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THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND
MRS. PRUDENCE W. KOFOID

f-
,

•2

in

MICROSCOPICAL STUDIES

IN

MARINE ZOOLOGY,

BY

JAMES HOENELL,

Director of the Jersey Marine Biological Station.

WITH TWENTY FULL-PAGE PLATES OF ORIGINAL ILLUSTRATIONS.

(A Reprint of Articles published originally in the " Journal of Marine
Zoology and Microscopy" from 1893-1897.)

VOL. I.

JEESEY,
THE BIOLOGICAL STATION,

1901.

COKEECTIONS.

P. 48, 6th line from bottom. " Tubularia " should be " Tubipora."

P. 53. Delete paragraph " C," also the whole of the last five paragraphs of the
same article from the words " so much for collateral evidence." This is
necessary as the dorsal processes or " tentacles " of Sabella are now known to
be processes of the collar, and thus are not homologous with the operculum
of Serpula.

Plate numbered "Vol. 2, PI. V." and which precedes p. 89. In the explanation
facing, for "Figs. A to D, Plumularia pumila" read "Figs. A to D,
Sertularia pumtta."

CLASSIFIED CONTENTS.

PAGE

PROTOZOA :-

SPHAEROZOUM PUNCTATUM, A COLONIAL RADIOLARIAN . . . 73

PORIFERA :—

SPONGES, AN INTRODUCTORY SKETCH ... ... 14

CCELENTERATA :-

THE LIFE-CYCLE OF OBELIA GENICULATA ... ... 58

THE HYDROID STAGE OF OBELIA GENICULATA ... 77

THE CORYNID^: ... ... ... ... .. 86

ON SERTULARIA PUMILA ... ... ... .. 91

THE PLUMULARHXE . . ... ... ... 103

HALICLYSTUS OCTORADIATUS — THE LAMP-POLYP ... 5

THE PERMANENCE OF THE SCYPHISTOMA-STAGE OF

AURELIA AURITA ... ... ... ... 101

THE STRUCTURE OF ANEMONES ... ... ... 43

TYPICAL ALCYONARIA ... ... ... ... 56

ANNELIDA :-

THE ANATOMY OF TOMOPTERIS ... ... ... 8

ON POLYNOE PROPINQUA AS TYPICAL OF THE HlGHER

ANNELIDS ... ... ... ... ... 62

VARIATION IN THE OPERCULUM OF SERPULA ... 50

BRYOZOA (POLYZOA) :-

FAMILIAR BRITISH BRYOZOA ... ... ... 116

ECHINODERMATA:-

THR STALKED LARVA OF ANTEDON ... 77

M374374

CLASSIFIED CONTENTS — continued.

PAGE

CRUSTACEA :-

A CONTRIBUTION TO OUR KNOWLEDGE OF THE COPEPOD

MONSTRILLA ANGLICA ... ... ... 21

THE SAPPHIRINID^B ... ... ... 122

THE CIRRIPEDIA ... ... ... ... ... 93

^THE METAMORPHOSES OF THE MANTIS-SHRIMPS

(SQUILLID^) ... ... ... ... 32

THE PHYLLOSOMA OR GLASS-CRAB LARVA OF SCYLLARUS 38

THE PROTECTIVE DEVICES OF THE GENUS HlPPOLYTE

(.ZEsop's PRAWNS) ... ... ... ... 113

MOLLUSCA:-

CRESEIS, A TYPICAL PTEROPOD ... ... ... 80

THE EGGS AND YOUNG OF CEPHALOPODS ... ... 104

THE VISUAL ORGANS OF CEPHALOPODS . . ... 106

CHOEDATA :—

THE ANATOMY AND LIFE-HISTORY OF SALPA ... 10

ABNORMALITIES IN THE MUSCLE BANDS OF SALPA ... 55

THE TADPOLE LARV.E OF ASCIDIANS ... ... 68

THE MAIN FACTS CONCERNING THE LiANCELET

(AMPHIOXUS) ... ... ... ... 27

MICROSCOPICAL STUDIES

IN

MARINE ZOOLOGY.

STUDY I. — HALICLYSTUS (LUCERNARIA) OCTORADIATUS.

pleasures of shore-collecting are many, and the one I fancy
_ the most enjoyable, is trudging about among gay weed-decked
pools and dyke-formed gutters in search of those delicate fern-like
sea-sprays, the Zoophytes. Here on this coarse brown Fucus are
numbers of serrate spikes of a Sertularian, bringing to memory
Silurian graptolites, while in that pool, tiny pinnate fronds anchored
to the very rock itself, bespeak a Plumularian. Coryne, too, on this
Jersey coast is not infrequent, twining its long clubbed branches
among the finer weeds. But the vast sea-meadows or prairies as the
French call them, are equally prolific arid harbour many beautiful
species never met with in rock pools. These meadows — where grows
the strange Zostera, a true flowering plant that has entirely renounced
fealty to its old home on dry land — are at times of spring tides fre-
quently left uncovered for short periods, and then we must watch our
chance. Campanularia and Clytia we may meet with, but by far
most conspicuous are rather large brownish bells of exquisite outlines,
that here and there are anchored to the long green blades of the
Zostera.

Such are easily recognized as Haliclystus octoradiatus, in these
parts the chief representative of the Lucernarians. In size these
bells (Fig. 1) are about one inch in height by nearly the same across
the oral face. The margin of this is drawn out into eight points,
each furnished with a bunch of closely set and numerous capitate
tentacles. In the centre is the mouth, standing up quadrangular
and prominent. The four angles (of the mouth) mark the four
primary radii that can be made out in these animals, and are usually
known as the perradial lines or radii. In allied forms, e.g. the
scyphistoma stage of Aurelia, these first radii are marked by the
appearance of the first four marginal tentacles. The second four
tentacles are alternate with the first and mark the secondary radii or
interradials. In Haliclystus their positions are the radial lines
beginning at points midway between the mouth angles. Thus they

6 MICROSCOPICAL STUDIES.

alternate with the perradials. Between each primary and secondary
radius lies one of eight radiating genital bands. Their position is tech-
nically known as adradial. The margin of the bell just beyond the
extremity of each genital band is marked by a great cluster of short
capitate tentacles. The remaining external organs are eight con-
spicuous hollow bodies, each one lying midway between every two
groups of tentacles. These are probably vestigial sense organs and
have been "termed colleto-cystophores. They will be referred to later
as c.-c. Four must be interradial and four perradial. Looking to
the internal anatomy, we find that the enteric or body-cavity is
divided by four delicate radiating walls or septa into four gastric
chambers — perradial in position. The septa — which by the way
do not represent the mesenteries of the Anemones — are interradial.
From their inner edges are given off numerous solid tentacle-like
threads — the gastral filaments.

Those unfamiliar with these animals are reminded that the
Hydrozoa are divided into the two great groups, Scyphoinedusse and
Hydromedusse. The former includes, as principal order, those fleshy
medusae or Jelly-fishes — without a velum (membrane all but closing
the mouth of the bell), with gastral filaments and with eight sensory
organs (tentaculocysts) — known so well under the forms of Aurelia
and Pelagia and termed collectively Discomedusse. Normally the
life-history of these animals is as follows : — A ciliated embryo (pro-
ceeding from the sexual or medusa stage), after a short period of
pelagic existence, settles down and becomes attached to some sta-
tionary object. A mouth forms at the free end, and sixteen tiny
tentacles appear. This form, iV to «-in. in height, is the scyphistoma
stage and is often termed the hydriform phase from its likeness to
the fresh-water polyp, Hydra. Soon transverse constrictions — stro-
bilation — cut the body into a rouleau of discs, appearing thus as a
tiny pile of sculptured plates. Each disc has eight arms, with a tiny
tentaculocyst at tip. This is ihe strobila condition. The discs
break off and begin a free swimming life, known at this period as
ephyrce, rapidly take on the form of ordinary Jelly-fishes, develop
sexual organs, and send out swarms of ciliated embryos to go through
the same strange cycle of life.

The Lucernarians form another order of the Scyphomedusse.
Contrasting their life-history with that of the large fleshy medusa3
just related, we find that the Lucernarians produce in the genital
bands both ova and sperm masses. These give rise to ciliated
embryos which settle down quickly and develop without metamor-
phosis into the adult bell-shaped form.

Until recently Haliclystus and the related forms were considered
as being more or less unchanged descendants of the ancestral form of

EVOLUTION OF THE LUCEENARIANS. 7

the Discomedusae, i.e. prior to their adoption of the two well marked
stages — hydriform and medusiform — that now characterise their life-
history. Quite recently, however, Dr. C. Herbt. Hurst and the writer
arrived independently (" Natural Science" Sept. 1893) at the novel
conclusion that the connection between the Lucernarians and the
Discomedusaa is much more recent and close. Thus we believe from
the review of considerable evidence that the former are descended
from a form having as well marked medusa-stage as Aurelia has, and
with well developed marginal sensory organs. Then by abbreviation
in the life-cycle, by a certain hastening of events, there were developed
genital products in the hydriform or scyphistoma fixed form. This
did away with the necessity for a free swimming sexual stage, and
being found advantageous, was permanently adopted by some — the
immediate predecessors of the Lucernarians of to-day.

Marginal sensory organs (e.g. tentaculocysts) can be useful only
among swimming forms (Hurst " Nat. Sc" vol. ii, part 16). Under
the changed conditions they became useless in the Lucernarians and
tended to become " vestigial." Such functionless organs are very
subject to variation — and the writer has found such to a really
extensive degree in these bodies in Haliclystus. It is well known
that the origin of tentaculocysts is from ordinary marginal tentacles,
and it is to this form that the marginal bodies (c. cystophores) of the
species under description usually reverts. All gradations from the
normal form of c.-c. up to the normal tentacle can be traced. The
capitate terminations of the tentacles contain great numbers of
nematocysts or stinging cells useful in paralizing prey, arid the first
stage in reversion is marked by the appearance on the apex of a
c.-c., of a tiny wart containing numerous nematocysts (Fig. 4). The
next shows a larger wart. In Fig. 5 this has a tiny stalk, while in
Fig. 6 there is a well pronounced peduncle. Again in Fig. 7, is
drawn a tentacle — one from a bunch of normal ones — where the
stem is bellied out, in fashion approaching the most abnormal of
the colleto-cystophores.

EXPLANATION OF FIGS, 1 TO 9, PLATE I.

Haliclystus octoradiatus.

Fig. 1. Two individuals adhering in natural postures to a blade
of Zostera. n s.

Fig. 2. Oral view : — i s. Interradial septum ; g b. genital bands ;
m /. muscular fibres ; g. f. gastral filaments ; s. sperm
mass ; c c. colleto-cystophore ; t. group of tentacles, x 2f .

Fig. 2a. Diagram of trans, section of body : — in. mouth ; i s. inter-
radial septum ; p c. perradial chamber ; g b. genital bands.

8 MICROSCOPICAL STUDIES.

Fig. 3. Normal Colleto-cystophore, x 17.

Figs. 4, 5 & 6. Abnormal series of same, X 17.

Fig. 7. Abnormal tentacle, showing shortening and thickening of

peduncle, x 17.

Fig. 8. Group of normal tentacles, x 30.
Fig. 9. Developing ovum, in optical section, x 25.

STUDY II. — THE PELAGIC ANNELID TOMOPTERIS.

Occasionally among the contents of the tow-net there appears
this tiny paddle-propelled worm, active and sprightly in movement,
and so glassy and colourless as to be well nigh indistinguishable from
the water it moves in. The species figured on Plate I. averages
scarcely J-inch long, but its breadth seems very great in proportion
owing to the great length of the paddle-like feet or parapodia. The
head is very distinct. At the front border are two stout gracefully
curved antennae (a), while just behind these is a pair of very delicate
processes (a1) which have also been called antennae. Next come the
most conspicuous appendages in the body — a pair of enormously
elongated tentacular cirri (t c.) In the centre of each one, and sup-
porting it, is a stout bristle, seen under a high power to be septate
(Fig. 13). Following these, about thirteen pairs of paddle-shaped
parapodia entirely destitute of setae, and consisting of a hollow cylin-
drical basal portion, expanding at the outer or distal end into two
foliaceous blades — upper and lower — which represent respectively,
the notopodium and the neuropodium of the typical annelid foot.
Every foot is controlled by two principal sets of muscular fibres
originating close to the median line in the body wall, one passing
obliquely forwards to be inserted in the anterior border of the foot,
the other backwards to the posterior border.

The mouth is situated between the tentacular cirri and leads
into a rather muscular portion, capable of at least partial extrusion
as a proboscis (Carpenter). This passes through a short oesophagus
into a long and wide stomach, reaching nearly the whole remaining
length of the animal. The body cavity is quite continuous. There
are no internal septa and the interior of the parapodia communicates
freely with the body cavity. The chief development of the nerve
system consists of a large anterior ganglionic mass, seated upon which
are two eyes, each composed essentially of a pigmented cushion
bearing two crystalline cones. In front of each eye is a large vesicle
of unknown function.

The sexes are separate. That depicted is a female and shows
how the ovaries arise from the growth of certain cells on the inner
surface of the peduncles of the parapodia. These cells grow to a

/ Fig. 14.

Jas. Hornell, del. ad. Nat.

JERSEY BIOL. STN.

Fig. 12.

Fig. 13.

HALICLYSTUS AND TOMOPTEBIS.

VoJ, I., PI.

Fig. 16.

Fig. 17.

end

end

ornell, del. ad. Nat.

RSEY BIOL. STN.

7 8

SALPA MUCRONATA-DEMOCBATICA,

THE PELAGIC WORM TOMOPTERIS. 9

very large size and then appear as very characteristic ova. Finally
these break loose and pass into the body-cavity. It is probable
that they normally pass thence to the water by rupture of the body
wall of the parent, but whether fertilization takes place prior to this
is uncertain. Curiously I ha've not lately met with the male form.
Carpenter describes it as having a long tail-like prolongation bearing
four or five minute appendages wherein are developed spermatozoa.
The tail-like prolongation is indeed given as being present in both
sexes of different species — but so far in the present species I have
not seen any trace of it in the females. Of males, I have not been
able to examine any.

The embryology is little known and we only become familiar
with the animal in an advanced larval stage. The earliest one
known to Dr. Carpenter belonged to a species having no posterior
antennas in the adult state, but in the larval it had no anterior
developed — while the posterior were very obvious and bore each a
distinct bristle, and were of comparative large size. The tentacular
cirri (t c.) were short, and approached the form of the succeeding
partially developed parapodia, saving that they (the tent cirri) pos-
sessed stout setae like the posterior antennae. It is very interesting
to note that the species figured here (Fig. 10), shows in each
posterior antenna a distinct claw-like bristle, and this inclines me
to the belief that these organs are not antennas but are vestigial
tentacular cirri. The large tentacular cirri in the larval stage ap-
proach very closely in form to the parapodia and differ principally in
the presence of setae. The secondary antennas again approach closely
in larval life to the appearance of the tentacular cirri, so the inference
is clear. It is only with the attainment of maturity, that this organ
becomes reduced and difficult to homologize, and even then, as seen
in our figure, there can in some species be traced distinct setae.
In the larger T. onisciformis (Carpenter) this appendage however
entirely disappears in adult life.

Rosette-shaped organs have been made out at the bases of
certain feet ; their function remains still obscure.

EXPLANATION OF FIGS. 10 TO 15, PLATE 1.

Fig. 10. Entire adult Tomopteris (female) ; a. anterior antenna ;

a1, posterior antenna (vestigial tentacular cirrus) ; t c.

tentacular cirrus ; p. a parapodium. X 17.

Fig. 11. Parapodium, nt. notopodium ; nr. neuropodium ; ov. ovary.
Fig. 12. Ovum. no. nucleolus or germinal spot ; n. nucleus or

germinal vesicle ; v. vitellus ; v m. vitelline membrane,

X 200.

10 MICROSCOPICAL STUDIES.

Fig. 13. Seta from tentacular cirrus, showing septations, X 100.
Fig. 14. Eye showing two crystalline cones.

Fig. 15. Posterior antenna showing sickle-shaped vestige of a seta
at a. x 100.

STUDY III. — ANATOMY AND LIFE HISTORY OF SALPA.

The great heat of the past summer was apparently very favour-
able to the development of surface-life in British latitudes. Pelagic
animals, usually rare, were this year sometimes abundant. Thus
Beroe, Medusce and Copepoda of southern species, Tomopteris and
the pelagic Tunicates, were taken much more frequently than I have
ever known before. For several days during August the tow-net
was full of a transparent colourless barrel-shaped Salpa, which
proved to be 8. mucronata-democratica, Forsk. Most were adult —
such as those figured on Plate II. were quite young, only a few hours
severed from the parent and still showing remains of a placenta.

The large figures (16, 17 & 18) show this animal in various
aspects. In all the most striking features are seven great hoop-
shaped muscular bands. By comparing the three figures, the central
four will be seen to encircle the body completely, while the two
most anterior, together with the one most posterior, which lies
in front of the exhalent aperture (a), fail to complete their respective
circles, one upon the dorsal, two upon the ventral aspect (Fig. 17).
On the dorsal side (Fig. 16) lying between and connecting the first
two hoops, are a pair of band-shaped muscles whose function is to

open the mouth. Another muscle of a < shape (Fig. 18) lies

horizontally on either side of the mouth, performing the opposite
function of closing its two lips. The remaining muscular bands are
two strap shaped ones, lying between the angles of the exhalent
aperture (a).

The body wall possesses externally a thick, serni-gelatinous layer,
which is the protecting tunic or test (t), formed originally of a glassy
homogenous secretion from the ectoderm or primitive superficial
layer of the body. In this test are subsequently found numerous
cells which have wandered in from the ectoderm. These are specially
numerous in the extremities (t c). The mouth or inhalent aperture
(o) lies at the anterior end of the body ; the exhalent (a) at the
opposite end on the dorsal aspect.

A great cavity is encompassed by the muscular hoops. An
anterior and a posterior division is formed by the presence of a
diagonal rafter or bar (br), stretching from a point behind the
ganglion (y), backwards and downwards to the beginning of the
oesophagus. This bar has been supposed to be the much modified

THE ANCESTRY OF SALPA. 11

remnant of the slit-perforated branchial pharynx, so well developed
in the simple Ascidians, such as Ascidia and dona, the slits
having gradually coalesced, and being now represented by the two
great spaces which lie on either side of the branchial septum.
Recent research (Brooks' " Salpa in its relation to the Evolution of
Life," Baltimore, 1893), however, makes it probable that the an-
cestors of Salpa had never a complicated system of branchial cfefts,
arid that the present represents the little changed primitive plan.
At first, as Prof. Brooks points out, the ancestral Salp had an elon-
gated digestive tube without pharyngeal clefts. The anterior part was
distended and ciliated. Later on slime cells appeared, to retain food-
particles swept in by the free current of water passing through the
body. But this stream would also be liable to carry partially
digested food particles away — so the appearance of one or more
clefts in the distended pharyngeal part, allowing the water, after
bathing the slime covered parts, to pass freely away without coursing
through the intestine, would be a distinct advantage and would be
retained by natural selection. The chamber anterior to the so-called
branchial septum, therefore represents the pharynx — while the pos-
terior chamber is the cloaca (cl), into which also empties the ali-
mentary canal by the anus. On the ventral surface of the pharynx
there stretches longitudinally a deep gutter with glandular walls, the
upper edges of which join along the greater portion of its length.
This appears optically to be a rod and is the endostyle (end) ; at
its front extremity it sends off two diverging ciliated ridges (ac) —
the peripharyngeal bands or ciliated arc — which, arching upwards,
join again and pass into the branchial septum. The cavity of the
endostyle is ciliated, and the slime secreted by its glandular walls, is
passed on by the cilia into the peripharyngeal bands, and thence to
the ciliated surface of the branchial septum. At the posterior
extremity of the pharynx is the short oesophagus, passing into a wide
stomach ; thence a short intestine leads to the cloaca (cl). This
digestive tract in all pelagic tunicates is concentrated into a very
small space, and forms the only opaque mass in the body, and is the.
so-called nucleus (TIC). Water passing in at the mouth laden with
food particles, has the latter arrested by the slime covered ciliated
arc and branchial septum. Passing through the two gill clefts the
water finds its way into the cloaca, whence it is discharged by the
exhalent aperture. The food particles arrested are sent by ciliary
action down the branchial septum and into the oesophagus.

The animals move through the water by repeated violent expul-
sions of water, due to contraction of the muscular hoops. According
as the water is expelled from mouth or exhalent aperture, the
movement is backwards or forwards.

12 MICROSCOPICAL STUDIES.

The form figured was, but a short time previous, attached to the
parent. At pi is seen a mass of cells marking the unabsorbed remnant
of the placenta ; el is a collection of large cells which are believed to
represent the urochord of the tail of an appendicularian-like ancestor.
It would thus also be homologous with the cartilage-like cord of the
tail of the tadpole larvae of sedentary ascidians.

The nervous system consists of a central ganglion (g) above the
anterior end of the branchial septum, with numerous nerves given off
to the different organs of the body. Upon the ganglion is a rounded
mass, the eye, containing dark pigment of horse-shoe shape. A little
way in front, is a ciliated sac situated immediately above a tongue-
shaped ciliated organ — languet — pendant in the pharynx and of
sensory value.

A heart is present beneath the alimentary canal, giving off a
large ventral longitudinal vessel. There is a similar vessel dorsally,
and the two are united by lateral branches. Vessels ramify in the
branchial septum. The peculiar blood circulation of Tunicates is well
marked in Salpa — after beating a certain number of times in one
direction, the heart remains still for a moment and then resumes
pulsating, but in an opposite direction, thus reversing the blood-flow
completely.

Life-history. The form under notice is asexual. The bud-shaped
part st is the first indication of the stolon, which in the adult develops
by growth and internal change into a long double-chain of tiny bud-
like salps (Fig. 19). When a certain size is attained, the chain breaks
free and swims away by rhythmic, and combined, alternate admission
and expulsion of water. These chain salps (Fig. 20) have quite a
different outward form, and a different — fewer — number of muscular
hoops. Each individual in the chain is connected with four others by
eight bars — two to each. Diagram Fig. 21 shows the method. The
chain salps are fully sexual ; both male and female organs are
developed in each individual, but the female organs mature earlier
than the male. A single ovum only is produced. It develops in situ
—being fertilized by spermatozoa that enter through the mouth of
the parent. It receives nourishment by the interposition of a true
placenta between it and the parent. It possesses a circulation
separate from that of the latter. When development is complete it
breaks loose and swims away. This is the solitary asexual form
we figure. In turn it again gives rise to a chain of sexual salps.
Thus the life-cycle continually proceeds.

13

EXPLANATIONS OF FIGS. 16 TO 21.

Salpa mucronata-democratica.

Fig. 16. Dorsal view ; Fig. 17, ventral view ; Fig. 18, lateral view.
All solitary asexual form. t. test ; tn. nuclei of test ;
m. mouth or inhalent aperture ; ph. pharynx ; ac.
peripharyngeal bands ; end. endostyle ; /. languet ; br.
branchial septum ; n. nucleus or gastral part of alimen-
tary canal ; cl. cloaca ; a. exhalent aperture ; el. eleoblast ;
pi. remnant of placenta ; st. proliferous stolon ; g. ganglion
with eye seated thereon and nerves radiating. Muscular
bands are distinguished by brown colouring. X 30.

Fig. 19. Posterior part of body of an adult solitary zooid, showing
the development of the proliferous stolon at. into a chain
of buds. n. nucleus, x 6.

Fig. 20. 3 chain salps showing method of connection, emb. embryo,
n. nucleus, x 2£.

Fig. 21. Diagram of a double row of 8 salps showing plan of
attachment. Two connecting bars link every two
individuals.

View of the Jersey Biological Station from the sea.

Aeries II.

STUDY IV. SPONGES ; AN INTRODUCTORY SKETCH.

THE Jersey shore between tide-marks is veritable " Spongeland."
Scarlet, brick-red, orange, yellowish green, yellow, white, grey,
and black patches clothe the rocks in chequered mantle, and with the
vieing colonies of gaudy-colored compound ascidians, relieve in a
pleasant manner the sombre brown of the fucus-covered rocks. Yet
common though sponges are, they remained until comparatively
recent years a puzzle group to naturalists. Grant is generally
credited with having, in 1825, given the first great impetus in the
right direction, by his observations on the passage of minute water
currents into the sponge by numerous small pores and their emergence
by a few large openings. The following extract from the third
edition of the Encyclopaedia Britannica, 1797, will, however, prove
that our fine old pioneer naturalist, London merchant Ellis, should
rather have the credit: — "Mr. Ellis, in the year 1762, was at great
pains bo discover these animals. For this purpose he dissected the
spongia urens, and was surprised to find a great number of small
worms of the genus of nereis or sea-scolopendra, which had pierced
their way through the soft substance of the sponge in quest of a safe
retreat. That this was really the case he was assured of, by inspect-
ing a number of specimens of the same sort of sponge, just fresh from
the sea. He put them into a glass filled with sea water, and then
instead of seeing any of the little animals which Dr. Peysonell
described, he observed the papillae or small holes with which the
papillae are surrounded, contract and dilate themselves. He examined
another variety of the same species of sponge and plainly perceived
the small tubes inspire and expire the water. He therefore concluded
that the sponge is an animal, and that the ends or openings of the
branched tubes are the mouths by which it receives its nourishment,
and discharges its excrements."

The same work describes "Spongia," as " a genus of animals
belonging to the class of vermes, and order of zoophytes. It is fixed,
flexible, and very torpid, growing in a variety of forms, composed
either of reticulated fibres, or masses of small spines interwoven
together, and clothed with a living gelatinous flesh, full of small

CANAL SYSTEMS OF SPONGES. 15

mouths or holes on its surface, by which it sucks in and throws out
the water."

Now to trace something of the progress that has been made in
the study of these animals during the last hundred years. By most
authorities, sponges are granted a separate phylum or branch, in the
genealogical tree of the division Metazoa or multicellular animals.
They form the lowest or least specialized phylum ; the name applied
to them collectively being Porifera, A short summary of the most
important points in the anatomy of the chief types of sponges is
however necessary to the intelligent understanding of such position
in the scale of nature.

The most primitive form of sponge organization is well seen in
the very simple sponge, Ascetta primordialis, so minutely described
by Haeckel. In appearance, Ascetta is a tiny, thin-walled, goblet-
shaped animal that lives anchored by the narrow stalk end to rocks
and weeds. At the free end is a wide opening (PI. iv. Fig. 1), the
OSClllum, while minute holes, pores, pierce everywhere through the
thin walls and open into the great central cavity or paragaster. These
walls, thin as they are, are of considerable complication, for three layers
of cells can be made out, an external, ectoderm, composed of a single
thickness of more or less mosaic-like cells ; a middle, mesoderm,—
here extremely thin, — and lastly an internal layer, endoderm,
composed in this sponge of oval shaped cells, each provided at the
free end with a well-marked circular upstanding collar, from within
the centre of which a strong whip-like thread or flagellum arises.
Such cells are termed flagellated collar cells or shortly, flagellated
cells — technically choanocytes.

In the first four figures on PI. iv, the outer black line repre-
sents both ectoderm and mesoderm, while the shaded layer stands
for flagellated cells. In the living sponge, the activity of the flagella
of the endoderm sets up minute currents of water flowing through
the numberless pores into the paragaster where nutrient particles
are picked up from the water and effete matter cast back. Hence
these currents, now gathered into a strong body of water, are directed
out through the great osculum at the summit of the sponge. Sponge
circulation is always fundamentally similar, even in the most complex :
ingress by very small openings, egress by a single large vent.

But to return to our Ascetta. Essentially its structure is a
thin walled sac, with pores opening direct into a great paragaster
lined with flagellated cells. This arrangement of water passages,
technically Canal System, is the simplest known, constituting what
Ha3ckel named the primitive Ascon Type (Fig. 1).

Complications are frequent, but the fundamental feature of
flagellated paragaster remains stable. Thus in our common Ascetta

16 MICROSCOPICAL STUDIES.

coriacea, budding, and branching, and anastomosing long continued,
produces a colonial network having a long ramifying paragaster
with numerous oscula. An intermediate form, Ascaltis botryoides,
helps us better to understand the change, for here the buds while
remaining attached to the parent and with their paragasters in free
communication with the parental one, have each a separate osculum.
Thus in an old colony, we can trace distinctly of how many indi-
viduals it is composed, by counting the number of branches, for
each possesses a single osculum, the sign of the sponge unit.

A foreign species furnishes another interesting complication
shown in Fig. 2. The walls become pushed out into numerous
radial tubes, into which the flagellated coating of the paragaster is
extended, and into which the pores open. Thus the extent of flagel-
lated surface and of the pore area is largely increased. The name
Chambered Ascon is applied to this form.

The next sponge type given us by Hosckel, the Sycon, is a
natural outcome of the Chambered Ascon, and in simplest organization
has the same structure minus the flagellated lining of the primary
paragaster. The cells of this become practically identical in form with
those of the ectoderm by loss of flagella and collars. Thus the Sycon
may be denned as a Chambered Ascon where the flagellated cells are
restricted to the radial tubes. Figs. 3 and 4 graphically exhibit
this change. These two types are practically restricted to the
division of sponges possessing a skeleton of calcareous spicules, which
is thus marked out as the lowest or most primitive division of the
Porifera, and consequently also of the Metazoa.

The third and highest type of sponge canal system, called
by Hseckel the Leucon from its being characteristic of the family
Leuconidse, and by Sollas the Rhagon, is accompanied, or rather
caused, by a great development of the middle layer of the body, the
mesoderm. This occasionally reaches immense proportions (see Fig. 8)
and as the paragaster does not share in this increase, the rather
dwindling, it is obvious that the pores must have, superadded, long
canals to enable the water to pass through the thickened walls into
the paragester, or even into its out-growing chambers. One origin
of the Rhagon is probably from the Sycon, as shown by the hypo-
thetical Figures 5 and 6 ; Fig. 5 is practically a thick-walled Sycon,
the paragaster pushing into the mesoderm fairly large rounded
chambers, henceforth to be called ciliated chambers. Narrow tubes,
incurrent canals, connect these with the pores on the surface, and
either one or several may serve each chamber. The flagellated form
of endoderm is entirely confined to the chambers. The next step
is where the mesoderm still thickening, the chambers lose their
direct connection with the central cavity and become connected by

CLASSIFICATION OF SPONGES. 17

a fairly long excurrent canal. The fresh-water sponge is organized
essentially upon this plan.

In the Leuconidae, e.y. Leucandra nivea, a further stage, Fig. 7,
can be made out, where instead of the excurrent canal of each
chamber pouring its tiny stream direct into the paragaster, those of
large groups of chambers are collected, as a river on its journey to the
sea gathers its tributaries, into a great and wide, but short stream
emptying by wide outlet into the central cavity.

This, the true Leucon type, is what Sollas terms the Aphodal
type of Rhagon. A further development, the Diplodal Rhagon, is
reached when the incurrent canals, in this highest type usually
restricted to one to each chamber, arise not singly and separately,
but rather in the manner of the numerous branches into which a
great river divides and sub-divides on its way through its delta.
A large and wide tubular cavity, the sub-dermal chamber, pene-
trates the crust of the sponge, and from this, numerous wide incurrent
canals lead inwards, throwing off at intervals still smaller tubules,
each of which feeds a ciliated chamber. The excurrent canals remain
the same as in the aphodal type. Often the sub-dermal chamber is
arched over by a finely perforated membrane, the pore area, a natural
filter against the entrance of enemies and coarse particles. A little
below this filter membrane (inwards) is usually a well defined sphinc-
ter muscle, adapted by its power of contraction to completely or
partially close the entrance to the water canals. The portion of
the large chamber inward of the sphincter has received the name
of Subcortical crypt.

A moment's consideration will show the great advantage that
will accrue to the sponge if the soft ground tissue be laced with
a network of intertwining fibres or supported by a cunningly arranged
scaffolding of strong and rigid rods. Without some such support,
the flagellated chambers would be apt to collapse and perform
their function indifferently, if at all. Based upon the nature of this
supporting skeleton, whether or not it is composed of calcareous
spicules, we get our two first great divisions, the Calcarea and
Non-Calcarea. The latter are by some termed Fibrospongiae, because
of a lacework of horny fibres more or less developed. But the
majority of the Non-Calcarea have, superadded, spicules formed of
silica (Silicispongiae), while others again want both spicules and
fibrous skeleton (MyxospongiaB). The Silicispongise are split up into
three orders according to the shape of the principal spicules
(megascleres), thus : —
Order I. — MONAXONIDA, megascleres simple, rod-shaped (Figs, la

and 2a, PL iii).

