will be seen that there are two slender flagella to a cell. Each pair
of flagella has a pair of basal bodies that are longer than thick, and
which are continued as a thin fiber towards the nucleus of the cell.
That these centrad continuations of the basal bodies extend to or past
the nucleus I could not determine. Sometimes the basal bodies with the
centrad continuations are pushed quite to one side of the cell (Fig.
27), while in other cells they are applied quite to the distal surface
(Figs. 7, 17, 27). Fig. 17, and the part of Fig. 7 that shows these
points, are taken just through the tips of the cells. The darker lines
within the polygonal areas are the intracellular basal bodies with their
centrad continuations, while the thinner lines are the flagella, and
are supposed to lie in the plane just below the plane of the figure.
In those instances in which the centrad continuations are applied to
the distal surface of the cells they could occasionally be seen to bend
centrad (Fig. 27b). While these cilia with their basal bodies and centrad
continuations are usually separate, as shown in the figures, yet they are
at times applied quite closely to each other so that the double nature
of the basal bodies and their centrad continuations is not evident. When
the intracellular continuations of the cilia become pushed to one side or
applied to the distal surface of the cells, I believe this to be due to
the turgor of the cells consequent upon the deposition of large masses
of secretion within them. But I must add that this explanation is not
altogether satisfactory, since in the endoderm cells of the pedalia of
both Charybdea and Tripedalia I found like conditions with no evidence
of a secreting function. (See below, under tentacles.) No one, to my
knowledge, has described the flagellation in detail, although both Claus
and Schewiakoff state that the endoderm is ciliated.
The “floating cells” in the stomach pockets and in the ampulla, described
by Conant, I believe are in part derived from the endothelial cells of
the ampulla. That a portion of them may arise from the ovary, as Conant
explains, I do not doubt; I have, further, found a mass of floating cells
in a small Charybdea quite as Conant describes for Tripedalia (his Fig.
71). In this Charybdea, however, I could find no traces of any ovary.
Conant speaks of larger and smaller floating cells, and that the smaller
ones are also found in the males. This latter fact agrees with what I
have suggested, that some of the floating cells arise in the ampulla.
My chief reasons for my supposition, however, are the following: I find
globules of the secretion of the ampulla cells in some of the floating
cells and also scattered loosely among them (Fig. 19). These globules
in and among the floating cells have the same general appearance and a
similar staining capacity as the secretion in the ampulla cells. Again,
in spaces within some of the ampulla cells I find bodies resembling
the floating cells with lumps of the secretion within them (Fig. 18).
The conclusion, therefore, lies near that some of the floating cells
originate within the cells of the ampulla, engulf within them some of
the secretion, and are then expelled into the lumen of the ampulla.
Better said, perhaps, they represent portions of the ampulla cells
with some of the secretion. I also found several instances in which a
floating cell had the appearance of being expelled from an ampulla cell.
Conant suggests for a similar observation that the cells were about to
be swallowed by the ampulla cells. I believe, however, that my finding
a secretion similar to that within the cells of the ampulla, in some
of the floating cells, as also bodies very much like them and filled
with secretion within the ampulla cells, together with Conant’s finding
floating cells in males, and finally the observation that the floating
cells are usually quite dilapidated, never showing a healthy cell
structure--all this leads me to conclude that some of the floating cells
originate from the ampulla cells, and that they have a nutrient function
in distributing the secretion. This is quite the reverse of what Conant
supposed,--that they were taken in as nourishment by the ampulla cells. I
also find what appears to be a secretion in the endoderm of the tentacles
of both Charybdea and Tripedalia, and believe this is another source of
the floating cells. (See below, under tentacles.)
