman (56, p. 36, Plate XI.
Figs. 7-9) also describes and figures very clearly and correctly this pro-
cess, and Braem (’90, p. 127) has recently confirmed their observations.

It is perhaps unnecessary to redescribe the more evident part of
this process, the contact of the polypide with the abatrial wall of the
branch. The mesoderm of the bud comes into contact with that of
the body wall, the cells of each of the two layers become attached to the
other, and by the withdrawal of the polypide the attachment persists
at two points forming a long drawn out string of tissue. Figures 36?
and 38 (Plate IV.) are contributions to a knowledge of the finer details
of this process. Apparently the upper funiculus is developed earlier
than the lower, as I have always found it longer at about this stage.
The lower funiculus at present consists of only the two mesodermal
layers of body wall and polypide intimately united. The funiculus
itself consists of a cord several cells thick; but I believe these cer-
tainly to be derived from the mesoderm only. Very early some of
these cells show an appearance of highly refractive and deeply staining
fibres, which I interpret as muscular differentiation (Plate IV. Fig. 38,
fun. su.), so that the funiculi must be regarded as partly muscular
in function. As in Phylactolemata, these fibres lie near the axis of the
funiculus. Braem (’90, pp. 66, 67,) has demonstrated that the muscular
fibres of the funiculus of Plumatella pass directly into the muscularis

MUSEUM OF COMPARATIVE ZOOLOGY. ol

of the body wall. It is interesting to find them persisting in the fu-
niculus of Paludicella, beneath the mesodermal covering, although there
is apparently no muscularis developed in the body wall of this region.

8. Tue ForRMATION OF THE NECK AND ATRIAL OPENING.

This is the last act in the history of the polypide that I shall con-
sider. The body wall around the neck of the polypide continues to
possess a less differentiated character than the remaining portion for
some time after the oral tentacles have undergone their revolution.
One still sees the cells of this region dividing, and the body wall is
gradually protruded at this point above the general level. (Plate II.
Fig. 14, cev. pyd.) The neck of the polypide to which the kamptoderm
is attached consists, at a somewhat earlier stage than that just referred
to, of a disk of greatly elongated columnar cells in the centre of which
there is a distinct notch caused by the presence of shorter cells at that
point. (Plate VI. Fig. 63 6.) At the inner ends of the columnar cells
of the neck lies a flat epithelium quite sharply marked off from the
latter, but which is nevertheless undoubtedly derived from the same
source as the columnar cells and the inner layer of the bud. This flat
layer is directly continuous with the inner layer of the kamptoderm.
At a later stage, the columnar cells of the ectoderm become elongated
still more, and lose their staining capabilities at their outer ends. Still
later one sees them arranged in the form of a cup whose cavity is sep-
arated from the outside world only by a cuticula which becomes slightly
invaginated at this point. The cells are soon found with their long
axes perpendicular to the edge of the cavity they line.

There is one point that I have not been able to determine; namely,
how the new cuticula, which is certainly formed at the ends of the cells
which lie next to the cavity, becomes continuous with the old cuticula
of the non-invaginated body wall, as it is in Figure 50 (Plate V.). The
presence on the new unstainable cuticula of the remains of the stainable
one, whose origin I have already discussed at length, may serve as a
guide to the limits of the old cuticula. The new cuticula is being secreted
by cells lying deep in the inner end of the neck, and apparently in one
rod-like mass. Unfortunately, I lack stages between this figure and
Figure 45 (Plate V.), which shows the neck of a nearly or quite adult
polypide cut lengthwise. The solid cuticular rod has now become a hol-
low cylinder, whose inner (deep) edge is embedded in the deep-lying cells
of the neck. Moreover, one finds superficial to the cuticula of the gen-
eral body wall a second cuticular cylinder, which is free at its outer end,

32 BULLETIN OF THE

but at its inner end fuses with the surrounding cylinder of cuticula. This
inner cylinder, which is probably formed, as Kraepelin (’87, p. 40) sug-
gested, by splitting of the delicate cuticula at the base of the marginal
thickening (Randwulst), has been compared by Kraepelin to the “ collare
setosum ” of Ctenostomes. The Randwulst itself I believe to be the equiv-
alent of the Diaphragma of Nitsche, as I shall try to show later.

At the deep end of the neck (Fig. 45), the inner layer of the bud is
seen to be continuous with the ectoderm. ‘The region of transition may
be called the atrial opening, of. air. Surrounding the atrial opening
is a fold in the ectoderm, and between the layers of this fold is a thin,
non-stainable homogeneous layer, slightly more refractive than the sur-
rounding protoplasm. This membrane extends also a short way into
the kamptoderm, and here lies between its two cell layers. Embedded
in this homogeneous membrane in the fold, one can distinguish still
more highly refractive bodies, spht. On account of their form and
high refractivity, I believe these to be muscle fibres cut across. The
homogeneous membrane has also the same general appearance and
relation to the muscularis as the so-called supporting membrane of
Nitsche, and it is the only representative of that structure that I
have found in Paludicella.

9. DEVELOPMENT OF THE COMMUNICATION PLATE.

In their description of Paludicella, Dumortier et van Beneden (750,
p- 40) say : “Il se compose de plusieurs loges ou cellules placées bout &
bout . . . en sorte qu'il n’y a aucune communication entre les différents
animaux.” Also Allman (’56, pp. 114, 115) refers to the presence of a
perfectly formed septum separating the cavities of adjacent “cells.” To
Kraepelin (’87, p. 38) belongs the credit of having first carefully studied
this structure in the adult by means of sections. He came to the con-
clusion from the appearances which he figures (cf. my Plate V. Fig. 49),
that there are small canals passing through the nearly homogeneous
central mass, and therefore ‘dass wir in dem ganzen Apparat eine Vor-
richtung zn erblicken haben, durch welche Nahrstofflésungen des einen
Tieres mittels siebartig wirkender Cautelen in die Kérperhdhle des
Nachbarindividuums ibergefiihrt werden.”

The descriptions of Kraepelin concerning the structure of the “ Roset-
tenplate” are confirmed by my own observations, and seem to justify his
conclusions concerning its function. The development of the organ has
not, however, been carefully observed heretofore. Korotneff (’74, Plate
XII. Figs. 1 and 2) gives figures to show this process, but I have never

MUSEUM OF COMPARATIVE ZOOLOGY. 30

seen any such circular groove surrounding the branch as he figures. In
all cases the two layers of the body wall form a circular fold, in which,
however, there is never, even at the earliest stages, a space between the
ectodermal layers, nor any infolding of the cuticula as Korotneff (’75, p.
369), according to Hoyer’s rather incomplete abstract, maintains (Plate
V. Fig. 47). When the circular fold has advanced until only a small pore
remains, by which the cavities of the older and younger individuals are
kept in communication, the mesodermal cells at the angle of the fold
begin to undergo a metamorphosis both in form and histological charac-
ter. In the first place they become much elongated and extremely
attenuated, passing from one surface of the septum to the other, and
forming the lips of the pore. In the second place their plasma becomes
first deeply stainable, and later, in addition, homogeneous and highly
refractive. These metamorphosed cells form what may be called the
teeth of the plate. They are derived wholly from mesoderm.

The cells in the upper mesodermal layer next increase rapidly in
number and size, and the number of teeth is also augmented (Plate V.
Fig. 48). The metamorphosis of the cells extends still farther away
from the communication pore, and involves the lower mesodermal layer ;
but, apparently, each cell of the latter is metamorphosed only to a
slight depth within its cell wall (Fig. 51), whereas in each of the upper
cells the ends which project into the communication pore are modified
through and through (Fig. 46). At a later stage (Fig. 49) the meta-
morphosed part of the cell seems quite sharply cut off from the active
part, and the slits between the metamorphosed teeth are considerably
reduced. Nevertheless, I believe a transfer of fluids may still occur
between them, for even in the adult communication plate one can trace
continuous lumina when the cells are by accident torn off from the
“teeth” which they have produced. It is important to note that the nu-
clei are not destroyed in the cell metamorphosis. Some lie above, others
below the pore, and become deeply stainable. The ectodermal layers of
the communication plate secrete a cuticula between them. This is thin-
ner than that of the body wall, and does not extend, of course, to the
centre of the communication plate, but ends in a thickened ring, whose
diameter is about one tenth the diameter of the plate, or, absolutely,
about 9.4 p.)

1 Reichert (’70, p. 267) first carefully described the Rosettenplate of Cteno-
stomes in Zodbotryon, and the organ in Paludicella must be regarded as homologous
with it. The central circular hole in the cuticula of Zodbotryon is from 7 to 10 «
in diameter, and from one ninth to one seventh that of the entire plate. Similar

VOL. XXII. — NO. l. 3

34 BULLETIN OF THE

10. ROLE oF THE MESODERMAL VACUOLATED CELLS.

Allman (56, p. 36) observed that at the time a lateral branch was
well formed, and before the origin of the polypide, the internal outline of
the body wall was uneven, and he figures (Plate XI. Fig. 4) very large
cells lying on the inside of the body wall. Korotneff (74, Taf. XII.
Figs. 1-3, ’75, pp. 369, 370) progressed a step farther, and recognized
a distinction between large, coarsely granular cells projecting into the
cavity of the bud, especially near the tip, and the surrounding epithelial
cells. Braem (’90, p. 126), finally, has described them more accurately.
He finds cells filled with numerous granules in the youngest branches of
the colony. Immediately around the bud, such cells are less abundant ;
probably, he says, because their granules have been absorbed in the
process of formation of the polypide. He compares the granules with
the yolk spherules of the statoblast cells, and believes that they are to
be regarded as food matter.

My observations and conclusions, achieved independently of Braem’s,
fuily confirm his. I have succeeded, moreover, in obtaining some addi-
tional evidence as to the function of these cells, a subject to which I
have paid some attention.

First as to the distribution of the cells, and their frequency in different
regions. We can best get an approximate idea of this by counting the
number of the reticulated cells in each section of a series which in-
volves a young polypide and the regions immediately above and below
it. It is not possible to do this with perfect accuracy, because there is
no sharp line of distinction between reticulated and non-reticulated cells ;
but I have made the count without prejudice, and I believe as fairly as
possible. When the bud of the polypide has reached about the stage
shown in Plate III. Figure 28, the number of reticulated cells seems to
have nearly reached a maximum. In the series from which this figure
was taken there was an average of 4.8 reticulated cells to the section in
the ten sections distal of the bud. There was an average of 11.2 reticu- ~
lated cells to the section for the twenty sections which passed through the
bud, and 11.2 for the eleven sections proximal of the bud in the region

perforated organs have been described by Smitt (’67, p. 426), Nitsche (’71, pp.
420-422), and Vigelius (’84, p. 26) for Flustra, by Freese (’88, p. 7, 13, 14) for
Membranipora, by Ostroumoff (’86%, p. 18) for Lepralia, by Claperede (’70, p. 160)
for Bugula and Scrupocellaria, by Ehlers (’76, p. 14) for Hypophorella, and by
Joliet (°77, p. 222) for Bowerbankia. Nitsche alone (’71, p. 455) has had anything
to say upon their origin, and this apparently not the result of direct observation.

MUSEUM OF COMPARATIVE ZOOLOGY. 39

at which muscle fibres were arising. A similar series through a slightly
older bud gives for the same regions respectively 5, 14, and 13 cells per
section. In series through older buds, a rapid decline in the number of
these cells occurs so that at the stage of Figure 30 (Plate IV.) there is an
average of only about 3.1 cells per section through the bud, and about
2.2 immediately below. These reticulated cells are not very numerous
in the region of the bud at the time this is about to arise, as a look at
the sections Figures 3 and 4 shows. One finds reticulated cells in the
mesoderm at the tip, and most abundantly at a rather early stage in
the development of the bud. The number of these cells diminishes as
one leaves the young individual to pass into the next older of the same
branch. In the adult such cells are rather rare; so rare, in fact, that
Kraepelin (87), who studied with care the body wall of the adult indi-
vidual, makes no mention of them. Nevertheless they do occur in the
cells which are to go into the lateral branch (Plate II. Fig. 15), as well
as elsewhere on the body wall. The place in which one finds the reticu-
lated cells most abundant, however, is in the young Jateral branches near
the time when the polypide bud is about to arise. Here every cell of the
mesoderm is greatly enlarged, and filled with the vacuoles (Plate VI.
Fig. 58). These are very apparent upon a surface view of the branches.
Reticulated cells occur not only in the mesodermic cells of the body
wall, but also in those of the polypide bud, which were, indeed, only
lately a part of the mural mesoderm (Plate III. Fig. 28, Plate VI. Fig.
56). Thus, in general terms, we may say that the reticulated cells of
the mesoderm are chiefly confined to regions in which there are young
buds developing; and since these arise at intervals only, there is a
periodicity in their appearance,—a time of maximum development
followed by one of decline, then one of reproduction of such cells in
the ends of branches culminating in another maximum, and s0 on.
Turning our attention now more particularly to the structure of these
reticulated cells at the period of their best development, we find (Plate
VI. Figs. 56, 57, 59) that they possess a large nucleus lying at the
deep end of the cell and containing a relatively large nucleolus, and that
this is surrounded by a granular protoplasm with included vacuoles. It
is very common to find the nuclei in various stages of division, and thus
it is frequently seen as a mass of chromatic substance without any nu-
clear membrane or nucleochylema. The vacuoles, which in the more reg-
ular cells lie in a semicircle nearly peripheral (the nucleus being at the
centre), are highly variable in number, some of the cells containing as
many as 20 to 30. They often appear as perfectly clear homogeneous

36 BULLETIN OF THE

spaces, but more frequently at this stage contain a spherical body, which
frequently fills the entire vacuole and is more refractive than the sur-
rounding plasma (Fig. 59). Not unfrequently one sees a less refractive,
clear space, surrounding the highly refractive body (Fig. 57).

The description just given corresponds to the condition seen in a ter-
minal branch whose polypide has attained the development of that shown
in Figure 28 (Plate III.). At the time immediately preceding the ori-
gin of the bad, the cuboidal cells of the mesoderm show traces of vac-
uolation, but their form and size have suffered no appreciable disturbance.
This vacuolation of cells proceeds hand in hand with the development of
the bud, and one first notices the homogeneous, highly refractive bodies
in the vacuoles when the bud is well established. At about the time the
alimentary tract has become formed, the reticulated cells begin to show
signs of degeneration. The highly refractive bodies have disappeared,
and the skeleton of the cell which remains becomes very irregular. As
already stated, the number of reticulated cells also decreases, until, at
about the time of “rotation” of the polypide, there are few reticulated
cells in the mesoderm, but these few are filled with vacuoles and their
highly refractive bodies.

The conditions of the mesodermal cells at the tip are slightly different
from those found elsewhere. Usually, instead of many small vacuoles,
one finds only one or two which fill almost the entire cell, — sometimes
perfectly homogeneous in structure, sometimes containing small highly
refractive granules.

These appearances I believe to be explicable only upon the assumption
that the mesodermal cells are capable, at the time at which the young poly-
pide is arising, of imbibing the fluids of the body cavity and storing them
up for the purpose of supplying the rapidly growing cells of the bud with
nutrition. It is desirable to show reasons for believing, first, that the
contents of these cells are nutritive matter ; secondly, that this has been
taken up from the body cavity; and, thirdly, that it is supplied to the
bud for its nutrition.

It must be admitted that the strongest argument for the belief that
these are absorbing cells is derived from a comparison of the appearances
which we find in these cells with those described for Protozoa, and by
Metschnikoff (’83, Taf. I. Figs. 18-35) for mesodermal trophic cells.
At the same time, it must be acknowledged that similar cells are found
in other cases where the function is believed to be not ingestive, but
excretory, as in the chlorogogen cells of Annelids, as shown by Kiiken-
thal (’85), Eisig (’87, pp. 751-762), and others, and indeed even in the

MUSEUM OF COMPARATIVE ZOOLOGY. ap

cells of coelomic epithelium. Lisig (’87, p. 752) has already clearly ex-
pressed how, in view of the many cases of high excretory activity of
peritoneal and blood cells demonstrated by him, “ kiinftighin bei der
Beurtheilung gewisser Zelleneinschliisse erst genau festzustellen sein wird,
ob man est mit von aussen aufgenommenen (gefressenen), oder aber mit
von der Zelle ausgeschiedenen Producten zu thun habe.”

A criterion for judging this matter may be found, in the first place, I
believe, in this: that the products of excretion increase with the activi-
ties of the cells, and are thrown out, usually in the shape of concrements,
either from the cell or with the cell into the coelom ; whereas bodies
taken in from without for digestion decrease with the activities of the
region. In the second place, vacuoles are less characteristic of excretory
tissue than of imbibitory. But vacuoles are the important feature of the
reticulated cells in Paludicella, and the highly refractive bodies are less
constant phenomena. As for the latter, they are not found in the later
stages, nor in the earliest. Moreover, these bodies differ from excretion
concrements in this, that they are always transparent, often almost indis-
cernible in the vacuole, except by their higher refractiveness, and there
is no sharp demarcation between cases of vacuoles filled by such bodies
and those the contents of which are less highly refractive. The degree
of refractiveness is variable, at one end of the series grading off into the
undifferentiated fluid of the vacuole. What significance is to be assigned
to these highly refractive bodies in the vacuoles? There are two reasons
why I do not believe that they represent solid food particles devoured
as such by the mesodermal cells. First, I do not find such highly
refractive bodies lying loose in the body cavity before the stage at which
they first appear in the cells; and, secondly, one can find all gradations
between less highly refractive vacuoles and highly refractive ones (which
I have assumed to be entirely filled by one highly refractive body), and
between the latter and vacuoles containing a small body surrounded by
a broad, clear area. I believe, therefore, that the vacuoles are rather
cavities filled with chemically different nutritive fluids, which are acted
upon differently by the reagent.

I have assumed that the contents of the vacuoles represent material
taken up from the body cavity, because it seemed most reasonable to
look there for the source of their supply. The ectoderm is covered on
its outer surface by an apparently continuous cuticula, so that food
cannot be gained from the outside world directly. It is, moreover, not
unreasonable to suppose that some of the products of digestion elabo-
rated by the adult polypides of the colony pass through the wall of the

38 BULLETIN OF THE

alimentary tract in solution, and thus into the body cavity, from which
they may be taken up by the mesodermal cells at the growing part
of the body wall. Nor is there anything unreasonable in insisting that
the body cavity functions, in these animals without blood-vessels, as a
hzemo-lymph system, for in many animals with incomplete vessels, such
as Arthropods, Hirudinea, etc., it evidently does so to a certain degree.
Moreover the constant motion of the fluids of the body cavity of Bryozoa
points to the same thing. It is conceivable that the food in the digest-
ive cells might be distributed throughout the body wall without passing
into the body cavity, since all parts of the body wall are continuous
with the digestive epithelia of the polypides of the colony. Two consid-
erations make it improbable that the cells of the tip gain their nutri-
tion in this manner from the digestive cells of the youngest functional

polypide: first, the considerable distance of the rapidly growing, and,

hence rapidly consuming tip, from the youngest functional polypide ;
and, secondly, the fact that the tip is separated from that polypide by
one or two septa, whose central cells are highly metamorphosed, and
apparently cuticularized, thus serving to break the continuity of the
cell wall. An objection to the assumption that the mesodermal cells of
the tip derive their nourishment from the products of digestion which
have been elaborated by the alimentary tract of the youngest polypides
and passed into the body cavity, might be based on the fact that the
communication plates are always fully formed between the bud and
the next older polypide before the older polypide has become functional.
If the communication plate were a closed septum, this would be a fatal
objection. But it is not closed to fluids carrying food in solution. The
very persistence of an opening indicates that it has a function, and favors
the hypothesis here presented.

Positive evidence for the conclusion that the reticulated mesodermal
cells take up food material from the body cavity is derived from the
fact that these cells often show evidences of being amoeboid. Thus they
are sometimes found with pseudopodia-like prolongations of the cell body
(Figs. 54 and 59). <A large percentage of all reticulated cells of this
stage show similar appearances. Although they here seem to keep their
places in the mesodermal epithelium, their movements being confined
to their free surfaces, the cells derived from the homologous Jayer in
marine Bryozoa are migratory. Therefore these may be considered as
morphological equivalents of migratory cells, which have come to remain
in or have never departed from the mesodermal layer, although possess-
ing some of the characters of these notoriously trophic elements.

oo)

MUSEUM OF COMPARATIVE ZOOLOGY. ae)

That the nutritive matter in the ccelomic cells is supplied to the
young bud is what we should expect, since the cells of the bud, being
most actively engaged in growth, will require most nutriment. The
actively dividing cells of the outer layer of the bud are thick and cuboid,
and are rarely so highly vacuolated as the more passive ones of the body
wall; yet occasionally one finds one or two huge cells in this layer full
of vacuoles, which contain highly refractive bodies. In most cases these
cells send out processes into the ccelom, and in a few instances I have
seen them united with similar processes from cells on distant parts
of the body wall. This remarkable phenomenon, shown in Figure 54
(Plate VI.), may possibly signify that cells of the coelomic epithelium at
times directly communicate with those of the outer layer of the bud to
supply it with nourishment. Nutrition of the bud is also probably
effected through the presence of large reticulated cells at the angle
between the bud and the body wall. A condition like that shown in
Figure 56, cl. ret., is very common.

Every author from Dumortier et van Beneden to Braem, who has
studied the origin of the polypide in Paludicella, has mentioned the
presence of highly refractive bodies in the alimentary tract at the time of
its formation. These are very striking in some living specimens, and
in whole animals after killing. I have found that this highly refractive
substance in the bud is exceedingly variable in amount and position,
and that sometimes it is apparently absent. When present, it usually
occupies the lumen of the forming alimentary canal ; but, as sections
show, it is often located in large vacuoles in the future digestive cells
of the alimentary tract. It seems highly probable that, as Braem sue-
gests, this is nutritive substance, and it has doubtless come from the
body cavity through the agency not only of the outer layer of the bud,
but also of other parts of the coelomic epithelium.

I am inclined to interpret the phenomenon of cells filled with nutri-
tive material as an adaptation to the peculiar conditions of Paludicella,
in which the individuals are early separated from one another, except
for the communication plate, through which at best fluids can pass only
slowly, and in which a rapid growth of the body wall to produce the
polypide takes place periodically. The mesodermal cells rapidly absorb
the nutritive fluids of the body cavity and store them in their substance
before the formation of the communication plate, and give them out
again during the period of the polypide’s most rapid growth chiefly to
this part of the individual. This hypothesis has been mainly derived
from considering the fact of the great development of the reticulated

40 BULLETIN OF THE

cells in the lateral bud and the very early completion of its commu-
nication plate, the immediate needs of the polypide, which arises only
after the formation of the plate, being met by this supply of stored
nutriment.?

But why is the septum (communication plate) formed so early, if it
is desirable for the species that the growing tip should be well nourished
by the fluids of the body cavity? Here again I must resort to pure
hypothesis. I assume that the early formation of the septum is a pro-
vision for the protection of the stock against a rapid influx of the sur-
rounding water in case the branch is broken. One can understand how,
if the body wall and growing regions depend upon the fluids of the body
cavity for nutrition, an open communication of this cavity with the out-
side world would be a serious obstacle to regeneration of the body wall in
the lost part, or the growth of the stock in any other direction. There is’
a fact which ought to be mentioned in this connection, as bearing on this
hypothesis of the function of the sept. One frequently finds that in
stocks which have been handled with reasonable care the median branches
are broken off at either end, and in almost every colony one or more lat-
eral branches are missing from the parent branch. Apparently, then,
the lateral branches are unusually subject to destruction, and we find
the septz developed at a much earlier period between them and the an-
cestral branch than between individuals of the median branch. Compare
Plate IT. Figure 14, in which the communication plate has not yet begun
to form, with Plate VI. Figure 58.

III. Budding in Marine Gymnolemata.

1. ARCHITECTURE OF THE STOCK.

I have already described the process of stock-building in Paludicella,
and have attempted to show that it follows a certain law. I desire now
to present a few observations upon the architecture of certain stocks of
marine Gymnolemata, which will aid in arriving at some general con-
clusions later on. Other observers have worked out the architectural
laws of single species or groups, and I shall refer to their studies either

1 Similar conditions to those in Paludicella exist in some marine Bryozoa, and in
one of these cases, Bowerbankia, I find them fulfilled by a similar arrangement. The
young buds of the stolon which give rise to the “nutritive zooids” are, at an early
stage, loaded with food granules. As in Paludicella, so in Bowerbankia the
communication plates are formed early.

MUSEUM OF COMPARATIVE ZOOLOGY. Al

in connection with the species which I have used in common with them,
or in the general part of this paper, in considering the process of budding
in Bryozoa as a whole.

I will begin my description with Bugula turrita? of Verrill, which I
gathered in the summer of 1889 at Wood’s Holl, where it occurs abun-
dantly on the piles of the wharf. The stock is bushy, and, when its
polypides are active, of an orange color. In its simplest form the
stock consists of a central axis, which is somewhat zigzag, and gives off
lateral branches like the trunk of a tree. The lateral branches are in-
serted on the trunk in a spiral line. Each lateral branch is fan-shaped
(Plate VII. Fig. 64), the part corresponding to the handle of the fan
‘being the point of attachment, and the fans are smaller the nearer they
are to the tip of the trunk. The attachment of the branch to the
trunk is effected by one primary individual. Each fan-shaped branch
extends from its point of attachment obliquely upward and outward,
and, although it is slightly concave on its upper inner surface, the
concavity is not sufficient to prevent its being spread out upon the slide
for study without materially disturbing the interrelation of the indi-
viduals in the stock.

I have studied several branches flattened in this way (one of 400
individuals), and have made camera drawings of them. Since the
results in the different cases are substantially in agreement, I have con-
cluded that they are significant. One of these camera drawings is shown
in the figure just referred to. ‘

To designate individuals in the stock, I have adopted a simple no-
menclature. The forty-four terminal individuals are numbered from
1 to 44. The successive generations (if I may be allowed to use this
word in a loose way) are indicated by the Roman numerals from I. to
XIII. Any one individual is indicated by placing the numbers of the
radial line or lines to which it belongs first, and following this by
the Roman numeral of the generation to which it velongs. Thus,
27-30 IV. is an individual near the base of the twig 27-30 and of
generation IV. Figure 64° (Plate VII.) is a diagram showing the

1 This species is very similar in general habit to B. avicularia, Linnzeus, and to
B. turbinata, Alder (Hincks, ’80, pp. 75-80). It differs from the first named spe-
cies by possessing only one spine, on the outer upper edge, as described by Leidy
(55, p. 142), instead of having three, — two outer upper and onc inner and upper.
It differs from Hincks’s diagnosis of the second in having only two “cells ” in each
branch, instead of 3-6 in the upper portions. The form of the avicularium would
seem to ally it more closely to B. avicularia.

42 BULLETIN OF THE

arrangement of the individuals in Figure 64. The radial lines repre-
sent the rows of individuals; the concentric lines separate adjacent
individuals of the same radial row. The same nomenclature is used |
as in Figure 64.

In studying Figures 64 and 64%, one of the first facts which attracts
our attention is that (1) the individuals of the twigs are in pairs, and
the adjacent individuals of the two rows “ break joints.” In general, one
finds that the individuals of the same twig are of the same length ; but
since the two rows of any twig ultimately rest upon one, either the prox-
imal two individuals of these rows must be of unequal length, or else
they must arise on different parts of the individual which supports
them. Both of these cases occur. Sometimes one individual (26 IX.)
has nearly twice the length of the other (25 IX.), and in other cases
(9, 10 VL, 11, 12 VI.) the more proximal of the two individuals
(9, 10 VI.) arises so far proximally on the side of the supporting indi-
vidual 9-12 V. as to have a total length quite equal to that of the more
distal (11, 12 VI.). Owing to their different positions upon the indi-
vidual 9-12 V., these two individuals may be designated as lateral
(9, 10 VI.) and terminal (11, 22, VI). Zhe terminal individuals con-
tinue the ancestral row, the lateral individuals are the first of lateral
branches.

This distinction is an actual, and by no means a meaningless one.
The constant difference in position of the two individuals which rest
upon one shows conclusively that this branching cannot be regarded as
dichotomous, and I may say parenthetically that I shall try to show
in the general part of this paper that true dichotomy is not com-
mon in Bryozoan stocks, if indeed it exist at all. Now, since in
the rows of individuals in which there is no lateral budding the
distal lies directly terminal to the proximal individual, that individual
which fulfils this condition at the region of bifurcation of the twig
must be regarded as continuing the ancestral branch; and _ that
individual, conversely, which arises from the side of the single prox-
imal individual must be regarded as the lateral one. Thus we have
the stock composed of ancestral and lateral branches as represented
in Figure 64°.

(2) When two lateral branches are given off from two ancestral ones
which have had a common origin (and are consequently themselves re-
spectively ancestral and lateral branches), they are given off towards
each other. This is equally true whether the two lateral branches in
question arise in the same generation (32 X., 33 X.) or in different

MUSEUM OF COMPARATIVE ZOOLOGY. 43

generations (24 X.,25 IX.). This may be expressed by saying branches
are given off on the side towards the axils.

‘By consulting Figure 64* and tracing out the finely dotted lines which
connect the second, third, etc. axils of all branches counting from the
proximal end of the fan, it will be seen that (3) dateral buds tend to arise
on two closely related branches in the same generation. There are several
slight deviations from this rule. The less closely related the branches,
the less marked the tendency, although it is still discernible. (Cf.
branches 9-16, 23-30.)

This rule does not hold, however, so well on the margins as in the
middle region of the fan, for here another and a superior rule seems to
obtain. This is that (4) lateral budding occurs more frequently at the
margins of “fans” than elsewhere. Thus in Figure 64* there is at the
margins, on the average, 1 case of lateral budding to 4.3 cases of median
budding. Elsewhere the average is as 1 to 6.5. In larger fans the
difference is even more pronounced. This is true not only for the
“fans,” but also, to a less degree, for the two “‘subfans” which arise re-
spectively from the two individuals of generation II. (but 17, 18 is very
anomalous in this respect). In general, any rule deduced for the mar-
gin of the fans holds true also for subfans to any degree of subdivision ;
but the less perfectly, the higher the degree.

By consulting again the diagram, it will be seen that the branches
have attained different. lengths. Thus 9, 10, 29, and 30 contain repre-
sentatives of generation XIII., while the terminal individual of branch 1
is of generation X., and those of branches 35-44 are of generation XI.
So the curve which connects the tips of the branches (see dot-and-
dash line, Fig. 64*) would rise from 1 to 9-10 as a maximum, and fall
again till it reached the margin of the first subfan; then rise again,
reaching a second maximum in the middle at 29-30, and finally fall
again to the other margin. In general, then, (5) the marginal branches
are shortest, the intermediate ones longest, i. e. give rise to the greatest
number of generations.

Although the marginal individuals of say generation III., IV., or V.
do not support branches with so many generations as the intermediate
ones, yet they are not therefore necessarily less prolific in individuals,
because the number of branches arising distally of such individuals is
greater according to rule 4 than the number arising distally of the
intermediate ones. Thus, if we count the number of individuals borne
on each of the eight individuals of the fourth (IV.) generation of
Figure 64, we find in the given case: —

44 BULLETIN OF THE

1-8 IV. (an outer individ.) gives rise to 8 branches and 34 individ,

9-12 IV. (an inner ee se oO O: CO EO 3
13-16 IV. (an inner “ “ 923 «
17,18 1V.(asubouter “ “ Ca | ae
19-22 IV. (asubouter “ “ fC LIOE Ores
23-26 IV. (an inner ~ < $0 OST ae
. 27-30 IV. (an inner a 2 $e One

Outer. } 31-44 IV. 2 outer“ ag ee

According to the rule that inner branches are slightly prolific, we should
expect cases numbered 4 and 5 in the above table to contain the fewest
branches and individuals; in accordance with the rule that marginal
branches even of subfans are more prolific, we should expect them, on
the contrary, to contain more branches and individuals than cases num-
bered 3, 6, etc. The result is usually a condition intermediate between
that of the middle and outer branches, such as is partially realized in
case number 5. Case number 4 seems to present an unusual condition,
which may be correlated with the fact of its close approximation to
number 5. (See Fig. 64, 17-20.) From the consideration of this and
other cases, I think this conclusion may fairly be drawn: (6) Of the
four proximal individuals from which a fan arises, the outer two will bear
the greater number of individuals, the inner two the lesser.

Since from rule 2 median individuals (ancestral branches) occupy the
margins of fans (or subfans of any degree) and the lateral branches are
intermediate, it follows, as a corollary to rule 5, that, in general, the an-
cestral branches are the shorter, the lateral branches the longer ; and, as
a corollary to rule 6, that from any axil the ancestral branch will of the
two give rise to the greater number of individuals ; the lateral branch,
conversely, to the less, other conditions being equal.

We have deduced the laws of lateral budding on different parts of the
circumference. We find also that there is a regular variation in the
frequency of lateral budding, dependent upon the distance of the region
from the primary individual of the fan. This rule, like any other, is not
invariable, whatever the other conditions may be ; but it is more or less
dependent upon them. A small and regular fan having seven genera-
tions gives this result.

Outer.

. if
2:
Inner. Le
4,
Inner. ie
6

lid
Pe PDE Pp

No. of Generation. Number of Individ. Increase per Cent.
i. 1
it 2 100
Oe 4 100
iN% 8 100
Vi 12 50
VI. 16 334

VII. 16 0

MUSEUM OF COMPARATIVE ZOOLOGY. 45

In this table the first column gives the number of the generation, the
second the whole number of individuals in the generation, and the third
column the increase per cent of individuals in each succeeding genera-
tion over the last. In this specimen the increase underwent a very
recular diminution.

With larger colonies so great a regularity as that just shown is hardly
to be expected, nor is it found. The following table is based on
Figure 64, and is like the preceding; but in addition the percentage
increases have been averaged —i. e. the means of successive increases
taken in pairs have been given—to eliminate what may be called
accidental variations.

1

Number of Increase

Genera- Genera- |Number of; Increase

tion. Individ. | per Cent. Average. tion. Individ. | per Cent. Average.
I. 1 29
VIII. 28 27
IE 2 100 23
100 IX. 33 18
Til 4 100 18
100 X. 39 18
IV. 8 100 16
88 XI. _ 44 13
Vv 14 75
49 XII 20
VI. 17 22 Incomp|lete.
26 XII 4
Vil 22 30

Hence we conclude, There is a diminution in the rate of increase of in-
dividuals in the “ fan” as tt grows older.

In searching for an explanation of this phenomenon, I first drew
a line from the centre of the primary individual of the fan to the
periphery, and divided it into four equal parts. I then described
arcs with the primary individual as a centre, and with radii equal to
4, 2, 3, and ¢ of this line respectively. Counting the number of in-
dividuals cut by these ares respectively, and dividing those numbers
by the length of the corresponding arcs, I found that there 2s almost
exactly the same number of individuals per unit of are for each of the
four arcs. (Rule 7.) The previous conclusion, that there is a dim-
inution in the rate of increase of individuals in the fan as it grows
older, may then be considered as a corollary to this rule, as it ob-
_ viously follows from it.

46 BULLETIN OF THE

Bugula flabellata, J. V. Thompson.*— I have studied this species for
the purpose of confirming the results obtained in B. turrita, and have
found the architecture of the two species alike in all essentials.

The entire colony of B. flabellata (Plate VII. Fig. 66) may be com-
pared to a single “fan” of B. turrita, only there are usually many more
individuals in the former, and of course there is no central stem to which
it is attached ; but the fan is fastened directly by its rhizoids to the
object which supports it.

Usually about four rows of individuals are united, instead of two as
in B. turrita,—a condition which can be easily derived from the latter
by imagining adjacent branches to become fused together. Here as
there adjacent individuals break joints. Here as there lateral branches
are given off towards the axils.

Rule 3 is not true for B. flabellata. This is entirely annulled by the .
establishment of a new rule, which depends upon the new conditions
found in this species ; namely, that more than two rows cling together,
and that consequently one or more rows of individuals are enclosed be-
tween outer marginal rows. In any such twig composed of more than
two rows (Rule 3a) lateral branches are given off only from the marginal
rows. (See Fig. 66, 49-54 XVII.) It might possibly result, then,
that certain of the middle rows of the twig should never give rise to
lateral branches. But I do not believe that this ever occurs in very
long rows, for by the splitting up of the twigs the middle rows sooner or
later become marginal (so 46-51 XV.). In one stock that I have
drawn, consisting of 17 to 21 generations, every middle row occurring
as such up to the 13th generation had become at the periphery a
marginal row.

As in B. turrita, so in B. flabellata lateral budding occurs most
frequently at the margins of fans, —in a fan of about 800 individuals in
the ratio of 1:10 for the margin, and 1:14 for the remainder of the
fan. By a comparison of these figures with those given on page 43 for
B. turrita, it will also appear that lateral budding is less frequent here
relatively to terminal budding than in B. turrita.

The fifth rule deduced for B. turrita holds equally well here. In one
case the curve of the tips of the rows rises from the margin of the fan at

1 The species which I have studied is identified by Verrill (’78, pp. 711, 889)
under this name, and my specimens also agree fairly with Hincks’s (’80, pp. 80-82)
diagnosis. The two pairs of spines, one longer than the other, could be distinctly
seen. Hincks says, “The rows of cells. . . are never, I believe, fewer than four,
and range as high as seven.” But his Figure 66 shows three rows only in some
places.

MUSEUM OF COMPARATIVE ZOOLOGY. 47

generation XXIV., reaches 3 maxima of XXVI., XXVII, and XXVIII.
respectively, and falls again at the other margin to generation XXIII.
In the subfan from which Figure 66 was taken, the curve begins at the
outer margin with generation XVIL., rises to generation XXII. at two
points, and falls again to XX. at the inner margin of the subfan.

Of the four proximal individuals in any fan here, as in Bugula turrita,
the outermost, ancestral give rise to the greater number of individuals.
In one case, for instance, the marginal individuals lie at the base of 31
rows with 184 individuals, while the inner ones support only 7 branches
with 65 individuals. Similar results were obtained from other stocks.

With the middle of the primary individual as a centre, I passed an
are of a circle through the extremities of the branches of a large camera
drawing of a fan of B. flabellata, divided the radius into eighths, and
passed arcs through these points. The number of individuals cut by the:
different arcs was then counted and tabulated; the arc with the longest
radius cut through 87 individuals. By measuring the length of the arcs,
the number which should be cut by each are on the assumption that the
number of individuals per unit of arc is constant for all radii was deter-
mined. This was then compared with the actual number found, with.
the following results : —

a

Length of No. of Individu- Theoretic Length of No. of Individu- | Theoretic
N

Radius. als observed. . Radius. als observed. 0.

In this instance, then, the 7th rule deduced for B. turrita evidently
holds true for B. flabellata.

While at Mr. Agassiz’s laboratory at Newport, during the summer of
1890, I had frequent opportunity to examine other stocks of Bryozoa,
which occur there very abundantly. I will take four species as typical
examples of the groups they represent, and treat of the architecture of
their colonies.

Lepralia Pallasiana, Busk.1.—It is not at all easy to determine

1 T do not feel perfectly certain that the specimen shown in Figure 71 (Plate
VIII.) belongs to this species, because the characters of the young stocks differ some-

48 BULLETIN OF THE

from a young stock what has been the order of succession of individuals.
One has to view the object from both sides, make a careful examination
of the walls of the zocecia and of the relation of the polypides to one
another, and, when he has done his best to determine what are the facts,
he must feel that his conclusions are after all more or less subjective.
By a careful study of the colony shown in Figure 71, I have constructed
the diagram shown in Figure 71°.

The stock of Lepralia is a creeping one, and all of its rows of individ-
uals are in juxtaposition. This juxtaposition is continued into the adult
stage. Even the young stock begins to show evidence of a quincunx
arrangement of individuals. This is less evident in the youngest indi-
viduals than in the older part of the stock, and is most evident in old
colonies. That there is not here a true dichotomous division of rows of
individuals, resulting in the annihilation of the ancestral row and the
establishment of two new ones, is evident from a glance at the youngest
generation in rows 11, 12, or, better, 2, 3, in which the relation of ter-
minal (11, 3) and lateral (12, 2) individuals is very different. The for-

mer continue the ancestral line, the latter establish new rows. Lepralia —

differs from Bngula in this: that two lateral branches may be given off
from the ancestral row in the same generation, as at B, C, and a, a
(enclosed in circles), Figure 71*.

In contradistinction to the conditions in Bugula, when only one branch

arises, it is not given off towards the axil, but away from it.

The synchronism of the budding process noticed in B. turrita is hardly
distinguishable in the adult stock of this species ; in the young, however,
it is quite marked, and gives to the whole a very symmetrical form. The
cleavage of eggs does not proceed by more regular steps. Of the three
individuals a, C, a (in circles), which follow 4, each has given rise to
three others, a median and two lateral. From each of the three individ-
uals derived from the two individuals a, a (in circles) has arisen a
lateral branch. Rule 3 is therefore well marked in the young stock of
Lepralia.

Rule 4, concerning the greater frequency of lateral budding at the
margin, is also exemplified in Lepralia. The ratio of cases of lateral
to median budding being 1:1 on the margin (rows 1-6 and 15-19)
and 1: 2.8 in the middle (rows 7-14.)

In Bugula, as will be recalled, it was concluded that the marginal

what from those of older ones. Yet it isan Escharine closely allied to Lepralia, and
Ihave seen in some cases the broad-based spine on the proximal border referred to
by Verrill as being found in L. Pallasiana.

MUSEUM OF COMPARATIVE ZOOLOGY. 49

branches were possessed of fewer generations than the intermediate ones.
Since by Rule 2 the lateral branches were given off towards the axils,
and the ancestral branches therefore always remained marginal, it re-
sulted that the ancestral branches were the shorter, the lateral branches
the longer. But in Lepralia lateral branches are turned away from the
axils, and here we find the conditions concerning the relative number of
generations in marginal and intermediate rows correspondingly reversed.
Thus, in Figure 71%, the terminal individual D of row 10, a median but
ancestral row, belongs to generation IV. while the lateral branches 6
and 15 have five generations of polypides. Thus it is true here, as in
Bugula, that the ancestral branches are the shorter, the lateral branches
the longer (page 44).

That the outer individuals a, a, of rows 6 and 15, have given rise to
more individuals than the inner C, is clear without further comment.
Finally, since the individuals retain a nearly constant width, the neces-
sity of the rule established for Bugula, — viz. that there is almost ex-
actly the same number of individuals per unit of are for all radii, — and
of its corollary, — that the increase of individuals in sucessive gener-
ations undergoes a regular diminution, — is apparent.

Flustrella hispida, Fabricius.‘ — This stock is a very dense corm-like
one. The primary individual becomes surrounded on all sides by the
younger zocecia. It is very evident from an inspection of the position
of this primary polypide with relation to the periphery, that growth
occurs most rapidly on each side and in front of the primary polypide.
In making any diagram of such a stock, it is not very difficult to decide
upon the origin of the more peripheral individuals of the stock, but it is
wellnigh impossible to say with any certainty what are the relations
of the individuals of the second generation to those of the first. Bar-
rois (77, pp. 227-229) has, however, determined this for this species,
and my diagram (Fig. 67) is based in part upon his observations. I
do not desire to insist that the diagram represents the exact method
of growth of the stock. It is an attempt to represent it, founded princi-
pally on careful study of Figure 69. The quincunx arrangement of in-
dividuals is already apparent in the young stock (Fig. 69) ; it becomes

1 Hincks (80, pp. 504-506) makes the existence of a larval bivalve shell a char-
acteristic of this genus, and therefore I assign to it a very common Alcyonidium-like
form which was extremely abundant on Fucus at Newport. F. hispida is the only
species of this genus. I found the bivalve shell still adhering to the primary indi-
vidual of a young colony (Plate VIII. Fig. 69, 0.). In Verrill’s (’78, p. 708) catalogue
this species is referred to under the name “ Alcyonidium hispidum, Smitt.”

VOL. xx11 — No. l. 4

50 BULLETIN OF THE

more evident in the adult, and when new individuals arise distad to any
two, one of the new ones is median (ancestral branch), the other lateral.
(So terminal individual of rows 11 and 10; 22, 23; 43, 44; etc.) In
the diagram, however, I have not always indicated which is the median
and which the lateral branch, for in the older parts of the colony, owing
to a shoving of individuals, it is not easy to distinguish them.

Lateral branches appear usually to be given off towards the axis.
Here, as in Bugula, the lateral branches tend to be longer; the ances-,
tral, shorter. ;

It is evident from the diagram that lateral budding is most frequent
at the margins of the corm, i. e. that part lying posterio-dextral or poste-
rio-sinistral of the primary individual, and that the descendants of the
two lateral individuals of the four belonging to generation II. are more
numerous than those derived from the middle two. Finally, it is evi-
dent that the number of individuals per unit of arc will be the same for
ares of all radii, and therefore the rate of increase of individuals will
diminish through successive generations.

In Crisia eburnea, Linn.,) we find the same laws illustrated. The
architecture of the genus has been carefully treated of by Smitt (’65%, pp.
115-142) as forming the basis of classification. Barrois (’77, pp. 76-85)
has described in a masterly way the formation of the young stock of
tubuliporid Cyclostomata, and the relationships of the different types
of budding in this group. Harmer (’91, pp. 145-173) has recently dis-
cussed the architecture of the stock in British species, adopting Smitt’s
graphic method of showing it. I have found his paper of great value
for my purpose.

This species grows as a shrub-like stock upon floating eel-grass, ete.
I was wrong in saying, in my Preliminary (’91, p. 282), that Crisia has
its branches united in pairs. The comparison of this species made by
Barrois (77, p. 82) with the “geniculata form” is conclusive evidence,
to my mind, that the apparent double row is in reality a single one, and
that such a branch as 18, Figure 65, is to be represented by a single
line in the diagram Figure 65%. We find here terminal and lateral
branches ; no true dichotomy. Branches are given off on the side away
from the axils, as in Lepralia, not as in Bugula. (But branch 11 is an
exception to the rule.) They are given off, as Harmer (91, p. 131)
has shown, alternately to the right and left.

1 This is the only species of Crisia given by Verrill, and, since my species
is very common, it must be the one to which he refers. Moreover, it agrees
fairly well with Harmer’s diagnosis (91, p. 131).

MUSEUM OF COMPARATIVE ZOOLOGY. 51

There is something of a tendency for lateral branches to be given off
in the same generation from closely related branches. Thus (Fig. 65*)
from the primary individual, 0, of the stock, two individuals, a median
and a lateral one, arise. Each gives rise in its first generation to two
individuals, a median and a lateral. Of these four individuals each
gives rise at the end of three generations of median buds to two buds,
a median and a lateral. Comparing 2 and 10, first descendants of the
two branches arising from the second individual of 8, we find that each
gives rise to lateral branches from their first individual and from their
fourth. Comparing 14 and 19, first descendants of the two branches
-arising from the first individual of 8, we find each giving rise to lateral
branches from their first individuals. The law breaks down, however,
when an attempt is made to carry it to extremes.

The fourth rule is not always so pronounced in Crisia eburnea as
elsewhere, although lateral budding seems to be slightly more frequent
at the margin.

The extreme marginal branches usually attain far fewer generations
than the more intermediate ones; thus, in Figure 65*, branch 20 ends
in the 7th generation and branch 13 in the 7th also, while the more
intermediate branches 15 and 18 attain 12 and 14 generations respect-
ively. So, too, while the outer branches 6 and 1 contain respectively
10 and 11 generations, the inner branches reach 12 and 14.

It is very noticeable that the outer branches give rise to more indi-
viduals than the intermediate ones. Figure 65* will serve to illustrate
this also. Here the outer branch 4, the intermediate 8, and the outer
15 possess, together with the branches arising from them, 33, 28, and 40
individuals respectively.. Harmer (’91, p. 168) finds this true for his
Crisia ramosa, for he says, “‘It is frequently remarked that the longest
and most branched parts of the colony are lateral branches, and not
parts of the main stems.”

There is, in the long run, a decrement in the rate of increase of indi-
viduals in successively older generations, yet it is not so regular a one
as that which we found to exist in Bugula. Thus, in the seven gen-
erations which even the shortest branches shown in Figure 65* had
attained, the average increase of the number of individuals in the
second, third, and fourth generations over the number in the preceding
is 67% ; in the fifth, sixth, and seventh, 44%. The generations beyond
the seventh are not complete; they would have contained more indi-
viduals at a later period, when the branches which have now attained
only seven generations had grown. Thus the number of individuals

be BULLETIN OF THE

in successive generations beyond the seventh increases more and more
slowly, and finally decreases to zero. Thus the average rate of increase
of individuals in the generations 7 to 10 over those in the preceding is
only 16%.

One finds here, as elsewhere, that the number of individuals cut by
any unit of arc, the primary individual being taken as a centre, remains
practically constant, whatever the radius of the are.

In studying the creeping stocks of Cheilostomes (Plate VIII. Fig. 71),
young corms have been chosen because they exhibit fewer irregularities
of formation than old ones. Such irregularities are chiefly due to some
unevenness of the surface on which the corms lie, but sometimes
apparently to a crowding of individuals. Old rows of individuals are
occasionally entirely cut off and end in the middle of the stock; some-
times two rows running side by side, perhaps derived from a common’
ancestor, suddenly merge into one again. In one case, Escharella varia-
bilis, Verrill, I have seen three rows thus merge into one at the margin,
suggesting the existence of a samknopp (common bud) in the sense of
Smitt (’65, pp. 5-16). Ostroumoff (86%, pp. 338, 339) has observed
a case in Lepralia Pallasiana. He says: ‘Dans quelques cas, qu’on
peut considérer comme des anomalies, il arrive parfois que deux bour-
geons, provenant de loges differentes, viennent 4 se fusionner.” It seems
to me, therefore, that while Nitsche (’71, pp. 445, 446), who opposed
with such vehemence and success the idea of Smitt that zocecia arise from
an undivided marginal zone of cells, was quite right in affirming (’71,
p. 447) that even the smallest marginal zocecia are sharply marked off
from the adjacent ones, yet he overlooked the possibility that under
certain circumstances the lateral walls might fail to develop, and thus
one zocecium might arise in the place of two, or even three.

I have not read Smitt’s Swedish paper, but I do not find anything
in the translation given by Nitsche to warrant the latter’s conclusion
(71, p. 446) that Smitt believed the “ Gesammtknospe ” to be “ formed
from the sum total of the mature peripheral zowcia.”’ If I understand
Smitt, he conceived the samknopp not to be derived from the most
peripheral mature zocecia, but to be self-proliferating, and to give rise
to the rows of zoccia, not to arise from them. It is the “bud of
the colony,” not the sum of the buds of the peripheral individuals of the
stock. In this I would agree with him exactly. Although uswally one
finds the marginal gemmiparous tissue forming the lateral walls at the
extreme edge of the corm, and thus apparently separated into wholly
distinct adjacent gemmiparous masses; under certain conditions, the

3

cr

MUSEUM OF COMPARATIVE ZOOLOGY.

lateral wall may not be formed between two or more rows, which will
then merge into one.
a
2. ORIGIN AND DEVELOPMENT OF THE INDIVIDUAL.

My studies on this subject, which were undertaken for the purpose of
showing the unity of the type of budding throughout Ectoprocta, have
been very fragmentary.

Figure 72 (Plate IX.) has been introduced for the sake of orientation.
It represents a longitudinal vertical section through the peripheral part
of a stock of Lepralia Pallasiana. The body wall is thicker at the mar-
gin (marg.), and gradually becomes thinner as one passes backward. A
septum (sep.) has already arisen cutting off the youngest zoccium from
the more proximal one, which contains a young polypide; proximal to
this is another septum, and the distal end of a third zocwcium.

Nitsche (’71, pp. 445-456) has already well described the process of
forming the zowciwm in Flustra membranacea. In fact, he has studied
the organogeny more thoroughly in many respects than I have. Nitsche
_ (71, p. 452) showed that the wall of the advancing margin of the colony
was composed of two layers of cells, — an outer, “ Cylinderepithelschicht,”
which secretes a cuticula, and an inner, ‘‘ Spindelzellschicht mit anliegen-
den Kornerhaufen.” As the body wall formed directly from these cell
layers is left behind by the advance of the margin, it becomes continually
thinner. ‘Die Cylinderepithelzellen der Wandung platten sich weiter
nach dem proximalen Ende zu ein wenig ab, besonders die der Unterseite
verkiirzen sich, die einzelnen Zellen riicken auseinander, die Zellgren-
zen werden undeutlicher, die Kerne jedoch bleiben deutlich erkennbav.”
Vigelius (84, p. 76) could not find the inner cell layer in Flustra, even
at the youngest stages, and consequently he believed that only one ex-
isted at the margin, and that this went to form the “ Parenchym-
gewebe” of the adult. Ostroumoff (’86*, p. 336) seems inclined to doubt
the existence of any mesodermal layer at the distal portion of the bud-
ding zoccium in Cheilostomes, and Seeliger (90, p. 580) has failed to
find in Bugula “eine zusammenhdngende dem Ectoderm dicht anlie-
gende Schicht von mesodermalen Spindelzellen.” Both Ostroumoff and
Seeliger, however, believe in the existence of csolated mesodermal ele-
meats at the budding end. |

According to my own observations, there is usually only one continu-
ous layer at the budding margin of the stock. Thus, in Flustrella
(Plate IX. Fig. 79) one can usually distinguish a continuous ectoderm,
but the mesoderm (ms’drm.) is represented by scattered cells only. At

54. BULLETIN OF THE

the margin in Lepralia (Fig. 73) one finds a thick ectodermal layer,
composed of columnar cells, but the mesoderm consists of an irregular
thick mass of cells, some of which appear to be ameeboid. They how-
ever show no signs of having been derived from the outer layer. The
condition of the budding margin of Escharella resembles that of Lepralia.
In older parts of the body wall, where the ectoderm is reduced to an ex-
tremely thin layer, only scattered mesodermal cells appear, and these are
amceboid or mesenchymatvid.

On the other hand, one finds in the body wall, around the nascent
neck of the polypide (Plate X. Fig. 88), even to a late stage, both ecto-
derm and mesoderm well formed as layers. The ectoderm is a columnar
epithelium ; the mesoderm is flatter, and often its cells are not sharply
delimited from one another. It is thus perfectly evident, to my mind,
that the mesoderm has in general lost its original epithelial character
in the marine Bryozoa, although it has retained it in Phylactolemata.
Whenever it does exist in the former group as an epithelium, it is at the
budding regions (neck of polypide, and Figures 74, 75, 78, 79, ex.).

Origin of the Polypide. —There are very few problems in modern
morphology, I fancy, the history of whose investigation shows a less
satisfactory aspect than that of the origin of the polypide in Gymnole-
mata. It is hardly to be wondered, however, that investigators have
sought for another interpretation of the process than the most obvious
one, because that seemed to oppose many long cherished and wellnigh
universally held dogmas. While the first recognition of the animal
nature of marine Bryozoa, which we owe to the studies of Bernard de
Jussieu in 1742 and John Ellis in 1755, brought with it a knowledge of
their colonial nature, yet it was not until much later that the most
characteristic part of this process—the formation of the polypide—
was clearly observed. Grant (’27, p. 115) and Farre (’37, pp. 400, 409,
415) first described the process by which is formed this complex of or-
gans, and settled once for all the controversy which had sprung up as to
whether these animals were truly stock-builders. Under the influence
on the one hand of the endosare theory of Joliet (’77), and on the other
hand of the view promulgated by Hatschek (’77), that similar organs
in larva and polypide are equivalent as far as regards their origin from
the germ layers, the more important papers ! between 777 and ’90 main-
tained either that the polypide arose independently of the body wall,

1 Excepting those of Barrois, who, from the study of the favorable material

presented by metamorphosing larve, has persistently maintained the correct
interpretation.

MUSEUM OF COMPARATIVE ZOOLOGY. 55

and secondarily acquired connection with it, or that it had a double
origin.

To Nitsche (’71, pp. 456-463) belongs the credit of having first described
the histological changes in the origin and development of the polypide
of marine Bryozoa, particularly with reference to the part which the
germ layers play in that process. He says (’71, p. 456): “ Die Anlage
des Polypids erscheint zunachst als eme Wucherung der Zellschicht der
Endocyste in der Mitte der Hinterwand der Knospe, und zwar in dem
Winkel, den die Hinterwand mit der oberen Wand macht. Bald ordnen
sich die Bestandtheile des regellosen Zellhaufens in zwei deutlich geson-
derte Schichten, und wir sehen nun einen rundlichen Korper, beste-
-hend aus einer dusseren einschichtigen Zellschicht, welche sich scharf
absetzt gegen die das Innere des K6rpers bildenden Zellen.”