Order II. — TETRACTINELLIDA, megascleres four-rayed (Fig. 4fr, PI. iii).
Order III. — HEXACTINELLIDA, megascleres six-rayed.

18 MICROSCOPICAL STUDIES.

We may tabulate the larger divisions of the Sponges thus : —

Phylum :— Porifera.
Branch A, Calcarea. Branch B, Non- Calcarea.

Family I.— Asconidae.
" II. — Syconidoe.
" III.— Leuconidse.
(Characterized respectively by the Canal
system indicated by the name).

Class I.— (Skeleton siliceous) SILICI-

SPONGI-E.
Order I. — Monaxonida.

II.-Tetractinellida.
" III.-Hexactinellida.
Class II. - (Skeleton fibrous) CERATOSA.
Class III.-- (Skeleton none)MYxosPONGi;E

Putting aside in the present article any consideration of the
origin of the phylum as a whole, which is indeed bound up and
identical with that of the entirety of multicellular animals, it seems
most probable that the sponges arose independently by two main
lines from a primitive stock, rather than that the Non-Calcarea were
derived from the Calcarea or vice versa. Were the question limited
to the Calcarea, there, would be little difficulty, for within the limits
of the division, forms are found ranging from the very simple Ascon
type, step by step up to the Sycon and thence to the complex Leucon
or Rhagon. The Non-Calcarea are on the other hand nearly all
of the Rhagon type, and were it not for the siliceous spicules in most,
might easily be derived from some form of the Calcarea. But the
nature of the spicules is a stumbling block. How derive a spicule
of flint (silica) from one of carbonate of lime ? Can we imagine the
spicule forming cells to suddenly alter their selective power and
to seize upon silica instead of lime ? It seems too much to ask.

As to the Ceratosa, this difficulty is wanting and it is not
improbable that their origin is due to the renunciation of the
silica -secreting power in some ancestral siliceous sponge, while the
ancestors of the Myxospongia? may have gone a step further and
have given up even the fibre forming power. But all is uncertainty
as yet. Even fossil records help us not at all, for the most highly
organized order, the Hexactinellida, are represented in our oldest
fossiliferous rocks, the Lower Cambrian,

All the figures of entire sponges on Plate III are reproductions
of photographs taken from living specimens, and show very clearly
the outward form of four very prominent species of our Siliceous
sponges — Halickondria and Clatkria (Figs. 1 & 2) an HIM! with rod-
like spicules are typical forms of the Monaxonida ; whilst the other-
two, Tethya and Pachymatisma, are representatives of the great
group of the Tetractinellida. The third group, the Hexactinellida,
familiar to us in the lovely Venus' flower basket (Euplectella), and
the strange Glass-rope sponge (Hyalonema) is not met with in
British waters. All belong to OIK- or other variety of the Rhagon type
of canal system, and except in Tethya, the widely open mouths of the

SOME BRITISH SPONGES. 19

oscula are plainly visible ; situated in Halickondria at the apex
of tall crater-like prominences ; less marked in Clathria, where they
crown low rounded swellings, and in Pachymatisma, peculiar as
.being collected into special elevated areas, and there arranged in
serried, closely set rows. Details of histology must, for want of space,
remain over to a future article, and with this reservation, I will
now proceed to deal with the four species in question.

Hallcltondria panicea (Johnston), the Crumb of Bread, and also
the Coxcomb Sponge of Ellis, varies much in colour, ranging from
a greyish yellow to various shades of green. It is noteworthy that
the higher up the littoral and the more exposed to light, the greener
becomes this sponge. The yellow and ash coloured varieties are,
conversely, found in the lower zones of the littoral or where matted
curtains of fucus cause obscure shadowy light. In this sponge,
the entire duty of keeping open the canals devolves upon the
spicules, no fibrous tissue being present. The spicules (Fig. 1 a) are
all of one form, curved pointed rods, arranged in a well ordered
meshwork. Around the larger passages, the rows become much
strengthened. Sub-dermal cavities are greatly developed.

Clathria seriata (Johnston), the Ophlitaspongia seriata of
Bowerbank, shows more complexity in its skeleton. A well developed
tough, square-meshed, horny network supports the sponge, beset,
urchin-fashion, with numerous stout smooth rodshaped spicules
pointed at one end only (smooth styli). The meshwork arrangement
of spicules seen in Halichondria is absent, and apparently the
horny skeleton is here used to keep open the canals — the spicules
ceasing such function and limiting their benefit to defence against
would-be enemies. A second and slender form of spicule, bow-shaped
(toxon) can also be made out.

Pachymatisma johnstonia (Bowerbank) grows to immense
proportions, and probably is the most massive of British sponges.
The one photographed was G inches long, weighing just half-a-pourid.
Others we have had, have much exceeded this, e.g. one which is now
deposited in the Guernsey Museum, weighed when alive fully C-lbs.,
and measured 12-ins. X 7 — 9-ins., and 4 inches high. In section,
this sponge shows many interesting points. An outer thick crust,
cortex or ectosome is greatly developed by the massing of immense
n umbers of sterrasters — rounded and oval spicules thick set with
spines radiating in all directions (4 d). Similar spicules are spread
throughout the inner tissues of the sponge, the subcortical or
choanosome region, but if examined carefully, it will be seen that
these are much more sharply spinous than those of the cortex, which
appear worn and battered. Probably these spicules are formed in the
choanosome, and then pass outwards to accumulate in the cortex as a

20 MICROSCOPICAL STUDIES.

dense stony defensive layer. Other minute spicules (4 e — 4 k) are
found scattered through the tissues. As to the larger spicules, the
megascleres, the principal or four-axial ones peculiar to the order, are
here disposed as a supporting scaffolding beneath the cortex. The
form they take (Fig. 4 b) is known as the orthotrisene. Others of
simple structure (4 a) are located in the inner tissues.

The water of circulation enters through sieve plates into large
subdermal chambers, partitioned into two by a strong sphincter
muscle, able thus to close the opening on necessity. From the
inner chamber proceed the incurrent canals feeding the ciliated
chambers.

Tetliya lyncurium (Johnston) is in many respects a remark-
able sponge. In appearance, it simulates perfectly a miniature
tangerine orange in colour and in shape. Extremely spicular and
furnished with a cortex — a true rind — as well developed as is that
of Pachymatisma, no pores or oscula can be made out by the naked
eye when the sponge is out of water, but in life in its native element,
the oscula seem to be collected upon a slightly papillate prominence
near the apex. Large canals are very sparse and it is at first difficult
to believe this sponge to possess a complicated canal system as it
undoubtedly does. The megascleres are strangely not four rayed
as we should expect, but are long slender rods (3 c — d) gathered
into great radiated bundles, quite obvious to the naked eye in a
hand section (3 b). Microscleres, in the form of beautiful starry
bodies, abound (3 / & 3 g). As regards ciliated chambers, I have to
confess I have never seen any in either Pachymatisma or Tetliya.
But this is not to be wondered at perhaps, as the size of even the
largest ciliated cells of any siliceous sponge is very small compared
with that of those of the calcareous species.

EXPLANATION OF PLATE III, FIG. 1-4 & PL. IV, FIGS. 1-8.

Sponge anatomy, &c.

Plate III, Fig. 1. Halichondria panicea, x f ; a. megasclere.
Fig. 2. Clathria seriata, x f ; a, megasclere ; 6, micosclere (toxon).

Fig. 3. Tethya lyncurium ; a, another (smoother) specimen ; b,
same split open to show cortex and radiating spicule
bundles ; all x § ; c — e, megascleres ; / & g, mi-
croscleres.

Fig. 4. Packymatisma julmxtoHui x -H ; a & b} megascleres;

c & d, st i Trust ITS : f to h , otlu-r microscleres,

Journ. of Mar. Zool. & Microscopy.

VOL. I., PL III.

SILICEOUS SPONGES.

Journ. of Mar. Zool. & Microscopy.

Vol. I., PL IV,

JAB. HORNELL. DEL AD NAT.

SPONGES, MONSTRILLI, SMPMIOXUS.

A CURIOUS COPEPOD. 21

Plate IV, Fig. 1 — 8. Diagrams of the types of Canal System,
f. 1. Ascon ; f. 2. Chambered Ascon ; f. 3 & f. 4. Sycon ;
f. 5. simplest possible Rhagon ; f. 6. Eurypylous Rhagon ;
f. 7. Leucon or Aphodal Rhagon ; f. 8. Diplodal Rhagon.
All these are shown in vertical section, saving Fig. 4
which shows transverse section. In the Rhagon diagrams,
the white portion represents the greatly developed^ meso^
derm. The shaded portion denotes where ciliated cells
occur. Arrows denote the direction of the water currents.

STUDY V. — A CONTRIBUTION TO OUR KNOWLEDGE OF THE

COPEPOD MONSTRILLA ANGLIC A.

This species is for many reasons extremely interesting. A single
specimen, a male, wras captured in 1857 by Sir John Lubbock (1) at
Weymouth, and at the publication of the concluding volume of
Prof. Brady's fine monograph on the British Copepoda (2) in 1880,
no further record had been made and the original specimen had been
lost. Just about this time the record was resumed by the capture off
Jersey, of a few specimens by Mr. J. Sinel, who however did not
identify his interesting find till the publication, by Mr. I. C. Thompson,
of the description of a specimen of the same animal taken off Anglesey
in the autumn of 1887. Mr. Thompson at first believing the animal
to be new to science, named it Cymbasoma herdmani (3) but later
on, having more material to examine, he recognized his animal to be
of the same species as Lubbock's. Since 1880, Monstrilla anglica
has appeared pretty regularly every year off Jersey during Aug. and
Sept., in sparing numbers. Mr. Thompson has also recorded a second
specimen from the Irish sea (5), and another from off Malta, while
one or two more have been taken on the south coast of England.
Apparently then, here in Jersey, we have been the most successful in
obtaining this rare animal. Indeed of late years we have been specially
so, for out of a small number of tow-nettings taken in Aug. and Sept.
of the last two years, we have picked out nearly 80 specimens.

Normal Copepoda may be defined as minute crustaceans of
simple organization, having an elongated body clearly divided into
numerous rings or somites, and without the shield-like shell or
carapace that covers the anterior part of the body being double or
bivalve, having an anterior pair of antennae or feelers (properly
antennules) ; a posterior pair (the true antenncv) ; 3 pairs of
mouth organs (1 pair mandibles, 1 pair maxillce, and 2 pairs
ofmaxillipedes), and five pairs of two-branched, biramous, swimming
feet attached to the anterior part of the body or cephalothorax. The
hinder end of the body consists of an abdomen of 5 somites bearing
no organs and terminated by a forked tail.

22 MICROSCOPICAL STUDIES.

With such definition Monstrilla closely agrees if the italicized
part be omitted. Every vestige of the usually well developed and
complicated mouth organs is absent ; the posterior antenna) have shared
a like fate, and further, no trace of alimentary canal can be made
out, though a very short tubular proboscis is apparent. This however
leads nowhere, and I am inclined to hazard the suggestion that these
animals may live during the greater part of life as suctorial parasites
upon or within some larger animal, but that at breeding time (Aug.
and Sept.) they leave their hosts and seek for mates, free-swimming
in the surface waters of the sea. Certainly many species of copepoda
do live as parasites, e.g. the whole family of Notodelphyidse affect some
or other of the simple Ascidians, while others live within the cockle,
pecten (6) and other shell-fish. Regarding the assumption that
MoiiHtrilla forsakes the host at the breeding time, and that stomach
and intestine become absorbed coincidently, such would not be
without parallel among other animals. Thus those small free-
swimming worms, the Syllida?, forsake their homes among the
corallines as the time for reproduction approaches, and are found
among the surface life of the sea with alimentary canal reduced to a
mere cord or else entirely atrophied, and the cavity of the body
wholly filled by masses of ova or of sperm. Reference to PI. iv,
Fig. 9, will show how the ova in Monstrilla is similarly disposed.
Mr. I. 0. Thompson has indeed (5) considered and condemned
the view that this animal may be a sucking parasite — but apparently
he has overlooked the probability now suggested, of its regularly
abandoning such habit and altering its anatomy at the breeding
season. He adduced the fact that all specimens of Monstrilla have
been recorded as free -swimmers near the surface — but considering
that a copepod, common in, and peculiar to the cockle, was only
discovered in 1892, there is plenty of chance of this supposed
parasitic habitat of Monstrilla having been overlooked. Hence
I cannot without positive evidence agree with Bourne (7) in the
possibility that " the adult may be preceded by a predaceous larva
supplied with mouth parts and an alimentary tract, which, after a
succession of rapid ecdyses, develops into the mature sexual form,
whose only function is that of reproduction." But we have no record
of such a larva having been seen — and as such would be less easily
overlooked than would a parasitic adult in some perhaps obscure host,
I think the suggestion I mention is the more probable. A great deal
of work has yet to be done ere the parasitic copepoda are even fairly
well known, arid I would therefore draw the attention of workers
to what assuredly is a promising field for research.

The few appendages possessed by Monstrilla are all exceedingly
interesting when viewed under a high power. Thus if we examine

SEXUAL DIFFERENCES IX ANTENNAE. 23

the antenna) of the male, we will find each to be five jointed, and
furnished with a most curious variety of spikes and sensory hairs.
First there are numerous short stiff spines, next a few much longer
ones with a row of regular dots along each margin. Some of these
hairs are equal in length to half that of the antenna itself. Of about
equal length are three strange much branched slender hairs set
around the apex of the terminal joint. Into these hairs, branch
nerves can readily be traced. At the apex of the last joint is a claw-
like spine. These spines and hairs are very definite in position and
number, thus the 1st joint bears 1 short spine,

the 2nd has 5 spines and 1 long hair,
" 3rd " 1 spine and 2 long hairs,
" 4th " about 5 spines and 1 long hair, while
" 5th " 1 stout claw spine, 2 slender ones, 3
branched hairs, 1 long straight hair and a
short slight apical thread-like process.

Between the 4th and 5th joints is a strange hinge arrangement,
peculiar to male copepods, and of use in holding on to the female.
The antennae of the latter are shorter and less deeply jointed
than those of the male; the ratio being as 8 to 11. The 4th and
5th joints are practically fused into one, so that the antenna seems
to consist of 4 joints only. The spinous hairs are more strongly
marked in the female, while the branched and the long hairs are
less developed. Apparently then, these being sensory, it falls to
the male to search for his mate. In arrangement, the hairs, &c.,
are much the same in both sexes — except that in the female the
part that answers to the 4th joint bears 5 spines and 3 long hairs,
while what represents the 5th, in addition to having a stout apical
claw spine has two others equally well developed and which are
equivalent to the two slender spines in the male. It has been
said that the claw spine of the male is for use in seizing the
female but, seeing that the latter is even better equipped, it seems
to me more likely that these are primarily of use in anchoring as
parasites to some host.

The cepalothorax to which the swimming feet are attached,
is, in its front part, covered by a great shield, the carapace. On
the under side, at the hinder edge of the region thus marked
out, is inserted the first pair of feet. Behind the carapace are four
distinctly marked off body rings, each bearing in the female a pair
of feet on the under side. In the male the fifth pair of feet are
suppressed. In structure the first 4 pair of feet are very much
alike. The fundamental plan of the typical crustacean foot can be
traced clearly. A stout basal part of two stout joints articulating
to the body represents the protopodite. To the joint away

24 MICROSCOPICAL STUDIES.

from the body are joined two branch limbs, one directed inwards,
the other outwards, respectively endopodite and exopodite. Each
again is divided into 3 short joints, bearing setcv or stout hairs
definitely placed (PI. iv, Fig. 12). The 1st pair differs from the
others in possessing one hair less on the distal joint of the exopodite.
All the setas of the feet are finely plumose. The fifth pair of feet,
present only in the female, is very different, as each foot consists
merely of two short weak joints, bearing at the termination a couple
of slender hairs.

The abdomen consists of 4 joints (Fig. 10, 1, 2, 3 & 4), ending in
a forked tail. Each fork bears 1 slender and 5 stout bristles in
the position shown in Fig. 11. Lubbock erred in writing " upon the
fourth candal seta (counting from the outside) is another, rather
smaller than the other five." In reality it arises from the tail fork
in the same way as its fellows, but being very slender, a mistake
is very liable to occur. Mr. I. C. Thompson has apparently over-
looked this slight hair in his diagnosis of the species as he says
" 5 setae to each furcal segment " (6).

Muscular System. — By selective staining, I have been fortunate
in being able to make out very clearly the principal arrangements
of the muscles. A glance at Figs. 10 and ] 1 will show how immensely
powerful this tiny creature (female 3 mm. long ; male 2*25 mm.) is in
proportion to its size. This is apparently against the idea of the
generally parasitic life of this animal, for such life in general leads to
partial atrophy of the muscles. Still it does not dispose of the
suggestion — there may be compensating causes.

To return. The largest muscles are found within the carapace,
lying longitudinally ; four pairs arranged as in Figs. 10 and 11. The
two upper or dorsal pairs are used in straightening or extending
the body, extensors ; the other two pairs for bending or flexing,
i.e. flexors. Each of the following body rings or segments possesses
but one pair of extensors and the same number of flexors, modified
however in the abdomen by the extensors of the first and second
segments, and both the extensors and the flexors of the third and
fourth being respectively wholly or in great part coalesced. Thus
these segments lose more or less their independence of action, the
first and second acting in concert in extension, the third and fourth
in all movements. To understand well the action of these body
muscles we must remember that the axis of movement between
adjoining body rings lies transversely across the body a little above
the articulation of the feet, so it is obvious that a pull below such
axis, will bring the rings together on the under side, producing
flexion ; conversely, if above, the opposite, i.e. straightening will

THE THREE EYES OF MONSTRILLA. 25

be produced. Hold a coin between finger and thumb, pull on the
uppermost point of the edge and the movement that produces
extension in crustaceans, is simulated ; if the lowermost edge be
pulled, then flexion is imitated. The anterior end of all these muscles
is attached well forward to the inside of the chitonous shell that
forms the protective skeleton' in these animals ; the hinder end being
inserted on the front edge of the body ring next following, and which
is governed in action by the muscle so placed.

The swimming feet are each governed in their larger movements
by two great fan-shaped muscles which pass upwards from the thigh
joint along the sides of the body. The smaller movements are
co-ordinated by a very complex series of small muscles which space
forbids the enumeration of. The antennae are each governed by two
strong muscles passing backwards close to the eyes. In both sexes
the muscular development of the antennae is great, particularly in
the male, and is of great assistance to the animal in swimming,
being, in this sex, virtually equivalent to the addition of another pair
of swimming legs.

Sense Organs. — These seem practically limited to eyes and
sensory hairs. The former are well developed, three in number, each
possessing a large crystalline lens. They lie somewhat in triangular
fashion, two paired ones on the upper surface of the head between
the bases of the antennae, and a third, the unpaired one, being
beneath these on the under side of the head. The structure is
essentially that of a convex glassy lens set in a mass of pigment and
connected by a stout nerve with the brain.

It is interesting to notice that the paired eyes look sideways,
while the unpaired one looks downwards and forwards, just the
best possible optical arrangement for the animal when it betakes
itself to free life at the surface of the sea. To pelagic animals there
is no above. Their world lies around and beneath, and there alone do
they require to cast inquiring glances, if indeed their modest optical
equipment will so permit me to phrase it.

In the females full of ova, the eyes are frequently much reduced
and apparently more or less absorbed and functionless.

As to sensory hairs, there are apparently two kinds, one having
a much branched form (Fig. 10, a), the other straight and un-
branched (6). It may be that a is olfactory and b tactile, but this
rests entirely upon supposition.

Respiration. — No organs adapted to this end. The general
surface of the body seems to function.

Reproduction. — The sexes are always separate ; the difference
expressing itself plainly in the outward form. The male is smaller
(2'25 mm.) than the female (3 mm.) ; he has more powerful antennae

26 MICROSCOPICAL STUDIES.

(ratio 11 to 8) ; the hinge between the 4th and terminal joints of
his antennae is absent in those of the female ; he is without the
rudimentary fifth pair of swimming feet present in the female, and
the sexual orifices which open in both sexes on the under side of the
1st abdominal segment, are in the male situated on stout low
prominences (Fig. 10, /.) ; in the female when mature, these are
produced into long tubes reaching backwards considerably beyond the
ends of the caudal bristles. Internally both ovaries and testes lie as
two great paired glands in the cephalothorax. Both sexes have in
this species two distinct efferent ducts whereby the genital products
are passed downwards and obtain egress at the openings already
mentioned. The function of the long tubular genital processes of
the female (c) is probably to give attachment to the ova after
being extruded, as Mr. I. C. Thompson has observed ova adherent
to them in an allied species (4).

REFERENCES :—

1. LUBBOCK, SIR JOHN. — Ann. & Mag. Nat. Hist,, Vol. xx, 2nd

Series, 1857.

2. Brady, Prof. G. S. — A Monograph of Br. Gopepoda (Ray

Soc.), Vol. iii, 1880.

3. Thompson, I. C. — Second Rep. on Copepoda of L'pool Bay

(Trans. Biol. Soc. L'pool, Vol. II), 1887.

4. — Copepoda of Madeira (Journ. Linn. Soc.

Zool, Vol. xx), 1887.

5. —Monstrilla & the Gymbasomaiidce (Trans.

Biol. Soc. L'pool, Vol. iv), 1890.

6. — Revised Rep. on Copepoda of L'pool Bay

(Trans. Biol. Soc. L'pool, Vol. vii), 1893.

7. Bourne, G. C. —Notes on the Genus Monstrilla (Quart.

Journ. of Micro. Sc.), Feb. 1890.

EXPLANATION OF PLATE IV, FIGS. 9 — 12.
Monstrilla awglica (Lubbock).

Fig. 9. Side view of a female full of ova (size 3 mm.), am antennary
muscles, e eye, o proboscis, c genital tubes. (Note — No
definite articulation should be shown between the fourth
and terminal joints of the antenna. Such is shown
here by a slip in drawing.

Fig. 10 & 11. Lateral and dorsal view of a male (size 2'25 mm.),
a branched sensory hairs, b straight tactile (?) hairs,
ml & m", the extensors muscles of the segment next
behind the carapace, 771"' & miv flexor muscles of same,
1, 2, 3 & 4 abdominal segments, / genital prominence,
d the 6th or slight seta of the caudal fork.

Fig. 12. View from behind, of the third pair of swimming feet.

27
VI. THE MAIN FACTS CONCERNING THE LANCELET (AMPHIOXUS

LANCEOLATUS).

Few animals are cosmopolitan. Changes of climate, food, and
habits, brought about by life in other latitudes, alter, directly or
indirectly, sooner or later, some features of the body, and the migrant
becomes a new variety, and even in course of time may have this
variation so indelibly impressed upon it, as to constitute a new
species. Even migrant civilised man, with all his special advantages
of constant inter-communication with his original stock, is affected
appreciably in comparatively a short time. The American — our
Brother Jonathan — has not our features, but bears a physical trade-
mark solely his own ; our cousin, too, in New Zealand — a really
nearer relative than he from the U. S. A. — is developing " points "
alien to ours. Naturally however, the land is less likely to present
cosmopolitan types than the sea. Under the waves vicissitudes of
climate are reduced to a minimum. But even there, we but seldom
find a species stable over widely extended areas ; those known to be
world- wide may practically be counted on the fingers.

Thence, when we find that perhaps the most curious of living
animals, the strange Lancelet, most lowly among the vertebrates, is
found without appreciable change of form or structure in the seas of
Europe (around Britain and in the Mediterranean), along the North
American coast, in the West Indies, Brazil, Peru, Tasmania, Australia,
and Borneo, we seize one of the many noteworthy facts concerning
this animal.

Spread thus universally, Awiphio&us lanceolatus is not only the
sole species in its genus, but also the only representative of the
family, and even of the group to which it belongs. Curiously enough,
the first example known, was caught off Cornwall, and passed into
the possession of the early Russian naturalist Pallas, who indeed saw
so little affinity with the vertebra ta, that he described it (1774) as a
slug, Limax lanceolatus. Some fifty years passed ere we have note
of a second specimen being caught (1831). This again was taken on
our English coast, at Polperro, Cornwall. It was well described by
Yarrell, who bestowed upon it the name we are now so familiar with,
Amphioxus lanceolatus. Yarrell recognised its relationship better,
and placed it at the bottom of the list of fishes, where it has ever
since remained.

The growth of the systematic study of marine life has of late
years shown Amphioxus to be both widely spread and frequently
numerous, so that now it may aspire to join the select circle of
martyrs to science, already adorned with the names of the frog
and the dogfish.

28 MICROSCOPICAL STUDIES.

The anatomy and description of few animals are better known,
hence I have little or no excuse for occupying space with details here.
Any zoological text-book will provide such, as for example Marshall
and Hurst's " Practical Zoology," a work specially commendable,
from its clearness and accuracy. I will therefore now give what
is intended as merely a running commentary upon the figures as
drawn on Plate IV.

External Characters. — In life, the Lancelot is a small, nearly
transparent fish-like animal, pointed at either end — of some two
to three inches in length. No scales are present, the body being
clothed in a thin transparent cuticle. Along the entire dorsal region,
and along the ventral from atrial pore to the end of the body, the
skin is raised into a fold or ridge best marked both dorsally and
ventrally in the part of the body posterior to the anus, and which we
may term the tail. The dorsal ridge of skin is strengthened, except
at the ends, by a row of cube-like compartments forming a supporting
skeleton, answering to the fin rays of true fishes. The ventral ridge
is strengthened by a similar skeleton between atrial pore and anus,
and this part is the ventral fin (vf.) ; the fold running along the
dorsal and ventral sides of the tail being the caudal fin, while the
dorsal fold anterior to the tail constitutes the dorsal fin (df.)

Alimentary Canal. — The mouth is a large oval aperture
placed anteriorly on the ventral aspect, and bordered on either
side by a line of tentacles (bt). The mouth leads into an elongated
dilated chamber, the pharynx, which functions also as the organ of
respiration (ph). Its walls are supported on either side by a frame-
work of cartilaginous arches set obliquely, the gill arches (#«), along
which course the branchial blood-vessels. Between every two arches
is a long narrow perforation, the gill cleft. Through these openings,
the water, brought in through the mouth by the action of the cilia
that line the pharynx, is directed into a cavity all but surrounding
the pharyngeal tube. This, the Atrial Chamber, corresponds closely
to that of similar name in the Ascidians, and indeed, the respiratory
plan is altogether exactly conformable in the two animals. The
water passing into the atrial cavity from the pharynx is conveyed
out by an opening, the atrial pore (<q>), situated at the front end
of the ventral fin. As in the Ascidians, an endostyle is present
in the ventral wall of the pharynx. It is however flattened in the
anterior part, but posteriorly it has the deeply grooved form charac-
teristic of Ascidians. The epibranchial groove found in Ascidians
is also well marked as a dorsal counterpart of the endostyle.
The pharynx leads into a straight intestine ending in an anal
opening (a) placed on the left side of the ventral fin.

THE MAIN FACTS CONCERNING THE LANCELET. 29

Immediately above the alimentary canal is a tough elastic rod,
the Notochord (nt\ reaching from end to end of the body. Above
this again, lies the Spinal Cord, a cylinder having slightly less
diameter, marked along the under side by black pigment cells.
No brain is apparent, but the more anterior part is slightly thicker
than posteriorly. Branching nerves are given off at intervals to
the various organs.

Sense Organs are rudimentary ; a pigmented patch at anterior
end of the spinal cord, serves as " eye," while a ciliated pit at the
same point may be olfactory in function.

The Muscular System is well developed and enwraps the various
organs as in a sheath. Its elements are composed of striated fibres,
arranged principally in peculiar < shaped bundles or myotomes
numbering 61 — 62 on either side of the body. On the ventral
surface are subsidiary muscles running transversely, whose function
is, by contraction, to expel water from the atrial cavity.

Blood System. — No definite heart is present. Impure blood
from all parts of the body is collected into a ventral vessel, the
cardiac aorta, which by the contractility of its walls is able to propel
this blood into paired vessels, aortic arches, that pass along each
alternate (primary) arch. The blood, purified in these vessels by
intimate exposure to the water passing through the gill slits, is
emptied into a right or left dorsal aorta according as it comes from
right or left side of the pharynx. The right and left dorsal aortse
unite to form, at the hinder end of the pharynx, a single vessel which
passes backwards on the dorsal side of the intestine. From the
dorsal aortaa the purified blood is distributed to the organs of the body.

Reproductive Organs. — The sexes are separate — ovaries and
testes have the same outward appearance, that of two rows of
enlargements along the body-wall, external to the atrial cavity and
parallel with the pharynx, a row on either side of the body. The
products escape by rupture of the atrial wall, into the atrial cavity
and escape by the atrial pore, or it may be by the mouth, by passing
through the gill clefts.

Want on Internal Symmetry. — It is a remarkable fact about
Amphioxus, that the internal organs do not show bilateral symmetry,
that is, are not arranged in balanced pairs. Thus any particular gill
cleft on one side is opposite a gill arch on the other side, instead
of opposite another cleft. The aortic arches necessary partake also
of this asymmetry. The muscle segments or myotomes, nearly all
the nerves arising from the spinal cord, and the reproductive glands
are also alternate on the two sides of the body. The liver too is
asymmetric, being turned to the right side, while the anus opens
on the left side.

30 MICROSCOPICAL STUDIES.

Development of Gill Arches. — These are of two kinds ; half
are forked at the ventral ends, others, which alternate, are imsplit.
The cleft in front of, and that behind each unsplit rod originally
formed together a single opening, which, by secondary growth
downwards of a portion of the wall, become divided into two in the
manner shown in Fig. 16, Plate IV. The down-growing rods may
be therefore termed secondary arches, the others primary. In adult
individuals connecting bars cross the clefts so as to join more
intimately the primary and secondary arches, an arrangement
reminding us of that in the Ascidians.

A comparison of Amphioxus with a typical Ascidian is extremely
interesting and suggests such a closeness of relationship that were
it not for the emphatic development of a central skeleton, there
would be more reason in classing it as a highly developed free-
swimming Ascidian, than as a little developed ancestral fish.

The points of similarity are well brought out by glancing at the
comparative diagrams of the two, shown in figs. 14 and 15. The
section shown in both figures is transverse. In the Ascidian, the
section is just posterior to the mouth and through the nerve ganglion
that serves as brain. That of Amphioxus is through the pharynx.
Examination shows how, except in minor details of relative thick-
ness and arrangement of the tissues, the fundamental similarity
(homology) is absolute, saving for the presence in the lancelet of a
central skeleton, or notochord (nt). In both the body is encased
in a more or less structureless cuticle. Within this is a ring of
muscular fibres, and more or less sunk in this muscular layer is the
central nerve-mass (n). Suspended from the muscular band at a
point just beneath the nerve centre, is a perforated pharyngeal tube
shown in figs. 14 and 15, by an interrupted line (gci.) intended to
represent the sections of alternate gill arches and gill clefts. Top
and bottom of this pharyngeal tube are two grooves, respectively
the epibranchial groove and the endostyle.

The minor differences as seen in such a section are : — In the
Ascidian the cuticle is immensely thickened to form a protective
test ; but the muscular hoop is infinitely less developed than in the
Lancelet, due to the want of much muscular effort in the sedentary
life led by the former. In the Lancelet again, the pharyngeal tube
is only attached dorsally. In the Ascidian, it is, at the points shown,
attached both dorsally and ventrally.

In both animals the mechanism of respiration and feeding is
alike ; the muscular arrangements are strictly comparable ; the
reproductive products are in both expelled from the genital glands
into the atrium and leave the parent by either the atrial pore or

THE MAIN FACTS CONCERNING THE LANCELET. 31

mouth. In both is the same lowly development of sense organs, and
want of any defined cephalic or head region.

The points of divergence are essentially the presence in the
Lancelet, of a notochord, of an elongated central nerve-mass, and of
a higher type of blood system.