I also found other very darkly staining bodies (Fig. 19) both within
the floating cells and free in the ampulla cavity, and more numerous
in the ampulla cells themselves. This again goes to show that floating
cells take their origin from the ampulla cells. What these darkly
staining bodies are, I cannot say. Perhaps they are something akin to the
“Chromatoider Nebenkörper” described by Lenhossek (L), or they represent
another kind of secretion. If these floating cells are derived from the
cells of the ampulla, the active nuclear division within these also
receives an explanation. Some nuclear matter can usually be observed in
the floating cells.
_The Endothelium of the Peduncle._--The endothelium of the peduncle
consists of flagellate columnar cells (Fig. 27, upper half). The cells
are vacuolated at their bases like some of the cells of the ampulla,
and contain a comparatively large nucleus with nucleolus. The flagella
are long and slender, quite like those described for the cells of the
ampulla, except that there is only one to each cell. The basal bodies of
the flagella are of a peculiar shape. They may be described as a bent
spindle, continuous at their distad ends with the cilia and at their
centrad ends with a fiber that can be traced quite to the neighborhood of
the nucleus. I could not trace these fibers into the basal parts of the
cells, except in one instance, and I could not be sure of that (Fig. 27a).
Another interesting observation in connection with the basal bodies is
that they are bent in one direction on one side of the canal and in
an opposite direction on the other side. In Fig. 27, which represents
a longitudinal section of the endoderm and the supporting lamella of
the dorsal (_i. e._ farthest from the eyes) side of the peduncle, the
distal ends of the basal bodies are bent towards the ampulla, while on
the ventral side they would be bent away from the ampulla. This seems
to suggest that the flagella move the contents of the canal in one
direction on the dorsal side of the canal and in an opposite direction
on the ventral side. Conant observed in living material that bodies in
the ampulla and the canal were moving about, and that bodies within the
tentacles were moving in opposite directions at the same time. This
last observation and the histological facts just described, I believe,
are mutually corroborative. Again, _a priori_, we should expect some
such mechanism as the one described to bring about an exchange between
the contents of the ampulla and that of the stomach pockets. I have not
as yet been able to demonstrate a similar flagellate mechanism in the
tentacles. Flagella and basal bodies are present in the tentacles, but I
could not determine that the basal bodies had any definite arrangement
like that shown in Fig. 27. (See under tentacles.) I may add, yet, that
the cells in the canal of the manubrium have cilia, similar to the ones
just described, with large basal bodies, and with centrad continuations.
Finally, I am not certain but that these cells form buds at their ends
quite like those I describe for the endothelial cells of the tentacles
(see below), and that they aid in the formation of the floating cells. I
thought I saw such buds just at the entrance of the lumen of the peduncle
into the ampulla, but could not find conclusive evidence.
_The Tentacles and the Pedalia._--My observations on the tentacles were
begun with the object of demonstrating a flagellate mechanism similar to
the one described above for the endothelium of the peduncle. While I have
failed to demonstrate such a mechanism for the tentacles, yet several
interesting points came to my notice. It will be remembered that the
tentacles of the Cubomedusæ are not directly attached to the bell, but
that a blade-like portion, the pedalium, intervenes between the tentacles
and the bell. For figures of the pedalia and the tentacles the works of
Haake, Claus, Conant and Maas[22] may be consulted.
_The Ectoderm._--The ectoderm of the tentacles is the seat of a number of
differentiations. It is quite thick, as the figures (28 and 29) show, and
in this respect is very different from the pedalia, on which the ectoderm
cells are quite cubical. I found evidence of cilia here and there, but
I can add nothing definite about them. Neither can I add any definite
statements regarding the ectoderm cells proper, but what I have to say
relates to their differentiations.
(a) The _thread cells_ are of two kinds, larger ones and smaller ones.
This is well shown in Fig. 29, which is part of a transverse section of
a tentacle of Tripedalia. Two kinds of nettle-cells are also present
in the tentacles of Charybdea, but they were specially well shown in
Tripedalia. The structure of these thread-cells seems to be typical, and
I have little more to say about them. I wish, however, to call attention
to the five or six unstriped muscle-fibers that are attached to their
basal lateral parts, and which connect them with the basement membrane
(Figs. 28, 29). Claus describes these muscle-fibers and mentions that Fr.