This stood until a year ago as the most satisfactory description of this
process in the adult stock. The appearance within the last year of the
two papers of Prouho (90) and Seeliger (’90) marks a distinct epoch in
the advance of our knowledge concerning the origin of the polypide in
Gymnolemata. The paper of Prouho treats of the process in the case of
the primary polypide of the metamorphosing larva of Flustrella, that of
Seeliger in the case of the young (practically adult) stock of Bugula,
According to both authors, the polypide arises from the body wall by an
invagination of it, and its two layers are from the first distinct and
separate, and go to form the two layers of the adult polypide, and the
whole of those two layers. The outer layer of the body wall gives rise
to the outer layer of the tentacles and the lining of the alimentary tract,
and the inner layer of the body wall gives rise to the mesodermal lining
of the polypide. Prouho alone is cognizant of the method of origin of
the ganglion, and in addition there are several points of difference be-
tween these two authors concerning the development of other organs, to
which I shall refer in the proper place. Thus the latest studies have
confirmed the assertions of Nitsche, that the polypide arises from a
single centre of proliferation of the body wall; they have made an ad-
vance in this, that they have shown that the two layers of the bud do
not become secondarily differentiated from a single cell mass, but are
respectively derived from the two cell layers of the body wall. My own
studies have led me to the same conclusion on this point.

Figure 75 (Plate IX.) is a vertical radial section through the margin
of an adult Flustrella stock. The ectoderm is relatively thick at the sole
(sol.) and margin, and very greatly thickened at the point marked gm.
Here two layers, sharply separated, are apparent. ‘The cells of the outer

56 BULLETIN OF THE

layer are columnar and full of granular protoplasm, the mesodermal cells
cuboid. The body wall has clearly begun to invaginate in this region.
Figure 79 is a similar section, and shows a later stage in this process.
The lumen of the bud is apparent, and has been formed by invagination,
not, as in Paludicella or Phylactolemata, by ingression. The two layers
of the bud are apparent; they have been derived from those of the
body wall.

Figure 73 (Plate IX.) shows a stage in the development of the poly-
pide which is intermediate between that of Figures 75 and 79, but from
another suborder, Cheilostomata. ‘The mesoderm has here a mesenchym-
atous character, and is looseiy attached to the inner layer of the bud ; it
is not always sharply marked off from it by boundaries, but is quite dis-
tinct in its reaction with staining reagents. This bud has evidently
arisen by invagination of the body wall. Seeliger (’90, p. 581) also finds
that there is an actual invagination of the ectoderm in Bugula, the open-
ing to which he calls “ blastopore.”

From what has been already shown, it is evident that in Flustrella, as
well as in Cheilostomata, the first appearance of the young polypide is
near the margin of the stock, not near the proximal part of the young
zocecium. This will also be apparent at 6 and 9, Figure 71 (Plate VIII.),
where the accumulation of nuclei immediately behind the margin indi-
cates the neck of the polypide, — the point at which the bud arose. To
be sure, at quite an early stage, but very much later than that of Figure
73, the polypides are found near the proximal wall of the zocecium, but
a delicate funnel-shaped sheath of tissue runs from the polypide to the
distal part of the zocecium, where the polypide is attached to the body
wall.

After invagination the pocket closes at its attached end by a growing
together of its lips (Figs. 79, 78). Thus the body wall becomes contin-
uous again over the lumen of the bud, and this union is first broken
when the fully formed polypide is ready to evaginate itself. Seeliger
(90, p. 582, Taf. XXVI. Figs. 8, 10) has described and figured a similar
condition in Bugula.

The young bud now becomes elongated (Fig. 80), the walls of the bud
sometimes becoming closely approximated. A little later it begins to
pass backwards relatively to the distal wall of the zocecium. A trans-
verse section through the young polypide and the neck of the colony
shows that the connection has become a less intimate one (Fig. 81, cev.
pyd.). The tissue by which the connection is still effected is that from
which the kamptoderm will be formed. It is apparently the existence

MUSEUM OF COMPARATIVE ZOOLOGY. 54

of this stage, in which the kamptoderm is long drawn out and easily
overlooked in optical as well as actual sections, that led to the belief that
polypide buds may arise independently of the body wall and only sec-
ondarily become connected with it.

At about this time the lumen of the alimentary tract begins to be
separated from that of the atrium. Thus, in the series from which Fig-
ure 81 was taken the more oralward lying sections show that the cavities
of the lower and the upper parts of the bud, which at the anal end are
broadly confluent, have here become separated by a constriction. A
sagittal section of a somewhat later stage is shown in Figure 76, which
is from Flustrella. Here we find the alimentary tract represented by a
space in the lower part of the bud, broader at its anal than at its oral
end and separated from the upper cavity — the common atrio-pharyngeal
cavity, @. + atr.—by a line of nuclei which represents the line of ap-
proximation of the inner layers of the two sides of the bud. The bud is
attached to the body wall at its marginal (anal) end, and is free from it
oralwards. (Compare with Paludicella, Plate III. Fig. 24.) It seems
to me highly probable from these and other series of sections that the
alimentary tract is separated from the rest of the lumen of the bud, not
by an approximation of the inner layers of the bud along the whole ex-
tent of the future alimentary tract at once, but that the rectal part is
first formed and constitutes a large cavity, at first broadly open to the
atrium above, and that the gastric portion is formed somewhat later by
a progressive enlargement of the lower cavity of the bud, which now
becomes constricted off from the atrium and cesophagus above. This
process is like that found in Paludicella (page 19), which forms a sort
of transition to that of Phylactolemata, described by Braem (’90, pp.
45, 46) and myself (90, p. 112).

Prouho (90, p. 448, Fig. 6) shows that the rectum at first appears
as a blind sac open to the atrium at its posterior end, although later
this opening is greatly reduced. Hence in the Flustrella larva also the
space from which the lumen of the future rectum is to arise is formed
before that of the stomach, although this part of the alimentary tract
is the last to be cut off from the atrium. Seeliger (’90, p. 585) says
concerning the formation of the alimentary tract in Bugula: “ Der ganze
Basaltheil des Polypids sich in der Mittelpartie durch zwei immer tiefer
werdende Furchen von dem vorderen abschniirt, wihrend er an zwei
Stellen, einer oberen und einer unteren, mit ihm in Verbindung bleibt.
Die obere Verbindung entspricht dem Anus, die untere dem Mund.” The
author here seems to imply that the whole alimentary tract is formed at

58 BULLETIN OF THE

one time ; but as he has not. attended particularly to this point, this can
hardly be said to militate against my view.

There is, however, in my opinion, a more important error in Seeliger’s
description of the origin of the alimentary tract, — an error into which
Nitsche (’71, p. 457) also fell. As in Phylactolemata and Paludicella,
so also in marine Bryozoa in general, so far as I have studied them, the
posterior and anterior parts of the alimentary tract are formed indepen-
dently, and their cavities coalesce only secondarily. The constriction
which separates the lumen of the bud into a cavity nearer, “ vorder,” and
one more remote from the body wall, “ basal,’”’ does not separate off the
whole alimentary tract from the atrium. Neither does that constriction
result in the formation of a space opening into the cavity nearer the
body wall, “ Vordertheil,” at an upper [distal] point (anus) and lower
[proximal] point (mouth). Thus if one examines a complete series of
sections through a polypide even of so late a stage as Figure 92
(Plate X.), one finds that, while there is an open connection between the
anal end of the alimentary tract and the atrium, the oral end is at all
points sharply separated from the cavity above by a double-layered wall
of cells, as is shown in Figure 92, between @. and ga. Such a condition,
moreover, has been found by Barrois (’86, pp. 73-76) in the primary
polypide of Lepralia, and by Prouho, as just stated, in the primary
polypide of Flustrella.

Origin and Development of the Ring Canal and Tentacles. — Nitsche
(71, p. 430) first described in Flustra a ring canal surrounding the
mouth-opening and lying at the base of the tentacles, but did not refer
to the origin of it. Seeliger (’90, p. 588) describes it in a young pol-
ypide of Bugula, as derived from the mesodermal layer.

My own sections also show that it arises on each side of the cesopha-
gus as a groove lined by mesoderm (Plate X. Fig. 92, right). This
canal, which is shown cut along its course in Plate IX. Fig. 82, can.
erc., is not wholly separated from the body cavity, but communicates
with it below the brain. This communication occurs in the section
below that shown in Figure 82, near the point can. erc. This ring
canal at an earlier stage is shown in Figure 87. It has not yet been
formed backwards nearly so far as the brain; anteriorly the section has
traversed the tentacles under which it runs. The canal is also shown
cut across in Figure 86 at the base of a tentacle, with whose lumen its
cavity is directly continuous.

The formation of the tentacles is closely connected with that of the
ring canal, from the upper wall of which they arise. Since the upper

—-_

MUSEUM OF COMPARATIVE ZOOLOGY. 59

wall of the ring canal is two-layered, the tentacles are two-layered also.
The outer layer of the tentacle is thus derived from the inner layer of
the bud ; the inner layer, on the contrary, from the outer layer of the
bud. It would be hardly necessary to make this statement, which
agrees both with early and the most recent observations, had not Bar-
rois (’86, p. 75, Fig. 48) referred to and figured the tentacles as having
been formed from the inner layer of the bud only.

My observations fully confirm Seeliger’s (90, p. 587) description of -
the manner of growth of the tentacles; that is, that the outer edge of
the ring canal, together with its tentacles, moves downward and outward
along the sides of the polypide, turning the axis of the tentacle from a
nearly horizontal to a vertical position, and increasing the area of the
kamptoderm. Thus in Figure 92 this process has progressed farther on
the left side than it has on the right.

Nitsche (’71, p. 458) lays some stress upon the statement that the ten-
tacles are not at first few in number, gradually becoming more numer-
ous ; on the contrary, he says, ‘Ich sah stets, beim ersten Auftreten von
Tentakelanlagen, 16, 17, oder 18 Stiick gleichtzeitig erscheinen.” See-
liger (’90, p. 584) agrees with Nitsche in this respect ; but Prouho (790,
p- 449) finds the conditions different in Flustrella. Here the tentacles
“ne se développent pas simultanément sur tout son pourtour, mais ap-
paraissent d’abord de chaque cdté du plan de symétrie, puis se multi-
plient vers Varriere.” As I have shown, 14 of the 17 tentacles arise
nearly simultaneously in Paludicella, for here there are few of them ;
and this is the case also in Escharella variabilis with its 17 tentacles.

As the tentacles of both Flustra and Bugula are few in number,! the
statements may easily be considered to be correct for these genera. The
tentacles of Flustrella hispida are much more numerous (30-35), and
Prouho’s statement may well be true for his form. In fact, my own ob-
servations on this species are fully in accord with those of Prouho.
Figure 77 (Plate IX.) represents a young polypide of a Flustrella corm,
viewed from the roof as an opaque object. Six tentacles were visible on
each side of the bud, but the oral and anal parts of the corona were yet
incomplete. The remaining nine or ten pairs of tentacles subsequently
arise oralward and analward of these rudiments.

Much disagreement has prevailed concerning the number of layers in-
volved in the kamptoderm of marine Gymnolemata, in both the adult
and the developmental stages. As in so many other cases, we owe to

1 Bugula avicularia has 14 or 15 tentacles, and Flustra (Membranipora) mem-
branacea 20, according to Hincks (’80, pp. 76 and 140).

60 BULLETIN OF THE

Nitsche (’71, pp. 431, 432) our first intimate knowledge of this organ.
He believed it to consist in the adult of Flustra of a single cell layer,
in which are imbedded (or applied?) longitudinal and circular muscle
fibres. He believed the kamptoderm to be formed gemmigenetically only
by the outer cell layer, the derivative of the mesoderm. Repiachoff (75,
pp- 138, 139) observed in Tendra (Membranipora) “ die Doppelschichtig-
keit der Tentakelscheide nicht nur bei den jungen Knospe sondern auch
bei den ganz ausgewachsenen, offenbar schon Jingst functionirenden, in
ihrem mittleren Theile ganz braunen ‘ Polypiden,’ ” and later (’76, p. 152)
a similar two-layered condition of the kamptoderm (Tentakelscheide)
in Membranipora and Lepralia. Ehlers (’76, p. 37) finds a single layer of
cells in the kamptoderm of the adult Hypophorella (Ctenostome), which
he believes is continuous with the endocyst of the body wall, and thus
is ectodermal. He finds neither longitudinal nor circular muscle fibres.
Haddon (’83, p. 517) believes the kamptoderm to be derived from both
the inner and outer layer of the polypide bud. Vigelius (’84, pp. 33, 82)
describes it as arising from the mesoderm only (Parenchymegewebe), and
as being essentially one-layered, both longitudinal and circular muscles
lying in this layer. Barrois (’86, p. 74) derives the kamptoderm from
the mesodermal layer only. Ostroumoff (’86%, p. 15) believes the kamp-
toderm to be two-layered and provided with muscles ; it is in his opinion
derived from both layers of the bud. Freese (’88, pp. 18, 19) studied
only the adult of Membranipora. He admits the presence of muscle
fibres, but believes the kamptoderm one-layered. Pergens (’89, p. 507)
states only that in the Cheilostomes studied by him the tissue of the
kamptoderm is composed “aus abgeplatteten Zellen, zwischen welchen
Langs- und Ringmuskelfasern eingebettet sind.” Prouho (’90, p. 451)
states that in the primary polypide of Flustrella this organ is early
differentiated, ‘ et les deux couches de rudiment prennent part a sa for-
mation.” Finally, Seeliger (‘90, p. 587): “Es kann danach keinem
Zweifel unterliegen, dass die Tentakelscheide ektodermalen Ursprungs
ist. . . . Das Mesoderm erscheint auf allen gelungenen Schnitten von
der Tentakelscheide scharf abgesetzt.”

It is my belief that throughout the group of marine Gymnolzmata, as
in Paludicella and Phylactoleemata, the kamptoderm is derived from both
of the two layers of the polypide bud, is provided with a strong system
of longitudinal and a slight one of circular muscles, and contains in the
adult two layers, or at least modified representatives of two layers. J
have arrived at this conclusion from a careful study by sections of the
following genera: Bugula, Lepralia, Escharella, Flustrella, Bowerbankia,

MUSEUM OF COMPARATIVE ZOOLOGY. 61

and Crisia. The existence of two layers was easily demonstrated in all
cases in the young polypide by cross sections of the “neck.” The two
layers are of nearly the same thickness, and distinctly separated from
each other. The presence of two layers in the adult is more difficult to
determine, but it was always indicated by the occasional presence of
two nuclei lying side by side, and especially at the attachment to the
diaphragm. The presence of muscles was demonstrated in all cases
(except Bowerbankia, where my few sections did not show the proper
region) upon tangential sections of the sheath. I may add, that the
existence of muscles is wellnigh conclusive @ priort evidence of the
existence of the mesodermal layer, since nowhere else in Bryozoa, so far
_as I know, do muscles arise from any other layer. Prouho’s evidence in
support of his position is perfectly satisfactory to my mind, certainly
more so than the negative evidence of Seeliger in support of his. In
further support of my statements I may refer to the condition of the
kamptoderm (kmp’drm.) in Figures 92 and 83, Plate X.

Nervous System. — Since Dumortier discovered, in 1835, a ganglion in
Lophopus, there has been seen in marine as well as fresh water Bryozoa
a body which has been considered, with greater or less certainty, to con-
stitute the central nervous system. Overlooked by Farre, it was, I be-
lieve, first described for marine Gymnolemata in 1845 by van Beneden,
co-worker with Dumortier, for Laguncula (Farrella). Nevertheless, up
to the present the evidence of its being a ganglion homologous with that
of Phylactoleemata has not been satisfactory. The homology can be estab-
lished only by determining its similar origin with the brain of Phylacto-
lzmata ; its function can be best established by showing the existence of
ganglionic cells and fibres. I hope to have advanced our knowledge in
both of these directions.

At about the time that the cesophagus and stomach have become con-
fluent, one notices a papilla-like elevation of the floor of the atrio-pha-
ryngeal cavity. This has been noticed by Korotneff (’74) in Paludicella,
and by Nitsche (’71, p. 459) and Seeliger (’90, p. 586) in Cheilostomes,
It has been called by them “ Epistome,” and compared with that of Endo-
procta or Phylactolemata. In my own opinion, it is merely a structure
brought into prominence by the sinking down of the floor behind it to
form the ganglion (Plate X. Fig. 86, gv.). This depression has been
seen by Barrois (’86, pp. 74, 75) and Prouho (’90, p. 450), and rightly
interpreted by them as probably destined to give rise to the central
nervous system. That this is the correct interpretation is shown by
later stages from different species, as Figures 89 and 83, in which we see

62 BULLETIN OF THE

the ganglion gradually assuming the position it has in the adult, on the
anal side of the pharynx at the base of the anal tentacles.

A section across the pharynx in such a stage as Figure 83 is shown
in Figure 87. A comparison with Figure 51 (Plate V.) of my Crista-
tella paper (Davenport, 90) will show a great similarity of conditions at
about the same age, and can leave no doubt concerning the homology of
the regions marked in both cases /u. gm. ; or compare Taf. VIII. Fig. 100,
nh., of Braem’s (’90) magnificent work. A section through a later stage
is shown in Figure 82. The brain has already sent out circumesopha-
geal nerves, as in Paludicella. The central part of the ganglion does
not stain; one sees only a granular mass, sometimes with signs of short
fibres. In the cornua (n’) one occasionally sees very large clear nuclei
with a single nucleolus, lying in the midst of a cell mass which is
spindle-shaped and stains more deeply than adjacent cells. These remind
one strongly of bipolar ganglionic cells, but fibres could not be traced
far from their pointed ends. Series of sections of Flustrella parallel to
Figure 82 show, as one passes below the level of the ganglion, a con-
tinuous band of cells extending down from it towards the cardiac valve
and between the cell layer lining the cesophagus and the surrounding
mesoderm. One is reminded of the exactly similar conditions in Palu-
dicella (page 26), and of the “linienartige Zeichnung” seen by Nitsche
(71, p. 431) and Vigelius (84, p. 42) in the same place in Flustra.
These facts go to indicate the existence of a gastric nerve.

At about the time at which the ganglion arises, the cavities of the
stomach and the cesophagus become confluent (Fig. 86 @.). At this
stage (somewhat earlier than Figure 86) the alimentary tract consists
of a U-shaped tube of nearly uniform calibre, and without any indica-
tion of the ccecum. The tentacles lie in two parallel rows in the middle
of the bud, the corona being incomplete both in front and behind, but
less so oralwards than towards the anus (Fig. 77, atr.). In fact, while
new tentacles are formed later towards the oral median line, they never
appear behind the line atv. This hinder region has another fate. Its
wall increases very greatly in area, diminishes correspondingly in thick-
ness, and forms a large part of the kamptoderm lying behind the post-
oral tentacle in Figure 86. With this growth of the kamptoderm the
anus is carried backwards, and farther and farther from the posterior
ends of the rows of tentacles, immediately behind which it formerly lay.

As the kamptoderm grows in area, the polypide comes to lie in the
proximal part of the zocecium. Pari passu with this process occurs the
rotation of the oral tentacles, as in Paludicella. The oral tentacles which

MUSEUM OF COMPARATIVE ZOOLOGY. 63

at first lie perpendicular to the roof of the colony (Fig. 86) gradually
come to lie parallel with it (Figs. 89 and 83). The cesophagus loses its
elongated, laterally compressed form, and becomes circular, and the gan-
glion lies just below the mouth-opening. Not until now, in fact, can one
speak ofa mouth. It was not at all formed synchronously with the anus.
To illustrate this process I have taken three different genera represent-
ing different stages. Similar stages could have been obtained from each
genus. By using three genera, the similarities as well as the dissimi-
larities of the process are indicated. Among other things, the larger
size of the polypide and shorter kamptoderm of the Ctenostome Flus-
trella (Fig. 89) is noticeable.

_ Lastly, the coecum is formed as a wholly petondirs differentiation of
the alimentary tract. This arises in some species relatively earlier than
in others; thus it is better developed in Figure 86 than in the later
stage of Figure 83.

The lining cells of the alimentary tract now rapidly undergo the dif-
ferentiations characteristic of the different regions. The most extreme
modification takes place in the pharynx. In Cheilostomes the cells of
this region gradually become vacuolated, until finally very little stain-
able protoplasma remains. The nucleus lies at the deep end of the cells.
A very peculiar modification of the cell walls takes place, in that they
become plainly perforated by holes through which the adjacent cells
are in communication (Fig. 85). It is in a region similar to this that
the cells become cuticularized in Bowerbankia to form the so-called
_ gizzard. The pharyngeo-eesophageal region is also provided with a very
powerful musculature of circular muscles (mw., Figs. 85, 86).

Concerning the orzgin of the muscles I have made very few studies.
The parieto-vaginal muscles seem to arise, as in Paludicella, from:
around the neck of the polypide, and the retractors from the oral end
of the polypide bud (mw. ret., Fig. 89).

The neck of the polypide sinks below the general level of the body
wall by an infolding of the latter, as described for Paludicella, and the
mass of columnar cells which passes down with it forms, I am confident,
the diaphragma of Nitsche (71, p. 432), which is thus exactly com-
parable with the mass of cells around the atrial opening of Paludicella
in Figure 45, of. atr. (Plate V.). According to this view, then, the dia-
phragma is not placed at about the middle of the kamptoderm, but at
its proximal end, and all that lies between it and the outer body wall —
the non-evaginable portion — has been formed in the elongated neck,
exactly as the non-evaginable portion is formed in Phylactolemata (see

64 BULLETIN OF THE

Davenport, ’90, Plate IX. Fig. 77, Plate XI. Fig. 98) and Paludicella
(Plate V. Figs. 50 and 45).

As my purpose is not so much to present a complete organogeny of
Bryozoa as to show the method of origin of the bud and the fate of the
layers, I have had to desist from carrying on my studies further in the
organography, and have left many interesting and important questions
unsolved ; such, for instance, as the development and structure of avi-
cularia, the presence of an excretory system, and the degenerative pro-
cesses which occur with regularity in the polypides.

3. REGENERATION OF THE POLYPIDE.

I have been led to study the regeneration of the polypide because -
Ostroumoff seems to believe that in regenerating buds the digestive epi-
thelium of the stomach is derived from an extraneous source, — the
brown body. Thus he says (’86*, p. 340) the brown body appears as a
coecal appendage of the young digestive tube. “‘C’est sur ce dernier
[tube digestif] qu’on trouve un groupe de cellules affectant la forme
d’un bonnet et se réunissant tres todt & langle proximal du rudiment
ectodermique. A mesure que les cellules du bonnet, ainsi que la masse
brune, sont employées a la formation de la portion moyenne du tube
digestif, ces dernieres se débarrassent de leur contenu,” etc.

The external phenomena of regeneration are well known. In the
Membranipora stock, for instance, one sees polypides being produced at
the margin, and one finds them older and older as one passes backwards,
until finally they are seen to be wholly degenerate, and to be replaced by
young polypides. Thus, in passing backward along a single row of indi-
viduals in a Membranipora stock about 18 mm. long, I have seen this
process of regeneration recurring four times. In Alcyonidiun, too, one
finds an apparently regularly recurring degeneration and regeneration
of polypides. In the mat-like Cheilostomata the regenerating polypide
(Plate VIII. Fig. 71, pyd. rgn.) is always found at one place, — namely,
on the operculum, — that is, proximal of the opercular opening.’ + In
Flustrella it is found in a similar position on the dorsal body wall, proxi-
mal of the cuticularized introverted portion. My studies have been
chiefly made on the Cheilostomata. Figure 91 (Plate X.) represents an
early stage in the formation of a regenerating polypide. Here, as in the
marginal polypides, there is a typical invagination involving the two

1 Haddon (’83, pp. 522, 523) has found the regenerating polypide arising from

the same place in Flustra membranacea and in Eucratea, and Ostroumoff (’86s,
p 38389) in Cheilostomes in general.

MUSEUM OF COMPARATIVE ZOOLOGY. 65

layers of the body wall (z., ex.). Owing to the reagent, the body wall is
shrunken from its contact with the operculum (qp.).

If one inquires what has been the histological conditions of this region
antecedent to this stage, one must look to younger adjacent and mar-
ginal zocecia, since they reproduce these conditions. I will again call
attention to Figure 88, which represents a cross section of the body wall
through the region of attachment of the kamptoderm of a young pol-
ypide of about the stage of Figure 83. This, then, represents the neck
of the polypide, and it is from about this region that the operculum and
finally the regenerating polypides will arise. The cells are columnar,
and stain deeply about the nuclei, and both cell layers are well devel-
oped. Elsewhere in this same individual the body wall is composed of
smaller, flatter cells, and two layers are not easily distinguished. The
region of the future operculum possesses at an early stage some of the
largest, most columnar cells of the body wall. The cells of this region
do not, however, retain their peculiarly large size throughout life, but
in the adult we find the same region occupied by a flat epithelium,
nearly as thin as the epithelium shown in Figure 90. Meanwhile
the epithelium of the rest of the body wall has become still more
attenuated. The difference between the body wall of the operculum
and that. of adjacent regions is best shown by the greater abun-
dance of nuclei under the opercular region when the stained stock is
looked at im toto from the roof (Plate VIII. Fig. 71). The regions of
the future opercula are seen, in young zocecia (Fig. 71, 4, 6), to be
patches of densely packed nuclei. The opercula of older zocecia show a
slight preponderance of nuclei, and thus indicate more numerous cells.
It is from such a region, then, that the young regenerating polypide
arises.

As in the case of the marginal polypides, so here, the lips of the
invagination pocket close and become fused to form the neck of the
polypide (Plate X. Fig. 84). The later stages of the development of
the regenerating polypides seem to be the same as those of the marginal
buds. Figures 74 and 89 are, indeed, regenerating polypides. I cannot
find any evidence that the alimentary tract, or any part of it, is formed
in regenerating buds by a method differing in any essential particular
from that in marginal buds.

It is well known, however, that the degenerated polypide which forms
a “brown body” in the old zocwcium eventually disappears. Haddon
(83, p. 519) maintains that in the developing regenerated polypide
“the walls of the stomach, or, more strictly, that portion of the stomach
. VOL. xx1I.— No. 1. 5

66 BULLETIN OF THE

which forms the gastric cecum, grow round and envelop the brown body,
so that the brown body passes as a whole into the alimentary tract of the
young Flustra.” It seems to me that the burden of proof of such a
remarkable occurrence lies with him who asserts its existence, and cer-
tainly sufficient evidence is not presented by Haddon.

To settle this question in my own mind, I cut a series of thin sections
through a part of a stock of Escharella (which in budding shows a prac-
tical identity with Flustra), in which all stages of regenerating polyp-
ides were to be found. From complete series, at critical ages, I utterly
failed to find any indication of the inclusion im toto of the brown mass
by the polypide. But I found the alimentary tract of the polypides
usually applied to the brown body (pyd. dgn.), as shown in Figure 92.
At this stage the degenerated mass is surrounded by spindle-shaped cells,
and just within these by a homogeneous or lamellated sheath. At later
stages the elements of the degenerated mass were seen to be more loosely
associated. The cells of the alimentary tract at the same time appear
highly granular, and a granular coagulum often partly fills the alimentary
tract. Before the new polypide is ready to expand itself, the brown body
as such has often wholly disappeared. Just as my sections leave no
chance for the brown body to be included en masse by the alimentary
tract, so too do they yield no evidence of the addition to the latter of
new cells from this degenerate mass, as Ostroumoff, in the sentence
quoted above, implies.

The interesting facts of degeneration in Bryozoa deserve a more careful
study than I have been able to give them. We are quite ignorant of the
physiological significance of the regularly recurring degeneration and
regeneration in certain Bryozoan colonies. Ostroumoff (’86%, p. 339) has
offered an interesting hypothesis, to the effect that the degeneration of
the polypides, the remains of which are taken into the stomach of the
regenerated polypide and the undigested portion of which is cast out with
the feces, is a method of excretion, made necessary to these animals from
lack of urinary tubules.

IV. Origin of the Gemmiparous Tissue in Phylactolemata.

After having found that in Paludicella and the marine Bryozoa, as in
Phylactoleemata, the growth of the colony takes place at the margin or
tips, and that it is here primarily that buds originate, and after having
thus found that throughout the group all of the organs of the polypide
are derived from two layers, of which the inner gives rise to organs so

MUSEUM OF COMPARATIVE ZOOLOGY. 67

dissimilar in origin as the central nervous system and the alimentary
tract usually are, it becomes a matter of no little importance to solve
the two problems, what is the origin of these growing regions, and what
that of the two layers. Through the works of Barrois (86), Ostroumoff
(’87), Vigelius (88), and especially Prouho (90), on the metamorphosis
of the larva and formation of the first polypide of Gymnolzemata we
are fairly well acquainted with the facts in this group; but a careful
study has not heretofore been made of the Phylactolemata with reference
to the points mentioned above. Korotneff (89) and Jullien (90) have
published quite extensive papers on the ontogeny of Phylactolemata,
which describe too incompletely the stages which should reveal the
Yequired facts.

In order to throw a little light on these questions, I undertook the
study of the embryology of two species of Phylactolemata. But before
beginning the account of what I have found, it is necessary to remind
the reader of some facts concerning the origin of the polypides in the
adult colonies. For our knowledge of these we are chiefly indebted to
Braem (’90, pp. 18-32) ; it has also been my privilege to confirm many
of them.

The details of the budding process are slightly different in Plumatella
and Cristatella. In the latter genus the body wall becomes highly mod-
ified as it grows older by the formation of secreted masses which nearly
fill most of the ectodermal cells. In Plumatella, on the contrary, the
ectodermal cells retain, for the most part, a more primitive, unmodified
condition. Here, moreover, by a rapid growth at the neck of the pol-
ypides, the individuals are carried to considerable distances from one
another, whereas in Cristatella there is a less rapid growth resulting in a
compact stock.

In Plumatella, the whole of the embryonic tissue from which any bud
arises does not go to the formation of a polypide, but a part of it re-
mains as the neck of the polypide, and gives rise by cell proliferation to
the body wall and the Anlage of a new bud. Thus the Anlage of each
bud is part of that of a preceding bud. The question remains yet un-
solved, Whence came the Anlage of the first polypide? Since the em-
bryonic tissue of the inner layer of the bud, which seems to take the
most active part in the formation of the bud, gives rise to both the lining
of the alimentary tract and the wall of the brain, it becomes an ex-
ceedingly interesting question, From what germ layer is this inner bud
layer derived ?

In Cristatella, as in Plumatella, not all of the embryonic tissue from

68 BULLETIN OF THE

which any bud-arises goes to form that bud; but some of it is, appar-
ently, passed along under the highly metamorphosed cells of the ecto-
derm, again to divide itself, one part going to form a new polypide, the
other to form the Anlagen of new buds. In Cristatella, this embryonic
mass of cells of the inner layer of the bud seems to be to a considerable
extent independent of the highly metamorphosed ectoderm, and to form
at places a sort of third layer, lying below the true ectoderm and above
the muscularis with the coelomic epithelium. Here, too, while it is
easy to see buds arise from preceding buds in the adult colony, we
cannot consider our question answered until we have discovered the
origin of the cells from which, as from a stolon, the Anlagen of polypides
successively arise.

I desire to say that I have avoided giving a full account of the on-
togeny of these species, both because it is not directly required for the
solution of the problems in hand, and because we are promised studies
in this field by Braem.

The eggs of Phylactoleemata arise, as has long been affirmed, from the -
ccelomic epithelium of the body wall. The evidence of this is conclusive,
for one often sees in a single section various stages in the development
of the eggs. (Plate XI. Fig. 93, ov.) It is also to be observed that
they do not arise indiscriminately from any region of the body wall, but
always close to the neck of a polypide. Sooner or later these eggs,
surrounded it may be by a few follicular cells, are enclosed in an ocecium,
and here undergo their development up to the stage of a young stock,
possessing perhaps a dozen immature polypides. In the figures on
Plates XI. and XII. the ocecium (o#.) has been usually drawn, but in
Figures 100 and 104 it has been omitted. As a result of cleavage, a
blastula is formed, and from one pole of this —¢the pole nearest to the
neck of the ocwcium —cells are given off which move into the blastoccel
(Figs. 94, 98) and finally come to line the cavity. It is important to
observe that in the earliest stage of this process found there were four
inner cells, of which two are represented in the section (Fig. 94, ms’drm.
+ en’drm.). Thus the two layers of the adult body wall are established.
Up to this stage the conditions are practically the same in Cristatella
and Plumatella. From now on, they are somewhat different in the two
genera.

The first difference to be noticed is in the ocecium itself. In Crista-
tella the cells composing this rapidly become a pavement epithelium
(Fig. 97); in Plumatella, on the contrary, the cells of the ocecium
remain columnar (Fig. 99). The neck of the ocecium also differs in the

MUSEUM OF COMPARATIVE ZOOLOGY. 69

two cases. In Cristatella it is long, thick, and filled with a dense mass of
large cells (Figs. 95, cev. ow., and 101 *, 102*). In Plumatella (Fig. 99)
it is very short.

The second difference concerns the embryo itself, and is connected
with the formation of the first polypide. In Plumatella (Fig. 99) the
first indication of the formation of the first polypide occurs at or
very near the neck of the owcium, or, since the ingression of cells
into the blastoccel took place at the pole of the blastula nearest the
neck, we may say near to the pole at which ingression occurred.
The cells of the outer layer (7.) are elongated and contain large ellip-
soidal nuclei which are often pressed close together. All of the cells
of the larva stain more deeply at this pole than elsewhere, and those of
the inner layer rather more deeply than those of the outer. The nu-
clei are also very large, those of the outer layer being possibly more
prominent than those of the inner ; but the difference is not so marked as
in the drawing, where too the nucleoli of the inner layer are represented
relatively too small. Even at this stage one finds in another section
of the same embryo the beginning of a second polypide, whose position
is indicated at *. This second polypide is indicated merely by a con-
siderably thickened inner larval layer, and a very slightly thickened
outer one. The two polypides are thus seen to be wholly independent
of each other. The first invagination further advanced is seen in cross
section of the whole larva in Figure 96. The entire outer layer would
seem at first sight to be involved in this invagination ; but even in this
figure there are seen one or two nuclei which lie under the occium at
the place of invagination. I believe that they will not be involved in
it, for at a very little later stage (Fig. 104) one finds a layer of cells
lying over the invaginated bud, which I believe are destined to ame the
ectoderm of the body wall at this place.

Later stages in the development of the larva in this species are
not shown. The bud follows, I am confident, the same steps that are
pursued by the bud in the adult colony. A placenta-like connection
of the larva with the ocecium, which was first described by Korotneff
(87, p. 194), begins at about this stage, and continues until two well
formed polypides are present. This “giirtelformige Placenta” begins
to form in about the middle of the young embryo, and the elongated
cell of the outer layer of the larva, in contact with the occium shown
on the left of Figure 99 below the *, is, I believe, the first indication
of it. The occium and larva both continue to increase in size, and
the walls of the former become thinner with their increase in area.

70 BULLETIN OF THE

The attachment of the ocwcium to the body wall of the mother stock
always remains small, as in Figure 99, and the embryo, in my experi-
ence, does not come in contact with it.

The formation of the first polypide in Cristatella is preceded by
another process. Just as in the adult colony the inner layer of the
polypide does not arise by invagination of the ectoderm, but from the
stolonic cells lying at the base of the ectoderm (see Davenport, 790,
pp- 108, 109, Figs. 4 and 15), so too in the embryo. The first process
then must be the formation of the stolonic cells. Figure 101 shows at
the point marked sto. (which is at the pole of the embryo whence the
inner-layer cells originated) that certain of the cells of the ectoderm ap-
pear to be arching over a disk, containing about six cells in section, and
thus coming in contact with the cylinder of cells (*) which projects
from the neck of the occium. By a continuation of this process, the
central disk of cells gradually comes to lie below the general level
of the ectoderm, and to be cut off from contact with the neck of the
ocecium (Fig. 97, sto.). The position of the stolonic mass with refer-
ence to the neck of the polypide in this last figure must be considered
abnormal; it is at any rate exceptional, as it lies at one side of the neck
of the occium, which does not, therefore, appear in this section. The
next later stage which I have found is shown in Figure 102. The sto-
lonic mass seen lying beneath the ectoderm in Figure 97 has here
already given rise to a young polypide (7., ev.), and its area is increas-
ing in all directions by cell division (sto.). The beginning of a sec-
ond polypide is indicated on the right at sto. The ectoderm is seen
lying above this stolonic mass, and closely applied to the neck of the
ocecium (*). ;

Neither at this nor at any subsequent stage have I been able to
detect in Cristatella any “giirtelformige Placenta” such as exists in
Plumatella. I am therefore of opinion that the process of nutrition,
which is effected in Plumatella from the ocecium through its placenta,
is effected in the Cristatella larva by its attachment to the neck of the
ocecium. I am pleased to see that Jullien (90, pp. 13, 14) has also
reached this conclusion in a paper which he has had the kindness to send
me. At a later stage, the embryo, or young colony, seems to become
detached from its intimate association with the neck of the ocecium, as
we see in Figures 95 and 103.

Figure 103 represents a stage in which there are two well developed
buds, both shown in the section. There is, in addition, on another section,
one less developed. The stolon is seen passing oralward of these twe

MUSEUM OF COMPARATIVE ZOOLOGY. TL

primary polypides, or rather the primary and secondary one. Moreover,
as the series of sections shows, the stolon does not exist merely in this
section, but it is a disk which is cut here in one of its diameters. A sepa-
ration of the stolonic mass has occurred between the two oldest polypides,
so that the ectoderm is here in contact with the coelomic epithelium,
just as is the case between buds in the adult stock. ‘As the colony in-
creases, the inner and outer margins of the stolonic tissue continue to
extend farther outward, and this tissue forms at first a broad ring of
ever increasing diameter. Later, as the area of the stock increases, the
ring becomes broken, so that, instead of growing along an infinite number
of radii, its growth is confined to a few, as in the adult colony.

I will defer a discussion of the significance of these facts to the gen-
eral part of this paper.

B. GENERAL CONSIDERATIONS.

I. Laws of Budding.

Carefully conducted studies on stock building have generally revealed,
just as these on Bryozoa have shown, a law in budding. This law in
budding results in the formation of a stock the interrelation of whose
individuals is a determinate one. I now propose to offer an hypothesis
to account for the existence of these laws, and then to show how facts
of budding in Bryozoa and other groups can be explained by means
of it.

And first of all I must acknowledge that this hypothesis, although
perhaps here first formulated, really depends upon observations and de-
ductions made long ago on this group, first by Hatschek, who from 1877
has maintained that individuals do not arise independently of one an-
other, and secondly and mostly to Braem, who in ’88 (pp. 505, 506)
declared of Phylactolemata “dass in dem Stock keine Knospe entsteht,
die nicht auf das embryonale, d. h. den specifischen Leistungen der
K6rperwand noch nicht angepasste Zellmaterial einer alteren Knospen-
anlage zuriickgienge und dass somit in der ersten Knospe des keimen-
den Statoblasten simmtliche Knospen des kiinftigen Stockes implicite
enthalten sind.” Not less is the following hypothesis indebted to the
ideas of Roux and Fraisse, and to Nussbaum, who has said (’87, p.
293): “ Kin lebendes Wesen ist somit als Ganzes oder in seinen Theilen
soweit individualisirt und verginglich, als die Gewebebildung und die
Theilung der Arbeit vorgeschritten ist ; das Ueberdauern der Einzelexis-

2 BULLETIN OF THE

tenz, die Theilbarkeit auf geschlechtlichem oder ungeschlechtlichem
Wege, spontan oder kinstlich bedingt, ist an das Vorhandensein undif-
ferenzirter Zellen gebunden und ist um so grésser, je weiter im Organis-
mus diese Zellen verbreitet sind”; and, finally, to the idea which is
implied in the conclusions of Nussbaum (’80, pp. 106-113) and Weis-
mann, that germplasma does not find its origin in the parent individuals,
but is merely borne by them in its unbroken passage from generation
to generation.

This hypothesis is simply that there as in every stock of Bryozoa @ mass
of indifferent cell material which is derived directly from indifferent cells
of the larva or embryo, and whose function is to form the organs of the va-
rious individuals, uncluding the polypides. This indifferent cell material
lies in the body wall, principally at the growing tip or margin of the
stock. By its growth and differentiation it gives rise to the body wall,
muscles, etc., and at intervals it leaves behind, as a portion detached
from itself, a mass of indifferent cells, which is capable of forming a polyp-
ide, or of becoming a new centre of growth, or of both. Which of these
possibilities will be fulfilled, where and when these masses of indifferent
cells will be left behind, depends upon the necessities of the species, and
the variations in these respects give rise to the peculiar characters of
the different stocks.

This hypothesis differs from that of Braem in that the pre-existence
of a Knospenanlage assumed by Braém is, according to my view, a non-
essential feature in the formation of the colony ; the pre-existence of an
indifferent cell mass, which does not itself constitute buds, but may give
rise to masses which can, is the only essential feature.

As a first application of this hypothesis I refer the reader to the con-
ditions of stock formation in Paludicella, already described. We find at
the tip of the colony a mass of large proliferating cells, which I regard
as histologically undifferentiated. These cells give rise to the body wall,
— the cystid, —and at intervals leave behind three masses of cells, which
I regard, from the fact that they retain their cuboid condition, as well
as from their ultimate fate, as indifferent or embryonic. The median
mass of each of these gives rise to a polypide, and to one only. The
lateral masses form centres of growth similar to the one from which they
were derived.

In order to reproduce the arrangement of individuals in the stock re-
sulting from this manner of budding, we may make use of some graphic
method of representation, as Smitt (65%, pp. 139, 140) did long ago, and
as Allman (’70), Semper (’77, pp. 67-78), Chun (’88, pp. 1167-1180),

MUSEUM OF COMPARATIVE ZOOLOGY. 73

Braem (’90, pp. 33 and 44), Ehlers (’90, p. 9), and others, have since
done. I shall represent the mass of indifferent cells by an asterisk,
and individuals (according to Chun’s nomenclature) by the use of the
large and small letters of the Roman alphabet, and, finally, by Greek
letters. The typical stock of Paludicella might then be graphically
represented thus (cf. Plate I. Figs. 2 and 2*) :—

*
*C*
se Se

*xaba*
* Seamer
*b* ** **
* * *¥BaaaBpx*
x% *aaa* Sese Se Se
* *ax* ke
(1) 3% D C B A
* *a * * *
* *¥aaax* KK
3g * BaaaB x
* b * Sage se 8
* x *
*¥abax
* *
*C *
*

Here the letters indicate polypides or their Anlagen, and the asterisks
indifferent tissue. The individuals represented by capital letters may be
called primary individuals; they may be said to belong to the primary
series, and to have been derived from the primary indifferent mass.
The individuals represented by small Roman letters will then be secon-
dary individuals, belonging to the secondary series and arising from sec-
ondary masses, etc. It is to be observed that this indifferent tissue is
here found only at the tips of branches or Anlage of such. No asterisks
are found adjacent to the adult polypides A, B, C, ete., which have
given rise to lateral branches, and these have therefore no power of pro-
ducing new parts of the colony. The asterisks must not be regarded as
having been descended from the letters which they adjoin, but from the
terminal asterisks only ; that is to say, in Paludicella embryonic tissue
has originated from terminal embryonic tissue, and not from indifferent
tissue left remaining alongside of the polypides.

Conditions differing in an interesting manner from these were found
by Braem (90, pp. 18-32) and myself (Davenport, ’90, pp. 103-106) in
Phylactolemata. In Plumatella Braem has shown in the clearest man-
ner how some of the embryonic tissue around a polypide at the proximal

74 BULLETIN OF THE

end of a nascent branch is carried away to the oral side of the “mother
polypide,” and lays the foundations of another polypide. In like man-
ner the embryonic tissue around the “ mother polypide ” may give rise
to one or several additional embryonic masses. He has also (pp. 29-
32) shown in the most convincing way that each mass, particularly in
the case of secondary buds, consists of two parts, of which one goes to
form the polypide ; the other contributes to the further growth of the
common cystid and the formation of new embryonic masses. Since
here every embryonic mass is in intimate relation with a polypide, and
since the polypides arise nearly in one plane, only secondarily moving
out from it, the relation of individuals may be expressed by a formula
occupying a single line. Braem has thus expressed it: —

(2) Re ue eles B

According to the system adopted for Paludicella, this may be given
thus :—

(3) *a *a *b *A *a *B *C ¥%
or, more developed, thus: — °
(4) *a, *a *B *a *a *b xc *¥A *a *¥a ¥b ¥B xa%C ¥D &

in both of which the right hand asterisk (#) takes the place of the A at
the right of Braem’s diagram. These symbols denote that we have a
mass of indifferent tissue connected with each polypide, or the Anlage of
such ; and this indifferent mass, as well as the adjacent polypide, was
derived from some other indifferent mass. Thus the masses connected
with A, B, C, D are to be regarded as having been cut off from the em-
bryonic mass at the extreme right ; and each of these secondarily gives
rise to the polypide buds a, b, etc., and their embryonic tissue. Thus
we have to do with centrifugal budding only.

In Cristatella the conditions are essentially similar to those in Pluma-
tella, the chief difference being that usually only two polypides with
their embryonic masses arise from each polypide. This condition may
be represented by the formula : —

(5) *a, *a *B *a *a *b [*]A *a *a *¥b [¥]B [3]

in which the embryonic masses originally attached to A, B, etc., are
bracketed to indicate that they are normally no longer active in giving

MUSEUM OF COMPARATIVE ZOOLOGY. Ta

rise to new polypides. As a matter of fact, the secondary rows often
make a greater or less angle with the primary ones, and as a result
‘lateral branches are formed. Taking this character into account, the
Cristatella formula might be written :—

*
* b
*a, — a |
| [*]
*B — *a — A
|
(6) *b — [IB — [a]
|
*a — a
*

This representation indicates the fact that the first formed buds (A, a, a,
etc.) are lateral ones; the second, median (Davenport, ’90, p. 106).
Intermediate stages between the condition in Plumatella, in which an
indefinite number of polypides and gemmiparous masses can be budded
off from pre-existing gemmiparous masses, and the condition in Crista-
tella, in which only two such arise, occur apparently in some species of
Plumatella, in which, as Braem (90, p. 31) has shown, few polypides
are produced from any gemmiparous mass, and all but two of these gen-
erally do not develop. In the young corms of Cristatella, on the other
hand, more than two polypides may thus arise.

Other Ctenostomata show a regularity in the budding process similar
to that of Paludicella, and exhibit instructive variations upon it.

Victorella, an interesting Ctenostome occurring in slightly brackish
water, and first described by Kent (’70) in 1870, possesses, according to
the pregnant observations of Kraepelin (’87, pp. 75, 76, 154-157), a
stolon-like tube, from which at intervals polypide-bearing “ cylindrical
cells” arise. Kraepelin (’87, pp. 155-159) has shown it to be in the
highest degree probable that the protrusion of the body wall in the neck
region of the polypide of Paludicella is the homologue of the “ cylindrical
cells ” of Victorella, and that the remainder of the zoccia of Paludicella
is homologous with the “stolon” of Victorella. While in Victorella the
cylindrical cell is developed to such an extent that the retracted poly-
pide is still included within it, and the stolon remains of small calibre,
in Paludicella, owing to its shortening, the retracted polypide must seek
refuge in the stolon, whose diameter is consequently increased to receive
it. Evidence for this is found in the stolon-like nature of the youngest
zocecia of a hatching winter bud of Paludicella Ehrenbergii, and in the
elongated cylindrical cell of the adult Paludicella Miilleri, Kraepelin,

76 BULLETIN OF THE

which must be considered a form intermediate between P. Ehrenbergii —
and Victorella.

The architecture of the Victorella and Paludicella stocks is, then, sim-
ilar, in that they both consist of a row of individuals successively formed
at a stolonic tip. The resemblance is heightened by the fact that, as in
Paludicella, so also in Victorella, a pair of lateral buds is given off from
each zocecium to form lateral branches (Kraepelin, ’87, p. 157). As in
Paludicella, so also in Victorella, communication plates, Rosettenplatten,
arise early to separate the zocecia from each other. But Victorella
differs from Paludicella in this, that while in the latter the neck of the -
polypide does not become the centre of origin of new buds, in the former
it does, just as is the case in Plumatella (Kraepelin, ’87, Plate III. —
Fig. 75) ; that is to say, there are laid down from the tip of the branch
three masses of bud-producing tissue, besides that which goes to form
the polypides of the primary branch. The graphic representation of —
this species will therefore be more complicated than that of Paludicella, —

and has this form :—
iN *

* * *
* * * * *
bx *Bx ax a*a «Be
* * * * * *
* * *
*a* *Qa* A*A*
i * * * *
*
(7) Dx Cea x Bx bx* ax a A* c* b¥ ax ax Bx ax
*
* * * * *
*Aaxn *4%* ARAX a
* * *
* * * * * *
«bs Bix Ox 8 #0 1* Bix
* * * * *
* * *
xa* b *a*
* *
*
* C x
*

Compare with (1), page 73, and (4), page 74.
From around each individual of the series A, B, C, etc., which has
been derived from the tissue of the stolon tip, there arise series of

MUSEUM OF COMPARATIVE ZOOLOGY. ih

lateral and of median buds. From around each of the lateral buds, in
like manner, both lateral and median buds of a higher order arise. But
from each of the median buds only median buds arise. These median
buds, are not, however, all of the same kind. The one first produced (a «,
of Formula 7, # of Form. 8) differs from all formed after it (b *, c *, d x,
etc.) in this, that it bears no polypide, but forms the tip of a stolon
from which both median and lateral buds arise (8, a, near extreme right of
Form. 8). From the second and all succeeding median buds (a b, ¢, etc.,
Form. 8), there arise only median buds of a still higher order. Of the
latter, the first, as before, produces no polypide, but becomes the tip of a
stolon giving rise to both median and lateral buds ; the others give rise
to only median buds of a still higher order, and so on. Our former for-
mula assumed that all median buds were alike, and all incapable of giving
rise to lateral individuals. Their dissimilarity introduces a complication,
so that the species must be represented by some such formula as
this*: —

*
*C x
nS
* *
*Q* b *Q*
ay * *
a
* * *
* ay * od * a, *
* * * *
*B* a* ay* sea xh *a, *a * B*
* * * * *
* * ay * * ay *
xb * B *
x *
(3) xe
* *
*#Qa* A *Q* a
* % * *
* a xe
*a* * * ay * *
* % * * Ay *
* * * *
De CeaxX Be be ax ax Axkce bDaeax Bx at 3k KB* Har a, * 3h
* * * * 2
* xe * * ay *
*a* a: * a, * us
* a rs
etc. etc

1 Tt must be borne in mind that such a graphic representation as this, while it
agrees with the descriptions and figures of Kraepelin and Hincks (’80, Plate 79) so

78 BULLETIN OF THE

in which the heavy asterisks represent the budding tips of the stock,
which give rise to new individuals (tips of the stolons), and a, B,, etc.
indicate individuals of the fourth order. The lighter asterisks indicate,
as before, points of proliferation from which new buds may arise.

It seems highly probable that Victorella finds near allies in Mimosella
and other genera of the Stolonifera.

In Hypophorella expansa, according to Ehlers (’76, pp. 5-9) and
Joyeux-Laffuie (’88, pp. 137-139), the stolon is composed (as in Vic-
torella), of a number of internodes, each separated from the other by
communication plates, and bearing on the distal end typically a feeding
zovid (Nihrthier) and a lateral stolon. It seems to me that the jointed
condition of the stolon is reasonably accounted for in the same way as
that of Victorella, by supposing that each internode, together with its
zocecium, is comparable with the whole indvidual of Paludicella. The
“feeding zodids” of Hypophorella will then be comparable with the
Cylinderzelle of Victorella. Two facts are opposed to this view : first,
the polypide is not formed primarily in the stolon, coming only secon-
darily to lie in the Cylinderzelle as in Victorella ; and, secondly, there is a
Rosettenplatte in Hypophorella between the feeding zodid and the stolon,
while none exists in Victorella. But upon this assumption one can best
account for the fact that the stolon is composed of as many joints as
there are feeding zodids, —a condition which appears to occur in only a
few other genera, and these closely allied to Victorella. Thus, in Cylin-
droecium pusillum and C. dilatatum of Hincks we have two species which
may be considered to represent two possible intermediate stages between
Victorella and Hypophorella, not only on account of the jointed stolon,
but also on account of the enlarged distal end of the joint, which is emi-
nently characteristic of the allies of Victorella. The first objection, that
the polypide is not developed in the stolon, but first arises in the well
formed zocecium of the feeding zodid, might result from the increased
importance of the zocecium over the Cylinderzelle. The formation of the
plate between the zocecium and the stolon might be accounted for by
the physiological need of such an organ resulting from the increased im-
portance of the zocecium (cf. p. 40). Such plates exist, in fact, between
the primary median individuals, and those secondary median ones in
Victorella which are budded from the Cylinderzelle. This hypothesis

far as they go, may not fit the conditions in all parts of the colony. Moreover, it
is to a certain degree idealized, i. e. subjective, for even in the figure of Kraepelin
(’87, Fig. 75) one of the individuals of the series a, b, c, etc. has given rise to no
stolon as its first bud.

MUSEUM OF COMPARATIVE ZOOLOGY. 79

is further supported by the fact that, as a stolon may arise from the
Cylinderzelle of Victorella, so in Hypophorella such a condition is not
uncommon, although hardly typical. In accordance with this hypothesis
the formula for Hypophorella might be given thus : —

*
Cc *
* ba*
(9) b * *
* aa aaB*
* a * * * *
x D C B A

Ehlers (76, pp. 127, 128), in founding the group of Stolonifera, clas-
sified the different methods of arrangement of the individuals in the
colony as follows :—

I. Many polypides (WVdhrthiere) on the single joints of the stolon
(Stengelghedern).

1. On the entire length of the joints.
(a.) Arranged in two rows.
(b.) Arranged in a spiral.
(c.) Arranged in one row.

2. At the ends of the joints.
(a.) In rows.
(b.) Massed.

II. Only one polypide Nahrthier on a joint of the stolon.
1. Polypide lateral, near it one or many stolonic joints (Hypophorella).
2. Polypide terminal.

In the present state of our knowledge, it is very difficult to say how
the types of budding shown in those Stolonifera which possess more than
one Vdhrthier on a joint of the stolon are related to, or are to be connected
with, the types of Paludicella, Victorella, Hypophorella, or other genera
possessing only one Ndhrthier to a joint. This could doubtless be deter-
mined, however, by studying the early stages in the development of the
stocks. Taking them as they are, however, we find a very simple condi-
tion in the stocks of Class I., in which the Ndhrthiere are arranged in a
single row, as in Vesicularia spinosa (cf. Hincks,’80, Plate 73, Figs. 3—7).
The tip of the stolon consists, as I have myself observed in allied spe-
cies, of somewhat cubical cells of variable thickness, and it is from this
tip that the Anlagen of the individuals arise. Lateral branches occasion-

80 BULLETIN OF THE

ally replace a Vahrthier, and the latter seems never to produce secondary
individuals. The formula of the stock might be written : —

*
b
a
(10) #F — BF — |=] dD = ¢C-— 8a
a
*

In Bowerbankia pustulosa we have two rows of individuals produced
side by side from near the end of the stolon. This condition would be
represented by
xe D * C..4.B et
= 6D 4£C #85B. #4
provided the individuals of this primary series possess the power of giy-
ing rise occasionally to secondary buds, as seems certainly to be the case
in some members of this genus which I have seen. The spiral arrange-
ment of some colonies is striking ; it is of evident advantage to the stock,
but its cause in these cases is wholly unknown.

In every one of these cases, and, in fact, in all of those figured by
Hincks, which belong to the Stolonifera, there is no trace of dichotomy.
Throughout we have to do with linear series, which give rise to lateral
branches.

Turning now from the Stolonifera to the other grand division of
Ctenostomata, the Alcyoniide, we find the same prevalence of a law in
budding. In its typical expression it may be written as follows : —

(11)

*
* b *
* * (*) *
* a * *aaa*
* % *
(12) x C (*) B (ye
rs * *
* a * *aaas*
* * (*) *
x» b *
*

Although secondary median individuals are not habitually formed,
yet, owing to the capacity of regeneration possessed by individuals
A, B, C, ete., an asterisk is affixed in parentheses to show the probable
persistence of embryonic tissue. Of the lateral series one or both may
fail to be developed.