Finally it is noteworthy that a series of minute tubules, probably
excretory, open into the upper portion of the atrial cavity on either
side of the pharynx. There can be but little doubt that these
represent the paired excretory tubules (nephridia), so characteristic
of the worms. Hence, as no kidneys of any vertebrate pattern are
present, the Lancelet exhibits in the structure of its renal organs,
the most unmistakable of its many plebeian characteristics.

EXPLANATION OF FIGS. 13-16, PLATE IV.

Amphioxus lanceolatus (Yarrell).

Fig. 13. View of a young specimen iVin long ; from the left side.
Fig. 14. Diagram of a transverse section of same through pharyngeal

region.
Fig. 15. Diagram of a transverse section through the anterior end

of the body of a typical section, e.g. A. mentula.
Fig. 16. Diagrams showing the mode of formation of a double gill

slit from a single.

Lettering the same in all figures, viz. : — a p. atrial pore ; a. anus ;
b t. buccal tentacles ; c. cuticle ; df. dorsal fin ; e. eye ; end. endostyle ;
ep [/. epibranchial groove ; g a. gill arches ; i. intestine ; L liver ;
m. muscles ; n. nerve system ; nt. riotochord ; ph. pharynx ; p c.
pigment cells ; sp c. spinal cord ; vf. ventral fin.

Aeries III,

-V, "VI

STUDY VII. THE METAMORPHOSES OF THE MANTIS SHRIMPS

OR SQUILLIDvE.

SQUILLA MANTIS.

The Mantis Shrimps, the Squillidse, are among the least known
of the larger crustaceans found on our shores. Essentially a southern
type, the two species of this family that occur in British waters, have
been met with on the southern coast only, and if we were to judge
from the few captures reported, we should account them extremely
rare. In reality, one of the two, — Squilla desmarestii — is not
uncommon along the shallower shores of Jersey, but as it takes up
habitation in deep burrows among the roots of the sea-grass (Zostera)
in a zone never uncovered by the tide, one can understand how rare
in appearance it may be — how abundant in fact in some favourite
localities. On several occasions, immense numbers have been cast up
on the Jersey coast after great storms. Their homes in the Zostera

JETSAM OF MANTIS SHRIMPS. 33

bods of the Laminarian zone had been devastated by heavy surf due
to the bursting of storms coincident with the furthest receding tides
of the year, and the Squillids forced or frightened from their burrows,
and helpless to withstand or get clear of the dashing breakers, had
been buffetted to and fro, to be finally thrown in multitudes upon
the beach.

The Squillidse, the sole members of the order Stomatopoda^ are
distinguished from the other order of large Crustaceans — the Deca-
poda (Lobsters, Crabs, &c.) — by a different arrangement for breathing
and by a different function to which certain of the anterior limbs
are put.

For the purpose of comparison, let us take the Lobster as type of
the Decapoda. In it, the three divisions of the body of an ideal higher
crustacean — head, thorax and abdomen — are reduced to two, by the
fusion of head and thorax to form the cephalothorax. This, pro-
tected by a great shield, the carapace, is furnished with 14 pairs of
appendages. Taking these in order from before backwards, we have
one pair of stalked and moveable compound eyes ; two pairs of
sensory organs, the antennae ; one pair of stout jaws or mandibles ;
two pairs of weaker jaw organs, maxillae ; followed by three pairs of
appendages which in structure are midway between that of the
walking limbs and that of the maxillae, and as they share in the work
of preparing food and closely surround the mouth, they have received
the name of foot-jaws, or maxillipeds. Next come five pairs of large
walking or ambulatory limbs, pereiopods. Of these, the anterior pair
are enormously enlarged and form the chelae, or pincers, powerful
organs for seizing and tearing prey. The second and third pairs have
also small pincer terminations, but the third and fourth end in
simple claws.

The abdomen consists of five well-marked rings or somites,
bearing each a pair of two branched (biramous) swimming feet or
swimmerets, followed by another somite bearing much enlarged
flattened swimming feet. A large, strong plate, telson, forms the
hinder extremity of the body and with the plate-like limbs of the
preceding somite, constitutes a powerful flapping tail — the so-called
caudal fin. In all probability, the telson represents a true somite
once provided with swimmerets, for the anus opens on the under side
of it, and further, minute moveable points, esteemed to be vestiges of
swimmerets, have been observed upon the telson of the common
prawn, Palcvmon serratus* If this be so, the abdomen consists of
seven somites ; and as each pair of limbs attached to the cephalothorax
is believed to indicate an original somite, we arrive at 14 as the

* Bell, History of Br. Stalk-eyed Crustacea, p. xx., London, 1853,

34 MICROSCOPICAL STUDIES.

number of somites composing this part of the body. But several
weighty reasons point to the eyes as not representing a somite, and
this reducing the number to 13, we find the entire body to consist of
20 somites. And this number not only characterises the Decapods, to
which the Lobster belongs, but equally the whole of the higher
Crustacea. In some species, indeed, the thorax is distinctly jointed
after the fashion of the abdomen, emphasizing clearly the primitive
segmentation of the former region.

In the Lobster as in all Decapods, the breathing organs consist
of lancet shaped gills composed of innumerable closely packed plates
or lamella?, connected with the ambulatory limbs and some of the
maxillipeds, and lodged in a special champer on either side, formed
by the down-turned edges of the carapace.

If we now turn to Squilla, we have to note the following radical
differences from the Decapod type. Most are apparent in the accom-
panying drawing of Squilla mantis, the larger of the two British
species.

This animal is much more active and lithe than the Lobster, by
reason of the fusion of the head and thorax being less complete.
The carapace leaves uncovered the last three somites of the thorax,
and the shortened ones bearing the hinder maxillipeds are also not
fused with this shield. Apparently then, Squilla shows a more
primitive form of structure than does the Lobster — for undoubtedly
the architypal crustacean had a body composed of a number of
somites of which none were fused together — all being separate and
independent. As to the appendages, the eyes are extremely curious
in shape, expanding at the summit in a broad bilobed fashion that
arrests the attention at once. Then follow two pairs of antennae, the
outer bearing a broad oval scale or squame ; next a pair of strong
mandibles and two pairs of maxillas, just as in the Lobster. But
here the similitude ends, for instead of three pairs of foot-jaws, there
are five pairs, — the first weak, the second formed into strong and
greatly developed prehensile claws, — with toothed terminal joint
capable of folding down into a groove on the inner side of the
joint preceding, while the succeeding three are weakly organs,
with rounded penultimate joint, bearing a tiny spine-like claw.
Next, instead of the five pairs of walking limbs characteristic
of Decapods, there are in Squilla but three pairs, and in struc-
ture they differ also, being weak and styliform and bearing a
delicate outer branch (exopodite), which disappears entirely in the
Decapods — one of several reasons stamping the latter group as more
modified, more distant, from the primitive co-parent, than the
Mantis Shrimps. As to the abdomen however, the form of the
appendages remains essentially the same, saving that in Squilla the

LIFE-HISTORY OF MANTIS SHRIMPS. 35

first five bear gills — beautifully tufted or feathered, and kept con-
stantly in movement by the incessant paddling of the limbs where-
from they spring. No gills belong to the anterior part of the body ;
hence the carapace is small as it does not require to bend down
laterally to form gill chambers as in the Lobster.

Good as the drawing given above, in life Squilla would scarcely
be recognised by it. No great seizing claws are visible, indeed none
of the maxillipeds are in evidence. I remember how, when I found
my first specimen, my heart sank very low — my capture was but a
sorry one — the great claws were gone ! And then as I little by little
examined more carefully, my spirits rose again — for there, snugly
folded up beneath the shelter of the projecting margins of the
carapace, were the two lost limbs, and equally safe were the other
foot jaws hidden closely away between the bases of the great claws.
A moment's thought will show how necessary it is for animals living
in a narrow- burrow to have means of packing away, in small compass,
great limbs that are of no service except in procuring food, and which
otherwise would be getting in the way continually. In leisurely
swimming, the abdominal limbs — the swimmerets — are used as
paddles — but they by no means do all the work for the large oval
squame of each of the second antennae paddles assiduously and must
be of great assistance.

The development is singularly interesting. Unlike the Deca-
pods, the Mantis Shrimps do not carry their spawn about till hatched,
attached to the swimmerets, but deposit it in their burrows in the
Zostera meadows — a great difficulty in the way of the study of the
embryology of this animal.

Upon emerging from the egg, the larva is very simple in struc-
ture, soon assuming the form shown in PI. vi, Fig. 3. A great shield
covers nearly the whole of the body. In front, this carapace is drawn
out into a long spine or rostrum ; behind, into two other but smaller
spines, with a third tiny one midway between these two last. The
eyes are very large and show no trace of any stalked condition.
Indeed this sessile form characterises the early larval stage of all the
higher crustaceans when normal, and clearly points to an ancestry
with unstalked eyes. Two pairs of tiny antennae, two mandibles and
two pairs of maxilla are present, together with five powerful biramous
maxillipeds, co-equal in size — saving the second pair, which in their
slightly stouter form, forshadow the great clawed prehensile second
maxillipeds of the adult.

The three succeeding somites of the thorax are clearly seen from
the first, but without sign of any appendages. In the very early
stage a large spinous-edged telson articulates with the hindmost of

36 MICROSCOPICAL STUDIES.

these limbless thoracic somites, and as time goes on, the true
abdominal somites appear at this point of junction and simul-
taneously tiny limbs sprout out from these newly formed parts. In
Fig. 3 two pairs are shown in an early sprouting stage. This, the
Erichthus or Glass Shrimp stage, was long mistaken as representing
a separate animal, and before going further, let me point out why it
does not receive the name of Zoea, as the young larvae of the
Decapods are so well known by.

If the newly hatched young of the Common Shore Crab
(Garcinus) be examined they will be seen to possess apparently
the same body parts as the Squilla Erichthus. A large carapace
covers the fore part of the body, and a tail unprovided with limbs
follows, ending too in a broad telson. Yes, but here most curiously,
the hinder part of the thorax is not yet in any way recognizable, and
the tail portion is true abdomen and not thorax as in Squilla ; seven
pairs of appendages are present ; the two pairs of antennae, the
mandibles, two pairs maxillae and two pairs of maxillipeds. The
third pair of the last named organs and the whole of the am-
bulatory limbs are absent and when they do appear, they sprout
out from the point ^-r~2^ Jus^ anteri°r to the

junction of thorax ^^^^^/•'''/^ with abdomen. The

swimmerets appear ^5^3*^ \ about the same time

as paired buds from ">^$?§|8£. ) the segments of the

tail-like abdomen. ^fl/^^^h^M Thus there is a wide

divergence between p$J^ ^O? the Zoea and the

Erichthus. In the TS> \*S one, the abdomen is

present from the ^\Str-~^s=— nrst,while the hinder

part of the thorax '^SL_ is absent — in the

other, the cepalo- ADVANCED ZOEA OF A CBAB. thorax is present in
full segmental number from the beginning, but the abdomen is
wanting, saving for the telson.

After several moults the Erichthus loses entirely the three
hinder maxillipeds, while synchronously the tiny abdominal somites
that have just appeared, develop their bud-like limbs into large
biramous swimmerets or pleopods, while each of the second maxil-
lipeds increases in size quite disproportionately to its neighbours
and becomes a huge somewhat chela-like limb — differing however
from the true chela or pincer form (seen so well in the Lobster)
in that the terminal joint is not opposable to an outgrown, huge
finger-like spine of the second, but instead folds down upon the
second, fitting when at rest, into a deep groove running along the
inner margin of this penultimate joint. In the adult the edges of
this groove are beautifully sculptured with most delicate serrations,
and in the larvae show also, but in a coarser form (PI. vi, Fig. 4).

Journ. of Mar. Zool. and Microscopy.

Vol I. PI. VI.

Jas Hornell, del ad Nat.

JERSEY BIOL STN.

METAMORPHOSES OF CRUSTACEA.

Journ. of Mar. Zool. and Microscopy

Fij.l

Jas. Hornell, del ad Nat-

JERSEY BIOL. STN.

STRUCTURE OF ANEMONES.

THE CYCLOPEAN EYE. 37

The larvae have now passed into what is known as the Alima
stage. The paired compound eyes now become stalked, and the
unpaired simple eye more easily distinguishable as a tiny X shaped
black speck, set at the base of the rostrum and between the bases of
the stalked eyes. As a point of interest, it may be noted that a
connection has been suggested between it and the pineal eye of
vertebrates.

In PL vi, Fig. 5, a later alima stage is figured — just prior indeed
to the assumption of adult form. Here the three suppressed maxil-
lipeds are reappearing, but extremely short (Fig. 56). In it also, the
three biramous walking limbs of the adult are beginning growth —
tiny buds on the underside of the three hinder thoracic segments
(Fig. 5c), which until the present have from the time of hatching
been free from any sign or trace of appendage.

During all these larval stages, the tiny animal leads a pelagic
free-swimming life, and is occasionally taken in the tow-net in the
sunny waters of the Channel Isles. Like other pelagic animals it is
glassy and colourless and a powerful swimmer.

EXPLANATION OF FIGS. 3 — 5, PLATE VI.

Metamorphoses of Squilla.

Fig. 3. The recently hatched animal in the Erichthus or Glass-
shrimp stage ; actual size 4 mm. (inclusive of rostrum).

Fig. 4. Early Alima stage of another species, ventral view ; actual
size 4J mm.

Fig. 5. Advanced Alima stage, dorsal view ; actual size 11 mm.
(In this figure, the rudimentary three hinder pairs of
maxillipeds — 56 ; the bud-like ambulatory limbs — 5c ;
and the well-developed ambulatory limbs — 5d, are not
figured for clearness sake).

5«, a mandible ; 56, one of the three hinder and rudimentary
maxillipeds, X 55 ; 5c, Section through the hinder part
of the thorax, showing the first appearance of the am-
bulatory limbs as buds, X 18 ; 5d, a swimmeret, X 13.
Lettering the same in all figures, viz : — I. anterior antenna? ;

II. posterior antennae ; III. mandibles ; IV & V. 1st and 2nd maxilla? ;

VI, VII, VIII,, IX & X. maxillipeds; XIV— XVIII. swimmerets ;

e. paired compound eyes ; e. unpaired simple eye ; lab. labium ;

II. branchial plate of maxilliped ; cp. carapace ; r. rostrum ; al. ali-
mentary canal ; a. anus.

NOTE. — Probably the two Alima forms figured, belong to the

same species of Squilla, viz., S. desmarestii.

38

VIII. — THE PHYLLOSOMA OR GLASS CRAB LARVA OF SCYLLARUS.

Pelagic animals arc, without exception, of the highest beauty,
but, saving for the wondrous loveliness of the pelagic Ccelenterates —
the elfin-locked Medusids, the glassy Cydippe, and the phosphorescent
and elaborate Siphonophores, — what can compare with the quaint
" Glass Crabs " of the older writers. These, long known by the name
of Phyllosoma, were considered a separate group of animals, till
Couch in 1857 hinted vaguely to the British Association that they
were in reality the larval forms of certain Decapod Crustaceans,
notably of Pcdinurus vulgaris, the Common Crawfish. Couch had
been studying for some years the development of the larger Crus-
taceans, and the pity is, that through inadequate training he was
unable to utilize to full, or even moderate advantage, the oppor-
tunities that the practically unexploited field of this study then
afforded.

Couch's figures were anything but accurate, and his work did
little but point the way. Indeed not till so long after as 1870, was
the full value of the relationship definitely traced and worked out,
and the achievement is one of the many that Biology owes to the
indefatigable perseverance of that prince among naturalists — the
veteran Dr. Dohrn.

In that year Dr. Dohrn detailed the development of a very
near relative of Palinurus, viz. of Scyllarus arctus, while in the egg,
and also during a short period in its free swimming life, showing
that there is absolute identity between the hatched larva and a
certain form of Phyllosome.

Other naturalists have extended these observations, and to-day
the only points requiring much elucidation, are the final metamor-
phoses just prior to the period when the Phyllosome larva changes to
the adult. A limit seems to be set to the age to which the larvaa
can be reared in confinement. For a while all goes well, then the
captives begin to find some necessary condition of life to be wanting,
and rapidly decrease in numbers, till not one survives.

But before describing the larval form, let us glance at the chief
points in the anatomy of the adult. Scyllarus arctus is one of the
rarest of the large Crustaceans living in British waters, and like the
Squillidse, found only in the English Channel ; just on the northern
boundary of the great Mediterranean zone — just where this zone
grades into that of the northern regions. Its captures on the
English coast can be traced in paragraphs in scientific journals, and
only in the Channel Islands is it frequently enough met with to
receive a vernacular cognomen. In these islands the fishermen speak
of it indifferently as the Bastard Crawfish and the Square-nosed

"GLASS CRABS/

39

Lobster ; sufficiently graphic epithets — strong in the descriptive
name-power that lurks so often in the rough harvesters of the sea.

Scyilarus is a strange mingling of the uncouth and the beau-
tiful. His form is clumsy ; short squat body with weak legs and
with disproportionate development of the second antennaa. These,
which in the Lobster and the Crawfish (Palinurus) are elegant,
long, gently tapering rods equal and exceeding in length that of the
body — dwindle in Scyilarus into short broad plates very evident in
the figure drawn beneath. — But the coloring ! That is superb : In

general tint a rather light chestnut brown,
the depressions and deep lines of the closely
covering fine sculpturing are of deeper tone,
almost black ; in striking contrast to this the
anterior portion of each of the abdominal
rings is of a brilliant scarlet. The short eye-
stalks are also scarlet, giving these organs,
with the black pigment disc showing distinct
through the transparent cornea and retina,
a striking resemblance to those little scarlet
and black beans (Abrus), which bottled up,
form such familiar objects on the mantel-
shelves of our seafaring men's homes. Un-
doubtedly Scyilarus is the most beautifully
coloured of our large Crustaceans.
The number and arrangement of the limbs are the same as
in the Lobster, but unlike the latter animal, all the five pairs of
ambulatory limbs are formed on the same pattern — each terminating
in a short sharp claw — none pincer-like as in the Lobster.

A very different creature issues from the egg. Instead of a
short legged, stout body, an elegant glassy-transparent and colour-
less, leaf-like organism appears, delicate, fragile, with four enormously
long, six-jointed limbs, freely armed with spines. And two of these
spider-like limbs give off branches ending in delicately plumose hairs.
Further and minute examination shows the body to consist of
three distinct divisions — a broadly oval flattened head, larger in size
than the remainder of the body ; a thorax, rounded and likewise
flattened leaf-like, and of about half the size only of the head ; lastly
the abdomen, least developed of the three parts, narrow, elongated,
and without appendages.

HEAD : From the anterior margin of the head spring two pairs
of simple antenna?, the posterior extremely small, only some fifth the
length of the anterior ones. Between these lie two great facetted
eyes, borne on long stout peduncles ; while in the median line just
between the bases of the eyestalks, is a tiny X shaped mass of dark

SCYLLAEUS AllCTUS.

40 MICROSCOPICAL STUDIES.

pigment representing the unpaired simple eye, of the same structure
as that of the Squilla larva*.

The mouth is situated on the under side of the head, midway
between the front and hinder edges, and is surrounded by an upper
-lip or labium (PI. vi, Fig. 2), two stout mandibles, and two pairs of
maxillae, the first large, with two appendages — and working inwards
in the same plane as the mandibles ; the second pair, on the contrary,
are small and rudimentary and appear not to function.

Of the maxillipeds — the first pair is non-existent, showing not
the slighest trace : a very peculiar fact and characteristic of Scyllarus,
distinguishing from the youngest Phyllosome ofPalinurus where this
appendage is just visible as a tiny cylindrical process.* The second
however, though slender, can be easily resolved into six joints, while
the third is more than thrice this length and proportionately stouter.
Behind this are three enormously elongated spider-like limbs, the
.true ambulatory legs or pereiopods ; each is six jointed — the terminal
one claw-shaped and reminding one sharply of the similar appearance
of this joint in the adult. The first and second ambulatory limbs are
biramous, for there springs from the further end of the second joint
in each, a paddle-functioning jointed and plumose appendage which
represents the exopodite. The third is unbranched, but a knobbed
projection on the second joint indicates where the exopodite is about
to sprout forth. In older larvae the third maxilliped also develops a
plumose branch. Four pairs of limbs, — the third maxillipeds, and the
six pereiopods are the only appendages of the thorax at this stage,
but as age advances and repeated moults take place other pereiopods
appear at the point between the base of the abdomen and the third
pereiopod ; these in turn assuming the biramous character of the
first formed.

* In this statement I give the accepted view (Dohrn, Zeitschr. fur iviss. Zool.
1870). My own examination of the young larvae, points rather to the missing
appendage being the second maxilla and not the first maxilliped. Undoubtedly
one or other is missing, for between the first maxilla and the second maxilliped,
there is but one organ, and the reason why I think this to be the first maxilliped is
that the somite it belongs to, is clearly defined and shows no trace of having another
somite between it and the equally well defined somite bearing the second maxilliped
(see Fig. 2). On the other hand, the region in front of the somite bearing this
uncertain appendage, and between the latter and the first maxilla, is extensive, and
bears no appendage. The shape too, of the uncertain limb, is in favour of my view ;
it consists of a stout, rather fusiform basal joint, bearing a tiny terminal joint from
which spring four long and highly plumose hairs. Now in the Phyllosome of
Palinurus which possesses both second maxillae and first maxillipeds, Cunningham
(Journ. Mar. Biol. Assn., New Ser., Vol. II, No. 2, p. 147) describes the former as
rather large and foliaceous and gives the figure of a distinctly biramous limb ; while
the latter he speaks of as being each a simple, small but distinct conical stump,
a description much more fitting the organ in the Scyllarus larva, than that of
the second maxilla, for it is in nowise foliaceous, nor yet biramous. Not having
examined the embryo nor yet any advanced Phyllosomes of Scyllarus, I cannot
however give my view as more than an opinion.

LARVAL CRUSTACEANS. 41

The third part of the body, the abdomen, is trivial and shows no
signs of the importance it will attain to in the adult condition. No
limbs are present, not even a caudal fin — the intestine can however
be traced, traversing the entire length, and opening by the anus at
the extreme end. A few very faint transverse markings can be made
out, indicating the limits of future somites.

Now what is the significance of this most peculiar larval form ?-

Only Scyllarus and Palinurus among the Decapods possess it.
Of the others, the vast majority, especially the solid phalanx of the
Crabs, leave the egg in a totally different condition, viz.. in the Zoe'a
form, i.e., with head and abdomen well developed but without thorax
and abdominal limbs. On the other hand the larvae of the Lobster are
never so primitive. Thorax and thoracic limbs are present from the
first though abdominal limbs are at first absent. A few others have
still further abbreviated metamorphosis, e.g., the Fresh-water Crayfish
is hatched practically in adult form, while conversely a few prawns
(Peneus) leave the egg in "the curiously primitive Nauplius con-
dition that characterises specially the Entomostracans and Cirripedes
and pass through numerous other stages ere reaching the adult.

To either of the last two, Phyllosoma bears no relation, and
analysing the other couple, it is at once seen that the Zoe'a form is
also inadmissable. This one has no . thorax developed, while in
Phyllosoma such is of great importance. We are thus left with the
Lobster larva (early stage), a form at first sight nowise resembling a
Phyllosome. But stay ; both show distinct head, thorax and abdomen ;

ADVANCED LARVA OF THE LOBSTER.

in both, limbs are developed on the first two divisions, and both are
without appendages on the abdomen. All parts bear comparison in
the two forms, and the differences which, first sight, appeared so
great as to forbid thought of any probable fundamental similarity
until arrived at by analysis, are after all but comparatively trivial
differences of proportion. But if the larval forms of the Palinurida3
be so closely akin in fundamental structure (homology) to those of
the Lobsters (Homarus) how did the present striking divergence in
the form of the respective regions arise ? The answer must be
sought in the different habits of these animals during the larval life.
And the chief determining habit centres in the different mode of

42 MICROSCOPICAL STUDIES.

progression .adopted by the two. The Lobster larva moves largely
by a jerky movement or flapping, produced by the muscular con-
traction of the powerful abdomen : the Phyllosome on the other hand
swims entirely by the paddling action of the thoracic legs. In the
one case, the animal chooses a mode of progression requiring a well
developed and muscular abdomen — in the other, Phyllosoma elects a
method that dispenses with the need for such a strong tail, hence the
non-development of that during such period when indeed it would be
an encumbrance arid a danger. Then as to the change in form of
the rest of the body — such is probably the outcome of the greater
pelagic habit of the Phyllosome. The latter has a much longer
surface-swimming larval life (so far as my observations go) than
larval lobsters, hence the necessity for a greater or more perfect,
defensive transparency. Such, obviously, can be better attained in
a thin flattened body, than in a thick muscular one.

Surely this study of individual development is without superior
in fascinating interest among Zoological problems — its interest, too,
enhanced by the great light it sheds upon the past development of
the race. But while its importance in this sense is so great, let us
beware of blind acceptance of that present day biological shibboleth
" Ontogeny recapitulates Phylogeny," meaning that the history of
the development of the individual sums up and points out the
various stages passed through by the particular race in the course
of its evolution. Such a theory I doubt not is useful to work by,
but it must have intelligent and reasoning and ultra-careful hand-
ling, or further false pages will be added to the already too many
that have of late years been inserted in our scientific journals by
hasty and theory-ridden writers. The harm done in this way is
incalculable and unfortunately difficult to cope with or to stem.
Every such wildly reasoned generalization or inference is a false
finger post upon the scientific highway. Therefore let us beware of
setting up even one more.

EXPLANATION OF FIGS. 1 AND 2, PLATE VI.

The Phyllosoma larva of Scyllarus.

Fig. 1. Early Phyllosome larva seen from the dorsal surface ; actual
length (tip of rostrum to end of abdomen) 1*5 mm. ;
e. paired compound eyes ; e. unpaired simple eye ; c. head ;
ill. thorax ; db. abdomen ; I. anterior antennas ; II. pos-
terior antennae ; III. mandibles ; IV & V. 1st and 2nd
maxillae ; VII & VIII. 2nd and 3rd maxillipeds ; IX, X
& XI. 1st, 2nd, and 3rd ambulatory limbs ; XIII. 4th
ambulatory limb beginning to sprout ; exp. exopodite ;
g. rudiment of green gland ; I. largely lobed liver.

THE FLOWERS OF THE SEA. 43

Fig. 2. Enlarged view of mouth organs ; lab. labium ; mand. man-
dibles ; 1 max. & 2 max. 1st and 2nd maxillae ; 2a, stout
limb of mandible ; 26, a 1st maxilla — both further
enlarged.

STUDY IX. THE STRUCTURE OF ANEMONES.

Ever since that comparatively recent period little more than a
century ago, when, for the first time, men's eyes were opened to the
beauties of the smaller marine creatures, the sea-anemones have held
perhaps the foremost place of honour in this artistic appreciation.
Their very name — the implied resemblance to the gorgeous scarlet-
rayed, black disc'd anemones that give such wealth of colour to our
old-fashioned gardens — suggests this thought. And our German
cousins vie in doing similar honour, a higher one if possible, by
calling them after the queen of flowers, for they name them Sea-roses
(Seeros'en). Even the learned and usually strictly practical framers
of our scientific nomenclature have experienced the same spell, for is
not Anthozoa — one of the terms applied to the Anemone group —
merely the Greek rendering of " Flower-animals " ? Few marine
animals are nowadays better known. Everyone who has started
even the smallest of small aquaria — if only in the form of a big
pickle-jar or an earthenware pan — has begun by stocking with some
common species of anemone ; mayhap the brownish-red Beadlet
(Actinia) with its necklace of lovely blue beads ; or perhaps the
stout fleshy Tealia, with body covered with strange warts, each
holding firmly some fragment of shell or pebble ; or yet again, he
may have started with the medusa-locked Anemonia sulcata
(Anthea cereus). Their hardiness, as well as their beauty, conduces
to this popularity.

If we take any typical anemone, we find it to be of extremely
primitive structure. Usually the body consists of a short, stout,
hollow cylinder (column), attached at the base to some rock or
boulder, by a sucker-like pedal disc, often spoken of as the foot.
The opposite or free end, the peristome or mouth disc, bears the
mouth, slit-like in shape, and surrounded by several concentric rows
of hollow, finger-like tentacles, the older towards the centre. At the
point where the peristome merges into the column, is a distinct
ridge, the margin (PI. vii. Fig. 3, m.)

No anus is present. The mouth, o, leads into a short oesophagus
or stomodseum (s£), not continuous with a stomach and intestine as
in the higher and more familiar animals, but ending in a free,
pendant margin, opening direct into the great body cavity, the
coelenteric space. The fundamental form of this simple alimentary

44 MICROSCOPICAL STUDIES.

arrangement can be at once understood if we take a hollow india-
rubber ball, cut a small slit at one end, and then push the edges of
the slit well down into the interior of the ball ; the short tube
thus formed will represent the stomodseum.

Each of the two angles that bound the extremities of the mouth
slit are continued downwards along the oesophagus as a deep, richly
ciliated groove — the siphonoglyph. Most anemones have two of
these grooves but some (Peachia, Cerianthus) have but one.

The siphonoglyphs remain open, even when the animal is
greatly contracted, and they appear to be useful in keeping up a
constant flow of water through the. oesophagus.

Numerous vertical partitions, ingrowths of the body wall — the
mesenteries — join the hanging cesophageal tube to the outer wall
of the body, and serve to break up the great body-cavity into a
number of radial longitudinal chambers ; an arrangement clearly
shown in Fig. 1, representing a transverse section through the upper
part of an anemone. The section of the oesophagus appears as a
small inner circle, connected to the large outer circle of the body
wall by twelve radial lines, the sections of the mesenteries. But in
the lower part of the Anemone's body — below the level of the
oesophagus, the mesenteries form incomplete partitions, and show
as in Fig. 2, as though a cart wheel had had the hub broken out
leaving the rim with the broken spokes projecting inwards. The
free edge of each mesentery is swelled out distinctly into three
longitudinal lobes, the middle one crowded with nematocysts and
gland cells, the lateral ones clothed with strong cilia.

The mesenteries are arranged in pairs. Some reach across
to the oesophagus — the primary ; others fall a little short of it —
the secondary, and yet others may be still shorter — the tertiary.
Of these the primary are the first to appear. The secondary appear
next in succession, in pairs between every two pairs of primary. In
Fig. 2, four pairs only of secondary mesenteries (2 m) are present^
while the full complement of primary, six pairs, is obvious. Each
mesentery has a very pronounced longitudinal ridge on one face
running from peristome to base (Im), and except in two pairs, the
ridges in each pair face one another. The two exceptional pairs are
on opposite sides of the oesophagus. In them, the ridges, in the
members of each pair, face outwards, and the presence of these
directive mesenteries (dm) serves to divide the animal into a right
and a left half, and in certain cases, even into a dorsal and a ventral
division. When two siphonoglyphes are present, each gives attach-
ment to the inner margins of one of these two pairs of special septa.

The chamber enclosed by the members of each pair of mesen-
teries is the intraseptal (im) ; that between the outer members of

HOW ANEMONES FEED. 45

adjacent pairs, the interseptal (is). Some slight direct communi-
cation with the exterior, is usually provided for these chambers, by
a pore (tp) at the tip of each tentacle, which are simply hollow
outgrowths of the peristome. Intercommunication is also allowed by
the presence of one, sometimes of two pores piercing the mesenteric
walls just beneath the peristome (ip and op).

Examining a transverse section with the microscope, we can
resolve the wall of the body and of the oesophagus (a mere down
growth of the mouth disc), into three well differentiated layers. The
most obvious is the middle one — mesoglaea or supporting lamina —
consisting of a thick layer of a clear, fibrillated tissue, approaching
somewhat the texture of tendon, denoted in Figs. 1 and 2 by black
bands and lines. Outer to this is the ectoderm or epidermal layer,
containing in certain regions, glands and stinging cells or nematocysts.
This is the seat of what poorly developed nerve elements there are
in these animals.

On the inner side of the mesogla3a, is the thin but important
layer of the endoderm, lining the entire body cavity in all its
chambers with a coating of ciliated cells, which give off strong
muscle fibres on the side in contact with the mesoglaea. The
principal functions of the endoderm are those of digestion and
the provision of muscular movement.

