Philip Henry Gosse.

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duncle, it is true, seems out of place, being on the out-


side of the dome, instead of hanging suspended from its
interior; but this difference is only apparent, and arises
from the circumstance that the disk is reverted. If you
suppose the edge of the disk to be turned in the opposite
direction, you will have the peduncle in its normal place:
the umbrella in these specimens is carried within, and the
sub- umbrella without; an inversion which is probably

Comparing now this strange production of a Medusa
by a Polype, with what I lately told you of the produc-
tion of Polypes by a Medusa (as in the case of the lovely
little Turris), you will have some acquaintance with the
wondrous phenomena which have of late years been sur-
prising and interesting naturalists; viz., those of the Al-
ternation of Generations; in which, as Chamisso, the first
discoverer of the strange facts, observed "a mother is
not like its daughter, or its own mother, but resembles
its sister, its granddaughter, and its grandmother." The
Polype gives birth to a generation of Medusae which lay
eggs, which develop into Polypes. The Medusa, on the
other hand, lays eggs (gemmules), which develop into
Polypes, which at length divide themselves into colonies
of Medusas.

At first you will perhaps see nothing remarkable in
another object which I collected in my rock- ramble to-
day. A Hermit-crab in an old Natica shell; both com-
mon things enough. Yet look more narrowly. The
greater portion of the shell is not smooth, has no such
porcelain- like polish as the Natica usually has, but is
clothed with a sort of downy nap, a coarse sponginess of
a grayish hue, splashed with yellowish and pink tints.
The shell is invested with ffydr actinia.


We restore the strange partnership shell, fleece, and
crab to the glass of sea- water; j^rhere we soon see the
whole tumbling about the bottom in uncouth agility. As-
sist your eye with this pocket lens, and look again. The
shaggy nap upon the shell now bristles with tall slender
polypes, crowded and erect, like ears of corn in a field.

No high power of magnification is necessary to furnish
us with considerable entertainment from this populous col-
ony. The polypes stand individually nearly half an inch
in height; each consists of a straight slender column, sur-
mounted by eight straight rod-like tentacles, four of which
stand erect, slightly diverging, and the other four, alter-
nating with these at their origin, extend horizontally like
the arms of a turnstile.

The rough jolting of the crab over the stones the ex-
panded polypes bear with equanimity; they are used to
it; and though their tentacles wave and stream hither and
thither, they are not retracted on this account. But just
touch with the point of the pencil in your hand any part
of the shaggy fleece, and instantly the whole colony retire
together, as if by a common impulse, apparently shrinking
into the substance of the shell. Yet they soon reappear,
one after another quickly protruding its closed tentacles,
which are presently expanded as before.

The explanation of this phenomena is, that the whole
colony of polypes are but the free points or feeding
mouths of a common living film, which invests the shell;
just as in Laomedea the polypes that inhabit the vase-like
cells are the off-shoots or free points of the common

The investing film will sometimes in captivity spread
upon the glass side of a tank, and then develop all the


polypes and organs proper to the complete organism.
When this is the case, an admirable opportunity is pre-
sented for studying with ease and precision the economy
of the creature; and it is to the skill with which Dr. T.
Strethill Wright has availed himself of such an opportu-
nity 1 that I am indebted for the chief part of the facts
that I am going to tell you, connected with the form and
appearance, of which you can here judge for yourself.

The spreading film or polypary is a thin coat of trans-
parent jelly, slightly colored with various tints, which se-
cretes and deposits within its substance a still thinner
horny layer of chitine. This rises here and there into
numerous spines and points, which are curiously ridged
with toothed keels; and these ridges run in various direc-
tions over the horny layer also, making a fine network
over it. The investing flesh, however, fills up all the
cavities and areas so enclosed.