MUSEUM OF COMPARATIVE ZOOLOGY. 81

It might be difficult to determine whether in this group we have to do
with dichotomy, did not the tips of the margins at times reveal the fact
that there is no division of the ancestral series, but that a new one is
added at the side of an ancestral one (Plate VIII. Fig. 69), where of
the marginal individuals 4 is clearly median (ancestral) and 3 is lateral,
13 median and 12 lateral, etc. (see page 49).

The members of the group of Cyclostomata seem to be closely related,
and the method of budding is so similar throughout the group that it
seems fair to interpret the more compact Tubuliporidz from the Crisiadee.
In Crisia, as we have seen, individuals are placed in rows, from which at
intervals lateral rows are given off to the right or left. One may say
that typically these are given off from each individual to both the right
and the left, although in some cases, as in Figure 65°, lateral branches
are typically given off alternately to the right and left, and are often
aborted. Perhaps the most general formula of all for Cyclostomes should
be that of two lateral branches from each individual, one or both of
which may remain undeveloped. Such a formula I believe to be also
the typical one for Bugula and its allies, and for the Plustrina and
Lischarina. It would be written thus: —

“55
* QQ *
x (*) *
Ie Mo Ge
* * *
x b *
* * (*) * *
* x (*) * *B*aaa* B*
*# a * ba GA Eh. Ce ea * * x *
* x *
(13) 3% D (x) C («) B (#) A
% * *
* &@ * * aaa * * * * *
* * (*) x * B (*)a a a(*) B *
* * (*) * *
x b *
*
* b a*
* (*) *
* @Q@ *
*

in which the parenthesized asterisks indicate the presence of regenera-
tive tissue. This is identical with (12) and similar to (1).
Braem (’90, pp. 130-133) has already called attention to the differ-
ence between Phylactolemata and Gymnolemata in the orientation of the
# VOL. Xx1I.— No. 1. 6

n

82 BULLETIN OF THE

polypide. In Phylactolemata the oral aspect of the polypide is turned
towards the margin of the corm or the tip of the branching stock ; in
Gymnolemata, on the contrary, the anal aspect is turned in that direc-
tion. This difference is a very striking and constant one. It is corre-
lated with another difference in the law of budding of the stock, which
will become evident upon comparing Formulas (4) and (5) on page 74,
of Phylactolemata, with Formulas (1) on page 73 and (7) to (13). In
all of these the margin or tip of the stock is at the left, the centre at the
right. In the formule of Phylactolemata the budding is centrifugal,
new individuals being produced from the embryonic masses towards the
margin; in the formule of Gymnolemata budding is centripetal, new
individuals being produced from the embryonic masses towards the
centre. Jn both Phylactolemata and Gymnolemata the anal aspect is
turned towards the gemmiferous region.

Braem calls attention to one other difference, namely, that, in the case
of the retracted polypide, in Paludicella the rectum lies next the at-
tached surface of the stock; in Phylactolemata, the cesophagus. A
mechanical cause of this is suggested when this statement is put in other
words : the polypide in its retracted position is stored in both Phylac-
tolemata and Gymnolzmata proximad of the atrial opening ; i. e. away
from the tip or margin, and towards the centre of the stock. May not
this be explained, in part at least, as an adaptation to room ?

I will here add four examples of regular budding taken from other
groups of animals, to illustrate the general applicability of this method
of representation. The first of these is that of the Siphonophore Hadz-
stemma whose formula has been worked out by Chun (’88, p. 1169), and
expanded and illustrated by Korschelt und Heider in their recent text-
book (p. 39). It runs as follows : —

(14) Decba-Cdeba Be deb as yopuoee

According to my interpretation of the case, this formula might be
written (15) :—

*xD xcxbea*C dc xb xa *B 3 #e ¥d ¥c xb xa xa #y ¥B a * A,

x

in which the # behind B has been derived from the embryonic mass at
A, that behind C from B., etc. The 3’s represent embryonic masses
from which a, b, ¢c, etc. are derived.

If we assume that the terminal individual (A) has not been derived
from the primary embryonic mass, at the extreme left, but has had its

eee ge ae

MUSEUM OF COMPARATIVE ZOOLOGY. 83

origin in the embryo, the formula would have to be written somewhat
differently ; namely, thus (16): —

xk Czk cx bx ax Bx dx ce be ax Aztex de ce bk ak ax y* Be ax [A]

In a species of Pennaria, common on our coast, which is probably
Pennaria tiarella, McCready,’ I have noticed the presence of a similar
law of budding. The whole stock lies in one plane, the lateral branches
arising alternately from the right and left of a central stock, like the barbs
of a feather. These lateral branches give rise to a series of secondary
ones, which are all placed on the same (axial) side of the branch. Each
branch, of whatever degree, originates as a bud bearing a polyp. From
the elongating stalk of this terminal polyp, buds arise, — the beginnings
of branches of the next higher order. The stock may be represented by
the following formula : —

A
*
|
d«x —
|
ca
a
RES ge ga
Sil
B x
c x | |
* i Roa?
(17) ODS a eam
ax—— d
|
bx —
|
cx
*
B

Expressed in a linear series, this formula may be written :—
(18) *% Dx Cx Bx ce be ax Ax dx cx beax ax Be at

which is identical in form with the second formula (16) given for Hali-
stemma.

1 This species is figured by Leidy (’55, Plate 10, Figs. 1-5) and Verrill (’75, Plate
XXXVII. Fig. 277). An allied species, P. gibbosa, is figured by Louis Agassiz’
in the “ Contributions” (Vol. III., Plate XV. Fig. 1). In describing P. Carolinii,
Weismann (Entstehung der Sexualzellen, p. 122) says that the lateral hydranths
do not possess the capacity of giving rise to new lateral hydranth-bads (of a higher
order). But, as indicated above, P. tiarella seems to do this regularly. Leidy’s
and Verrill’s figures show the same thing.

84 BULLETIN OF THE

Lastly, this formula may be applied to certain cases of fission, as in
Sresh water Annelids, As is well known, the fissiparous process is pre-
ceded by the formation of the so-called budding zones (Knospungszone).
These arise in Ctenodrilus, according to Kennel (’82, pp. 403, 404), be-
tween two dissepiments in the middle of a metamere, and new ones are
continually formed behind the others as the animal grows in length
by cell proliferation at the tailend. The budding zones are, according
to Kennel, regions composed of embryonic cells. I think it probable
that this embryonic tissue has been derived from the embryonic tissue
of the anal end of the animal. There are as many budding zones pro-
duced as there are new metameres added by the anal growth, and since
the budding zones are intrasegmental, each zodid consists of four parts ;

viz. (naming them from anterior to posterior end) of the posterior half

of the preceding budding zone, of the posterior half of the metamere in
which the budding zone arose, of the anterior part of the next follow-
ing metamere, and, finally, of the anterior part of the following budding
zone. Zodids then are made up of parts of two adjacent metameres,

and the middle of each zodid is intersegmental. The zodid has progressed —

little beyond the state of possessing two (half) metameres at the time it
becomes free. New metameres must become formed by caudal growth.
The animal is, then, according to my conception of the significance of the
process, derived chiefly from these budding zones. Evidently, the law
of production of new individuals (or new budding zones) is a simple
one, and may be written, in accordance with my nomenclature,

(19) a E (x) * D (x) * C (x) * B(#) * A

in which A, B, C, etc. represent successive individuals (adjacent halves
of two metameres), and the asterisks, as before, embryonic tissue. The
two adjacent asterisks together represent the budding zone, of which
the posterior half (parenthesized) proves itself the least active.

The conditions given by Semper (’77, pp. 69, 77) for Chcetogaster
(and Nais) are much more complicated, but may be expressed by
the use of a formula constructed upon the same plan. Chetogaster
differs from Ctenodrilus in this: that young budding zones, and event-
ually young individuals, are produced between older ones, instead
of always at the anal end; and the new zodids often acquire several
metameres before becoming free. It seems to me probable that, as in
Ctenodrilus, the budding zones are derived ultimately from the anal
zone; but here, in contradistinction to Ctenodrilns, new budding zones
may secondarily arise from other budding zones produced earlier, thus

err

”

— Me ie:

MUSEUM OF COMPARATIVE ZOOLOGY, 85

giving rise to the phenomena of young individuals interpolated between
older ones. Representing, then, individuals by the budding zones from
which they have arisen, we may convert the following formula of Semper
into one based on our own nomenclature :

E D H B G C F A

phe Ue, een) 9 Le eee

az.—3+0—0 44+0—1+0—0 4+4+1—1+0—0 4+4+0—2+0—0 471
in which the succession of generations of zodids is
os A 8 Or ey rome

In the above formula A, B, C, etc. represent zodids; the numerals
below the letters, the number of metameres of which each is composed ;
0, an incomplete metamere about to be derived from a budding zone ;
az., the anal zone. Written in accordance with my conception of the
facts, this formula would read :

(20) x D(x) *C(*) *a(*) *B(*) *b(*) *a(*) xa! (*) # A,

which somewhat resembles Formula (15) of Halistemma, and signifies
that two embryonic masses are left behind by the anal zone, of which
the one anterior to the zodids proper (represented by letters) goes merely
to form the head parts, and is represented parenthesized. The second
is caudad the zodid, and may form a secondary “anal zone” giving rise
to new zodids. From one zodid two or more anal zones may take their
origin. Thus, from the embryonic mass caudad of A there have arisen
that caudad of b, which has given rise to b (*) * a (), and that caudad
of a’, which has given rise to a! (*).}

The most general formula given on page 81 undergoes many modi-
fications in the different groups, but in the midst of these modifications
certain laws are to be discerned, to some of which I have already called
attention. I will now proceed to a discussion of the significance of
these laws.

The quincunz arrangement of individuals, which is so noticeable in

1 From a study of surface views of many specimens of Autolytus collected
at Newport during June, 1891, I am convinced that the sexual individuals are
produced by proliferation of cells in the metamere XIII. or XIV. of “ parent
form,” —the last which remains behind after breaking off of sexual form. Rep-
resenting the proliferating metamere by (2%), we may write the budding formula
of Autolytus thus:

(202) te E(*) D(*) C(*) B(*) A (x)

in which the parenthesized asterisks indicate the proliferating, but not gemmif-
erating anal metameres of the sexual form. (Cf. A. Agassiz, ’63, pp. 397-400.)

86 BULLETIN OF THE

the phytoid stocks of Bugula, and in creeping corms like Lepralia or
Cristatella, may be explained as affording additional strength on the one
hand, and as a device for saving space on the other.

The absence of true dichotomy, which I have sought to show charac-
terizes the budding of Bryozoa, is interesting as seeming to indicate
the fundamental similarity of the process of budding in Paludicella to
that found elsewhere. The tip of the branch does not divide equally
in the first nor in the other instances, but constantly maintains its
precedence, giving off parts of itself to form lateral branches. These
parts may grow out at right angles to the primary branch, as in Palu-
dicella, but generally they grow forward nearly parallel to it, as in
most marine Gymnolemata.

In Bugula (Plate VII. Fig. 64%) branches are always given off
toward the axils, and therefore an ancestral branch gives off all lateral
branches from one side and the successive orders of branches are given
off alternately to the right and left. In Crisia, on the contrary, branches
are given off abaxially, and they are given off not from one side only,
but alternately to the right and left. In both cases the two facts are
mutually dependent. The first case gives rise to a stock in which the
branching tends as greatly as possible towards compactuess and the for-
mation of a closely built stock ; the second case gives rise to a diffuse
and loosely built stock (ef. Figs. 64, 65, and 64°, 65%). In the sec-
ond case there is a maximum space to each individual ; in the first,
a maximum economy of space.

The rule that lateral buds on two closely related branches tend to
arise in the same generation is one that, as has been shown, is more
or less apparent in some cases, but is easily obscured by other rules.
May not the tendency be due to the same causes that produce the
synchronism of division in related cells of a cleaving egg?

That lateral buds should occur in Bugula flabellata on the outermost
rows only is not surprising when we reflect that there is abundant room
on the margin, whereas the inner individuals are hemmed in from lat-
eral expansion by the pressure of adjacent rows. This is very marked in
certain repent colonies, as, for instance, occasionally in Membranipora
(Plate VIII. Fig. 70). Here the intermediate branches 6, 7, 8, and 9
have produced no lateral buds for many generations, while almost every
individual of the marginal rows has given rise to a lateral branch. It is
merely a result of the same cause, it seems to me, that lateral budding
occurs more frequently in Bugula turrita at the margins of fans than
elsewhere. Here there is room to spread.

MUSEUM OF COMPARATIVE ZOOLOGY. 87

The rule (5) that ancestral rows contain fewer generations of indi-
viduals than lateral ones may perhaps receive a partial explanation from
the further fact (rule 6) that of the two rows starting from any axil the
ancestral branch will give rise to a greater total number of individuals
than the lateral one will in the same time. We should expect a less
rapid forward growth if the lateral growth is extremely vigorous. One
might also say that the intermediate rows had grown abnormally in
length, since that is the direction in which there is most room.

The reason why the ancestral branches in Bugula give rise to the
greater total number of individuals is, to my mind, because they are
marginal. In Crisia it is the lateral branches which are the most
prolific, and for the same reason.

The existence of the 7th rule in mat-like species is a mechanical
necessity ; in the phytoid species, like Bugula and Crisia, it must be ac-
counted for on another ground ; namely, on the relations of food supply
to demand, — on the deterrent effects of overcrowding. And this, to my
mind, is the key to the significance of the 4th, 5th, 6th, and 7th rules.
The form of the stock is determined by the same law which has deter-
mined the form of the individuals, — the struggle for existence and the
survival of the fittest, — the fittest in the present case being those which
are most advantageously placed with reference to food supply. Abundant
food supply has made possible the rapid production of lateral individuals:
at the margin, and less abundant food supply has retarded such produc-
tion in the middle. Therefore has lateral budding occurred more rapidly
at the margin ; therefore has the number of individuals produced at the:
margin been greatest ; therefore have the median rows grown in length
only with great rapidity ; therefore has the distance between adjacent
rows of individuals in phytoid stocks remained constant.

Many observations on different groups of animals agree in demonstrat-
ing a relation between rapidity of the budding or fission process and food
supply. Thus Zoja (90, pp. 25-27) has shown for Hydra, and Zacha-
rias (86, p. 274) and von Wagner (790, p. 360) for Turbellarians, that
abundant food supply results in an acceleration of the processes of
non-sexual reproduction, and Braem (’90, p. 24) has shown that bud-
ding in Cristatella proceeds less actively during the late fali. This
diminution in activity has been attributed by Braem to diminished
temperature ; but we know also that this period is one of scarcity of the
small fresh water organisms upon which the fresh water Bryozoa live
(cf. Parker, ’90, pp. 597-600), and this fact also must be considered as
having an important influence in this case.

88 BULLETIN OF THE

II. Relation of the Observations on Budding in Bryozoa
to the Germ Layer Theory.

No question in Bryozoan morphology has been more thoroughly dis-
cussed than that of the part played by the germ layers in the production
of the polypide, and upon none has there been less agreement. Nitsche
first boldly opened the question, and concluded that we have in this pro-
cess a fatal objection to the idea of the homology of the germ layers, in
so far as their homology depends upon a similarity of fate throughout the
Metazoa. A single layer, the invaginated ectoderm, gives rise to the outer
covering of the tentacles, to the pharynx, and to the brain, — structures
elsewhere considered as ectodermal, — and also to the lining of the ali-
mentary tract, elsewhere universally accounted entodermal. In view of
these facts, “sind die Keimblatter,” concludes Nitsche (75, p. 398), “ kei-
neswegs mit einer besonderen histologischen Pradisposition ausgestattete
Zellschichten, sondern lediglich die flichenhaft ausgebreiteten Elemente,
aus denen die den Metazoenkérper zusammensetzenden, ineinander
geschachtelten Réhren sich bilden.” Prouho, although recognizing the
facts to be as stated by Nitsche, has not discussed the theoretical bearing
of the question. Seeliger (’89°, p. 204) finds in the budding process of
Endoprocta a shortening and confusion of the embryonic process. “‘ Wie
die gesammte Knospenentwicklung verkiirzt ist, erscheinen auch die
beiden Processe der Einstiilpung durch welche im Embryo zuerst Ento-
dermkanal, dann Atrium sich bilden, in einen zusammengezogen.” In
another place (Seeliger, ’90, p. 595) the budding process is considered as
an “immer sich erneuerende Gastrulationsvorgang.” Braem (90, p. 116)
regards the inner layer of the bud as entoderm, and the process of its
formation as one of gastrulation. In a preliminary notice published last
February (Davenport, ’91, p. 279) I suggested that the embryonic tissue
from which the inner layer of the polypide arises is to be regarded as
“neither ectoderm nor entoderm, but as still indifferent, and capable of
giving rise to either.” A few weeks ago I saw for the first time the paper
of Oka (’90), in which he offers (p. 145) @ priori a similar suggestion
concerning the significance of the embryonic tissue from which the inner
layer of the polypides arises. I am pleased to find that our ideas, thus
independently arrived at, are so fully in agreement. My idea of the re-
lation of the germ layers to the layers of the polypide bud chiefly grew
out of my studies on the embryology of Phylactoleemata as described in
earlier pages.

As there are two layers to the bud, the question of the part taken by

MUSEUM OF COMPARATIVE ZOOLOGY. 89

the germ layers in the polypide bud may be subdivided into two: What
is the significance of the outer layer of the bud? and, What is the sig-
nificance of the inner ?

The outer layer of the bud is derived from the ccelomic epithelium.
The views of those who have studied the formation of this inner layer
of the cystid in Phylactolemata may be classed in two categories :
(1) those in which it is regarded as entoderm, and the process of its
formation as gastrulation; and (2) those in which it is regarded as
mesoderm. To the former class belong the views of Reinhard (’80,
p- 208), Korotneff (89, p. 403), and Jullien (90, p. 19); to the latter,
those of Kraepelin (86, p. 601) and Braem (’90, p. 116), and in this
class the views of Barrois (’86, p. 68) and Haddon (’83, p. 543), founded
‘on a@ priorz considerations, must be placed.

It seems to me that, since, as Barrois has demonstrated, there is a great
similarity between the Phylactolematous and Gymnolematous larve,
and especially since the former show evident signs of degeneration, we
are bound to study the phenomena they exhibit in the light of our
knowledge of the ontogeny of Gymnolemata.

But first it is necessary to give reasons for believing that the larva of
Phylactolemata is to be regarded as homologous with that of Gymnole-
mata; and to do this I will first name the points of similarity in the two
larvee, and then try to show that the differences which exist are not suf-
ficient to invalidate the attempt to establish a homology. And, first of
all, it may be said that, since the adult Phylactolemata and Gymnole-
mata are strikingly similar to each other, and since no one doubts their
close relationship, we should expect a priort that their larvee would be
homologous, especially since the larve of Gymnolemata are admitted to
belong to the trochosphere type, of whose ancient origin there can be
little doubt. In the second place, the very existence of a larval stage
in Phylactolemata is indicative of its inheritance from an earlier condi-
tion, for two reasons: (a) because in general fresh-water life tends to
eliminate larval stages from species which have inherited them from ma-
rine ancestors, and tends little to form them de novo (Hydra, fresh-water
Turbellarians, Rotifera, Oligocheta, Hirudinea, Astacus, and fresh-water
Mollusca); and (6) because, specifically, the early stages of development
of Phylactolemata are passed within a uterus-like sac, from which the
embryo is released only when a colony is already well established. In
the third place, the Phylactoleematous larva possesses, in common with
all Gymnolzmatous larvee, the following characteristics. The primary
polypides arise in both at a pole, and this pole is in both a prominent disk,

90 BULLETIN OF THE

surrounded by a circular fold, — the so-called mantle fold, — from which
it is separated by a circular groove, — the so-called mantle cavity. This
organ has a similar origin and fate in the two groups, as shown by Barrois.

The following points of difference, however, must be recognized.
First, the absence of a definite ciliated ring, cowronne (Barrois), of an
internal sac, and of a pyriform organ. But, as Barrois (’86, p. 67) has
shown, these are absent, or at least (Ostroumoff, ’87, pp. 182, 183) little
developed, in Cyclostomatous Bryozoa. The ciliated ring and pyriform
organ are doubtless organs connected with a free locomotive larval life,
which is greatly abbreviated in Phylactolemata. A second difference
exists in the fact that, while most Gymnolezematous larvee possess either,
rarely, (1) a functional alimentary tract, or (2) a mass of loose tissue
lying inside of the ectoderm, the Phylactolemata possess (3) a central
space lined by an epithelium placed next to the ectoderm. However
great the difference between the first and third conditions mentioned
above, it is to a large extent bridged over by the widespread existence of
the second. In some Cyclostomes, moreover, a similar condition to that
in Phylactolemata seems to exist. Compare Metschnikoff (’82, p. 310,
Taf. XX. Fig. 62). Lastly, the origin of two primary polypides, instead
of one, at the aboral pole, upon which Barrois has laid some stress, can-
not be considered a very strong objection to the homology, because in
reality the two polypides do not arise at the same time even in Pluma-
tella, and in Cristatella this difference is still more pronounced. In fact,
it is not the formation of two polypides which requires explanation, but
that of a young stock before hatching.

There remains, therefore, to my mind, no serious objection to regard-
ing the larve of Phylactolemata and Gymnolemata as having been
derived from some common ancestral larva, possessing, of course, more
points of resemblance to the Gymnolzmatous than to the Phylactolema-
tous type; and therefore it is perfectly justifiable to interpret the latter
by aid of the former.

Admitting the larve to be homologous, we should expect the process
of gastrulation to be comparable throughout Ectoprocta. As a matter
of fact, we do find a great similarity in the earliest stages. Thus, the
first indication of the inner layer is the ingression of four cells at one
pole, which by multiplication give rise to a layer of cells lying inside of
the ectoderm.’ It is to the comparative study of the fate of this inner

1 This has been shown for Membranipora (Tendra) by Repiachoff (’78, pp.
416-420) ; for Alcyonidium polyoum by Harmer (’87, pp. 445, 446); for Bugula
by Vigelius (’86, p. 519) ; and for Cristatella in the present paper (page 68).

MUSEUM OF COMPARATIVE ZOOLOGY. 91

layer in the different Ectoproct larve that we must look for an explana-
tion of the layer in the specific case of the Phylactolemata.

For the purposes of this study, it is desirable to begin with species in
which there has been a minimum amount of degeneration. Such are
Membranipora (Cyphonautes), Alcyonidium, and Flustrella, to which
we must now turn our attention.

The studies of Repiachoff on Membranipora lead up to a stage in which
the entoderm lies as a solid mass inside the ectoderm, and is separated
from it at all points. Neither the origin of the mesoderm nor the forma-
tion of stomodzum or proctodzeum was observed at this time. As for
the fully formed Cyphonautes, it is certain, as I can confirm from personal
observation, that there is a well developed functional alimentary tract,
and that it is provided with a well developed muscular system, including
cross-striped muscle fibres. There is, therefore, every reason for believing
that typical entoderm and mesoderm have been formed in it.

In Alcyonidium (polyoum), Harmer (’87, p. 445) has shown that after
gastrulation a great mass of cells occupies the former blastoccel. This,
in the author’s opinion, represents entoderm and mesoderm. The young
larva possesses a mouth, an cesophagus, and a large stomach, but never
an anus. No evidence is presented that the oral pole corresponds with
the pole of ingression.

Flustrella, which is nearly related to the last species, possesses in
its young larval stages a pocket, which Prouho (’90, pp. 424-426) has
shown to represent the anterior part of the alimentary tract, directly
comparable with that of Aleyonidium polyoum, but less developed. Mus
cle fibres and an epithelial lining of the entoderm and ectoderm exist to
indicate the presence of mesodermal tissue.

These three genera, Membranipora, Alcyonidium, and Flustrella, are
the only Ectoprocta in whose larve the presence of an alimentary tract
has as yet been demonstrated.

In Bugula, a very careful study of which was made by Vigelius (’86
and ’88), one finds after gastrulation and cell multiplication a mass of
cells filling the whole interior of the larval body, at first appearing as
an epithelium surrounding a central space, but later without arrangement
and often showing signs of degenerescence. No definite separate meso-
derm could be found, and at no time was any trace of an alimentary tract
to be seen. Vigelius calls the mass derived from the four entodermal
cells Fiillgewebe, and he believes it to correspond moiphologically to
both “hypoblast and mesoblast.” It is to be noted, however, as a
point of considerable importance, that in his figures of the metamorphos-

92 BULLETIN OF THE

ing larva Vigelius (’88, Taf. XIX. Fig. 6) represents this tissne as hav-
ing almost entirely disappeared ; that which remains giving rise to the
mesodermal lining—the outer layer of the bud —of the developing
polypide.

There can be no doubt that the so-called oral pole of the Bugula larva
corresponds to the mouth-bearing pole of Alcyonidium, but does it cor-
respond to the pole of ingression of entoderm? This question has not
been answered by Vigelius. The existence of homopolar stages like that
represented in his (86) Figure 25, Taf. XXVI., makes it very difficult
to establish this doubtful point.

The formation of the inuer layer of Cyclostomes has been studied by
Barrois (’82, p. 141). He says: “ Des les premiers stades les sphéres
vitellines glissent les unes sur les autres de maniére & former une espéce
de gastrula par épibolie et l’on ne tarde pas & rencontrer des stades d’un
volume extrémement exigu et déja composés d’une couche exodermique
et d’une masse endodermique libre dans son intérieur, La masse endo-
dermique s’atrophie rapidement et l’on arrive 4 une petite blastula qui
succéde non pas & un stade composé de cellules radiaires dans lequel
se forme une cavité centrale, mais qui est issu, au contraire, d’une vraie
gastrula née par épibolie dans les premiers stades de la segmentation
et dans laquelle la masse endodermique est déja disparue.” I have
quoted Barrois thus at length, since his description will show forcibly at
least one thing, that the fate of the cells which by ingression had entered
the blastoccel is quite different from that of those in Bugula, where a
great Fiillgewebe is formed. Ostroumoff (’87, p. 183), however, has
shown that the inner layer of the Cyclostome larva does not disappear,
but comes to line the ectoderm as a very thin layer. In the adult larva,
however, we find the contents of the ectodermal sac “filled with me-
senchymatous cells, which are commingled with yolk granules and glob-
ules of albumen.” It is these cells that produce the very considerable
mesodermal layer of the first polypide, which arises in the metamorphosis
of the larva. Here, as elsewhere, an apparently homopolar stage inter-
venes between gastrulation and the formation of larval organs, making
orientation difficult.

Thus, passing from Cyphonautes, through Aleyonidium and Flustrella,
Bugula, and finally Cyclostomes, we have a series in all of which the
inner germ layer is derived from one pole by ingression or by ‘ epiboly,”
and in which there is a gradual reduction of the functional entoderm until
it seems, in Cyclostomes, to be lost, and a gradual transformation of the
mesoderm from a cell mass nearly filling the larva, and producing muscles

MUSEUM OF COMPARATIVE ZOOLOGY. 93

and a lining to the body wall and alimentary tract, to a single thin cell
layer lying next to the ectoderm, or to mesenchymatous cells extending
through the ccelom.

This same series may be said, also, to be one in which there is a
gradual decline in the complexity of larval organs. These find their
maximum development in the bivalve Cyphonautes and Flustrella, and
the complicated and beautiful Aleyonidium larva, They find their mini-
mum development in the Cyclostomes, whose larvee, instead of a girdle of
flagella, possess merely an undifferentiated clothing of cilia, are reduced
to a cylindrical or ellipsoidal form, lack the pyriform organ of other spe-
cies, and in some cases possess only the rudiment of the internal sac.

If we were to imagine still another term at the degraded end of the
series, it would be a form in which the four inner-layer cells that arise
by ingression at one pole of the larva should give rise to little or abso-
lutely no entoderm, in which the mesoderm should come to form an
inner lining to the ectoderm, and in which the internal sac should be
entirely absent. It is just these conditions which are fulfilled by the
Phylactolematous larva.

Of all these changes, the loss of the entoderm is the most striking.
What can be said in explanation of it? I would suggest this hypoth-
esis: that the entoderm of the Bryozoan larva has become rudimentary
through less of the alimentary function.

In direct support of this hypothesis I have little experimental evidence
to offer. One observation, however, which I made last summer, seems
to favor this conclusion strongly. This is that larval life is of consider-
able duration in Cyphonautes, which possesses a functional alimentary
tract, but is very brief in Bugula, in which no alimentary tract arises.
As is well known, Cyphonautes occurs in enormous numbers in the
“tow ” at certain seasons of the year, and this is alone evidence of a con-
siderable length of life. I have taken Cyphonautes thus obtained from
the tow and have kept them for three or four days, at the end of which
time they died, or had settled to the bottom of the glass vessel to un-
dergo their metamorphosis. In fact, from several hundred Cyphonautes
which I collected, not more than half a dozen completed their full meta-
morphosis, the others apparently succumbing to unfavorable conditions.}

1 Just as the manuscript of this paper is going to the printer, after long delay
caused by an accident necessitating the re-engraving of the plates, I find that Dr.
Prouho read last summer (790), before the Association Francaise pour |’ Avancement
de la Science, a preliminary communication on the development of Cyphonautes.
This is published in the printed report of the proceedings of that association. The

94 BULLETIN OF THE

The Bugula larvee, on the contrary, I have never found in the tow, but
they swarm out from stocks gathered in the morning and placed in a
glass vessel ; and I can confirm Nitsche’s (69, p. 9) observation that they
settle and begin their metamorphosis within “a few hours” after hatch-
ing. One rarely or never finds these larvee succumbing to the unfavor-
able conditions of the aquarium before metamorphosing. From these
observations I conclude that the Bugula larva has a very much shorter
life than Cyphonautes. Now, since the larva, owing to its shortened life,
has no need of functional entoderm, and since entoderm can be of use to
the larva only, no part of it going over into the tissues of the primary
polypide of the stock (except as food material), functional entoderm is
not developed. In other genera, its rudiments have become less and
less important in the ontogeny, and, finally, in Phylactolemata are
wholly lost.

That the entoderm should reach its last stage of degeneration in
Phylactolemata is easily understood when we consider that the larval
period is passed in a closed ocecium, from the wall or neck of which it
receives nourishment as a parasite does. Moreover, by the delay in the
period of hatching, as well as by precocious development of polypides, one
at least of the latter is usually functional in the just hatched stock, for
there is sometimes found at least one polypide in the newly hatched
larva, which is partly extruded, and therefore capable of feeding, and
thus of supplying the whole stock with nutriment. Of what advantage
to a species could be the development of a functional larval entoderm,
which should go to form no part of its adult tissue, provided the larva
was contained in a uterus during its early stages, and was provided with
the adult digestive organs in a functional condition before leaving the
uterus %

Those who maintain that the inner layer is to be regarded as entoderm,
and are still unwilling to place the Bryozoa among the Coelenterata, must
account for the absence of mesoderm. Korotneff (’89, p. 400) finds de-
generating cells in the blastoceel before this is wholly obliterated by the
extension of the inner layer. These he seems to regard as degenerate
mesoderm. According to his view, then, the entoderm gives rise to
the muscularis, — for this arises from the inner larval layer, according

author does not there state whether stomodzum and proctodeum are formed on
the blastoporic side of the larva. He accounts for the existence of an alimentary
tract in Cyphonautes by the fact that it undergoes its development disconnected
with the parent, while almost all other Bryozoa pass their early stages in the
parent or some protecting zodid (ocecium, ovisac, ovicell).

MUSEUM OF COMPARATIVE ZOOLOGY. 95

to Braem’s (’90, Taf. VII. Fig. 89 mb.) observations, which I can abun-
dantly confirm, — and to the celomic epithelium of the adult stock. In
the few series of sections of the proper stage which I possess, I have not
found with certainty the degenerating cells of which Korotneff speaks ;
but even if they regularly occur, I should be inclined to regard them as
the degenerated entoderm, the mesoderm persisting to give rise to the
muscular tissue and the ccelomic epithelium.

From a consideration of these facts, —that the larve are homol-
ogous and the process of gastrulation is comparable throughout the
Ectoprocta, that in the least modified larvee both functional entoderm
and mesoderm are produced by that gastrulation, that one of these
two germ layers has become rudimentary in Phylactolemata, that
it is highly probable that the entoderm has disappeared from loss of
function, and that the layer which persists gives rise to the muscula-
ture, sexual cells, and coelomic epithelium, — I conclude that the inner
layer of the Phylactolematous larva, and therefore the outer layer of the
bud, is mesoderm.

If we accept the point of view of Kleinenberg (86, pp. 1-19) and ad-
mit the existence in general of only two layers, ectoderm and entoderm,
a clearer conception of the modification undergone by the Phylactoleema-
tous larva may be gained. We may divide the entoderm arising in
Bryozoa into two parts; viz. (1) that which gives rise to the lining
of the midgut, as in Cyphonautes, and (2) all the rest of the inner
layer. Now, since no midgut is formed in the Phylactolematous larva,
part (1) of the entoderm has ceased to be differentiated ; all which
remains, then, is part (2); but this is equivalent to ‘‘ mesoderm” in
the sense in which I have employed it, and therefore I am justified
in saying that “mesoderm” only is produced.

The question has now to be answered, What is the significance of the
inner layer of the bud? Two different answers have been given to this ques-
tion. It has been maintained, on the one hand, that it is to be regarded’
as ectoderm; on the other, as entoderm. There are serious difficulties
in the way of accepting the first view, — so serious, in fact, that few
authors have maintained it, although at first glance it seems to be re-
quired by the facts. Although we have not yet sufficient grounds for
declaring that organs formed by budding must be built up from the
same germ layers as corresponding larval ones, — although we may ad-
mit that gemmigenesis recapitulates phylogeny and coriesponds with
ontogeny only in an imperfect and confused way, — still, from the expe-
rience gained by tracing the development of hundreds of animals from

96 BULLETIN OF THE

the most widely separated groups of the animal kingdom, the idea that
a functional alimentary tract™is ever wholly derived from differentiated
ectoderm will not be accepted by most embryologists without conclusive
evidence.

The second view is that the formation of the inner layer of the bud
is a process of gastrulation, giving rise to entoderm, and that the so-
called ‘‘ gastrulation ” of the sexual ontogeny of Phylactolemata is to be
regarded as a precocious ingression of mesoderm only.

Two considerations are opposed to this view. In Membranipora there
is a gastrulation which gives rise to the entoderm and mesoderm of the
larva; and since the gastrulation of Phylactolemata is similar, these
elements must be potentially present here also. The “gastrulation”
in Bryozoa is a normal one; if there is any entoderm in the body wall
giving rise to the inner layer of the bud, it must have been ento-
derm which failed to become invaginated. But what, in the second
place, is to be gained by assuming that the inner layer of the bud is
formed from entoderm? Here is as great a difficulty as before, since the
nervous system origivates from this layer. It has been maintained in
many cases that the nervous system arises from mesoderm, and Seeliger
(89, p. 602) believes that it is formed from that layer in the non-sexual
reproduction of some Tunicates ; but I know of no good evidence of its
origin in any of the Triploblastica from entoderm.

Before going on to state my conception of the significance of the
inner polypide layer, I desire to call attention to the conditions in the
region at which it is first formed. I have shown above (page 69) that
the primary polypide or polypides arise from the pole of ingression in
Phylactolemata, and that therefore in this group the aboral pole (in the
sense of Barrois) corresponds to the pole of ingression. As I under-
stand Barrois, he means by oral pole merely the pole which in Cypho-
nautes, for instance, bears the mouth,—the pole also by which the
larva attaches itself. Braem (’90, p. 123, foot-note), however, interprets
“oral side” in Barrois’s sense to mean in the last instance the place at
which gastrulation takes place. Perhaps Barrois does somewhere state
such to be the significance of his term (I have not found the place),
but in that case I can only say that, to my mind, he has not produced
sufficient evidence to prove that the oral pole of the larva of Gymno-
leemata is the same as the pole of ingression in the gastrula ; nor, in my
opinion, has any other investigator done so. Nearly all species studied
have a stage early in their development when their poles are very sim-
ilar, and orientation certainly would be exceedingly difficult. One of the

* MUSEUM OF COMPARATIVE ZOOLOGY. 97

best figured series in which to trace the homology of poles is that shown
by Repiachoff (80, Taf III.) for Bowerbankia. So far as the figures
go, one would conclude that Figure 10 A and its predecessors were
oriented in the opposite direction to Figure 11 and its successors,
which would result in placing the pole of ingression (Fig. 9) at the.
aboral pole of the larva, — the pole which here, as in all other Gymno-
lemata, and, I believe, in Phylactoleemata also, gives rise to the primary
polypide. I have given above additional evidence for this conclusion,
in my argument to prove the homology of the larve and larval organs in
Phylactolemata and Gymnolemata.

The polypides arise in Phylactolemata at the pole of ingression, which
is probably homologous with the aboral pole of Gymnolemata. The pole
of ingression, or the region of the lips of the blastopore, must be regarded
as being a region of less pronounced differentiation than the rest of the
gastrula. Its cells cannot be said to be either ectodermal or ento-
dermal. It is an interesting fact, that it is just these indifferent cells
—not yet either ectoderm or entoderm—that give rise to the inner
layer of the polypide, from which organs usually considered ectodermal
as well as those considered entodermal arise.

My conclusion, then, the objections to which I fully realize, may be
stated in the following words: Zhe inner layer of the polypide bud is
composed of cells derived from the rim of the blastopore. Such cells are to be
regarded as still indifferent, and as first becoming differentiated into ecto-
derm and entoderm in the formation of the young polypide.

Just when and where, on this hypothesis, the differentiation into
ectoderm and entoderm occurs, is an important question; but unfor-
tunately I cannot answer it decisively. It may be pointed out, however,
that it has now been shown for most Ectoprocta that the lining of the
middle part of the alimentary tract is formed independently of the
cesophagus, and by an actual or potential outpocketing of the primitive
simple sac of the bud. In Endoprocta there is a similar outpocketing,
which, however, arises in connection with the cesophagus, and is formed
independently of the rectum.

This is perhaps the proper place to call attention to the fact that the
mesodermal outer layer of the bud has a very embryonic character at
the budding region. This is indicated by the fact, that in Phylactolemata
(in which group alone I have studied the subject) eggs always arise
from that part of the ccelomic epithelium which lies in the budding
region (cf. Plate XI. Fig. 93). In Pyrosoma, also, according to the
researches of Seeliger (’89, pp. 598-602) the mesoderm of the budding

. VOL, XXII. — No. 1. 7

98 BULLETIN OF THE :

region, the stolon, gives rise to eggs. The same condition seems to exist
in other Tunicates.

III. On some Characteristics of Gemmiparous Tissue.

In the preceding part of this paper the words “ embryonic tissue,”
“undifferentiated tissue,” have often recurred, and they are terms in
wide usage in modern zodlogy. I do not know of any attempt to define
further the real character of this tissue, nor to give its more detailed
characteristics, other than that usually employed in the term plasma-
reich, or ‘‘rich in plasma.” The persistence of yolk granules is, as
Nussbaum (’80, pp. 2-14) and Goette (’75, pp. 31, 32, 831) have shown
in the case of amphibian embryos, indicative of the embryonic condition
of cells, when these have been derived from an egg filled with yolk.

It is very far from my purpose to go into a detailed discussion of the
significance of embryonic tissue, for which I am not yet fitted ; neverthe-
less, I wish to call attention to the minuter characters of gemmiparous
tissue as I have found it in Phylactolemata and Paludicella. I have
described it in some detail in preceding pages.

First, then, gemmiparous tissue seems to stain more deeply than non-
gemmiparous tissue in the same section. This character has been re-
peatedly observed before by others, and Braem calls attention to it
several times. I have already described how I found, by the use of
high powers, that much of this depth of stain was due to the unusually
large number of deeply staining granules scattered through the cell, but
chiefly gathered about the nucleus (Figs. 6, 17, 18, etc.). So marked
is the greater depth of the stain around the nuclei, that, with a power so
low that the nuclei are hardly distinguishable, their position is indicated
by a deeply staining band.

Secondly, gemmiparous tissue, as I have found it in the cases referred
to, is distinguished by the possession of large cells, nuclei, and nucleoli.
I had already noticed this fact in my studies on budding in Cristatella,
and I find that Braem has figured the nuclei in the budding region as
larger than the average (cf. Braem, ’90, Taf. VII. Figs. 86, 88-90).
My own figures show this repeatedly (Plate I. Figs. 3, 4, 5, 6, Plate IL.
Figs. 15, 17, Plate XI. Fig. 99, etc.). I have also noticed this to a
certain extent in the marine Bryozoa, but, since the cells of the latter
are smaller, and as I did not succeed in obtaining from them sections so
satisfactorily stained, the results are not so reliable. In attempting to
obtain an explanation of this phenomenon one involuntarily recalls to

MUSEUM OF COMPARATIVE ZOOLOGY. 99

mind the condition in young egg cells, where the nucleus attains a rel-
atively enormous size. This great size of the nucleus in young egg cells
is explained by Korschelt (’89, p. 92) as due to its participation in the
trophic activity of the cell: “Sein grésster Umfang fallt in die Zeit des
energischen Wachsthums der Eizelle.”’ So in the gemmiparous regions
the large size of the nuclei must be considered as connected with the
growth of the cells.

But if the growth of the cells is accompanied by a rapid ingestion of
food material (which the larger nucleus implies), some evidence of that
fact should be observed in the cells themselves in the presence of food
granules. Such food material in rapidly growing ovarian egg cells lies
near the nucleus. Stuhlmann (’87, pp. 13, 14) describes such a condi-
tion in the ovary of Zoarces. ‘‘Neben dem Keimblaschen, jedoch ein
klein wenig von seiner Membran entfernt, bilden sich an verschiedenen
Stellen jetzt eigentiimliche Verdichtungen des Protoplasmas, die sich
ein wenig starker mit Saffranin firben als das Zellplasma.” Such a
thickening of the protoplasma is represented in the figures as minute
granules. Korschelt (’89, pp. 123-125) mentions several other such
instances.

It has seemed to me possible to interpret the stainable granules lying
near to the nucleus in gemmiparous tissue as such food material,’ par-
ticularly since we know that food material does exist in the coelomic
epithelium lying next to the cells which are about to divide rapidly and
to give rise to the inner layer of the polypide. That food is being taken
in by the inner layer cells from the cceelomic epithelium is indicated by
the fact that the nuclei of the former cells lie near the latter epithelium
(cf. Figs. 15, 17, 18, 28, 56, etc.) ; for, as Korschelt has shown, the nu-
cleus tends to move towards the centre of activity of the cell. That these

1 Granules similar to these appear to exist in the protoplasm of all cells. It
is their extraordinary abundance in the gemmiparous tissue upon which I lay
stress. They have been variously interpreted by different authors. Biitschli (’88,
pp. 1469-1472) describes various kinds of stainable granules in Ciliata which are
food products, and the general character of which accords with that of the gran-
ules referred to above. ‘Excretion granules” of Ciliata do not stain, according
to this author, which is an indication that the bodies in gemmiparous tissue are not
such. Iam particularly struck by the fact that the food products of Protozoa are
chiefly found in parasitic forms, — Gregarinide and parasitic Ciliata. These take
up food in solution from their hosts exactly as the cells of the body wall of Bryo-
zoa do from the body cavity. Altmann (’90) has recently interpreted similar
deeply staining granules in other cells, as “die Elementarorganismen.” I can
see no reason, on Altmann’s theory, for the peculiar distribution of the granules
that I have found.

100 BULLETIN OF THE

granules observed in the cells are food material is indicated by their
abundance in cells lying next to the reticulated cells of the ccelomic
epithelium (Figs. 6, 28, 56).

My conclusion, then, is this: Gemmparous tissue is a rapidly as-
similating tissue, possessing large nucler because actively assimilating, and
staining deeply because full of food material.

While for Nussbaum, as already quoted (page 71), “ indifferent cells”
are essential to the reproduction of individuals by non-sexual as well as
by sexual methods, Seeliger (’90, p. 596) has concluded that ‘die Vor-
ginge bei der Knospung der Bryozoen uns zeigen, wie histologisch sehr
bestimmt differenzirte Gewebe einen ganz embryonalen Charakter wie-
dergewinnen kénnen. Mehr noch als bei der normalen Knospung am
freien Stockende ist dieses Vermégen bei der Regeneration der Polypide
der Ektoprokten oder der Képfchen der Pedicellinen ausgebildet. ‘In
diesen Fallen sehen wir ein plasmaarmes, dusserest feines Plattenepithel,
das iiber sich eine machtige Cuticula ausgeschieden hat, sich in kubische
und cylindrische plasmareiche Zellen zuriickverwandeln und durch eine
Einstiilpung ein neues Polypid bilden, in welchem schliesslich die man-
nigfachsten Gewebsformen vertreten sind.”

It seems to me that many facts in the budding of Bryozoa are strongly
in favor of Nussbaum’s hypothesis. On this assumption, we can best
understand why in Cristatella there is not an invagination of the ecto-
derm, and why instead a stolon is formed in the embryo, which passes
along at the base of the ectoderm and at intervals gives rise to the
inner layer of the body wall. I believe it is because the outer layer
of the body becomes so rapidly differentiated by the secretion of the

1 Other observers describe gemmiparous tissue as being either rich in food or
deeply staining. Seeliger (’85, p. 588) speaks thus of the mesodermal gemmiparous
tissue in Salpa: “ Die einzelnen Zellen sind grossblasig, enthalten einen runden
Kern und fiihren Oel- und Fettsubstanzen die als Reservematerial beim Aufbau
des embryonalen Leibes weiterhin in Verwendung gelangen.” Von Wagner (’90,
p. 877) says of the indifferent cells which are being transformed into the new
pharynx of dividing Microstoma: ‘‘ Dieselben nehmen an Grosse zu, . . . indem
gleichzeitig ihre Protoplasmaleiber feinkornig granulirt und fiir Farbstoffe imbibi-
tionsfahiger werden.”

In some sections of gemmules of Esperella fibrexilis, H. V. Wilson, of which
Dr. Wilson has very kindly sent me several slides, I find the outer layer of young
gemmules, in which the inner layer has been newly formed, stained very deeply.
Observed with a Zeiss Apochr. 4.0 mm., Ocs. 8 and 12, the cell contents are seen to
be evidently of two kinds, —light and deeply stained. The latter appearance is
due, in part at least, to small dark granules, which can be discerned without much
difficulty.

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MUSEUM OF COMPARATIVE ZOOLOGY. 101

gelatinous balls in its cells as to be incapacitated for the work of build-
ing organs. In Plumatella the outer layer of the body wall, which is
derived, as Braem has shown, from the neck of the older polypide, re-
tains for a long time its embryonic condition, so that its deeper cells can
and do go to form the inner layer of the polypide bud.

On Nussbaum’s hypothesis we can best understand why in Paludicella
the Andagen of the lateral branches exist from the beginning as cuboidal
cells, quite different from those of the rest of the body wall; we can
understand why the cell layers of the margins of the stock, the tips of
branches, and the ends of stolons from which buds arise, are thicker
and more rapidly dividing than the rest of the body wall (cf Figs. 14,
71, 73, 75); and we can also understand why the regenerating buds
always arise from the region of the neck of the degenerated polypide,
—the same region from which that degenerate polypide had arisen by
budding.

There is no doubt, however, that at times buds do arise from tissue
which, as Seeliger says, has lost its cuboidal nature only to regain it.
From such tissue apparently the polypide of Figure 79 has arisen ;
from such tissue certainly, as Seeliger says, do regenerating polypides
arise. But is the process by which cuboidal cells become a pavement
epithelium one of so fundamental differentiation that, in accordance
with Nussbaum’s doctrine, we should not expect, under favorable condi-
tions, to see these cells regain their cuboidal form? No doubt we have
many other cases in the animal kingdom in which flat epithelial cells
reeain their cuboidal form. Thus, for instance, among the Bryozoa,
Oka (90, p. 132) has shown how the flat cells of the outer layer of the
statoblast begin to thicken again at the return of warmth, and at the
beginning of the active assimilative processes, not only at the pole from
which the primary polypide is to arise, but also opposite to this.

Many facts indicate that cells may become flattened epithelia, and yet
not lose their embryonic character. Maas (’90, pp. 541-544) has re-
cently shown step by step how the columnar ectoderm of the fresh water
sponge is forced, on account of the great increase in surface which it is
called upon quickly to cover, to become broad and flat. It finally gives
rise to an epithelium so flat that its existence was long overlooked, and
has been denied by so competent an observer as Goette ; and yet in its
flattened condition it possesses to a remarkable degree the capacity of
sending out pseudopodia-like processes, a condition indicative much less
of a high degree of differentiation or specialization, than of an unspecial-
ized, primitive or embryonic condition.

102 BULLETIN OF THE

I have already stated (page 65) that the region from which the re-
generating buds of Cheilostomes arise, although one of flattened epithe-
lium, is one in which many more nuclei persist than elsewhere in the
adult (cf. again Fig. 71). This fact, coupled with the constancy of —
position of regenerating buds with.reference to the degenerated polypide,
is to my mind evidence against the assertion that buds arise here from
“ histologically very definitely differentiated tissue.”

As for regeneration in Endoprocta, no one is more competent to speak
than Seeliger himself. I am the more surprised, therefore, to find that
in Ascopodaria macropus, which is quite closely allied to the species
studied by Seeliger (’89), the cells at the part of the stalk immediately
below the ‘‘ head,” from which regenerated buds arise, are, as Ehlers’s
magnificent Pedicellina work shows, very large and cuboidal (Ehlers,
790, Taf. I. Figs. 26-33). I think one may conclude that a similar
condition obtains in some cases in Pedicellina, even judging from Seeli-
ger’s own drawings, although they are drawn to a scale that is not quite
large enough to allow of settling this point (Seeliger, 89, Taf. X. Pig.
35, a, Fig. 41, etc.).

If the increase in size of the flattened cells, and their subsequent rapid —
division and invagination to form a bud, are due to their more active nour-
ishment, it would be difficult to see why certain cells of any region should
quickly undergo this modification, while the adjacent cells apparently
as favorably situated with reference to the acquirement of food retain
their flattened, quiescent condition, if we assumed such favorable situation
to be the only requisite. Still less satisfactorily would such an assump-
tion explain the regular position of regenerating buds. It is taking only
one step farther back, but, to my mind, a helpful step, to assert that cell
proliferation in any region which produces invagination depends upon
the capacity of the cells*of that region to become better nourished than
their fellows. This may evidently be effected by a diminution in the
feeding capacity of the surrounding cells, or by an increase in this respect

‘in the growing cells.

IV. Relationships of Endoprocta and Ectoprocta.

I discussed this topic in my earlier paper (Davenport, ’90, pp. 132,
133). I have only to add, that later studies have confirmed my
opinion of Nitsche’s correctness in placing these two groups close to-
gether, and in regarding the Endoprocta as nearer the ancestral types.
The stages of Figures 25 (Plate III.) and 77 (Plate IX.) probably rep-

MUSEUM OF COMPARATIVE ZOOLOGY. 103

resent roughly a phylogenetic stage ancestral to both groups of Bryozoa,
but most clearly allied to adult Endoprocta. The formation of new ten-
tacles anteriorly and posteriorly in Figure 77, would reproduce the adult
Endoproct condition. Two changes lead to the Ectoproct stage: first,
the closure of the tentacular corona posteriorly zz front of the anus (Plate
V. Fig. 43), and, secondly, the formation of the pharynx or anterior
part of the cesophagus by the growth of the oral tentacles over the floor
of the atrium towards the atrial opening. Thus the brain, which lies at
the floor of the atrium in Ectoprocta, comes to lie on the pharynx. The
pharynx would, upon this assumption, be a new structure, not found in
Endoprocta. Such appearances as are exhibited by Figure 77 lead me
to retract my former expressed opinion, in which I agreed with Nitsche in
saying that the earliest condition of the tentacular corona is a U-shaped
one. Rather, the tentacles are formed first on each side of the atrium,
and only secondarily grow around the mouth in front, as later they grow
in between mouth and anus. The U-shaped stage is therefore not the
primary one, but secondary.

The close relationship of Endoprocta and Ectoprocta has recently been
doubted by Cori (’90, p. 16), but his chief argument depends upon the
dissimilarity of the Endoproct and Ectoproct kidney. Unfortunately,
our knowledge of the latter is still very imperfect, and we may well hope
for renewed researches in the subject by this skilful investigator.

Ehlers (790, pp. 149-154) has recently re-expressed his former (’76, p.
132) utterances concerning the lack of homology between the tentacles
of Ectoprocta and the “cirri” of Endoprocta. He finds the homologue
of the latter in the “ Diaphragma” or “ Kragen ” of Ectoprocta. This is
the organ which I have believed to be homologous with Kraepelin’s
“ Randwulst” (which may be Anglicized as marginal thickening), —an
organ occurring in all Ectoprocta. It is nothing but the “neck of the
polypide,” which has sunk below the general level of the body wall. It
is always provided with sphincter muscles, and in Ctenostomes forms the
base of insertion of the cylindrical or comb-like “ collare setosum.” It
can hardly be that Ehlers refers to this latter structure by the term
‘“Kragen,” since this is merely cuticular. In my opinion the “ Dia-
phragma” of Nitsche cannot be homologized with the cirri of Endo-
procta, because it is merely a part of the body wall comparable to that
part from which the “ polypide” of Endoproctous Bryozoa arises, and
beneath which the tentacles or “cirri” arise. This part of the body wall
is provided with a sphincter in Endoprocta as well as Ectoprocta, and by
it the atrial cavity may in both cases be closed.

104 BULLETIN OF THE

To my mind, the most significant difference between the two groups
exists in the fact that the outpocketing to form the stomach arises from
the oral end of the future alimentary tract in Endoprocta, and from the
anal end in Ectoprocta. One is led to believe that in the ancestral form
either two nearly equally important outpocketings from both the oral
and anal sides existed, or that the two existing methods are remnants
of a method different from either (such as the formation of the whole
alimentary tract at once), or, finally, that the Endoproct condition repre-
sents the ancestral one, and that the rectal evagination has secondarily
become of greater importance in Ectoprocta, and that the oral evagina-
tion has become less significant. Oka (90, pp. 134, 141) has recently
asserted that in the polypide buds of the statoblast and adult colony of
a Pectinatella of Japan (P. gelatinosa) the cesophagus and stomach are
formed by one evagination, which acquires secondary connection with
the rectum. This condition reminds one, then, of Endoprocta. I must,
however, doubt the accuracy of Oka’s conclusions until more satisfactory
evidence is forthcoming; the more so, since Pectinatella magnifica,

Leidy, presents a method of budding exactly comparable to that in —

Cristatella and Plumatella, as my own sections show with sufficient
clearness.

The homology of the Ectoprocta and Endoprocta implies a homology
of their larvee, and demands that the life history of the two groups should
be directly comparable.

It is well known from the researches of Hatschek (’77) on Pedicellina,
and of Harmer (’85) on Loxosoma, that the surface of the larva which
bears the mouth and anus, i.e. its oral side, corresponds with that of the
blastopore. How, then, is the oral aspect of the Ectoproct larve, which
I have tried to show is opposite to the pole of the iio to be
homologized with this?

The month and anus of the Endoproct larva undergo a rotation after
the larva has settled, so that they come to occupy the pole opposite to
that at which the blastopore was. This stage of the Endoproct larva
is comparable to the whole larval stage of Ectoprocta. I believe the
two stages to be homologous, and that, just as polypides are pre-
cociously formed upon the Phylactolematous larva, its larval digestive
tract. having dropped out from the ontogeny, so the mouth and anus of
Gymnolemata are precociously formed on the pole opposite the blasto-
pore, the primitive stage during which they existed at the blastoporic
pole having dropped out of the ontogeny.

It is well known from the works of Harmer (’86) and Seeliger (89),

pens, -

MUSEUM OF COMPARATIVE ZOOLOGY. 105

that in Pedicellina, in which the metamorphosis of the larva has been best
studied, the stolon arises from the base of the stalk —that is, at the pole
where mouth and anus were first formed — at the pole of invagination.
I have shown that this is true for Phylactolemata, and probably for
Gymuolzmata.

If the interpretation which I have put on Gymnoleematous ontogeny
becomes confirmed, the larvee and the budding areas will be homologous
throughout all Bryozoa. The following diagrams will explain my idea
of the relation of the different ontogenetic stages in the two groups.