Most anemones have great powers of contraction, being able in
many cases to reduce their bulk to less than one-seventh of that
when fully expanded. The principal muscles employed are strong
longitudinal ones running in the ridged surface of each mesentery.
The supporting lamina is much folded at this point, forming in
section, a beautiful arborescent pattern, and along these multiplied
faces run from base to peristome, great numbers of muscle fibres,
whose duty it is to pull down the tentacles and mouth-disc, and so
shorten and retract the animal. On the other face of the mesen-
teries the muscle fibres run transversely ; so that we may describe
the disposition of the mesenteric muscles as usually longitudinal on the
intraseptal surface, and as transverse on the interseptal. The latter
towards the base of each mesentery alter their course so as to run
obliquely from the wall downwards to the base — the parieto-basilar
muscle (pbm). In the walls, the peristome, the oesophagus, and
usually also in the base, the muscular processes of the endoderm cells
are arranged in a circular direction.

No animal is more ravenous. Crabs, molluscs, and small fishes
wandering incautiously close, are entwined and pulled inwards by the
long tentacles, the while that cruel stinging cells are conveying into
the poor quivering body, a poisonous, numbing juice through innu-
merable thread-like barbs. Still struggling, the prey is passed

46 MICROSCOPICAL STUDIES.

into the oesophagus and thence downwards. At this stage, ner-
vous excitement brings about a remarkable occurrence. The free
edges of the mesenteries close together and form an improvised
stomach by the approximation of the lateral lobes. If death has not
yet occurred, the powerful stinging-cells that load the central ridge
of the mesenterial filaments complete the work, while the associated
gland cells provide digestive fluid in plenty. It is surprising how
powerful and rapid this is in action. A few hours, three to four,
secure the complete digestion of a fish or a crab nearly as large as
the anemone itself. As the prey dissolves, this nutrient fluid is
permitted to leave the improvised stomach, and flows freely into the
various septal chambers, even too, into the tentacles ; the cells in
contact taking up what quantity they can. Any hard undigested
parts are ejected by the mouth.

The sexes are usually separate. Both ova and sperm arise from
similarly placed glands lying a little way from the free edges of the
mesenteries (Figs. 2 and 3, gg and ov ). Many species are viviparous,
the young undergoing their early development within the septal
chambers, and only when their tentacles are just long enough arid
sufficiently provided with sting cells to capture prey, are they cast
out from the mother, by way of the mouth. Often have I obtained
these baby anemones by gently squeezing the parent's body, when,
one by one, minatures of the parent popped out through the mouth.
The Gem (Bunodes) ; the Beadlet (Actinia) ; and the Sand-
Anemone (Sagartia bellis) are examples in point.

Classification. The anemones belong to the phylum Coelen-
terata, consequent upon having no definite tubular alimentary canal,
the mouth and oesophagus leading into a great bag-like cavity
without anal aperture. No cavities are developed within the walls of
the body ; neither is a ganglionic chain present, only an irregular
loose network of ganglia and nerves.

The Coelenterata are subdivided into two classes ; a simpler,
without oesophagus or mesenteries — the Hydrozoa ; a more complex,
with well marked oesophagus, and numerous mesenteries — the
Anthozoa or Actinozoa, and it is to this latter division that the
animals we are now dealing with belong, and here I must remark,
that I am using the term Sea-anemone, in a wide sense, as equivalent
to the whole of the Anthozoa.

Within the bounds of this class, many very divergent forms are
found. These are ranged in two sub-classes : —

I. The Hexactinia or Zoantharia and
II. The Octactinia or Alcyonaria.

The first contains the true Anemones, most generally simple, rarely
colonial in habit, and which have their mesenteries in pairs in mul-

A BURROWING ANEMONE. 47

tiples of six, and with usually two siphonoglyphs. The Octactinia
on the contrary, are all but entirely colonial, growing usually in
masses of many hundreds of associated individuals ; the mesenteries
are some multiple of eight ; only one siphonoglyph is present, and
the longitudinal muscle ridges of all the mesenteries face towards it
(Fig, 5). For convenience, -I shall call these the colonial anemones,
in contrast to the true or simple ones.

Let us now examine briefly the special points about the types
chosen in our plates to illustrate the characteristic features of these
two divisions.

SipJionactinia (PeacJiia) triphytta (Gosse), which we use as
type of the true anemones, is in many ways remarkable. Its body
is cylindrical, tapering to the base, which unlike that of other
anemones, is not broadened into a flat attachment disc but is nar-
rowed to a blunt point, and still more remarkable, is perforated by
a small opening. Around the mouth are set twelve stout swollen
tentacles, beautifully marked with dashes and lines of chocolate as is
too, in rather more irregular manner, the whole surface of the body,
on a ground tint of very pale pinkish brown. A stranger to the
strange convergence of outward form wrought upon animals of dif-
ferent groups by similarity in environment and in habits, would
never guess the true relationship of these animals living in the shell-
sand gravel that here and there accumulates in patches along the
shores of the Channel Islands ; he would surely presume them to be
some queer coloured sea-cucumber — some Holothurian not figured
by Forbes.

In habit Siphonactinia burrows down several inches into the
sand when the tide goes down, cautiously ascending and spreading
its tentacles level with the surface as the sea returns.

Fig. 1 shows what is seen in a transverse section close under the
mouth disc. Notice the single siphonoglyph (si) giving attachment
to the ventral pair of directive mesenteries. The mesoglaea forms
the central layer in all the threefold walls and mesenteries of the
body. In the section from which this is drawn, the mesoglaea has
absorbed most of the stain used and has become very conspicuous by
reason of its bright crimson and glassy appearance. Fig. 2 represents
a section below the level of the oasophagus, and shows the swollen
free edges or craspeda of the primary mesenteries, as well as a
swollen region (gg) — the ovary — some distance from the edge.

Few anemones arc so useful to use for a due understanding of the
general anatomy of the class, and the pity is, that this species is becom-
ing extremely rare. The trouble connected with the commoner species,

48 MICROSCOPICAL STUDIES.

is that they all combine in the possession of so many and so well
developed subsidiary mesenteries that in section the apparent com-
plication becomes bewildering and confusing beyond measure to the
student to understand, to the teacher to explain.

The representative used to illustrate the second sub-class, is the
common Alcyonium, a colony of polyps cemented together by a
gelatinous or semi-cartilaginous matrix strengthened by calcareous
spicules. On some parts of our coasts it is plentiful, forming when
living and with tentacles fully expanded, an exquisite feathery mass
of life — strangely contrasting with the woeful, gruesome appearance
it takes on when dead, and battered, and cast up, a sea-waif, upon
the beach. Fishermen give it all sorts of names expressive of their
loathing, " Deadman's fingers," " Deadman's toes," " Cow's paps," and
the like.

The colony is formed of tiny, anemone-like polyps, — each with a
row of eight pinnate tentacles, — united together by a wonderful develop-
ment of the mesoglaea ; indeed a distinctive name is now applied to
this tissue — coenosarc — and it adds a great defensive device against
predatory enemies, by the development within its substance of
curiously warted spicules of carbonate of lime. And these tiny flesh-
spines are not only found in the connecting matrix, but even in the
thin layer of mesoglaea of the oesophagus are some smaller ones.

Note the different number and arrangement of the mesenteries.
Instead of being in pairs, they occur in two series, a right and a left,
and the muscular swellings face downwards (towards the siphonoglyph)
in each series. Fig. 6 shows a section cut low down in the stalk of
the colony, a region equivalent to that of Siphonactinia shown in
Fig. 2 ; here the mesenteries are reduced to low folds or ridges.

Reproduction is rather different ; the ova and sperm masses are
not produced in special glands in the substance of the mesenteries,
but arise singly in bud-like fashion on the edge of the mesenteric
ridges (ov' and ov).

Besides Alcyonium, there are several other and diverse repre-
sentatives of this class found on our shores. There is the lovely,
light-emitting Sea-Pen (Pennatula) ; the equally curious if less
elegant Virgularia, and the grand Sea-Fan or rather Sea-Bush,
Gorgonia verrucosa. The organ -pipe Coral (Tubularia) and the
true red Coral (CoraMium rubrum) are also members — their ul-
timate structure being identical with that of Alcyonium as described
and figured, and differing almost solely in the method of spicule
arrangement : in the one, loosely scattered ; in the other, densely
packed and soldered intimately together.

49

EXPLANATION OF PLATE VII.

Structure of Anthozoa.

Fig. 1. Trans, sec. of Siphonactinia triphylla, through region of

oesophagus, i.e., cut along the line indicated by the letters

A— B in Fig. 3. X 3J.
Fig. 2. Trans, sec. of same, at a lower level, i.e., along line indicated

by C— D in Fig. 3. X 3J.
Fig. 3. Diagram of anemone structure, shown by a vertical section

along the plane indicated by letters A — B in Fig. 1.

A mesentery is cut through longitudinally on the left

side ; on the other, the section passes through an inter-

septal space.
Fig. 4. 8. tripliylla, actual size.

Fig. 5. Surface section through a colony of Alcyonium digitatum,
the polyps retracted wholly. For the sake of clearness,
the tentacles which are retracted within the oesophagus,
are omitted from the section. D, dorsal region ; V, ven-
tral region. X 9.

Fig. 6. Trans, sec. thro' portion of stalk of a colony of A.palmatum.

Lettering : — cce, coenosarc ; cr, mesenterial filament or craspedon ;
dm, dorsal directive mesenteries ; dm, ventral ditto ; e, ectoderm of
body walls ; e, ectoderm of oesophagus ; en, endoderm ; gg, genital
gland ; im, intraseptal chamber ; is, interseptal chamber ; ip, inner
pore ; Im, longitudinal muscle band ; m, margin ; 2 m, secondary
mesenteries ; o, mouth ; op, outer pore ; ov, ovary ; ov', loose ovum ;
pbm, parieto-basilar muscle ; pm, primary mesenteries ; pr, peristome ;
rm, radial or transverse muscle fibres ; si, siphonoglyph ; sm, sphincter
muscle ; sp, spicules ; st, stomodseum or oesophagus : t, tentacle ;
tp, tentacle pore.

50 MICROSCOPICAL STUDIES.

X. DUPLICATION AND ORIGIN OF THE OPERCULUM IN SERPULA.

It is of frequent observation that certain animals are charac-
terised by more or less mutability, either as entire organisms or else
in some particular organ. Such mutable species are, however, greatly
in the minority — the vast majority being so remarkably stable in all
save trivial degrees, as really to be cause for wonderment, considering
the diversity of environment that most species must encounter in
life's struggle. Accordingly the forms exhibiting marked mutability,
are of the greater interest. These variations fall naturally into three
categories ; a, where the mutation is due to an atavistic cause, i.e.,
recalling some phase in the past history of the race to which the
animal belongs ; b, where it is spontaneous or original, and usually
limited either to one individual or to a few nearly related ones — a
variation often pathological ; lastly, c, where the change is due
directly to altered environment and altered habits — a change which
will probably become fixed, and therefore producing a distinct and
permanent variety — liable to become sufficiently stable to constitute
finally a new species.

The following instances fall, I believe, to be explained by the
first of these causes : —

I. Serpula.* Having recently occasion to examine a large
number of that most beautiful Serpulid, 8. (Hydroides) pectinata,
Philippi, to my surprise, I found 25 % of the examples — which be it
noted were not all from the same cluster of tubes or vermidom, but
from several — affected in more or less degree with abnormality in the
antenna.-f- The proportion was very constant ; out of two large
batches, the variation was not more than 1'6% viz., 8 abnormal out
of 32, and 14 out of 60. Others I have examined since, have shown
a like proportion.

In the present note, the two antennae are distinguished for con-
venience under the terms respectively of antenna and of operculum ;
the former term being applied to the process which, while homologous
to the long filament modified to form an operculum, is normal short

* For those unacquainted with the Serpulinse, I may here explain that they are
those tube-building worms, whose sinuous limy tubes are frequently seen upon old
and sea-worn shells— oysters, scallops and the like. Attached to the head in these
animals, are two half circlets of delicate bipinnate plumes, useful as breathing (gills)
and touch organs, while close to the first gill-filament on either side on the dorsal
aspect is a non-pinnate organ — on one side, long stalked and stopper-like, the oper-
culum ; on the other, short and weak and nearly aborted. Serpulids have the power
of withdrawing entirely within their tubes, and of stopping the entrance with the
plug-like operculum.

t I adopt here Quatrefages' nomenclature, viz., call the appendages that belong
to the prostomium, antennae ; and reserve the term tentacles for the appendages
of the peristomium. (Peristomium:^ mouth somite; prostomium — region anterior
to such).

A STUDY IN VARIATION. 51

and slender. Neither the right, nor the left antenna is permanently
responsible for the furnishing of the opercular stopper, for out of
92 specimens examined, in 50 cases the right antenna — i.e. that one
belonging to the right branchial fan — performed the opercular duty,
having the stalk elongated and the extremity swollen into the usual
opercular plug. In the remainder, viz. in 42, the left antenna was
become the functional operculum.

This fact that in practically equal number of cases, the operculum
is developed indifferently from either the right or the left antenna,
is obviously of extreme importance in any attempt to trace the story
of its origin and subsequent history. Before making this attempt, ,
we will proceed to notice the more important of the aberrant forms of
antenna and contrast them with the normal form, and with its
homologue, the functional operculum.

The Operculum : — The normal form is doubly infundibuliform,
fairly well figured by Johnston (1) for his Serpula reversa, which
I am convinced is the same species as the present.* The upper cup
is beset with 12 to 17 bipinnate spinous processes, while the lower
has a multiserrulate margin, the serrations being continued as grooves
for some distance downwards on the inside as well as on the outside
(PI. v, Fig. 11).

The form is subject to not inconsiderable variation within certain
limits. Thus the larger specimens count more pinnate process than
the smaller, and the relative proportions of the two cups are
inconstant.

One case was however very remarkable, for the lower cup was
absent, and represented solely by a large elongated swelling as shown
in Fig. 14, while the processes which represented the pinnate spines
of the normal upper cup, were merely rather deep crenulations with
smooth margins. Fig. 12 and 13 show7 intermediate stages in this
variation, showing in Fig. 12 a great swelling of the lower cup and
a decrease in size in the pinnate processes above, while in Fig. 13,
these spines are still further reduced and all trace of the crenulated
margin of the lower cup lost. In this case also, the part representing
the lower cup is much swollen. Figs. 12, 13, and 14 are therefore
perfect gradational steps in the retrogression in shape of a normal
operculum (Fig. 11).

The Antenna : — The normal form is i to | the length of the
operculum. The average length of those of adult specimens of

* The only differences I can trace are that S. reversa is solitary and has more
branchiae and more lateral teeth on the spinous processes of the opercular cup ;
S. pectinata occurring in colonies and being on the average smaller than S. reversa.
But I have traced all intermediate grades, so that the differences are not great
enough to constitute more than a variety. Fig. 15 shows typical form of operculum
of S. reversa.

52 MICROSCOPICAL STUDIES.

15mm. long is -75mm. The apex is swollen into a somewhat conical
bulbous form, and beneath this is a narrow constriction, followed by
another slight swelling, which passes gently into a short cylindrical
stalk (Fig. 1).

Of abnormal antennae, there was a perfect series grading from
the normal form as described, to one that could scarcely be distin-
guished either in size or shape from that of a perfectly formed
normal operculum. These gradations are outlined in Figs. 2 to 10.
Fig. 2 represents a form common to several specimens. In it the
equator of the terminal swelling is scored by shallow vertical grooves.
The next stage (Fig. 3) is where the equator besides being grooved,
is slightly raised into a serrulate and grooved rim. In Fig. 4, is a
form where this is accentuated, while the constriction beneath the
terminal swelling is much more emphatic. Another specimen had
,the antenna (Fig. 5) one-third the length of the operculum, the
terminal knob being modified into a miniature of a true opercular
upper cup, and hiding entirely — for the first time in the series —
the conical apex of the organ.

In all these instances, the lower swelling was nearly normal.
Following on Fig. 5, we have a form such as Fig. 6, where, with
as well developed an upper cup as in the preceding, the lower has also
started to develop, taking the form of an obscurely serrated collar
at the base of the upper cup.

Finally in Figs. 7, 8, 9 and 10 we have a number of cases where
both cups are well developed, and closely approach the form of the
normal operculum. Keeping pace with this series of gradations in
development, was the growth in length of the stalk of the pseudo-
operculum. That shown in Fig. 2 was rather stouter, but not
much longer, than the normal form of antenna, 4 was rather longer,
5 was one-third the length of the operculum, while the remainder
varied from one-half to all but equal length with the same organ.

The forms shown in Figs. 2,7, 8, 9 and 10 — those at the begin-
ning and the end of the series — were the most common.

Summing up the foregoing facts we find that : —
a. The operculum is developed on either the right or the left

antenna inconstantly.
br The non-opercular antenna is normally cirrus-like with two slight

swellings towards the further end.

c. The same organ in 25% of instances is abnormal, showing all
manner of degree of approximation to the form and size of
the functional operculum.

Before considering further the meaning attaching to the varia-
tions as above set forth, let me enumerate the principal points

EVOLUTION OF OPERCULUM IN SERPULA. 53

already known concerning the homologies of the branchiae and the
operculum in Serpulids and their near neighbours, the Sabellids.

A. Firstly, from an examination of the nerve supply to these
organs, Quatrefages (2) found " that in the Sabellinae as in the
Serpulinse, the branchial nerves arise directly from the cerebral
ganglia as antennary nerves " (i.e. in the position which such nerves
have in such forms as Nereis) " and among the Serpulids a^slemier
branch springs, on each side, from the principal trunk and leads to
the base of the two opercula, as well to the rudimentary one, as to the
one completely developed. The branchiae and the opercula therefore
correspond to antennae." Pruvot (3) further shows that the antennas
modified into gills in Serpula, are the second pair, those large
organs that in Nereis, Polynoe, &c., are known as palpi.

B. Embryology shows that very early there appear (Sabella)
two ciliated wing-like processes on the dorsal aspect, which shortly
after divide each into two slender lobes which constitute the first
four branchial rays, their number augmenting rapidly by budding
on the ventral side (4).

C. Next examining the near relatives of Serpula, we find in
Sabella no opercula, but in place, there are two slender, simple dorsal
processes occupying the same relative position and having the same
innervation or nerve-supply as the opercula of Serpulids — whence we
may justly infer that they had similar origin.

In some Sabellids (Othonia) these simple antennae are wanting,
as is the case too with a number of the Serpulids. Thus Apomatus
and Filigrana possess only branchiae and to make amends for want
of a true operculum as in the more typical species, in these the
summit of one or more of branchiae — which are of the usual bipinnate
style — is enlarged in a bulbous manner into a pseud-operculum.

D. Finally Fritz Mliller (5) has described a Serpulid which
when first observed had but three pairs of pinnate gill-filaments, but
which in a few days time, he found had developed a clavate oper-
culum at the extremity of one of the filaments. In the course of
three days more a new pair of branchial filaments had sprouted forth
and the opercular peduncle had lost its lateral filaments.

So much for collateral evidence. Now let us see if we can
gather the threads together, and make a web of fairly good strength.

From the frequent assumption of opercular shape by the or-
dinarily non-functioning and simple antenna in Serpula, and from
its inconstancy to one particular side, we may justly infer that this
variation is atavistic, and therefore that at one time, Serpula pos-
sessed two functional opercula. Then, from the corresponding
relative position of the organs, we have already inferred that the

54 MICROSCOPICAL STUDIES.

opercular processes of Serpula are identical with the simple antennae
of Sabella.

Now in the latter animal, we have evidence (B, ut sup.) that in
the course of development, the branchial filaments are at first simple
and antenna-like, so as we know by A that the branchiae and the
antennae are in reality homologous — having the same innervation —
we may conclude that the antennce in Sabella are the unaltered
first dorsal pair of organs that result from the splitting of the
wing-like processes of the very young larva, while the other two
lobes of this winged organ and the others that arise by budding on
the ventral side, become bipinnate and function as gills.

Now in Serpula} I believe the course of evolution was probably
as follows : — First came a Sabella-like stage with simple antennae,
but probably these were larger proportionately than those now seen
in this animal. Next the ends of the antennae became swollen to act as
stoppers and to close the tube against intruders. Finally one aborted,
and being useless, was reduced to an insignificant filament, which
occasionally reverts to its former well developed condition. By this
explanation I avoid Fritz Mliller's supposition of a Filigrana and
Protula ancestry, and this seems to me advisable, as there appears
no record, save Miiller's own very incomplete and vague observation,
of the opercular filament ever being pinnate, either in variation or in
larval development.

I incline to the belief that Filigrana, Protula, &c.3 had inde-
pendent evolution to Serpula ; probably by the development of all
the processes of larval " wings " into pinnate gills, and the subsequent
formation of false opercula on the summit of one or more of these.

REFERENCES :—

1. Johnston, Geo. —Gat. of Worms in Br. Mus., 1865,

p. 270, PI. xx, Fig. 6—7.

2. Qnatrefages, A. de.— Hist. Nat. des Anneles, 1865, Vol. ii,

p. 401, also PL iii.

3. Pruvot. — Archiv. de Zool. Experim. et Gen., 2nd

Series, t. iii, 1885.

4. Clans, C. —Traite de Zoologie, 1884, p. 601.

5. Mnller, Fritz. —Facts for Darwin, 1869, p. 113.

EXPLANATION OF PL. V, FIGS. 1 — 15.
Serpula pectinata.

Fig. 1. — Normal antenna ; Figs. 2 — 10. — Abnormal forms of the
antenna.

Journ. of Mar. Zool. and Microscopy

Jas. Hornell del ad Nat

JERSEY BIOL. STN.

ABNORMALITIES IN SERPULA AND IN SALPA.

THE MUSCLE BANDS OF SALPA. 55

Fig. 11. — Normal form of Operculum ; Figs. 12 — 14. — Abnormal

forms of same.
Fig. 15. — Operculum of 8. reversa. Note : — All the figures are

drawn to the same scale.

III. ABNORMALITIES IN THE MUSCULAR BANDS OF

Of over 200 specimens of larval Salpa mucronata-demoeratica
(solitary form) that I recently examined one by one, only some three
shown any marked sign of abnormality. Of these, two are figured
PI. v, Figs. A, B, and C. The first two figures, A and B, represent the
two lateral views of the same animal ; C, the dorsal view of another.

In every respect saving in that of muscle arrangement these
individuals were quite normal, but C showed a blending of bands iii
and iv for a short distance, as shown, and this case is of comparatively
little importance. The other example, figured in C and D, is a
much more curious instance, and is of high value to the student of
variation. Therein all the muscle bands save the 1st and the 7th,
branch and anastomose in an extremely complicated manner — ren-
dered clear however, by reference to the drawings.

Without entangling ourselves in the rival theories as to the
primitive character or otherwise of the pelagic Tunicates, the
variation I now record can be used as one link in the chain of true
evidence that will some day be forged explanatory of Ascidian
descent. Probably the variation is atavistic, and if so, points directly
to a state when the musculature was not a nearly regular arrange-
ment of more or less encircling bands, but was continuously, or at
least irregularly, disposed over the whole body, perhaps much in
the manner now7 to be seen in the muscle arrangement of- Ascidia
mentula.

Gegenbauer (Comp. Anatomy, 1878, p. 395) from reasoning
based on other foundations, arrived at the same result, stating that
in the Thaliacea, " the hoop-like formation arises from the differen-
tiation of a primitively continuous muscular layer. Gaps arising in
this, became gradually larger until the breaking up of the layer into
separate hoops is brought about " ; — a statement that receives very
important direct confirmation from the instances of irregular banding
that I have figured.

I may add that the abnormal specimens, described in the
above note, as well as in the preceding one dealing with the Serpulid
operculum, are carefully preserved in the permanent collection of the
Jersey Marine Zoological Station.

56 MICROSCOPICAL STUDIES.

STUDY X. — TYPICAL ALCYONARIA.

The general characters of the central or typical form of these
colonial Anthozoa, have already been dealt with in outline in the
preceding note, and it therefore only remains to fill in some details.

Two species of Alcyonium are found comparatively plentiful in
European seas ; the one, A. digitatum, stout and massive, with few
or no branches ; the other, A. palmatum, slender, arborescent, and
with fewer, but larger polyps. Normally the colonies of both species
are found attached by an extended base, but instances are known
where A. digitatum occurs in free, ball-like masses.

The latter species is usually snowy white, but occasional pale
orange coloured varieties are found, the tint being due to the dif-
fusion of colour throughout the cellular tissue. A. palmatum on
the other hand, has very frequently a well marked variegated rosy
hue, extremely pretty and not affected at all by the extractive action
of alcohol. Curiously this is due to certain of the superficial spicules
containing iron oxide. The bright red tints of the fiery Pennatula
(Sea-pen) are due to a similar cause, and more important still, to
this is also due, the colour that gives commercial value and beauty
to red coral.

In many ways these spicules are of great interest. Their shape
and arrangement, in conjunction with the form of the colony, furnish
the principal guides to the classification of the group. In A. pal-
matum there are five principal forms : (a) those of ruddy hue and
the largest in size (TOO -in. long), are arranged in eight bundles at the
bases of the tentacles. The spicules in each of these bundles con-
verge from right and left, arid form a strong framework support for
the free extremity of the polyp. The shape of each spicule is that
of a stout bent rod, tapering abruptly to a rough point at either end ;
warted too, but much less prominently than any of the others to be
mentioned. The foregoing pass at the apex of each bundle into
those (b) that act as the supporting skeleton of the tentacles. Their
general shape is rather more irregular, they are colourless, shorter,
and the warting is much stronger. Size 5oo-in. (c) A dense irre-
gularly disposed layer crusting the general surface of the colony,
consists of small, strong-spiked straight rods .vSo-in. long. Most
peculiar forms are sometimes assumed, due to the great and irregular
development of the spines ; being sometimes broadly bilobed, some-
times even trifid. (e) In the interior of the colony, in the stiff
mesoglaea that divides and yet joins the different polyps, scattered
spicules, very slightly spined, and nearly straight, occur; while a
fifth form of spicule (d) occurs in the thick wall of the oesophagus.
These last are the smallest of any in the colony and barely measure
6^0 -in. long.

SPICULAR ORIGIN OF RED CORAL. 57

In Alcyonium digitatum, the spicules differ very charac-
teristically from all the preceding, in their much greater profusion,
in their greater massiveness, and in their peculiar shape. The rod-
like form, so closely adhered to in A. palmatum, is here nearly
obliterated, and the spicules are often irregularly branched, and all
the limbs beset by enormous wart-spines. (Fig. 3).

In the Organ-Pipe Coral (Tubipora) the spicules of the nrpsoglsea
surrounding each individual, become locked firmly together by
numerous minute serrations, and form perfect calcareous tubes. In
the Red Coral of commerce, (CoralUum rubrum), on the other
hand, a strong central stony axis is formed by an even more intimate
association of the spicules of the axis of the colony, due to an actual
cementing together of these tiny limy rods. In Tubipora the polyps
can retract within their protective tubes, but in the Red Coral
there is scarcely any provision for the retraction, for safety, of the
polyps.

As in the Anthozoa generally, so in Alcyonium the sexes are
separate ; indeed even the sexes of different colonies are distinct ;
the individuals in any one commonwealth are thus either all males,
or else all females. The ova and the sperm masses are borne on
little stalked capsules upon the free edges of the mesenteries, and
development takes place outside the parent. The embryos are free
swimming by means of a complete investment of lashing threads
or cilia ; a little while they sport thus amid the waves, and then
affix themselves to some rock, and by continued budding produce
extensive colonies.

Note the very large size of the hollow pinnate tentacles, and the
thickness of the walls of the oesophagus (st.) Below the latter, the
upper parts of the mesenteries are very apparent because of their
greatly convoluted and thickened margins (PL x, Fig. 1, m. /.) ; from
this point downwards, the mesenteries decrease rapidly in prominence,
and soon show us very slight ridges only. The two dorsal ones
are of greater length than any of the others, i.e., descending lower
down the gastric cavity, and whereas their thickened edges or
mesenterial filaments (craspeda) are composed of strongly ciliated
cells derived from the downgrowth of two lines of cells from the
lining of the oesophagus (ectoderm cells*), the thickened edges of the
remaining mesenteries are less ciliate and their cells are endodermal

* Ectoderm and endoderm are terms of extreme importance. The embryo very
early in its history consists of two layers of cells, an outer ectoderm and an inner
endoderm, between which develops quickly a third, the mesoderm. All succeeding
tissues owe origin to one or other of these, and roughly we may take it that
epidermal tissues have ectodermal origin ; the alimentary canal and its offshoots
being lined with endoderm, while muscle, connective tissue, &c., are of mesodermal
origin.

58 MICROSCOPICAL STUDIES.

in origin. By the combined action of the cilia of the two dorsal
mesenterial edges, an ascending current of water is kept in motion.

The gastric cavities of the zooids are sometimes very long,
extending downwards along the axis of the colony for several inches.
Those of adjoining zooids are put into communication by a network
of fine ramifying tubes, buds from whose walls produce the fresh
zooids of the commonwealth.

The group Alcyonaria is of some importance geologically. Thus
Syringopora of Palseozoic times was probably allied to the Organ-
Pipe Coral (Tubipora). The common fossil Favosites was also an
Alcyonarian, while Corallium has been found in the Jurassic rocks.

STUDY XI. — THE LIFE-CYCLE OF OBELIA GENICULATA.

A few weeks since, a friend in the North of England was good
enough to send me some living specimens of a Zoophyte not found in
Jersey waters. Confined in a comparatively small jar, the somewhat
unnatural conditions had apparently hastened the birth of the
developing reproductive buds, and these were swimming freely in
the water as so many rythmically pulsating salver-shaped jelly fishes
of the most wondrous transparency and delicacy of form. A circlet
of regular and rather short thread-like arms stood out from the
margin, while upon the disc could just be made out, with the aid of
a lens, two intersecting lines with a handle-like stalk pendant from
the point where these two lines crossed. And the tiniest pin's head
was not larger in size. Some were born before my eyes from ovate
sacs in the branch axils of the Hydroid parent.

Very generally the Hydrozoa, to which the subject of our
sketch belongs, present well-marked instances of that many phased
strange phenomenon, known familiarly as Alternation of Generation.
At one period living attached to rocks, or weeds, or shells, under
the form of tiny anemone-like animals, they often form by a con-
tinued process of budding, a shrub-like colony of many individuals.
This is termed the Hydroid Stage, from which arises by budding
and fission, free-swimming individuals or Medusae — the true sexual
stage. The sexes are separate, some producing ova, and some
spermatozoa. The resulting embryos — tiny things that progress by
rhythmic lashing of cilia — attach themselves after a short period of
activity to some fixed object and soon develop into tiny Hydra-like
creatures, to circle once more with absolute fidelity through the
strange alteration of stages gone through by innumerable multitudes
of progenitors.

Seldom are these two great Life-Phases at all equal in size-
importance. One is nearly always magnified at the expense of the

THE DIVISIONS OF THE HYDROZOA. 59

other. One usually sinks into insignificance, slurred over and fre-
quently even entirely suppressed. And according to which phase is
magnified, have we one of the principal points characteristic of one
or the other of the two sub-classes of the Hydrozoa. If the free-
swimming sexual or Medusid-stage be the chief life-form, and the
Hydroid be all but suppressed, then we have the division of the
Scyphomedusae — the Acelephse of some writers. Herein are in-
cluded all the large Jelly-fishes so familiar in summer time on our
coast, during warm weather, and moving at times in shoals of
immense numbers. The other division is that where the Hydroid-
stage is exaggerated and usually colonial, and where the Medusid or
swimming stage is tiny or even eliminated. Such constitute the
Hydromedusae which are further distinguished from the Scypho-
medusa3, in that the Medusae of the former have the edge of the bell
turned horizontally inwards forming a delicate veil, the velum,
partially closing the mouth of the bell. This character constitutes a
Craspedote Medusa, as contrasted with the Acraspedote form of the
Scyphomedusaa, where the velum is absent.

The Hydroid Zoophytes, or Hydroidea, constitute the central
order of the Hydromedusse, and possess the typical life-history. In
passing it is well to remember that besides the Hydroidea, there are
two other orders, viz., the Trachymedusaa and the Siphonophora, both
characterised by pelagic habit, and the fact that they never have a
fixed or stationary hydroid phase.