The mode in which the polypary increases is by throw-
ing out from its edge a creeping band, exactly analogous
to the root- thread of the Laomedea. This "propagative
stolon, after leaving the point of its origin, increases
rapidly in diameter, and sends out irregular branches.
The tips of these branches are covered with a glutinous
cement, by which they attach themselves tenaciously to
glass, or other surface near them. Having attached them-
selves, they expand laterally, at the same time throwing
out finger-like prolongations, which, as they come in con-
tact with each other, coalesce, until a fleshy plate is found
adherent to the glass. Polypes are developed both from
the loose branches and the attached polypary; and the

1 See "Edin. New Philosophical Journal," for April, 1857.


latter is clearly seen to be permeated by a beautiful sys-
tem of anastomosing canals, connected with the hollow
bodies of the polypes. Within these canals may be de-
tected an intermittent flow of fluid, containing particles,
the dancing motion of which indicates the presence of
ciliary action, and which, having passed in one direction
for a short time, are arrested, and, after a slight period of
oscillation, commence to flow in an opposite direction."

The polypes which are developed from this living car-
pet are not all of the same form. No fewer than five dis-
tinct sorts exist, at one and the same time, and I doubt
not we shall be able to find and to identify them all, on
this well- grown specimen.

First, there are the alimentary polypes, which we have
already cursorily glanced at. Within the space enclosed
by the two circles of tentacles there is a mouth with soft
protrusile lips, which can be pushed out and folded back
so as to hide tentacles, column, and all.

Scattered among these we see numerous polypes, which
agree in general form with these, but with some remark-
able abstractions and additions. They have no mouth nor
stomach, and the tentacles are reduced to the smallest pos-
sible warts or protuberances denticulating the dilated tip.
But the additions are still more peculiar. From the mid-
dle part of the column a number, from four to nine, of
great oval sacs project, each attached by one end, while
the other stretches out horizontally, thus surrounding the
slender column. Each of these sacs is an ovarian capsule,
and contains several ova of a brilliant yellow or crimson
hue. Thus we have the second form that of the repro-
ductive polypes.

In some places single ovarian capsules stand up alone


from the fleshy carpet, agreeing in every respect with those
which we have just examined, except that they are sessile,
instead of being carried by a polype.

The fourth form is that of the tentacular polype. Here
and there, from amid the forest of shorter polypes ali-
mentary and reproductive white threads are seen pro-
truding, which extend to a length four or five times as
great as theirs, and hang down or loosely float in the
water. They are found on the outskirts of the whole
compound structure, and at each extremity of the long
diameter of the mouth of the supporting shell, so that
they must, in their natural condition, reach to the ground,
along which the crab -tenanted shell is carried, enabling the
Zoophyte to seize and appropriate the atoms scattered by
the crab whenever he takes his meals. The tips of these
organs are covered with a dense pavement of large thread-
cells; and they must doubtless perform the office of gen-
eral purveyors to the composite animal.

But still more remarkable, more extraordinary than all
we have been considering, are the objects which are now
in view in the field of the microscope. You see a num-
ber of bodies, which Dr. Wright calls ophidian or spiral
polypes, and which, as he truly observes, are "like small
white snakes, closely coiled in one, two, or three spirals,
and grouped immediately round the mouth of the shell."
The habits of these polypes are still stranger than their
forms. "When touched, they only draw their folds more
closely together. But if any part of the polypary, how-
ever distant from them, be irritated, the spiral polypes
uncoil, extend, and lash themselves violently backward
and forward, and then quickly roll themselves up again;
and that not irregularly or independently of each other,


but all together, and in the same direction, as if moved
by a single spring. A violent laceration of the polypary
causes these polypes to remain extended and stretched like
a waving and tremulous fringe across the mouth of the
shell, for several minutes. The ophidian polypes (evi-
dently a barren modification of the reproductive polype)
are never found in any other situation on the polypary
than in that before described, or round the margins of ac-
cidental holes in the shell. They have no mouth, and the
tentacles are rudimentary. The walls of the body are very-
transparent, from the extreme vacuolation of the inner tis-
sue. The muscular coat, as might be expected from the
active movements of the polypes, is highly developed, and
forms a beautiful object on the dark polarized field of the
microscope, each spiral coil shining out as a bright double
ring, divided by four dark sectors. The outer tissue of
the whole body and tentacles is crowded with the larger
thread-cells. The ophidian polypes are, doubtless, organs
of defence or offence, like the motile spines and bird's-
head processes of the Polyzoa, or the pedicellarise of the
Echinodermata; but it is difficult to assign a reason for
their peculiar situation. They vary much in number and
size in different specimens of Hydr actinia, but are rarely
altogether absent." '