Müller has described them before him, but I have not found them mentioned
elsewhere in the literature of nettle-cells. Professor Brooks tells me,
however, that he has often found them. It would appear from Fig. 29 that
they serve to retract the thread-cells from the surface. Claus suggests
that the muscles are developed from the cnidoblasts.
(b) The plain subectodermal _muscle-fibers_ are of interest. In
Charybdea they lie wholly enclosed within canals of the supporting
lamella (Fig. 32, upper part). They run longitudinally, and near the
base of each tentacle pass out of their canals and become strictly
subectodermal (Figs. 31, 32). This is for Charybdea. In Tripedalia they
rarely come to lie in closed canals as in Charybdea. These facts show
beyond doubt that these muscles are developed from the ectoderm. Claus
has suggested their ectodermal origin, but did not demonstrate it. He
also suggested that they become inclosed in canals by the supporting
lamella pushing up around them and finally fusing above them. This, I
believe, is demonstrated by the conditions in Tripedalia (Fig. 29). Here
the canals usually remain open, but occasionally, as in the left-hand
canal, one may become completely inclosed. This condition of things
suggests the intra-lamellar muscles found in actiniarians. The nuclei
found in the canals with the muscle-fibers probably belong to the cells
from which the muscles become differentiated. Claus figures these
muscle-fibers and nuclei, and it may be added that the supporting lamella
he figures, for C. marsupialis, is much thicker than I have figured it
for C. Xaymacana and Tripedalia cystophora. The number of muscle-canals
also is greater and occupies a much greater depth of the thickness of
the lamella. Since Claus gives a figure of a transverse section showing
the muscles in their enclosed canals, I have not deemed it necessary to
duplicate his figure. In the transition from a tentacle to a pedalium,
the muscles are most strongly developed toward and at the edges of the
pedalium. This is true for the pedalia in general, and accounts for
the readiness with which they can be bent inwards, as noted in the
physiological part of this paper.
(c) I have found a single _ganglion-cell_ among the cells of the ectoderm
of the tentacles. This showed so plainly that I have figured it (Fig.
28). Other ganglion-cells no doubt exist, but could probably not be
distinguished from other cells. In its position in Fig. 28 it appears to
be associated with the nettle-cell shown just above it. Its position is
very much the same as that figured by Lendenfeld (25a).
_The Endoderm._--The cells of the endoderm of a tentacle are long and
quite slender (Fig. 31). At their bases they are vacuolated quite like
the cells of the ampulla and the canal of the sensory clubs. They contain
a well-formed nucleus with a nucleolus. In their distal half small light
bodies with a dark center are very evident. These bodies are evidently a
secretion.
Another peculiar phenomenon presents itself in these cells. The distal
part of each cell becomes separated off from its body by what appears
to be the formation of a transverse cell-wall (Fig. 31, c-d). I have
found the ends of these cells quite separated off in some series. The
formation of the walls seems to begin as a thickening at the sides of the
cells, and a section through this region, transverse to the cells, would
appear like Fig. 30. The dots in the centers of the polygonal areas of
this figure are the centrad continuations of the cilia to be described
below. As already remarked in describing the endoderm of the ampulla, I
believe we here have another place of origin of the “floating cells.” The
secretion just described moves into the distal parts of the cells prior
to their separation (Fig. 31). In some series I could see these secretion
bodies much more numerous within the distal ends of the cells than in
Fig. 31.
As will be seen in Fig. 31, each of the endoderm cells of the tentacles
has a flagellum that extends into the lumen of the tentacle. Each
flagellum has a thickening just within its cell, which may be regarded
as a basal body. From this basal body, again, a small fiber extends
centrad into each cell. It does not appear that the flagella are thrown
off with the distal parts of the cells; at all events, I never found
them connected with any of the floating cells except in a few doubtful
instances.