The Hydroidea show much variation in the form of their Hydroid
stage and in the completeness of their life-history. Obelia is
very typical of unabbreviated life-cycle, so is specially useful to
use as an introductory type for study. The colonial stage is
remarkably beautiful, its delicate zig-zag branches forming dense
miniature forests on the broad brown oar-weed. An old writer
speaking of a nearly related and not more beautiful species, says,
" Delicacy, transparency, and grace pervade the entire structure ; the
spirit of beauty has thrown itself into every curve and line : the eye
rests with full satisfaction on the little cups, so perfect in their form ;
and hardly less beautiful are the ringed and twisted pedicles that
support them."

The colony is protected in all its parts by a delicate transparent
horny substance — the perlsarc, and consists of a zig-zag stem, jointed
at each curve, and giving off on alternate sides, a short ringed pinna,
bearing aloft a tiny crystal cup (hydrotheca or calcycle), wherein
lodges an equally tiny polypite or hydranth (PL ix, Fig. 2, p.), armed
with a well-marked proboscis and numerous tentacles. To the polypite
is delegated the sole duty of capturing prey. The whole organism is
the truest, of commonwealths ; each polvpite captures not for its own

60 MICROSCOPICAL STUDIES.

sustenance only, but equally for the whole colony, for the base of the
body of each individual passes into a tubular prolongation, cCBnosarc,
continuous with a similar tubular tissue in the main stem. If one
polypite capture food, part of the products of digestion pass into the
tubular coenosarc, and is conveyed to neighbouring parts of the
colony for purposes of nutrition. And upon this unselfish mutual
help, depends the power of the colony to set free from the purely
nutritive (vegetative) function, certain individuals or zooids, charged
specially with the reproduction of the species. These specialized
zooids are developed in the axils of the branches and are elegant
elongated urns in shape, gonothecae (g), wherein the coenosarc breaks
up into granular bud-shaped masses that gradually evolve into
transparent delicate swimming-discs. Their gracefulness has to be
seen to be understood. One has to watch them as, so many streamer-
decked bells, they sink slowly through the water, of a sudden to
regain activity and pass upwards by a series of vigorous jerking
pulsations, to cease after a number of strokes and become inert,
slowly-sinking parachutes once more.

Medusae are generally bell-shaped, with the true edge turned hori-
zontally inwards to form the velum (Fig. 5, v.)> but in the form under
notice, the shape is nearly that of a flattened disc, and the velum in
consequence of this difference is all but absent. From the apparent
edge of tne disc proceed a number of tentacles beset with stinging
cells, while from the centre depends a tubular process, the manubrium
(m.), having the mouth at the free extremity and a slightly dilated
cavity, the atrium (a.), at the attached base. From the atrium proceed
four radial canals (re), while around the edge of the disc, just inside
the ring of tentacles, is a circumferential canal (c.c.), into which the
radial canals empty. All these cavities are lined with ciliated endo-
derm, which shows little divergence in form in the various regions.
The ectoderm forming the exterior coat of the Medusa exhibits much
more differentiation ; while on the upper surface it consists of flat-
tened cells, on the under it developes radially disposed muscle fibres,
and on the manubrium, longitudinally disposed ones. Between the
ectoderm of the upper surface of the disc, and the endoderm of the atrium
and radial canals, is the intermediate body layer, the mesoglsea. In
Obelia, it is thin, but in some species it is often enormously developed
as a thick jelly-like substance (Aurelia, Pelagia, &c.), that gives
cause to the popular name of the Medusae. The term umbrella (u.), is
bestowed upon this layer. The sub-umbrella (s.u.), another layer of the
same tissue, but quite thin in even the best developed instances, is
found between the endoderm and the lower surface of the animal.
A point sometimes overlooked is that the radial canals are joined
together by a horizontal layer of endoderm cells, so that where the

PI. IX.

JAS. HORNELL, DEL. AD NA1
JERSEY BIOL. STN.

THE LIFE-HISTORY OF OBELIA GENICULATA

PROBLEMATICAL SENSE-ORGANS. 61

umbrella and the sub-umbrella are not separated by an cndoderm-
lined space (atrium or canals), they are by a solid layer of endoderm
cells.

The tentacles are here solid, consisting of a single row of large
endoderm cells encased in a layer of small ectoderm ones, which
develop numerous stinging cells.

Eight so-called " otocysts " (ot.) are found on the inner sirfe-of the
bases of certain of the tentacles. Each consists of a sac containing
an otolith. The function has long been supposed to be auditory,
but Hurst (Nat. Sc., June, 1893) has with much plausibility argued
for their true use as organs designed to give warning of approach to
an unquiet, wave-disturbed region, in the turmoil of which their frail
anatomy might suffer. (The thick umbrella of some contains up to
95% to 98% of water !)

The sexes are separate. In Obelia, the genital glands (gg.) are
developed as four masses upon the radial canals, one for each midway
between manubrium and margin. The ova after fertilization become
ciliated embryos, which soon affix themselves and develop into
hydroid colonies.

It is painful to have to record that these tiny marvels of
Nature's excellence of workmanship, are sordidly greedy and vora-
cious. The power of the sting-cells has great paralysing action and
comparatively large animals are easily captured, and sucked into the
mouth. Fig. 6 shows how an Arrow-worm (Sagitta) had been
captured and partly doubled in two and so partially swallowed.
Copepods, notably Temcra, form another common food.

Obelia, save in the slight development of the velum of the
Medusa, and the form of the latter being rather that of a disc than
bell-shaped, is thoroughly typical of the form and development of
that division of the Hydroidea where the polypites are borne in
cups — the Calyptoblastic Hydroidea.

Endless and complicated modifications exist in other species,
and some of these I hope to illustrate and explain before long.

EXPLANATION OF PLATE IX.
Life-History of Obelia geniculata.

Fig. 1. Natural appearance of the fronds of the Hydroid-stage, as
they grow upon the surface of Laminaria. Life size.

Fig. 2. A single frond of the same much enlarged, pr, perisarc ;
c, ccenosarc ; h, hydrotheca ; p, polypite ; b} bud devel-
oping to form a polypite later on (note that the perisarc
covers the entire surface of the bud ; as growth goes on

62 MICROSCOPICAL STUDIES.

a thinning takes place at the apex, and finally gives way
to permit of the extrusion of the polypite's tentacles) ;
g, gonotheca ; m, medusid buds in different stages, within
the gonotheca.

Fig. 3. View from below of a freed medusa.
Fig. 4. Diagram of same,

Fig. 5. Diagrammatic vertical section through same. The section
follows the course of a radial canal on the right side,
while on the left, an interradial portion of the disc is
sectioned.

Fig. 6. A Medusa, considerably older than that shown at Fig. 3,
seen reverted and from the side. It had just captured
an Arrow-worm (Sagitta), which is doubled up, the bend
being within the digestive cavity of the Medusa.
Lettering the same for Figs. 3 — 6, viz : — a, atrium ; c.c, circum-
ferential canal ; en, endoderm ; g.g, genital glands ; m, manubrium ;
o, mouth ; ot, otocyst ; r.c, radial canal ; s.u, sub-umbrella ; t, ten-
tacle ; u, umbrella ; v. velum.

STUDY XII. — ON POLYNOE PROPINQUA AS TYPICAL OF THE
HIGHER ANNELIDS.

Polynoe propinqua (Malmgren) is an elegant marine annelid,
short and slender in its proportions, rapid and lively in its movements.
When the tide recedes, its haunts are to be found wherever boulders
litter the shore, and many a weary backache have I had through a
course of such stone-turning. It is easily recognized by reason of
two rows of oval overlapping brownish scales that lie upon its back,
and from under which project, oar-like, on either side, serried banks
of lovely translucent paddling-bristles. A pretty creature, but loath
to be captured. Alarmed at the approach of the forceps, it squirms
and makes desperate effort to escape, and indeed if it be lifted
roughly and by force, instead of being taken by some gentle snare,
lo ! it breaks into pieces and is to you but a worthless capture.

A cursory examination suffices to show that except for the two
extremities, the body is divisible into about 41 ring-like portions, all
broadly or obviously of the same value one with the other — formed
fundamentally upon the same plan, though some are either internally
or externally modified in particulars for special functions. The
typical form of these equivalent body-rings, or somites as they are
termed, possesses on either side a fleshy two-branched lobe, the
parapodium, in which are implanted bundles of finely sculptured
bristles or setae. The upper branch, the notopodiuin, is considerably

THE ORIGIN OF ELYTRA. 63

smaller than the ventral or neuropodium, and its setae are shorter
and of a different pattern to those of the latter. The drawings
on PL XI sufficiently illustrate the general arrangement and the
details of divergence. Besides the ordinary setae, each branch of the
parapodium contains a single stout spine, aciculum, buried, all but
the point, in the flesh.

The form of the parapodia — often termed rather loosely- the
feet — and of their bristles, is remarkably stable throughout the whole
length of the body, excepting only in the case of the first somite, the
peristomium, the one bearing the mouth. Here each parapodium
is reduced to a long slender lobe, obscurely divided into rudimentary
upper and lower branches, and with but one aciculum and two or
three tiny seta3.

The tactile appendages garnishing the various somites show
much divergence. Thus the somites 2, 4, 5, 7, 9, 11, 13, 15, 17, 19,
21, 23, 26, 29, 32, bear each one pair of the characteristic scales, or
elytra, while the remaining ones bear on either side a long filiform
appendage, the dorsal or notopodial cirrus, arising from the base of
the notopodium. Reference to Fig. 1 will explain this arrangement
and show how, in the major part of the body, these two organs
roughly alternate, giving place in the last ten somites to cirri only,
thus leaving this short portion naked. The neuropodium bears also a
short ventral cirrus, but this shows no variation except in the
peristomium, where it is greatly elongated.

In structure, the elytra are thin membranous two-layered plates,
borne on broad low peduncles, and so loosely attached, that it is
extremely difficult to obtain a preserved specimen with the full
number present. This extreme looseness is peculiar to this species.
In others, such as the common Lepidonotus squamatus, they adhere
with such firmness that they frequently tear rather than lift off, and
between these two extremes, there is every intermediate degree.
The surface of the scale is prettily marbled, while around the exposed
edge is a row of all but globular tubercles, very diagnostic of this
species. Occasionally I have noticed the elytra to be distended in a
bladder-like manner. Some observers have supposed this to be an
incubatory device, as they have found them filled with ova. This
however does not necessarily follow, for the ova when freed, find their
way into all the spaces of the body-cavity, and of this, the hollows of
the elytra are but offshoots.

Probably elytra are modifications of certain dorsal cirri — the two
never being found co-existent upon the same somite in Polynoe,
though in Sigalion, a scale-covered worm of great length, they do
exist together. In the latter case however, the common phenomenon
of duplicative variation (see Bateson's " Materials for the Study of

64 MICROSCOPICAL STUDIES.

Variation ") has probably been at work ; if so, then Polynoe shows
regular modification from a form possessing dorsal cirri to every somite/
while Sigalion shows such modification with duplication superadded.
The head, the prostomium, consists of all to the front of the
mouth-somite, and indeed is apt to be confounded in part with the
latter, as its upper surface is bent back and lies partly obscuring it.
Viewed from above, after the concealing first pair of elytra are
removed, it appears sharply defined and roughly heart-shaped, with
two pairs of black eyes set widely apart (Fig. 3). Long appendages
of sensory function, borne on separate peduncles, are given off from
the fore edge. Four are in pairs, while a median unpaired one, the
median antenna, is given off, rostrum-like, from the central point.
On either side of this is a rather short, almost conical process, the
superior-lateral antenna ; while attached immediately beneath each
is a stout, very extensile organ, the inferior-lateral antenna or palp.

In addition to these, the dorsal and ventral cirri of the peris-
tomium have to be considered as supplementary head appendages, as
they are specially elongated and are directed forwards at the side of
the true appendages, acting in unison in sensory duties. They
receive the distinctive name of tentacular cirri.

From the paired nature of the prostomial organs, it has been
suggested that, as happens among the Crustaceans and the Insects,
the head has resulted from the coalescence of several somites, which
in losing locomotive duties have been profoundly modified to subserve
sensory uses. But a very serious objection to this is, that all the
prostomium results from one particular part of the larva, known as
the pra3-oral lobe, and which at no period of its history shows any
suggestion of segmentation.

Turning now to internal arrangement, we find that the mouth
leads into a well-marked pharynx, the anterior portion of whose walls
lie in puckered folds capable of being everted like the finger of a
glove, and thus allowing of the protrusion of the hinder portion, so as
to form a proboscis. This hinder portion has walls of great thickness
and muscularity, and the anterior end when protruded, is crowned
with a circlet of conical transparent papilla?, each containing a dark
pigment spot. Just within this ring are four horny beak-like teeth,
that bespeak plainly the essentially carnivorous nature of the Poly-
noinae. Indeed one has but to keep a number of them together for
some time to find proof of their cannibalism, in the bitten and torn
parapodia of the weaker individuals, and undigested bristles can
frequently be traced in the matter contained within the intestine
of newly captured ones.

From the pharynx, the alimentary canal passes direct in a
straight course to the anus. As in the closely related Aphrodite, it

ANATOMY OF POLY.NOE. 65

gives off in each somite to the rear of the muscular pharynx, a right
and a left glandular pouch or caecum, whose function we are yet uncer-
tain of. Curiously enough, the anus is not terminal, but, as in the
Copepoda, is found upon the dorsal surface of the penultimate
segment.

A definite respiratory, or pseud-haemal system, was long denied
to the Aphroditida?, bat Salenka and others have demonstrated in
Aphrodite and other species, a highly developed series of fine closed
tubes containing fluid apparently respiratory in use, but almost
invisible because of its all but entire lack of colour.

These vessels are in no way concerned with the diffusion of
digested nutriment. That duty is taken charge of by a corpusculated
fluid filling the general cavity of the body (Coelome), and which
circulates readily through the whole length of the body by reason
of gaps being present in the septa that break the coelome up into
numerous chambers.

Each of the septa here mentioned is a vertical partition wall
or rather transverse membranous mesentery, parting the coelome of
adjacent somites throughout the greater part of the body, but
suffering modification in the anterior portion of the animal, where
the evertible pharynx requires special freedom of movement.

The nerves consist of a large cerebral mass above the mouth,
connected by a commisure passing on either side of the pharynx,
with a chain of ganglia in the ventral wall of the body. In reality
this chain is double, but is so far coalesced as to appear single.
Each somite possesses one of these double ganglia. From the upper
and anterior edge of the cerebral nerve mass, nerves are given off to
the median and to the superior lateral antenna?, while the palps are
innervated from the ventral surface. Segmental organs, excretory in
function, are also present, but extremely minute.

REPRODUCTION. The sexes are separate, but no special ovaries'
or testes are present ; the genital products being developed as cellular
masses from the internal surface of the body walls. The products
ripen and are set free in the coelome, whence they obtain egress,
either by rupture of the body- wall, or by way, perhaps, of the
sogmental organs in some cases.

The embryos have the characteristic Polychsete form, being
trochophcres, that is, they are rounded bodies with an encircling
band of cilia immediately in front of the mouth, the portion in
front of the band, forming the prse-oral region already referred to
as the precursor of the adult prostommm.

Adult form is soon assumed, but for some time after EO doing
the young pursue a pelagic existence, swimming freely on the surface
of the sea, and frequently falling victims to the snare of the tow-net.

66 MICROSCOPICAL STUDIES.

Like the adults these larvae are brightly phosphorescent upon irri-
tation— the luminous areas being the elytra.

The Polychaetous Annelids, or Polychsetes, to which Polynoe
belongs, include nearly all the marine bristle-bearing worms. Very
few (only some half-dozen rarities) are inhabitants of fresh water ;
whereas, on the contrary, the Oligochaetes (the few-bristled annelids),
extremely rare in the sea, have in fresh water and upon the land,
practically the entire monopoly.

Polynoe is very closely akin to the lovely iridescent Sea-mouse
(Aphrodite aculeata), so often dredged in sandy estuaries. Both
belong to the same family, Aphroditidae, but to different tribes,
namely to the Polynoinae and the Hermioninae respectively. The
former comprises a great number of species, marked off from one
another chiefly by differences in the number and ornamentation of
the scales, and in the sculpturing of the setae.

I might have chosen a much simpler type whereby to illustrate
the anatomy of the Polychaetes, but on the principle of the axiom
that the greater includes the less, I chose Polynoe, as in it, com-
plexity of anatomy reaches its highest development and if we become
familiar with its general features, we need not be afraid of being
puzzled to understand the modifications seen in other forms.

The present species, P. propinqua, is dominant in the Channel
Isles between tide-marks, but in the Irish Sea I found it extremely
rare, its place being taken by the stouter P. imbricata. Both these
are prowling robbers, without home or sojourning place, but many
species take up uninvited lodging with some of the larger tube-
forming worms, or with Echinoderms. Thus two species live with
the strange Chcetopterus in his great parchment tube, one with the
giant Eunice sanguinea, one with Terebella, and another in the
ambulacral groove of the starfish Astropecten, while a tiny one lies
sometimes among the tube-feet of Echinus, and yet another, one of the
most beautiful, finds safe dwelling among the spines of the purple heart
urchin Spatangus. Such are termed commensals or messmates, but
the mutual relations subsisting between the host and the guest are
obscure and little understood. It may be that the annelid frequents
the host for protection only, sallying out in quest of food when
hunger presses, but that there is something more seems argued by
the fact that each species is always found with its own particular
host. If it were a question of protection only, would not the tube
of one worm be as good as that of another ?

Another curious point about these worms is the great power
possessed of reparation of injuries. If in danger, it is the invariable
habit of P. propinqua, in common with many allied species, to break

THE KENEWAL OF LOST PARTS. 67

np into two or three fragments in the hope of the head part being
able to escape under cover of the consequent confusion. If it be
able to do so, in a very short time a number of rudimentary somites
appear sprouting from the broken end, and these grow and increase
until finally the full and complete size be once again attained. I
have seen individuals in all stages of this regeneration, but have
never seen the hinder or tail fragment of a ruptured worm reproduce
a fresh head, as has been recorded by some writers. Such however
would, I believe, be likely to occur were the fracture close to the
head, but usually it occurs much nearer to the tail than to the head,
and in such cases I feel sure that the tail portion dies.

68 MICROSCOPICAL STUDIES.

STUDY XIII. — THE TADPOLE LARV.E OF ASCIDIANS.

The Tunicates or Ascidians, may be either fixed or free ; simple
or colonial. The central type of the free is seen in the Appen-
dicularise, transparent tadpole-like animals that sport in the surface
waters of our seas, in profusion, at certain seasons. In size these are
extremely minute, the British species averaging only i-in. to i-in.
in length, tail included, while the length of IJ-in. which a foreign
species reaches, is altogether exceptional and monstrous. In this
type, the tail is supported arid strengthened by a firm central rod,
the notochord, believed to be a similar structure to the first sup-
porting stiff axis of the embryos of vertebrates, and which in them
is subsequently usually obliterated by the encroaching growth of the
vertebral column. Another curious point is that two openings com-
municate between the pharynx and the exterior, and serve as gill
slits.

These tiny ocean wanderers are never colonial, always free and
simple. The fixed Tunicates, the Ascidians proper, are, on the
contrary, very frequently colonial, or as some writers term it, com-
posite or compound. In such latter, there is usually a certain amount
of federation, such for example in those where the anal apertures
of a circlet of individuals open into one common atrial or cloacal
chamber, to be expelled by a centrally place atrial opening.

In size, the colonial individuals are usually very much smaller
than the simple, but in structure the two are essentially similar,
having the anterior portion of the alimentary canal distended into a
large chamber, with walls perforated by numerous gill slits, a nervous
system reduced to a single rounded mass (ganglion) between mouth
and cloacal aperture, a blood system of much simplicity and an
enveloping case of nearly structureless semi-cartilaginous or gela-
tinous tissue, the tunic or test.

July and August is the breeding season of many species, and if
one of these animals be then dissected, eggs and embryos in various
stages of development will be found.

Taking one of the most advanced, the following points can be
observed. The body is a tiny oval, slightly flattened from side to
side, while from the one end is given off a long broad tail, containing
centrally a clear rod of a cartilaginous substance. Both the body and
the tail are invested in a thick coat of gelatinous material, equivalent
to the test of the adult fixed animal. Turning the animal on to one
side (when the tail is found to be now on edge) one can, by staining,
make out clearly the thick investing test,in which lies the darker stained
kernel-like body. At five points the test is broken through ; three
of these are where, at the anterior end, there pass an equal number of

THE COMPLEX NERVOUS SYSTEM OF ASGIDIAN LARV.E. 69

tiny rod-shaped papillse spreading' into wide heads on their emer-
gence. These are glandular in -function, secreting a tough glutinous
cement whereby the larva when tired of a free life, attaches itself
to a rock or weed. The other two points where the test is pierced,
are upon the dorsal side, and in the larva of Aplidium elegans are
situated far back. The anterior is the opening of the mouth (o),
and is separated by only a short interval from the posterior, which-
is a depression indicating where the atrial aperture breaks
through. The mouth opens into a wide pharynx occupying a great-
part of the larval body space. In the stage figured, the stomach
is just beginning to be apparent as a thick walled canal in a ventral
position towards the hinder part of the body, and connection is
just being made between the atrial cavity and the intestine. Ill
the advanced larva several openings pierce the pharynx and
allow water entering through the mouth to pass into the atrial
cavity without having to traverse the stomach and intestine. Such
openings are obviously the same as are so numerous and so apparent,
in the adult. In Fig. 4, PL x, they show as two rows of disc-shaped
thin places in the pharyngeal walls.

The nervous system, of the most extreme simplicity in the adult,
has in the larva a complicated and highly developed arrangement/
As in the Yertebrata, it takes its origin as an open furrow stretching
longitudinally along the dorsal side of the body. The edges gradually
grow upwards and inwards to meet, and thus form a tube which now
constitutes the central nervous system of the animal.

The anterior end gradually swells into a large vesicle, while from
the hinder end of this, there runs a rapidly narrowing tube which is
prolonged into the tail as the caudal nerve. The large anterior
vesicle contains two peculiar sense organs, an eye, and an otolith
perhaps of auditory value. These can readily be made out in
mounted specimens, as both are darkly pigmented and show
conspicuously, rendering easy the location of the cerebral vesicle
lying between the mouth and the atrial opening. Of the two, the
eye is much the more complex, for it possesses a cup-shaped retina
in which is placed a projecting and complex lens. It is placed at
the posterior upper corner of the vesicle and projects downwards
towards the centre of the cavity. The otolith on the other hand,
rises upon a stalk from the floor of the vesicle more to the front end.
It is noteworthy that both are within the vesicle.'

The after history of the animal is quickly told. The larva
affixes itself by the glutinous secretion of pne or all of its three,
papillae to some object ; the tail with its contained' notochord, as well
as the three anchoring papillae become absorbed ; the test becomes
enormously, thickened and strengthened, and the perforations of the

70 MICROSCOPICAL STUDIES.

pharynx become multiplied great ly, and most significant of all, eye
and otolith vanish utterly, the well developed nervous system being
reduced to a fairly large ganglionic mass occupying the position of the
cerebral vesicle of the larva, i.e. midway between the mouth and the
atrial opening. Radiating nerves to the various organs are thence
given off. The course of these changes brings about a certain alter-
ation of placing of the two external apertures, as may be seen in the
diagrams ; thus the mouth in the fixed larva of Aplidium is at first
not terminal, but gradually becomes so, thus necessitating a corres-
ponding travel of the atrial opening. There is, however, no real
travel of these parts, simply a more rapid growth than of the opposite
side, of that part of the body wall and test lying below the mouth,
i.e. between it and the point of attachment to the rock. This
naturally pushes the mouth upwards, and finally places it in a
terminal position, at the point of the body furthest removed from
the point of fixation. Budding produces a cake-shaped colonial mass
of a general pink colour, flecked with white points indicating the
position of the mouths of the various individuals or ascidiozooids.

With the assumption of adult form by Simple Ascidians, the
genital glands develop, but among the Compound, a frequently long-
continued course of budding, takes place prior thereto. All species
are hermaphrodite, but as a rule the male and female organs do
not ripen at the same time. The young produced are the tadpole
larvae we have above described.

Only within the last 28 years have the Tunicates bulked with
large importance in scientific ken. Until 1866, when the Russian
naturalist Kowalewsky published his famous researches and specu-
lations upon the embryology of the group, they occupied a position
of comparative isolation, with ill-understood affinities, and were
generally treated as aberrant forms of little importance. Some were
for placing them among the Mollusca, largely upon the count of their
acephalous (headless) condition ; others from the peculiar looped
form of the alimentary canal would have that they were peculiarly
developed relatives of the Polyzoa. The lowly development of the
venous system favoured alike either of these views.

But Kowalewsky 's researches altered all that, and gave the
Tunicates a status of great importance. He pointed out how the
adult Appendicularias and the tadpole larvaa of the fixed Ascidians
bear many close resemblances to the lower vertebrates, especially to
the Lancelet (Amphioxus), such for instance as the presence in both
of a stiff central axis, the notochord, and the occurrence of a central
nervous system expanding into a large cerebral vesicle at the anterior
end. Finally he pointed out the perfect concordance of the perfor-

PI. X.

I . \^^»y.' r, i^ -^'-~TC \ I

JA8. HORNELL, DEL. AD. NAT.
JERSEY BIOL. STN.

ALCYONIUM AND LARVAL ASCIDIANS.

EXPLANATION OF PLATE X.
Figs. 1 to 3, Alcyonaria.

Fig. 1. Single polyp of Alcyonium palmatum, greatly magnified.
st. Stomodaeum or oesophagus ; mes. mesenteries ; m.f.
mesenterial filaments or craspeda ; g.c. gastric cavity ;
s.s. supporting spicules.

la, a spicule from lower end of a tentacle ; Ib, a supporting
spicule ; Ic, some of the superficial-lying spicules that
form the protecting cortex of the colony ; Id, spicules
from the supporting lamella of the stomodaeum ; Ic, a
spicule from the deeper parts of the mesoglaea.

Fig. 2. A branch of Alcyonium, with polyps in various stages
of expansion, x 2.

Fig. 3. Spicules from mesoglaea of Alcyonium digitatum.

Figs. 4 to 6, also A to D, Larval Ascidians.

Fig. 4. A tadpole larva of Aplidium elcgans (Giard), just freed

from the parent. Viewed from left side.
Fig. 5. Diagram of the structure of a similar larva, seen from right

side.
Fig. 6. Diagram showing stages in the metamorphosis of a tailed

larva into the adult sessile condition.
Fig. 7. A colony of Aplidium elegans, when in adult stage ;

natural size ; c.c.o. common cloacal orifices.
Figs. A to D, Larvae where the papillae are abnormal in number or in

arrangement.

Lettering the same in all figures, viz. : — a. atrium ; a.o. atrial or
cloacal orifice ; a.p. adhesive papillae ; c.v. cerebral vesicle ; c.n. caudal
nerve ; br. c. branchial or pharyngeal clefts ; en. endostyle ; g. gan-
glion ; g.s. cells homologous to the rudimentary gemmiferous tubules
of other species, which give rise, by rowth and budding, to new
individuals, when the larva becomes attached, and proceeds to form a
colonial mass (fide Giard) ; o. mouth ; oe. oesophagus ; nt. notochord ;
ph. pharynx ; st. stomach.

EXPLANATION OF PLATE XI.

Polynoe propinqua, one of the higher Annelida.

Fig. 1. Optical section of an individual viewed from above, the
elytra having been removed.

Fig. 2. Appearance of the animal with elytra in place — life size.

Fig. 3. View of head and its appendages.

Fig. 4. Anterior portion of body showing the extruded proboscis,
bearing at the extremity a ring of papillae, and having
four pairs of horny jaws (2 only visible here) just within
the orifice.

Fig. 5. An individual showing regeneration of the hinder end,
after a breakage that had taken place at the point
marked *.

Fig. 6. Diagram of a transverse section of a somite bearing dorsal
cirri.

Fig. 7. Diagram of a similar section through an elytra-bearing
somite. These two figures are useful in the understand-
ing of the possible origin of elytra from dorsal cirri.

Fig. 8. A parapodium or foot.

Fig. 9. A dorsal or notopodial bristle.

Fig. 10. A ventral or neuropodial bristle.

Fig. 11. An elytron or scale, showing the row of globular tubercles
around the outer margin.

Fig. 12. Edge of same highly magnified, to show one of these
tubercles.

Fig. 13. A portion of an elytron still more highly magnified, to
show the fine papillae of the surface.

Lettering the same in all figures, viz. : — a.c. anal cirri ; ac.1
aciculum of 1st somite ; acd. aciculum of notopodium or dorsal branch
of foot ; acv. aciculum of neuropodium or ventral branch ; cac. caecum
of alimentary canal ; d.c. dorsal cirrus ; el. elytron ; el. ped. peduncle
of elytron ; int. intestine ; m.a. median antenna ; nr. notopodium or
dorsal branch of foot ; np. neuropodium or ventral branch ; ph.
pharynx; ph. t. pharyngeal teeth; p. palp; pr. prostomium ; s.l.a.
supero-lateral antenna ; t.c. tentacular cirri ; v.c. ventral or neuropo-
dial cirrus.

PI. XI.

. HORNELL DEL. AD N»
JERSEY BIOL. STN.

THE ANATOMY OF POLYNCE FROPINQUA,

THE SIGNIFICANCE OF THE TADPOLE STAGE. 71

ations of the Ascidian pharynx, both larval and adult, with the gill
clefts of the Lancelet specially, and of fishes generally.

Huxley and Haeckel warmly espoused this view so carefully and
logically put forward, and now it reigns as the orthodox opinion.
Prof. W. K. Brooks, who has within the last few weeks published
an extremely valuable monograph upon the Salpce, a group of much
modified and altered pelagic Tunicates,* after a fresh and independent
investigation from new stand-points and with many new facts to put
into witness, fully endorses the same view, and states his belief
that a simple pelagic form, of which Appendicularia is the nearest
living representative, is the common ancestor of all the Chordata, i.e.
alike of the Tunicata as of the Lancelet and all the Yertebrata.

Of course such theory can never be proved with mathematical
certainty. It is at best a plausible probability, the most probable
explanation of the mode of descent of the higher animals we at
present know of. But there are, and have been, capable investigators
who cannot bring themselves to accept it Thus Prof. Giard, who as
the first occupant of the chair of Darwinism at the Sorbonne, cannot
be considered in any way a scientific reactionary, in 1872, after
elaborate investigation of the Compound Ascidians, refused to endorse
this opinion. He then could see nought but a convergence or coinci-
dence in general form between Ascidian larvas and lowly vertebrates,
due he believed to a similar mode of life, i.e. free-swimming. He thus
considered the adult as the true or fundamental form of the Tunicate
group, and the larvae not as a reminiscence of ancestral freedom, but
as a larval form that for its special and temporary needs, assumed
through like requirements of mechanical stresses, due to the adoption
of a similar mode of progression, swimming, a form akin to that of
a lowly vertebrate.

If we want to go astray in reasoning, it is often easy enough
with the exercise of a little ingenuity or else of some obtuseness to
sink deep in the mire of false deduction. Anyone not thoroughly
master of an intricate subject may easily mistake cause for effect,
and conversely, and I remember once when considering this Ascidian
problem, thinking what a grand opportunity exists in the life-history
of Appendicularians for such an one to go astray. Among these tiny
tailed swimmers, the habit exists, at certain times, of forming a
gelatinous envelope in which the animal lies enveloped for a short
time — the " Haus " this has been termed ; and it is obviously
homologous to the test of the fixed Ascidians. Now a very
probable line of descent of the latter is from Appendicularians
that have taken this " haus " stage as a permanent adult condition

* " The Genus Salpa," Baltimore, 1893.

72 MICROSCOPICAL STUDIES, rr .

and so have deserted the free-swimming life — evidence being that
the fixed Ascidians recapitulate very closely, in their larval condition ^
the general form, together with many of the essentially characteristic
internal features of adult Appendicularians. But the student not
thoroughly on his guard against the pitfalls of evolutionary reasoning,
might easily deduce that the Appendicularians are arrested larvas
of fixed Ascidians ; that is, that certain larvae instead of performing
the full life-history of their race, retained the tailed form all their
adult life, and that the occasional formation of the " haus " is the
atavistic recollection of the fixed Ascidian condition ! !