ENDOPROCTA. EcToProcta.

The left hand vertical series represents stages in the development of
Endoprocta ; the right hand one, stages of Ectoprocta. The blastopore (*)
is throughout turned upwards in the figures. Stage I. is in both cases a
young gastrula. Stage IT. is that of the free-swimming larva of Endo-
procta. This stage is lost in the ontogeny of Ectoprocta, in which, by °
abbreviation of larval life, the free-swimming stage corresponds to the
condition of the fixed Endoproct after it has undergone its rotation.
This stage, or one slightly later, is shown in III. Both larve are fixed,
the Endoproct by the blastoporic, the Ectoproct by the opposite pole.
The position of the stolon, or of the first polypide of the colony produced
by non-sexual methods, is represented at gm., near the blastoporic pole.

106 BULLETIN OF THE

Summary.

The following general scheme of the budding process in Ectoprocta,
derived from my own and other recent studies, may be now drawn up.
The references are to pages of this paper.

All Ectoprocta build stocks or corms. The individuals in these are
arranged in rows radiating from a centre, —the larya or statoblast, —
and are placed one in front of another (Figs. 2, 64*, 65%, 67, 71%, etc.).

New rows or branches are constantly being produced peripherally.
There is no dichotomy in the branching (page 86), but the ancestral or
median branch gives rise to one or more lateral branches, which in turn
become median branches of their part of the stock.

The body wall and polypides of the median branch, as well as the
Anlagen of lateral branches, arise from a pre-existing mass of embry-
onic tissue, the gemmiparous mass (pages 72-82). This may exist cen-
trally of the forming region, as in Phylactolemata, or peripherally, as in
Gymnolemata.

The anal aspect of the polypide is turned towards the gemmiparous
mass (page 82).

The outer layer of the body wall in the budding region is one.

of rapidly assimilating and rapidly dividing tissue ; the inner layer of
the body wall becomes filled with food taken from the body cavity in
species in which the latter is early cut off by a partition (Paludicella,
Bowerbankia, Lepralia ?) ; it shows no tendency to do so in species with
a cenocel (Phylactolemata, Aleyonidium).

The first impulse to the formation of the polypide is found in the
outer layer of the body wall (excepting when this is highly modified, as
in Cristatella), and many cells seem to be involved in its formation from
the beginning (pages 8, 56).

This outer layer of the body wall is embryonic tissue, derived from the
tip of the stock (margin of the corm) as in Gymnolemata, or from the
neck of pre-existing polypides, as in Phylactolemata. It is the direct de-
scendant of the gemmiparous tissue of the larva, which in turn has been
derived from the region around the blastopore, — in Phylactoleemata cer-
tainly, in Gymnolemata probably (pages 8, 11, 12, 69).

The inner layer of the body wall is also embryonic in the budding
region, as indicated by the fact that ova arise near the neck of the
polypide, in Phylactolemata at least (page 68).

The outer mural layer becomes the inner bud layer by invagination,
with or without the formation of a cavity. In the former case (many

MUSEUM OF COMPARATIVE ZOOLOGY. 107

Gymnolemata) the mouth of the invagination pocket rapidly closes to
give rise to the neck of the polypide (page 56). In the latter case, the
cavity of the bud arises only secondarily by a separation of its walls
(page 18).

By a rapid growth of the walls of the bud, its distal part, in which the
alimentary tract is to arise, is formed. Since this rapid growth occurs
earlier at the anal side than at the oral, the rectum is formed first, the
stomach last (pages 19, 57).

By an approximation of the lateral walls, alimentary tract and atrio-
pharyngeal cavity become separated.

The cesophagus* arises as a pocket of the atrio-pharyngeal cavity, and
secondarily unites with the stomach (pages 19, 58).

The lophophore arises first as two lateral thickenings of the atrio-
pharyngeal wall, then as two lateral folds, whose cavity becomes the ring
canal (pages 20, 58),

Tentacles appear on the ridge of the lophophoric fold thus established,
and like it are formed first at the sides of the polypide, then anteriorly
and posteriorly (pages 22, 59).

The posterior end of the lophophoric ridge is the last to be formed,
and, in forming, it cuts off the anal part of the atrium from the inter-
tentacular cavity (pages 23, 62).

The compressed intertentacular cavity becomes circular by change in
position of the oral tentacles (pages 24, 62).

The ganglion arises as a depression in the floor of the intertentacular
room, and becomes included in the pharynx, which is differentiated by
the change in position of the oral tentacles (pages 26, 61).

Muscles and funiculi arise from the cclomic epithelium of both the
body wall and the bud (pages 27-31, 63).

The neck of the polypide may sink to a considerable distance below
the general level of the body forming the “ Randwulst” of Phylactole-
mata or “ Diaphragma ” of Gymnolzmata (pages 31, 63, 103).

The atrial opening first arises at a late period by separation of the
cells of the neck.

The communication plate arises in Paludicella as a circular fold
of the layers of the body wall, the mesodermal cells at the centre of
which become cuticularized. It is not so completely closed as to pre-
vent communication between the cclomata of the two individuals it
separates.

The mesodermal cells of Paludicella become stored with food mate-

108 BULLETIN OF THE

rial before the formation of the communication plate. and yield it up
the rapidly growing bad.

The regenerated polypides, like the marginal ones, arise in :
stomes in a definite position, — on the wall of the operculum from tissue

the “ brown body,” and cause its disintegration.
—

The more important theoretical conclusions to which I have arrived
are:—

a. There is im every stock or corm of Bryozoa a mass of indifferent
cell material, which is derived directly from the indifferent cells of the
larva or embryo, and whose function is to form the organs of the different
individuals, including the polypides. This mass by constant growth and
division affords the embryonic material for lateral branches.

5. The form of the stock and interrelation of individuals is in large
part controlled by food supply.

e. The immer layer of the Phylactolemstous larva represents meso-
derm only: the entoderm has become rudimentary through loss of the
alimentary fanction.

d. The polypides arise in Phylactolemata at the pole of ingression,
which is probably homologous with the aboral pole of Gymnolemata.

e. The imner layer of the polypide bud is composed of cells derived
Goon tha vim of the: bientopore, mul they amis ba
indifferent, and as first becoming differentiated into ectoderm and ento-
derm in the formation of the young polypide.

f. Gemmiparous tissue is a rapidly assimilating tissue possessing
large nuclei becamse actively assimilating, and staining deeply because
full of food material.

g. The Endoproct and Ectoproct larve are to be compared by assum-
ing that the act of rotation of the axes occurring in the former has been
leaped over in the ontogeny, the mouth and anus arising at once on the

pole opposite the blastopore-

Cawzerpce, Mass, June 1, 1591.

;

MUSEUM OF COMPARATIVE ZOOLOGY. 109

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der Molluskenschalen. Kongl. Svenska Vetenskaps-Akad. Handl., XIX. 3.
57 pp. 12 Taf.

“VOL. XXII.—NoO. 1. 8

114 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY.

Verrill, A. E.
73. Report upon the Invertebrate Animals of Vineyard Sound, ete. Rept.
U. S. Com. Fish and Fisheries, 1871-72, p. 295.
Vigelius, W. J.
°84. Die Bryozoen, gesammelt wahrend 3. u. 4. Polarfahrt des ‘‘ Willem
Barents.” Bijdragen tot de Dierkunde, XI. 104 pp., 8 Taf.
°86. Zur Ontogenie der marinen Bryozoen. Mitth. zool. Stat. zu Neapel,
VI. 4, p. 499.
°88. Zur Ontogenie der marinen Bryozoen. Mitth. zool. Stat. zu Neapel,
VIIL. 2, p. 374.
Wagner, F. v.
°90. Zur Kenntniss der ungeschilechtlichen Fortpflanzung von Microstoma
u.s. w. Zool. Jahrb. (Spengel), Abth. f. Anat. u. Ontog., IV., p. 329.
Zacharias, O.
°86. Ueber Fortpflanzung durch spontane Quertheilung bei Siisswasser-
planarien. Zeitschr. f. wiss. Zool., XLIII. 2, p. 271.
Zoja, R.
°90. Alcune ricerche morfologiche e fisiologiche sull’ Hydra. Bollettino
Scientifico, XII. 3, p. 65.
°91. Quelques recherches morphologiques et physiologiques sur l Hydre.
Arch. ital. de Biol., XV. 1, p. 125. [Résumé of Zoja, ’90.]

_—_

Davenport. — Budding in Bryozoa,

Fig.

Fig.

PLATE I.
ABBREVIATIONS.
cev. pyd. Neck of polypide. gn. Ganglion.
cta. Normal cuticula of adult i. Inner layer of bud.
body wall. kmp’drm. Kamptoderm.
cta. Cuticula secreted by tip. ms’drm. | Mesoderm.
ec’drm. Ectoderm. mu. pyr. Pyramidal muscles.
ex. Outer layer of bud. @. (Esophagus (pharynx).
ga. Stomach. rt. Rectum.
gm. Bud. ta. Tentacle.
All figures are of Paludicella Ehrenbergii.
1. Stock of Paludicella Ehrenbergii, viewed as an opaque object. X 4.5.
2. Diagram representing the interrelations of individuals in stock shown in
Figure 1. A-H are individuals of the ancestral (median) branch;
a, b,c, etc., lateral branches given off from the ancestral branch to the
right; a’, b’, branches given off to the left; a, 8, etc., lateral branches ~
of second order given off in the direction of the distal end of the
ancestral branch; a’, B’, etc., given off in the direction of proximal end; ~
a,’, lateral branches of third order — to left.
2*, Diagram of another (smaller) stock. Letters have same significance as
in foregoing.
3. Cross section of branch near tip, showing the first trace of the bud of the
polypide at er.,7. XX 685.
4. Cross section of branch near tip, showing bud of polypide slightly older
than in Figure 8. X 635.
5. Cross section of slightly collapsed branch near tip, showing ingression
of cells at ex. to form inner layer of bud. X 635.
6. Longitudinal section of tip of branch to show cell structure. Zeiss, 7;

oil immersion, Oc. 1. > 1000.

Figs. 7, 8,9. Optical sections (nearly in sagittal plane) of three tips of branches

in successive stages of development, showing relations of young bud,
gm., to next older polypide. In Figure 8 the branch is slightly
shrunken. X 87.

kmpdrm.
=} +
——

qa gn. rt TT

CRD. del. Y B Meisel lith.Boston.

.
DAVENPORT. — Budding in Bryozoa.

PLATE II.
ABBREVIATIONS.
cev. pyd. Neck of polypide. ec’drm. Ectoderm.
cta. Normal cuticula of body —= gm. l. Anlage of lateral bud.
wall. kmp’drm. Kamptoderm.
cta. Cuticula secreted by tip. ms’drm. |Mesoderm. -

All Figures from preparations of Paludicella Ehrenbergii.

Fig. 10. Surface view of cuticula near the end of a branch at intervals, a being

nearest the tip, and d farthest from it. The branch was stained in
Erlich’s hematoxylin, the color being taken up by superficial cuticula
only. X 3820.

Figs. 11, 12, 13. Cross sections of the cuticula taken at different distances from

Fig.

Fig.

Fig

5

Fig.

Fig.

Fig.

Fig.

14,

15.
16.

Wf

18.

19.

20.

the tip, to show the stainable and non-stainable cuticule. Figure 11
is from near the tip, Figure 13 farthest from it. > 1000.

Longitudinal median (sagittal) section through the tip of a branch show-
ing cells of tip and an early stage in the development of the polypide.
x 410.

Cross section of branch showing origin of lateral bud. 635.

Longitudinal section of body wall of branch through the point at which
a lateral bud is originating. Polypide of ancestral branch is nearly
adult. XX 63869.

Longitudinal section of body wall from near the tip through the Anlage
of alateral bud. X 410.

Cross section of branch showing histological conditions of Anlage of
lateral bud. The polypide has reached a stage of development cor-
responding to that of Figure 86, PlateIV. > 1000.

Longitudinal section through body wall from the same branch as Figure
17, but farther from the tip. Histological conditions are to be com-
pared with those of Figure 17, which represents a less differentiated
condition. X 410.

Cross section of branch in which the polypide has reached a stage slightly
younger than that of Figure 36. To show Anlage of two lateral buds
with their cuboidal undifferentiated cells. X 410.

Eyl.

ORT — BUDDING IN BRYOZOA.

B Meisel lth. Boston.

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DAvenport. — Budding in Bryozoa.

PLATE III.
ABBREVIATIONS.

An. Anal side of polypide. kmp’drm. Kamptoderm.
atr. Atrium. loph. Lophophore.
cev. pyd. Neck of polypide. ms’drm. | Mesoderm.
cl. mu. ret. Young cells of retractor mu. par. Parietal muscle.

muscle. @. (Esophagus.
eta. Cuticula. Or. Oral side of polypide.
ec’drm. Ectoderm. rt. Rectum.
ga. Stomach. vlv. cr. Cardiac valve.
gn. Ganglion.

All figures from preparations of Paludicella Ehrenbergii.

a.

re AULD epee Og

Tigs. 21-25. Longitudinal sections through buds of polypides at successively older —

Fig.
Fig.

Fig.

PA
22.

stages. The tip of the colony, and therefore the anal aspect of tle

polypide, is to the right in all cases. All figures X 410.
Stage of Figure 37 (Plate IV.). Few nuclei in central region.

a
«

Shows rapid growth of bud, chiefly at neck of polypide. The two inner —

cell layers are about to separate to form the common cavity of atrium
and esophagus.

Beginning of formation of alimentary tract at rectum, rt. The row of
nuclei separating the atrio-cesophageal cavity from the alimentary tract
is due to the fusion of the two inner layers of the bud along this line.

Rectum and stomach completed. Retractor muscles begin to form.

Lophophore and young tentacles have made their appearance, and
cesophagus and pharynx are separated from atrium. Beginning of
formation of brain at gn.

Part of cross section of a branch of stage of Figure 30. Parietal mus-
cles, mu. par., occupy a diameter of the section, and are attached to
the cuticula. XX 635.

Young parietal muscle at stage of Figure 28. This is one of the pair
which in a later stage are found lying together in Figure 26. XX 630.

Cross section of branch showing young polypide, and reticulated vacuo-
lated cells. X 410.

Bit of body wall, with cuticula separated from underlying ectoderm to
show ends of parietal muscles. X 690.

2

; OQ” :
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ee

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——.

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DavEnPoRT. — Budding in Bryozoa.

PLATE IV.

ABBREVIATIONS.
An. Anal side of polypide. ae Inner layer of bud.
an. Anus. loph. Lophophore.
atr. Atrium. ms’drm. | Mesoderm.
can.cre. Ring canal. mu. Muscle fibre in funiculus.
ec’drm. Ectoderm. n.’ Circumeesophageal nerve.
ex. Outer layer of bud. @. Chsophagus.
Jun. inf. Inferior funiculus. Or. Oral side of polypide.
Jun. sup. | Superior funiculus. ie Rectum.
ga. Stomach. vac. Vacuole.
gn. Ganglion. vlv, cr. Cardiac valve.

All figures from preparations of Paludicella Ehrenbergii.

Fig. 30. Cross section of polypide bud of stage of Figure 24, Plate III. The posi-
tion is indicated by the line 30, Figure 24. x 410.

Figs. 31-34. Four cross sections of a branch through a young polypide, some-
what younger than that of Figure 25. Figure 81 is nearer the anal,
Figure 34 nearer the oral surface. In Figure 34 that part only of the
section of the polypide which lies near the body wall is represented.
x 410.

Fig. 85. Cross section of branch through polypide of age of Figure 25. To show
origin of tentacles and ring canal. X 410.

Fig. 36. Sagittal section of young polypide at period of closure of ganglion, gn.
x 410.

Fig. 36%. Bit of same polypide a few sections to one side of plane of Figure 36,
showing origin of inferior funiculus. X 410.

Fig. 37. From cross section of branch showing early stage in development of the
bud. x 410.

Fig. 88. From a sagittal section of nearly adult polypide, showing the two funiculi
and their muscles. 410.

Figs. 39 and 40. Two neighboring sections parallel to the body wall through a bud
of the stage of Figure 23. Figure 40 lies three sections below Fig-
ure 39. Figure 89 shows the atrial cavity, formed as yet only on the
anal side. Figure 40 shows the beginning of formation of the alli-
mentary tract at the analend. Note the vacuolated condition of the
mesoderm. X 410.

Fig. 41. Polypide of about the stage of Figure 25 looked at en face. The anal
tentacles, being turned under, do not appear. To show compressed
condition of polypide, and alternating position of tentacles. Cf.
Figure 77, Plate IX. X 320.

ENPORT. — BUDDING IN BRYOZOA.

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DAVENPORT. — Budding in Bryozoa.

PLATE “Y;
ABBREVIATIONS.

an. Anus. kmp’drm. Kamptoderm.
cev. pyd. Neck of the polypide. loph. Lophophore.
clr. set. | Collare setosum. ms’drm. Mesoderm.
cta. Normal cuticula of adult mu. par. Parietal muscles.

body wall. mu. pyr. Pyramidal muscles.
cta.! Cuticula secreted by the tip of. atr. Atrial opening.

of branch. rt Rectum. i
ec’drm. Ectoderm. spht. Sphincter.

All figures from preparations of Paludicella Ehrenbergii.

Fig. 42. Cross section of branch of age of Figure 37, Plate IV., to show origin of
primary parietal muscles. X 410.

Figs. 43 and 44. Successive sections through a polypide slightly older than that
of Figure 25, cut perpendicularly to the long axis of the branch. Dur-
ing this period the lophophore becomes more nearly circular, and its
aboral ends meet oralwards of the rectum, rt. Figure 44 is nearer the
tip of the branch. x 410.

Fig. 45. Axial section of neck and atrial opening of polypide just sufficiently devel-
oped to be capable of extrusion. Shows the collare setosum in place.
x 410.

Fig. 46. Section of communication plate cut across the branch. Two sections
(10 «) above Figure 51. x 635.

Figs. 47-49. Three stages in the development of the communication plates. Lon-

* gitudinal sections of the branch. In Figure 47, the polypide has
reached the stage of Figure 22; in Figure 48, the stage of Figure 23 ;
and in Figure 49, the stage of Figure 24. X 635.

Fig. 50. Longitudinal section through neck of young polypide, showing the sink-
ing of the neck below the general surface of the body, and the method
of forming the inner cuticula of neck. > 890.

Fig. 51. Cross section of branch through communication plate. The left side
of the section includes the cuticula and the underlying flat ectodermal
layer. The right side cuts a little lower into the mesodermal cells.
x 635.

ecam .
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msdrm.

B Meisel, lith Boston.

DAVENPORT. — Budding in Bryozoa.

PLATE VI.
ABBREVIATIONS.

an. Anus. (he Inner layer of bud.
can. crc. Ring canal. kmp’drm. Kamptoderm.
cev. pyd. Neck of the polypide. la. comn. Communication plate.
el. rel. Reticulated cells. ms’drm. | Mesoderm.
cta. Normal cuticula of adult mu. par. Parietal muscles.

body wall. mu. pyr. Pyramidal muscles.
eta.’ Cuticula secreted by tip. n Circumeesophageal nerve.
ec’drm. Ectoderm. @. Csophagus.
ex. Outer layer of bud. rt. Rectum.
gm. Bud. vae. Vacuole.

gn. ganglion.

All figures from preparations of Paludicella Ehrenbergii.

Fig. 52. Cross section of a branch through a polypide slightly older than that
shown in Figure 56. The section passes through the brain and whole
extent of the ring canal, together with its opening into the celom.
x 635.

Fig. 58. Next section below Figure 52 of same series ; showing the beginning of the
circumeesophageal nerve ring. X 635.

Fig. 54. Shows connection of mesodermal cells of body wall, ms’drm, with those
of the outer layer of bud, ex. > 1030.

Fig. 55. Origin of the secondary parietal muscle cells from mesoderm of body
wall. XX 635.

Fig. 56. Histological conditions of the budding regions. The cells have large nu-
clei, the mesodermal cells are vacuolated and rapidly dividing; the
cells of the bud are densely granular. Zeiss, 7; oil immersion, Oc. 1.
x 1070.

Fig. 57. Normal vacuolated cell, full of food particles. > 10380.

Fig. 58. Longitudinal section of young lateral branch, showing highly reticulated
character of mesoderm, and nearly complete formation of communi-
cation plate. X 410.

Fig. 59. Reticulated cell, showing one of the pseudopodia-like processes which
frequently appear on them, projecting into the celom. X 1030.

Figs. 60-62. Three successive sections from a series across the tentacles of a pol-
ypide which has 15 tentacles, and is of about the stage of Figure 36.
The odd tentacle (*) is shorter than the others, and lies opposite the
rectum, rt. XX 295.

Fig. 63. Cross section of branch through neck of polypide of about the age of Fig-
ure 86. Shows also the young pyramidal muscles. X 410.

DING IN BRYOZOA.

DAVENPORT - BUD

ry

|. Amparm.

B Meisel Jith.Boston

Davenport. — Budding in Bryozoa.

PLATE Vil.

For explanation of notation employed on this plate, see page 41.

,

Outline drawing of one of the lateral “fans” of Bugula turrita, taken’
from the axis of the colony and spread out flat on the slide.
X ca. 12.

. Diagram showing arrangement of individuals in Figure 64.

Outline drawing of one of the lateral branches of a stock of Crista eburnea
spread out flat on the slide. X 16.

’

58, Diagram showing arrangement of individuals in Figure 65.

Part of stock of Bugula flabellata. X 10.

EN

PORT. — BUDDING INBRYozoA. PL.VII.

20

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Davenport, — Budding in Bryozoa,

PLATE VIII.

ABBREVIATIONS.

op. Operculum. pyd. rgn. Regenerated poly pide.
pyd. dgn. Degenerated polypide.

Fig. 67. Diagram to show interrelation of individuals in the corm, Figure 69.

Vig. 68. A part of a corm of Membranipora pilosa, to show regular arrangement,
with a single median branch, each of whose individuals gives rise to
two lateral branches. The * indicates margin of frond on which
stock was growing. X ca. 8.

Fig. 69. Young corm of Flustrella hispida, to show arrangement of individuals.
x 10.

Fig. 70. Young corm of Membranipora pilosa, with several median branches, show-

ing regular arrangement. The marginal ones alone give rise to lateral
branches. X 10.

Kig. 71. Young corm of Lepralia Pallasiana, showing arrangement of individuals.
On the left, the nuclei of the cells of the body wall are shown, to
indicate the inequality of their distribution. On the right, nuclei are

omitted. At pyd. rgn. a regenerating polypide is seen, on the opercu-
lum. xX 43.

Fig. 71%. Plan of Figure 71.

Pu. VIL.

pyd rn

D dan.

B Meisel, lith Boston

DAVENPORT. — Budding in Bryozoa.

Fig.

Fig.

ig. 79.

PLATE IX. ‘
ABBREVIATIONS. ,

An. Anal side of polypide. lu. gm. Lumen of bud. i

alr. Atrium. marg. Margin of corm.

can. cre. Ring canal. ms’drm. Mesoderm.

cev. pyd. Neck of the polypide. n’ Circumeesophageal nerve.

cta. Cuticula. @. C&sophagus.

ec’drm. Ectoderm. Or. Oral side of polypide.

ex. Outer layer of bud. rt. Rectum.

ga. Stomach. sep. Wall of zocecium in the corm.

gm. Bud. sol. Sole of the corm.

gn. Ganglion. tet. Roof of the corm.

a. Inner layer of bud.

72. Longitudinal vertical section through the peripheral part of the corm of ;
Lepralia Pallasiana, showing the margin of the corm and two zoecia, —
the older of which contains a polypide. x 160.

73. Longitudinal vertical section through the margin of a corm of Lepralia
Pallasiana, showing the two layers of this region and the origin of the
polypide. x 410.

. 74. Young regenerating polypide of Flustrella hispida. The section passes
through the sagittal plane. X 380.

75. Vertical section through margin of corm of Flustrella hispida, to show
origin of polypide. x 410.

76. Sagittal section through young polypide of Flustrella hispida, to show
early stage of development of alimentary tract. 410.

77. Superficial view of young polypide from upper surface of corm of Flus-
trella hispida, showing young tentacles and their relation to the anus
(at atr.). XX 3820.

78. Bud of polypide of Flustrella hispida at the time of closure of the pore of
invagination. X 3890.

Radial section through margin of corm of Flustrella hispida, showing bud
of polypide. x 410.

. 80. Young polypide of Flustrella hispida. X 380.

.81. Bud of Lepralia Pallasiana immediately before the formation of alimen-
tary tract, showing relation of the rectal pocket (rt.) to the atrio-
pharyngeal cavity above. X 410.

82. Section through polypide, through lately formed brain and circum-

cesophageal nerves (n.’) growing around cesophagus (@.). X 410.

NPORT. — BUDDING IN BRYOZOA.

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DAVENPORT. — Budding in Bryozoa.

PLATE X.
ABBREVIATIONS.

An. Anal side of polypide. kmp’drm. Kamptoderm.

an. Anus. lu. gn. Lumen of the ganglion.

atr. Atrium. ms’drm. Mesoderm.

can. erc. Ring canal. mu. Musculature of esophagus.

cev. pyd. Neck of polypide. mu.rel. Retractor muscle of polypide.

ce. Cecum. @. (Esophagus.

cta. Cuticula. op. Operculum.

di’sep. Wall of zoecium in the corm. Or. Oral side of polypide.

ec’drm. Ectoderm. or. Mouth.

ex. Outer layer of bud. pyd. dgn. Degenerated polypide, “brown

Sun. Funiculus. body.”

ga. Stomach. rt. Rectum.

gn. Ganglion. ta. Tentacle.

as Inner layer of bud.

Fig. 83. Sagittal section through young polypide of Escharella variabilis. < 320.

Fig. 84. Regenerated polypide of Lepralia Pallasiana on operculum (op.). X 880.

Fig. 85. Cross section of pharynx of adult polypide of Escharella variabilis, show-
ing perforated cell walls. X 635.

Fig. 86. Sagittal section of young polypide of Lepralia Pallasiana, showing forma-
tion of brain. X 320.

Fig. 87. Section parallel to sole of a corm of Escharella variabilis at about the stage
of Figure 86, showing atrium, ganglion, and rectum. 430.

Fig. 88. Vertical section through a bit of roof of corm of Escharella variabilis at
neck of polypide, showing also the region of future operculum and of
origin of future regenerated buds. Compare with Figure 90. Xx 410.

Fig. 89. Sagittal section of young regenerated polypide of Flustrella hispida inter-
mediate in age between Figures 86 and 83. Shows the origin of the
ganglion and rotation of the oral tentacles. X 320.

Fig. 90. Vertical section of a bit of body wall from same individual as Figure 88,
to show the comparatively less embryonic condition of cells here than
at neck of polypide. x 410.

Fig. 91. Operculum of Lepralia Pallasiana cut perpendicularly to surface, show-
ing origin of aregenerating polypide. Body wall somewhat shrunken
from cuticula. > 410. ‘

Fig. 92. Section through a regenerated polypide of Escharella variabilis, showing

relations of alimentary tract to “brown body” (pyd. dgn.). 410.

ee eee

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DAVENPORT. — Budding in Bryozoa.

PLATE XI.

ABBREVIATIONS.
cev. oe. Neck of oecium. ms’drm. Mesoderm.
cel. Celom. oe. Occium.
ec’drm. Ectoderm. ov.’ Ooblasts.
en’'drm. Entoderm. pyd. Polypide.
ex. Outer layer of bud. sto. Stolon.
z. Inner layer of bud. tet. Roof of stock.

lu.gm. Lumen of the bud.

Fig. 98.

Fig. 94.

Fig. 95.

Fig. 96.

Fig. 97.

A portion of a longitudinal section through a young stock of Plumatella
polymorpha, about two weeks after hatching from statoblast (killed
12th May, 1890), showing the body wall just analward of the neck of
a young polypide (pyd.), at the oral side of which a younger bud-has
already arisen. The inner (mesodermal) layer of the body wall
shows odblasts (ov.’) in various stages of development. X 600.

Longitudinal section of ocecium of Cristatella showing embryo which is
giving rise to the celomic epithelium by ingression of cells at its
proximal pole, —i. e. the pole nearest the neck of the owcium. There
are in the next section two other cells in the cavity of the blastula,
one of which appears degenerate in that it contains a huge vacuole,
and has no distinct nucleus, the chromatic substance lying scattered
loose near the cell wall. X 600.

Longitudinal section through ocecium of Cristatella and its contained em-
bryo. One polypide bud and the stolon (sto.) are shown here. There
are two other buds in the embryo further developed than this one,
lying to one side of it, and on the side of each of these buds is the
Anlage of another. The stolon is seen to be well developed, lying be-
tween the ectoderm and mesoderm throughout the region bounded
by the three older buds, and extending as a zone beyond them, and
even beyond the An/age of the youngest polypides. The embryonic
tissue thus forms a disk about 75 X 150 win extent. X 390.

Transverse section of oecium of Plumatella, showing origin of first pol-
ypide. Compare with Figure 99, which represents an earlier stage.
x 390.

Longitudinal section through oecium and contained embryo of Cristatella.
The stolon is already cut off from the ectoderm. This stage imme-
diately follows that of Figure 101, Plate XII. The forming bud is
that of the first polypide. X 390.

Oblique section through owecium of Plumatella, showing a later stage in
development of the inner layer of the larva (cf. Fig. 94). X 600.
Longitudinal section of occium and contained Jarva of Plumatella. The
bud shown at 7., ex. is the first in the colony. An incipient (second)
bud is shown five sections to one side in the region indicated by an

asterisk. XX 410.

ENPORT — BUDDING IN BRYOZOA.
95.
COs Ome
; ye @@) 2 a : . nee
iP o a8 Q4@ & ee, (as S

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—— BMeisel,lith. Boston.

DAVENPORT. — Budding in Bryozoa,

PLATE XII.
ABBREVIATIONS.
ec’drm. Ectoderm. ms’drm. Mesoderm.
ex. Outer layer of bud. ow. Ocecium.
2. Inner layer of bud. sto. Stolon.

lu. gm. Lumen of the bud.

Fig. 100. Longitudinal section of a larva of Plumatella polymorpha, in which the
two layers are established; the pole of ingression is directed upward,
on the plate. sand:

Fig.101. Section of upper part of zocecium of Cristatella mucedo, with its contained
larva. Showing the formation of the stolon at the pole of ingres-
sion and the attachment of this pole to the placenta-like neck of the
oecium (*). x 390.

Fig. 102. Section through an ocecium of Cristatella, with its contained larva. One
polypide is already established, and a second is arising. The two
are the only buds in the larva. On the left of the older bud the
stolon is seen to be intruding itself between the ectoderm and meso-
derm of the larva. X 390.

Fig. 108. Section through the two oldest polypides of the Cristatella larva, to-
gether with the stolon. This larva contains one other less developed
bud at one side of these two. X 390.

Fig. 104. Plumatella polymorpha. Stage of first bud later than that shown in
Figure 96, exhibiting pore of invagination closed by overgrowth of
ectoderm. X 390.

DAVENPORT. ~ BUDDING IN BRYOZOA.

SO
jecodsbe%

5 Sad SIS.
ecdrm. KPoe 2 Bl Sip Soe )

SO.

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B Meisel lith Boston.

Bulletin of the Museum of Comparative Zoology
AT HARVARD COLLEGE.
fy VOL DOE NOL eZ,

Soa By Frank Smita.

WitH Two PLATES.
a

CAMBRIDGE, U.S. A:
PRINTED FOR THE MUSEUM.

DECEMBER, 1891.

Bulletin of the Museum of Comparative Zoology
AT HARVARD COLLEGE.
Vou. XXII. No. 2.

THE GASTRULATION OF AURELIA FLAVIDULA, Pér. & Les.

Br Frank SMITH.

Wira Two PLAtes.

CAMBRIDGE, U.S.A:
PRINTED FOR THE MUSEUM.

DecemsBer, 1891.

No. 2.— The Gastrulation of Aurelia flavidula, Pér. & Les.
By Frank Smitu.!

PRECEDING the appearance of Goette’s (’87) publication in 1887 upon
the development of Aurelia aurita and Cotylorhiza tuberculata, the gas-
trulation of Aurelia had been regarded, in the light of the studies of
Kowalewsky, Haeckel, Claus, and others, as the result of invagination or
at least of a process nearer to invagination than to any other method of
gastrulation.

Gvette’s work seemed to show, however, that, instead of an invagina-
tion, there is an ingression of cells to form the entoderm, and that the
first result of this ingression is the production of a solid gastrula, or
sterrogastrula, which is only.subsequently hollowed out, and is put into
communication with the exterior through the formation of a prostoma
at a still later period. Recently, in a paper dealing especially with the
development of Cotylorhiza tuberculata, Claus (’90) reaffirms the posi-
tion taken in his previous paper (’83), in which the gastrulation in
Aurelia was represented as being simply a modification of invagination.
In recent papers by Hamann (’90) and McMurrich (’91), Goette’s views
are adopted, and form part of the basis for statements that, in the devel-
opment of the Scyphomeduse, invagination, instead of being the rule, is
the exception. |

This want of agreement among those who have given the subject
most attention makes the determination of the actual method of gastru-
lation in Aurelia a matter of considerable interest, and it may be
assumed that any contribution to the solution of the question will not
be unwelcome.

Early in the current year, at the suggestion of Dr. E. L. Mark, I
undertook to investigate the method of gastrulation in A. flavidula.

Through the kindness of Mr. B. H. Van Vleck of the Boston Society
of Natural History, I was enabled to spend two months of the summer
of 1887 at his seaside Laboratory at Annisquam, Mass., where I then
collected the material used in the present study. The embryos were
Killed with picro-nitric acid, and preserved in 90 per cent alcohol, in
which they have been kept during the three intervening years. Of the

1 Contributions from the Zodlogical Laboratory of the Museum of Comparative

Zodlogy, under the direction of E. L. Mark, No. XXIX.
VOL. XXII. — NO. 2.

116 BULLETIN OF THE

various staining fluids tried, Erlich’s acid hematoxylin gave decidedly
the best results for sections. For examination of the whole embryos,
Grenacher’s alcoholic borax-carmine and Czokor’s alum-cochineal each
gave good results. The latter stain possesses the peculiarity of stain-
ing embryos of different ages with corresponding degrees of intensity,
the youngest stages being stained the least, the degree of intensity in-
creasing with the age of the embryo up to the planula stage.

The result of segmentation is a one-layered blastosphere, as in
A. aurita. Although the diameter of the blastocel, or segmentation
cavity, presents some individual variations at a given stage of develop-
ment, it in general corresponds very nearly with that of A. aurita, as
described by Goette (’87, p. 3). It increases slightly as the process of
gastrulation advances. ‘he cells of the blastosphere are usually some-
what shorter at one pole than elsewhere, and it is from this region .that
the entoderm is formed. The nuclei of all the cells are situated very
near the outer surface of the blastosphere. Small spheroidal bodies con-
stitute the greater portion of each cell ; they are very evenly distributed
through its substance, except in the vicinity of the nucleus, where they
are somewhat less abundant. Vacuoles of variable sizes are usually
found in some of the cells. The nuclear region stains a little more
deeply than the remaining portion.

The method of gastrulation in A. flavidula is similar to that in A.
aurita as described by Claus (’83, pp. 2 and 3), although it resembles
even more closely a typical invagination. When the process of cleavage
has resulted in the formation of a blastosphere composed of somewhat
more than four hundred cells, a depression of limited extent appears in
the portion of the wall which is composed of the shorter cells. From this
depressed region is formed the entoderm, which develops as a single con-
tinuous layer of cells surrounding a small cavity, the coelenteron. At the
beginning of the process, and throughout its duration, the ccelenteron is
in communication with the exterior by means of a narrow passage, the
blastopore, or blastoporic canal. See also Explanation of Figures (Plate
I. Figs. 1-4). From these figures it is apparent that only a small por-
tion of the wall of the blastosphere is concerned in the invagination,
and to that extent it must be regarded as deviating from the typical
invagination, where one half of the wall of the blastosphere is infolded
to form the entoderm. The ccelenteron is, however, at all stages of gas-
trulation, an open sac-like cavity, and therefore noticeably different from
that of A. aurita, of which Claus (83, p. 3), says: “Mit dem weiteren
Nachriicken der die Mundspalte begrenzenden Zellen in das Innere des

+)

MUSEUM OF COMPARATIVE ZOOLOGY. ELT.

Larvenleibes indert sich jedoch allmiihlig das friihere Verhaltniss zu
Gunsten der Entodermfiillung, die noch immer keine wahre Hohle, sondern
eine schmale lineare, mit der Hauptachse des Leibes zusammenfallende Spalte
besitet.” 1 With the growth of the entodermal layer, the ccelenteron
enlarges, and the cleavage cavity is diminished, until finally it is
entirely obliterated and the entoderm everywhere comes into -contact
with the ectoderm (Plate I. Figs. 4-6, Plate II. Fig. 11).

During the process of gastrulation, and also for a short time after its
completion, the thickness of the entoderm, which is much less than that
of the ectoderm, does not increase. Figures 5 and 6 (Plate I.) are
from sections of two embryos at different stages of development.
Figure 5 is from an embryo soon after the completion of gastrulation ;
Figure 6 is from an older stage. Since in each case the section is from
the middle of its series, it follows that a decided thickening of the ento-
derm takes place between the stages represented by these Figures. This
thickening is apparently due to an increase in the number of the cells,
which are soon unable to find room for themselves except by elongation.
The entodermal cells are quite different in appearance from those of
the ectoderm; they are approximately spherical, and do not have as
numerous spheroidal yolk bodies as the latter. Their nuclei, however,
closely resemble those of the ectoderm, and usually lie in the portion of
the cell nearest the ccelenteron.

As is to be seen from Plate II. Fig. 7, — a section nearly perpendicular
to the blastoporic canal, — the blastopore in A. flavidula is very small.
A similar condition has been shown by Claus to exist in A. aurita, and
by Metschuikoff (’86, Taf. X. Fig. 14) in Nausithoé marginata.

The nuclei of the cells composing the wall of the blastosphere are sit-
uated, as has been stated, near the surface of the sphere. But at about
the time of the beginning of the invagination, sometimes a little earlier,
a few of the nuclei are found in the deeper portion of the wall. At first
there are only one or two such displaced nuclei to be observed in the
whole embryo, but as development progresses they increase in number.
A careful examination of sections shows that the cells to which they
belong do not extend, like the remaining cells of the wall, through its
whole thickness, but that they are wedged in as it were between the
bases of the ordinary cells. The latter are much elongated, and from
mutual pressure are prismatic, whereas the deep cells are spheroidal and
project in some cases into the segmentation cavity. Since these cells
are found at various intermediate positions between the outer and inner

1 The original is not Italicized.

118 BULLETIN OF THE

surfaces of the wall, I infer that they result from a process of migration
inward, either at the time of cell division or independently of that pro-
cess. Indeed, there is obviously no other possible source whence these
cells could come, but the exact process of transfer is not easily determined.
I believe that this increase in number is at first for a considerable time
due exclusively to the migration of cells which once shared in forming
the external boundary of the sphere, but later the division of cells which
have already migrated into the deeper portion of the ectoderm undoubt-
edly contributes to this increase.

We have now to turn our attention to a phenomenon of considerable
importance, the study of which from preserved material is, however, |
attended with difficulties. I refer to the ingression of cells from the
wall of the blastosphere into the cleavage cavity, which begins a con-—
siderable time before the invagination commences. The latter does: not
take place until the number of cells forming the wall of the blastosphere
has exceeded 400, whereas the ingression, as far as can be inferred from
the cases which I have studied, may occur at any time after the blasto-
sphere contains about 100 cells up to the period of invagination. The
phenomenon of ingression in A. flavidula is not of constant occurrence,
but when it does take place is similar to that represented by Goette
(87, Taf. I. Figs. 1-5) for the earlier stages of the blastula in A.
aurita. It consists of a migration into the cleavage cavity of one or two,
rarely more than three, of the cells of the blastospheric wall. With
the exception that they assume a spherical form, because relieved from
pressure, they are at first similar in size, as well as in nuclear and other
characters, to the cells remaining in the wall.

The study of ingression upon preserved material is attended with diffi-
culty, since in any one specimen we have the condition at only one stage
of development, and cannot say with certainty what its condition has
been in past stages, or what it might have been during some subsequent
period. This can be determined only by studying the conditions exist-
ing in other embryos killed at other stages, and arranging all in their
probable natural sequence. In view of this fact, I have sectioned and
examined several hundred embryos which were killed at different stages of
development. As faras possible the results obtained from these sections
have been verified by the study of embryos cleared and mounted whole.
Although this ingression occurs before invagination, I have deferred the
discussion of it until now, because invagination is constant in its occur-
rence, whereas the ingression does not appear to be so; indeed, the
majority of the specimens have shown no indications of it.

MUSEUM OF COMPARATIVE ZOOLOGY. 119

The subsequent history of these cells, as shown by the comparison of
specimens of succeeding stages of development is both interesting and
peculiar. I imagine that it is such cells as these to which Claus (90,
p- 3) refers when he says: “Ich habe den vereinzelt eingetretenen zwei
bis drei Zellen, weil sie nicht regelmassig in jeder Blastula sich ablésen,
der am vegetativen Pole einwuchernden Zellenmasse gegeniiber keine
weitere Bedeutung beigemessen, so dasse ich dieselben zwar auf einer
Abbildung darstellte, im Texte aber nicht besonders erwihnte, und bin
auch jetzt noch der Ansicht, dass diese auffallend kleinen Zellen wieder
riickgebildet werden und itiberhanpt nicht zur Bildung des Entoderms
beitragen.” In my judgment, a part of the difference of opinion be-
tween Goette and Claus is due to the fact that there are two kinds of
cells which find their way into the cleavage cavity. These are the large
cells described by Goette as beginning to be formed at an early stage of
the blastula, and much smaller cells, of which I shall have more to say
hereafter, that make their appearance only at later stages of develop-
ment. Claus seems to have seen “very small cells,” and to have
assumed that they were equivalent to the large cells figured by Goette.
I am unable to say with certainty that the cells seen by Claus are the
equivalents of those figured by Goette, but Claus assumes that they are,
and I have the more reason to believe it because the large cells are of
more frequent occurrence than the small ones. But if this be so, I do
not understand how Claus could speak of them as “diese auffallend
kleinen Zellen.” But however that may be, I have reason to believe
that the supposition of Claus, that they ultimately degenerate, is
correct.

Soon after the ingression of a cell its nucleus undergoes changes
which result in its disappearance as such, for instead of a nucleus there:
can be seen only one or more small, isolated, deeply stained particles,.
which I judge to be scattered portions of the nuclear chromatine-
(Plate II. Figs. 8 and 10). Even these are often wanting. I have:
said that this nuclear change follows soon after the ingression of the
cell, because out of the numerous instances in which these cells have:
been present there is not one in which the nucleus retains its original
condition after the cells in the wall of the blastula have given evidence,.
by their diminished size, that they have undergone division since the:
ingression took place. This conclusion is in part based on the assump-
tion that at the time of ingression the ingressing cells are cf about the
game size as those which remain in the wall of the blastula. The in-
gressing cells sometimes persist, without any further apparent changes

120 BULLETIN OF THE

than the disintegration of the nucleus, until the process of gastrulation
is completed. Such cases are not as common, however, as others, where
there is to be found in the cleavage cavity material which appears as
though it had resulted from the disintegration of similar cells. This
material has a spongy or vacuolated appearance, and contains faintly
staining bodies or granules similar to those found in the ectodermic
cells; it does not possess definitely circumscribed boundaries ; on the
contrary, it fills the cleavage cavity more or less completely, but is not
of uniform density throughout. The fact that this material is not homo-
geneous, and that it contains granules, etc., prevents the conclusion that
it has been produced as a simple secretion into the cleavage cavity,
although it may have been formed in part by such a process. The fre-
quent association of this material with ingression cells in the same spe-
cimen (Plate II. Fig. 8), and the lack of other ways of accounting: for
its presence, lead me to believe that it is produced by the disintegration
which I have suggested.

There is another peculiarity of the development which I believe to
be connected with this process of nuclear disintegration. It is this:
after having once entered the cleavage cavity the immigrating cells seem
to lose their power of division, and consequently do not become more
numerous, while the cells composing the blastospheric wall undergo
repeated divisions, as is shown by their increased number and dimin-
ished size.

The number of these immigrating cells is small, usually only one or
two, very rarely more than three, so that I have not been successful in
finding the ‘‘ Verbindungsglieder” connecting the conditions shown by
Goette (’87, Taf. I.) in his Fignres 5 and 6, which Claus (90, p. 4) re-
garded as essential to the substantiation of Goette’s view of the method
of gastrulation.

Reference has been made to the fact that in some cases the ingrowing
cells persist both during and after the process of invagination. In the
latter case, they are to be found in the ccelenteron rather than in the
cleavage cavity. Figure 11 (Plate II.) is drawn from such a specimen.
Figures 9 and 10 represent two sections of one individual in which the
invagination is not completed, and furnish a hint as to the process by
which the cells pass into the ccelenteron from the cleavage cavity. The
entoderm being composed of less closely fitting cells than the ectoderm,
doubtless admits the passage of the large immigrated cells through it
more readily than the latter would (Plate II. Fig. 9). The immigrated
cell is of course passive in this process. Since it is prevented by the

MUSEUM OF COMPARATIVE ZOOLOGY. il

firm wall of the ectoderm from escaping, the pressure exerted upon it by
the enlarging entoderm is probably sufficient to cause it to be forced
through the entodermic wall into the celenteric cavity. From Figure 10
it is to be seen that one cell has already reached the gastral cavity. In
speaking of these peculiarly situated cells I have thus far assumed that
they are such as originally reached the cleavage cavity by an early
ingression, where, with changed nuclear condition, but apparently with
no further alteration, they have remained until the time of gastrula-
tion. That this is their source is evident from the following consid-
erations. First, the small diameter of the blastoporic canal (Plate II.
Fig. 7), which is from the same series as Figures 9 and 10, precludes
the assumption that they might have entered the gastrula cavity from
without. Secondly, in their large size and general appearance they are
unlike the cells of either ectoderm or entoderm at any time during
gastrulation, and so could not have been derived from those sources
during that process. ‘Thirdly, they do correspond in size and general
characters, except in their nuclear conditions, with the cells of. the
blastospheric wall as the latter appear at the time when ingression
takes place.

It is difficult to state either the cause or the purpose of this immigra-
tion. That it is not essential to the welfare of the embryo, either by
affording nourishment to the developing cells of the entoderm, or in
any other way, is evident from the fact that in a large number of cases
it does not occur. That it is not an inherited tendency, derived from a
more primitive method of gastrulation by ingression, is probable from
the fact that the immigrating cells do not appear to have any share
whatever in the formation of the entoderm. On the other hand, its
occurrence seems to be much too frequent to be considered as acci-
dental.

I have stated previously (p. 119) that two very different kinds of cells
are to be found at times in the cleavage cavity. Besides the large immi-
grating cells already described at length, I have found in a much smaller
number of cases very small cells (Plate I. Fig. 2), one or two in num-
ber, that appear precisely like the deep-lying ectodermal cells already
described. Because of their strong resemblance to the latter, their
exceptional occurrence, and the fact that they do not appear until after
the beginning of the development of the deep-lying ectodermal layer,
I incline to the opinion that they are derived from that layer, and that
their occurrence is entirely accidental.

At first it appeared to me surprising that two investigators could

122 BULLETIN OF THE

reach such different conclusions as those published by Claus (’83 and
90) and Goette (’87), concerning the method of gastrulation in the
same animal, A. aurita. Since studying this process in A. flavidula, it
scems less strange. ‘The results obtained from my first sections led me
to think that the conclusions reached by Goette would be confirmed in
the case of A, flavidula, Better staining, thinner sections, and more
uccurate orientation have made it certain, however, that the method of
gastrulation in this species is much more in accord with the description
given by Claus, and that the process really is one of invagination.

Certain considerations weaken my confidence in the position defended
by Goette. A comparison of his Figures 6-9 (’87, Taf. I.) with some
of my thicker sections, or with those which were made when the gastrula
was so oriented as not to be cut parallel to the blastoporic canal, makes
it appear to me probable that his results are based upon similar inade-
quate sections. In Figure 8 (Plate IL) there are only about one half
as many nuclei visible as there are cells, the nuclei of a portion of the
cells being contained in adjacent sections. In figures of corresponding
stages of A, aurita as represented by Goette (’87, Taf. I.), nuclei are
figured in nearly all the cells. 1 believe this to be evidence that his
figures were drawn from thick, sections. The blastopore, because of its
very small diameter, is quite easily overlooked in thick sections, and
especially if the plane of sectioning is somewhat oblique to the longitu-
dinal axis of the blastopore. Since, as previously stated, the nuclei of
the entodermal cells are usually situated in the portion of the cell near-
est the coclenteron, it is easy to find in thick sections of an invaginating
embryo conditions like those represented by Goette in his Figures 6-8,
My Figure 12 (Plate II.) reproduces a section of the same series as
that represented in Figure 3 (Plate I.). The intervening section (not
figured) is quite similar to Goette’s Figure 8. An examination of the
cells bordering the blastoporic canal in Figure 3 will show how sections
like Figure 12, or such as are a little oblique to the chief axis of the
embryo have the appearance of containing immigrating cells. Such
sections also exhibit the flattening in the region of the shorter cells to
which Goette (’87, p. 4) has called attention in the following words :
“Schon wiihrend der Gastrulation zeigt sich eine Stelle des Keims im
Bereich seiner kiirzeren Zellen etwas abgeplattet.”

Additional considerations increase the probability of the correctness
of the view which I have advanced to explain Goette’s error. With
advancing stages of development, I have found an increase in the num-
ber of the cells composing the ectodermic wall. This is undoubtedly

|

,

MUSEUM OF COMPARATIVE ZOOLOGY. Bde

subject to slight individual variations, but the number of such cells is

nevertheless in quite close correlation with the stage of development. An
examination of Goette’s Figures 6-9 (’87, Taf. I.) reveals such a simi-
larity in the number and size of the cells composing the ectoderm in each
of the four supposed stages, that I am driven to the conclusion that

they represent sections from specimens of a single stage of development,
which may have been produced by cutting in planes having different

relations to the chief axis of the embryo.

When we consider that in the majority of embryos there are no signs
of ingression, and that in the cases where it does occur the immigrating
cells in some instances degenerate early, and in others persist undivided
throughout the process of gastrulation, and that they at no time show evi-
dences of even sharing in the formation of an entoderm, — and when we
further reflect that all the conditions shown in Goette’s Figures 6-9 can
easily be reproduced from sections of invaginating gastrule of a single
stage of development, —it seems improbable that the entoderm of Au-
relia develops even occasionally by ingression. At present, therefore,
there seems to me to be no evidence that in this genus gastrulation
occurs by both methods, invagination and ingression.

The Scyphomedusz present several interesting variations in gastru-
lation. The anomalous development occurring in Lucernaria is as far
removed from the usual process as that group itself is from the other
Scyphomedusz. According to McMurrich (91, p. 314), the solid plan-
ula in Cyanea arctica is formed by the immigration of certain of the
blastula cells. This planula is subsequently hollowed out, and gives
rise to a structure like an invaginate gastrula, but it is formed without
any invagination. In Cyanea capillata (Hamann, 790, pp. 16, 17) there
seems to be a solid ingrowth of cells from one pole of the embryo, and a
simultaneous development of the coelenteron. The entoderm of Chry-
saora (Claus, ’83, p. 5, Taf. I. Fig. 21 2) is developed in a way which is
somewhat similar to that described by Hamann for Cyanea capillata,
According to Claus (783, p. 2, and 790, p. 4), the gastrulation of Aurelia
aurita approximates the method by invagination a little more closely
than that of Chrysaora, since its cells are arranged in a single layer
about the fissure-like coslenteron. Aurelia flavidula exhibits a still more
nearly typical invagination, since the ccelenteron is from the beginning
an open sac-like cavity. Cotylorhiza tuberculata (Cassiopea Borbonica)
has an invaginate gastrula which closely resembles that of Aurelia
flavidula (Claus, '90, Taf. I. Figs. 2 and 3; Kowalevsky, ’73, Taf. II.
Fig. 1). Finally, in Pelagia noctilnca and Nausithoé marginata, as

124 BULLETIN OF THE

shown by Metschnikoff (’86, pp. 66-68, Taf. X.), there is a typical in-
vagination.

If the observations of McMurrich (791, p. 314) on Cyanea arctica are
substantiated, we have among the Scyphomedusz one example of the
formation of a sterrula by ingression, with the subsequent formation of a
gastrula-like structure, without an invagination. From the preceding
summary it is to be seen that there are in Scyphomeduse two cases in
which the mode of gastrulation appears to be intermediate between
ingression and invagination, and at least four cases of unquestionable
invagination. If, in the light of so much variation in the mode of
gastrulation in this group as is shown by the few forms studied, it is
safe to conclude that any one mode is typical, that mode would cer-
tainly appear to be invagination, and not, as Hamann and MeMurrich
have recently maintained, ingression.

CAMBRIDGE, June 20, 1891.

MUSEUM OF COMPARATIVE ZOOLOGY. 125

BIBLIOGRAPHY.

Claus, C.

83. Untersuchungen tiber die Organization und Entwicklung der Medusen.
Prag u. Leipzig, 96 pp.

°90. Ueber die Entwicklung des Scyphostoma von Cotylorhiza, Aurelia und
Chrysaora, sowie tiber die systematische Stellung der Scyphomedusen, I.
Arbeiten a. d. zool. Inst. Wien, Tom. IX. p. 85.

Goette, A.

°87. Abhandlungen zur Entwicklungsgeschichte der Tiere. Viertes Heft.
Entwicklungsgeschichte der Aurelia aurita und Cotylorhiza tuberculata.
Hamburg u. Leipzig, 79 pp.

Hamann, O.

790. Ueber die Entstehung der Keimblatter. Ein Erklarungsversuch. In-

ternat. Monatsschr. f. Anat. u. Physiol., Bd. VII. pp. 1-28.
Kowalevsky, A.

73. Untersuchungen iiber die Entwicklung der Coelenteraten. Nachrichten
Gesellsch. Freunde Naturerkennt., Anthropol. u. Ethnog. Moskau, 1873.
(Russian.)

See also Hoffmann u. Schwalbe, Jahresbericht, Bd. II. p. 279.
McMurrich, J. P.

91. Contributions on the Morphology of the Actinozoa. II. On the Devel-
opment of the Hexactinie. Jour. Morphol., Vol. IV. p. 303.

*91*. The Gastrea Theory and its Successors. Biological Lectures delivered
at the Marine Biol. Laboratory, Wood’s Holl. Boston, p. 79.

Metschnikoff, E.
°86. Hmbryologischestudien an Medusen. Wien, 159 pp.

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EXPLANATION OF FIGURES.

All the figures were drawn from sections with the aid of an Abbé camera. The
sections from which the figures were made were 5 yu in thickness.

Sairu. — Gastrulation in Aurelia.

PLATE. 1.

ABBREVIATIONS.
bl’ po. Blastopore.
cav. sg. Segmentation cavity.
el. Immigrated cell.
celent. Celenteron.
cog. Coagulum.
ec’drm. Ectoderm.
en’drm. Entoderm.
nl. Chromatic portion of degenerated nucleus.

nl. ec’drm. Nuclei of deeper portion of ectoderm.

Figures 1-4. Sections to illustrate the nature of the invagination.

An early stage of invagination. 460.

A slightly later stage than that of Figure 1. x 540.

A stage in which the invagination is well advanced. X 385.

A gastrula with invagination completed. x 410.

Section of a gastrula cut in a plane (equator) perpendicular to the axis of
the blastoporic canal. X 385.

Section of an older individual through the equator, showing increase in
thickness of the entoderm. X 385.

. ——

“nlecdrm.

A /
endrm.__{f

B Meisel, lith.Bastan.

= Ae is , ‘ "

cabs vf é -
: 1 J 7 . a ar)

st * ; n
OT : “une
NPs &
«

=

mf

7

: i}

>

Pe :

Smita. — Gastrulation in Aurelia.

PLATE II.

ABBREVIATIONS.
bI’po. Blastopore.
cav. sg. Segmentation cavity.
cl. Immigrated cell.
ceclent. Ceelenteron.
cog. Coagulum.
ec’drm. Ectoderm.
en’drm. Entoderm.
nl. Chromatic portion of degenerated nucleus.

nl. ec’drm. Nuclei of deeper portion of ectoderm.