What I have said for the endoderm of the tentacle of Charybdea applies
equally to Tripedalia.
Claus, in his figure of a transverse section of a tentacle of C.
marsupialis shows the endoderm as cubical. I cannot explain why there
should be such a difference between the endoderm of the tentacles of _C.
marsupialis_ and that of the tentacles of _C. Xaymacana_ and _Tripedalia
cystophora_. Claus does not describe the endoderm in detail.
The endoderm cells of the pedalia of both Charybdea and Tripedalia are
cubical and possess flagella, basal bodies, and centrad continuations,
quite like those I have described for the endoderm cells of the ampulla.
The double nature of the basal bodies and the centrad continuations is,
however, not so evident. A secretion I did not find. Histologically,
therefore, the endothelium of the pedalia corresponds rather with that of
the ampulla, and that of the tentacles with that of the peduncle of the
clubs.
SUMMARY.
The most important results in the histological part of this paper relate
to the structure of the retinas of the eyes of the sensory clubs.
The retina of the distal complex eye is composed of three kinds of cells:
two kinds of sensory cells (the prism and pyramid cells), and the long
pigment cells (Figs. 1-9). The prism and pyramid cells have each an axial
nerve fiber in their prisms and pyramids respectively. These fibers I
could, however, trace only to the neighborhood of the nuclei. But since
I could trace similar fibers in the retinal cells of the simple eyes
(Fig. 16) past the nucleus into the subretinal nerve tissue, I believe
that the axial fibers in question also extend centrad as nerve fibers
into the subretinal nerve tissue. Other observers also figure such fibers
as extending centrad as nerve fibers. The axial fibers of the prism
cells have each a dumbbell-shaped basal body at their entrance into the
pigmented part of a cell. The evidence for a body of such shape in the
pyramid cells was not conclusive, though a basal body for the axial fiber
exists. The long pigment cells project or retract their pigment in light
or darkness respectively and thus seem to serve to check the diffusion of
light in the retina. I have also supposed that these cells may serve for
conducting impulses to the lens, and that the latter is adjustable.
The proximal complex eye (Fig. 13) has only the prism cells present in
its retina, and not two kinds of cells as Schewiakoff has described (see
text, pp. 53, 60, 63) for all the eyes.
The simple eyes (Fig. 12), two on each side of a club, four in all,
also have only one kind of cells in their retinas, and each cell has
a flagellum extending into the vitreous secretion of the lumen. These
flagella could be traced centrad as a nerve fiber (Figs. 12, 16).
Similarly, a nerve fiber could be traced centrad from the flagella of
the epithelial cells of the clubs. Dumbbell-shaped basal bodies for the
flagella of the simple eyes could also be demonstrated, but the evidence
for this in the epithelial cells of the clubs was not so satisfactory.
Other points of interest are: A secretory epithelium lining the ampulla
of the clubs, and a somewhat similar epithelium lining the canals of
the tentacles (Figs. 7, 27, 31); the partial origin of the “floating
bodies” in the canals of the clubs and tentacles and the stomach pockets
from these epithelia (Figs. 18, 19); two flagella to each cell of
the endothelium of the ampulla and of the pedalia (Figs. 7, 17); the
peculiar nuclei in the endothelial cells of the ampulla (Fig. 20); the
longitudinal muscles of the tentacles being completely inclosed within
canals of the supporting lamella, but near the base of a tentacle
becoming subectodermal. This demonstrates their ectodermal origin. In
Tripedalia it is seldom that any of these muscles become enclosed as in
Charybdea (Fig. 29).
If to the reader my results seem to embody a somewhat heterogeneous
detail, he must remember that the work consists partly in corroborating
and partly in supplementing the work of previous observers, and that,
in general, histological detail does not usually make the most readable
paper.
BIOLOGICAL LABORATORY, JOHNS HOPKINS UNIV., May 1899.