The reflections of the able zoologist who first called
attention to these varied developments, and his compari-
sons of them with those of another polype- form which we
have lately been observing, are so interesting and instruc-
tive that you will not deem it needful that I should apolo-
gize for citing them. "In our consideration of the Hy-
dractinia," he observes, "our attention is arrested by the

1 Dr. Wright, op. cit.


multitude of objects grouped together to constitute a sin-
gle animal, their variety in form, and the sympathy which
subsists between the different parts. The singular spinous
skeleton; the expanded membrane of the polypary, with
its beautiful internal network of tubes and delicate peri-
pheric prolongations; the alimentary polypes, some white
and filiform, others thick, fleshy, crimson, or yellow sacs,
obligingly everted, to expose their interior to our micro-
scopic eye; the reproductive polypes, with their richly-col-
ored generative sacs; the sessile generative organs of the
polypary ; the ophidian polypes, coiled in neat spirals when
at rest, but starting into furious action, like a row of well-
drilled soldiers, when injury is inflicted on the body to
which they are attached; and, lastly, the tentacle polypes,
floating in the water like long and slender threads of gos-
samer, or dragging up heavy loads of food for the common
good; these, together with the intimate relation and sym-
pathy subsisting between the polypary and its associated
organs, all combine to form an object of the highest inter-
est, and indicate that, in this fixed yet travelling zoophyte,
we have a type of structure transitional between the den-
dritic Hydroidaz and the more highly organized Acaleph.
In the simplest acalephoid form, such as the medusoid of
Companularia [or Laomedea] (which is nothing more than
an extension of the polypary specially organized for inde-
pendent and motile life), we have (as in Hydractinia) an
expanded polypary, represented by the umbrella, and per-
meated by vascular tubes from the confluence of which
last spring, at the centre, the tentacular polypes, various
in number; and between them the reproductive polypes,
represented by the sessile generative sacs." '

1 Ibid., op. cit.


You see here a jar, on the glass side of which are
traced a number of very fine white lines, barely discerni-
ble by the unassisted eye. But by the aid of the lens
you see that each line is a long and slender thread, which
creeps along the glass, and at length starts out from it free
for a short distance, and is then terminated by a long
club-shaped body, which carries at its extremity four hori-
zontally divergent organs, like the arms of a turnstile.
Tracing down the threads to their lower extremities, you
see that they are branches of one thread, which creeps
irregularly over a filamentous sea- weed growing from a
stone in the jar. The sea-weed had been in the vessel for
several weeks, and the water having been undisturbed,
the knobbed thread, which was originally confined to the
plant, continued to grow, and coming into contact with
the glass spread upon it. Many other threads have ex-
tended from the creeping root, some of which stand up
freely in the water, with their knobbed extremities float-
ing in the wave.

This is one of the Polype tribe, named Stauridia pro-
ducta, and as its form and structure are interesting, we
will devote a few moments to its examination. We can
easily sever one or two of the freely floating threads, and
transfer the amputated portions to one of the live-boxes
of the microscope. The motions and appearance of the
club with its organs will be, for a while, little affected by
the violence.

The long cylindrical thread is enveloped in a transpar-
ent horny tube, which, however, so closely invests it that
it is with difficulty distinguished. The club-shaped head,
or individual polype, is an enlargement of the thread,
which protrudes from the investing tube. It is swollen