Figures 7, 9, and 10 are from different sections of the same individual.

Fig. 7.

8.

9.

10.

Wile

12.

Section through the blastoporic canal and nearly perpendicular to it.
x 410.

Section at a stage preceding invagination. It shows an immigrated cell
in which the’ nucleus has degenerated. X 385.

Section before the close of gastrulation, showing an immigrated cell in
the segmentation cavity. X 410.

Section from the same individual as Figure9. It contains an immigrated
cell in the ceelenteric cavity. 410.

Section of a gastrula with two immigrated cells contained in the ccelen-
teric cavity. xX 385.

Section from the same individual as Figure 3, to show the appearance
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Bulletin of the Museum of Comparative Zodlogy
eee AT HARVARD. COLLEGE, _
VOL. x LE .NOs23:

IN THE EMBRYONAL ENVELOPES OF
THE SCORPION. _

By H. P. Jounson.

Wirh THREE PLATES.

; CAMBRIDGE, U.S. A.:
PRINTED FOR THE MUSEUM.

JANUARY, 1892.

Bulletin of the Museum of Comparative Zoology
AT HARVARD COLLEGE.
Vou. XXII. No. 3.

AMITOSIS IN THE EMBRYONAL ENVELOPES OF
THE SCORPION.

By H. P. Jounson.

WitH THREE PLATES.

CAMBRIDGE, U.S.A:
PRINTED FOR THE MUSEUM.

JANUARY, 1892.

No. 3.—Amitosis in the Embryonal Envelopes of the Scorpion.
By H. P. Jounson.}

Ty the fall of 1889, at the suggestion of my instructor, Prof. E. L.
Mark, I decided to work upon the problem of the so-called “ direct ” or
amitotic division of nuclei. While in search of suitable material, my
-attention was called to a brief article by Blochmann (’85), describing a
very well marked amitotic division for the large nuclei of the embry-
onal membrane of the scorpion. A number of Centrurus embryos
were kindly given to me by my friend, Dr. G. H. Parker. These em-
bryos had lain in 90% alcohol since the summer of 1886. The mode
of fixation (for the purpose of studying the development of the eyes)
was somewhat unusual; for, immediately after their removal from the
mother, they were immersed in 35% alcohol, and thence carried up
quite rapidly, through 50 and 70%, to 90%. Notwithstanding this
rather crude method, the membranes were in excellent histological
condition, in no way inferior to material afterwards prepared by the
most approved methods of fixation. —

In addition to the material above mentioned, I received from Mr.
Richard Goeth, of Burnet County, Texas, during the following winter
and spring, about three dozen live specimens of Centrurus (sp. incog.).?
A lot that arrived in the latter part of May contained several pregnant
females, with embryos.in different stages. The scorpions were chloro-
formed, and the ovarian tubes with the embryos enclosed were dissected
out as quickly as possible. A number of killing agents were used,
including Flemming’s weaker chrom-aceto-osmic, Rabl’s. chrom-formic,
Perenyi’s fluid, Kleinenberg’s picro-sulphuric, and Merkel’s fluid.

For staining, I have used chiefly Ehrlich’s hematoxylin. Grena-
cher’s alcoholic borax-carmine and Czokor’s alum-cochineal have given
fair results. Safranin, employed according to Flemming’s method, I

1 Contributions from the Zodlogical Laboratory of the Museum of Comparative
Zoology, under the direction of E. L. Mark, No. XXX.

2 This is the species used by G. H. Parker in his study on the development of
the eyes (see Bull. Mus. Comp. Zool., Vol. XIII. No. 6, p. 173, 1887), and was then
undescribed. Iam not aware that it has since received a name.

VOL. XXII. — NO. 3.

128 BULLETIN OF THE

have found less serviceable than the stains above mentioned. After
staining, the preparations were dehydrated, cleared with oil of cloves,
and mounted in benzole-balsam.

The embryo is enveloped by three epithelial membranes, the ovarian
capsule, the membrana serosa, and the amnion, —named in order from
without inward.

The serosa and amnion are strictly embryonic structures, analogous
to the foetal membranes of the higher Vertebrates. There are two
contradictory accounts as to the manner of their formation. Possibly
they do not arise in the same way in all genera of scorpions. In a
brief communication by Kowalevsky und Schulgin (’86, p. 526) upon
the development of Androctonus ornatus, it is stated that they originate
as a fold from the edge of the blastoderm, the outer layer of the fold
forming the serosa, the inner the amnion. The fold grows up over the
blastoderm, the edges coalesce, and the membranes finally separate from
the ovum. The more recent account by Laurie (’90, p. 114) states that
in Luscorpius the serosa arises by a proliferation of the peripheral cells
of the blastoderm, extends as a delicate membrane forward and back-
ward over the egg, which it finally covers completely, and then becomes
entirely separate from the blastoderm. The formation of the amnion
begins when the serosa has covered about two thirds of the embryo, and,
like the serosa, its origin is ectodermic. The amnion, however, ‘“ never
loses its connection with the epiblast as the serous membrane has now
done, but remains attached to its edges and only extends round the
egg as the epiblast extends” (p. 116). Unfortunately, I have not
obtained sufficiently early stages of Centrurus to ascertain how its mem-
branes arise, but, in removing the latter from the embryo, I have never
found the amnion attached to the ectoderm. The membrane which I
have called the “ovarian capsule” I at first wrongly took to be the
follicular epithelium, and under this supposition it was indicated as e’th.
fol. in Figure 2. Like the follicular epithelium, it arises from the
ovarian tube; but the follicle is formed as a diverticulum of the tube,
previous to the maturation of the ovum, and serves as a nutritive cap-
sule for the latter during its growth. The ovarian capsule, on the
contrary, is that part of the ovarian tube which receives the ovum after
fertilization, and enlarges to accommodate the growth of the embryo.

The feetal membranes fit so loosely over the embryo that they can be
easily removed in a single piece. In late stages, the ovarian capsule is
readily separable from the membranes ; in earlier stages, it adheres closely
to them. It is rarely possible to separate the serosa from the amnion,

MUSEUM OF COMPARATIVE ZOOLOGY. 129

and a transverse section (see Fig. 2) shows only a trace of a dividing
wall between them, although in surface view the cell walls of both mem-
branes are clearly seen (Fig. 1). Metschnikoff (71, p. 219) describes
the membranes of Scorpio (EHuscorpius) italicus as connected with each
other by delicate fibres, which terminate just over the amniotic nuclei.
I have found such fibres in the earlier stages of my material, but not in
the older ones, nor are they everywhere present in the younger mem-
branes. The membranes of the Brazilian scorpion examined by Bloch-
mann (85, p. 481) were found closely applied to each other.

I. The Serosa.

Plate I.; Plate II. Figs. 14,15; Plate III.

The cells of the serosa have great superficial extent, measuring
half a millimeter or more in diameter; but proportionally they are
very thin. Their size is exceedingly variable, as may be seen by com-
paring Figure 3 with Figures 1] and 13 of the same magnification,
although the last two represent cells of only average size. Both
small and large cells are apt to be aggregated in certain parts of the
serosa, yet very small cells often occur sporadically in the midst of
large ones. The cell walls are extremely distinct in late stages of the
embryo, but in earlier stages are often difficult to trace in an ordinary
stained preparation. As remarked by Blochmann, they have a distinct
fibrous structure. The cells are irregularly polygonal in shape, usually
elongated, sometimes nearly square or triangular. Not infrequently
they are bounded by curved outlines (Fig. 13).

The nuclei of the serosa measure from 25 to 60m or more in
diameter, but as a rule are small in proportion to the cells (Figs. 1-3
and 11-15). In the membranes of young embryos the nuclei are larger
absolutely and in proportion to the cells than in old membranes. In
face view the resting nucleus is nearly circular ; in section, it is seen
to be considerably flattened, in accordance with the thinness of the cell
(Fig. 2, nl. sr.). It occupies the full thickness of the serosa, and some-
times causes a bulging of the cell at the point where it lies, as is shown
in Figure 2. Blockmann states (’85, p. 480) that the nuclei of the se-
rosa always cause that membrane to encroach cnward upon the amnion ;
but a dividing line between amnion and serosa is so seldom visible in
Centrurus, that I am unable to say whether such is the case:

The nuclear membrane is thin, but clearly visible, except in nuclei that
have undergone degeneration. The chromatic substance, or nuclein, is

VOL. XXII. — NO. 3. 9

130 BULLETIN OF THE

for the most, part in the form of granules distributed evenly throughout
the nucleus. Indications of a reticular or filamentous structure are,
however, frequently present. I believe there is a chromatic network
throughout the nucleus, but the abundance of granular chromatin pre-
vents one from tracing it. Several nucleoli are always present. They
are extremely variable in size and shape, and in many cases appear to
be only aggregations of granular chromatin. They take a stain with
hematoxylin and carmine in no way different from the rest of the
chromatin, except that it is more intense.

A very large proportion (about four to one) of the cells of the serosa
contain two nuclei. These pairs of nuclei have all arisen from single
nuclei by amitotic division. It is obvious that division of the cell is not
contemporaneous with, and does not immediately follow, the division of
the nucleus. In many cases, especially when the embryo is far ad-
vanced, cell division probably does not occur at all. Very few cells out
of the thousands I have examined have had more than two nuclei; but
I have found several with three nuclei, and two cells with four. This
seems to be the maximum number. These cells of the serosa, therefore,
are not to be classed with multinucleate cells in which the nucleus
divides into a great number of irregular and unequal fragments. Here
the division takes place in an orderly fashion, and division of the cell
follows nuclear division in regular sequence, though not immediately.

In every serosa examined, nuclei were found in process of division.
Some preparations furnish many more examples of division than others ;
and occasionally three or four adjacent cells will contain dividing nuclei
(Fig. 15). Very frequently, however, only one or two dividing nuclei
will be found in the whole serosa. It cannot therefore be supposed that
nuclear division is frequent; and I have found that there are more cells
with dividing nuclei in the membranes of late stages of the embryo
‘than in the earlier ones.

The first sign of approaching division is an elongation of the nucleus
(Fig. 4), almost always parallel to the long axis of the cell. Naturally,
the elongation progresses by insensible gradations from the nearly circu-
lar form of the resting nucleus, so that one cannot say positively that
the nucleus is going to divide until the elongation has become marked.
The absolute amount of elongation varies greatly, and is less in the
membranes of young embryos than in those of older ones. The example
represented in Figure 4 is from an old membrane, and shows almost the
extreme of elongation. This stage, while giving not the slightest evi-
dence of ordinary mitosis, is characterized by a longitudinal arrange-

MUSEUM OF COMPARATIVE ZOOLOGY. tt

ment of the chromatic substance, as indicated in Figure 4. The effect
is most marked upon the nucleoli. Blochmann (’85, p. 482) found only
two nucleoli at this stage, and these were usually situated one at each
end of the elliptical nucleus. Where there are several nucleoli, as is
usually the case with the nuclei I have studied, there is an approxi-
mately equal distribution of them to the daughter nuclei. The nucleoli
vary So much in size and shape, that it is impossible to say how precise
is the apportionment of chromatin by this method.

Most nuclei in the elongated condition already show a slight constric-
tion, generally more marked on one edge than on the other (Fig. 4).
If no further elongation takes place, the constriction beeomes deep and
narrow, as represented in Figures 5 and 12. This style of division is
characteristic of young membranes, and gives rise to daughter nuclei
which lie close together, or even in contact (Fig. 13). It is doubtless a
more vigorous and rapid type of division than that found in the older
membranes, to be described directly. If the nucleus continues to elon-
gate while constricting, it assumes the dumb-bell form represented in
Figures 6 and 7. The daughter nuclei, at first ovate or pyriform, be-
come rounder as the connecting thread becomes thinner. Division of
this type is almost confined to old membranes; I have rarely found it
in those from young embryos.

The nuclei represented by Figures 6 and 7 show more clearly than
usual a peculiar arrangement of the chromatic threads. The filaments
have the appearance of a fascicle of slender rods, which lie very close
together in the connecting bridge, and thence radiate into both daughter
nuclei. They are stainable both with carmine and hematoxylin. Some-
times these threads can be resolved into rows of granules (Fig. 7, right-
hand daughter nucleus). The later stages also show traces of these
longitudinal threads (Figs. 8, 9, 10). In the example represented by
Figure 6, the nucleoli partook of the general longitudinal disposition of
the chromatic substance, but were probably arranged in this manner at
an earlier stage of division, as explained for Figure 4. In the later stages
of division, this arrangement of the nucleoli is gradually lost.

The final stages, represented in Figures 8, 9, 10, may be briefly de-
scribed. These stages are far commoner than the early ones; hence, it
must be supposed that they require more time. The constricted por-
tion is drawn out into a thin, deeply staining thread. This thread
undoubtedly contains chromatin, and in a peculiarly condensed form.
In this respect these nuclei differ from the nuclei of the Malpighian
vessels of Aphrophora spumaria, as described and figured by Carnoy

132 BULLETIN OF THE

(85, Plate I. Fig. 7) ; for the connecting thread in the dividing nucleus
of Aphrophora remains unstained, and therefore contains no chromatin.

The dividing nucleus represented by Figure 8 is peculiar in several
respects. In the first place, the daughter nuclei are very unlike in
form, though this is by no means unusual with dividing nuclei from old
membranes. All the stainable nucleoli are in one daughter nucleus,
while the other still shows a faint longitudinal arrangement of its
chromatic threads. The sharply stained connecting thread is notched
at a point midway between the daughter nuclei, probably indicating
the place where, at a later stage, rupture would have occurred. The
daughter nucleus on the left is nearly destitute of chromatin in the
crescent-shaped space lying next the connecting thread, and an inner
contour line is visible («), from the central. point of which a stainable
cord extends to the proximal end of the connecting thread. I have seen
a similar appearance in the late stages of other dividing nuclei, and it
undoubtedly indicates the manner in which the daughter nuclei some-
times attain a rounded form. Occasionally, however, daughter nuclei
entirely separate from each other have a conical or tapered form.

In the last stages of division, the connecting thread is drawn out to
extreme tenuity (Figs. 9 and 10). So exceedingly fine does this thread
become, that, with the highest power accessible to me (Zeiss’s homoge-
neous immersion objective ys), I could barely trace its course through
the cytoplasm, though in most cases I made out that it was continuous
from nucleus to nucleus. It is finally broken at or near the centre, and
the proximal tips, as Blochmann suggests, are probably absorbed by the
daughter nuclei. In even so late a stage as that shown by Figure 10,
the longitudinal chromatic filaments are still perceptible. The right-
hand daughter nucleus contains four loop-shaped bodies that strongly
resemble chromosomes. They are, however, almost unstained by hema-
toxylin.

Blochmann states (’85, p. 482) that in no case did he find a division
of the cell following the division of the nucleus. As already said, the
great proportion of binucleate cells renders it certain that cell division
is not an emmediate consequence of nuclear division. Although I have
carefully examined great numbers of binucleate cells, I have only
once seen a cell wall in process of formation (Fig. 27). Yet one finds
plenty of evidence that cell division does take place. Pairs of cells like
those in Figure 11 are of frequent occurrence. It is safe to infer, I
think, from the arrangement of the binucleate cells which surround
these, as well as from the correspondence in size and shape of this pair,

MUSEUM OF COMPARATIVE ZOOLOGY. 133

that they have arisen from an elongated binucleate cell by the forma-
tion of a divisional cell wall. In one instance, I have found a cell wall
fully formed before division of the nucleus was completed (Fig. 27). It
cuts across the fine connecting thread at about the middle point of the
latter. This must be considered as in some degree abnormal, especially
since it was found in a serosa the nuclei of which had evidently degen-
erated.

Although division of the cell is almost always accomplished by the
formation of a cell wall, I have found several constricted cells, showing
that division may be partly, or even wholly, effected in this manner.
Sometimes the constriction is so deep that the opposite walls meet
(Fig. 28) ; but it is more usual to find that, after the cell has become
considerably constricted, a cell wall is formed joining the inward curves
of the constriction, and completing the division. At first, I thought it
possible that the constriction was mechanically produced by the pres-
sure of growing cells on either side. But this would not explain the
invariable occurrence of the constriction at precisely the point where it
would take place in a free cell, — equidistant from the daughter nuclei.
Furthermore, the curvature of cell walls (see Fig. 13), which is almost
certainly caused by the growth of cells and consequent tension, has no
reference to the position of the nuclei.

As far as can be judged, the daughter nuclei are, as a rule, of equal
size, and alike in shape. I have found many instances of beautifully
symmetrical division (Figs. 9 and 10); but the nuclei of the serosa are
not altogether exempt from the irregularities that seem to be inseparable
from amitotic division wherever it occurs. Sometimes the resulting
nuclei are obviously unequal (Fig. 13), even in young membranes ; and
in old membranes, where the nuclei have undergone degeneration, not
only are the daughter nuclei extremely irregular in shape, but often
very dissimilar in size.

Relations of the Nuclei to the Cell. — A very brief examination of a
preparation of the serosa convinces one that the nuclei are symmetri-
cally arranged in the cells. When there is but one nucleus, it occupies
the centre of the cell ; when there are two or three nuclei, each presides
over a half or a third of the cytoplasm. This arrangement is so con-
stant, that any marked deviation from it catches the eye at once. In-
stances of decidedly unsymmetrical arrangement of nuclei, one of which
Figure 13 represents, are very unusual. As regards elongated cells, the
daughter nuclei lie in the long ams of the cell, and at approximately
equal distances from its ends. Occasionally, however, the nuclei lie in

134 BULLETIN OF THE

the short axis (Fig. 12), and much more frequently are placed obliquely,
as in cell a, Figure 14. We would suppose that, in the event of division
of an elongated cell with nuclei lying transversely, the cell wall would
pass longitudinally between the nuclei; but I have not been able to find
evidence of longitudinal divisions. From the large number of cells with
nuclei lying obliquely, one would infer that oblique division of the cell
often took place. I am unable to discover, however, that such is the
case ; and it seems extremely probable that the divisional plane of the
cell does not always coincide with that of the nucleus.

I have found about 25 cells of the serosa with three nuclei. This
seems to be a matter of individual variation in the make-up of the
membrane, for all but three of the trinucleate cells were in membranes
from the brood of a single scorpion, and membranes from some broods
appear to have none. I have in one instance found a group of tri-
nucleate cells (Fig. 14, 1 2, 3, 4). At this spot nuclear multiplica-
tion has outstripped cell multiplication. It is nearly always easy to see
which of the two original nuclei has divided, for we find two of the
nuclei smaller than the third, and nearer to each other than to the
latter. In cell 2, for instance, the pair of nuclei on the left have arisen
from a nucleus occupying a position about midway between them. The
same statement would doubtless hold true for the two nuclei on the right
in cell 3, and here the odd nucleus is elongated. When the cell is long
and the nuclei all lie in the longitudinal axis, as_is the case in cell 7,
it is usually impossible to determine which of the two original nuclei
has divided ; for the nuclei are equidistant, and nearly alike in size.
Another type of equidistant nuclei is shown in cell 4, —a distribution
quite as characteristic of very large, broad cells as the linear arrange-
ment is of elongated cells. I have spoken of the division of one of the
two original nuclei as though it always took place after the nuclei were
completely separate, and had taken their positions in the cell. This
seems to be the usual method, for I have several times found one of
the original nuclei in the act of dividing. But it is possible, of course,
for them to arise by a tripartite division, in which the three nuclei
would be formed simultaneously. I have found only one instance of
a true triple division, represented in Figures 29 and 30, and as this
occurred in a serosa which had plainly undergone degeneration, I do
not consider it as altogether normal. It will be noticed that the origi-
nal nucleus became trilobed, and that the lobes became daughter nuclei
of approximately equal size by the formation of three divisional planes,
meeting at the centre of the original nucleus. The daughter nuclei on

MUSEUM OF COMPARATIVE ZOOLOGY. 135

the right are still united to each other by strands at the corners. Very
similar tripartite divisions were found by Overlach (’85, Plate XI. Figs.
35 and 41) in the epithelium of the cervix uteri. In two other cases,
I have found one of the daughter nuclei in a late stage of division
(Figs. 31, 32) dself elongating and undergoing constriction. It will
be noticed that the constricted daughter nucleus is considerably larger
than its mate.

I have found but two cells with more than three nuclei, and these both
contained four. This condition is brought about by the division of both
nuclei of a binucleate cell. On a priori grounds, one would reason that
quadrinucleate cells would be nearly as abundant as those with three
nuclei, for, apparently, it must often happen that a pair of daughter
nuclei, arising as they do by a symmetrical and accurate constriction,
are ready to divide at almost the same moment. Yet there are doubt-
less influences which operate to prevent the division of one of the
nuclei. Although it is of course impossible to generalize on the char-
acteristics of quadrinucleate cells, it may be of interest to mention the
peculiarities of the two found. They are both large cells, of nearly
equal width at the ends, and the breadth of both exceeds half the
length. In one, both pairs of nuclei lie transversely, showing that the
second divisional plane was at right angles to the first. In the other,
represented in Figure 33, the lower pair of nuclei lie in the longitudinal
axis, the upper pair almost transversely. One of the quadrinucleate
cells is considerably larger than any cell near it, while the other (Fig.
33) though by no means small, is of much less dimensions than the im-
mense bi- and uninucleate cells around it. I am unable to assign any
reason for the multinuclear condition of this cell. One fact, however,
is worthy of note. The united volume of its four nuclei does not
exceed the bulk of the single nucleus of a neighboring cell. One can-
not, of course, ascertain what the size of the primitive nucleus of the
multinucleate cell was, but it is very improbable ‘that it exceeded in
volume the nucleus of the uninucleate cell in question, for the latter
cell is considerably the larger of the two, and throughout this serosa the
size of the nuclei bears a direct ratio to the size of the cells.

As regards the influence or influences impelling nuclei to divide
independently of the division of the cell, nothing very definite can be
stated. It is certain that the absolute or relative size of the cell has little
or no influence upon the division of the nucleus. There are cells of all
sizes, from the largest to the very smallest (Fig. 3), which are binucle-
ate; and it is usual to find, side by side with bi- or multinucleate cells,

136 BULLETIN OF THE

others with a single nucleus that are actually larger than the former
(compare the cells in Figure 14). In such cases, the single nucleus is
always larger than the daughter nucleus of the other cells. I am unable
to see that multiplication of nuclei in the cell leads to any immediate
increase of nuclear material. The more they divide, the smaller they
become. Probably the most important office of division is @ more
extensive distribution of nuclet throughout the cytoplasm, with correspond-
ing increase of nuclear surface ; and this, considering the great superfi-
cial extent of the cells, and the comparatively small size of the nuclei
(at least in the older membranes) must be a matter of some importance -
for the activities of the cell. It is especially so in the case of elongated
cells. If such cells have but a single nucleus, a large part of the
cytoplasm must be remote from it; and if the nucleus is at the centre
of the cell, the cytoplasm at the ends of the cell will be most remote.
So, to restore the equilibrium between cytoplasm and nuclei, the nucleus
must elongate in the longitudinal axis of the cell, and the daughter
nuclei move toward the ends of the cell.

As a matter of fact, nearly all elongated cells have two nuclei, and
these lie in the long axis of the cell, usually rather nearer its ends than
toeach other. It cannot be denied that many short or squarish cells
also contain two nuclei; and, conversely, a few much elongated cells
can be found that have but one. In the latter case, it is interesting
to observe that almost invariably the nucleus has begun to elongate
in the longitudinal axis of the cell, and is often far advanced towards
division. We can say almost with certainty, then, that such cells are
of recent formation, and that the equilibrium between cytoplasm and
nucleus is promptly restored by division of the latter. It is true that
cases like that represented in Fignre 12, where nuclear division takes
place in the short axis of an elongated cell, cannot be explained in this
manner. Such instances are so rare that they might almost be con-
sidered as abnormal ; but the difficulty of the matter lies in the fact
that we get all gradations between nuclei ranged in the true longitudi-
nal axis, and those placed in the transverse axis. It is common to find
them lying more or less obliquely in the cell, though the obliquity is
seldom so great as to prevent them from practically fulfilling the con-
ditions of the hypothesis,

It is not supposable that all the agencies impelling nuclei to divide,
and controlling the direction in which division shall take place, reside
in the cytoplasm ; possibly the most potent of them exist in the nuclens
itself. That axial differentiation, with definite pole and antipole, is as

MUSEUM OF COMPARATIVE ZOOLOGY. 137

characteristic of the resting nucleus as of the mitotic nucleus, was
postulated by Rabl (’85, p. 323) from a careful study of the chromatic
network in the “skein stage” of mitosis. In a recent paper (’89, pp. 23,
24), the same writer states that the “polar depression,” usually visible
in young daughter nuclei, persists much longer than usual in the epi-
thelial nuclei of the Triton ; so that for these mitotically dividing nu-
clei it is highly probable that polar differentiation is always present in
_ the resting state. Carnoy (’85) has shown that, in the resting nuclei
of the testicular cells of certain Arachnids, the chromatic filaments are
distinctly arranged with reference to a definite axis (Planche V. Figs.
_ 165-169), and Van Gehuchten (’89) has found the same in glandular
cells of a Dipterous insect, Ptycoptera contaminata.

It is obvious that the discovery of an “organic axis,” as Van Gehuch-
ten calls it, in amitotically dividing nuclei is more difficult, for here there
is no polar depression or longitudinal arrangement of chromatic fila-
ments to indicate its direction in the resting nucleus. It is usual for
each division of the nuclei of the serosa to take place at right angles, or
nearly so, to the plane of the previous division. This is well seen in
many multinuclear cells, where one or both pairs of nuclei lie trans-
versely in the cell, and therefore at right angles, or nearly so, to the
direction of the first division (see cells 2 and 3, Fig. 14). In other
cases, however, two consecutive divisions take place in the same direc-
tion (Fig. 14, cell 2). It occurred to me that possibly there was an
organic axis in the nuclei of the serosa which in some cases exerted a

controlling influence upon the direction in which division took place,
but which in most instances was counteracted by influences residené in
the cytoplasm. Transverse divisions of the nucleus (Fig. 12) could then
be accounted for by assuming that the influence of the organic axis is
dominant in these cases, while oblique divisions would be explainable on
the ground that neither influence was predominant, but that both acted
with about equal force in directions at right angles to each other. A
question of interest in this connection is, whether, when the cytoplasmic
influence is dominant, and tends to make the nucleus divide in a plane
parallel to its organic. axis, division actually does take place in that
direction. If such were the case, an organic axis would be a fact of
slight morphological importance, and the longitudinal arrangement of
chromatin, which takes place in the earlier stages of constriction (Figs.
4, 6, 7), might occur in any direction, without reference to an organic
axis. If, on the contrary, it were necessary that the longitudinal fila-
ments should be arranged parallel to the organic axis, in order that

138 BULLETIN OF THE

division might take place transversely to the axis, this result could still
be attained by a rotation of the nucleus, even when the tendency was for
the nucleus to divide at right angles to the previous division. It is
obvious that rotation would occasionally be apparent, provided it took
place soon after division, and previous to the absorption of the proximal
end of the connecting filament. JI examined a large number of prepara-
tions to find evidence of rotation, but I must admit that the evidence
was slight, and hardly sufficient to establish the hypothesis which I had
formulated. It is therefore put forth provisionally, in the hope that it
may lead to further investigations in this line.

The most striking instance of rotation was found in one of the quadri-
nucleate cells (Fig. 33, nuclei a and 6). It is evident that three nuclear
divisions have taken place without any division of the cell, producing
two, three, and four nuclei. The arrangement of nuclei makes it rea-
sonably certain that the Jower pair arose by division of one, and the
upper pair by division of the other nucleus of the binuclear stage.
Only under this supposition could the daughter nuclei of that stage
have had the normal arrangement, to which all the neighboring cells
rigidly conform. We further find, that, while the upper pair of nuclei
has arisen by a division in the long axis of the cell, the lower pair has
been produced by division in the transverse axis, and therefore in con-
formity with the law previously stated (p. 136). One nucleus of each
pair (2 and 8) retains a remnant of the connecting filament, which is
directed, not toward the sister nucleus, but to a point 90° distant from
it. This condition could have been brought about only by rotation of
the nuclei, which in both cases has been through an are of 90°.

In the serosz from older embryos, the daughter nuclei almost inva-
riably recede from each other in the course of division. The amount
of recession is governed by the length of the cell (Fig. 15). In the
younger membranes, as already stated, the constriction is deep and
narrow, so that the nuclei not infrequently lie very near together
(Fig. 13). In these young membranes, however, the nuclei are larger,
and the cells are usually smaller, than in the old membranes. Since,
moreover, the /arge binucleate cells of young membranes almost always
have their nuclei symmetrically placed at the ends, it is probable that
the nuclei gradually move apart ajter division, as the cell increases in
size.

It will be seen that my interpretation of the primary cause of the
division of these nuclei agrees in part with the hypothesis advanced by
Chun (’90) for the explanation of amitotic division in general. This is,

MUSEUM OF COMPARATIVE ZOOLOGY. 139

in brief, that the object of amitotic division is the distribution of nuclear
material throughout the cytoplasm, with corresponding increase of nu-
elear surface. He considers it the final phase of a series of conditions
which begins with a simple lobed nucleus, and includes branched nuclei
of various degrees of complication. In support of this interpretation,
Chun lays stress on the statement that cell division, after an amitotic
division of the nucleus, has seldom or never been observed with cer-
_ tainty, thereby implying that amitosis cannot have in view the multi-
plication of cells. I do not consider this as essential to the hypothesis,
nor, in fact, do I believe him correct on this point. The evidence of
eell division after amitosis seems to me abundant and conclusive. It
_ was observed by F. E. Schulze (75) in Ameba polypodia; by Ranvier
(75), Biitschli (76), Flemming (’82), Arnold (’87), and others, in leu-
cocytes ; by Kiikenthal (’85), in the lymphoid cells of Annelids ; and by
Carnoy (’85), in various cells of Arthropods. As the foregoing shows,
there is abundant evidence that, in the serosa of the scorpion, division
of the cell sometimes, at least, follows amitotic division of the nucleus.
Furthermore, the extremely regular and well ordered manner in which
the nuclei divide, and the similarity as to size and shape of the daughter
nuclei, seem to me decidedly against the notion that the sole object of
the division is to disseminate nuclear substance in the cytoplasm ; for
in those cases where amitosis is not followed by division of the cell, and
assumably takes place simply for the purpose of dissemination, the
nuclear products are very variable as to number, size, and shape.

II. The Amnion.
‘Plate I. Figs. 1 and 2: Plate I. Figs. 16-20.

The amnion is much thinner than the serosa, and like it is composed
of a single layer of flat, polygonal cells (Fig. 1, am.). But, while both
the cells and nuclei of the serosa have become enormously larger than
the blastodermic cells from which they originated, those of the amnion
have changed little as regards size. The boundaries of the amniotic
cells are not always visible, and I find that preparations, even when
hardened and stained in the same manner, show the greatest variation
in this respect. As a rule, the cell walls in the amnion are sharply and
clearly defined only in preparations of membranes from advanced em-
bryos. The same is true of the cell walls of the serosa.

In general, the amniotic cell has but one nucleus, which usually oceu-
pies the centre of the cell. Blochmann makes the same statement as to

140 BULLETIN OF THE

the number of nuclei in each cell, and he found no evidence of division
among them. The outline of the nuclei, which measure about 15 p» in
diameter, is frequently somewhat irregular or lobed. Like the nuclei of
the serosa, they are flattened tangentially (Fig. 2, nl. am.); but not-
withstanding this, they cause an outward bulging of the cell upon the
serosa, as shown in Figure 2. They contain always one or more highly
refractive, deeply staining nucleoli. The rest of the scanty chromatic
substance is in the form of minute granules, occasionally arranged partly
in a very faint network (Fig. 18, 6 and c). As in the nuclei of the
serosa, chromatic threads frequently unite the nucleoli.

Division of the amniotic nuclei is of rare occurrence. In only one of
my preparations are dividing nuclei at all abundant. The division
takes place without mitosis, but is of a different type from that of the
nuclei of the serosa. The only alteration of the chromatin is possibly
a change in the position of the nucleoli; I have not been able to detect
any modification of the reticulum. The first sign of approaching divis-
ion is elongation of the nucleus (Figs. 16 and 18, a). A deep narrow
constriction appears at the equator of the nucleus (Fig, 17). This is
followed by the formation of an equatorial septum, at once partition-
ing off the nucleus into two daughter nuclei (Fig. 18, 6). If there are
but two nucleoli, it is the rule to find one in each daughter nucleus ; but
where there are several, they are often unequally apportioned. After
the formation of the septum, the daughter nuclei still adhere to each
other, and division seems always to be attained by deepening of the
equatorial constriction in the plane of the septum (Figs. 18, 6, c, and 19).
I have not found any evidence of a recession of the nuclei before
division of the cell. Furthermore, the rarity of binucleate cells makes
it very probable that cell division follows nuclear division promptly.
As in the serosa, division of the cell takes place by the formation of a
cell wall without marked constriction (Fig 20). The position of the
nuclei in this figure, and the frequency with which nuclei are found
near the boundaries of the cells (Fig. 1, am.) is evidence of the prompt-
ness of cell division after the division of the nucleus.

It is clear that Chun’s hypothesis will not hold in this case, for there
is even less tendency than in the serosa to accumulate nuclei in the
cell. This may be owing in part to the shape of the cell, for it is sel-
dom elongated. It would seem that, in case the cell becomes elongated,
nuclear division takes place and the cell divides immediately after the
nucleus. The orientation of the nuclei with reference to the cytoplasm
of their respective cells would then be accomplished by their migration
to the centre of the cells.

MUSEUM OF COMPARATIVE ZOOLOGY. 141

III. The Ovarian Capsule.

=
Plate Il. Figs. 21-26.

The epithelium of the ovarian capsule is not often easily made out in
ordinary stained preparations, for the nuclei of muscle fibres and con-
nective-tissue cells lie not only just external to the epithelial nuclei,
but frequently in the same plane with them. In most of my prepara-
tions the boundaries of the epithelial cells cannot be seen at all, and I
have therefore confined my attention mainly to those which show them
distinctly. In shape, the cells are more or less irregular, oblong hexa-
gons (Figures 24 and 25 represent typical shapes). The cell walls are
broad and fibrillated, like those of the serosa, though the cells them-
selves are smaller even than those of the amnion. The nuclei are not
only larger in proportion to the cells, but often larger absolutely, than
the amniotic nuclei. The amount and arrangement of the chromatin
in the capsular nuclei (except in a certain phase) is almost precisely
like that already described for the nuclei of the amnion, but there is usu-
ally only one conspicuous nucleolus. The small amount of chromatic
substance, aside from the nucleolus, has a granular appearance, but
sometimes shows indications of a filamentous or reticular arrangement
(see Figs. 21, 23, 24). Seen in face view, the nuclei are circular, and
have a distinct nuclear membrane. The section (Fig. 2, n/. fol.) shows
that they are less flattened than the amniotic nuclei.

Here, again, we have amitotic division, and of precisely the same
type as prevails in the amnion. Apparently, division is not of common
occurrence, for I have been able to find only a few instances, and have,
unfortunately, not seen its earliest stages. Figures 21, 22, and 23 show
the simple manner in which it is effected. As each daughter nucleus
contains a nucleolus, and the ordinary resting nucleus has but one,
division of the nucleolus must precede division of the nucleus. In one
important respect the division of these nuclei differs from that of the
amniotic nuclei. The cell does not divide immediately after the nucleus,
and consequently a great number of cells are binucleate. Some even
contain three nuclei. I have obtained no evidence whatever of cell
division.

142 BULLETIN OF THE

IV. Degenerative Changes.

Plate II. Figs. 14, 24-26; Plate III. Figs. 28, 34.

The striking difference in the appearance of cells and nuclei, and
the different manner of division of the nuclei, exhibited by serosz of
different ages, have frequently been referred to. Such changes, in
part at least, I believe to be due to degeneration of the membranes,
which, with the exception of the ovarian capsule, are temporary struc-
tures, soon to be cast off by the embryo. Hence it is not surprising to
find them undergoing degeneration zz toto. The degenerative changes
are about equally well marked in all three membranes; but on account
of the great size of cells and nuclei, the changes are most conspicuous in
the serosa. If the membrane comes from a young embryo, the walls
of the cells are unstainable, and therefore often difficult to make out.
The nuclei have a vesicular appearance, with smooth, rounded contour,
abundant karyoplasm, and scanty chromatic substance. For this reason
the nuclei seldom stand out clearly from the cytoplasm in a stained
preparation, often being no darker than the rest of the cell.

Serose from somewhat older embryos, while giving no sure signs of
degeneration, have nuclei slightly different from those of the youngest
membranes. The amount of chromatic substance appears to be larger.
It is gathered into denser and more deeply staining masses, and the
nucleoli become larger and more stainable (compare Figures 4 and 5, the
former from an older membrane than the latter). Many nuclei at this
stage become irregular in outline, and are more or less shrunken in
appearance, changes which prepare the way for complete degeneration,
found in membranes from the oldest embryos. The nucleus here
becomes shrunken into a formless mass, which stains deeply and uni-
formly. This condition seems to be due almost wholly to loss of the
karyoplasm, for the nuclear membrane is seen to be drawn closely
over the much condensed chromatic substance. The uniformly staining
effect, however, is generally believed to be produced by the solution of
a part of the chromatin in the karyoplasm ; this is best seen in nuclei
that have not completely degenerated, where the deeply stainable solid
chromatin is immersed in the less stainable matrix. Not all the nuclei
in a membrane are affected to the same degree by the degenerative
change. This is shown in Figure 14, where the nuclei of cell a, and that
of the cell farthest to the left, are more affected than any others. But
in the oldest membranes almost every nucleus has undergone extreme
degeneration.

MUSEUM OF COMPARATIVE ZOOLOGY. 143

It is an interesting fact, that even the most thoroughly degenerated
membranes have numerous nuclei in all stages of division. The divid-
ing nuclei have undergone the same degenerative alteration as the rest.
It is impossible to state whether these nuclei had begun to divide after
the regressive change, or had been overtaken by these changes while
undergoing division; and it is equally impossible to say whether
degeneration would have prevented the nuclei from completing their
division. The division is essentially like that of younger nuclei, but
often unsymmetrical.

Not all the degenerative changes are confined to the nuclei. The
cells also give evidence of modification. Their walls become more
distinct, not only because they are denser and thicker, but on account
of their stainability with hematoxylin. The cytoplasm frequently has
a reticulated structure, which is densest about the nucleus. In the
oldest membranes, certain large groups of cells have nuclei surrounded
by a narrow bright ring, and outside this a much broader halo of a
radiating structure, which takes a deeper stain than the rest of the
cytoplasm (see Fig. 34). The appearance of the whole is strikingly
like that of the “attraction spheres” of ovarian and other cells, but in
this case has certainly nothing to do with mitosis. If the cell contains
two nuclei, or a dividing nucleus, each daughter nucleus is surrounded
by ahalo. In early stages of division, however, the elongated nucleus
has a single halo. I am unable to account for these appearances ; I do
not regard them as attraction spheres, but rather as a result of degener-
ation. The attraction sphere should radiate from a centrosome ; here
it radiates from the nucleus as a centre. I may state, in passing, that
my search for centrosomes in the serosa has been wholly unsuccessful.
The pale ring is very generally present around nuclei that have under-
gone degeneration. It seems to have no intimate connection with the
radiating zone, being frequently found where the latter is absent.

The life history of the serosa cells corresponds closely with that of
certain cells in the Malpighian vessels of Aphrophora spumaria de-
scribed by Carnoy (’85, p. 219). The cells at the two extremities of
the tubes contain nuclei not greatly different from those of young
serose, but the nuclei of the middle portion are irregular, jagged,
and filled with amorphous chromatin. They therefore bear a strong
resemblance to the degenerated nuclei of the serosa. Furthermore, the
origin of the peculiar nuclei of the middle portion of the Malpighian
vessel agrees closely with that of the degenerated nuclei of an old
serosa. It is thus described by Carnoy (p. 220): “Sur les petites

144 BULLETIN OF THE

larves on rencontre tous les intermédiaires entre les noyaux des extrémi-
tés et ceux du milieu. Peu @ peu le boyau s’efface, Je noyau lui-méme
se rétrécit et perd la regularite de ses contours 4 cause du plissement
de sa membrane ; @ la fin la nucleine ne forme plus a l’intérieur qu’une
masse compacte et homogene, & peu pres comme cela se présente dans
la téte des spermatozoides.” In both cases the degenerated nuclei are
found in stages of division ; in both, the cytoplasmic reticulum is distinct
only in old cells, and where these cells are binucleate it is dicentric,
with filaments radiating from the nuclei. The dicentricity of the binu-
cleate cells is a point to which Carnoy calls special attention (p. 229).
He considers that here the radiating filaments of the cytoplasmic retic-
ulum answer to the polar asters of karyokinesis, and that the nucleus
has the function of a centrosome. The same reasoning would apply
to the degenerated cells of the scorpion’s serosa.

The regressive metamorphosis undergone by the epithelial cells of
the ovarian capsule (Figs. 24-26) is very peculiar. Here, again, the
cell walls are affected in the same way as in the serosa and amnion, for
they are not distinctly seen until after the nuclei have degenerated.
Nearly all of the epithelial cells of an old capsule have two nuclei, which
are dissimilar in size and appearance (Figs. 24 and 25). The smaller
takes a rather deep, uniform stain, almost as dark as that of the chro-
matin of the other. A nucleolus is always present, and frequently
minute granules of chromatic substance. The uniformly staining char-
acter of the nucleus is doubtless produced by chromatic substance held
in solution by the karyoplasm, a condition of common occurrence with
degenerating nuclei. The larger nucleus (Figs. 24 and 25) takes oniy a
slight stain, owing to the scantiness of its chromatic substance, which is
present in the usual form of isolated granules and an imperfect network.
By examination of a large number of cells, I found nuclear differentia-
tion of every degree, beginning with nuclei almost alike in size and
stainability (Fig. 24), then passing to examples of marked dissimilarity
(Fig. 25), where the pale nucleus has become almost invisible, and the
smaller deeply staining one has attained a very sharp, definite outline.
As the pale nucleus becomes more and more shadowy, its shape becomes
irregular. Near cells of this sort others can be found which contain only
a single deeply staining nucleus (Fig. 26), the other having disappeared
altogether. In case of trinucleate cells, I have invariably found two of
them to be of the pale sort.

I am unable to offer any other explanation of these changes than that
they are the result of degeneration or of decreased activity of the tissue.

MUSEUM OF COMPARATIVE ZOOLOGY. 145

But why one nucleus should become altered in one way, and the other
in an entirely different manner, is difficult to say. A very similar dif-
ferentiation of nuclei has been observed by Chun (’90) in the egg germs
of a Siphonophore (Stephanophys). He found only one nucleus in the
youngest germs, while the middle-sized and larger egg cells contained
two of different size, the larger being pale, and the smaller staining in-
tensely. The smaller nucleus moves to the periphery of the egg and is
no longer visible when the latter is ripe. ‘The larger nucleus persists
as the germinative vesicle. In only one instance did he see a stage
that showed that the smaller nucleus budded out of the larger. Chun
compares the small, deeply staining nucleus to the “ Stoffwechselkern”
(macronucleus), and the pale one to the “ Fortpflanzungskern ” (micro-
nucleus) of the ciliate Infusoria.

Summary.

1. The embryo of the scorpion is enveloped by three membranes, the
ovarian capsule, the serosa, and the amnion.

2. The ovarian capsule is an enlargement of the ovarian tube; the
serosa and amnion arise from the blastoderm of the egg.

3. Serosa and amnion are at first distinct, and joined to each other
by minute fibres. These afterwards disappear, and the membranes
coalesce.

4, The serosa is composed of immense flat cells, very variable in size
and shape. The cell walls are fibrillated.

5. The majority of the serosa cells have two large nuclei of equal
size. There are rarely more than two.

6. The nuclei are disk-shaped, have a distinct nuclear membrane, and
chromatin in the form of granules and filaments, the latter forming an
indistinct reticulum. ‘There are usually several nucleoli.

7. The cytoplasm of the serosa has a distinct reticular structure.

8. Nuclear division in the serosa is amitotic, and takes place by con-
striction, preceded by elongation of the nucleus. It is followed or ac-
companied by recession of the daughter nuclei, which remain for some
time connected by a fine strand.

9. Constriction of the nucleus is usually accompanied by a longitudi-
nal arrangement of some of the chromatic threads, radiating from the
constricted part. The nucleoli are distributed about equally to the
daughter nuclei.

“ VOL. XXII. — NO. 3. 10

146 BULLETIN OF THE

10. Nuclear division may be followed by division of the cell, but not
often immediately. The cell divides by the formation of a cell wall,
either with or without constriction.

11. The binucleate condition of cells is independent of their size ;
but, in general, the size of the nucleus, or nuclei, is proportional to the
size of the cell.

12. Elongated cells of the serosa are generally binucleate. The
nuclei almost invariably lie in the long axis of the cell, near the ends.

13. A binucleate cell becomes trinucleate by division of one of its
nuclei, and quadrinucleate by the division of both. Very rarely the
division is tripartite, and the three nuclei are produced simultaneously
from a single one.

14. Division of the amniotic nuclei is also amitotic, but the constric-
tion is supplemented by a septum at the equator of the elongated
nucleus.

15. ‘There is apparently no rearrangement of the chromatic substance.
Nucleoli are apportioned equally to the daughter nuclei.

16. Division of the nucleus is quickly followed by division of the cell,
so that binucleate cells are not common.

-

17. The epithelium of the ovarian capsule is composed of small
hexagonal or rectangular cells, which frequently contain two or more
nuclei.

18. The nuclei are very similar to those of the amnion, but usually
contain only one nucleolus.

19. Nuclear division is amitotic, and precisely like that of the amni-
otic nuclei. Each daughter nucleus contains one nucleolus.

20. No instance of cell division was observed.

21. All three membranes undergo degeneration as the embryos ap-
proach maturity.

22. In the serosa the cytoplasmic reticulum becomes more distinct,
and is seen to radiate from the nuclei. The cell-walls become stainable.

23. The chromatic substance of the nuclei becomes grouped into
dense masses ; the reticulum and nucleoli become more distinct. The
outlines of the nuclei become irregular.

24. As degeneration proceeds, the cytoplasm frequently forms a halo
of radial structure around the nucleus.

MUSEUM OF COMPARATIVE ZOOLOGY. 147

25. The nuclei finally become reduced to uniformly staining, irregu-
lar masses of chromatin, which has. partly entered into solution. Such
nuclei are found in all stages of division.

26. In binucleate cells of the ovarian epithelium the nuclei become
dimorphic.

27. The chromatic substance of one of the nuclei enters into solution
in the karyoplasm, and the nucleus becomes reduced in size.

28. The other nucleus loses its stainability, and increases in size. It
finally disappears.

V. Discussion of Amitosis.

As long as karyokinesis was supposed to be a uniform process, all the
complicated details of which were carried out with the greatest exact-
ness and in the same sequence, wherever it occurred, no one sought to
homologize it with the little known and far simpler “direct” division.
The latter had, apparently, so restricted a range, and had received so
little attention, that its very existence was denied ; and it was generally
anticipated that, in the few kinds of cells in which it was stated to oc-
cur, a better technique and more careful study would reveal mitotic
phenomena. This opinion seemed to receive confirmation by the dis-
covery of mitotic division in leucocytes and the Protozoa, thus carrying
mitosis back to the simplest types of cells and to the lowest forms
of life. The ascertainment of two facts has brought about a radical
change in our views regarding amitosis: (1) the variability of karyo-
kinesis, including, in some cases, the omission of apparently essential
steps ; and (2) the wide occurrence of amitosis, new instances of which
are constantly coming to light in various parts of the Animal Kingdom.
Inasmuch as it became necessary to recognize the existence of direct
division, efforts were naturally made to find links connecting it with
mitosis; the variability of both mitosis and amitosis seemed to lend
strength to the theory which refers them to a single fundamental plan
of division. In this scheme, amitosis is considered either as a primitive
method from which mitosis was evolved, or else is looked upon as a
degenerate form of mitosis, occurring in nuclei which, from their patho-
logic or exhausted condition, have lost the power of dividing by the more
complicated process. By fixing epithelium of the salamander larva with
osmic acid, then treating it with Miiller’s fluid, and finally staining with
hematoxylin, Pfitzner (’86*) has shown conclusively that, even in cases of
very perfect mitosis, the karyoplasm maintains its integrity, and divides

148 BULLETIN OF THE

by a simple constriction, as in direct nuclear division. This fact has led
Waldeyer (’88) to the conclusion that karyokinesis in based upon the
simple scheme of division conceived by Remak. He says: “I would
interpret the facts in such a way that we have to regard as the funda-
mental form the simple amitotic division, which is now proved for many
cases ; it always takes place where the nucleus either is poor in chroma-
tin, or when it does not matter about strict bipartition of the chromatic
material. Should the latter be required, then we shall find mitosis,
since it is the most direct, most certain, and most simple manner in
which an exact bipartition of chromatic substance is brought about.”

It seems to me, however, that there are differences of so fundamental
a character between mitosis and amitosis, as at present understood,
that it is impossible to refer them to a single plan of division. Both,
indeed, achieve the same result, — division of the nucleus, including its
two constituents, chromatin and karyoplasm. In both cases, the karyo-
plasm divides by constriction. In amitosis, the chromatin undergoes
little if any change in preparation for division ; in mitosis it becomes con-
solidated into a limited number of thickened rods or loops (chromosomes),
which arrange themselves in the plane of division (‘“ mother star,”
“couronne équatoriale”) and segment either longitudinally or trans-
versely, the halves moving to opposite poles (“ diaster ”), and undergo-
ing a reversed metamorphosis to form two daughter nuclei. If this
were all there is to karyokinesis, — and in some cases the process is
much simpler, — we might hope to find transitions between it and ami-
tosis ; for there are examples of amitosis in which the chromatic net-
work undergoes changes during division, and it would be conceivable
that the highly organized changes of the chromatic substance during
mitosis were either evolved from them, or that they were a simplifica-
tion of the more detailed changes. In mitosis, however, other struc-
tures besides chromosomes make their appearance, — the centrosomes,
attraction spheres, and spindle. These structures are not known to take
any part whatever in amitosis, and in this respect at least the two kinds
of division are fundamentally different. The most recent workers upon
karyokinesis agree in assigning to the spindle rays the function of
separating or dividing the chromosomes, and drawing (or pushing) the seg-
ments towards the poles. The centrosomes are focal points towards which
the spindle rays converge, and lie entirely outside the nucleus. The for-
mation of the spindle has been carefully studied by many investigators
of karyokinesis, and, while there are very divergent views as to its ori-
gin and mode of action, the most recent workers in this field (of whom

MUSEUM OF COMPARATIVE ZOOLOGY. 149

E. van Beneden, Boveri, and Watase may be mentioned) are agreed that
the spindle arises from the cytoplasm. The same view with regard to
the spindle in the mitosis of vegetable cells was expressed by Stras-
burger, Guignard, and other botanists.

The centrosome, as a converging point for the spindle fibres and
polar rays, plays a most important part in karyokinesis, and, so far as
known, none at all in amitosis. The centrosome has indeed been found
by Flemming (91) in leucocytes, which certainly divide amitotically ;
but there it is a single structure, and as Flemming’s figures show,
takes no part in the amitotic diwision of the nucleus. Whether it also
remains passive during the mztotzc division of leucocytes and in amitosis
followed by division of the cell, is not known. It has been supposed by
Carnoy (’85) that spindle rays were present in certain nuclei which
divide amitotically, but this seems extremely doubtful, especially since
they have no perceptible action on the chromatic substance. I believe
it can be shown in every case of amitosis known, that the division of
the chromatin is accomplished independently of chromosomes, spindle rays,
or any other visible influence outside of the nucleus.

The persistence of the nuclear membrane in amitosis, and its dis-
appearance in mitosis, were formerly considered points of distinction ,
between the two kinds of division; but, as is well known, more recent
studies have shown that the membrane persists in many cases of un-
doubted karyokinesis, especially among the Arthropods (Carnoy, ’85) and
Protozoa (Gruber, ’83, R. Hertwig, 84, Pfitzner, ’86°, and Schewiakoff,
88). Its presence seems to offer no obstacle to the karyokinetic
changes, and Watase (’91) has pointed out that it need not prevent
the formation of an extra-nuclear spindle, the rays of which may pene-
trate the membrane. In the nuclei of Opalina ranarum, and in the
micronuclei of Infusoria generally, where, according to all observers, the
nuclear membrane persists, the mitotic division is accompanied by con-
striction ; but the fact that constriction is here visible may be considered
as in some measure a vesult of the persistence of the membrane, thereby
making evident the outline of the karyoplasm. Yet constriction does
not always take place when the membrane persists, for in the spermatic
cells of Pagurus striatus, figured by Carnoy (’85, Plate VII. Fig. 244),
the nuclear membrane is visible at all stages, and gives no evidence of
constriction. |

The modification of the chromatic substance into chromosomes is
usually the most conspicuous feature of karyokinesis, and in most cases
serves to distinguish mitotic nuclei from any of the amitotic ones. The

150 BULLETIN OF THE

chromosomes invariably include ail the stainable substance of the nu-
cleus, so that the presence of nucleoli in a nucleus undergoing constric-
tion may be taken as perhaps the strongest evidence of direct division.
The behavior of nucleoli in amitosis is of peculiar interest. Where
there is a single nucleolus, it constricts previous to the constriction of
the nucleus, according thus with the Remakian scheme. The division
of the nucleolus, however, has rarely been observed. It was first de-
scribed, I believe, by F. E. Schulze (75), in the division of Ameba poly-
podia ; has since been figured by Carnoy (’85, Plate I. Figs. 10, 12, 13)
for various amitotically dividing Arthropod cells, and by Hoyer (°90)
for the intestinal epithelium of Rhabdonema nigrovenosum. A peculiar
modification of the nucleolus, and its division into four segments pre-
vious to the constriction of the nucleus, was observed by Platner (89,
pp. 145-149) m the Malpighian vessels of Dytiscus marginalis. It is
extremely probable that, whenever the nucleolus is a single and defi-
nitely organized structure, it always divides previously to or during con-
striction of the nucleus. Where there are several small nucleoli, they
may indeed arrange themselves so as to be equally apportioned to the
daughter nuclei ; but they are not known to divide, as the chromosomes
in mitosis do.

Amitotic division, even more than karyokinesis, is variable in its
phenomena. It takes place by constriction, by formation of division
planes, by gemmation, and by enlargement of one or more perforations
(Arnold, *88, Flemming, *89). It is either simple or multiple, and it
may or may not be accompanied by division of the cell. The resulting
nuclei may be equal or unequal. Amitosis occurs throughout both the
Animal and Vegetable Kingdoms ; but as far as animals are concerned,
it is far the most frequent among waicellular organisms, ameboid cells
(leucocytes), and epithelial tissues. There seem to be no authentic instances
of it in connective tissues (except possibly the fat-cells of Arthropods,
described by Carnoy), none in nervous tissue, and but one or two in
muscle fibres (Carnoy, ’85, p. 221). Not only the nuclei of fixed tissues —
divide by the direct method, but also those of nascent tissues, at least
among the Arthropods. Direct division is, however, of rare occurrence
in the embryo. I believe there are only two authentic imstances of
it, — that discovered by Carnoy in the ventral plate of an embryo of
Hydrophilus piceus (785, p. 224, Plate I Fig. 11), and that found br
Wheeler (89, p. 313) in the formation of the blastoderm of Blatta
germanica, where no instance of mitosis was detected. The embryonal
membranes of the scorpion I do not include under this head, because
they are temporary structures forming no vital part of the embryo.