FOOTNOTES
[a] It was at one time supposed that the concretions in the marginal
bodies of medusæ represented lenses and the surrounding nerve tissue the
optic nerve, a supposition so highly improbable that it never gained any
acceptance. (Ib., p. 41, note.)
[b] Eimer’s results I get from Romanes and Hesse[III].
[c] By no means do I wish to attribute intelligence to these animals.
[d] Haake[2] says that in the adult _Charybdea Rostonii_ the vitreous
bodies of the complex eyes are absent but present in the young. It is
difficult to explain this observation except on grounds of imperfect
preservation of the adult material, for in all observations on other
forms a vitreous body is described. Haake evidently did not use sections,
and for this reason his results must be regarded as of doubtful accuracy.
Haake also says that the simple lateral eyes of the clubs are absent in
the adult, but present in the young.
[e] In the series from which Fig. 3 is taken the pyramid-cells are not
so readily demonstrated. Indeed, I missed them altogether at first in
this and some other series and supposed that there were only two kinds of
cells (19), but upon a careful re-examination I could demonstrate them to
my satisfaction. They did not show, however, in the particular section of
Fig. 3, so that they are not indicated in this figure.
[f] I go into this at some length because the cell-walls in the series
that showed the nuclei best differentiated as lighter and darker ones did
not show well, and there might be some doubt that these lighter nuclei
belonged to the pyramid cells. I could, however, in many instances,
trace the axial fibers of the pyramids through the pigmented zone to
these lighter nuclei (as already noted) which fact can leave no doubt
but that some of these nuclei belong to the pyramid cells. (Similar
nuclei, however, are found to belong to the long pigment cells, to be
described below.) Centrad these pyramid cells are continued into a single
process just as the prism cells were shown to be (Fig. 7). Figures 6,
8, 9, and 21 show samples of all the pigmented cells found in macerated
preparations, and none of these (except Fig. 9, long pigment cells) show
more than a single centrad process. Hence, I conclude that centrad both
the pyramid cells and prism cells are continued as a single prolongation.
[g] I have been able to demonstrate nucleoli in all the different nuclei
of the cells of the sensory clubs.
[h] It may be objected that my criterion, the presence of axial fibers,
is not necessarily characteristic of visual cells. However, the great
general occurrence of such axial fibers (Patten,[5] Grenacher,[16]
Schreiner,[12] Hesse,[13] myself, in simple complex eye, see below, and
perhaps others) in eyes in which the retina has only one kind of cells,
would seem to indicate that they are quite characteristic of visual
cells. Note again that in the proximal eye of Charybdea there is only one
kind of cells and with axial fibers.
[i] Mr. J. C. Olsen, of the Chemical Laboratory, kindly made these tests
for me.
LITERATURE.
LITERATURE REFERRED TO IN THE SECTION ON PHYSIOLOGY.
I. ROMANES, G. J. a. ’75, ’77. The Locomotor System of Medusæ.
Philosophical Transactions. London. Vol. CLXVI, pt. 1. Vol. CLXVII, pt. 2.
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II. MURBACH, LOUIS. ’95. Preliminary Notes on the Life-history of
Gonionemus. Journal of Morphology. Vol. XI.
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VII. (See also 8, below.)
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1. CARRIÈRE, J. ’85. Die Schorgane der Thiere. München u. Leipzig.
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5. PATTEN, WILLIAM. a. ’89. Studies on the eyes of Arthropods. II. Eyes
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b. ’98. A Basis for a Theory of Color Vision. American
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Cells of Palæmonites, and their Relation to the Central Nervous System.
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(Brooks and Herrick). Natl. Acad. Sciences. Vol. V, p. 454.
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Medusen. Leipzig.
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LITERATURE REFERRING TO THE CENTRAD CONTINUATIONS OF CILIA AND FLAGELLA.
A. HAECKEL, E. ’72. Die Kalkschwämme. Vol. I, p. 141; Vol. III, Pl. 25,
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