in the middle and rounded at the end, and many of the
heads, which are more ventrieose than the rest, contain a
bubble of air in the centre. This air is doubtless taken
in at the mouth, which is situated at the extremity; for,
though you can discern no perforation, yet there is aa
aperture capable of being opened widely at the pleasure of
the animal, and surrounded by protrusile, contractile, and
expansile fleshy lips. I have several times seen this mouth,
opened, and partly everted, in kindred species; and once
I had an opportunity of witnessing a quite unexpected use
to which it was applied; viz., that of a great sucking disk.
I had put the animal in such a live-box as this the two
glass surfaces being just sufficiently wide apart to allow
it free liberty to turn about in all directions as far as it
wished. On my looking at it after a momentary interval,
I saw that the extremity had suddenly become a large cir-
cular disk of thrice the diameter of the body: its sub-
stance was gelatinous, full of oblong granules, arranged
concentrically. I neither saw this disk evolved nor re-
tracted; but after some time, on looking at it, the same
phenomenon was repeated. In order to obtain a better
sight of it, but without suspicion of what I was about to
effect, I slightly turned the tube of the box, carrying with
it the alga to which the polype was attached, my eye upon
it, attentively observing all the time. The base of the
polype moved away from its position, but the broad disk
was immovable. I continued to turn the upper glass, un-
til at length the body was dragged out so as to be consid-
erably attenuated; still the disk maintained its hold on
the lower glass, with no other change than that of being
elongated in the direction in which it was dragged. At

length it slowly gave way, and resumed its original shape


by gradual and almost imperceptible diminution of the

Around this expansile, but now fast-closed mouth, you
observe four tentacles, radiating, in a plane at right angles
to the axis of the thread, toward the four cardinal points;
they are long, slender, straight, and each is terminated by
a globose head of considerable size, resembling the arms
of certain screw-presses, which are loaded with terminal
globes of metal to increase their impetus when turned.

The structure of these tentacles is very interesting.
The stem contains a core or central chain of large cells,
which take a somewhat square outline from mutual press-
ure. The surface is roughened with small swellings, from
each of which projects a long and excessively attenuated
hair (palpocil) , which is probably a very delicate organ of
touch. The terminal globe is filled with proportionally
large oval vesicles, each with a central cavity, which are
arranged in a divergent manner around the centre, so that
their tips shall reach the surface of the globe; these are
those potent weapons of offence called thread-cells (cnidce).
The surface of the globe is covered with short thick pal-
pocils, which Dr. T. S. "Wright considers as prehensile
organs. ''These palpocils arise, each as a somewhat rigid
process, from the side of one of the large thread-cells
buried in the head of the tentacle; and they probably
convey an impression, from bodies coming into contact
with them, to the thread-cell, causing the extrusion of
its duct."

Besides these globe-headed tentacles, there are, on the
lower part of the club-foot, four other organs similar in
every respect, except that they are not furnished with
heads, nor any terminal dilatation whatever. They pro-


ject horizontally as the knobbed ones, but their origin,
and the respective lines of their radiation, are intermedi-
ate or alternate; in other words, if we consider the globe-
heads as pointing N. E. S. and W., the simple ones point
N.E., S.E., S.W., and KW.

From the carefully made observations of several excel-
lent naturalists as Dujardin, Steenstrup, Dalyell, Loven,
and others it appears that
this beautiful and elegant little
Polype gives birth to medusa-
shaped young. Contrary, how-
ever, to the rule in Laomedea,
the Medusa is in this case pushed
forth as a bud from the side of
the club, without any protect-
ing capsule. The process is ex-
ceedingly like a plant develop-
ing a flower; for the bud grows
until it at length expands blos-
som-like, and a beautiful little
umbrella-form Medusa is seen
adhering to the Polype. At
length the brilliant little living flower becomes detached;
and, after swimming freely for a time, discharges ova or
gemmules from its ovaries, which develop into a creeping-
root thread, and finally into the club- headed threads of
the Stauridia.

Some objects which I have to exhibit to you are alto-
gether unique as to their appearance: and, if you are not
as imperturbable as a philosopher of the 2Voa, or a Mo-
hawk Indian, will certainly excite both your risibility
and your wonder. For some little time I have been keep-


ing in this tank a specimen of that rather rare and very
interesting Sabella, the Amphitrite vesiculosa of Montagu. 1
You see it is a worm, inhabiting a sort of skinny tube,
much begrimed with mud, about two inches of its length
being exposed; the remainder, or about as much more,
being concealed among the sand and sediment of the