In reality such conclusion is easily refuted, and there is really
no reasonable doubt that the tadpole larvas show the ancestral form
fairly clearly. To mention one argument only, why should they have
a nervous system infinitely superior to that of the adult, formed too
on a plan entirely different from any to be found among inver-
tebrates, but characteristic of vertebrates ?

Correction. — On page 8, line 6, read "ovary" instead of "ovum.

THE HIGHER PROTOZOA. 73

STUDY XIV. — SPH^ROZOUM PUNCTATUM, A COLONIAL
RADIOLARIAX.

No group of animals possesses such intense interest to the
Biologist as does that of the Protozoa. Located on the very outskirts
of life, one searches among their lower forms and studies their every
phase and attribute, in the hope of obtaining the faintest clue as to
the origin of life itself. Their higher developments we scrutinize
equally closely, for evidence as to the particular evolution of the
sponges, simplest among the higher animals — those Metazoa whose
bodies are made up of aggregations of cells, not one of which is, of
itself, capable of prolonged separate existence, but requires the co-
operative assistance of other units, other cells, to carry on " life."

The Protozoa are, we know, typically unicellular, but many of
the most interesting forms seem very closely to counterfeit the me-
tazoan plan ; though ever with this distinction, — separate one of their
cells, and straightway it can sustain long life and multiply its species
as though nothing radical had occurred. With these latter, our
attention now lies.

Most of us have seen, and admired with enthusiasm, that lovely
emerald-jewelled rotating globe of colonial life, the tiny Volvox of
our ponds. And though we cannot nowadays accept the firm belief
entertained by mariners of ancient times, that the sea contains coun-
terparts of everything moving on the land and in fresh water, yet as
ivgards Volvox, we may claim in SpJtcerozoum and its allies, at least
forms having many outward resemblances.

Sphcerozouni is a colonial Radiolarian in which the skeleton con-
sists of loose spicules surrounding each individual of the colony, but
before going into details of anatomy, it will be well for us to cast a
survey over the group wherein it is included. In the first place,
Radiolaria belong to that group of the Protozoa known as the Rhi-
/opoda, animals where locomotion and the capture of food is effected
by extensions (pseudopodia — " false-feet ") of the outer layer of the
body, ectosarc. The well-known Amcebci — long ago known as the
proteus animalcule on account of its constant change of shape, due to
the thrusting out of these pseudopodia, first from one spot and then
from another— is one of the most primitive members. It is little else
than an animated microscopic speck of granular jelly-like protoplasm,
endosarc, surrounded by a slightly denser and clearer layer, the
ectosarc; having a peculiarly- endowed dense speck, termed the
nucleus, embedded in the endosarc, and wherein lies the poten-
tiality for future multiplication.

74 MICROSCOPICAL STUDIES.

A higher division of the same Rhizopoda are the Foraminifera,
animals of the amoeba-type endowed with the faculty of building up
a skeleton, usually of lime (calcium carbonate), from whose surface
and from apertures in which, are given off numerous long whip-like
threads of protoplasm, or pseudopodia, locking and inter-locking with
one another (anastomosing) ; the same in kind, though differing mark-
edly in degree, as the few coarse and short pseudopodia of Amoeba.
Then we cross at once to the class we have to deal with, the Radio-
laria, where the power lies of building up a skeleton of flinty matter
(silica) the same in chemical composition as the fine quartz crystals
from which much optical glass is made. But this spicular coating is
not essential to existence, for many species (Collozoum) possess none.
Let me therefore consider such an individual, which may be taken as
representing the fundamental or primitive type of Radiolarian, the
skeleton being an after assumption in the class, though in Collozoum
the absence is not due to primitive want of it, but rather to dege-
neration.

Comparing with Amoeba, we would Fay that in the Radiolaria
the body is usually of a globular form, and what answers to the
endosarc of the other, is separated from the outer layers by a
membrane (chitonous ?) which we term the capsular membrane.
This is pierced usually by numerous minute openings and bedded
in the protoplasm within the capsule (intra-capsular), lie several
nuclei — a characteristic of the group, a very large oil-globule, and
a number of tiny crystals.

The extra-capsular substance consists of two well defined layers,
the inner (sarcomatrix) which invests closely the capsule, is proto-
plasmic and granular ; while the outer layer, the calymna, is of a
structureless, gelatinous nature. From this layer arises an often
wonderfully beautiful flinty (siliceous) skeleton, built up sometimes
as a lattice-work bell, or it may be into a lace-work globe with great
projecting spines. The calymna is penetrated by delicate tubules
through which pass fine threads of protoplasm originating from the
sarcomatrix. Having passed through the calymna, these threads piss
out on the surface of the globe into a network, the sarcoplegma, and
from this are projected into the water around, long filamentous
pseudopodia, closely akin to those of the Foraminifera. With these
long tendrils, prey is entangled and is then passed inwards.

The vast majority of Radiolarians — and their name is legion—
are such as we have described, but a small group live colonial lives,
numerous individuals massed in tiny communities, and modified in
certain points consequent upon the mutual duties devolving upon
the several individuals.

THE REPRODUCTION OF RADIOLARIA. "75

Thus the individual skeleton is reduced and even lost. In
tiphcvrozoum, each individual is surrounded by a lattice-work of loose
spicules of the elegant six-spin ed form shown at fig. E, PI. XII. In
other species, it is absent (Collozoum). Sometimes these colonies
reach considerable size. Collozoum attains a full inch in length.
tij)/tcvrozoum is smaller and usually globular, perhaps iVin. in length,
but sausage-shaped colonies of J-in. long are fairly common. — 200 to
300 individuals are frequently associated together, being arranged
peripherally in a hollow gelatinous sphere, arising from the general
coalescence of the gelatinous outer extra-capsular layer (calymna)
of each member. This layer being common to all, it follows that the
protoplasmic network of the surface, and the radiating pseudopodia
are also common, ensuring the even distribution of nutriment. Thus
in a Radiolarian colony such as Sphcvrozoum, we have each individual
with its own separate central capsule, its own separate sarcomatrix
and its own protecting lattice work of spicules ; but calymna,
sarcoplegma and pseudopodia are shared in common by the colony.

If we examine carefully the sarcomatrix of Spkcerozoum, we see
a varying number of deeply stained bodies lying irregularly spread in
the sarcomatrix of each individual. Some have many, some have
few, and it may happen that we may see some possessing none. In
life, these bodies are yellowish, and it is inferred that they are
parasitic, or, more probably, symbiotic algas. It appears that these
yellow cells can live equally well, and even multiply, when separated
from their host. Each has been found to possess a distinct cell-wall
of cellulose, a nucleus, two colouring matters, one of which is
chlorophyll, and lastly, to complete the vegetal characters, the power
of forming starch. They are present in nearly all species, though
some individuals are occasionally free from them. In the present
species, some individuals are crowded with them, while others have
comparatively few. These cells multiply within the host by the
division of their protoplasm into four parts which secrete separate
cell-walls and then break through the parent membrane. If removed
from the host, they eventually become biflagellate, i.e. provided with
two whip-like threads of protoplasm, flagella, their locomotive organs.
Some have referred them to a distinct genus of algae, while others
believe them to be the swarm spores of several species of olive-
green seaweeds (Fucus, &c.) It is probable that they assist in the
respiration and nutrition of their hosts, by contributing oxygen
and starch.

The reproduction of the Radiolaria is most intricate, and
betokens the high development to which the group has attained. If
we take a fully adult colony of Spkcerozoum, we find that the

76 MICROSCOPICAL STUDIES.

individual members, at a certain period, break np into innumerable
tiny spores ; these spores may be of two distinct series. Thus one
colony may give rise to spores all of the same size, isospores, while
another may give rise by another method to spores of two sixes
(anisospores). The former are probably asexual ; the latter sexual,
giving a typical alternation of generation. Both forms are produced
within the central capsule. In the formation of isospores, the nuclei
of the parent multiply by fission and scatter throughout the capsular
protoplasm : each nucleus appropriates a certain amount of protoplasm,
and a minute crystal, and receives several tiny oil globules from the
breaking up of the great oil globule. When ripe, each of these
masses assumes a pear-shaped form, with the nucleus at the narrow
end, whence proceed two flagella which propel the spore through the
water, when liberated by the breaking down of the capsular membrane
and when disintegration of the extra-capsular matter takes place.

Anisospores arise also from the multiplication of the mother-
nuclei, but the mode is somewhat different. Within the same
individual, two well-marked sizes occur ; the larger are termed
macrospores, the smaller microspores, and they escape in the same
way as do the isospores. Analogy suggests that in these macro- and
microspores we have a sexual stage, but the conjugation of these two
bodies, which is required to prove this theory, has not been observed.
The shape of both forms of anisospores is reniform (kidney-shaped) :
they are propelled either by one or by two flagella. Isospores and
anisospores alike give rise to an ordinary Radiolarian having the
typical structure. This by fission of the central capsule repeated
frequently, and by gemmation also(?), produces the colonial mass we
have before us. Then when the full of adult life is reached, the
intra-capsular protoplasm breaks up into either iso- or anisospores.
The Life-cycle of such a Radiolarian can be tabulated thus : —

1. Isospore (asexual spore).

2. Young Radiolarian individual.

3. Colony (produced by fission and gemmation).

4. Anisospores = macrospores, and microspores (Sexual spores) (?).

5. Conjugation of macro- with microspore (?).
G. Young Radiolarian individual.

7. Colon}-.

8. Isospore (asexual spore).

Stage 4 may not necessarily alternate with stage 8 ; indeed it is
probable, by analogy, that under favourable life-conditions, the forma-
tion of anisospores seldom occurs — many repetitions of isospore
generations taking place before one of the anisospore stages recurs.
The latter probably occurs when new vigour requires to be infused

VOL. [., PI. IX

FIGS. A TO E, AND 1, 2, 3 & 4.

SPHAEROZOUM AND LARVAL ANTEDON

EXPLANATION OF PLATE IX.
Figs. A to F, Sphcurozoum punctatutn.

Fig. A. Natural appearance of a colony, showing the numerous

individuals surrounded by the clear layer of the calymna.

X 6.
Fig. B. Diagrammatic section through the same, showing it to

consist of a hollow sphere ; cl. calynma : c. #p. central space.
Fig. C. View of an isolated individual surrounded by a Loaaejuetwork

of spicules.
Fig. D. The same, with spicules removed.

o. gl. great oil-globule of capsule ; nu. one of the several

nuclei ; cp. capsular membrane : sm. sarcomatrix : alg.

symbiotic algae.

Fig. E. Three of the six-rayed spicules.
Fig. F. Scale of magnification of Figs. C, D, E, 3 & 4 (all original).

Figs. 1 to 9, Crinoids.

Fig. 1. Free-swimming larva of Antedon (Rosy Feather Star), with

the calcareous plates of the stalked larva formed within.

c. z. one of the four ciliary zones. (After Thompson).
Fig. 2. Young attached larva of same ; t. pi. terminal or attachment

plate ; x. articulation of the joints of the stalk ; bs. a basal

plate of the calyx ; or. an oral plate ; r. a radial plate just

beginning to form ; t. circle of tentacles round mouth.

(Original).

Fig. 3. An oral plate magnified to scale of fig. F. (Original).
Fig. 4. Halves of adjoining joints of stalk, to show their cribriform

nature and mode of articulation at x. Same magnification.

(Original).
Fig. 5. A later stage than fig. 2, and just prior to commencement of

adult life. The dorsal cirri (dr.) and 5 pairs of arms

have just appeared. (After Thompson).
Fig. 6. Pentacrinus caput-meduscu (after J. Mliller), a form stalked

throughout life. The stalk has whorls of cirri (wh. dr.)

at intervals.
Fig. 7. Ekizocrinus lofotensis, a young individual (after Sars).

This species remains stalked all through life, but instead

of a basal plate of attachment, is anchored by ramifying

root-like processes which twine round stones and other

objects.

Fig. 8. Magnified view of the " head " of an older stage of same.
Fig. 9. Encrinus liliiformis, one of the most numerous of fossil

crinoids,

(The original figures copyrighted, March, 1895).

EXPLANATION OF PLATE X.

Creseis acicula.

Fig. 1. Cresei* « cicala. Several of the internal organs are drawn
in optical section, a. anus ; al. gl. receptaculum seminis :
c. f. ciliated furrow for conveying spermatozoa from the
sexual orifice to the penis ; ci. sh. ciliated shield, respira-
tory in function ; /. n. main branch of fin-nerve ; f/.'sub-
oesophageal portion of central nerve mass, showing the
great fin-nerves being given off from the anterior corners,
and the otoconia lying beneath ; h. d. duct of receptaculum
seminis ; h. yl. ovo-testis, or hermaphrodite gland ;
i. intestine ; 1. liver ; in. I. middle and rudimentary lobe
of foot ; in. n. mantle nerve ; up. nephridium : o. mouth ;
oe. oesophagus ; ot. one of the two otocysts, containing,
not a single spherical body or otolith, but numerous small
calcareous bodies, whose mass is termed an otoconia,
(the function of these bodies is supposed to be auditory) :
p. o. penial aperture situated at the base of the rudimen-
tary right tentacle; p. cj. penial gland, or rather, the
indrawn penis ; r. m. retractor muscle ; sit. shell ; st.
stomach : siv. I. swimming lobe or fin ; ut. di. uterine
dilatation ; ve. ventricle of heart.

Fig. 2. View of an entire Creseis (Fig. 1. had to be drawn in two
portions, as the length was too great for the size of the
plate).

Fig. C shows the homologies of a typical Pteropod larva, (Cymlulia),
with the larvae of typical Gastropods, A and B ; A being
a younger and B an older stage. (After Gegenbauer).
v. velum ; c. shell ; /. foot ; op. operculum : t. tentacles.

Fig. D. Diagram of a simple bilaterally symmetric or Isopleurous
Gastropod (Chiton).

Fig. E. Diagram of an asymmetric or Anisopleurous Gastropod.

Fig. F. Diagram of a naked Pteropod.

Fig. G. " thecate or shell-bearing Pteropod.

Fig. H. " Cephalopod.

(All after Lankester, G being modified).
D, V, A, and P point respectively to the dorsal, ventral, anterior

and posterior aspects of the body.

The extent of the foot in each case is denoted by the dntted

shading.

o. mouth ; a. anus ; ff. fore-foot ; in. f. mid-foot : h. f. hind-foot :

ep. epilobium ; c. e. cephalic eyes : s. p. sub-pallial space : in. s. mantle

skirt or flap : ?'-s. visceral hump or dome.

(The original figures copyrighted, March, 1895).

VOL. I PI. X.

J AS. HORNELL, DEL. AD NAT.

FIGS. 1 a. 2.

PTEROPOD ANATOMY.

FOSSIL HAD10LA1UA. 77

into the organism, cither through weakening occasioned by too frequent
repetition of the isosporulation, or else from external life-conditions
of an unfavourable nature.

It is worthy of note that the tendency among colonial forms
is towards the suppression of a skeleton. Collozoum has none ;
Sphcerozoum has loose spicules only. The reason probably is the
hindrance to the formation of new individuals by the fission of the
central capsule, which a hard resistent casing to the latter would
entail. With loose spicules, if the central capsule divides, then each
half simply takes its share of the spicules with it.

Distribution. All latitudes know the Radiolarians, but they
abound most in the warm seas between the tropics. The majority
are pelagic ; Sjihcerozoum and Collozoum among the number. Many
of the great depths of the sea are covered by ooze formed all but
entirely of their decaying remains, e.g. 2 — 3000 fathom depths of the
Pacific and Indian Oceans. To other deep ocean oozes, the Red-clay
deposits, and the Globigerina-ooze, they contribute largely. The
familiar Tripoli powder, used for polishing, consists largely of their
remains ; many fine whetstones are slaty rock formed in great part of
their siliceous skeletons. In many lands they largely compose
certain clays and marls, thus indicating, albeit in fragmentary
manner, the localities of uprisings of some ancient sea-bottoms of great
depths. Deposits in the Barbadoes and the Nicobar Islands, in
Algeria and Greece, are the best known of these — and it is from such
localities, especially from the first-named, that are obtained by careful
washing and separation, those beautiful fossil forms so well known as
microscopical preparations. These are all of Cainozoic age, but other
fossil species date from early Palaeozoic times, while in Jurassic rocks,
they even form quartzite, so compactly are they knit together.

STUDY XV.— THE HYDROID STAGE OF OBELIA GENICULATA.

Obelia constitutes a very typical form of Thecate Zoophyte,
and a study of the slide now sent out, taken in conjunction with
reference to Study XI, and Plate IX will furnish materials for a
ready comprehension of the essential details of the anatomy and of
the life-historv.

STUDY XVI— THE STALKED LARVA OF ANTEDON,

Few of us are unfamiliar, at least by name, with Antcdon> the
"Rosy Feather Star. The extreme elegance of its long slender arms
has long made it famous among the artistic triumphs of the world of

78 MICROSCOPICAL STUDIES.

life, rivalling in slender gracefulness even the rare beauty of the
ferns. To those who have however seen it in life among its natural
surroundings, the charm deepens, and Antedon is for ever linked with
happy life-marks fondly remembered. Shall I ever forget that day
out lobster-potting with an old fisherman, when the first pot we
pulled up was fairly encrusted with the rosy twining pinnated arms
of this most lovely of starfishes ! Surely if the fisherman's calling is
rough and uninviting at times, such experiences as these go far to
compensate. Rough fellows most are, but the sea has a silent
eloquence that finds its way to their hearts, and to those who have
served the apprenticeship, its fascination is magical ; even I, who
have other pleasures, and have never been fairly inoculated, have still
at times to respond to the urgent calling of the sea.

Antedon is fairly common around the British Coast ; in favorable
localities occurring in great multitudes. In anatomy it differs
extremely from the ordinary stout starfishes, such as the common
cross-fish Axtcrias miens, but as we are not concerned at the present
with its anatomy, suffice it to note that its body consists of a disc
some J inch across, from which proceed ten long slender arms bearing
numerous pinnules on either side. These arms often reach 3J inches in
length, so that the animal has a full span of 7 inches. The sexes are
separate, and the genital organs are located riot in the body disc, but
in the tiny pinnules of the arms. The fertilized ova are set free
as barrel-shaped embryos which acquire four encircling or zonal
bands of cilia — the hoops of the barrel — propelling it through the
water. Next appear a few minute calcareous plates within this
embryo, forming as it were, a tiny cask set up on an even more tiny
stalk. Free-swimming life being now all but ended, a disk containing a
perforated plate appears at the lower extremity of the stalk, and by
this, attachment is made to any object that happens in the way ; it
may be the stiff framework of a colony of Hydrozoa or of Polyzoa, or
it may be a frond of the great oar-weed (Laminaria). All this time
the soft barrel-shaped mass of the swimming larva has been shrinking
and adapting itself to the form of the enclosed calcareous skeleton,
and now the creature is fairly launched upon the stalked and anchored
period of its life.

In this stage the skeleton is made up of a basal plate (PL XII,
fig. 2, t. pi.) where the animal is rooted to its host ; a considerable
number of joints set end to end, forming the stalk, upon which
is seated the cup-shaped framework of the body, consisting of
two circles of large perforated plates, the members of each superposed
to one another. These are respectively the basals (Is) and the
orals (or), the former forming the base of the cup, supported on

THE GROWTH OF THE LARVAL SKELETON. 79

the summit of the stalk, while the orals are the upper ones, receiving
their name from their encircling of the mouth. All these plates can
be made out in the last stage of the swimming embryo (fig. 1) and
characterize the stage of most of the fixed larvaB in the microscopic
preparations accompanying this article. A few however show a
further stage, where a third row of tiny plates is intercalated between
the two original rows of basals and orals; these small plates- are the
first radials (r), each is alternate with the larger plates of the
skeletal basin. The several rows may be formulated thus : —

o o o o o

R R R R R
B B B B B

Each ring will be noticed to comprise five plates, the fundamental
echinoderm index. The mouth, as before mentioned, is centrally
in the calyx formed by these perforate or cribriform plates, and
is surrounded by a row of tentacles armed with a limited number of
delicate thread-like processes.

Growth after this is rapid, a second circle of radials appears
superposed to the first and then a third upon the second. From the
third proceed the arms double the index number, two being borne on
each third radial, which has two fascets for this purpose on its upper
surface. At the same time the topmost joint of the stalk has been
enlarging and becomes a great plate-like structure, the centro-dorsal
plate from which arise a number of claw-like jointed organs, the cirri.

Soon after this, the body with its now long arms, breaks off from
its stalk at a point just below the centro-dorsal plate, and enters
upon adult life, free at will either to creep amid the mud or
rocks, or to swim with rythmic beats of its feather-like arms through
the water. It is however doubtful if it makes much use of its
powers. It certainly docs not travel far from certain favorite
localities, where it is usually found gripping stones or weed with the
circle of hooked cirri borne on the centro-dorsal plate. When
disturbed, its mode of swimming is extremely graceful, the arms being
alternately contracted and expanded as in the pulsations of a medusa.

For long, the stalked larva wras considered a distinct animal
from the adult, receiving the name Pcutacrimts ctnoprens, as it was
believed to be a tiny relative of that large and lovely stalked crinoid,
Pcntacrinus caput-mcdnsm, from the Antilles, then known from rare
specimens held precious by a few fortunate museums.

Special interest attaches to this beautiful creature from the great
part played by its relations, if not its ancestors, that lived during former
periods of the world's history, for the Encrinites whose remains have

80 MICROSCOPICAL STUDIES.

contributed so greatly to build up the huge masses of our mountain
limestones, and many of our Jurassic beds, were but gigantic
Pentacrinoids of structure practically identical with the stalked larva1
of Antcdon that seem so like tiny attenuated counterpart?.

STUDY XVII. — CRESELS, A TYPICAL PTEROPOD.

The struggle for mastery and bare existence gives many
unexpected results : we see the huge monsters of ocean, not of
true finny lineage, but interlopers from the land ; we see the cousins
of our starfishes and sea-urchins taking on the outward form of
burrowing worms; insects become, in appearance, indistinguishable
from sticks and leaves ; birds leave their kingdom of air, and pursue
their livelihood amid the waters, seeking prey by diving and swim-
ming ; but perhaps stranger than all, the butterflies of ocean, whose
winged and shimmering myriads are familiar to voyagers on the high
seas, are nowise akin to the gaudy visitants to our flowers : neither
have they relationship, as we might excusably guess, with the great
group of the Crustaceans. The latter, diverse as the insects in habit,
and ready as they, to change form, and to adapt themselves to any
new life where there may be a prospect of easier existence, yet put in
no claim to the title, and it is reserved to the humbler molluscs — to
creatures allied to the slow creeping snail, and lethargic limpet — to
furnish representatives charged with the duty of peopling the waves
with gay flutterers. Yes, the Pteropods, as the Butterflies of the Sea
are called, are undoubted molluscs, closely related on the one hand to
such Gastropods as the snail, on the other to the Cephalopods — the
Octopus and Cuttlefish. But before discussing their place in Nature,
let us examine the anatomy of the typical form, Creseis acicula
(Rang), which is the subject of this paper.

Creseis is the most slender, but not the shortest of Pteropods.
The body is lodged in a delicate needle-shaped shell (whence the
name aciculci), not f-in. in length. This shell, transparent and
colourless, and composed of carbonate of lime, is very gradually
tapered and extremely narrow, even at the broader end. The pointed
end is closed, while from the other protrude two liny wing-like fins,
the means of locomotion — hence the significance of the term Pteropod
or " wing-footed." Coinciding with the form of the shell, the body is
greatly elongated, especially that part lodging the central portion of
the viscera — the visceral hum]) <.r dome, which is spoken of as the
upper end of the animal (see last paragraph of this article). The
shell is lined and produced by a told of the body-wall, called the
mantle, between which and the body, a large space, the mantle cavity,

THE ANATOMY OF A PTEROPOT). 81

is formed, lying on the posterior aspect of the body, and opening to
the exterior by a slit at the ventral end, i.e. at the mouth of the
shell/1)

There is no distinguishable head, and of head appendages only
two tiny, easily overlooked tentacles lying just behind the fins.
These have evidently suffered degeneration, showing in their minute
size, but little resemblance to the great organs so familiar upon jthe
head of the snail.

Two slight eminences guard the entrance to the mouth. Within
this a radula or teeth-bearing ribbon is found, whence a long
oesophagus leads straight backwards or rather upwards, into a dilated
stomach. The intestine is continued backwards for some distance,
then abruptly turns and passes forwards (downwards) to open laterally
into the mantle cavity at a point on the left side.

Lying close to the intestinal bend, is the anterior end of the
enormous sausage-shaped secretive organ which for convenience we
may term liver (I). It runs backwards parallel with the anterior
half of the ovo-testis.

As regards muscular tissue, such is developed sparsely except in
the fins, and in a great strand of fibres that originates from a point
only a little below the apex of the shell, runs parallel with the
ovo-testis and liver, thence forward and to the right, to the oral
end of the body, and to the copulatory organs. Its name, the
retractor muscle, denotes its function.

On the right side, in the region of the intestine, lies an elongated
cylindrical organ, the nephridium or kidney. This has at one
end an opening communicating with the exterior, while at the other
— the end turned towards the apex of the visceral hump — a passage
is found leading into the pericardium. Probably this is a means for
introducing sea-water into the blood at stated intervals, thus giving
an additional and interesting function to the nephridium.

The heart, lying dorsal to the nephridium, and like it, on the
right side of the body, consists of a globular ventricle and of a
delicate auricle. From the former a large artery is given off, leading
into several smaller branches. These however, instead of in turn
leading into capillaries and thence into veins, open into an irregular
chain or network of indefinitely shaped spaces (lacunae) disposed
in the tissues, and without definite walls. From these the impure
blood is gathered into a large venous or pericardial sinus, whence it
is passed into the auricle.

(1). To arrive at the right application of the terms dorsal, ventral, anterior, and
posterior, to the body of a Pteropod, one must picture it as in fig. G, PI. XIII, the
mouth downwards and the apex of the shell directed upwards.

82 MICROSCOPICAL STUDIES.

The respiratory region in this species lies on the inner side of
the mantle, therefore on what is apparently the ventral aspect of the
animal, but which strictly is the posterior. In some species the
general surface of the mantle functions, but in this, the chief seat of
respiration is a shield-shaped area in the region of the stomach,
where the mantle is thrown into curved and transverse folds, bearing
cells richly ciliated, whereby the water is kept continuously in
motion.

The central mass of the nervous system is formed by the
concentration of three pairs of ganglia around the anterior end of the
oesophagus ; that part lying above, representing the supra-oesophageal
ganglia ; that beneath, of two pairs, named respectively the
visceral and the pedal ganglia. Nerves going to the mantle and
to the alimentary organs can readily be traced proceeding from the
hinder part of the nerve-mass, but in size, these are far surpassed by
two enormous nerves (/. n.) given off, one on either side, by the pedal
ganglia, for the nerve supply of the swimming fins. Each on entry,
throws off a smaller branch, and then proceeds to give off with
remarkable regularity, some 20 pairs of lateral nerves at short
intervals. Each pair consists of a right and a left nerve originating
from the same point. The same arrangement is repeated by the
smaller branch.

For so small an animal, the reproductive organs are extremely
complex and are complicated by the creature, like all Pteropods, being
hermaphrodite. Ova and spermatozoa are produced in the same
gland, the ovo-testis or hermaphrodite gland. This lies, as a compact
elongated mass, in the hinder (dorsal) end of the body, parallel with
the liver. It is connected by a fine efferent duct with the sexual
orifice which opens on the right side just dorsal to the base of the
right fin. Connected with the lower end is a side pouch — the uterine
caecum. Another pouch-like organ of equally great size, opens close
by the genital aperture, and just at the base of the right rudimentary
tentacle (p. g.) This is the invaginated (indrawn) penis or ponial
gland, the external male sexual organ, highly specialised as in the
gastropod molluscs, and here as in other Pteropods, of very large sixr.
The spermatozoa pass from the common sexual orifice to the penis by
a short ciliated external gutter or furrow (c. /.) Self fertilization is
obviated by the male and female elements maturing at different
periods. When copulation with another individual takes place, the
great penis is evaginated and inserted into the uterine caecum, the
spermatozoa pass in, and thence are conveyed to a small vesicle, the
receptaculum seminis, there to await the arrival of mature ova from the
hermaphrodite gland. When this occurs, the sperm escapes from its

THE FOOD OF WHALES. 83

confinement and fertilizes the ova, which are then ejected in long
gelatinous cords that float hither and thither at the mercy of the
waves till hatching takes place.

Adult Pteropods all progress by jerky flappings of the wings.
Agassiz says they can remain suspended in the water for hours,
simply by spreading these wings, and then suddenly drop to the
bottom by folding them. They are also said to creep about bjnrreans
of these same appendages.

The group of Pteropoda is not large, and its members fall
naturally into two well marked divisions — those like Creseis, with a
well developed shell, form the order Thecosomata ; those naked and
without shell, the Gymnosomata. Few are ever seen near land, they
prefer the high seas, and are spread under all latitudes, little more
plentiful in the Tropics than in the Northern regions of Baffin's Bay
and Davis Strait and the Polar Sea generally — where indeed the
multitudes of two species, Clione borealis and Limacina arctica,
form a substantial item in the dietary of the whale.

In considering the place in nature of these animals, the possession
of an odontophore (lingual ribbon or radula) at once discovers their
close relationship to the Gastropods and to the Cephalopods, and with
these and the little group of Scaphopods (Dentalium), form the com-
pact branch, Glossophora, ("tongue-bearers"), of the phylum Mollusca.
(a) In the arrangement of the genital system, the Pteropods are
extremely like many forms of hermaphrodite Gastropods ; the snail
and the sea-slug (Aplysici) for example, agreeing closely in all the
larger details, while in this, they differ markedly from the Cephalopoda,
where the sexes are always separate. (6) Outwardly usually bilaterally
symmetric like the Cephalopods, Pteropods are all fundamentally
asymmetric, and here again approach to the most usual Gastropod like-
ness, for as in the latter, both the anus and the sexual organs are lateral
and asymmetric, the one in Creseis being turned to the right, the others
to the left, (c) A third link with the Gastropods is found in the
possession by certain genera (Spirialis) of an operculum. (d) On
the other hand, Pteropods of the shell-less group, have processes
developed from the " head," of arm-like form ; in some cases even
bearing suckers — a wonderfully close approach in appearance to the
familiar arms of the Octopus and the Cuttlefishes. So close, indeed,
is this resemblance, that Prof. Ray Lankester has not hesitated to
class both Pteropods and Cuttlefish in one all-embracing division, the
Cephalopoda, forging a new term, Siphonopoda, for the diverse com-
pany of the Octopus, Nautilus and Cuttles. Such considerations as
a b and c make against this view, and it is significant that the nerve
supply to these head-arms has different origin in the two divisions,

84 MICROSCOPICAL STUDIES.

being supplied from the brain (cerebral ganglia) in the Pteropods,
and from the pedal or foot ganglia in the Cuttles. Hence it seems
much more likely that the resemblances between the Pteropods and
Siphonopods are rather homoplastic than homologous, i.e., have arisen
independently rather than being possessed of common origin. Like
circumstances not infrequently produce analogous shapes and organs
in animals of distant relationship, and the case in point is probably
of this nature. It is to be remembered too, that it is only the division
of shell-less Pteropods that in any way simulates the appearance of
the Siphonopods; the shell-bearing forms (Thecosomata), such as
Creseis, are very closely approximated to the Gastropods in all details
of organization. Thus we may conclude that the Pfceropods aiv a
branch from the Gastropod stock, modified by pelagic habit, and in
some respects even degenerate (i.e. degenerate from the stand-point
of the Gastropod) and having their most specialized members approx-
imated in outward form to the Siphonopod type. As to this latter
designation, it appears thus more fitting to displace it and to restore
the term Cephalopoda to its older and more restricted meaning
whereby it is applicable to the Octopus class alone.