MUSEUM OF COMPARATIVE ZOOLOGY. 151

ber and the most interesting cases of amitosis. Furthermore, as Ziegler

(791) bas very recently shown, epithelial cells of unusual size, with some
peculiar functional activity (generally secretion) are most apt to exhiint
this method of division. Cell division has seldom been observed to fol
low amitosis in such large cells, which therefore become multinucleate.
Other epithelial cells which frequently furnish imstances of amitosis are
those which are near the end of their functional actimty. Cells of the outer
layer of a stratified epithelium sometimes divide amitotically, while
those of jhe deeper (and therefore younger) layers of the same epithelium
divide by mitosis. A good imstance of this was recently described by
Dogiel (90) in the epithelium of the bladder of Mammals. The nuclei
of the large epithelial cells lining the intestime of Arthropods very com-
monly divide by amitosis. as was found by Frenzel (85) m the midgut of
Astacus and Maja ; by Carnoy (35) im the intestinal epithelium of Iss
pods; and by Faussek (°S7) in the digestive tract of a Cricket (Eremoiaa
muricata) and in the larva of Zschaa. The miestimal epithelium m all
Arthropods has an important secretory function. Cells whose function
is excretory likewise exhibit amitotic division of the nucleus, as in the
Malpichian vessels of Insects. The oceurrence of amitosis m glandular
and exeretory epithelium is readily explaimable on Chun’s hypothesis,
for the functional activities of such cells are peculiarly miense, and it is
easy to see thai a distribution of nuclear material m the cytoplasm is
_ of advantage to the cell The occurrence of nuclei of unusual size (as
compared with the nuclei of other cells of the same animal) seems to
me likewise referable to the pecaliar needs of the cytoplasm m these
cells.

Cases of amitosis peculiarly dificult of explanaiion are these pre
sented by the germinal epithelium of the testis. So many observers
have reported direct division in sperm mother-cells, that there seems
no reasonable doubt of its occurrence. It has been suggested thai the
cells which divide amitotically never produce spermatoaa, but merely
serve to secrete a fluid. This explanation, however, will not serve m
ee ene eels (eens enter and Ideiea sp.) m the testes
of which Carnoy (°85, p. 222) found amitosis ihe prevailing type of di-
Vision, and mitosis of very rare occurrence. Direct division is found
more or less frequently im the testicular cells of many ether Crustacea,
as the extensive work of Gilson (84-37), and the vestigations of
Sabatier (85) show, and occasionally in the other groups of the Arthro-
pods) Among Vermes, it was found by Lee (°87) im Nemertianms and

152 BULLETIN OF THE

by Lowenthal (’89) in a Nematode (Oxyuris ambigua). It need hardly
be said that amitosis in sexual cells is unexplained by any hypothesis
yet offered regarding the biological significance of this type of division,
and further investigations on this point are absolutely necessary before
we can form any general opinion in regard to it.

In the maturation and segmentation of the ovum no instance of direct
division is known, and it is here that karyokinesis is exhibited in its
most complete form. The well known observations of Boveri (’87) on
the segmentation of the egg of Ascaris megalocephala are of special in-
terest on this point. He found a modification of the chromatio threads
as early as the two-blastomere stage, one of them (cell A) retaining the
four chromosomes characteristic of the nucleus after fertilization, the
other (cell B) undergoing a reduction of its chromosomes into the form
of granules. The two blastomeres arising by division of cell A undergo
the same differentiation, the nucleus of one (cell A’) retaining the
chromatic loops, the other (cell A?) undergoing reduction, so that in
the four-cell stage only one nucleus has retained its chromatic loops.
The systematic reduction of chromosomes was observed up to the 64-
cell stage. The important deduction Boveri makes from these facts
is, that the cells retaining their ancestral nuclear characters are the
Anlage of the sexual cells of the developing animal, and that the cells
whose nuclei undergo a modification of the chromosomes are all somatic
cells. In accordance with this hypothesis, the division of both male
and female sexual cells ought always to be karyokinetic, and of a
somewhat different type from the karyokinesis of the somatic cells of
the same animal. The latter statement, indeed, holds true for the
testicular cells of the salamander, as was discovered by Flemming (’87).
It also appears from the work of Carnoy, that in the post-embryonic
life of Arthropods mitotic division is of rare occurrence in the tissue
cells, but is of constant occurrence in the reproductive cells of the same
forms.

As has already been stated (p. 147), attempts have been made to
find a morphological connection between karyokinesis and direct divis-
ion, and thus to solve the puzzling question of the relations they bear
to each other. Carnoy (85, p, 398) believes he has found transitions
between them in the division of the numerous nuclei of Opalina rana-
rum. Some of these show a distinct spindle, others none ; in both cases
the nuclear membrane persists, and division is accomplished by constric-
tion. Pfitzner (’86°), however, found only mitosis in 0. ranarum. Car-
noy has also seen transitional forms of division in the spermatic cells of

MUSEUM OF COMPARATIVE ZOOLOGY. 153

Pagurus striatus, and P. callidus (Planche VII. Figs. 244, 245). A nu-
clear plate is here formed, both in perfect mitosis and in degenerated
mitosis ; but in the former instance a spindle is formed, and the chromo-
somes segment individually, while in the latter the plate divides zz tto
by constriction, without the help of a spindle. This modified type of
mitosis, if we may so regard it, Carnoy considered as the result of
degradation (pp. 316, 317), inasmuch as it appeared only in old sperm
mother-cells after spermatozoa had become numerous in the testis.
This accords with the earlier view that direct division is concomitant
with senescence of the nuclei, based especially upon nuclear division in
plants (Schmitz, ’79, Johow, ’81). I have regarded this as a possible
explanation of the occurrence of amitotie division in the embryonal
envelopes of the scorpion, for these tissues are temporary structures
which obviously are near the end of their functional activity. This
explanation, however, will not fit all cases; for instance, the occurrence
of amitosis in embryonic cells, and its prevalence in the testicular cells
of some Isopods, already mentioned.

The hypothesis advanced by Chun seems to throw light upon many
of the cases of amitotic division which are referable to a sort of bud-
ding or branching of the nucleus, carried to such a point that the
buds or branches become constricted off as separate nuclear elements.
These cases are, of course, not to be confounded with a disintegration
of the nucleus, such as takes place in the macronucleus of Infusoria
after conjugation, and sometimes in the degeneration of tissues. The
distribution or extension of nuclear substance in the cytoplasm, whereby
the surface of the nucleus is increased, is an event of frequent occur-
rence. It is seen in the many forms of lobed nuclei, such as those of
the ovarian capsules of Amphibia (see Flemming, ’82), and in those of
leucocytes ; in hollow or perforated nuclei (giant cells); in branched
nuclei (spinning glands and Malpighian vessels of Lepidoptera) ; and in
the band-shaped and moniliform nuclei of many Infusoria. These pecu-
liar shapes are evidently produced by the activity of the nucleus itself,
probably correlated with a special function of the cytoplasm. From
the deeply incised lobation or band-shape of such nuclei it is an easy
step to the formation of separate smaller nuclei by the deepening of a
constriction already formed. Such daughter nuclei will as a rule be
irregular in shape and unequal in size ; but if their production subserves
a definite and important function, we should expect that in some cases
their formation would become a regular process, governed by definite
laws. It is possible that the more symmetrical kinds of direct division

154 BULLETIN OF THE

are to be explained in this way, and such an explanation seems to apply
well, as suggested on a preceding page, in the case of the scorpion’s
serosa. Division of the cell does not follow as a rule, and upon this fact
Chun lays stress. But, so far as we know, there is nothing to exclude
the subsequent occurrence of cell division, and it is even probable that
cell division is induced by the presence of more than one nucleus. This
I take to be the case in the scorpion’s serosa, where I believe the division
of the cell is due in part to the dicentricity set up in the cytoplasm by
the division of the nucleus.

The study of nuclear division among the Protozoa seems likely to
throw much light upon the relations of amitosis to mitosis, for there can
be little doubt but that this group presents the most primitive types of
nuclear division. So far as known, the very lowest forms of animal cells
(Amcbe) always divide by the direct method, as the study of Ameba
polypodia by F. E. Schulze (75), and of Pelomyxa villosa, Amceba secunda,
and A. proteus by Gruber (’83 and 85), has shown. The division of the
nucleus of Ameba proteus takes place by a sharp equatorial cleft, passing
through the large, centrally placed nucleolus, and dividing that and the
peripheral zone of chromatin into two exactly equal halves, which after-
wards move apart. This is regarded by Gruber (’83, p. 385) as a simple
type of karyokinesis, because an exact division of the chromatin is accom-
plished. No kinetic change of the chromatic substance is necessary to
bring this about, hence none occurs. It seems to me that the absence
of centrosomes and a spindle effectually separates this type of division
from true karyokinesis, and until these are discovered, the nuclear di-
vision of Ameba proteus must be relegated to amitosis. The presence of
so perfect a type of karyokinesis as that found in Huglypha alveolata,
worked out so completely by Schewiakoff (’88), is strong evidence against
the hypothesis that karyokinesis was gradually evolved from direct di-
vision. For here, among the lowest forms of animal life, we have nuclei
dividing both by a simple constriction, and by the most highly developed
kinetic changes.

Nuclear division among the Infusoria is of special interest, for we
regularly find in the same individual nuclei very different in structure
and function, — macro- and micronuclei. The former divide directly,
the latter hy karyokinesis. Apparent exceptions are seen in Spirochona
gemmipara, where, according to R. Hertwig (’77) the macronucleus
divides by karyokinesis ; and in Opalina ranarum, studied most carefully
by Pfitzner (’86%). As only one kind of nucleus is found in Opalina,
it is probable, as Biitschli suggests (’88, p. 1500), that these are of

/

MUSEUM OF COMPARATIVE ZOOLOGY. 155

the micronuclear type, inasmuch as the division is in all essential re-
spects like that of micronuclei, and in the resting state the nuclei bear
no resemblance to macronuclei. The direct division of macronuclei is
often accompanied by a longitudinal arrangement of the chromatic fila-
ments, resembling that found in the scorpion’s serosa (see Figs. 6, 7, 8).
It seems to me that Carnoy is wrong in speaking of these longitudinal
filaments as a “ spindle,” for it has never been shown that they converge
to the poles of the nucleus, and frequently they can be resolved into
granules, which is never the case with spindle fibres. Their resemblance
to the spindle of karyokinesis is deceptive. From their behavior with
stains, I regard them as consisting of chromatin, and Biitschli (88,
p. 1526) speaks of this stage of the macronucleus as the “ Kniuelsta-
dium,”’ implying that the parallel filaments are chromatic threads.

Among the Vertebrates, amitosis is unusual, and where it exists kary-
okinesis is generally found to occur in cells of the same kind. It is
almost confined to cells which do not form fixed tissues, as leucocytes of
all kinds, and “giant cells,” especially those of the red marrow. It also
occurs in testicular cells of Vertebrates. In leucocytes, according to
all observers, the nuclear division takes place by constriction, and is
frequently accompanied by division of the cytoplasm (Ranvier, 775;
Flemming, ’82, p. 344; Arnold, ’87). But, as the recent work of
Fiemming (91) and others shows beyond a doubt, leucocytes also di-
vide by karyokinesis. It is difficult to say whether there is more than
a single kind of leucocyte, one dividing directly, the other indirectly,
or whether cells of the same kind divide in two different ways. In
case of giant cells, it has been shown by Arnold (84), Denys (’86),
Demarbaix (’89), and others, that division occurs both directly and by
multiple karyokinesis. Both kinds of division are followed by division
of the cytoplasm, leading to the formation of a brood of daughter cells
within the mother cell.

After going over the literature of amitosis, taking especial note of
the manner of its occurrence and distribution in the Animal Kingdom, I
have become convinced that it is not derived from mitosis, and, on the
other hand, is not the forerunner of the more complicated process. I con-
sider it another type of division altogether, which, along with karyoki-
nesis, has been transmitted from the simplest forms of life to the most
highly organized. While apparently every kind of nucleus may, at
some stage of its existence, divide by karyokinesis, many afterwards
exchange this type of division fer the simpler process. The special
conditions which evoke the exchange are very imperfectly understood,

156 BULLETIN OF THE

and no hypothesis has yet been offered that will explain all the known
instances. Some of the hypotheses that have been suggested I have
already dwelt upon at length; others, as scantiness of chromatin, and
even its entire absence in the nucleus (Léwit, 90), seem to me still more
inadequate.

One fact in favor of the independence of the two types of division is
the sudden change from mitosis to amitosis, without any visible interme-
diate stages. Phylogenetically, this is seen in the abrupt transition from
the amitotic division of Amebe to the very perfect karyokinesis of the
nearly related Huglypha. Ontogenetically, of course, the exchange is far
more abrupt. In the conjugation of Infusoria, all divisions of the micro-
nucleus are undoubtedly mitotic, while the jirst (after conjugation) and
all subsequent divisions of the macronucleus, ztself formed from modified
micronucler, are by direct division. Again, the amitosis of the blasto-
dermic nuclei of Blatta (Wheeler, ’89) is an abrupt change from the
perfect mitosis of segmentation. Other instances are the sudden change
from mitosis to amitosis in the layers of stratified epithelium, and in
the generations of spermatic cells.

Another fact in favor of my view is the almost universal distribution of
amitosis, and its occurrence in many kinds of cells with widely different
functions. It seems more reasonable to suppose that a process so widely
extended is ixherited, and exists potentially in all cells, rather than to
look upon it as independently assumed in a multitude of special cases.
The latter supposition is opposed to all we know of the transmission of
fundamental characters.

While it is evident that both mitosis and amitosis appeared at a very
early period of organic life, it is impossible to say which appeared first.
But, on a priort grounds, we may conclude that the simpler type pre-
ceded the more complex.

CaMBRIDGE, September 28, 1891.

It was not until this paper had gone to press that I had access
to the recent communications on amitosis by Flemming (’91*), Léwit
(791), Verson (791), Frenzel (791), and O. vom Rath (91). In his review
of recent work on cell division, Flemming says (p. 139): ‘Es ist also
nicht nur als feststehend anzusehen, dass Amitose vorkommt, sondern
auch, dass sie in normal lebenden Geweben vorkommt, und dass sie zur

MUSEUM OF COMPARATIVE ZOOLOGY. 157

Zellenvermehrung fiihren kann.” When, however, both mitosis and
amitosis occur in the same tissue, he considers it probable that only the
former is the normal method of regeneration and of growth.

The brief papers by Lowit, Verson, and Frenzel are replies to Ziegler’s
(91) recent article on amitosis, and contain little that is new. Verson
describes briefly the early stages in the spermatogenesis of the silkworm
(Bombyx morz). He states that the spermatocytes originate from a
single large nucleus (‘‘ Riesenkern”), which divides repeatedly and
unequally by amitosis. The small daughter nuclei thus produced divide
by mitosis, and at length form the spermatocytes. Frenzel adduces
instances of amitosis in the intestinal epithelium of Crustacea and
Insects which do not fall within Ziegler’s generalizations.

Vom Rath’s paper is a valuable contribution to our scanty knowledge
of the occurrence of amitosis in spermatogenesis. He shows very con-
celusively that, in the testis of the crayfish, amitosis does not occur in
the generations of sperm-forming cells, but only in abortive nuclei
(‘‘ Randkerne’’), which soon degenerate into an amorphous mass. If
such a fate could be established for all amitotically dividing nuclei in
the testes of animals, it would be much easier to form a logical estimate
of amitosis.

158 BULLETIN OF THE

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EXPLANATION OF FIGURES.

All figures are from drawings made with the aid of an Abbé camera.

Jounson. — Nuclear Division.

PLATE I.

Fig. 1. Five cells of the serosa, two of them covered by the amnion, which is
omitted from the rest of the figure for the sake of clearness. am.,
amnion; sr., serosa. x 150.

Fig. 2. Section through the embryonal membranes and ovarian capsule. The
fibrous appearance of the ovarian capsule is due to the presence of
muscle fibres and connective tissue. The boundary line between
amnion and serosa is visible only in the vicinity of the amniotic
nuclei. e’th. fol., epithelium of ovarian capsule (when the plates were
engraved [I still took this to be the follicular epithelium, hence the
error in the abbreviation) ; nl. fol., nucleus of capsular epithelium ;
nl. sr.. nucleus of serosa; nl. am., nucleus of amnion. XX 680.

Figs. 3-15 are all from the serosa.

Fig. 3. Very small, binucleate cell. x 130.

Figs. 4-10. Nuclei at different stages of division. vac., vacuole; x, new nuclear
wall within the old one. > 580.

Fig. 11. Two cells produced by division of a binucleate cell. x 130.

Fig. 12. Cell from the serosa of a young embryo, with dividing nucleus; the axis
of elongation corresponds with the short axis of the cell. X 130.

Fig. 13. Cell from serosa of a young embryo, with nucleus unequally divided and
daughter nuclei eccentric in position. X 130.

BE Meisel lith.Boston.

#

TEN OZ RUM HON py 9 RIEL SUT NA Re em OR a

Jounson. — Nuclear Division.

PLATE II.

Fig. 14. Piece of the serosa from an advanced embryo, with four adjacent tri-
nucleate cells (1, 2, 3, 4); nuclei of cell a and the large cell farthest
to left have undergone degeneration. X 90.

Fig. 15. Three cells of the serosa from an old embryo to show recession of daugh-
ter nuclei towards the ends of the cells. > 90.

Figs. 16-20 are from the amnion.

Figs. 16-19. Stages in the division of amniotic nuclei. In Figure 18 three stages
are shown, a, b,c. > 800.

Fig. 20. Two amniotic cells, apparently formed by recent division. X 375.

Figs. 21-26 are from the capsular epithelium.

Figs. 21-23. Cells showing successive stages of nuclear division. X 800.

Figs. 24-26. Cells to show the degeneration of nuclei. In Figure 24 the nuclei
a.e but slightly differentiated; in Figure 25 the pale nucleus has
become much larger and very faint; in Figtre 26 it has disappeared
altogether. X 800.

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Jounson. — Nuclear Division

PLATE III.

Figs. 27-34 are all from the serosa.

Fig. 27. A cell undergoing division by formation of a cell plate. The daughter
nuclei are still united by a connecting thread. The dotted line on the
left indicates the edge of the fragment of membrane in which this
cell occurs. From the serosa of an advanced embryo. X 304.

Fig. 28. A cell divided by constriction, without the formation of a cell plate. The
nuclei have undergone degeneration. From the serosa of an advanced
embryo. X 150.

Fig. 29. A cell, the nucleus of which has undergone tripartite division. From an
old serosa. XX 150.

Fig. 30. Nucleus of the same, more highly magnified. The chromatin is grouped
in granular masses. Two of the daughter nuclei are still united by
strands of the nuclear membrane. X 630.

Figs. 31-82. Constricted nuclei from a young serosa. One of the daughter nuclei
of each is larger than its mate, and has itself become elongated and
constricted. x 304.

Fig. 83. Quadrinucleate cell. The upper of the two original nuclei has divided
in a longitudinal, the lower in a transverse plane. Nucleus a still
shows a remnant of the connecting thread, and nucleus 6 retains the
conical form it had in division. Both nuclei have rotated 90° from
the plane of elongation. X 304.

Fig. 34. Cell from the serosa of a far advanced embryo. The nuclei have under-
gone extreme degeneration. Each nucleus is surrounded by a bright
ring, outside of which is a broad zone of a radiate structure, more
stainable than the rest of the cytoplasm. % 160.

ee
eee

B Meisel, lith.Boston.

NucLEsAR DMsIon.

EP. del

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Bulletin of the Museum of Comparative Zoology

AT HARVARD COLLEGE.

W792 == Vou, XXII. No. 4.

a
—

A FOURTH SUPPLEMENT TO THE FIFTH VOLUME OF THE TER-
_ RESTRIAL AIR- BREATHING MOLLUSKS OF THE UNITED
_ S$TATES AND ADJACENT TERRITORIES.

w > =

as By W. G. BInney.

WitH Four PLATES.

CAMBRIDGE, U.S.A:
PRINTED FOR THE MUSEUM.
JANUARY, 1892.

Bulletin of the Museum of Comparative Zoology
AT HARVARD COLLEGE.
Vou. XXII. No. 4.

A FOURTH SUPPLEMENT TO THE FIFTH VOLUME OF THE TER-
RESTRIAL AIR-BREATHING MOLLUSKS OF THE UNITED
STATES AND ADJACENT TERRITORIES.

By W. G. BINNEY.

WitH Four PLATES.

CAMBRIDGE, U.S. A:
PRINTED FOR THE MUSEUM.

JANUARY, 1892.

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No. 4.— A Fourth Supplement to the Fifth Volume of the Terres-
trial Avr-Breathing Mollusks of the United States and Adjacent
Territories. By W. G. Binney.t

THE following pages are believed to contain all that has been added
to our knowledge of the subject prior to date.

Students are requested to note that in the Third Supplement, p. 214,
- the figures of Arionta Diabloensis and Bridgesi are reversed. On p. 225,
Explanation of Plate VII., the references E and F are reversed: on
p- 226, Explanation of Plate XI., Figures D and G are reversed.

Buruineton, New Jersey, July 1, 1891.

Glandina decussata, Desu.

Plate I. Fig 4.

Under the name of decussata, specimens are found in most collections which
can hardly be referred to that species. I have figured one of them, and its
dentition has already been described and figured in my Third Supplement.
The shell is readily recognized by its more cylindrical form. Should it prove
distinct from decussata, I would suggest for it the specific name of Singleyana.
I received it from Bexar County, Texas, collected by Mr. Wetherby.

Selenites Vancouverensis, Lea, var Keepi, Hemputtt.

Plate II. Fig. 5.

Shell umbilicated, greatly depressed, thin, smooth, shining, transparent, scarcely
marked by the delicate wrinkles; very light horn-color; whorls over four, some-
what flattened above and beneath, and scarcely descending at the aperture ; spire

? The Terrestrial Air-Breathing Mollusks of the United States and the Adjacent
Territories of North America, described and illustrated by Amos Binney. Edited
by A. A. Gould. Boston, Little and Brown, Vols. I, II., 1851; Vol. III, 1857.
Vol. IV., by W. G. Binney, New York, B. Westermann, 1859 (from Boston Journ.
Nat. Hist.). Vol. V., forming Bull. Mus. Comp. Zodl., Vol. IV., 1878. Supplement
to same, in same, Vol. IX. No. 8, 1883. Second Supplement, in same, Vol. XIII.
No. 2, 1886. Third Supplement, in same, Vol. XIX. No. 4, May, 1890.

VOL. XXII. — NO. 4.

164 BULLETIN OF THE

flat, not rising above the body whorl; suture well impressed ; umbilicus moderately
large, exhibiting most of the volutions; aperture transversely subcircular, wider
than high; lip simple, thickened, sinuous above, very slightly reflected at the base,
ends scarcely approached. Width ; inch, height #4; inch.

Hills near Oakland, California. One specimen only.

This rare and interesting little shell I collected some years ago. It is a perfect
miniature form, in every respect, of S. Vancouverensis. I regard it as an extremely
small variety of that so called species. It is about the size of the variety of
S. Duranti, lately described as S. celatus, Mazyck, but differs very materially in form,
sculptnre, and the general texture of the shell. It differs from var. Catalinensis in
being more robust, larger, and has a smaller umbilicus. I dedicate this pretty little
shell to Prof. Josiah Keep, of Mills College, California, who has done so much
through his interesting little book to stimulate the study of West Coast shells.

The above is Mr. Hemphill’s description, from “The Nautilus,” Vol. IV.
p. 42, 1890. My figure is drawn from an authentic specimen.

Selenites Vancouverensis, var. hybridus, Hemrui1t.

Shell broadly umbilicated, depressed, slightly convex above, surface shining,
polished, of a dark yellowish green color, lines of growth coarse, rib-like and regu-
lar on the spire, finer and more irregular on the body whorl, crossed by fine revolv-
ing lines that become fainter on the last whorl, suture well impressed ; aperture
rounded, broader than high, greatly indented above; lip simple, very little reflected
below at its junction with the columella, very sinuous above, its terminations joined
by a very thin callus. Height § inch, breadth 1 inch.

Astoria, Oregon.

In the strong rib-like sculpturing of the spire, depressed form, and sinuous lip, it
resembles sportellus. In its greater diameter, dark greenish color, and the absence
of the decussating sculpture on the last whorl, it approaches Vancouverensis.

All our American Selenites commence life with a finely granulated shell. When
they have attained about two whorls, the strie begin to appear, and increase in
strength as the shell increases in size.

It is well known that all shell-bearing mollusks construct their shells m obedi-
ence to the laws of their constitutional characteristics and the environment, among
which I include affinity of matter and mechanical skill, the latter a faculty pos-
sessed to a greater or less degree by all animals. Some individuals in a colony of
shells display greater mechanical skill than others, or possess stronger mitative
powers, and closely follow the lines and styles of their forefathers, strictly attend-
ing to the details of sculpturing, not omitting a rib or line. Other individuals of
the same colony, not having this imitative faculty so strongly developed, may
change or vary the form of the shell by constructing it with more convex whorls,
generally resulting in a narrower or more elevated shell; or they may flatten the
whorls, resulting in a broader and depressed form. Some modification of the um-
bilicus generally follows the change in the form of the shell. In both cases the
sculpturing may be what we call characteristic of the’ species, or may be more or
less modified by the omission of one, two, or more ribs, or the ribs may be more

MUSEUM OF COMPARATIVE ZOOLOGY. 165

irregular in shape. A few lines may also be dropped, perhaps some added, or the
entire surface may be modified in obedience to the laws of the mechanical skill
possessed by the individual, and the affinity of matter secreted by the animal, for
the purpose of constructing the shell. An examination of a large number of
Selenites concarus, and of our West Coast forms, convinces one that the entire group
of American Selenites is the offspring of a single common type.

The above is Mr. Hemphill’s description, from ‘‘ The Nautilus,” Vol. IV.
p. 42, 1890.

Selenites Duranti, var. Catalinensis, Hemruitt.

Plate Il. Fig. 3.

_. I figure an authentic specimen. See Third Suppl., p. 221.

Selenites Vancouverensis, var. transfuga, Hempuitt.

Shell very much depressed, planulate, broadly umbilicated, of a dirty white
color; whorls 34 or 4, flattened above, more rounded beneath, with regular strong
rib-like striz; suture well impressed, becoming deeper and channel-like as it ap-
proaches the aperture; aperture hardly oblique, slightly flattened above, with a
tendency to a corresponding depression below ; lip simple, roundly thickened inter-
nally, its terminations approaching, forming in some specimens a short columellar
lip, joined by a heavy raised callus in very adult specimens. Height 4; inch,
greatest diameter ;%, lesser 7% inch.

San Diego, California, to Todos Santos Bay, Lower California.

This is the small flat shell that has been distributed as a variety of sportella, and
also as a variety of Voyanus. I find, however, on comparing it with the typical
Voyanus collected by me last fall, that it is quite a different shell. The ribs are
closer and finer than either sportellus or Voyanus, the umbilicus is much larger,
and it is a very much more depressed shell. I consider it, however, a deserter from
the Northern forms, and name it accordingly. It is a much larger and a more
globose form than simplilabris of Ansey.

The above is Mr. Hemphill’s description.

Selenites Vancouverensis, Lza.

The only differences that I can detect between this shell and Selenites concava,
Say, are these. The umbilicus in the California shells is a little more contracted, the
color is a shade darker, the striz are a little closer, stronger, and more regular, and
the body whorl is a little more flattened at the aperture. Height § inch, breadth
4 inch.

Sonoma Co. to Santa Cruz Co., California.

The above is Mr. Hemphill’s description of what he calls S. concavus, var.
_ occidentalis.

166 BULLETIN OF THE

Selenites Vancouverenis, var. tenuis, HemMPuHILt.

Shell broadly umbilicated, depressed, nearly planulate ; of a dirty greenish brown
color; whorls 5, flattened above, more rounded beneath, the last expanding later-
ally as it approaches the aperture, and crowded with fine oblique strie ; suture well
impressed ; aperture rounded, slightly flattened above; peristome simple, hardly
reflected below. Height $ inch, breadth ;% inch.

Napa Co., California.

The small size, nearly planulate form, and thin, lean body whorl as it emerges
from the aperture, will serve to distinguish this shell from the other forms of
concavus found on the West Coast.

The above is Mr. Hemphill’s description. He refers ali these varieties to
concavus, but I use the specific name Vancowverensis for all Pacific Region forms.

Limax Hemphilli.

Plate III. Fig. 1.

Length (contracted) 19 mm. Mantle long, 9mm. End of mantle to end of
body 9mm. Foot wide 2mm. Median tract of foot gray, lateral tracts brown.
Median area of foot rather wider than either lateral area. Mantle free an-
teriorly as far as respiratory orifice. Body tapering posteriorly, not carinate.
Mantle somewhat granulose, not concentrically striate. Color dark brown,
obscurely marbled with gray ; sides anteriorly grayish and paler.

Limax Hemphilli, W.G Brxney, 3d Suppl. T. M. V., p. 205, Plate VIII. Fig. E ;
Plate I. Fig. 18; Plate II. Fig. 3 (1890).

A species of the Pacific Province, having been found from British Columbia
to San Tomas River, Lower California, by Mr. Henry Hemphill, in whose
honor it is named.

The general outward appearance of this species resembles that of campestris,
but every specimen examined by me from numerous localities had a peculiarity
in its lingual dentition which seems to me of specific value, — the presence of
an inner cutting point to the lateral teeth, very much the same as is found in
agrestis. The anatomy of this species is specifically distinct from agrestis in
wanting the trifurcate penis sac of the latter, even did its distribution not
preclude its being a form of agrestis. I have ventured therefore on giving it a
specific name.

The penis sac is large, long, gradually tapering to the apex ; the genital
bladder is globular, on a short, stout duct.

I figure on the plate a variety from San Tomas River, Lower California,
called pictus by Mr. Cockerell. Its body is pale, reticulated with gray spots;
mantle with black or gray spots. Resembling L. Berendti, Strebel, from
Guatemala.

For lingual dentition, etc., see Third Supplement.

MUSEUM OF COMPARATIVE ZOOLOGY. 167

Zonites Shepardi, Hemputtt.

Shell umbilicated, very small, depressed ; whorls 3 or 34, shining, transparent,
smooth, somewhat flattened; spire scarcely elevated above the body whorl; aper-
ture oblique, oval; peristome simple, acute, its ends hardly approaching; suture
well impressed; umbilicus pervious, and moderately large for so small a shell.
Great diameter,2 mm. Height, 1 mm.

Santa Catalina Island, California.

This little shell belongs to the planulate forms, and somewhat resembles a minute
Z. Whitneyi.

I dedicate it to Miss Ida Shepard in recognition of her active services among the
mollusks of Long Beach, Cal., where she resides.

The above is Mr. Hemphill’s description.

Zonites Lawe.

Shell small, umbilicated, globose, flatter below, shining, light horn-colored,
marked with coarse wrinkles of growth; spire rounded; whorls 8, gradually
increasing, slightly convex, the last excavated below around the umbilicus ;
aperture oblique, rounded; peristome simple, acute, thickened with callus
within. Greater diameter 9 mm., lesser 7 mm.; height 4 mm.

Zonites placentula, part, W. G. Binney, formerly, Terr. Moll. U.S. V., p. 124, Fig.
44; Plate III. Fig. L (dentition).

Zonites Lawi, W. G. Binney, Suppl. to Vol. V. p. 142; Plate II. Fig. E (also,
Ann. N. Y. Ac. Sci., Vol. L, Plate XV. Fig. E, as undetermined).

Mountains of Tennessee (Miss Law); a species of the Cumberland Subregion.

Readily distinguished from placentula by its larger size, higher rounded spire,
greater number of whorls, and more widely excavated umbilical region.

Jaw as nsual in the genus.

Lingual membrane (Vol. V. Plate III. Fig. L, as placentula) with 25-1-25
teeth; three laterals and one transition tooth.

Zonites Caroliniensis, Cockere.t.

. Plate III. Fig. 7.

Among the specimens of Zonites sculptilis collected in the mountains of
North Carolina are many which differ from the type widely enough to be
considered a distinct species. Mr. Cockerell suggests for it the name Caro-
linensis, thus describing it :—

This species differs from sculptilis in its fewer whorls, straighter columellar
margin, less junate aperture, fewer radiating stria, and other points. It is figured
as sculptilis in Manual of American Land Shells, Fig. 281.

168 BULLETIN OF THE

Zonites sculptilis.
Plate III. Fig. 9.

For the sake of comparison with the preceeding species, I have given other
figures here of the true Z. sculptilis.

Zonites Simpsoni, Pitssry.

Plate I. Fig. 8,

I give an enlarged figure of an authentic individual of this species. For
the description see Third Suppl., p. 218.

Zonites Diegoensis, HEmMpPHItt.

Plate Ill. Fig. 2.

Shell minute, umbilicated, thin, light horn-colored, with delicate incremental
strie, globose; whorls 34, convex; base swollen; suture deep; umbilicus broad ;
aperture narrow, rounded ; peristome thin, acute, its ends approximated, the inner
one slightly reflected. Greater diameter 3} mm., lesser 14; height 12 mm.

Near Julian City, San Diego Co., California. On Cuyamaca Mountain, 4,500
feet elevation.

The above is Hemphill’s description. My figure is drawn from an authentic
specimen.

Zonites cuspidatus, Lewis.

Vol. V., Fig. in text; Suppl., Plate II. Fig. C.

Shell imperforate, small, slightly convex above, flattened below ; light horn
color, shining; whorls 6, gradually increasing in size, with wrinkles of growth,
the last not descending at the aperture; peristome thin, acute; aperture
rounded, bearing within behind the peristome a white callus, on which is
one subcentral and a second basal, erect, recurved tooth-like process, sepa-
rated by a rounded sinus; base often blackish, showing the white callus
prominently. Greater diameter 8 mm., lesser 6; height 4¢°mm.

Zonites cerinoideus, var. cuspidatus, Lewts, Proc. Phila. Ac. Nat. Sci., 1875, p. 334.
Zonites cuspidatus, W. G. Binney, Ann. N. Y. Ac. Nat. Sci., Vol. I. p. 359, Plate
XV. Fig. C; Suppl. to Terr. Moll. V., Plate II. Fig. C.

Mountains of Tennessee and North Carolina: a species of the Cumberland
Subregion.

The tooth-like processes within the aperture, strongly curved towards each
other, form an arched space.

MUSEUM OF COMPARATIVE ZOOLOGY. 169

Miss Law thus wrote from Philadelphia, Tenn., of this species: “ Unlike
gularis, it seems to be a rare shell, and I find it only by scraping off the sur-
face of the ground in the vicinity of damp mossy rocks. Its habits are more
like placentula than gularis. I never mistake one for a gularis, even before
picking it up; the thickened yellow splotch near the lip, and the thinner spot
behind, showing the dark animal through it, as well as its more globular form,
particularly on the base, make it look very different when alive.”

Zonites macilentus, SHutTTL.
Plate III. Fig. 3.

The individuals of this group are very often difficult to identify, on account
of the blending of their specific characters. The typical macilentus is distin-
guished by a very wide umbilicus and a single revolving lamina starting from
near the basal termination of the peristome. The figure of macilentus in Vol-
ume V. shows a second revolving lamina and a much smaller umbilicus. I
give here another figure of what appears to me to be the shell described as
macilentus. How constant are the characters of the species can be shown only
by a large suite of individuals.

Tebennophorus Hemphilli.

Plate III. Fig. 4.

I give a figure of the jaw already described by me.

Patula strigosa, Goutp, var. jugalis, Hempuri.

Shell umbilicated, depressed with numerous prominent oblique strie; spire very
moderately elevated or depressed; whorls 53, somewhat flattened above, but more
convex beneath, the last falling in front, with two dark revolving bands, one at the
periphery and the other above; the body whorl subcarinated at its beginning, but
more rounded as it approaches the aperture; suture well impressed; color ashy
white, with occasional horn-colored stains; umbilicus large, pervious, showing the
volutions; aperture oblique, ovate, but in very depressed specimens the aperture
is at right angles with the axis of the shell; peristome simple, thickened, its ter-
minations approaching and joined by a thick heavy callus, making the peristome
in very adult specimens continuous. Height of the largest specimens 4 inch,

breadth 1 inch. Height of the smallest specimens 3% inch, breadth 44 inch.

Patula strigosa, var. jugalis, HEMPHILL, The Nautilus, 1890, p. 134, in Binney’s
3d Suppl., p. 215, figure.

Banks of Salmon River, Idaho.

This is another interesting form of the very variable strigosa. It inhabits stone
piles, and other places where it can find shelter and protection against the fatal
rays of the summer’s sun, close along the banks of the river. It is interesting on

170 BULLETIN OF THE

account of its very depressed form and the ovate form of the aperture, the heavy
callus joining or “ yoking”’ together the extremities of the peristome.

The above is Hemphill’s description.

The figure in the Third Supplement is drawn from an authentic specimen.

Patula strigosa, GouLp, var. intersum, Hempuitt.

Shell umbilicated, sublenticular, depressed, thin, dark horn-color, more or less
stained with darker chestnut. Whorls 5} or 6, somewhat flattened above, more
convex beneath, obtusely carinated at the periphery, and bearing numerous coarse
oblique rib-like strie, and two dark revolving bands; suture well impressed; um-
bilicus large, pervious; aperture oblique, subangulated ; peristome simple, thick-
ened, its terminations joined by a thick callus. Height of the largest specimen 4
inch, breadth inch. Height of the smallest specimen ~; inch, breadth 7% inch.

Patula strigosa, var. intersum, HEMPHILL, The Nautilus, 1890, p. 185.

Bluffs along the banks of Little Salmon River, Idaho.

This shell inhabits stone piles at the foot of a steep bluff back some distance
from the river. It seems to be quite rare, as I found but few specimens during
the two or three days of my stay in its vicinity, and many of them were dead. I
regard it as one of the most interesting shells found by me during the season, for
it combines the depressed angulated or keeled forms of the Haydeni side of the
series with the sculpturing of /dahoensis, two shells representing opposite charac-
ters in every respect. It thus becomes the companion of Wahsatchensis, a beautiful
shell, combining the same characters, but much more developed, and connected
with the large elevated forms. Var. interswm fills the opposite office, by uniting
these characters with the small depressed forms. Taken as a whole, this series of
shells, as now completed, seems to me to offer the best guide or key to the study
of species that the student can have. Every known external character belonging
to the genus Helix is so gradually modified and blended with opposite characters,
that, if one had the moulding or making of the many and various intermediate
forms, he could scarcely make the series more complete than Nature has done
herself.

The above is Hemphill’s description.

Patula strigosa, Goutp, var. globulosa, CocKERELL.

Small, globose, dark above periphery, with two bands, transverse grooved striz
rather well marked. Diameter 11}, alt.84mm. Black Lake Creek, Summit Co.
The specimen seems immature, but is remarkable as being the only form I have
seen in Colorado that is nearer to strigosa than Cooperi. It is doubtless allied to
var. Gouldi, Hemphill. (Cockerell.)

Patula strigosa, var. globulosa, COCKERELL, The Nautilus, 1890, p. 102.
The above is Cockerell’s description.

The above varieties of Patula strigosa are transversely ribbed. The following
are smooth or striate

MUSEUM OF COMPARATIVE ZOOLOGY. 7

Patula strigosa, Goutp, var. Buttoni, Hempuxitt.
Plate I. Figs. 2 and 10.

I figure the typical and the toothed forms. See 3d Suppl., p. 220.

Patula strigosa, Goutp, var. albofasciata, HempPuitt.

Plate IV. Fig. 9.

Shell globose, elevated or depressed; whorls six, convex, with a broad white
band at the periphery, which shows just above the suture on two or three whorls
of the spire as it passes towards the summit or apex, separating two variable
chestnut-colored zones; the upper one in some specimens is often very dark, in
“others very light passing into horn-color, and broken into blotches, stains, or
irregular lines, which pass up a few whorls of the spire and blend with the
horn-colored summit; the lower zone spreads towards the umbilicus in irregular
stains, often beautifully clouding the base of the shell, or is often broken into
irregular revolving lines, and other varied patterns of coloring; strie rib-like,
quite coarse in some specimens, in others finer and closely set together; aperture
circular, ovate, and occasionally pupzeform; peristome simple, thickened, sub-
reflected at its junction with the columella, and partially covering the umbilicus,
the ends approached and often joined by a callus, the peristome sometimes bearing
a tooth-like process; umbilicus deep, moderately large, narrower in elevated and
broader in depressed specimens; suture well defined. Greater diameter of the
largest specimen 17 mm., height, 12 mm.; greater diameter of the smallest 12
mm., height 7 mm.; with all the intermediate sizes.

Box Elder Co., Utah.

Among leaves, brush, and grass, on limestone rock. Altitude, about 4,600 feet
above the sea.

This variety of strigosa is so very variable in all its characters I find it quite
difficult to draw a description that will cover all the individuals which I include in
it. I have given the measurements of the largest and smallest specimens, but there
are all the intermediates between those figures.

The above is Mr. Hemphill’s description. An authentic individual is figured
on the plate.

Patula strigosa, Gout, var. subcarinata, Heupuitt.

Among the shells recently collected by Mr. Hemphill at Old Mission, Coeur
d’Alene, Idaho, was a marked variety of this species, for which Mr. Hemphill
suggests the name subcarinata. The specimens vary greatly in elevation of
the spire, and in the number and disposition of the revolving bands, often
quite wanting, as in the specimen figured in the Third Supplement. All have
a very heavy shell, the body whorl of which has an obsolete carina which
is well marked at the aperture, modifying the peristome very decidedly. See
_ the figure.

2 BULLETIN OF THE

In examining the genitalia I find the base of the duct of the genital bladder
greatly swollen along a fifth of the total length of the duct.
Mr. Hemphill (The Nautilus, 1890, p. 133) thus describes it : —

The shell in general form resembles a large, coarse elevated or depressed Cooperi-
It has six whorls, well rounded above and beneath, and subcarinated at the periph-
ery. The body whorl has two revolving dark bands, one above and the other
below the periphery ; sometimes the upper band spreads over the shell to the su-
ture, forming a dark chestnut zone that fades out as it passes toward the apex.
The peristome is simple, thickened, its terminations joined by a callus; aperture
obliquely subangulate; the suture is well impressed. Height of the largest speci-
men 1 inch, breadth 14 inches; height of the smallest specimen ? inch, breadth
1 inch.

Rathdrum, Idaho.

An authentic specimen is figured in the Third Supplement.

Patula strigosa, Goutp, var. bicolor, HEMPHILL.
Plate IV. Fig. 7.

This shell is a colored variety of the last. It may be characterized as being of
a general dark horn-color mingled with dirty white; there are occasional zones of
dark horn-color above and fine dark lines beneath, but no defined bands. In some
of the specimens the light color prevails, in others the horn-color spreads over —
the shell in irregular patches. Height 7 inch, breadth 1} inches.
Rathdrum, Idaho. (Hemphill.)

Patula strigosa, var. bicolor, HEMPHILL, The Nautilus, 1890, p. 133.

An authentic specimen is figured.

Patula strigosa, Goutp, var. lactea, Hemputtt.

Plate [V. Fig. 8.

This is a beautiful clear milk-white shell, with 5} whorls, subcarinated at the
periphery. In the elevated forms the aperture is nearly circular, as broad as high;
but in the depressed forms the aperture is broader than high, obliquely suban-
gulate. The lip is simple, thickened, its terminations joined by a heavy callus, —
the thickening of the lip and callus is a shade darker than the body of the shell.
Heicht of the largest specimen 1 inch, breadth 1} inches.

Rathdrum, Idaho.

The above varieties represent a colony of the largest specimens of the strigosa
group that I have collected. They are an important and very interesting addition
to the series, and serve to confirm my previous views on the relationship of what I
call the strigosa group. This colony inhabits open places in the dense pine forests
of the mountains, overgrown with deciduous bushes. They hibernate among

MUSEUM OF COMPARATIVE ZOOLOGY. 173

leaves, brush, and roots of trees, and in protected and secure places, generally
on the north slopes of the mountains. (Hemphill.)

Patula strigosa, var. lactea, Hempuiti, The Nautilus, 1890, p. 134.

An authentic specimen is figured.

Patula strigosa, var. Utahensis, HempPui1t.

For locality, see 2d Supplment, p. 30. This is a rough, coarse, carinated variety,
figured 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. (2d Suppl., p. 33.)

Patula strigosa, Goutp, var. depressa, CocKERELL.

Shell flattish, maximum diameter 214, altitude 123 mm. Specimens of this
variety were sent to me by Miss A. Eastwood, who found them in a cafion near
Durango, Colorado. The same variety is figured by Binney, Man. Amer. Land
Shells (1885), p. 166, Fig. 158. (Cockerell.)

Patula strigosa, var. depressa, COCKERELL, The Nautilus, 1890, p. 102.

Patula strigosa, var. albida, Hemputtt.

Shell broadly umbilicated, greatly depressed, white, tinged with horn-color; sur-
face covered with fine oblique striz and fine microscopic revolving lines; whorls
6, convex, the last falling in front; spire very little elevated, apex obtuse, aperture
oblique, nearly round; peristome simple, thickened, subreflected at the columella,
its terminations approaching, joined by a thin callus. Height 3 inch, greatest di-
ameter 1 inch, lesser # inch.

Near Logan, Utah.

Patula strigosa, var. albida, Hemputty, The Nautilus, IV. p. 17, June, 1890.
The above is Hemphill’s description.

Patula strigosa, var. parma, Hemeutzt.

Shell broadly umbilicated, greatly depressed, of a dark dirty horn-color, surface
somewhat rough, covered with coarse irregular striz, and microscopic revolving
lines ; whorls 53 or 6, subcarinated throughout, somewhat flattened above, rounded
beneath, and striped with two chestnut-colored bands, one above and the other
just at the periphery; spire very little elevated, umbilicus moderately large and
deep; aperture ovately round, oblique; peristome simple, subreflected, its termi-
nations approaching and joined by a thin callus. Height 4 inch, breadth 1 inch.

Near Spokane Falls, Washington.

Patula strigosa, var. parma, Hemputtt, The Nautilus, IV. p. 17, June, 1890.

The above is Hemphill’s description.

174 BULLETIN OF THE

Patula strigosa, var. rugosa, HEMPHILL.

Shell umbilicated, elevated or globosely depressed, of a dull brown ash-color;
surface rough, covered with coarse irregular oblique stri#, and microscopic re-
volving lines; whorls 5, convex, with or without one or two narrow faint revolv-
ing bands. In most of the specimens the bands are obsolete; spire elevated,
obtusely conical; suture well impressed; umbilicus large, deep; aperture nearly
round; peristome simple, thickened, its terminations approaching and joined by
a thin callus. Height of the largest specimen ? inch, greatest diameter 1 inch.
Height of the smallest specimen 4 inch, greatest diameter } inch.

New Brigham City, Utah.

A large rough robust form, with very convex whorls. Some of the specimens
so closely resemble solitaria, Say, that one not well acquainted with both forms
would be easily deceived, and refer it to that species. In its adolescent state the
lip is very thin or easily broken, and on the surface of the adult shells these frac-
tures give it a rough and uneven appearance.

Patula strigosa, var. rugosa, HEMPHILL, The Nautilus, 1890, Vol. IV. p. 16.

The above is Hemphill’s description.

Patula strigosa, var. carnea, HempuIty.

Shell umbilicated, greatly depressed, dark horn-color, rather solid, shining, sur-
face somewhat uneven and covered with irregular oblique strize; whorls 53, con-
vex, the last faintly subcarinated in the depressed specimens, falling in front,
sometimes faintly banded, but most of the specimens are plain and without bands ;
spire subconical, apex obtuse; suture well impressed, umbilicus large; aperture
circular; peristome simple, thickened, its terminations well approached and joined
by acallus. Height § inch, greater diameter {, lesser $ inch.

Near Salt Lake, Utah.

Patula strigosa, var. carnea, HemPuILy, The Nautilus, Vol. IV. p. 15, June, 1890.

The above is Hemphill’s description.

Patula strigosa, var. fragilis, HemPxi..

Shell umbilicated, elevated or globosely depressed, translucent, thin, fragile,
somewhat shining, of a dark horn-color, surface covered by fine oblique stric;
whorls 5, convex, the last descending in front and striped by two dark chestnut
bands, one above and the other below the periphery ; suture well impressed ; aper-
ture oblique; peristome simple, thickened; umbilicus moderate, deep, partially
covered by the reflected peristome at the columella. Height of the largest speci-
men ;°; inch, greatest diameter § inch, lesser ? inch.

Near Franklin, Idaho, among red sandstone.

A very thin and almost transparent variety of the very variable strigosa. By its

MUSEUM OF COMPARATIVE ZOOLOGY. 175

peculiar shade, it is very evident that the animal has drawn largely from the red
sandstone for the material to build its shell.

Patula strigosa, var. fragilis, HEMPHILL, The Nautilus, Vol. IV. p. 17, June, 1890.
The above is Hemphill’s description.

Patula strigosa, var. picta, Hzmputt.

Shell umbilicated, elevated or globosely depressed, of a dirty white color, stained
more or less with chestnut ; surface somewhat rough and uneven, covered with
moderately coarse oblique strie#, and fine revolving lines; whorls 6, convex, sub-
carinated, with a broad white band at the periphery, and a dark zone of chestnut
on the upper side, extending from the peripheral band to the suture, fading out as
- it traverses the whorls of the spire; beneath, on the base of the shell, it is striped
with numerous bands that sometimes extend into the umbilicus, and also into the
aperture; spire elevated; apex obtuse; suture well impressed; umbilicus moder-
ately large and deep, broader in the depressed than in the elevated forms; aper-
ture nearly circular; lip simple, subrefiected, its terminations approaching and
joined by a thin callus. Height % inch, greatest diameter 1} inches, lesser 1 inch.

Rathdrum, Idaho.

Patula strigosa, var. picta, Hempuity, The Nautilus, Vol. IV. p. 16, June, 1890.

The above is Hemphill’s description.

Patula strigosa, var. hybrida, Hempnitu.

Shell umbilicated, depressed, white, spire horn-color, surface of the shell cov-
ered with fine oblique striz#, and widely separated revolving raised lines; whorls 5,
flattened above, rounded beneath, the last falling in front, and striped with two
faint chestnut bands; suture well impressed ; umbilicus large, showing nearly all
the volutions; aperture nearly circular; peristome simple, thickened, its termina-
tions approaching and joined by a thin callus. Height % inch, diameter # inch,
lesser 3 inch.

Near Logan, Utah.

This is an interesting shell, as it is the beginning of the forms of strigosa that
finally develop the revolving lines into prominent ribs, as seen on the surface of
var. Hayden, Gabb.

Patula strigosa, var. hybrida, HemPuity, The Nautilus, Vol. IV. p. 17, June, 1890.

The above is Hemphill’s description.

Mr. Cockerell (The Nautilus, 1890, p. 102) mentions by name say the fol-
lowing Colorado forms: —

P. strigosa Cooperi, form trifasciata, Ckll. Mesa Co.

P. strigosa, Cooperi, form confluens, Ckll. West Mountain Valley, Custer Co.;
Garfield Co.; Mesa Co.

176 BULLETIN OF THE

P. strigosa Coopert, form elevata, Ckll. Delta Co.

P. strigosa Cooperi, form major, nov. Shell with diam. 25mm. Near head
of North Mam Creek, Mesa Co., Sept. 14, 1887.

P. strigosa Coopert, var. minor, Ckll. Near Egeria, Routt Co., abundant. It
is quite a distinct local race.

Pristiloma, Ancey.

Animal as in Patula.

Shell small, imperforate, horn-color, shining, many whorled; spire de-
pressed conic; aperture sometimes armed with radiating, rather crowded,
palatal lamellee.

Northern and Arctic North America.

Types: Zonites Stearnsi and Lansingi, BLAND.
Formerly Pristina, ANCEY, and Anceyia, PILSBRY, preoc.

Jaw low, wide, slightly arcuate, ends little attenuated, blunt, with numer-
ous crowded broad ribs, denticulating either margin.

Lingual membrane with tricuspid centrals, bicuspid laterals, aculeate mar-
ginals, as in Zonites.

Separated from Microphysa by the ribbed jaw combined with the lingual
membrane of Zonites: a very unusual occurrence.

Pristina Lansingi, Bianp.

Piate III. Fig. 6.

I give a better figure of this species.

Pristiloma Stearnsi, Buanp.
Vol. V., figures in text. Suppl., Plate I. Figs. N (dentition) and O (jaw).

Shell minute, imperforate, globose conic, striate, shining, horn-colored ;
suture impressed ; whorls 7, regularly increasing, the last not descending, very
globose, swollen below, excavated closely around the imperforate umbilical
region; aperture rounded; peristome simple, acute. Greater diameter 4 mm.,
lesser 33; height 25 mm.

Zonites Stearnsi, Buanp, Ann. N. Y. Lyc., XI. 74, Figs. 1, 2 (1875).
Microphysa Stearnsi, W. G. Binney, Terr. Moll. V., figs. in text; Suppl., Plate II.
Figs. N (dentition) and O (jaw).

Astoria, Portland, Oregon ; Olympia, Washington ; Alaska. A species of
the Oregonian region.

It is larger, more.elevated, and more distinctly striated than Lansingi, with
wider, more rounded, unarmed aperture.

MUSEUM OF COMPARATIVE ZOOLOGY. aT

The jaw is of the same type as described under P. Lansingi, with over 19
ribs. (Suppl., Plate II. Fig. O.)

The peculiar lingual membrane also is the same as in that species, with four
laterals on each side of the central tooth. (Suppl., Plate I. Fig. N.)

Punctum, Morssz.

Animal as in Patula.

Shell minute, umbilicated, thin, horn-colored, depressed globose; whorls 4,
the last not descending ; spire slightly elevated ; aperture rounded ; peristome
thin, acute.

Europe and North America.

Jaw slightly arcuate, ends blunt, not acuminated, composed of numerous
‘subequal, overlapping distinct plates.

Lingual membrane as usual in the Helicide ; bases of attachment sub-
quadrate, reflection small, tricuspid in the centrals, bicuspid in the laterals,
marginals irregularly denticulated.

Distinguished by the peculiar free plates of the jaw.

There are two species of Punctum, conspectum and pygmeum.

Helicodiscus fimbriatus, Weruersy, var. salmonaceus, HempuHitt.
Plate III. Fig. 8.

I give a figure of this variety from an authentic specimen. See 3d Suppl.,
p- 189.

Anadenus, Hernemann.

Animal limaciform, subcylindrical, tapering behind ; tentacles simple; man-
tle anterior, concealing an internal shell-plate ; no longitudinal furrows above
the margin of the foot, and no caudal mucus pore ; a distinct locomotive disk ;
external respiratory and anal orifices on the right posterior margin of the
mantle; orifice of combined genital system behind and below the light eye-
peduncle. (See Plate I. Fig. 1.)

Internal shell-plate small, oval, flat, with posterior nucleus and concentric
strie. (See Plate.)

Jaw with numerous ribs. See Plate III. Fig. 5.

Lingual membrane with tricuspid centrals, bicuspid laterals, and quadrated
marginals. (See same.)

Differs from Prophysaon by its posterior respiratory orifice, by the position
of the genital orifice, and by its locomotive disk.

Himalaya Mountains ; recently found in San Diego County, California, by
Mr. Hemphill.

VOL. XXII. —NoO. 4. 12

178 BULLETIN OF THE

It will be remembered that Fischer considers Prophysaon a subgenus of
Anadenus.

The geographical distribution of Anadenus would seem to preclude its being
found in California, but to that genus only can J refer the species whose de-
scription here follows.

Anadenus Cockerelli, Hemruixu.
Plate I. Fig. 1; Plate III. Fig. 5.

Length (contracted) 133 mm. ; mantle, length 43, breadth 22 mm. End of
mantle to end of body, 8mm. Foot, breadth 2mm. Foot with the locomotive
disk, being distinctly differentiated into median and lateral tracts. Respira-
tory orifice slightly posterior on right side of mantle. Genital orifice below
right tentacle. No caudal mucus pore. Locomotive disk about half as wide
as either lateral area. Sides of foot wrinkled, but not differentiated from
lateral areas, nor specially marked, the wrinkles being a continuation of the ~
transverse grooves of the lateral areas. Mantle tuberculate-rugose, oval in
outline, bluntly rounded at either end; not grooved as in Amalia. Mantle
free in front as far as respiratory orifice. Back rather bluntly keeled its
whole length; rugz rather flattened and obscure, consisting of grooves en-
closing mostly hexagonal lozenge-shaped spaces, which are themselves rugose.
Color uniform brown-black, without markings, except some dark marbling on
the lighter sides. The portion beneath and in front of the mantle is pale, and
the head and neck have a gray tinge. Foot brown. Shell internal, thinnish,
white, oval in outline. Stomach large, swollen, broad. Liver pale ochrey.

Anadenus Cockerelli, HEMPHILL, The Nautilus, Vol. IV. No. 1, May, 1890, p. 2.
Anadenulus, CocKERELL, Ann. Mag. Nat. Hist., Oct., 1890, p. 279.

Cuyamaca Mountains of San Diego Co., California. Mr. Henry Hemphill.

Jaw low, wide, slightly arcuate, ends blunt, anterior surface with about
twenty wide, flat ribs, squarely denticulating either margin. (Plate III.
Fig. 5.)