A beautiful object is presented by the gill-fans of this
worm. These organs are always elegant, whatever species
of the genus is before us; but here, in addition to the
charm of the slender filaments, so delicately fringed with
their double comb -like rows of cirri, the tip of each bears
a dark purple spherule. That of the anterior filament on
each side is much larger than the rest, and forms a stout,
globose, nearly black ball; the others diminish to about
the twelfth on each side, where they disappear. These
balls are placed on the inner or upper face of the filament-
stem, at the point where the pectination ceases, the stem
itself being continued to a slender point beyond it, and
constituting the " short hyaline appendage" of Montagu.
From their great resemblance to the tentacle-eyes of the
Gasteropod Mollusca, I have little doubt that these are
organs of vision. If so, the profusion with which the
Sabella is furnished in this respect may account for its ex-
cessive vigilance; which is so great that not only will the
intervention of any substance between it and the light
cause it to retire, but very frequently it will dart back
into its tube almost as soon as I enter the room, even while
I am ten feet distant.

It is not, however, to the tube, nor to the worm, that

1 "Linn. Trans.," xi. 19.


I wisli specially to direct your attention: yet it is necessary
that I say a preliminary word about tlie former. Ordi-
narily the tubes of these worms are formed of the fine
impalpable earthy matters (clay, mud, etc.) held in sus-
pension in the sea, incorporated with a chitinous secretion
from the body of the animal; and therefore the surface
of the tube is always rough and opaque. But in this
individual case, probably owing to the habitual stillness
of the water in the vessel not holding in suspension the
particles of mud that ordinarily enter into the composition

of the tube, the latest-formed portion is composed of pure
transparent chitine, without any perceptible earthy ele-
ment. This clear terminal portion of the tube you may
perceive to be occupied by a curious parasite. About
twenty bodies, having a most ludicrously close resem-
blance to the human figure, and as closely imitating cer-
tain human motions, are seen standing erect around the
mouth of the tube, now that the Sabella has retired into
the interior, and are incessantly bowing and tossing about
their arms in the most energetic manner.

As soon as you have recovered from your surprise at


this strange display, we will begin to examine the per-
formers more in detail. A slender creeping thread, irreg-
ularly crossing and anastomosing, so as to form a loose
network of about three meshes in width, surrounds the
margin of the Sabella 1 s tube, adhering firmly to its exterior
surface, in the chitinous substance of which it seems im-
bedded. Here and there free buds are given off, especially
from the lower edge; while from the upper threads spring
the strange forms that have attracted our notice. These
are spindle-shaped bodies, about iVth of an inch in height,
whose lower extremities are of no greater thickness than
the thread from which they spring; with a head -like lobe
at the summit, separated from the body by a constriction,
immediately below which two lengthened arms . project
in a direction toward the axis of the tube.

Such is the external form of these animals, and their
movements are still more extraordinary. The head -lobe
of each one moves to and fro freely on the neck, the body
sways from side to side, but still more vigorously back-
ward and forward, frequently bending into an arch in
either direction; while the long arms are widely ex-
panded, tossed wildly upward, and then waved down-
ward, as if to mimic the actions of the most tumultuous
human passion.

"Whenever the Sabella protrudes from its tube, these
guardian forms are pushed out, and remain nearly in con-
tact with the Annelid's body, moving but slightly; but
no sooner does it retire than they begin instantly to bow
forward and gesticulate as before. These movements are
continued, so far as I have observed, all the time that the
Sabella is retracted, and are not in any degree dependent
on currents in the surrounding water, whether those cur-


rents be produced by the action of the Annelid or by
other causes. They are not rhythmical; each individual
appears to be animated by a distinct volition.

Applying a higher magnifying power than we have yet
used to the animals, we find that the head-lobe encloses
a central cavity; that the arms are also hollow, with thick
walls, marked with transverse lines, indicating flattened
cells, and muricated on the exterior; and that the body
contains an undefined, sub-opaque nucleus, doubtless a
stomachal cavity.

I cat out, with fine scissors, a segment of the tube, in-
cluding two of the parasites, with the portion of the net-

Online LibraryPhilip Henry GosseEvenings at the microscope (Volume 1) → online text (page 26 of 32)