The diagrams PI. XIII, figs. D to H (modified from Lankester)
show graphically the mutual relation and modification of the several
parts of the body as seen among the principal types of Glossophorous
Molluscs. Fig. D shows a simple type of Gastropod, such as Chiton,
where the mouth and arms are at opposite ends of the body, the foot
large and extending the whole length of the body on the ventral side,
while the central part of the back is more or less humped — forming
the visceral hump or dome, as in it most of the viscera are lodged,
Fig. E indicates the modifications in the relative arrangement of parts
due to the bending and coiling of the visceral hump, as seen in such
Gastropods as the snail and the whelk. G and F represent respec-
tively a shell-bearing and a naked Pteropod, and show how in these
animals the visceral dome is much elongated and drawn out, causing
thus a great bend in the alimentary canal. The foot in both is
represented by little else than two wing-like fins, believed to arise
from two lateral flaps — epipodia — of the middle division of the foot-
In several Gastropods, such flaps are well developed ; thus in the
sea-slug Aplysia, they rise from either side of the foot and fold over
the back. In F, the " head-arms " or " buccal cones," that are so
curiously like the arms of Cephalopods, aiv represented, but are not
here shaded similarly as having a like origin for the reason already
given.

Fig. H is a diagram of a Cephalopod given for comparison.
Here part of the epipodia (?) form arms beset with suckers in place
of swimming fins, while the funnel is also formed from part of the

CLASSIFICATION OF PTEROPODA. 85

ancestral foot. The figures also illustrate the true application of the
terms dorsal, ventral, anterior and posterior to the body aspects in
Pteropods and Cephalopods.

It may now be useful to give a summary of orders and other
divisions, and in so doing, to follow, merely for the sake of con-
venience, the former method of separating the Pteropods as a distinct
Molluscan class. It must, however, be clearly borne in mind that
the present and more satisfactory view is to cancel entirely the
division Pteropoda, and to distribute its families among the Gastro-
poda. The name Pteropoda will thus henceforth be a term of
convenience used to designate a number of pelagic molluscs, in-
cluding animals belonging to widely separated divisions of the
Gastropoda.

Pteropoda.

Order I. — ThecOSOmata ; body protected by a shell.

Family I :— HYAL.EIDJE, shell calcareous or horny, symmetric. Types —

Hyalaea (horny) ; Creseis (calcareous) ; Cleodora.
Family II :— CYMBULINID^E, shell slipper or boat-shaped and with some

short " arms." Types — Cymbulia and Tiedemannla.
Family III : — LIMACINIDJE. Type — Spirialis, with spirally coiled shell

having sinistral flexure, i.e. coiling in the reverse direction

to that usually seen in Gastropod Shells.

Order II.— Gymnosomata ; body naked.

Family I :— CLIONID.E, without gills, but with short arms devoid of suckers.

Type — Clione (Clio) borealis.
Family II : — PNEUMODERMONID.E, with gills at apex of body, and with arms

beset with suckers. Type—Pneumodermon.

Cleodora pyramidata is phosphorescent and probably others
are also. In Cymbulia, the small chitonous shell is internal. Spi-
rialis is the most closely related to the Gastropod form, its pecu-
liarities extending to the possession of both a spiral shell and an
operculum. The larvae or veligers of Cymbulia and Tiedemannia
also possess opercula.

Tiedemannia, like the Cephalopods, possessed well developed
pigment-spots (Chromatophores) on the surface of the body, doubtless
a protective device.

geries IV,

STUDY XVIII.— THE CORYNID.E.

The family Corynidse, in its inclusion of the two distinctive
genera Ooryne and Syncoryne, furnishes a perfect object lesson in
the gradations of development that prevail among Hydroid Zoo-
phytes ; ranging from that fullness of development characterized by
definite and distinct Hydroid and Medusoid stages, down to the utter
suppression of the latter stage and its replacement by what are mere
sessile bags containing the reproductive elements — degeneration of
the most marked description. Such gradations are always of great
interest and value to the evolutionist, for though the series is
one of degeneration rather than of progress upwards, still, it bears
conclusive evidence of the readiness and ease with which organisms
can undergo radical alteration in vital and conspicuous organs, and if
a species can so easily retrogress, the inference that others may as
readily advance by the elaboration of new organs, is logical and
reasonable.

Intimate knowledge of a representative species in each of the
two genera referred to, is readily obtained, for both Coryne and
Syncoryne are present on many parts of the British Coast.

Syncoryne, which, of the two, has the more typical life-cycle,
grows in littoral pools in low bushy colonies, comparatively little-
branched, and with a creeping stolon connecting the various main
stems. The latter, in S. eximia, are brown and horny, and annulated
only towards the base ; the twigs on the other hand are closely ringed,
transparent and colourless.

The polypites are not seated in cups at the extremities of the
branches as in Obelia, but are naked and without any protective
envelope into which they can retract upon irritation. As a natural
compensation, or rather adaptation, the polypites are much larger
and stouter, and their tentacles better equipped with stinging cells.
Some slight suggestion of a cup is, however, present, as the edge of the
chitonous tube which forms the branchlet is expanded slightly as a
very delicate tiny chalice at the very base of the polypite. It is
however of absolutely no use as a protective sheath, both on account
of its extreme thinness, being cuticular rather than horny or chitinous,
and on account of small size, only J*.1.1 of the length of the polyp.

NEMATOCYSTS. 87

Indeed in specimens mounted in balsam, it is so transparent as to be
most difficult to see. The polypites, while possessed of as great
retractile power as those of the Thecate Zoophytes, have not the
same rapidity of movement, and answer to a stimulus or irritation
much more slowly.

Among the Calyptoblastic Hydroids, the hydranth or polypite
is usually cup-shaped, with the tentacles arranged in one_or more
rings around the mouth. In Syncoryne, the body is as a rule
spindle-shaped, though by elongation it may at times appear almost
cylindrical ; while the tentacles are disposed irregularly over the
whole surface, standing out stiffly, so many spikes on a war-club.
The form of the tentacles, too, is peculiar, each being swollen at the
extremity — capitate — a characteristic shared by Syncoryne and
other members of the family. The reason for this capitate form is
not far to seek : it owes origin to the peculiar grouping or massing
of the nematocysts at the apex — a striking divergence from the
prevalent arrangement among other families, where the collections or
batteries of stinging cells are situated at intervals on the general
surface of the tentacles. It is interesting to note that the tentacles
of the medusa-stage of Syncoryne have the ordinary arrangement of
stinging cells at intervals along the length, i.e. without any suggestion
of the massing seen in the tentacles of the Hydroid stage.

Viewed with good illumination, the unburst stinging-cells can
readily be observed in the terminal knobs as more or less lenticular
bodies, and by judicious squeezing of a living polypite, some of these
may be pressed out, and a number will be certain to project the long
whip-like process which serves as the active agency in conveying the
poisonous secretion of the cell into the organism against which it is
launched.

The isolated undischarged nematocyst can be made out to be a
cell of unusual size, somewhat ovoid in shape, and in which the most
conspicuous content is a great clear cyst, highly refractive, and filled
with a clear fluid, lying wherein is a spirally coiled filament. The
cyst does not occupy the entire cavity of the parent cell, but leaves
a space, most marked towards the base, filled with dense protoplasm,
in which lies a well-defined nucleus. From the apex of the cell
projects a pointed process of the cell wall, named the ''trigger"
and which functions as such on contact with a suitable body
(prey). It appears to stimulate the cell to a contraction, resulting in
the violent expulsion of the sting thread. The thread thus expelled
is not solid but is hollow, and in reality a tenuous prolongation of the
upper end of the cyst. It arose as an ingrowth or invagination of
the summit of the cyst, and when projected went through an instan-
taneous process of evagination, i.e. was turned inside out as the

88 MICROSCOPICAL STUDIES.

finger of a glove can be turned, and if we remember that the content
of the cyst is a watery fluid under considerable tension, one can
easily understand that if this tension be greatly and suddenly
intensified by pressure upon the walls from without, an instantaneous
throwing out of the ingrown hollow thread must ensue.

A working model of such a cyst can be made of india-rubber
tissue, if fashioned in the form of a hollow bulb with the apex dwin-
dling down into a finger-shaped hollow appendix. If this hollow
model were partly filled with water and the filiform apex thrust
inwards (invaginated), then by squeezing the bulbous part, the
pressure of the contained water would force outwards the invaginated
finger — the equivalent of the hollow filiform thread of the nematocyst.
In the Corynidae, the base of the thread is stout and furnished with
barbs.

The stem of the tentacle is formed as in Obelia of a solid
core of vacuolated stiff-walled cells of endodermal origin, that act as
a supporting axis. The ectoderm is thin, but furnishes very delicate
yet powerful muscle elements that control the elongation and re-
traction of the tentacles.

The mouth that is fed by these ministering and food-capturing
tentacles is small and terminal and difficult to distinguish, appearing
as a mere opening at the anterior end of the polypite. The large
cavity of the polypite is where digestion takes place, the endoderm
cells of this region secreting a fluid which rapidly dissolves the tissues
of the prey. Thence this nutrient fluid is passed along the hollow
ccenosarc to aid in the sustenance of the general body of the colony.

Reproduction. — Normally Syncoryne produces buds at various
and indefinite points scattered over the body of the polypite and
between the tentacles. These buds at first consist of a layer of
ectoderm covering a hollow button-like outgrowth of endoderm. Next
this endoderm projects four hollow radial processes which ultimately
become the four radial canals of the Medusa, into which the bud
eventually develops. At the same time a median outgrowth of
hollow endoderm, the future manubrium, grows down between the
four radial bands.

With growth the form becomes distinctly bell-shaped, the
four marginal tentacles appear associated with the four radial canals,
and a pigmented eyespot — ocellus — develops at the base of each
tentacle. Thus, little by little, the bud changes into a well marked
medusiform organism connected to the polypite by a narrow neck.
At this stage the medusiform bud is usually nearly as large as the
polypite itself. At length, it begins to pulsate, to long for separate
and free existence, and its efforts quickly effect severance from the
mother polypite.

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EXPLANATION OF PLATE IV.
The Corynidce.

Fig. 1. Syncoryne eximia, natural size of colony.

Fig. 2. Normal hydranth of same showing developing niedusiform
persons, mbl to mb5, in various stages, disposed irregularly
between the capitate tentacles ; mb5 is the oldest and is
all but ready to be set free ; pr. perisarc. X 30.

Fig. 3. A free medusa (Sarsia) of Syncoryne, fully mature (probably
two months after being set free) ; m. manubrium, within
whose walls sperm has been developed, this individual
being a male ; i.e. a captured Copepod being digested
within the cavity of the manubriurn ; r.c. radial canals ;
c.c. circular canal ; e.s. eye-spot or ocellus ; o. mouth ;
v. velum ; t. tentacle. X 4f.

Fig. 4. Hydranth showing abnormal medusiform person, a.m.b.,
wherein, while the bell is fully developed, the tentacles
are aborted, and the manubrium functions solely as a
reproductive organ (in this case, a spermarium). The
bell remains permanently attached and the reproductive
products are ripened in situ ; d.m.b. developing medusa-
bud ; e.s. eye-spot ; p. perisarc ; c. coenosarc ; o. mouth.

Fig. 5. A row of axial endoderm cells from a tentacle of Syncoryne.
X 180.

Fig. G. Colony of Coryne vaginata, nat. size. (The annulations

of the stem are not visible to the naked eye, in living

specimens).
Fig. 7. Hydranth from a male colony of same species ; in.g. male

reproductive capsule, representing a degenerate medusa.
Fig. 8. Hydranth from a female colony; f.g. female capsules filled

with ova ; t. tentacles ; n. stinging threads of nematocysts ;

o. mouth ; c. tiny membraneous cup at the base of the

hydranth. X 30.
Fig. 9. Nematocysts from tentacle of Coryne vaginata, X 600.

A & C, two burst nematocysts, showing barbs (6.) in different

positions ; th. the evaginated threads ; B, an unburst

nematocyst, showing the trigger (t), and the coiled thread

lying within the cyst (c) ; n. nucleus.

EXPLANATION OF PLATE V.

Figs 1 to 8, Cirripedia.

Fig. 1. Sacculina carcini (Thomps.) seen in plan, showing by
means of the dotted outline of the crab upon which it is
parasitic, the manner in which the root- tubules ramify
through the host's body. Natural size.
b.s. body-sac of Sacculina ; cL cloacal opening ; b.m. basilar
membrane ; i.r. the roots which ramify around the
intestine and the associated organs ; h.r. hepatic roots
ramifying among the caeca of the liver ; br.c. branchial
cavity of the host.

Fig. 2. Lateral view of same.

Fig. 3. Life appearance of Rock Barnacle (B. balanoides), enlarged.

Fig. 4. The same seen from above, «, 6, c, d, e, and /, the six
plates making up the circular mantle " rampart."

Fig. 5. Dissection (partly diagrammatic) of B. balanoides , the right
half of the mantle-wall removed ; the " liver," cement
gland, and branchiae are omitted ; the alimentary canal
is depicted black ; for clearness, the male organs are not
lettered, but reference to Fig. 7 will indicate their parts.

Fig. 6. A Ship-Barnacle (Lepas) having the right side of the mantle
removed. The penis should not be apparent, as it lies
normally folded up between the cirri.

Fig. 7. Dissection of same, on the lines of Fig. 5.

Fig. 8. External appearance of Lepas anatifera, natural size.

Lettering the same for all the figures : — a remains of the

anterior antennae ; an. anus ; a.m. adductor muscle ; c. carina ;

c.f. caudal forks ; e.g. cement gland ; cr. cirriform feet ; c.s. calcareous

rampart-shell of mantle ; f.a. filiform appendages of 1st pair of feet ;

h. liver ; I. labrum ; m retractor muscle of scutum : m" retractor

muscle of tergum ; m.c. mantle cavity ; od. oviduct ; or.c. buccal

eminence ; o. mouth ; ov. ovary ; p. penis ; pd. peduncle or stalk ;

s. scutum ; t. tergum ; ts. testis ; v.d. vas deferens ; v.s. seminal

vesicle.

Figs A to D, Plumularia pumila.

Fig. A. Branches of P. pumila, slightly larger than life. g. gonangia ;

8. creeping stem or stolon connecting the various bundles.
Fig. B. Portion of branch, highly magnified, hydranths or polypites

in various stages of extension ; k. body of the hydranth ;

Jd. hydrotheca lodging hydranth ; g.c. gastric cavity of

hydranth ; c. coenosarc ; c.c. cavity of the coenosarcal tube ;

pr. perisarc ; z. tissue connecting hydranth with lateral

and internal surface of hydrotheca ; ec. ectoderm ; en.

endoderm ; d.hc. developing hydrocaulus or stem ; d.h.

developing hydranth.
Fig. C. Female gonangium ; bl. blastostyle ; c. swollen hollow apex

of blastostyle nearly ready to force its way through the

mouth of the gonangium ; ov. ova.
Fig. D. The same fully developed, showing the acrocyst containing

ova. (After Lindstrom).

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REPRODUCTION OF THE CORYNID^. 89

Once freed, it begins a long, free-swimming existence and rapidly
increases in size till it reaches fully J-in. in length. The manubrium
in this species attains enormous proportions — sometimes, when fully
extended, quite thrice the length of the bell. In this and allied forms
(i.e. among all the Gymnoblastic Hydroids), the genital organs
appear in the walls of the manubrium of the medusa. The sexes
are separate, and the embryos that are produced settle tlown and
develop hydroid stocks or colonies.

I have said that the foregoing is the normal course of repro-
duction— but certain species, and among others that under present
consideration, S. eximia, have an alternative mode. This however
is practised only at the end of the breeding season (April) when the
reproductive buds, in place of developing into free medusae (Sarsia,
as this form of medusa was called before it was recognised as one
stage in the life-cycle of this Hydroid), remain permanently attached
to the hydroid stock. In form they have the same bell shape
as the true medusa-buds, but they seldom produce tentacles
(stunted when produced), and the manubrium becomes enormously
swollen with the reproductive products. The lack of tentacles is to
be adduced to the fact that owing to the permanence of attachment
to the parent, all nutritive matter is obtained from that source, and
the manubrium has no call to act as a digestive organ, but simply
as a reproductive gland.

The next and final stage of degeneration is found in such forms
as constitute the genus Coryne, of which the lovely species C.
vaginata, grows luxuriantly in Jersey rock-pools and gullies — where
it forms elegant branched colonies that appear miniature shrubs,
crowded with delicately tinted pink florets. Both the main stem and
the branches are hornv and closely annulated. In the details of the
anatomy of the polypites there is practical identity with those of
Syncoryne. In Coryne, however, the polypite is considerably larger,
but it is solely the divergence of the reproductive plan that entitles
this species and its congeners to the dignity of a separate genus.

The colonies are again unisexual, some bearing only male
buds, while others bear female ones. These appear as numerous
rounded bodies clustered on the polypites between the bases of
the tentacles. The male ones consist solely of masses of cells —
spermatoblasts — which produce spermatozoa ; while each of the female
buds becomes filled with 20 to 25 large ova. When the male
capsules burst, it is probable that the spermatozoa find their way
to the female organs, guided by some sense or attraction we know
not what, and pierce the membranous envelope, thereby gaining
admission to the ova. The latter, thus fertilized, by segmention form
tiny embryos, which issue forth as four-armed hydriform larvae, that

90 MICROSCOPICAL STUDIES.

crawl about like so many miniature Octopods. This free life is rapidly
run and then they settle down and become attached to rock or weed.
In this situation they rapidly reproduce, by continued budding, the
typical hydroid stock. Here, then, there is no trace whatever of
medusae, whether fully developed as free-swimming organisms, or
bereft of a free existence and tied for life to the mother polypite :
nought is left of the medusa-stage save the reproductive organs,
and as these are, among the Gymnoblastic Hydroids, situated in the
walls of the manubrium, we may homologize the sexual buds of
Coryne, with the manubria of such medusa?.

As Obelia may be taken as typical in every sense of the
Calyptoblastic Hydroidea, where the polypites are lodged in
cup-like expansions of the horny perisarc, the medusa? usually
provided with otocysts (rarely with eye-spots), and the genital
glands developed upon the radial canals, so Coryne and Syncoryne
may be taken as the types of that other great division of the
Hydroidea, known as the Gymnoblastic — characterised by the
polypites being naked or athecate, the medusae, when produced,
provided with eye-spots (ocelli) and never with otocysts, and
with the genital glands lodged in the walls of the manubrium, and
not in the course of the radial canals.

To the student of the smaller forms of marine life, the stems
of the Corynidae offer endless material for research, so abundantly
are they clothed, at times, with a fluffy growth that under the
microscope is revealed to consist of multiform Diatoms, lovely in the
delicacy of their glassy sculpturing and in the rich hues of the living
matter within them ; of more minute Infusorians, the cups, and bells
and tassels of those that live their lives attached, and still smaller
forms, cilia-rowed and free-swimming, that speed and rotate and take
eccentric course among the miniature undergrowth upon the crowded
stems ; here and there too, can be spied a slow-crawling Foraminifer
whose porcellain-white shell gleams brilliantly, while from innu-
merable pores stretch living threads along which hurry, this way
and that, the tiny particles that are engaged in the life-building
of the tiny creature ; the stout bobbing heads of that curious Polyzoon,
Pedicellina, are frequent, curtseying and bowing to one another,
with old world homage ; to the keen-eyed, interesting forms of
Rotifers, so rare in the sea, may occasionally reveal themselves spin-
ning erratic course through the water or climbing about with jerk
and double among the rich growth of the tiny algae that form never-
theless the giants of this tiny microscopic forest.

None of these can be accounted parasites ; they occasion no
harm to the host and simply live together — a crowd of commensals.

SERTULARIA PUMILA. 91

A true parasite, however, sometimes afflicts colonies ofSyncoryne,
as one of the curious Pycnogonida? (sea-spiders) makes use of the
developing buds as incubatory sacs, wherein their larvae may develop.
How the ova are deposited in the Zoophyte is unknown — but as the
larva? are only found in young buds, it is likely that these are selected
as being without the hard perisarc which is present at other parts
of the colony and which would render an incision difficult. Probably
the Pycnogonid breaks a hole in the crown of the bud and introduces
therein the ova. The effect is to arrest normal growth and to convert
the bud into a "gall" — wherein the larva? live, nourished by the
nutrient fluid of the ccenosarcal tube, a branch of which penetrates
the bud. In due season the larva? burst from the gall and become
free.

STUDY XIX. — ON SERTULARIA PUMILA.

Just as Obelia genicidata forms miniature forests on the broad
leaves of Laminaria (oar-weed) at a horizon seldom left bare except
at very low tides, so another species of the Hydroidea, Sertularia
pumila, in favourable situations, monopolizes the fronds of Fucus
at a zone some feet higher. Ellis, the worthy pioneer in our know-
ledge of these forms, named it the " Sea-oak Coralline," an appropriate
name, and one suggestive of the strong, stunted and rather coarsely
denticulated appearance it assumes when removed from the water.
It seldom attains luxuriant growth ; most frequently it is barely
f of an inch in height and as it retains the same breadth from base
to apex and is hardly branched at all, it has an incomplete and
truncated appearance that does not make for gracefulness.

Occasionally, however, it grows to the height of an inch and a
quarter and is then beautified with several branches arranged
symmetrically in pairs.

In texture it is horny, owing to the perisarc being strongly
chitinized. Examining a living branch in water under a low power
of the microscope, we forget its apparently coarse nature in the
loveliness of the expanded polypites. They are exquisite in their
slenderness, and have a great power of protrusion. Equally long
and graceful are the hyaline tentacles, a living rosette that surrounds
in a single wreath the broad and button-shaped proboscis, whose
summit breaks into a large and mobile mouth. The cups (hydrothecae)
that lodge these polyps are paired, one on either side of each segment
or internode in the stem. Somewhat tubular in form, each cup is,
at the lower end, pressed to the side of the stem internode, while
the upper extremity is free and bends outwards, so that each pair,
with their stem internode, form a V-shaped figure. The aperture

92 MICROSCOPICAL STUDIES.

of each hydrotheca is somewhat narrowed and sculptured into points
— mucronate. The body of each poly pi te is nearly cylindrical
(compare with the cup-shaped body in Obelia) and has a special
bundle of retractile fibres inserted on the outer surface of the body,
some little way beneath the tentacles on the side turned towards
the axis of the stem. Thence they pass inwards and slightly down-
wards to become attached to the wall. of the hydrotheca where fused
with the stem perisarc. By contraction these fibres energetically
assist in the retraction of the polypite.

The body wall of each polypite, as also the coenosarcal tube,
consists essentially of a simple ectoderm layer separated from a
ciliated endoderm by a delicate supporting lamina.

The endoderm is usually separated by a space from the investing
perisarc, except at the base of each hydranth and at the points where
growth is taking place.

The perisarc is a secretion of the ectoderm and thus, where a
polyp bud or a new branch is originating, the ectodermal cells are
of enormous size. As the perisarc is completed the ectodermal cells
dwindle and shrink away from it.

The special growth of the branch is as follows : — the perisarc
between the two terminal hydrothecse becomes absorbed and the
blind termination of the ccenosarc pushes through ; next, this throws
out a hollow bud on either side. In these three buds, the ectoderm
is very thick and active and rapidly forms a layer of perisarc, the
lateral buds becoming hydranths, the median, an internode of the
hydrocaulus or stem.

The branches bear in their number a direct ratio to the
abundance of nutriment and other favourable life conditions ; when
present, they have always one definite point of origin, and that is,
from the hydrocaulus just beneath the base of a hydrotheca. There
the perisarc is absorbed and the ccenosarc pushes out a tiny bud
which in further development repeats the process of apical growth
already described.

The tentacles have the same structure as in Obelia.

Eepr eduction. — In the breeding season numerous large ovate
sacs — the gonothecaB or gonangia appear here and there on the
main stems and branches. Their origin is similar to that of the
branches, by absorption of the perisarc and thrusting out of a hollow
bud of coenosarc. These sacs produce in due course the reproductive
elements.

The sexes are separate and in separate colonies. Male gonangia
can usually be distinguished from female by their shape — the
former being regularly oval, the latter irregularly ovate.

THE CIRRIPEDIA. 93

The prolongation of the coenosarc into the gonangium is termed
the blastostyle. This fills but a small space and is little more than
a narrow column in the centre. In its walls arc developed sperm or
ova as the case may, be, and thus while it (the blastostyle) represents
really the medusiform person, the medusa itself is entirely abortive,
the reproductive organs alone being retained.

Fertilization takes place as in Coryne, and then a peculiar
occurrence takes place. The apex of the blastostyle gradually
expands into a hollow globe with gelatinous walls, which pushes its
way through the aperture of the gonangium to hang from the
mouth as a miniature bladder. Into this pouch, the acrocyst or
marsupium — the fertilized ova are passed and therein undergo
segmentation. They pass out as planulse — which after a short free
life settle down, and by the usual process of growth and budding
complete the life-cycle by developing new colonial organisms.

Sertularia obviously belongs to the Calyptoblastic or Thecate
Hydroids, the polypi tes being lodged in thecse, and it is significant
to note that it occupies the same relative position to Obelia in regard
to mode of reproduction, as Coryne occupies to Syncoryne among
Gymnoblastic Hydroids. In both Sertularia and Coryne there is
suppression of a medusiform stage. In Obelia and Syncoryne, free
sexual medusae are produced — a striking parallel.

From the geological standpoint, Sertularia is of considerable
interest, as it seems to offer the most probable relationship to the
curious Graptolites, those most abundant fossils of Silurian rocks ;
the short sessile hydrothecse of Sertularia, giving its stems a serrate
appearance, offering great suggestive resemblance to the denticulated
margins of the fossils in question.

STUDY XX.— THE CIRRIPEDIA.

Than the Barnacles or Cirripedes (" cirrus-footed "), few marine
animals are more familiar to dwellers by the sea ; the sessile forms
exist everywhere upon the littoral ; the stalked are known world-wide
as Ship-Barnacles, adhering to the bottoms of ships or to wave-tossed
timbers.

The greatest diversity of form is found in this order, from the
great stalked forms and the mollusc-like Rock-Barnacles, encased in
shelly walls, that cover in multitudes all high-tide rocks ; from
parasitic species, more or less degraded, yet endowed with optional
freedom, down to curious bag-shaped parasites whose lives are bound
up absolutely with that of the host, and through whose vitals their
ramifying roots bend and twist. All agree, however, in larval history,

94 MICROSCOPICAL STUDIES.

passing successively through those special phases known as the
Nauplius and Cypris stages.

The most primitive type is that of the stalked or pedunculate
forms, and of these, Lepas is the most typical genus. The young
of this, emerge from the egg as very tiny Nauplii — minute larva?
furnished with but three pairs of appendages, all used at first as
swimming organs (Fig. 19, PI. viii, Vol. I). The two anterior pairs
represent the two pairs of antennae while the third pair ultimately
become the mandibles in the adult. The first pair of these limbs
are simple ; the others are biraniosc (two-branched). One eye,
unpaired and median — the Nauplius-eye — is developed, and the body
is protected by a dorsal shield-shaped fold of integument, the broad
anterior margin produced on either side into a fronto-lateral horn.
Mouth, alimentary canal and anus are present, and the creature feeds
eagerly. Frequent moults (ecdyses) take place, and with each such
change, important additions are made to the number of the organs
and appendages ; a series of segments are produced posteriorly,
destined to form the adult thorax ; limbs sprout from these, and a
compound eye appears on either side of the Nauplius-eye.

At last a moult occurs when a larva quite different to any of the
preceding Nauplius gradations issues from the old skin. In this
new phase the larva has the general form of an Ostracod — hence is
called the Cypris-stage — being provided with a bivalve shell,
composed of two oval convex valves, open along the ventral edge,
within which the entire body and its limbs can be retracted. All
three regions of the typical crustacean body, head, thorax and
abdomen, can be traced (Fig. 24, PL I). The thorax has six strong
limbs, while the abdomen, short and insignificant, possesses but a
single pair. Of the appendages of the head, the second pair repre-
senting the posterior antennae— have' disappeared, while the third
pair are reduced from their former important biramose character to
small mouth organs — the mandibles. Tiny swellings, that ultimately
become the first and second maxillae, are also to be seen. The first
antennae on the other hand, increase in size and become provided
with a bell-like sucker on the penultimate joint, and on this sucker
opens a cement-producing gland. The larva now ceases feeding,
much food reserve appearing as oil-globules, especially at the anterior
end of the body.

The time has now arrived for the assumption of adult life, and
this is set about by the larva attaching itself — preferably to some
floating body — by means of the suckers on the first antennae. Next
the cement glands pour out their secretion at the same spot, and
embed the anterior end of the body firmly. The head region elongates,
becomes a mere stalk, the bivalve cypris-shells fall away, a chitinous

PI. VIII

¥ it?!

THEO. T. GROOM, on., AO NAT.

THE DEVELOPMENT OF BALANUS.

THE ANATOMY OF LEPAS. 95

fold of the integument grows around the trunk, and in the substance
of this mantle or pallial fold, five protective calcareous plates are
formed, one unpaired and the others paired. Early adult form is
now attained.

When fully grown and sexually mature, Lepas has the external
appearance shown in Fig. 8, PL 5. The anterior end of the head
has become a great wrinkled peduncle or stalk, terminated posteriorly
in a shelly pouch, the mantle, enveloping the main mass of the body
and open only along a slit on the ventral border. Of the calcareous
plates strengthening this mantle, the larger of the two pairs, situated
towards the insertion of the peduncle, are termed the scuta (s) ; the
other pair placed at the far end of the mantle sac, are the terga (t),
while the unpaired plate, the carina (c), is a long and narrow keel
and separates, on the dorsal aspect, the opposite plates of the terga
and the scuta.

Removing one side of the mantle, with its scutum and its tergum,
the actual body of the Barnacle is exposed — an obscurely segmented
fleshy mass, bearing conspicuous tendril-like limbs. What corresponds
with the typical Crustacean head lies before these latter, and is
divided into 3 regions ; the anterior lies without the mantle and is
the peduncle ; the median is short and narrow and being attached
to the mantle and connected along the inner surface with the peduncle,
forms an " isthmus " ; the posterior, the most important, is large and
fleshy, and bears the mouth and its organs.

Succeeding the posterior division of the head lies the partly
segmented limb-bearing thorax, and behind this again is found a very
small and rudimentary truncated abdomen terminating in two tiny
pointed processes. Tiny though it be, the abdomen is of importance,
for upon the dorsal surface is the anus, and it as well gives origin
to an organ many times larger than itself; an organ long, stout,
cylindrical, annulated and setose, that functions as the male copulatory
organ, and may be termed the penis. In life this organ is bent down
between the thoracic limbs, as shown in Fig. 5 (p), and not as
in Figs. G and 7, where it is straightened for the purpose of
clearness in the drawing.

Of the appendages of the head, the anterior antenna persist in
a very minute and attenuated condition, at the anterior end of the
peduncle, where they lie embedded in the attaching cement;
posterior antennae are absent, and the mouth parts are much reduced,
forming a small eminence surrounding the mouth. The parts com-
prise an upper lip or labrum with labial palps, two mandibles and
four maxillae, of which the hinder pair form a lower lip.

The thoracic appendages or feet, six pairs in number, are all
tendril-like, long, slender, many-jointed, and closely set with a double

96 MICROSCOPICAL STUDIES.

row of stiff hairs. Each is biramose, i.e. composed of two branches,
which arise from a single stout basal joint, the protopcdite.

Alimentary Canal. — The mouth opens into a short straight
oesophagus, leading into a capacious stomach, beset at the anterior
end with glandular diverticula (liver). Posteriorly the stomach
narrows gradually to merge into a long intestine, with anus opening
on the dorsal face of the truncated abdomen. Food is obtained by
the sweeping motion of the thoracic appendages, which by alternate
protrusion and retraction sweep inwards towards the mouth such
microscopical food as suffices.

The nervous system is limited to a paired cerebral ganglion
and a short ventral chain of 5 paired ganglia. Except a double pig-
ment-spot representing the eyes, no definite sense organs are known.
In the isthmus attaching the main body mass to the mantle, is
a strong transverse adductor muscle connecting the scuta of opposite
sides. By means of this, are controlled the opening and the closing of
the mantle cleft through which are protruded the cirriform feet.
Numerous other muscles are also found in the posterior head region,
chiefly concerned in controlling those movements of the body which
alternately elevate and depress the limbs and allow their sweeping
motion to perform at fullest advantage. In the walls of the peduncle
we also find strong muscles, having a longitudinal arrangement.