Lingual membrane short and narrow. Teeth 20-1-20, of which eight only
on either side are laterals. Centrals tricuspid, laterals bicuspid, marginals
quadrate, bluntly bicuspid. (Same Plate.)

Prophysaon Hemphilli.

From Portland, Oregon, Mr. Hemphill brought seventy-seven individuals of
a slug which may prove a variety of P. Hemphilli. They have the tawny color
of flavum. The internal shell is so delicate, it is impossible to remove it
without breaking it. The penis sac is as in P. Hemphilli. The mantle is
sometimes smooth, sometimes tuberculate; its fuscous lateral bands are some-
times united by a transverse posterior band. Some of the individuals had the
tail constricted preparatory to excision. (See below, under Phenacarion.)

MUSEUM OF COMPARATIVE ZOOLOGY. 179

Prophysaon Andersoni, J. G. Coorrer.

3d Suppl., Plate III. Fig. 1? Plate VII. Fig. C; Plate I. Fig. 3 a Fee
Plate IX. Figs. I, J (enlarged surface).

Shield strongly granular-rugose, the respiratory orifice nearly median on its
right margin ; tail acute, with small gland; reddish gray, the body somewhat
clouded with black, the shield paler, clouded, or more usually with a dark
band on each side above the respiratory orifice, converging in an elliptic form;
a pale dorsal streak ; head uniform pale brown, tentacles darker ; foot and
often the mantle tinged with olive. Length 2.5 inches (Cooper).

_ Arion Andersoni, J. G. Cooper, Proc. Phila. Ac. Nat. Sci., Plate III. Fig. F.
Prophysaon Andersoni, J. G. Coorrer, Pr. Amer. Phil. Soc., 1879, p. 288.
Prophysaon Andersoni, W. G. Binney, Terr. Moll. V., 3d Suppl., Plate IIL Fig.

1? Pl. VII. Fig. C; Plate I. Fig. 3 (dentition); Plate IX. Figs. I, J
(surface).

A species of the Pacific Province, Straits of De Fuca to Oakland, California.

The characteristic of this species is the light dorsal band, which is not
present in P. Hemphill. It has the broad vagina, stout, short, cylindri-
cal penis sac, and genital bladder of P. Hemphilli, as well as the foliated
reticulations.

In the many living and alcoholic specimens which I have examined, I have
failed to detect any appearance of a caudal mucus pore, which Dr. Cooper is
confident of having observed, excepting in eight individuals out of thirty col-
lected by Mr. Hemphill on San Juan Island.

Many individuals examined by me are excided as described under Phena-
carton foliolatus.

Figure 1 of Plate IIT. of 3d Suppl. was drawn froma specimen received from
Dr. Cooper. It represents the true Andersoni, distinguished by a light dorsal
band, and by genitalia such as I have described for P. Hemphilli. The same
form, also received from Dr. Cooper, is drawn by Mr. Cockerell on Plate VII.
Fig. C. Mr. Cockerell has shown me that I have confounded with it another
species, which he proposes to call P. fasciatum. See next species.

Specimens collected by Mr. Hemphill at Old Mission, Coeur d’Alene, Idaho,
appear to agree with specimens of this species received from Dr. Cooper.
The jaw is low, wide, slightly arcuate, with over 12 broad, stout ribs, denticu-
lating either margin. The lingual membrane is given in Plate IL. Fig. 2, of
3d Suppl. The central and lateral teeth are slender and graceful. The latter
have, apparently, a second inner cutting point, as is found in Limax agrestis.
T have so figured it, hoping to draw attention to it, and thus settle the question
of its being there. On Plate IX. I have given enlarged views of the surface,
drawn by Mr. Arthur F. Gray. (See Explanation of Plate IX. Figs. I and J
-of 3d Suppl.)

180 BULLETIN OF THE

Prophysaon fasciatum, CocKkERELL.

Length (in alcohol) 19 mm. Mantle black, with indistinct pale subdorsal
bands, — an effect due to the excessive development of the three dark bands of
the mantle. Body with a blackish dorsal band, commencing broadly behind
mantle and tapering to tail, and blackish subdorsal bands. No pale dorsal
line. Reticulations on body squarer, smaller, more regular, and more sub-
divided than in P. Andersoni, Cooper. Penis sac tapering, slender. Testicle
large. Jawribbed. (Cockerell.)

Prophysaon fasciatum, COCKERELL, The Nautilus, 1890.
Prophysaon fasciatum, W. G. Binney, 3d Suppl. to Terr. Moll. V., p. 209, Plate
VII. Fig. A.

Coeur d’Alene Mountains, Idaho; a species of the Central Region.

This species is described by Mr. Cockerell as distinct from Andersoni, with
which I have formerly confounded it. (2d Suppl. to Vol. V., p. 42.) It has a
dark band on each side of the body, running from the mouth to the foot, and a
central dorsal dark band. To this must be referred the descriptions of animal,
dentition, jaw, and genitalia formerly published by me as of Andersone.

I am indebted to Mr. Theo. D. A. Cockerell for a figure and description of
this species. The former is given on Plate VII. Fig. A, while the latter is
given here in the words of Mr. Cockerell, whose name must consequently be
associated with it as authority.

The animal extends itself into a long, cylindrical worm-like body with ob-
tuse ends; the mantle is covered with minute tubercles.

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

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. Another membrane has 50-1-50 teeth.

Mr. Cockerell describes the penis sac as tapering; in specimens examined by
me it is cylindrical, as in Hemphill.

The internal shell is thick, easily extracted without breaking.

Phenacarion, CockEeRrEtu.!

Animal limaciform, cylindrical, blunt before, tapering behind; tentacles
simple; mantle large, anterior, pointed behind, concealing a delicate, thin,
subrudimentary calcareous shell-plate, easily fractured; no longitudinal fur-
rows along the margin of the foot; a caudal mucus pore; no distinct locomo-
tive disk; external respiratory and anal orifices on the right anterior margin

? Phenax = an impostor, and Arion. Cockerell, The Nautilus, Vol. III. p. 126,
March, 1890.

MUSEUM OF COMPARATIVE ZOOLOGY. 181

of the mantle; orifices of the combined generative organs behind and below
the right eye-peduncle. (See 3d Suppl., Plate VIIL. Fig. A.)

Jaw arcuate, with numerous ribs. (Plate IX. Fig. B of same.)

Lingual membrane with tricuspid centrals, bicuspid laterals, and quadrate
denticulated marginals. (Plate 1X. Fig. C of same.)

Northwestern parts of North America, in the Oregon Region.

Allied to Prophysaon, but distinguished by its more anterior respiratory
orifice, its rudimentary shell-plate, and decided caudal pore.

Phenacarion foliolatus, Gouxp.

Color a reddish fawn, coarsely and obliquely reticulated with slate-colored
. lines, forming areole, which are indented at the sides, when viewed by a mag-
nifier, so as to resemble leaflets; the mantle is concentrically mottled with
slate-color, and the projecting border of the foot is also obliquely lineated.
The body is rather depressed, nearly uniform throughout, and somewhat trun-
cated at the tip, exhibiting a conspicuous pit, which was probably occupied by
a mucus gland. The mantle is very long, smooth, and has the respiratory ori-
fice very small, situated a little in front of the middle. The eye-peduncles are
small and short. Length 85 mm.

Arion foliolatus, Goutp, Moll. U.S. Exp., page 2, Fig. 2, a, b (1852); Binney,
Terr. Moll., II. 30, Plate LXVI. Fig. 2 (1851); W. G. Binney, Terr.
Moll., 1V. 6; copied also by Trron and W. G. Binney, L. & Fr. W.
Sh., I. 377.

Phenacarion foliolatus, CocKERELL, The Nautilus, 1890, III. 126; W. G. Biyyey,
38d Suppl. to Terr. Moll. V., p. 206, Plate VIII. Fig. A; Fig. B (shell-
plate); Plate IX. Fig. B (jaw); Fig. C (dentition); Fig. D (genitalia).

Discovery Harbor, Puget Sound (Pickering) ; Olympia and Seattle, Wash-
ington (Hemphill).

Dr. Gould adds to the above description these words (Vol. II. p. 31): “ That
this animal belongs to the genus Arion there can be little doubt, from the
peculiar structure of the tail, as represented in Mr. Drayton’s figure, and from
the anterior position of the respiratory orifice. It is a well marked species,
characterized especially by the leaf-like areole by which the surface is
marked.” :

It is with the greatest pleasure that I announce the rediscovery by Mr.
Henry Hemphill of this species, which has hitherto escaped all search by
recent collectors. It has till now been known to us only by the description
and figure of the specimen collected by the Wilkes Exploring Expedition,
almost fifty years ago, and given in Vols. II. and III. of Terrestrial Mollusks.
A single individual was found in December, 1889, at Olympia, Washington,
and sent to me living by Mr. Hemphill. It can thus be described. (See
Fig. A of Plate VIII. of 3d Suppl.)

Animal in motion fully extended over 100 millimeters. Color a reddish

182 BULLETIN OF THE

fawn, darkest on the upper surface of the body, mantle, top of head, and eye-
peduncles, gradually shaded off to a dirty white on the edge of the animal,
side of foot, back of neck, and lower edge of mantle, and with a similar light
line down the centre of back; foot dirty white, without any distinct locomo-
tive disk ; edge of foot with numerous perpendicular fuscous lines, alternating
broad and narrow; mantle minutely tuberculated, showing the form of the
internal aggregated particles of lime, the substitute of a shell-plate, reddish
fawn-color, with a central longitudinal interrupted darker band and a circular
marginal similar band, broken in front, where it is replaced by small, irregu-
larly disposed dots of same color; these dots occur also in the submarginal
band of light color. Body reticulated with darker colored lines, running
almost longitudinally, scarcely obliquely, toward the end of the tail, and con-
nected by obliquely transverse lines of similar color, the areas included in
the meshes of this network covered with crowded tubercles, as in Prophysaon
Andersoni, shown in Plate IX. Figs I, J. Tail cut off by the animal. (See ’
below.) Excepting its being of a deeper red, it agrees perfectly with Dr.
Gould’s description.

Mr. Hemphill writes of it: “TI have to record a peculiar habit that is quite
remarkable for this class of animals. When I found the specimen, I noticed
a constriction about one third of the distance between the end of the tail and
the mantle. I placed the specimen in a box with wet moss and leaves, where
it remained for twenty-four hours. When I opened the box to examine the
specimen, I found I had two specimens instead of one. Upon examination of
both, I found my large slug had cut off his own tail at the place where I no-
ticed the constriction, and I was further surprised to find the severed tail piece
possessed as much vitality as the other part of the animal. The ends of both
parts at the point of separation were drawn in as if they were undergoing a
healing process. On account of the vitality of the tail piece, I felt greatly
interested to know if a head would be produced from it, and that thus it would
become a separate and distinct individual.” The animal on reaching me still
plainly showed the point of separation from its tail (see Fig. A). The tail
piece was in an advanced stage of decomposition. I have noticed the con-
striction towards the tail in many individuals. The edges of the cut were
drawn in like the fingers of a glove, after the excision.

The tail of the foliolatus having been cut off, I was unable to verify the
presence of a caudal pore from this individual. It was plainly visible in an-
other specimen from Seattle.

In the large Olympia individual, the irregularly disposed particles of lime
in the mantle, of unequal size, seemed attached to a transparent membranous
plate. With care I removed this entire, and figure it. It is suboctagonal in
shape (Plate VIII. Fig. B). Under the microscope it appears that the par-
ticles of lime do not cover the whole plate; at many points they are widely
separated. This aggregation of separate particles is the distinctive character of
the subgenus Prolepis, to which foliolatus would belong if retained in Arion.

MUSEUM OF COMPARATIVE ZOOLOGY. 183

The genitalia of the large individual from Olympia is figured on Plate IX.
Fig. D. The ovary is tongue-shaped, white, very long and narrow ; the ovi-
duct is greatly convoluted ; the testicle is black in several groups of ceca ;
the vagina is very broad, square at the top with the terminus of the oviduct,
and the duct of the genital bladder entering it side by side; the genital blad-
der is small, oval, on a short narrow duct ; the penis sac is of a shining white
color, apparently without retractor muscle; it is short, very stout, blunt at the
upper end where the extremely long vas deferens euters, and gradually narrow-
ing to the lower end. There are no accessory organs. The external orifice of
the generative organs is behind the right tentacle. (See 3d Suppl., Plate IX.
Fig. D.)

The jaw is very low, wide, slightly arcuate, with ends attenuated and both
' surfaces closely covered with stout, broad separated ribs, whose ends squarely
denticulate either margin. There are about 20 of these ribs. (See Plate IX.
Fig. B.)

The lingual membrane is long and narrow, composed of numerous longitu-
dinal rows of about 50-1-50 teeth, of which about 16 on each side (Plate IX.
Fig. C) may be called laterals. Centrals tricuspid, laterals bicuspid, marginals
with one long inner stout cutting point, and one outer short side cutting point.
The figure shows a central tooth with its adjacent first lateral, and four extreme

marginals.

Phenacarion Hemphilli.

This form is figured on Plate VIII. Fig. C of 3d Suppl. When extended
fully, it is 70 mm. long. It is more slender and more pointed at the tail than
foliolatus. The body is a bright yellow, with bluish black reticulations. The
edge of the foot and the foot itself are almost black; shield irregularly
mottled with fuscous ; the body also is irregularly mottled with fuscous, and
has one broad fuscous band down the centre of the back, spreading as it joins
the mantle, with a narrower band on each side of the body. The other charac-
ters, external and internal, are given below. It loses its color on being placed
in spirits, becoming a uniform dull slate-color. Mantle lengthened oval.
Shell-plate represented by a group of calcareous grains concealed in the mantle;
it is impossible to remove it as one shell-plate. A decided caudal pore.

Phenacarion foliolatus, var. Hemphilli, W. G. Binney, 3d Suppl. to Terr. Moll. V.,
p- 208; Plate VIII. Fig. C; Plate X. Fig. H (genitalia).

Gray’s Harbor and Chehalis, Washington, and Portland, Oregon (Hemphill);
a species of the Oregon Region.

On the only living one of the lot from Gray’s Harbor, the pore was dis-
tinctly visible, and is figured on Plate VIII. Fig. C. Usually it seemed more
“a conspicuous pit” than a longitudinal slit, as in Zonites. At one time I
distinctly saw a bubble of mucus exuding from it. It opened and shut, and is

184 BULLETIN OF THE

still plainly visible on the same individual, which I have preserved in alcohol
and added to the Binney Collection of American Land Shells in the National
Museum at Washington.

Jaw low, wide, arcuate, ends attenuated, anterior surface with 16 ribs, den-
ticulating either margin.

Lingual membrane as in foliolatus ; teeth 50-1-50, with 19 laterals on each
side.
- Genitalia (8d Suppl., Plate X. Fig. H) ; the form from Gray’s Harbor has
its generative system very much the same as described for foliolatus above. The
ovary is much shorter and tipped with brown, and is less tongue-shaped. The
penis sac tapers to its upper end. The vagina is not squarely truncated above.
The system much more nearly resembles that of Prophysaon Andersoni (see
Terr. Moll., V.) than that of the Olympia foliolatus.

Binneya notabilis, J. G. Cooper.

Plate I. Fig. 9.

A new figure is here given, drawn by Mr. Cockerell.

Triodopsis Mullani, Buanp, var. Blandi, Hempuitt.
Plate II. Fig. 6.

Shell with the umbilicus partially closed, orbicularly depressed; dark horn-color,
obliquely striated; spire short, very slightly elevated, nearly planiform; aperture
semilunar, at a right angle with axis of the shell, with a very short nipple-like pari-
etal tooth; peristome thickened, white, plain, without teeth and roundly reflected.
Height + inch, breadth 3} inch.

Post Falls, and banks of Salmon River, Idaho.

Helix Mullani in form and size resembles very much the common tridentata of
the Eastern States. Among the various forms it assumes, nore are more marked
than the little depressed shell before me. It can be very readily separated from
the typical Helix Mullani, or its other varieties, by its very depressed form, small
size, and the absence of the teeth-like processes on the inner margin of the
peristome.

I cannot detect any microscopical revolving lines, or tubercles bearing hairs,
mentioned by Bland in his description of H. Mullani.

The above desciption is by Mr. Hemphill, who furnished me with the
specimen figured.

Polygyra septemvolva, var. Floridana, Hemruitt.

Shell deeply umbilicated, elevated, globose conic, light horn-color, with numerous
fine ribs above, but smooth beneath; whorls 53 or 6, the last subangular at the
periphery ; suture well impressed; spire greatly elevated with an obtuse apex:

MUSEUM OF COMPARATIVE ZOOLOGY. 185

aperture lunate, well rounded, and nearly circular; peristome reflected, rounded ir
front, the margins joined by a triangular tooth on the parietal wall. Greater diam-
eter 6 mm., altitude 5 mm.

Oyster Bay, Florida.

This is a small, very elevated form of the P. cereolus group.

The above is Mr. Hemphill’s description.

Mesodon ptychophorus, A. D. Brown, var. castaneus, HEMPHILL.

Shell umbilicated, globosely depressed, of a dark chestnut color; surface covered
with coarse, irregular, widely separated lines of growth, and crowded, microscopical
_ revolving lines; whorls 53, convex, the last slightly descending in front, spire ele-
vated; suture well impressed, aperture subcircular; lip white, reflected and par-
tially covering the umbilicus, its terminations approaching; umbilicus small and
deep. Height % inch, diameter 1 inch.

Old Mission and Rathdrum, Idaho.

I regard H. ptychophorus as the progenitor of what I call the J’ownsendiana group
of West Coast land shells, and this colored variety seems to still further indicate
its relationship to Townsendiana, for the spire whorls of nearly all the specimens
of Townsendiana that I have collected are chestnut-colored. Yownsendiana does not
begin to put on its wrinkles until it has made about four revolutions of the shell. ,
The wrinkles are probably due to its environment.

The above is Hemphill’s description, from The Nautilus, Vol. IV. p. 41,
1890.

Aglaja fidelis, var. flavus, Hempuitt.

Shell umbilicated, elevated, very faintly subcarinated, of a uniform light yellow
color throughout, without bands or other stains of coloring; whorls 64, convex, with
coarse oblique striz, and microscopic irregular revolving lines; peristome reflected
below, simple above; aperture roundly ovate; umbilicus moderate, and partially
covered by the reflected peristome; suture distinct. Greater diameter 34 mm., alti-
tude 23 mm.

Chehalis and San Juan Islands, Washington ; Port Orford, Oregon.

This is a rare and beautiful variety of this well known West Coast land snail.

The above is Mr. Hemphill’s description.

Aglaja fidelis, var. subcarinata, Hempnitt.

Shell orbicularly depressed ; umbilicated; of a deep dark chestnut-color without
bands; whorls 64, convex or somewhat flattened, the last subcarinated at the
periphery ; strie coarse, oblique, crossed by numerous well defined wavy revolving
lines; peristome simple, thickened above, reflected below, and nearly covering the
umbilicus ; umbilicus moderate; aperture roundly ovate; suture well impressed.
Greater diameter 37 mm., altitude 20 mm.

Humboldt Co., California.

186 BULLETIN OF THE

This is a very dark, intermediate form of jfidelis, which in its southern march
under changed conditions assumes a more carinated form, and is known to con-
chologists as infumata, Gould.

The above is Mr. Hemphill’s description.

Arionta Coloradoensis, STEARNS.

Shell orbicular, moderately depressed, whorls slightly elevated, apex obtuse,
number of whorls four to four and a half, rounded. Umbilicus narrow, showing the
penultimate whorl, though partially covered by the reflection of the lip at the point
of junction with the base of the shell. Aperture obliquely ovate, nearly circular,
and almost as broad as high. Lip slightly thickened and reflected, or simple, vary-
ing in this respect; more reflected and aperture more effuse at the columella,

Parietal wall in the heavier examples calloused, the callus connecting with the
inner edges of the outer lip above and below. Shell rather fragile, thin, translu-
cent ; surface smooth and shiny, and sculptured with fine incremental lines. Color
pale horn to white, and otherwise marked by a single narrow revolving reddish
brown band just above the periphery, which in some specimens is obscure or
absent. In some individuals certain faint scars upon the upper whorls imply an
occasionally hirsute character.

mm.
Maximum diameter of largest . . . . ». - «+ + 15.25
Minimum diameter of largest . . . .- - + +» + + 18.25
Altitude oflargest . . . se eee OZ
Maximum diameter of ePaleuts adult . | ca. Cy DS res
Minimum diameter of smallest adult . . .. . - 12.00
Altitude of smallest adult ...... =... s+ 8.75

!

Grand Cafion of the Colorado, opposite the Kaibab plateau, at an elevation of
38,500 feet. (Mus. No. 104,100.)

The above, while exhibiting a facies or aspect of its own, its nevertheless sug-
gestive of H. Remondi, Gabb, Mazatlan, in the Mexican State of Sinaloa, and also
from the high mesas or table lands in the neighborhood of Mulege, Lower Cali-
fornia. HH. Carpenteri, Newcomb, which is a synonym of H. Remondi, is credited
by the author to “ Tulare Valley,” and has been found in other localities in Cali-

MUSEUM OF COMPARATIVE ZOOLOGY. 187

fornia. A glance at the map will show how widely separated geographically
H. Coloradoensis is from its nearest allies, and this discovery of Dr. Merriam’s
extends the distribution of the West Coast type of Helices farther to the eastward
than heretofore, and adds an area of great extent to that previously known.

The above description and figure were published by Stearns in Proc. U. S.
Nat. Mus., Vol. XIITL. p. 206, Plate XV. Fig..6, 7, 8, 1890, all copied above.

I have examined the jaw and lingual dentition to find them similar to those
of the other species of Arionta.

Arionta Traski, var. proles, Hemet.

Shell umbilicated, very much depressed, thin, shining, of a dark horn-color;
whorls 54, somewhat flattened above, convex beneath, the last slightly falling in
front, with a dark band above the periphery, and crowded with strong oblique
strie; suture well impressed; umbilicus moderately large and deep; aperture
hardly oblique ; peristome simple, thin, subreflected, its terminations approaching.
Height % inch, breadth # inch.

Tulare Co., California, near Fraser’s Mill.

A much flatter and more depressed form than any of the varieties of Traski that
Ihave seen. There are no revolving microscopical lines, as in Traskz.

The above is Mr. Hemphill’s description.

Arionta tudiculata, var. Tularensis, Hempurrt.

Shell umbilicated, very thin and frail, shining, of a light greenish horn-color,
globosely depressed; whorls 53, convex, the surface minutely granulated, and
crowded with fine oblique striz, with a single chestnut revolving band; suture
well impressed; umbilicus very small; aperture oblique, subcircular; peristome
simple, hardly thickened, its columellar portion expanding and nearly covering the
small umbilicus. Height § inch, breadth 7 inch.

Tulare Co., California..

This is one of those puzzling intermediate forms uniting two species that can be
with equal propriety placed in one or the other. It has the exact form of the
typical Traski found at Los Angeles, and along the coast, though much smaller
and thinner, and it has the sculpturing of tudiculata much modified. It seems to
fill the gap quite completely between those two species.

The above is Mr. Hemphill’s description.

Arionta tudiculata, Bryyey.
Plate II. Fig. 7, 8.

New figures are here given of the form cypreophila.
In The Nautilus, Vol. IV. p. 41, 1890, Mr. Hemphill also describes a
var. subdolus thus: —

188 BULLETIN OF THE

Shell narrowly umbilicated ; globosely depressed, of a dark yellowish color, sur-
face somewhat shining, covered with oblique striz, interrupted by numerous wavy
lines and oblong blister-like wrinkles, hardly perceptible to the naked eye; whorls
54, convex, striped by a single chestnut band, double margined by lighter ones;
spire very little elevated, suture well impressed; lip simple, reflected, and nearly
covering the umbilicus, its terminations approaching and joined by a thin callus ;
umbilicus narrow and small. Height 3 inch, greatest diameter 1 inch, lesser 7 inch.

San Jacinto Valley, San Diego Co., California.

A very depressed form, quite variable in size, some of the specimens not being
more than half the size of the measurements given. It is lighter colored than any
of the southern varieties of tudiculata except var. Binney?.

Arionta Ayresiana, NEwcoms.
Plate I. Fig. 7.

I give a new figure of this species.

Arionta intercisa, W. G. Binyey. ;

In “ Zoe,” Vol. I. No. 11, January, 1891, p. 330, Mr. Hemphill describes
these varieties of A. intercisa : —

Var. minor. Smallest specimen, greatest diameter 18 mm., altitude 11 mm.
Uniform light yellowish chestnut-color, with and without a band, and varies
very much in form and elevation or depression of spire.

Var. elegans. Uniform ashy buff-color, faintly banded, and variable in form,

Var. nepos. Uniform ashy white; spire horn-color, variable in form and
sculpturing.

Var. albida. Uniform milk-white, sometimes with a faint band at the
periphery; sculpture nearly obsolete.

In the same journal (p. 434) Mr. Hemphill thus describes several varieties
of redimita, which species he refers, however, to Kelletti: —

Var. castaneus. Uniform, polished, chestnut-color, darker band at the periph-
ery, spire sprinkled with fine ashen specks.

Var. hybrida. Uniform ash-white color, and a dark band at the periphery,
flecked with transverse markings and specks of dark brown and light chestnut.

Arionta ruficincta, Gass.
Plate I. Fig. 3.

A new figure is given of this species.

Arionta Kelletti, Forzes.

Mr. Hemphill, in Terr. Moll. V., 3d Suppl., has thus described several
varieties. I figure authentic specimens of each.
Var. albida (Plate IV. Fig. 3). This is a beautiful clear white translucent

ea

MUSEUM OF COMPARATIVE ZOOLOGY. 189

&
variety, with no markings or stains of any kind. It is quite thin and frail,
and a trifle smaller than the average size of Kellett.

Santa Catalina Island, California. Two specimens only found by me.

Var. castanea (Plate IV. Fig. 4). Among the numerous patterns of coloring
assumed by H. Kelletti, none are more conspicuous than this well marked va-
riety. The body whorl is of a deep shiny chestnut-color above the periphery,
and becomes lighter as it follows the whorls of the spire to the apex. The
band at the periphery is quite variable in the different specimens; it is gener-
ally light and well defined above, but below it is irregular, and spreads over
the base of the shell more or less.

Santa Catalina Island, California. This variety is not rare.

In “ Zoe,” Vol. I. No. 11, pp. 333, 334, Mr. Hemphill has also thus described
several other forms.

Var. nitida (Plate IV. Fig. 2). Uniform, translucent, shining, dark horn-
color, with a poorly defined dark band, coalescing with a poorly defined whit-
ish band below it, at the periphery; spire faintly flecked with ashen gray.

Catalina Island.

Var. multilineata (Plate IV. Fig. 1). Shell marked by alternate shades of
ashen white, chestnut, or brown, arranged in an irregular series of revolving
and sometimes wavy lines, with a broader and poorly defined band at the
periphery; markings finer beneath than above. _

Var. frater. Shell of a beautiful, uniform, horn-buff color, sometimes fad-
ing into lighter horn-color, with a darker band at the periphery, and numerous
faint, alternate revolving lines of ashen or dark horn-color above and below;
generally, not always, lighter colored beneath, and sometimes with a whitish
zone beneath the band at the periphery.

Var. Californica. The shell is colored with a darker shade of uniform buff
than the above, dark band at the periphery, generally uniform in color above
and below; sometimes flecked with squarish dots.

Var. Forbest. Ground.coloring whitish buff, with a revolving series of poorly
defined and coalescing lines, bands, and blotches.

Var. bicolor. Color very dark horn or brownish, flecked with numerous re-
volving very fine dots or irregular lines, with or without a very faint band at
the periphery.

Var. tricolor. Irregularly painted with numerous revolving whitish, brown-
ish, and chestnut flecks, blotches, and stains, with or without a band at the
periphery.

Var. albida. (See below.)

Var. albida, a. Milk white ground, very faintly stained with light horn,
and with poorly defined and fading lines.

Mr. Hemphill considers redimita as a form of Kelletti. (See that species.)

190 BULLETIN OF THE

Euparypha Tryoni, Newc.

Mr. Hemphill has thus described several varieties. (See Zoe, Vol. I. pp. 331,
332.)

Var. varius. The upper or dark zone is of a lighter shade of bluish brown
or chestnut than the type, and is flecked and sprinkled with ashen white;
band at the periphery dirty white beneath.

Var. nebulosa (Plate IV. Fig. 5). Lighter colored above than var. varius,
marbled and clouded with various patterns of dark brown and dirty white ;
dirty white beneath.

Var. fasciata (Plate IV. Fig. 6). Uniform light chocolate above and be-
neath, with a dark band at the periphery.

Var. Californica. Creamy buff-color, darker above than below the periph-
ery, very faintly banded.

Var. albida. Uniform creamy, and sometimes milk-white above and be-.
neath, and without band.

Var. subcarinata. Among the subfossils that occur on Santa Barbara Island
we find a form of H. Tryoni which adds an interesting link to its history and
to its present form. It may be characterized as follows. Shell depressed glo-
bose, consisting of about 54 whorls, the last subcarinated at the periphery; in
other respects closely resembling the recent form. Greater diameter 23.15 and
20.11 mm., largest and smallest specimens.

Pomatia Humboldtiana, Vat.

Texas, at Altuda, at an elevation of 5,000 feet, where it, a single specimen in fair
condition, had been thrown out with soil by a prairie dog. (Mus., No. 118,366.)
William Lloyd.

This species has not before been reported from any locality within the territory
of the United States. It was described from Mexico, where it is found in the
neighborhood of the city of Mexico, and in other localities. The national collec-
tion contains several examples from the Real del Monte. It has a pretty close
resemblance to some of the varieties of the European H. (Pomatia) pomatia, and it
may possibly be an introduced form. H. pomatia has for centuries been esteemed
as an article of food in various parts of Europe, and was regarded as a dainty by
the ancient Romans. It was propagated and raised in large quantities for their
use, and specially fed on certain plants to give the flesh a particular flavor.

Unmistakable specimens of another favorite edible snail common to Europe,
H. (Pomatia) aspersa, is found in Mexico, and examples from Puebla, in the prov-
ince of Puebla, Mexico, were presented to the National. Museum by the Mexican
Geographical Commission a few years ago. The presence of these two forms most
certainly suggests the question as to whether they were not introduced by the
Spaniards many years, centuries, ago, either for food purposes or incidentally in
the routine and accidents of commercial intercourse.

The above was published by Stearns in Proc. U. S. National Museum, Vol.
XIV. p. 96, 1891. It will be remembered that Helix Buffoniana was figured
as aspersa by Dr. Binney in Volume III.

MUSEUM OF COMPARATIVE ZOOLOGY. 191

Bulimulus Ragsdalei, Pitspry.

Plate II. Fig. 9.

It is about the size and form of B. Mooreanus, but rather more slender and
elevated. The surface is not smooth, as in the other American Bulimuli, but
strongly ribbed-striate longitudinally. The apex is blunt; peristome thick-
ened within ; columella reflexed over the narrow but open umbilicus. The
aperture is less than half the length of the shell; color brownish, corneus
somewhat translucent, the riblets opaque white. Height 22 mm., diam.
10 mm.; height of aperture 10} mm., diameter 7 mm.

Bulimulus Ragsdale, Pitspry, The Nautilus, Vol. III. p. 122, March, 1890.
Proc. Acad. Nat. Sci. Phila., 1890, p. 296, Plate V. Fig. 3.

St. Jo, and at Warren’s Bend, twenty-five miles from Gainesville, and in
Cook and Montague Counties, Texas (Ragsdale).

A figure of an authentic specimen is given 13 the natural size. The descrip-
tion is a copy of the original.

Bulimulis Dormani.

Plate I. Fig. 6.
A new figure is given.

Rhodea Californica.

This extralimital species has actually been received by Dr. Cooper from.
Lower California. (Proc. Cal. Acad. Nat. Sci., 1891, p. 102.) It had been
quoted as an Achatina from Monterey. (See Vol. V.)

Pupa Californica.

Dr. Sterki in Nautilus, Vol. IV. page 7, mentions a variety, elongata, from
San Clemente Island ; on page 18, varieties trinotata, Diegoensis, and cyclops.

Pupa Coloradensis, Cocker. t.

Shell brown, shiny, thinnish, striate, especially on penultimate whorl ; out-
line oblong-oval, barrel-shaped ; apex blunt; whorls 4; aperture pyriform ;
peristome brown, thick, continuous by a well marked callus on parietal wall ;
outer lip not constricted. The teeth within the aperture are brown, one long,
one on parietal wall, one on columella, and two (the lower one largest) on outer
wall. Long. 15, lat. 1 mm. Allied to P. corpulenta, but decidedly smaller,
more striate, and slightly narrower. (Cockerell.)

192 BULLETIN OF THE

Pupa Pilsbryana, Srerx1.

Shell minute, narrowly perforate, cylindrical-oblong to cylindrical, somewhat
attenuated towards the rather blunt apex, colorless (when fresh glassy) with a
very delicate bluish tint, smooth and polished, with few, irregular microscopic
strie which are more marked near the aperture. Whorls 43-53, moderately
rounded with a rather deep suture, especially in the upper half, regularly and
slowly increasing, the embryonal being relatively large, the last somewhat
ascending toward the aperture; the latter of moderate size, lateral, subovate,
margins approached, peristome somewhat expanded, without a thickened lip or
a callus in the palatal wall; outside is a barely perceptible trace of a crest near
the margin, and behind that a slight impression most marked upon the inferior
palatal fold. Lamelle 4 or 5; one apertural, rather high, of moderate length,
simple; one columellar, horizontal, of moderate size, simple; basal very small or

wanting; palatals the typical, inferior deeper seated, of moderate size, superior’

small or very small. Alt. 1.5-1.7, diam. 0.8-0.9 mm.
Pupa Pilsbryana, Sterxt, The Nautilus, Vol. III. p. 123, March, 1890.

There is a slight variation; the example from New Mexico being of lesser diam-
eter, and having no trace of a basal lamella.

The soft parts have not been seen so far, but will be of high interest, since, to
judge from the shell, our species seems to be an intermediate form between the
hordeacella, ete. group, and P. curvidens, especially its var. gracilis.

P. Pilsbryana has much resemblance in shape and size to small albino examples
of P. hordeacella, Pilsb., but under a glass is at once distinguished by the shorter
simple apertural lamella not ending at or very near the upper termination of the
palatal margin, as it does in hordeacella, and by the smooth surface. The fine bluish
hue may also be a distinguishing character if it prove constant.

The above is Sterki’s original description.

Pupa calamitosa.
Plate II. Fig. 1.

See 3d Suppl., p. 219. A reduced copy of one of the original figures is given
here.

Pupa Hemphilli, Srerxt.

In examining a lot of about forty-five specimens of Pupa calamitosa from the
banks of San Tomas River, Lower California, I found there were two distinct
forms in them. The author says, in his description of P. calamitosa: “ Several
specimens have only one lamella on the outer lip, and are rather larger than the
typical form described,” represented in Plate XII. Fig. 16 (loc. cit., No.7). Probably
I had a greater number of examples at disposition than Mr. Pilsbry. The two
forms proved to be distinct by an entirely different formation of the lamelle, as

a,

MUSEUM OF COMPARATIVE ZOOLOGY. 193

well as of the basal part of the shell. And among the whole number I found not
one intermediate or doubtful specimen. There is no doubt but that we have to
consider them as being specifically distinct, the more so since they live together in
the same locality. For the new species I would propose the name P. Hemphilli, in
honor of the man to whom we owe so many valuable additions to our malaco-
logical fauna.

As in shape and general appearance the two species are almost alike, it may be
the best way to characterize the one in question by comparing it with P. calamitosu,
Pilsb. P. Hemphilli averages a trifle larger than its companion, but either is some-
what variable in size. While calamitosa has a
minute perforation, Hemphilli is umbilicated in
quite a peculiar way. There is a nodule-like pro- Ba
jection on the umbilical part of the last whorl,
producing a rima beside the umbilicus ; in ca/am-
wtosa there is nothing of this formation. On the
other hand, the latter has a small but distinct
groove-like impression just at the base, near the
aperture appearing as a slight projection inside. 7
This feature is wanting in Hemphilli. Lamelle:
in the latter species, when looking from front, only one is generally seen in the
palatal wall, corresponding to the superior one in calamitosa, but longer; i.e. be-
ginning deeper in the throat, and fairly seen on the outside; also marked there by
a corresponding impression, ascending in a curve from near the base. A little dis-
tant from its inner end, just above the projection mentioned, there is another
lamella beginning, directed toward the base and ending there, also seen on the
outside. Quite generally there is a very small, thin, but well formed lamella in
the palatal wall, near the projecting auricle. The columellar fcld is quite short
and small in Hemphilli, yet consisting of a vertical and a horizontal part. The
(main) apertural lamella is decidedly longer in our species, and the supra-
apertural higher and entire, while in calamitosa it is evidently composed of two
parts marked by an indentation in the middle, or even entirely separated, in quite
mature specimens.

About twenty examples, collected at San Diego, Cal., by Mr. Hemphill, are all
P. Hemphilli, no calamitosa among them. They are little different from the San
Tomas River specimens, except by a somewhat shorter palatal lamella.

The above is Sterki’s description (The Nautilus, July, 1870, Vol. IV. p. 27).
My figure was drawn by him from the type.

Pupa hordeacella, Prussry.

Plate II, Fig. 2.

The shell is of a long-ovoid shape, smaller and slenderer than P. servilis, Gould,
translucent, waxen white, finely striate; the aperture is rounded, with a thin, ex-
panded peristome. Within, there is, on the parietal wall, an entering fold arising
near the termination of the outer lip, its edge a trifle sinuous or nearly straight;
the columella has a fold about in the middle. There is a tiny deep-seated fold on

VOL. XXII. — NO. 4, 13

194 BULLETIN OF THE

the base of aperture, near the columella, an entering fold within the outer lip,
equidistant from the above described parietal and columellar folds, and a tiny
denticle above it. The columellar fold is not situated so high on the pillar as in
P. servilis. The latter half of the body whorl is flattened on the outer lower por-
tion, as the Figure J shows. There is a low wave-like ridge or “crest” also, but
scarcely visible in many specimens. Alt. 1.8, diam. 8 mm.

Pupa hordeacella, Pitspry, Proc. Acad. N. Sci. Phila., 1890, p. 44, Plate I. Figs.
G; Hy, deck:

Arizona to Florida.

The figures were drawn with the aid of the camera lucida. They should be com-
pared with Gould’s excellent figures of P. servilis in the Boston Journal of Natural
History, Vol. IV., Plate 16, Fig. 14, and those of P. pellucida, in Strebel’s Beitrag
zur Kenntniss der Fauna mexikanischer Land- und Siisswasser-Conchylien, Theil
IV. Plate XV. Fig. 10. The latter are the more valuable in this connection, as.
they are not only faithful drawings on a sufficiently large scale, but are the only
ones drawn from continental specimens (Vera Cruz, Mexico). The measurements
given by Strebel and Pfeffer are, alt. 24, diam. of last whorl fully 1 mm., alt. of
aperture mm. Gould’s P. servilis and Pfeffer’s P. pellucida were both described
from Cuba. Isee no reason for not following W. G. Binney in considering them
synonymous, pellucidus having precedence. (Pilsbry.)

The above is Pilsbry’s description. I give also a reduced view of one of his
figures.

Pupa Clementina, STerx1.

Shell very minute, narrowly perforate, cylindrical, pale horn-colored, transpar-
ent, with rather obtuse apex ; whorls 54, regularly increasing, moderately rounded,
with rather deep suture, smooth, with few microscopic striz, somewhat
shining ; last whorl occupying rather more than two fifths of altitude,
somewhat ascending to the aperture, with a slight, revolving impression
on the middle of its last one third, ending at the auricle; a very slight,
flat crest elevation near the margin, only in the lower part; aperture lat-
eral, scarcely oblique, subovate with the palatal margin slightly flattened,
upper part of same somewhat sinuous, peristome a little expanded with
a slightly thickened lip just at the margin; lamelle 6, white, two on
the apertural wall, the apertural typical, and a rather long supra-aper-
tural, ending in acallus at the upper termination of the palatal margin; columel-
lar one typical, horizontal; basal very small, nodule-like, deep-seated ; palatals
two, typical, the inferior a little longer. Alt. 1.9, diam. 0.8 mm. ; apert., alt. 6,
diam. 0.5 mm.

Three examples of this species were collected by Mr. H. Hemphill on San Cle-
mente Island, California, among numerous P. Californica, Row. All were exactly
alike, well formed and fully mature. They cannot be referred to any one of our
species published, and doubtless represent a form of their own, although so far it
was not possible to examine the soft parts.

Pupa Cle-
mentina.

MUSEUM OF COMPARATIVE ZOOLOGY. 195

In size, shape, and general appearance it somewhat resembles /sthmia, yet lacks
the rib-like striation; the lamelle would be typical for Vertigo and some of the
smaller Pupe but for the presence of the well developed supra-apertural which
P. Clementina has in common with P. calamitosa, Pilsbry, and Hemphilli, Sterki;
but, on the other hand, there is nothing of the characteristic palatal or gular folds
of these two species. Thus, in several regards, our form is an intermediate and
connecting one between different groups, and consequently deserves our special
interest.

Pupa Clementina, SterK1, The Nautilus, Vol. IV. No. 4, Plate I. Fig. 4, August,
1890.

The above is a copy of Sterki’s original description and figure.

Pupa Dalliana, STerx1.

Shell conic or ovate-conic, of greenish horn-color, transparent, finely irregularly
striate in the lines of growth, polished ; whorls 44, well rounded, with deep suture
rather rapidly increasing, the last occupying about 2 of altitude
towards the aperture, somewhat ascending on the penultimate.
Aperture lateral, somewhat oblique, subovate, with just percepti-
bly flattened palatal margin; margins approximate, the ends pro-
tracted; peristome shortly but decidedly expanded, with a very fine
thread-like lip near the margin, the same continuing as a very fine
callus on the apertural wall inside of the line connecting the ends of
the margins; palatal wall quite simple; no lamelle. Alt. 1.2, diam.
1.3 mm.

This form has been collected by Mr. Hemphill near Clear Lake,
Lake Co., Cal., and I propose to name it in honor of Mr. William H. Dall. The
specimens before me were fifteen, fresh, remarkably uniform in their whole appear-
ance; all were more or less covered with a dark brown hard crust of slime and
dirt, generally thickest around the aperture. Doubtless this coating is done
“purposely ” by the animals, as in many other species also. When cleaned, it
shows about the size and shape of a well grown Vertigo ovata, Say; but by a good
eye, or under a glass, is at once recognized as something else, by the rounded
aperture and the absence of lamelle. (Sterki.)

Pupa Dallia na.

Pupa Dalliana, StErK1, The Nautilus, Vol. IV. No. 2, p. 19, June, 1890.

Dr. Sterki’s description is copied above. My figure was drawn by him from
the type.

Pupa syngenes, PILsBry.
Shell subcylindrical but wider above, composed of eight narrow, convex whorls,

sinistrally convoluted ; texture as in P. muscorum, but color rather lighter brown.
Last whorl ascending, imperforate, bearing a strong high crest just behind the

196 BULLETIN OF THE

outer lip. Aperture shaped as in muscorum, having a single small parietal denticle.
Altitude 3%, diameter 13 mm.

Pupa syngenes, Pitspry, The Nautilus, 1890, Vol. III. p. 296, Plate V. Figs. 1, 2.

Two specimens of this form are before me, and I am in doubt whether to give
them a new name, as they may be only sinistral monstrosities of the common
P. muscorum. The shells are labelled “ Arizona” in the Academy collection, col-
lector not known.

(Since the above paragraphs were in type, I have received a communication from
my friend, Dr. V. Sterki, to whom I sent a specimen of P. syngenes, which I at first
described as a variety of muscorum. He says: —

“Tam satisfied that it is a species, and not a var. of muscorum; the shape of the
whole shell, the last whorl so considerably flattened, and ascending, the number of
whorls, seem to me to prove its specifical rank. . . . After washing out the aper-
ture of your specimen, I saw a rather strong lamella or tooth on the columella, and
a barely perceptible trace of an inter-palatal lamella, which, however, is validified °
by the impression on the outside.’’)

The above is Pilsbry’s description. An authentic specimen drawn by Dr.
Sterki is figured here. :

Vertigo ovata, Say.

Of V. tridentata Sterki writes (The Nautilus, 1890, p. 135): “It has a
wide distribution in the northern part of the country ; originally found in
Illinois, it has been collected in different parts of Ohio and New York, as
well as in Minnesota and Colorado. In general it is remarkably constant in
its characters ; yet there are slight differences ; here I found a few examples
from low ground, together with V. ovata; they were a trifle larger, with a
thicker and deeper colored shell than those from upland places.”

MUSEUM OF COMPARATIVE ZOOLOGY. 197

Vertigo Oscariana, STerx1.

This is the most peculiar of our species. It is of the size of milium, but oblong,
with either end nearly equally pointed, the last whorl being considerably narrowed
and flattened towards the subtriangular, small aperture; shell thin, delicate, of
pale horn-color, as is the palatal wall and margin; the latter simple and straight,
with a very slight, thin callus inside ; lamellz 3, whitish, rather small; one aper-
tural, one columellar (longitudinal), and the inferior palatal; some-
times there is also a very small superior palatal. Length 1.5, diameter
0.8 mm.

This remarkable Vertigo has been detected in Eastern Florida, on the
coast at Mosquito Island, etc., by Mr. Oscar B. Webster and his father,
Mr. Geo. W. Webster, of Lake Helen, Florida. These gentlemen took
much pains to ascertain the range of distribution of this form and some VY: Oeeatls
others, and it is consequently only just to name the species in honor of aan
Mr. Webster. The most striking character of it, besides the narrowed ‘
last whorl, is the thin and straight palatal wall and margin, so that, indeed, the
shell appears to be immature. But when seen under a glass of sufficient power,
the margin is completed, and, as already mentioned, there is a thin callus at a
little distance from the margin. Moreover, Mr. Webster wrote me that, of more
than 150 examples he had seen, all were alike.

A few days ago, in a lot of P. corticaria, Say, from Ithaca, N. Y., sent from
Texas, there was one example of this species, the shell dead, but in fair condition,
a little larger and less fragile than the Florida examples, and with a well marked
callus corresponding to a slight but distinct crest. The specimen may have been
collected in New York, and from its appearance at least I would ascribe to it an
origin north of Florida. Since the above was written, I have found a few exam-
ples in drift from Guadalupe River, Texas, collected by Mr. J. A. Singley, sent by
Mr. Wm. A. Marsh.

By the kindess of Mr. Webster I was enabled to see a living example. The foot
and the lower parts of the head are nearly colorless; head, eye-tentacles, and neck
light gray. Jaw very tender, thin, pale yellow, consisting of about 14 longitudinal
plates, shorter and wider in the middle, longer and narrower toward either end; it
is much like that of V. tridentata, Wolf. Odontophore about 0.36 mm. long, 0.1 mm.
wide, about 110 square rows in each 3+ 3-47 teeth; central very small; laterals
gradually passing into marginals; the latter serrate. Different from that of
V. tridentata.

In drift with numerous minute shells, from Guadalupe River, Texas, kindly sent
by Wm. A. Marsh, I found one specimen of this species, which consequently is not
confined to Eastern Florida, where it was detected by Messrs. Webster, but may be
widely spread over the southern part of our country.

—\
KW

Vertigo Oscariana, STERKI, Proc. Ac. Nat. Sci. Phila., 1890, p. 33; The Nautilus,
1890, p. 136.

The above is Sterki’s description, and the figure is drawn by him from the
type.

198 BULLETIN OF THE

Vertigo Binneyana, STerx1.

They are of the size and general appearance of V. callosa, very narrowly per-
forate, cylindrical oblong, light chestnut-colored; whorls 5, moderately rounded,
nearly smooth; aperture relatively small, peristome little expanded; outer wall
with a well formed crest interrupted by a rather long revolving groove;
corresponding to the crest there is a callus of lighter color; lamelle 6;
on the apertural wall a small supra-apertural and a well developed
apertural; columellar appearing rather massive; at the base, one
rather small but well formed, appearing tooth-like; palatals 2, long,
especially the inferior. Length 2.0 mm., diameter 1.0 mm.

Last year, Mr. W. G. Binney kindly presented me with two exam-
V. Binney- ples of a Vertigo collected at Helena, Montana, by Mr. H. Hemphill,

a which seemed to be of a new species; but yet I did not like to publish

Tr a description founded upon only these two specimens. Lately among’
a number of small Pupide from different parts of British America sent by Mr. Geo.
W. Taylor of Ottawa, there were a few examples of this same species, from Win-
nipeg, Manitoba, dead and weathered, but good enough to be identified.

Probably there are other examples of this species in collections, and more will
be found in the Northwest. It is named in honor of Mr. W. G. Binney, to whom I
owe the two beautiful specimens in my collection.

Vertigo Binneyana, StERKI, Proc. Ac. Nat. Sci. Phila., 1890, p. 33.

The above is Sterki’s description. I am also indebted to him for the figure.

Vertigo callosa, Srerxt.

There are in collections two different species under the name of V. Gouldii, Binn.
Their size and coloration is nearly the same, at least in most variations, as are also
the apertural lamellz as to number and position. Yet they are decidedly and con-
stantly distinct, especially by the formation of the outer wall at the aperture.
Judging from the descriptions and more especially from the figures, the true V.
Gouldii is the one characterized as follows: the last whorl is somewhat predomi-
nating, thus rendering the whole shell more ovate or conic ovate; the palatal wall
near the aperture is decidedly flattened, or impressed, the impression comprising
also the crest and being especially well marked at the “auricle” (as I name the
more or less projecting part about the middle of the outer margin, to have a con-
cise expression), forming a roundish groove outside and a decidedly prejecting
angle inside, thus producing the “two curves meeting in the centre of the peri-
stome.” <A feature not striking, but only seen by careful examination, is the posi-
tion of the short tooth-like lamella at the base, somewhat nearer the margin than
the end of the columella, the base perceptibly widened at that place; the said
lamella is probably an equivalent of the inferior columellar lamella, which in most
Vertigos stands very low, in many exactly at the base.

The other species, V. callosa, has the last whorl relatively less wide, so that the
whole shell is of a more oblong shape. In the palatal wall, only the part behind

MUSEUM OF COMPARATIVE ZOOLOGY. 199

the crest is somewhat flattened, while the latter itself forms one unbroken curve
from the base up to the suture, and at the moderately projecting auricle there is
only a slight flattening. The inferior columellar lamella is at the end of the col-
umella, sometimes wanting or a mere trace. Well worthy of notice is a peculiar
formation of the surface, the epiconch showing microscopic wrinkles or foliations
in the direction of the lines of growth producing a peculiar silky gloss, especially
on quite fresh examples, and more in some forms than in others.

The first two examples of this species I obtained in 1885 from Mr. Henry Moores,
of Columbus, Ohio, and in 1889 I saw a few more in his collection. In 1887, Mr.
E. W. Roper sent me some others from Massachusetts. Last year in different
collections I saw quite a number of specimens from different places in New York
near the metropolis, under various names: V. Gouldii, milium, ovata, and also mixed
with Bollesiana. Of the Ohio examples the color is somewhat lighter, the callus and
the lamelle are strong and white, while in the Eastern examples they are somewhat
thinner and more of the color of the shell. The name callosa was thus mainly
derived from the Ohio form (which, however, may be regarded as a variety).

It is with some hesitation, however, that I now bring it under this head ; it is the
equivalent of the European V. pygmca, Drap., of which I have examples for com-
parison from different countries of the Old Continent, which I have partly col-
lected myself there during a number of years. The two may even be identical;
at least it would be absolutely impossible to distinguish New York examples
from most Europeans. Both forms agree also in certain variations of the aper-
tural lamelle; the inferior columellar lamella may be absent in either, or there
may be present a small supra-palatal fold, thus rendering the number variable
from 4 to 6, the typical, however, being 5. An examination of the soft parts will
probably decide the question; so far I have not had an opportunity to make it.

On our continent, the range of distribution of the two species —V. Gouldii and
callosa —seems to be somewhat different, the former having been found in New
York, Ohio, Illinois, and Colorado, the latter from Massachusetts to Ohio.

Vertigo callosa, Srerx1, Proc. Ac. Nat. Sci. Phila., 1890, p. 31.

The above is Sterki’s description.

Vertigo parvula, STERKI.

Among several hundred small Pupide collected in Northeastern Ohio (Summit
and Lake Counties) by Mr. A. Pettingell, there were two examples of a doubtless
new species, which I in the same way named V. parvula. It is about of the size,
shape, and appearance of V. (Angustula) milium, Gould; but ranges in quite another
group, having a quite simple palatal wall and margin, and only three lamelle.

In Texas, Vertigos seem to be decidedly rare. In many hundreds of Pupide
from that State which Mr. J. A. Singley and Mr. Wm. A. Marsh kindly forwarded
me there were only about half a dozen such; a few milium, one rugosula, one
Oscariana, as mentioned above, and one specimen of a form penels probably will
prove to be a new species of quite peculiar formation.

Vertigo parvula, SterK1, The Nautilus, 1890, p. 136.

The above is Sterki’s description.

200 BULLETIN OF THE

Vertigo approximans, Srerx1.

In 1887, Mr. A. A. Hinkley, of Dubois, Ill., sent me, with other Pupide, one
specimen of a Vertigo, probably new, and in 1889 another of the same. The said
gentleman and Mr. William A. Marsh kindly forwarded me all their Pupide for
examination, but so far I have found no other example, yet I am satisfied such will
be found. The form is related to Vertigo ovata and Gouldii, but different, and is
characterized by the two palatal lamelle being close together, for which reason I
gave it the manuscript name V. approximans.

Vertigo approximans, StERKI, The Nautilus, 1890, p. 186.

The above is Sterki’s description.

Vertigo rugosula, STerx1.

Related to V. ovata and Gouldi:; in shape more elongated than the latter, more
cylindrical, and somewhat larger. Apertural parts and lamellze much like those of
ovata; but the columella is decidedly longer and straighter, and the inferior colu-
mellar lamella is distinctly placed on it. Length 1.8-2.0, diameter 1.1mm. Of a
peculiar formation is the surface. Of the five well-rounded whorls, about one and
a half of the upper are nearly smooth; the following, with exception of
the last, are distinctively and regularly striated; the last is very finely
but distinctly rugose in the sense of the lines of growth, near the aper-
ture again striated. Color, dark chestnut.

This is a beautiful species, of which I saw the first example in the
collection of Mr. Bryant Walker, who had found it in April last at
Pass Christian, Mississippi. Last September, Mr. W. G. Mazyck col-
lected a number of them on Sullivan’s Island, S.C. In either place
they were in company of Pupa rupicola, Say. Quite lately I have seen
one example from Lee County, Texas, sent by Mr. J. A. Singley; it was a dead
shell, and not fully mature, but recognizable. The species consequently seems to
be widely distributed along the South Atlantic and Gulf coasts. Two specimens
were sent in by Mr. H. Hemphill, who collected them at Fish Camp, Fresno Co., Cal.

In Eastern Florida, Volusia County, etc., a form has been found to be quite com-
mon which I refer to this species, but as a distinct variety which may be called
ovulum. It is somewhat smaller, ovate; the striation and rugosity of the surface
are less marked, and the inferior apertural lamella is wanting. In turn it has in
most examples a lamella at the base (between inferior columellar and inferior
palatal), and the callus in the palatal wall is rather strong. The coloration of part
of them is somewhat lighter. It cannot be confounded with V. ovata, Say, its rela-
tions to the type of rugosula being evident, and, in addition, ovata has been found
with it. Nor can it be referred to ventricosa. It is Jarger and stronger, of much
darker color, its surface is not so smooth and polished, it has three or even four
lamelle more, and the columella is longer.

Vertigo rugulosa, SteR«K!I, Proc. Acad. N. Sci. Phila., 1890, p. 34.

AG

ain

ini)

' V. rugosula.

The above is Sterki’s description. The figure was drawn by him.

MUSEUM OF COMPARATIVE ZOOLOGY. 201

Liguus fasciatus, Mott.

Plate I. Fig. 5,

The Vaccas Key variety, noticed in page 435 of the Manual of American
Land Shells, is figured in the plate.

Orthalicus undatus, Bruce.
Plate II, Fig, 4,

I give a new figure of the variety of this species.

Holospira Arizonensis, Stearns.

Shell dextral, elongately cylindrical, pupiform, dingy white to pale horn-color,
translucent. Number of whorls, twelve to thirteen. Slightly convex, the su-
tures distinctly defined. The upper six or seven
whorls rather abruptly tapering towards the obtuse
apex, which has a slightly twisted and rather a
papillose aspect. The last whorl is curved under
and constricted back of the mouth, forming an
umbilical notch. The apex and following whorl
are smooth; the three or four succeeding whorls
sharply and somewhat obliquely plicated longitu-
tudinally, the median and following whorls be-
coming somewhat obscurely sculptured other than
by distinct growth lines. The basal whorl is
strongly sculptured below, and back of the mouth,
and obtusely angulated underneath. Aperture
ovate, slightly angulated anteriorly, somewhat
effuse, rimmed and projecting. The dimensions of two examples are as
follows : —

mm.
GOW SIGHUC empresa isay eet oi, aR) 'e YRS c /raty aia rece (nk Gd eoe Oe
Mon eCitudern nye (ik alyetach esp IA or oar) oe GG ds
Greatestiatameter ys aii04 <soraw oi oCLae ch ent OS i ase hee Wn
Greatesindiameteris 406 ofits, oie e ole So) Shae al eee a or

Dos Cabezas, Arizona, where the above two specimens and numerous fragments
were found in a cave in November, 1889, by V. Bailey, and contributed to the
United States National Museum (No. 104,392) by Dr. C. Hart Merriam.

Among the species of this group that are geographically related is H. Remondi,
Gabb, described from Arivechi, Province of Sonora, Mexico, a form sharply sculp-
tured throughout, and in minor features also different; H. Pfeifferi, Menke, col-
lected by Remond at Hermosillo, in the same province, with the previously named

202 BULLETIN OF THE

species; and H. (Calocentrum) irregulare of Gabb, from the high table-lands back of
Mulege, in the peninsula of Lower California. All of these are separable at a
glance from <Arizonensis.

The above is Stearns’s description and figure from Proc. U.S. National Mus.,
Vol. XIII. p. 208, Plate XV. Figs. 2, 3, 1890.

Onchidella borealis, Datt.

Coos Bay, Oregon.

It is gregarious in its habits. Fifty specimens were taken in a small crevice of
clay shale, near high tide. Single individuals, or several clustering together, were
taken afterwards lower down on the tide under loose stones. When in motion, the
animal moves off quite rapidly for so small a creature, with two short, stout pedun-
cles protruding in front of the mantle, bearing keen, sharp black eyes. The color is
dark slate, splashed with blotches and streaks of ashen white. The body when in
motion is 4 inch long, 3; wide, § high, and oblong-oval in form, a little broader
behind than before. It is covered with small tubercles, which are larger around
the edge of the mantle than those higher up on the body, giving the edge of the
mantle a serrated or tooth-like appearance when the animal is at rest. When
it is at rest on a smooth surface, the base of the animal is nearly circular,
or a little longer than wide, the centre of the body is elevated to quite a sharp
apex, which together with its color resembles some varieties of a very young
Acmea pelta, aad would be very readily taken for such by an inexperienced col-
lector. The foot is white, and works in rapid undulations when the animal is in
motion.

The above remarks are made by Mr. Hemphill in a recent letter.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Figs.
Fig.

Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.
Fig.

Sat no ans Oo CONG ta) RO re

—

SON fy eS oe

MUSEUM OF COMPARATIVE ZOOLOGY.

EXPLANATION OF PLATES.

PLATE i.

Anadenus Cockerelli. Animal and internal shell.
Patula strigosa, var. Buttoni.

Arionta ruficincta.

Glandina decussata, var. Singleyana.

Liguus fasciatus, var. from Key Vaccas.
Bulimulus Dormani.

Arionta Ayersiana.

Zonites Simpsoni, enlarged.

Binneya notabilis, enlarged.

Same as Figure 2, toothed variety.

PLATE II.

Pupa calamitosa, reduced from original figure.
Pupa hordeacella, from original figure.
Selenites Duranti, var. Catalinensis, enlarged.
Orthalicus undatus, variety.

Selenites Vancouverensis, var. Keepi, enlarged.
Triodopsis Mullani, var. Blandi.

1, 8. Arionta tudiculata, var. cypreophila.

$y

Bo IS eC OO yal a) il

Bulimulus Ragsdalei, enlarged one half.

PLATE III.

Limax Hemphilli, var. pictus. Animal and internal shell.

Zonites Diegoensis, enlarged.

Zonites macilentus, enlarged.

Tebennophorus Hemphilli, jaw.

Anadenus Cockerelli, jaw and tongue.

Pristiloma Lansingi, enlarged.

Zonites Caroliniensis, enlarged.

Helicodiscus fimbriatus, var. salmonaceus, enlarged.
Zonites sculptilis, enlarged.

203

204 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY.

PLATE IV.
Fig. 1. Arionta Kelletti, var. multilineata.
Fig. 2. Arionta Kelletti, var. nitida.
Fig. 3. Arionta Kelletti, var. albida.
Fig. 4. Arionta Kelletti, var. castanea.
Fig. 5. Euparypha Tryoni, var. nebulosa.
Fig. 6. Euparypha Tryoni, var. fasciata.
Fig. 7. Patula strigosa, var. bicolor.
Fig. 8. Patula strigosa, var. lactea.
Fig. 9. Patula strigosa, var. albofasciata.

BINNEY: 4TH SUPPL. TO TERR. MOLL.

PLATE I.

Me.
eee ‘

ere,
tee

f
(
%&

BINNEY: 4TH SUPPL. TO TERR. MOLL. PLATE Ih.

ee

BINNEY: 4TH SUPPL. TO TERR. MOLL.

PLATE tit.

BINNEY: 4TH SUPPL. TO TERR. MOLL.

PEATE IVs

PUBLICATIONS

OF THE

MUSEUM OF COMPARATIVE ZOOLOGY

AT HARVARD COLLEGE.

ANNUAL REPORT of the Trustees, together with a Report of the Director, for *1859, *1860,
*1861, *1862, *1863, *1864, *1865, *1866, *1867, *1868, *1869, 1870, 1871, *1872, 1878, 1874, 1875.
1876.

ANNUAL REPORT of the Curator to the President and Fellows of Harvard Coliege for *1877-78,
*1878-79, *1879-80, 1880-81, *1881-82, *1882-83, 1883-84, 1884-85, 1585-86, 1886-87, 1887-88,
1888-89, 1889-90, 1890-91.

>

BULLETIN. Vol. I., April, 1863 —November, 1869, contains the following papers : —
No. 1. List of the FISHES sent by the Museum to different Institutions, in exchange
for other Specimens, with Annotations. By F. W. Putnam. pp. 16. April,
1868. 5c.
No. 2. List of the ECHINODERMS. By Atexanper AGassiz. pp.12. August, 1863. 10c.
. List of the POLYPS and CORALS. ByA.E. Verritt. pp. 32. January, 1864. 20c.
No. 4, List of BRACHIOPODS from the Island of Anticosti. By N.S. SHater. pp. 10.
' June, 1865. 10c.
No. 5. The FOSSIL CEPHALOPODS of the Museum of Comparative Zodlogy. By
AupHeus Hyatt. pp. 382. December, 1867. 20c.
No. 6. Contributions to the FAUNA of the Gulf Stream at Great Depths. By L. F.
DE Pourratks. pp.18. December, 1867. 10c. ;
Do. Second Series. pp. 22. December 10, 1868. 15c.
Catalogue of the MAMMALS of Massachusetts. ByJ.A.ALLEN. pp.110. October,
1869. 5c.
No. 9. Preliminary Report on the ECHINI and STARFISHES dredged in deep water
between Cuba and the Florida Reef, by L. F. de Pourtalés. Prepared by ALEX-
ANDER AGASSIZ. pp. 56. October, 1869. 40c.
No. 10. Preliminary Report on the OPHIURID and ASTROPHYTID4 dredged by
L, F. de Pourtalés. Prepared by THEopoRE Lyman. pp. 46. November, 1869. 35c.
No. 11. List of the CRINOIDS obtained on the Coasts of Florida and Cuba, in 1867,
1868, 1869. By L. F. DE PourtaLis. pp.4. November, 1869. 5c.
* No. 12. List of HOLOTHURIDA dredged by L. F. pp Pourtatis. pp. 8. November, 1869. 5c.
* No. 13. Report upon the DEEP-SEA DREDGINGS during the Third Cruise of the
U. S. Coast Survey Steamer “ Bibb.” By Louts Acassiz. pp. 24. November 16,
1869. 15c.

a
9
9

*
A

as

oi

Vol. II., August, 1870 — April, 1871, contains : —

* No.1. On the EARED SEALS. By J. A. ALLEN. With an Account of the HABITS of
the NORTHERN FUR SEAL. By CuHartes Bryant. pp. 108. 6 Woodcuts and
8 Plates. August, 1870. $1.00. Plates destroyed by fire.
* No.2 Preliminary Report on the CRUSTACEA dredged by L. F. de Pourtalés. Pre-
pared by WILLIAM Stimpson. Part]. pp. 52. December, 1870. 50c.
* No.3. On the MAMMALS and WINTER BIRDS of Hast Florida. By J. A. ALLEN.
pp. 290. 5 Plates. April, 1871. $8.25.
No. 4. Directions for DREDGING. Drawn up by L. F. DE PourTaLes. pp.4. 5c.
No. 5. Appendix to Preliminary Report on ECHINI. By ALexanDeR AGassiz. pp. 8. April,
1871. 5c.

* Out of print.

mY PUBLICATIONS OF THE

Vol. III., May, 1871 —July, 1876, contains : —

* No. 1. BRACHIOPODS of the Straits of Florida. By W.H. Datu. pp. 45. 2 Plates. May,
1871. 85c.

* No.2. Application of PHOTOGRAPHY to Illustrations of Natural a pp. 2.
2 Plates. November, 1871. 25c. Plates destroyed by fire.

No.3. A Letter concerning DEEP-SEA DREDGING addressed to Professor Peirce. By
Louris AGAssIz. pp. 5. December, 1871. 5c.

No. 4. Preliminary Notice of a few Species of ECHINI. By Atexanper AGassiz. pp. 4.
January, 1872. 5c.

* No.5. FOSSIL CEPHALOPODS of the Museum. Embryology. By A. Hyarr. pp. 63.
4 Plates. June, 1872. $1.25.

* No. 6. ORNITHOLOGICAL RECONNAISSANCE of Kansas, Colorado, Wyoming, and
Utah. By J. A. Auten. pp.71. July, 1872. 50c.

No. 7. Interim Report on the HYDROIDS collected by L. F. de Pourtalés. By GzorGE
J. AttmMan. pp. 2. January, 1878. 5c.

No. 8. The ECHINI collected by the Hassler Expedition. By ALEXANDER AGASSIZ. pp. 4
January, 1873. 5c.

No.9. Catalogue of the TERRESTRIAL AIR-BREATHING MOLLUSKS of N. Amer-
ica. By W. G. Binney. pp. 30. 1 Plate. October, 1878 50c.

* No. 10. OPHIURID and ASTROPHYTIDA, Old and New. By THEopoRE LYMAN. pp.
51. 7 Plates. February, 1874. $1.75.

+ No.11. Exploration of LAKE TITICACA, by Alexander Agassiz and S. W. Gar-
man. I. FISHES and REPTILES. By S. W. Garman. pp. 6. 1 Plate. No-
vember, 1875. 20c.

+ No.12. Exploration of LAKE TITICACA. II. Notice of the PALAOZOIC FOSSILS.
By Orvitte A. Dersy, M.S. With Notes by ALEXANDER AGassiz. pp. 8. March,
1876. 10c.

+ No. 13. Recent CORALS from Tilibiche, Peru. By ALexanpER AGAssiz and L. F. pE Pour-
TALES. pp.4. 1Plate. March, 1876. 1é5c.

+ No. 14. The Development of SALPA. By Wm. K. Brooxs. pp. 58. 34 cuts, March, 1876. 75c.

+ No. 15. Exploration of LAKE TITICACA. III. List of MAMMALS and BIRDS. By J.
A, ALLEN. With Field Notes by S. W. Garman. pp. 11. July, 1876. 10c.

+ No.16. Exploration of LAKE TITICACA. IV. CRUSTACEA. By Watrer Faxon. With
87 cuts. pp. 15. July, 1876. 5c.

* Vol. IV., July, 1878, contains :—

The TERRESTRIAL AIR-BREATHING MOLLUSCA of the United States and Adjacent
Territories of North America. By W. G. Bryyey. Vol. V. pp. 449. 104 Plates, 312
Cuts. July, 1878. $7.50.

Volume V., April, 1878 — December, 1879, contains : — 5
No.1. Letter No.1 to C. P. Patterson, Supt. U. S. Coast Survey, on the DREDGING
OPERATIONS of the U.S.C. S. Str. “Blake.” By A. Acassiz. pp.9. April,
1878. 10c.

* No. 2. On the Presence of DEMODEX FOLLICULORUM in the Skin of the Ox. By W.
Faxon. pp.7. 1 Plate. May, 1878. 15c.

* No.3. The RICHMOND BOULDER TRAINS. By E.R. Benton. pp. 26. 2 Maps. May,

1878. 45c.

* No. 4. Description of a New Species of CORBICULA, with Notes on other Species of the
Corbiculade Family. By TempLe Prive. pp.4. 1 Plate. July, 1878. 12c.

* No.5. Notes on the Anatomy of CORBICULAD (Mollusca) and a Translation from the
Danish of an Article on the Anatomy of Cyclas by Jacobsen. By TEMPLE PRIME.
pp. 8. 1 Plate. July, 1878. 20c.

* No.6. Letter No. 2 to C. P. Patterson, Supt. U. S. Coast Survey, on the DREDGING
OPERATIONS of the U.S. C. S. Str. “Blake.” By A. Acassiz. With Prelim-
inary Report on the Mollusca of the Expedition. By W. H. Datu. pp. 10.
2 Plates. July, 1878. 20c.

* No.7. OPHIURIDZ and ASTROPHYTID of the ‘‘Challenger” Expedition. By T.
Lyman. Part I. pp. 104. 10 Plates. July, 1878. $1.50.

* Out of print. + Nos. 11-14, also 15-16, are not sold separately.

MUSEUM OF COMPARATIVE ZOOLOGY. 3

No. 8. Reports on the DREDGING OPERATIONS of the U. S.C. 8S. Str. “Blake.” I.
Description of SOUNDING MACHINE, Water-Bottle, and Detacher. By
Lieut.-Commander ©, D. Siaspez, U.S. N. pp.1l. 5 Plates. December, 1878. 60c.

*No. 9. Revorts on the DREDGING OPERATIONS of the U.S. C.5. Str. “Blake.” II.
ECHINI, by A. AGassiz. CORALS and CRINOIDS, by L. F. pr Pourratts.
OPHIURANS, by T. Lyman. pp. 58. 10 Plates. December, 1878. $1.50.

No.10. Reports on the DREDGING OPERATIONS of the U.S. C.5S. Str. “Blake.” III.

Report on HYDROIDA. ByS. F. Ciarke. pp. 14. 5 Plates. January, 1879. 65c.

* No. 11. On some Young Stages in the Development of HIPPA, PORCELLANA, and
PINNIXA. By W. Faxon. pp.16. 5 Plates. April, 1879. 66c.

* No. 12. Reports on the DREDGING OPERATIONS of the U.S.C. 5. Str. “ Blake.” IV.
Preliminary Report on the WORMS. By Prof. Ernst Eauers of Gottingen. pp. 6.
June, 1879. 5c. ;

* No. 13. On the Classification of ROCKS. By M. E. Wapsworts. pp. 138. June, 1879 5c.

No. 14. Letter No. 3 to C. P. Patterson, Supt. U. S. Coast Survey, on the DREDGING
OPERATIONS of the U.S. C. S. Str. ‘‘ Blake.” By A. Acassiz. pp. 14. 2 Maps.
June, 1879. 35c.

No. 15. On the Development of PALAAMONETES VULGARIS. By Wa tTER Faxon. pp. 28.

. 4 Plates. September, 1879. 68c.

No. 16. On the Jaw and Lingual Dentition of certain TERRESTRIAL MOLLUSKS. By

W. G. Bryyey. pp. 88. 2 Plates. December, 1879. 55c.

Vol. VI., Part I., September, 1879 — October, 1880, contains Nos. 1-11:—

No.1, List of the DREDGING STATIONS occupied by the U.S. C. 8. Steamers ‘‘Cor-
win,” “ Bibb,” ‘* Hassler,” and ‘‘ Blake,” from 1867-1879. By BrensaMIn PEIRCE
and CarLite P. Parrerson, Superintendents of the U.S. Coast Survey. pp. 16. Sep-
tember, 1879. 5c.

No. 2. OPHIURID and ASTROPHYTID/ of the ‘‘ Challenger” Expedition. By Turo-

DORE Lyman. PartII. pp.67. 9 Plates. December, 1879. $1.50.

No. 3. Reports on the Results of DREDGING under the Supervision of ALEXANDER
Agassiz, in the Gur of Mexico, 1877-78, by the U. 8. C.S. Str. “Blake.” Lieut.-
Commander C. D. Siasper, U.S. N., commanding. V. General Conclusions from
a Preliminary Examination of the MOLLUSCA. By W. H. Daw. pp. 9.
February, 1880. 10c.

No. 4. Report on the Results of DREDGING, by the U. S.C. S. Str. ‘‘Blake.”” VI. Report
on the CORALS and ANTIPATHARIA. By L. F. pre Pourratis. pp. 26.
3 Plates. February, 1880. 55c.

* No. 5. The Ethmoid Bone in the BATS. By Harrison ALLEN, M.D. pp.2. April, 1880. 5c.

* No. 6. On Certain Species of CHELONIOIDA. By S. W. Garman. pp. 4. April, 1880. 5c.

* No. 7. Contribution to a Knowledge of the Tubular JELLY FISHES. By J. Watrer
Fewkes. pp. 20. 3 Plates. April, 1880. 50c.

* No. 8. Letter No. 4 to C. P. Patterson, Supt. U. S. Coast Survey, on the DREDGING
OPERATIONS of the U.S. C.S. Str. ‘“‘ Blake,” Commander Bartlett, U.S. N.,
during the summer of 1880. By A. Acassiz. pp.8. September, 1880. 10c.

* No. 9. Reports on the Results of DREDGING by the U. 8. C. 8. Str. ‘‘ Blake”? VII.
Description of a GRAVITATING TRAP for obtaining Specimens of Ani-
mal Life from intermedial ocean Depths. By Lieut.-Commander C. D. SicsBEe,
U.S.N. pp.4. 1Plate. September, 1880. 15c.

No. 10. On some Points in the Structure of the Embryonic ZOHA. By Watrer Faxon.
pp. 8. 2double Plates. October, 1880. 40c.

No.11. New Species of SELACHIANS in the Museum Collection. By 8. Garman. pp. 6.
October, 1880. 5c.

Vol. VI., Part II., October, 1881, completing the volume, contains : —

No. 12. Maturation, Fecundation, and Segmentation of LIMAX CAMPESTRIS Binney,
By E, L. Marg. pp. 458. 5 Plates. October, 1881. $7.50.

* Out of print.

4 PUBLICATONS Ol THE

Vol. VII., July, 1830 — August, 1884, Geological Series, Vol. I, contains :—

No. 1. Notes on the Geology of the IRON and COPPER Districts of LAKE SUPERIO},
By M. E. Wapsworta. pp. 164. 6 Plates. July, 1880. $2.25.
No.2. The FELSITES and their Associated Rocks North of Boston. By J. 8. Dinter
pp. 16. May, 1881. 1he. :
7 No. 3, Onan Occurrence of GOLD in Maine. ByM.E.Wapswortu. p.1. May, 1881. ic.
+ No. 4. A Microscopical Study of the IRON ORE or PERIDOTITE of Iron Mine Hill,
Cumberland, Rhode Island. By M. E. WapsworrH. pp. 5. May, 1881. 5c.
No. 5. Observations upon the Physical GEOGRAPHY and GEOLOGY of Mount Ktaadn
and the adjacent District. By C. E. Hamun. pp. 35. 2 Plates. June, 1881. 55c.
No.6. Report on the recent additions of FOSSIL PLANTS to the Museum Collections.
By L. LesQuerevx. pp. 6. October, 1881. 5c.
No.7. The great DIKE at HOUGH’S NECK, Quincy, Mass. By J. E. Woxrr. pp. 12.
July, 1882. 10c.
No. 8. On some specimens of Permian FOSSIL PLANTS from Colorado. By Lzo
LESQUEREUX. pp.4. October, 1882. 8c.
¢ No.9. On the relations of the TRIASSIC TRAPS and SANDSTONES of the Eastern
United States. By Witt1am Morris Davis. 3 Plates. pp. 59. January, 1888. 5c.
t+ No. 10. The Folded Helderberg LIMESTONES east of the Catskills. By Witt1am Morris
Davis. pp. 20. 2 Plates. January, 1888. 25c.
No. 11. The AZOIC SYSTEM andits Subdivisions. By J. D. Warrney and M. E. Wapsworrta.
pp. Xvi. and 835. August, 1884. $2.50.

Vol, VIII., December, 1880 — March, 1881, contains : —

No. 1. Reports on the Results of DREDGING by the U.S. C. S. Steamer ‘‘Blake.” VIII.
Etudes preliminaires sur les Crustaces. Par A. Mitne-Epwarps. Ie. Partie.
pp. 68. 2 Plates. December, 1880. 90c.

No. 2. Reports on the Results of DREDGING by the U. S C. &S. Str. “Blake.” IX.
Preliminary Reports on the ECHINI. By A. Acassiz. pp.7. December, 1880. 5c.

No. 3. New and little-known REPTILES and FISHES in the Museum Collections. By
S.GarMAN. pp.1l. February, 1881. 10c.

No. 4. List of DREDGING STATIONS occupied during the year 1880 by the U.S. C. 8.
Str. “Blake.” pp.4. February, 1881. 5c.

No. 5. Reports on the Results of DREDGING by the U.S. C. 8. Str. “Blake.” X. Re-
port on the CEPHALOPODS and on some additional Species dredged hy the
U. S. F. C. Str. ‘“‘ Fish-hawk,” during the Season of 1880. By A. E. VERRILL,
pp.17. 8 Plates. March, 1881. $1.00.

No.6. The Stomach and Genital Organs of ASTROPHYTIDA. By T. Lyman. pp. 8.
2 Plates. February, 1881. 30c.

No. 7. Reportson the Results of DREDGING by the U.S. C.S. Str. “Blake.” XI. Re-
port on the ACALEPHA. By J. W. Fewxes. pp.14. 4 Piates. March, 1881. 50c.

No. 8. Studies of the JELLY-FISHES of Narragansett Bay. By J. W. FewKEs. pp. 42.
10 Plates. February, 1881. $1.50.

No. 9. List of MAMMALS collected by Dr. Edward Palmer in Northeastern Mexico,
with Field-Notes by the Collector. By J. A. ALLEN. pp. 7. 5c.

No. 10. The TRILOBITE : New and Old Evidence relating to its Organization. By C. D.
Watocorr. pp. 41. 6 Plates. March, 1881. $1.00.

No. 11. Reports on the Results of DREDGING by the U. 8. C. S. Str. “Blake.” XII Re-
port on the SELACHIANS. ByS. Garman. pp. 8. March, 1881 5c.

No. 12. Reports on the Results of DREDGING iy the U. S. C. S. Str. “Blake.” XIII.
Report on the PYCNOGONIDA. ByE. B. Wuson. pp. 18. 5 Plates. March

1881. 65c.

No. 13. On some CRUSTACEAN DEFORMITIES. By W. Faxon. pp. 18. 2 Plates. March
1881. 40c. :

No. 14. The DEVONIAN INSECTS of New Brunswick. By H. A. Hagen. pp. 10. March,
1881. 10c.

+ Nes. 3-4, also 9-10, are not sold separately.

Cn

MUSEUM OF COMPARATIVE ZOOLOGY.

Vol, IX., June, 1881 — April, 1882, contains : —

No.1. Reports on the Results of DREDGING, by the U.S. C. S. Steamer ‘‘Blake.” XIV,
Déscription sommaire des Espéces nouvelles d’ASTERIES. Par HE. Perrier. pp. 81.
June, 1881. 30ce.

No. 2. Reports on the Results of DREDGING by the U.S.C. S. Str. “Blake.” XV
Preliminary Report on the MOLLUSCA. By W.H. Dau. pp. 112. December,
1881. $1.00.

No. 3. Letter No. 5 to C. P. Patterson, Supt. U. S. Coast Survey, on the EXPLORATIONS
in the vicinity of the Tortugas, during March and April, 1881. By A. Acassiz.
pp. 5. July, 1881. 5c.

No. 4. Report on the Results of DREDGING by the U.S. C. S. Steamer “Blake.” XVI.
Preliminary Report on the COMATULA. By P. H. Carpenter. pp. 20.
1 Plate. October, 1881. 20c.

No. 5. Observations on the Species of the Genus PARTULA Fer.,with a Bibliographical
Catalogue of all the Species. By W. D. Harrman. pp. 26. 2 double Plates,
December, 1881. 50c.

No.6. BIBLIOGRAPHY to accompany ‘Selections from Embryological Monographs,”
compiled by A. Acassiz, W. Faxon, and E. L. Mark. I. CRUSTACEA. By W.
Faxon. pp. 54 March, 1882. 50c.

No.7. Explorations of the SURFACE FAUNA of the Gulf Stream under the Auspices
of the U.S. Coast Survey. By A. Agassiz. I. Notes on ACALEPHS from the
Tortugas with a Description of New Genera and Species. By J. W. FEWKEs.
pp. 40. 7 Plates (3 double). April, 1882. $1.25.

No. 8. On the ACALEPH/ of the East Coast of New England. By J. W. Fewxes. pp. 20.
1 double Plate. April, 1882. 30c.

Vol. X., June, 1882 — May, 1833, contains : —

No.1. Reports on th: Results of DREDGING by the US. C.S. Steamer ‘* Blake. °
XVII. Report on the CRUSTACEA. PartI. DECAPODA. By §. I. Sma
pp- 108. 16 Plates. June, 1882. $2.50.

No. 2. BIBLIOGRAPHY to accompany ‘Selections from Embryological Monographs,”
compiled by A. AGassiz, W. Faxon, and E. L. Marg. II. ECHINODERMATA.
By A. AGAssiz. pp. 26. August, 1882. 25c.

No. 3. Ona Revision of the Ethmoid Bone in the MAMMALIA. By Harrison ALLEN.
pp. 27. 7 Plates. November, 1882. 75c.

No. 4. Reports on the Results of DREDGING by the U.S. C. 8S. Steamer “Blake.”
XVIII. The STALKED CRINOIDS of the Caribbean Sea. By P.IL. CaRPENTER-
pp. 16. December, 1882. 15c.

No. 5. Reports on the Results of DREDGING by the U. 8. C. S. Steamer ‘‘ Blake.” XTX.
Report on the FISHES. [East Coast of the U.S.] By G. Brown GoopE and
TarLeTonN H. Bean, pp. 37. April, 1883. 30c.

No. 6. Reports on the Results of DREDGING by the U.S. C. 8. Steamer ‘‘ Blake.” XX.
Report on the OPHIUROIDEA. By THroporr Lyman. pp. 50. 8 Plates. May,
1883. $1.00.

Vol. XI., July, 1833 — July, 1885, contains *—

No.1. Reports on the Results of DREDGING by the U.S, GS. Steamer “Blake.” XXT.
Report on the ANTHOZOA and on some Additional Species dredged by the
‘Blake ” in 1878-79, and by the U. S. Fish Commission Steamer “‘ Fish Hawk”
in 1880-82. By A. E. Verriwy. pp. 72. 8 Plates. July, 1888. $1.25.

No.2. Reports on the Results of DREDGING in the U. S. CO. S. Steamer “Blake.”
XXII. A Chapter in the History of the Gulf Stream. By ALEXANDER AGASSIZ.
pp.5. May, 1883. 5c.

* No.3. Exploration of theSURFACE FAUNA of the Gulf Stream, under the Auspices
of the U.S. Coast Survey. By Atrxanper Acassiz. IV. Ona few MEDUSA
from the Bermudas. By J. WatTer Fewkes. pp. 10. 1 folding Plate. August,
18838. 20c.

* Out of print.

6 PUBLICATIONS OF THE

No. 4. Reports on the Results of DREDGING by the U. S. C. S. Steamer ‘‘Elake.”
XXIII. Report on the ISOPODA. By Oscan Harcer. pp. 13. 4 Plates.
September, 1883. 40c.

No. 5. Reports on the Results of DREDGING by the U. 8. C. S. Steamer ‘ Blake.”
XXV. Supplementary Report on the ‘‘Blake” CEPHALOPODS. By A. E.
VERRILL. pp.12. 38 Plates. October, 1888. 40c. ;

No.6. Descriptions of Two Species of OCTOPUS, from California. pp. 8. 3 Plates.
October, 18838. 40c.

No. 7. Reports on the Results of DREDGING by the U. S. C. S. Steamer “Blake.”
XXVI. Verzeichniss der von den United States Coast Survey Steamers
“‘ Hassler” and ‘‘ Blake,” von 1867 zu 1879, gesammelten MYZOSTOMIDEN.
Von Dr. L. v. GrarF. pp.9. November, 1888. 10c.

No. 8. A Supplement to the Fifth Volume of the TERRESTRIAL AIR-BREATHING
MOLLUSKS of the United States and adjacent Territories. By W. G.
Binney. pp. 22. 4 Plates. December, 1883. 60c.

No.9. Studies from the Newport Marine Zoological Laboratory. XIII. On the De-
velopment of certain WORM LARVA. By J. W. Fewxss. pp. 42. 8 Plates.
December, 1883. $1.25.

No. 10. BIBLIOGRAPHY to accompany ‘‘Selections from Embryological Monographs,
compiled by A. AGassiz, W. Faxon, and E. L, Marx.” III. ACALEPHS. By J.
W. Fewskes. pp. 30. July, 1884. 30c¢.

No. 11. Studies from the Newport Marine Laboratory. XV. On the Development of
AGALMA. By J. W. Fewxes. pp. 36. 4 Plates. July, 1885. 5c.

Vol. XII, July, 1885 — September, 1836, contains: —

No.1. CHLAMYDOSELACHUS ANGUINEUS Garm. A Living Species of Cladodont
Shark. By SamMueL Garman. July, 1885. 385 pp. 20 Plates. Tc.

No. 2. Reports on the Results of DREDGING by the U. S.C. S. Steamer ‘‘ Blake.”
XXVII. Report on the Specimens of BOTTOM DEPOSITS. By Joun Murray.
25 pp. October, 1885. 50c.

No. 3. Contributions from the Embryological Laboratory. VIII. Observations on the
Development of AGELENA NAIVIA. By Wuuiam A. Locy. 41 pp. 12 Plates.
January, 1886. $1.50.

No 4. Studies from the Newport Marine Laboratory. XVII. Preliminary Observations
on the Development of OPHIOPHOLIS and ECHINARACHNIUS, By J. W.
Fewkes. 48 pp. 8 Plates. March, 1886. $1.50.

No. 5. Reports on the Results of DREDGING by the U. S. C. 8S. Steamer “Blake.”
XXVIII. Description of thirteen Species and two Genera of FISHES from
the ‘‘Blake” Collection. By G. Browne GoopE and TarLeron H. Bean. 28 pp.
July, 1886. 50c.

No. 6. Reports on the Results of DREDGING by the U.S. C. S. Steamer “Blake.”
XXIX. Report on the MOLLUSCA. PartI. BRACHIOPODA and PELE-
CYPODA. By W.H. Dau. pp. 148. 9 Plates, September, 1886. $2.50.

Vol. XIII., October, 1886 — August, 1888, contains —

No.1. Reports on the Results of DREDGING by the U S.C. S. Steamer “Blake.”
XXX Report on the HOLOTHURIOIDEA. By H. Tater. pp. 22. 1 Plate.
October, 1886. 30c.

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. Bryney. pp. 26. 3 Plates. December, 1886. 30c.

No.3. Simple Eyes in ARTHROPODS. By E. L. Marg. pp. 58. 5 Plates. February,
1887. $1.00.

No. 4. Studies from the Newport Marine Laboratory. XVIII. On the Development of
the Calcareous Plates of AMPHIURA. By J. W. Fewkes. pp. 44. 3 Plates.
May, 1887. $1.00.

No. 5. Preliminary Account of the FOSSIL MAMMALS from the White River Forma-
tion contained in the Museum of Comparative Zodlogy. By W. B. Scorrand
H. F. Osporne. pp. 22. 2 Plates. September, 1887. 40c.

MUSEUM OF COMPARATIVE ZOOLOGY. i

No. 6. The EYES in SCORPIONS. By G. H. Parker. pp. 36. 4 Plates. December, 1887. 75c.

No. 7. Studies from the Newport Marine Laboratory. XIX. On certain MEDUSA
from New England. By J. W. Fewxes. pp. 32. 6 Plates. February, 1888. $1.00.

No. 8. On certain Vacuities or Deficiencies in the CRANIA of MAMMALS, By D.D.
Snape. pp.6. 2Plates. March, 1888. 25c.

No. 9. The Superior Incisors and Canine TEETH of SHEEP. By Fuorence Mayo.
pp. 12. 2 Plates. June, 1888. 25c.

No. 10. The RATTLE of the RATTLESNAKE, By S. Gapman. pp. 10. 2 Plates.
August, 1888. 18c.

Vols, XIV.-XV. [April, 1888] contain : —

A Contribution to American THALASSOGRAPHY. Three CRUISES of the United
States Coast and Geodetic Survey Steamer “Blake” in the GULF OF
MEXICO, in the CARIBBEAN SEA, and along the ATLANTIC COAST of
the UNITED STATES, from 1877 to 1880. By ALEXANDER Agassiz, 2 vols. pp.
xxii,. 814, and (6), 220 Maps and Woodeuts. [April,] 1888. For sale by Houghton,
Mifflin, & Co.

Vol. XVI., Geological Series, Vol. II. [March, 1888-] contains : —

No. 1. On the Petrographical Characters of a DIKE of DIABASE, in the BOSTON
BASIN. By W.H. Hoss. pp. 12. 1 Plate. March, 1888. 25c.

No. 2. On the Geology of the CAMBRIAN DISTRICT of Bristol County, Massachusetts.
By N.S. Ssater. pp. 30. Map and 2 Plates. October, 1888. 4c.

No. 3. FOSSIL PLANTS collected at Golden, Colorado. By Leo Lesquereux. pp. 18.
December, 1888. 5c. -

No. 4. The FAULTS in the TRIASSIC FORMATION near Meriden, Connecticut. By
W.M. Davis. pp. 28. 5 Plates, April, 1889. 25c.

No, 5. On the Occurrence of FOSSILS of the CRETACEOUS AGE on the Island of
Martha’s Vineyard, Massachusetts. By N.S. Saater. pp. 10. 2 Plates. June,

: 1859. 25c.

No. 6. The Intrusive and Extrusive TRIASSIC TRAP SHEETS of the Connecticut
Valley. By W. M. Davis and C. L. Wurrtis. pp 47. 5 Plates. December, 1889. 80c.

No. 7. The TOPOGRAPHY OF FLORIDA. By N.S. SHater. With a Note by ALEXANDER
Agassiz. pp. 20. 1 Plate. March, 1890. 25c. _

No. 8. Onsome Occurrences of OTTRELITE and ILMENITE SCHIST in New England.
By J. E. Wourr. pp.8. April, 1890. 5c.

No. 9. On KERATOPHYRE from Marblehead Neck. By J. H. Sears. pp. 6. July,
1890. 5c.

No. 10. METAMORPHISM of CLASTIC FELDSPAR in Conglomerate Schist. By
J. E. Worrr. pp. 12. 2 Plates. September, 1891. 45c.

(Vol. XVI. to be continued.)

Vol. XVII. [July, 1888-December, 1889] contains :—

No. 1. Studies from the Newport Marine Laboratory. XX. On the Development of
the Calcareous Plates of ASTERIAS. By J. W. Frewkes pp. 56. 5 Plates.
July, 1888. $1.00

No. 2. On the LATERAL CANAL SYSTEM of the SELACHIA and HOLOCEPHALA.
By S. Garman pp. 64. 53 Plates. September, 1888. $150.

No. 3. The CORAL REEFS of the Hawaiian Islands. By ALexanDER AGAssiz. pp. 50.
13 Plates. April, 1889. $1.25.

No, 4. Studies on the Primitive Axial SEGMENTATION of the CHICK. By Jota B.
Piatt. pp. 20. 2 Plates. July, 1889. 30c.

No. 5. The Morphology of the CAROTIDS, based on the Study of the Blood-vessels of
CHLAMYDOSELACHUS ANGUINEUS, Ganman By H. Ayers. pp. 33 1
Plate. October, 1889. 42c. i

No. 6. CAVE ANIMALS from Southwestern Missouri. By Samurt Garman pp. 25.
2 Plates. 25c. December, 1889.

Vol. XVIII. contains : —
Reports on the Results of Dredging by the U.S. C.S. Steamer ‘Blake.’
XXIX. Report on the MOLLUSCA. Part II. GASTROPODA and SCAPHO-
PODA. By W.H. Datt. pp 492. 31 Plates. June, 1889. 5.50.

8 PUBLICATIONS OF THE -

Vol. XIX. [March-May, 1890] contains : —

No. 1. Studies on LEPIDOSTEUS. Part I. By E. L. Marg. pp. 128. 9 Plates (Zodl.
Lab., XV.) March, 1890. $2.50.

No. 2. On the Egg Membranes and Micropyle of OSSEOUS FISHES. By C. H. Eicen-
MANN. pp. 25. 3 Plates. (Zodl. Lab. XVI.) March, 1890. $1.00.

No. 3. Reports on the Results of DREDGING by the U. S.C. 8S. Steamer “Blake.”
XXXII. Report on the NUDIBRANCHS. By Rup. Berea. pp. 27. 3 Plates,
March, 1890. 75c.

No. 4. A Third Supplement to the Fifth Volume of the TERRESTRIAL AIR-BREATH-
ING MOLLUSKS of the United States and Adjacent Territories. By W. G.
Binney. pp. 44 11 Plates. May, 1890. $1.50.

Vol. XX. [May, 1890-January, 1891] contains :—

No. 1. Contributions from the Zodlogical Laboratory. XVII. The History and Devel-
opment of the EYE in the LOBSTER. By G. H. Parker. pp. 60. 4 Plates,
May, 1890. $1.00.

No. 2. On the Rate of GROWTH of CORALS. By ALExanpeR AGassiz. pp.4. 4 Plates.
August, 1890. 10c.

No. 3. Preliminary Account of the FOSSIL MAMMALS from the White River and
Loup Fork Formations. Part II. CARNIVORA and ARTIODACTYLA, By
W. B. Scorr. PERISSODACTYLA. By H. F. Oszorn. pp. 86. 3 Plates.
November, 1890. 40c.

No. 4. Contributions from the Zoological Laboratory. XIX. CRISTATELLA: the
Origin and Development of the Individual in the Colony. By C. B. Daven-
PoRT. pp. 52. 11 Plates. November, 1850. $1.25.

No. 5. Contributions from the Zoological Laboratory. XX. The EYES in BLIND
CRAYFISHES. By G.H. Parker. pp.12. 1 Plate. November, 1890. 165c.

No. 6. Notice of CALAMOCRINUS DIOMEDA, a new stalked Crinoid from the
Galapagos, dredged by the U. S. Fish Commission Steamer ‘ Albatross.” By
By ALEXANDER AGassiz. pp. 4. December, 1890. 5c.

No. 7. Contributions from the Zoological Laboratory. XXI. The Origin and Develop-
ment of the CENTRAL NERVOUS SYSTEM in LIMAX MAXIMUS. By
Annie P. Hencuman. pp. 40. 10 Plates. December, 1890. $1.25.

No. 8. Contributions from the Zoological Laboratory. XXII. The PARIETAL EYE
in some LIZARDS from the Western United States. By W. E. Ritter. pp.
20. 4 Plates. January, 1891. $1.00.

Vol. XXI. [April-August, 1891] contains : —

No. 1. Contributions from the Zoological Laboratory. XXIV. Contributions to the
MORPHOLOGY of the TURBELLARIA I. On the Structure of PHAGO-
CATA GRACILIS, Leripy By W. M. Woopworts. pp. 44. 4 Plates. April, 1891.
75e.

No. 2. Contributions from the Zoological Laboratory. XXV. The COMPOUND EYES
in CRUSTACEANS. By G. H. Parker. pp 98 10 Plates. May, 1891. $1.25.

No. 3. Contributions from the Zoological Laboratory. XXVI. On some Points in the
Anatomy and Histology of SIPUNCULUS NUDUS, L. By H. B. Warp.
pp. 48. 8 Plates. May, 1891. 75c.

No. 4. THREE LETTERS from ALEXANDER AGASSIZ on the Dredging Operations
of the “Albatross,” off the WEST COAST of Central America to the
GALAPAGOS, etc. pp. 16. June, 1891. 10c.

No. 5. Contributions from the Zoological Laboratory. XXVII. The Development of
the PRONEPHROS and SEGMENTAL DUCT in AMPHIBIA. By H. H.
Fietp. pp. 140 8 Plates. August, 1891. $1.75.

Vol. XXII. contains :—
No. 1. Contributions from the Zoological Laboratory. XXVIII. Observations on the
Budding of Paludicella and some other Bryozoa. By C. B. DavenrorT. pp.
114. 12 Plates. November, 1891.
No. 2. Contributions from the Zoological Laboratory. XXIX. The Gastrulation of
Aurelia flavidula, Pér. & Les. By Frank Smita. pp. 12. 2 Plates. December,
1891.

MUSEUM OF COMPARATIVE ZOOLOGY. 9

The Quarto Publications will hereafter be issued as Muemorrs. The Jilustrated Cata-
logues thus far published have been collected into Vols. I-IV. of the MEmorRs.

MEMOIRS.

Vol. I., October, 1864 — February, 1865, contains Nos. 1, 2, Illustrated Catalogue.
No.1. OPHIURIDA and ASTROPHYTIDA. By TueEopore Lyman. pp. 200. 19
Woodcuts and 2 Plates. October, 1864. $3.50
No. 2, NORTH AMERICAN ACALEPH/. By ALExanpER AGassiz. pp. 234. 360
Woodcuts. February, 1865. $4.00.

Vol. I1., April, 1870 — May, 1876, contains Nos. 3, 4, 5, 6, Illustrated Catalogue, and No. 9
of Memoirs.
No. 3. Monograph of the NORTH AMERICAN ASTACIDA, By Dr. Hermann A,
Hacen. pp. lll. 11 Plates. April, 1870. $4.00.
* No.4. Deep-Sea CORALS. By L. F. pr Pourrares. pp. 93. 8 Plates. 1871. $8.00.
No. 5. Immature State of the ODONATA. Part I. Sub-family Gomphina. By Louis
Capot. pp.17. 3 Plates. July, 1871. $1.00.
No.6. Supplement to the OPHIURIDZ and ASTROPHYTIDA. By THEODORE
Lyman. pp.17. 2 Plates. October, 1871. T5c.
* No.9. On some INSECT DEFORMITIES. By Dr. H. A. Hagen. pp.22. 1 Plate.
May, 1876. 75c.

* Vol. III., 1872-74, contains No. 7 Illustrated Catalogue. 1vol. Text;1-vol.Plates. (Plates
partly destroyed by fire.)

No. 7. Revision of the ECHINI. By Arxanper Acassiz. pp. 796. 69 Woodcuts. 94
Plates. 1872-74. 50.00.

Vol. IV., February, 1874, — May, 1876, contains No. 8 Illustrated Catalogue and No. 10 of
Memoirs.
No. 8. The Zodlogical Results of the Hassler Expedition :—
*T. ECHINI, CRINOIDS, and CORALS. By AtexanpER AGassiz and L. F. DE
Pourtates. pp. 54. With 15 Cuts and 10 Plates. February, 1874. $3.00.
*II. OPHIURID and ASTROPHYTID4, including those dredged by the late
Dr. Stimpson. By THeoporE Lyman. pp. 384. With 5 Plates and 4 Cuts. Feb-
ruary, 1875. $1.50. é
No. 10. The American BISONS, Living and Extinct. By J. A. Auten. In connection
with the Geological Survey of Kentucky. pp. 246. With 12 Plates and Map.
May, 1876. $5.00.
For this number apply to Prof. N. 8. SHater, Cambridge, Mass.

Vol. V., April — November, 1877, contains :—
*No.1. North American STARFISHES. By ALEXANDER AGAssiz. pp. 137. With 20
Plates and 20 Cuts. April, 1877. $5.50.
No. 2. Report on the HYDROIDA collected during the Exploration of the Gulf
Stream by L. F. de Pourtalés, Assist. U. S. Coast Survey. By Grorce J.
AtmaN, M.D., LL.D., F.R.S. pp. 66. With 34 Plates. November, 1877. $4.00.

Vol. VI., January, 1878 — October, 1880, contains : —
No.1. The AURIFEROUS GRAVELS of the Sierra Nevada of California. By
J. D. Warrney. pp. xviii. and 569. With 24 Plates and 2 folded Maps, one of
which is in 2 sheets. pp. 1-288, April, 1879 ; pp. 289-569, October, 1880.
No. 2. Report on the FOSSIL PLANTS of the Auriferous Gravel Deposits of the
Sierra Nevada. By Leo LesqueReux. pp. viii. and 62. With 10 Double Plates.
January, 1878.
Vol. VI. of the Memoirs is published in connection with Prof. J. D. Whitney, to whom
application must be made for copies by parties‘nof on the regular exchange list of the Museum.
Vol. VII., May, 1880 — October, 1882, contains : —
No.1. Report on the FLORIDA REEFS. By Lovrs Agassiz. Accompanied by Illus-
trations of FLORIDA CORALS, from drawings by Sonrer, BurKHARDT, A.
* Out of print.

10 PUBLICATIONS OF THE

Acassiz, and Rorrrer. With an Explanation of the Plates, by L. F. pz Pour-
TaLEs. Published by permission of A. D. BacHe and CaRLiLe P. Parrerson, Super-
intendents of the U. S. Coast Survey. pp. 61. 23 Plates. May, 1880. $5.50.

No. 2. The CLIMATIC CHANGES of Later Geological Times. A Discussion based
on Observations made in the Cordilleras of North America. By J. D.
Wairney. Part I., containing pp. viii and 120, October, 1880. Part I1., contain-
ing pp. 121-264. Part III. pp. 265-394. October, 1882.

For sale. Apply to Prof. J. D. WHITNEY.
Vol. VIII., August, 1881 — July, 1884, contains : —

No. 1. Immature State of the ODONATA. Part II. Subfamily ASCHNINA. By
Louis CaBor. pp. 40. 5 Plates. August, 1881. $1.50.

No.2. Exploration of the SURFACE FAUNA of the Gulf Stream under the Aus-
pices of the U.S. Coast Survey. By Auexanper AGassiz. III. Part I. The
PORPITID2 and VELELLIDA. By Atexanper AGAssiz. pp.16. 12 Plates.
July, 1883. $1.50.

No. 3. North American REPTILES. By S. Garman, in connection with the Kentucky
Geological Survey, N. S. Suater, Director. pp. 200. 9 Plates. [Issued by the
Museum, July, 1884.]

Apply to Prof. N. S. SHaLer.
Vol. IX., July, 1882 — September, 1884, contains : —

No.1. Selections from EMBRYOLOGICAL MONOGRAPHS, compiled by A. Acassiz,
W. Faxon, and E. L. Mark. I, CRUSTACEA. By W. Faxon. pp. 28, 14
Plates. July, 1882. $3.00.

No. 2. Selections from EMBRYOLOGICAL MONOGRAPHS, compiled by ALEXANDER
Agassiz, WALTER Faxon, and E. L. Marx. II. ECHINODERMATA. By
ALEXANDER AGASsiz. pp. 45. 15 Plates. July, 1883. $3.00.

No. 3. Selections from EMBRYOLOGICAL MONOGRAPHS, compiled by A. Acassiz,
W. Faxon, and E. L. Marx. III. ACALEPHS. By J. W. Fewxes. POLYPS.
By E. L. Marg. pp. 52. 183 Plates. September, 1884. $3.00.

(Vol. IX. to be continued.)
Vol. X., September, 1883 — September, 1885, contains : —

No.1. Reports on the Results of DREDGING by the U. S. C. S. Steamer “‘ Blake.”
XXIV. Part I. Report on the ECHINI. By AtexanpER AGassiz. pp. 126.
82 Plates. September, 1888. $7.00.

No.2. Onan Extinct Type of DOG from Ely Cave, Lee County, Virginia. By J. A.
Aten. 13 pp. 3 Plates. December, 1885. Apply to Prof. N. S. SHater.

No.3. Results of an Examination of SYRIAN MOLLUSCAN FOSSILS, chiefly
from the Range of Mount Lebanon. By C. E. Hamtty. pp. 68. 6 Plates.
April, 1884. $2.50.

No. 4. A Revision of the ASTACIDA. By Watrer Faxon. pp. vi, 186. 10 Plates.
September, 1885. $5.00.

Vol. XI. contains : — :

No.1. LITHOLOGICAL STUDIES. A Description and Classification of the ROCKS
OF THE CORDILLERAS. By M. E. Wadsworth. pp. xvi, 208, and xxxii.
8 Plates. Cambridge, October, 1884.

Apply to Prof. J. D Watney.
(Vol. XI. to be continued.)
Vols. XII.and XIII., April — August, 1884, contain: —
The WATER BIRDS of North America. Vol. I., pp. xi and 537; Vol. II., pp. 552.
With numerous Woodcuts in the Text. By 8. F. Barrp, T. M. Brewer, and R. Ripeway.
Issued in Continuation of the Publications of the Geological Survey of California, J. D.
Wauitney, State Geologist. April and August, 1884.
For sale by Little, Brown, & Co., Boston, Mass.
Vol. XIV. contains : —

*No. 1. Studies from the Newport Marine Laboratory. XVI. Development of OS-
SEOUS FISHES. I. Pelagic Stages of YOUNG FISHES. By ALsxanDER
Agassiz and C. O. Wairman. pp. 56. 19 Plates. September, 1885. $8.50.

* Out of print.

MUSEUM OF COMPARATIVE ZOOLOGY. 11

é
*No. 1, Part II. 1. Studies from the Newport Marine Laboratory. XVI. The De-
velopment*of OSSEOUS FISHES. Part II. The Pre-embryonic Stages of
Development. Part I. The History of the Egg from Fertilization to Cleavage.
By ALEXANDER AGassiz and C. 0. Wuirman. pp.40. 12 Plates. June, 1889. $2.00.
(Vol. XIV. to be continued.)
Vol. XV. contains : — :
Reports on the Results of DREDGING by the U. S. C. S. Steamer “Blake.”
XXXI. Report on the ANNELIDS. By Ernst Esuers. pp. vi, 835. 60 Plates.
October, 1887. $12.50.
Vol. XVI. contains : —
No.1. Notes on the TAXODIUM DISTICHIUM, or BALD CYPRESS. By N. 8.
SHALER. pp. 16. June, 1887.
No. 2. On the original CONNECTION of the Eastern and Western COAL FIELDS
OF THE OHIO VALLEY. By N.S.Saater pp. 12. June, 1887.
(For Nos. 1 and 2, apply to Prof. N. S. SHALER.)
No. 3. Genesis of the ARIETIDA. By AtpHeus Hyrarr. pp. 288. 14 Plates. Decem-
ber, 1889. $5.00.
(Published in connection with the Smithsonian Institution.)
_Vol. XVII. contains : —

No. 1. Immature Stages of the ODONATA. Part III. Subfamily CORDULINA.
By Louis Cazor. pp. 52. 6 Plates. February, 1890. $1.50.
(Vol. XVII. to be continued.)

No. 2. Reports on an Exploration off the West Coasts of Mexico, Central and
South America and off the Galapagos Islands, in charge of Alexander
Agassiz of the U.S. Fish Commission Steamer “‘ Albatross” during 1891,
Lieut. Commander Z. L. Tanner, U.8.N., commanding.
I. Calamocrinus Diomedz, a new stalked crinoid, with Notes on the Apical
System and Homologies of the Echinoderms. By ALEXANDER AGASSIZ.
With 32 Plates. (Jn press.)

In preparation : —

Reports on the Results of Dredging Operations in 1877, 1878, 1879, and 1880, in charge
of ALEXANDER AGAssIz, by the U.S. Coast Survey Steamer ‘‘Blake,” as follows :—

A. MILNE EDWARDS. Crustacea of the ‘‘Blake.” In press, the Paguride, with 12
Plates.

E. EHLERS. The Annelids of the ‘Blake.”

G. B. GOODE and T. BEAN. Deep-Sea Fishes of the East Coast of the United States.
“Blake” and “Albatross” Collections published in connection with the National
Museum.

A. A. HUBRECHT. The Nemerteans.

C. HARTLAUB. The Comatule of the “Blake,” with 15 Plates.

A, E. VERRILL. The Alcyonaria of the “Blake.”

Illustrations of North American MARINE INVERTEBRATES, from Drawings by
BURKHARDT, SONREL, and A. AGAssiz, prepared under the Direction of L. Acassiz.

Selections from EMBRYOLOGICAL MONOGRAPHS, compiled by A. AGAssiz, W. Faxon,
and E. L. Marx (discontinued for the present).

AGASSIZ and WHITMAN. Pelagic Fishes. Part II., with 14 Plates.

W. G. BINNEY. 4th Supplement to the Fifth Volume of Terrestrial Air-breathin«
Mollusks of the United States. With 2 Plates. (Jn press.)

LOUIS CABOT. Immature State of the Odonata, Part IV.

S. GARMAN. The Discoboli. With 13 Plates. (Jn press.)

E. L. MARK. Studies on Lepidosteus, continued.

iF On Arachnactis. :
W. B. SCOTT and H. F. OSBORN. White River Fossils, continued.

* Out of print,

12 PUBLICATIONS OF THE ZOOLOGICAL MUSEUM.

N. S. SHALER. Boulder train of Rhode Island.

M. E. WADSWORTH. Lithological Studies. Part IT.

J. D. WHITNEY. Origin and Mode of occurrence of Iron and its Ores.

Nomenclature and Classification of Ore-Deposits.

Contributions from the ZOOLOGICAL LABORATORY, in charge of Professor E, L. Marx,
as follows : —

E. R. BOYER on the Mesoderm of Teleosts.

H. P. JOHNSON. Embryonal Envelopes of the Scorpion. (t-press-)

W. WHITNEY. The Histology of Thyond.

Contributions from the PETROGRAPHICAL LABORATORY, in charge of Dr. J. E
Wo rr, as follows: —

Acmite Trachyte from the Crazy Mountains, Montana. V. By J. E. Wotrrand R §. Tarr.

Reports on the Results of the Expedition of 1891 of the U. S. Fish Commission Steamer
‘* Albatross,” Lieutenant Commander, Z. L. Tanner, U.S. N., commanding, in charge of
ALEXANDER AGaAssIZ, as follows : —

A. AGASSIZ. Report of the Cruise. With 22 Plates. (Jn press.)

> The Acalephs and the Pelagic Fauna.
3 The Echini.

J. E. BENEDICT. The Annelids.

W. H. DALL. The Mollusks.

Cc. B. DAVENPORT. The Bryozoa.

S. F. CLARKE and Y. E. PEABODY. The Hydroids.

W. FAXON. The Crustacea.

S. GARMAN. The Fishes.

A. GOES. The Foraminifera.

C. HARTLAUB. The Comatule.

W. E. HOYLE. The Cephalopods.

R. VON LENDENFELD. The Phosphorescent Organs of Fishes.

H. LUDWIG. The Holothurians.

C. F. LUTKEN. The Ophiuride.

E. L. MARK. The Actinarians.

JOHN MURRAY. The Bottom Specimens.

ROBERT RIDGWAY. The Alcoholic Birds.

W. PERCY SLADEN,. The Starfishes.

L. STEJNEGER. The Reptiles.

THEO. STUDER. The Alcyonarians.

H. V. WILSON. The Sponges.

W. M. WOODWORTH. The Planarians.

ALEXANDER AGASSIZ.
CamBRInGE, Mass., Dec. 20, 1891.

Application for the Publications of the Museum should be made to the Director of the Museum of
Comparative Zodlogy, Cambridge, Mass.

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