Reproduction. — Lepas is hermaphrodite, possessing both testcs
and ovaries. The former consist of ramified arborescent whitish
tubules lying along either side of the digestive canal and penetrating
even into the basal joints of the limbs. The product of these glands
is gathered into canals tributary to larger, which finally pour it into
two conspicuous milk-white seminal vesicles, whose vasa differentia
run separate almost to the base of the penis. At this point the two
unite and form a common ejaculatory duct passing through the penis.
The ramified ovaries, purplish in colour, lie within the posterior
portion of the peduncle, and the two oviducts (ov. Fig. 7) after
passing through the isthmus, open, one on either side of the head, at
the base of the first pair of thoracic feet — a forward position wholly
exceptional among Crustaceans where the usual position for the
female orifices is upon the first abdominal segment among the lower
forms (Copepods, &c.), while in the higher (Malacostraca), it is
constant to the antepenultimate thoracic segment.

The ova when extruded become cemented together into two
large purplish plate-shaped masses enfolding the main body region.
These plates are nearly always present, and on removing the mantle
are most conspicuous objects. Two small simple folds of the mantle
integument — the ovigerous frena — arising close to the isthmus,
furnish attachment to these ova masses, and prevent them being

THE ANATOMY OF BALANUS. 97

washed away. It is interesting to note that among the sessile
Cirripedes, the Balanidse, &c., these mantle folds are greatly
developed, and in some cases have their surface area increased by
further folding. Very probably their function under such con-
ditions is branchial, and we may be warranted in describing them as
branchiae.

As in all other Cirripedes, no distinct blood system can be
traced in Lepas.

The second common Cirripede type in our seas, is the little
Acorn-shell, or Rock-barnacle (Balanus). In larval history it is
identical with Lepas, but in external adult form, it presents a
wonderful contrast. Fleshy stalk has entirely disappeared and the
pallial sac, which lodges the body proper, is therefore sessile. Much
modification of the shelly plates of the mantle has taken place, the
parts being so arranged as to form a shelly palisade, wherein six
distinct pieces are to be traced, roofed in by two pairs of plates, one
pair representing the terga of Lepas, the other and larger pair, the
scuta. When the tide flows over these tiny creatures, a slit-like
opening between these opercular plates is revealed, through which
sweep in and out, with elegant motion, tiny feather cirri, the thoracic
feet (Fig. 3). With the receding tide, life-functions are partly
suspended, the cirri are retracted, and the scuta and terga are shut
down tightly, so as to retain some moisture till the tide returns.
Quite an appreciable noise is made in the tightening of the valves
when in this quiescent condition, and the low crackling murmur
heard when walking over rocks thickly coated with Barnacles, is very
familiar to me. Apparently the vibration of a heavy footstep is
perceptible to them, and lest it betoken danger, they take the
precaution of tightening their opercular valves, and in so doing form
some tiny water-bubbles, which in breaking give out sufficient sound
to be very noticeable when joined in by thousands of individuals.

In the anatomy of the body, apart from the mantle, there is
practical similarity to that of Lepas ; the main differences are that
the cement gland is greatly increased, the ovigerous frcna developed
into two large folds functioning probably as branchiae, while two special
and strong muscles are developed at either end of the rampart-like shell
to control the closing of the scuta and terga (m1 and m2, Fig. 5).
Yet another and more important difference is seen in the ventral
nerve ganglia being concentrated into a single large ganglionic mass.

The third type of Cirripede which I select, is as utterly unlike
either of the preceding as it is possible to conceive, appearing simply
as an oval bag without calcareous plates or even sculpturing, attached
to the under surface of the abdomen of crabs. From this external
sac penetrate into the interior of the host long branching tubuli,

98 MICROSCOPICAL STUDIES.

twining around the viscera and insinuated among the caeca of the
liver. Nutrient matter is there obtained and is thence conveyed to
the sac-like body. The latter contains neither alimentary canal,
limbs, or other appendages. Shortly stated, its structure is that of
a double walled sac, the inner of which contains large lobate ovaries,
closely united, 2 testes, 2 cement glands, and a single nerve ganglion.
The ovaries and the cement glands open by small apertures into a
large space, the brood cavity, occupying the space between the
outer and the inner sacs. Here the ova undergo their early develop-
ment, and as Nauplii pass forth through a well-marked opening, the
cloaca (d.y Figs. 1 and 2, PL 5) possessed of a strong closing or
sphincter muscle. Externally the cloacal aperture is obvious as a
prominent papilla.

The young issue forth as fairly typical Nauplii, but differ from
those of Lepas and Balanus in being destitute of paired eyes, mouth,
and alimentary canal ; a central cellular mass, the rudiment of the
ovaries, is conspicuous. The Cypris-stage, into which the larva
enters after its fourth moult, also resembles a normal Cirripede
Cypris-larva, but deviates also in the absence of alimentary canal and
paired eyes. To this point the larval history is that of an ordinary
Cirripede, and by this fact alone are we enabled to class Sacculina
definitely as a Cirripede Crustacean. Without such knowledge it
would be practically impossible to properly access its position in
nature's scale.

After a short free life, the Cypris-larva attaches itself by the
anterior antennae to the base of a seta or bristle upon the abdomen of a
young crab. In Jersey, I find Cancer pagurus (the edible-crab) to
be the most frequently attacked ; Pilumnus hirteUus is also com-
monly infested. On the other hand, I scarcely ever see Carcinus
mcenas attacked, and this is strange, as elsewhere this species is
credited with being the favourite haunt of the parasite.

Following upon attachment, the thoracic region and its limbs,
together with the abdomen, are severed and thrown away ; the head
appendages wither arid the cellular mass which alone remains of the
contents of the Cypris-valves, secretes a containing bag-shaped cuticle,
marking the formation of the Kentrogon larval stage ; the Cypris-
valves fall away ; a second cuticle forms within the first cuticle of the
kentrogon sac ; the anterior end is produced into a hollow arrow-like
.process, which, passing forwards through the cavity of the anchoring
antenna, forces its way into the body of the crab-host. Through this
channel the contents of the sac pass, and then become surrounded by
a fresh cuticle. From this sac are thrown out branched roots rami-
fying in the course of time among the whole of the organs of the
crab. .

CLASSIFICATION OF C1RRIPEDIA. 99

By these complicated phases Sacculina becomes primarily an
internal parasite, but as the size of the sac gradually enlarges, it
exercises so great pressure upon the integument of the abdomen of the
host as to cause such thinning as permits the sac to burst its way
through, and to appear as an external parasite. It is probable that
the internal stage is assumed to obviate the danger of being thrown
off and thereby destroyed, on the occasions of its host's moulting
during the early period of the attachment and before its roots have
had time to ramify extensively. It is significant of the paralizing
effect exercised upon the growth of the crab, that once the sac has
become external, i.e. when it has reached adult life, with its roots
ramifying extrusively through the viscera, that moulting ceases,
the crab remaining stationary in size.

Occasionally I have found two Sacculince parasitic upon the
same crab. An interesting feature in Sacculina, is that, although
hermaphrodite, complimental males exist, located usually around the
cloacal aperture of the sac. They have a Cypris-like appearance.

The three species of Cirripedes above described are thus all
connected by similarity in larval history (ontogeny). The diverse
adult forms are also linked together by a gradation of intermediate
types of great interest, that throw much light on the evolution of the
more changed. Thus the change from the stalked Lepas to the
sessile Balanus, can be understood by reference to Scalpellum, a
stalked genus where the peduncle is reduced and the number of the
calcareous plates of the mantle so augmented, some being intercalated
between the terga and scuta and the border of the peduncle, that if
the latter be lost and the carina and certain of the additional plates
join laterally and arrange themselves as a circular wall pushing away
the terga and scuta, we obtain the modification seen in Balanus —
a ring of plates with the opening closed, lid-like, by the four plates
of the terga and scuta. To the sac-like and limbless form of
Sacculina, the gap is largely bridged by our knowledge of such
genera as Alcippe and Cryptophialus, degenerate forms enveloped in
bag-shaped mantles, and provided with but three pairs of cirriform feet,
and which live parasitically in holes bored in shells. More degenerate
still is Proteolepas, a remarkable grub-like form living in the mantle
cavity of other Cirripedes ; limbs are entirely absent and the
digestive tube is rudimentary.

Classification : —

Class.— CRUSTACEA. Sub-Class.— Entomostraca.
Order. — CIRRIPEDIA.

Sub-Order I. — Thoracica ; thorax always present, usually provided
with cirriform feet ; mouth and alimentary canal
present.

100 MICROSCOPICAL STUDIES.

Tribe I. — PEDUNCULATA ; stalked, six pairs thoracic limbs.

Families. — Lepadidw (stalks without calcareous plates or
hairs) ; and PoUic&pedidce (stalks with hairs or
plates).

Tribe II. — OPERCULATA ; sessile, limbs same as in Peduncidata.
Families. — Balanidce and Chthamalidce (closely related,
both with a symmetric calcareous ring, each
branchia a single fold) ; Coronulidcc (symmetric
ring of plates, each branchia doubly folded) ; Ver-
rucidce (calcareous ring asymmetric).
Tribe III. — ABDOMINALIA ; thorax reduced, bearing three pairs

of cirri form limbs.
Family I. — Alcippidce, four pairs thoracic limbs, three

pairs being cirriform.
Family II. — Cryptophialidce, three pairs only of thoracic

appendages — all cirriform.
Tribe IV. — A POD A ; no thoracic limbs, grub-like.

Family. — Proteolepadidcc.

Sub-Order II. — Rhizocephala ; parasitic — body sac-like — without
mouth or alimentary canal ; possessing root-like
processes that ramify in the viscera of the host.
One family only. — Kentrogonidce. The chief genera are
Peltogaster, parasitic on Hermit Crabs, and Sac-
culina, parasitic on Cancer, Carcinus, &c.

101
STUDY XXA.

THE PERMANENCE OF THE SCYPHISTOMA STAGE

OF AUEELIA.

Three years ago, in 1893, large numbers of the Scyphistoma or
Hydra-tuba stage of the Medusa Aurelia aurita appeared on boulders
in several of the tanks of the Jersey Biological Station. Since then,
colonies produced from these individuals have been permanent on the
same stones. The continuity has been absolute, individuals having
practically been under daily observation since their first appearance.

Under favourable conditions of food supply and temperature the
increase in their numbers by budding was very rapid. The buds
grew out from any part of the body ; lengthened each into a
stolon that crept along the rock till some quarter inch away from the
parent, then made adhesion by a part that would finally become the
basal disc, quickly budded forth a ring of tiny tentacles, opened a
mouth aperture and finally constricted and then cut through the bond
with the parent, the two parts of the stolon being absorbed by the
respective individuals. Sometimes a Scyphistoma would give off two
or even three stolons at the same time, and as the growth of the young
individuals from these outgrowths is sometimes very rapid, the vast
increase of the colonies is comprehensible. No wonder that Aurelice
some seasons swarm in countless millions in our seas !

While this process of multiplication goes on very rapidly during
the greater part of the year, towards the end of January and the
beginning of February a second mode of reproduction, strobilation,
takes place. This, as is so well known, is the constriction of the
polyp-like body of the scyphistoma into short-armed plate-like divi-
sions or discs, arranged in a manner similar to a rouleau of coins.
One by one the discs broken off from the stock, float away as ephyrse
—little pulsating plates that by gradual change and growth, pass
imperceptibly into the adult sexual medusa, the female producing
ciliated embryos that, after a short free-swimming existence, settle
down, form tentacles and mouth and assume the alternate sexless or
Scyphistoma-stage.

Every year since 1893, my captive colonies have thrown off their
ephyrae,but the individuals never assume the polydisc or typical
form, usually — I believe — most common in strobilating individuals
in the open sea. Mine have all been monodisc strobilae, producing
not a rouleau of ephyrse discs, but each a single ephyra. This I am
inclined to attribute to a lower vitality than is possessed by those in
the sea, induced by the smaller food supply available in the tank
water, which is to a large extent filtered prior to admission to the
tanks.

Apparently a colony can exist indefinitely ; the specimens I now

102 MICROSCOPICAL STUDIES.

have are exactly of the same appaaranca as those that appeared three
years ago, save that they have spread and multiplied exceedingly
Excepting accidents they are likely to exist as long as they receive
the moderate attention they have had so far. I do not, however,
mean to assert that the same individuals are now alive as in the
baginning, though it is probable they may live two or more seasons.
The chapter of accidents is long and those living to-day are in most
cases, at least, the budded off and replace successors of the original
ones.

On PI. VI., figs. A. to D., are drawn a group of four as seen when
in active budding on Christmas Day, 1894. They were attached to
the side of a bell jar in a most favourable position for observation-
Fig. Aa shows side view of one of these to show how in some
cases the stolon has been given off from the polyp body at a point
considerably above the attachment disc ; thus the stolon bends down
to root at a distance from the parent, after the fashion of the branches
of the banyan and the mangrove. In others it emerges low down as
at fig. C*.

EXPLANATION OF PL. VI. FIGS. A TO C.

Fig. A, B, C & D. A group of Scyphistomata of Aurelia aurita,
drawn on Christmas day, 1894, when attached to the
side of a bell jar. d is the adhesion disc, b a prolife-
rated bud ; B shows in the best manner, the development
of a stolon. A" and Ca are profile views of A and C
respectively.

103

V,

STUDY XXI. — THE PLUMULARIDAE.

None of our Zoophytes are more graceful than are the Plumu-
laridae — their form justly entitles them to the name they bear, so
exquisitely beautiful are their feathery plumes, borne sometimes on
the green blades of the sea-grass (Zostera), or on the stout brown
edges of Fucus, or even on the bare rocky sides of some sheltered
pool.

Very nearly related in general form to the Sertularidae, this family
differs in two important points : in the former, the polyps are
arranged along both sides of the branches, in the latter, a row is
found on one side only ; again, among the Plumularidae, minute and
degraded individuals are found, known under the name of nemato-
phores — organs entirely wanting among the Sertularidae. In the
species here figured, one occurs just beyond, and another below each
hydrotheca, whilst two are located in the axils of the stem and
branches. Considerable mystery attaches to these structures, their
function being still problematical. In form they are tiny chitinous
cups wherefrom project extremely extensile sarcodal threads. The
term sarcotheca is applied to the cups ; sarcostyle to the thread.
The latter, though extremely slender and tenuous, and not unlike
the gigantic pseudopodia of some monstre Foraminiferon, are truly
cellular, composed of an outer ectodermal layer sheathing an endq-
dermal core. A remarkable feature is the projection of pseudopodia-
like processes from the surface of the sarcostyle. The cell-walls are
all extremely tenuous and thus capable of great elongation. The
extensile power of these threads is indeed marvellous. Fig. VI.,
PI. VI., gives but a faint idea of this. When active, they may be
seen winding and coiling with snake-like litheness around the hydro-
thecae and the branches. Especially active are they in the neigh-
bourhood of dead polyps, and here perhaps is their sphere of useful-
ness, in the removal of decaying matter — a theory strengthened by the
presence of foreign particles in certain amoeboid cells of the surface.

The great reproductive capsules or gonangia are especially well-
developed in this species, crowding the lower end of the main stem
(hydrocaulus), the lower branches, and especially the creeping
stem or stolon that connects the various plumes of the commonwealth.
In these the reproductive cells mature and undergo segmentation,
but, thanks to Weismann's researches (Die Enstetnung der Sexual-
zellen bet den Hydromedusen) we now know that in this family, the
Plumularidae, they do not originate within the gonangia, but arise in
the endoderm of the stem, whence they migrate to the gonangia as
into incubatory pouches. Figs. 3, 4 and 5, PI. VI., illustrate these
protective sacs in various stages, and show how the sexual cells con-
gregate in a sphaerical mass — a false ovary.

104 MICROSCOPICAL STUDIES.

The family Plumularidae is represented by three genera in British
waters, Pliimularia, Aglaophenia, and Antennularia. The last
named is distinguished by the whorled arrangement of its character-
istically short or bristle-like branches. The two former are plu-
mously branched ; in Plumularia, the gonangia are scattered along
the branches and the stems ; in Aglaophenia, they are collected into
great basket-like structures, called corbulae, formed by the modifica-
tion of an entire branch or pinna. The arrangement of the nema-
tophores is also distinct in the two genera.

EXPLANATION OF PL. VI; FIGS. I. TO "V.

Fig. I. Natural appearance of fronds of a species of Plumularia
growing upon the extremity of a blade of Zostera. The
black buds are gonangia, attached to the creeping and
connecting stolon or hydroriza and to the lower parts
of the fronds. (Original).

Fig. II. A young frond, greatly enlarged, showing polyps in various
positions, and also the position of the nematophores (n)
both below and above the hydrothecae, and in the axils
of the branches ; dh. developing hydranth ; dhc. deve-
loping extremity of the stem or hydrocaulus. (Original).

Fig. III., IV. and V. Various stages in the history of a gonangium ;
o. ova. (Original).

Fig. VI. Shows two nematophores of another species, n. the
chitinous sarcotheca, emitting the highly extensile
whip of sarcostyle (after Hincks).

STUDY XXII. — THE EGGS AND YOUNG OF CEPHALOPODS.

In the Cephalopods, we see the highest development of the Mol-
lusca, a superiority at once obvious when we consider their powers
for rapid locomotion, their powers of offence, their keen vision, and
the large size of their central nervous mass, the brain. In their
development, this vast gap that separates them from their fellows in
the common phylum, is emphasized strongly. Lamellibranchs,
marine Gastropods, &c., have all one characteristic larval form, the
veliger — a tiny, free-swimming larva propelled by powerful cilia,
and housed in a transparent shell. Among Cephalopods no trace of
this is seen.

Of the species found upon our coasts, the large Loligo Forbesii
deposits her eggs in masses of candle-shaped cocoons, attached at one
end to seaweed or other objects. This spring, on one occasion, we
found a considerable number of cocoons attached to the buoy rope of
a lobster pot (Plate VII., Fig. A), from which they hung in bunches,
recalling the primitive "dip" candles of auld lang syne. These

CHROMATOPHORES. 105

cocoons are transparent, gelatinous, and tough, and composed of
several layers, enclosing a large number of eggs — each, egg in turn
encased in a transparent spherical membrane.

The course of development of the embryos is abbreviated, for
when they free themselves from the egg-membranes, they possess
the general structure of the adult. Indeed, as soon as born, they
swim and dart about with all the confidence of full-grown indivi-
duals. Even the ink bag is developed at the time of hatching, and
is to be seen as a tiny black spot, and upon irritation, the little crea-
tures can cause the contents to be ejected in a tiny black cloud.
There are also present chromatophores — very conspicuous vesicles
of pigment, governed by sets of muscles that, produce by alternate
expansion and contraction the pretty blushings and pallor so marked
a feature among the adult Cephalopods. I noticed, however, that
the chromatophores are normally kept in a state of contraction so
long as the animal is unhatched, the whole mass being glassy trans-
parent till then. For a long time before freedom is gained, the
embryos can move freely in their capsules. In these young forms,
a tiny remnant of the yolk sac, attached in the centre of the arms, is
sometimes unabsorbed at the moment of birth. Two flap-like fins
are present at the extremity of the abdomen — and of very different
shape to the adult fins.

The young of Sepia have a similar history, but here the eggs are
laid in separate egg capsules and not in cocoons. Black and of the
form of grapes, these eggs produce each a single embryo.

In the mounted specimens of the embryo, notice the pair of gills at
the hinder part of the mantle cavity, a number characteristic of all
living Cephalopods excepting the pearly Nautilus which possesses
four gills. On this account we class all Cephalopods as either
DIBRANCHS or TETRABRANCHS. The present day representatives of
the class are grouped as follows : —

Class .—CEPHALOPODA.

ORDER I :— TETRABRANCHIATA. One living genus only ;—
Nautilus.

ORDER II :— DIBRANCHIATA.

SUB-ORDER I : — Octopoda (possessing eight arms), whereof the

best known genera are Argonauta, Octopus, and Eledone.
SUB-ORDER II :— Decapoda (possessing ten arms), containing a

very large number of genera ; among others being Sepia,

Sepiola, Loligo, Rossia, Otntnatostrephes, Loligopsis, and

Spirula.

EXPLANATION OF PL. VII. Figs. A. B. & C.
Fig. A. A cluster of egg capsules of Loliga Forbes ii, attached to a
rope, x ^.

106 MICROSCOPICAL STUDIES.

Fig. B. Young of L. Forbes it just after it has broken through the

egg membrane ; chromatophores shown relaxed.
Fig. C. The same viewed as a transparent object. /. fins ; g. gills ;

z. ink sac ; rd. radula ; s. siphon ; x, chromatophores ;

y. remnant of yolk sac, as yet unabsorbed ; the eyes are

shown in optical section.

(All these figures are from original sketches).

STUDY XXIII.— THE VISUAL ORGANS OF THE MOLLUSCA.

The organs of sight in their frequently parfect adaptation to the
sensory function they perform, claim our admiration in a degree
greatly superior to that which we acoord to any other organ of the
body. Nor is our interest lessened when we see the manifold modi-
fications of structure presented by them ; how, even in the same
phylum, one family may be endowed with such organs formed in the
most complex manner, whilst closely related forms may possess but
the simplest of structures, crudely functioning towards a similar
end ; how here, the optic mechanism is prominently and closely
associated with the brain ; how, among others, organs arise inde-
pendently from the most diverse regions to assume a physiological
equality with the cephalic eyes of other types.

Nowhere do we find greater variability in the origin and structure
of the visual organs than among the Mollusca. Thus, while the
Gastropoda and the Cephalopoda possess paired cephalic eyes, the
Lamellibranchs possess none, their place being taken by numerous
peripheral eyes arranged along the edge of the mantle.

In structure, apart from the mere pigment spots that are borne
upon the extremities of the siphons in Solen, Venus, &c., there exist
five principal types of eye among the Mollusca.

The simplest form, found in the eyes of the Limpet (Patella), is
a mere bowl-shaped depression of the epidermis, the lining of which
has become modified into a visual layer, or retina, into which the
optic nerve penetrates by numerous fibre-branches. A slightly higher
modification is seen in the eyes of Nautilus, where the ocular pit is
excavated out of a broad conical stalk, and with the aperture con-
stricted to a mere pin-hole, the whole recalling forcibly both the
outline and the section of a young Fig-fruit. In this eye, as in that
of the Limpet, the retina is bathed directly by the sea- water. (Figs.
II. and IX, PL VII.).

The second type of Molluscan eye shows considerable advance
upon the first. It has the form of a closed capsule and is directly
derivable from the simple cup-form, by the ingrowth and fusion of
the lips of the cup. This optic capsule usually separates from the
epidermis from whose ingrowth it arose, the superficial epidermal
layer closes over, becomes transparent; and then may be termed a
cornea, as it becomes a transparent protective window for the capsule

Journ. of Mar. Zool. & Microscopy.

VOL. 2, PL

/

c*.

JAMES HORNELL, DEL. AO NAT
*• FIG. VI EXCEPTED)

AURELIA AND PLUMULARIA.

Journ. of Mar. Zool. & Microscopy.

VOL. 2, PI. VII.

JAMES HORNELL, DEL. AD NAT

FIGS. A, B, C 4 1.

CEPHALOPODA.

STRUCTURE OF THE CEPHALOPOD EYE. 107

beneath. Another advance is made by the formation of a gelatinous
substance in the cavity of the capsule. This is a vitreous humour
and is a prelude to the appearance of a lens. The eyes of the Roman
Snail ( Helix pomatia) and of Tritonium are typical examples.

The third type, found solely among the Cephalopoda, is formed in
direct sequence with the form last mentioned, but before treating of
its origin, we will detail the chief points in its structure, taking for
our text the eye of the Cuttlefish (Sepia officinalis). In this species,
as is usual among the Cephalopods generally, the eyes are placed
prominently upon either side of the head. Each consists of a hollow
bulb sunk in a deep orbit in large measure hollowed out of the
cephalic cartilages. This orbit becomes a closed chamber, the optic
capsule, by the extension across it, and in front of the optic bulb, of
a transparent fold of skin, which functions as a cornea.

If we now bisect the optic bulb we find it contains but a single
chamber filled with gelatinous vitreous humour, bounded in front by
a very large bipartite crystalline lens, and elsewhere by thin walls
that are stiffened, and thus prevented from collapse, by the presence
of delicate plates of cartilage in their middle subtance. External to
these cartilages, and obvious to the naked eye as a brilliant bronze-
hued coating, are two layers of pigmented membrane, the argentea
externa and interna.

Internal to the cartilaginous and fibrous layers of the bulb is the
retina, lining the hinder part of the ocular cavity, the front being
occupied in large measure by the lens. The latter is almost globular
in shape, the longest diameter coinciding with the visual axis. It is
made up of the junction along a transverse plane of two unequal
plano-convex lenses. The anterior is the smaller. As a consequence,
the posterior has much greater convexity, and projects boldly into
the ocular chamber. After hardening in spirit or otherwise, each
portion of the lens can readily be split into a large number of con-
centric layers, whose curvature coincides with the external convexity
of that half of the lens to which they respectively belong. A fine
membrane stretches across the lens at the junction of the two halves,
and passes at the edge into a fibrous and muscular sphincter-like
organ, known as the ciliary body. This, in turn, merges with the
fibrous wall of the ocular bull. The use of this ciliary body is the
regulation of the convexity of the lens, to permit of its adaptation to
near or to distant vision.

A fold of the external coat of the bulb is carried part way over
the outer aspect of the lens, and is the iris entrusted with the im-
portant duty of regulating the quantity of light passing through the
lens. It is strengthened internally with thin plates of cartilage. In
Sepia, it has an upper and a lower fold that have much superficial
resemblance to eyelids and give the eye a slit-like pupil. In passing,
it may be mentioned that Sepia possesses a true eyelid, consisting of

108 MICROSCOPICAL STUDIES.

a horizontal external fold of skin extending along the lower side of
the eye. In Octopus the eyelid is sphincter-shaped.

The retina, bounded internally by a thin transparent or hyaline
membrane, consists of two distinct portions, the outer and the inner,
separated by a sharply denned layer of black pigment. The inner
layer is made up of rols, the outer of nerve cells and nerve ramifica-
tions. The optic nerve in Cephalopods is very short and stout. On
entering the optic capsule it forms an immense ganglion whence
arise very numerous nerve fibres. These gain access to the interior
of the optic bulb through sieve-like openings in the cartilaginous
layer of the wall of the bulb. Thence they pass to the external
surface of the retina. In front, and partly at the sides, of the gan-
glion lies a peculiar soft whitish organ, the white body (w.b.).

Examined superficially, the general structure of such an eye
seems partially identical with that of a Vertebrate eye, except in the
absence of an anterior chamber. In reality, there are some very
radical divergences ; thus in the Cephalopoda the retina has its layer
of rods turned inwards, i.e., pointing towards the interior of the eye ;
in Vertebrates, this layer of rods is external, directed outwards ; in
Cephalopods the pigment layer divides the retina into two regions ;
in the Vertebrates it lies external to the rods and cones. Most im-
portant difference of all, the optic fibres proceeding from the large
optic ganglion pass into the retina from the exterior in Cephalopod
eyes, whereas in Vertebrates the optic nerve forms no gang] ionic
mass, but passes through the wall of the optic bull) by a single
opening and then breaks through the retina in the same way,
spreading a network of fibres over the infcrtifi/ surface of the retina.
Hence light entering the eye of Cephalopods, impinges first upon the
retina and pas-338 directly downwards to the nervous layer beyond.
In the Vertebrate eye, the impressions of sight fall first upon the
nervous layer, are transmitted thence through the various layers till
the rods and cones are reached and thence returned by them through
the same layers to the nerve fibres upon which they first impinged.
This fundamental divergence is clearly diagrammatised in figs. X.
and XL, Plate VII.

A less important difference is that of the cornea being part of the
optic bulb in the Vertebrates, separate and part of the optic capsule in
the Cephalopods.

In the latter the bulb represents the Vertebrate eyeball, minus the
cornea and sclerotic, the equivalents of these being here possessed
by the optic capsule, which here functions as an orbit.

The development of the Cephalopod eye is very instructive, both
as throwing light on its origin and relationship with the other forms
of molluscan eyes, and also in regard to the origin of its divergences
from the Vertebrate type of eye. Figs. I. to V., Plate VII. graphically
describe the stages.

The earliest stage (Fig. II.) is the equivalent of the optical stage

DEVELOPMENT OF THE CEPHALOPOD BYE. 109

attained in the eye of the Limpet ; the epidermis at one spot, having
sunk down to form a shallow depression wherein the cells forming
the floor of the cavity constitute a primitive retina.

Tn Fig. III., the edges of the optical pit have grown horizontally
inwards so as to reduce the mouth of the pit to a small round open-
ing. This pit raised up on a stalk marks the permanent condition of
the eye in Nautilus (Fig. IX.). In the embryo Sepia, the aperture is
early obliterated by the approximation of the free edge of the epi-
dermal fold. This accomplished, we have a hollow globe formed
overlaid by a continuous epidermal layer (e, Fig. IV.) A condition
of eye exactly corresponding to this stage, is the adult form of eye of
Helix as described above.

By a second downgrowth of the surface epidermis, another pit-
like cavity is formed, the floor of which impinges upon and fuses
with the anterior wall of the previously formed hollow ocular sphere.
Fig. V. illustrates this stage. At the centre of the area where the two
layers fuse, a transparent nearly spherical body, the future lens,
begins to form. According to Carriere the external of the two fused
layers forms the external part, whereas the anterior wall of the optic
sphere forms the larger internal half. Hence the plane of division
that cuts the mature lens into two parts represents two fused epi-
dermal layers, and the fibrous strands of which it is composed merge
equatorially into the surrounding ciliary body. The lens itself is
composed of structureless layers, that are however only revealed
after treatment with chemical reagents. Naturally, it is transparent,
tough, semi-gelatinous, and apparently homogeneous. The folds in
front of lens (e) represent the origin of the ultimate iris ; the cornea
is likewise formed by another fold of the epidermis turning inwards
and fusing in the same manner as the layer e in .figs. III. and IV.

The mature form of the eye is now reached, the posterior wall of
the ocular sphere becoming modified into the retinal layer by
differentiation of the cells. Comparing the development of the
vertebrate eye, we find the retina is there formed, not directly from
an epidermal invagination, but as an outgrowth from one of the
primitive vesicles of the brain (Fig. VII.), which eventually assume
the form of a double walled stalked cup, through the external wall
of the outgrowth becoming pushed in upon itself, while the hollow
stalk comes finally to represent the optic nerve. Synchronizing with
these changes, an epidermal invagination has been taking place,
which by ingrowth of the lips is at first a closed sac connected at one
spot with the overlying epidermis, but which is quickly severed and
sinking inwards, is subsequently converted into a transparent lens,
filling the mouth of the retinal cup. The cornea here, as in the eye
of Sepia, is formed by the epidermal layer that overlies the lens
losing its cellular nature and becoming transparent and colourless.

It will be seen from the foregoing that in Sepia, except for the
nerve fibres that surround and penetrate the retina, and for the

110 MICROSCOPICAL STUDIES.

supporting tissues (cartilages, muscle fibres, &c.) of the wall of the
bulb, all parts of the eye have direct epidermal origin, whereas in
the Vertebrate eye the cornea and lens alone have direct epidermal
origin, as the retina is entirely derived from an outgrowth from the
embryonic brain. The heavy black lines in Figs. III. to VII. indicate
the external margin of the layer of retinal rods. They show how in
in the Cephalopoi eye this layer is turned towards the light, while in
the Vertebrate eye it is turned in the opposite direction. Thus
while the higher Cephalopod eye reaches what is practically the same
perfection and same plan of optical mechanism as the Vertebrate eye,
it does so by a different avenue of development.

As already noticed, the majority of Molluscan eyes belong to one
or other of the three types so far described, and which may be
exemplified respectively by the the eyes of the Limpet, the Snail and
the Cuttlefish, ranked in order of development. These in structure
and development are in direct sequence. Their homologies are
definite and fixed. All are cephalic eyes, and in close relationship
to the central nervous mass.

Hence, when among the Pectens and allied Lamellibranchs
we find visual organs that from their position are obviously not
homologous in origin, it is specially interesting to see what
differences in structure prevail. In such forms cephalic eyes are
wanting, their place being taken by small organs placed upon short,
deeply pigmented papillae, arranged at intervals along the edge of the
mantle or pallium, whence they derive their name of pallial eyes.
Stated briefly the structure is as follows. The ooular papilla is clothed
with an epithelial layer, deeply pigmened except at the summit, where
the cells are colourless and flattened. Beneath this layer lies the tiny
ocular sphere divided into two halves by a partition, the anterior
containing a transparent cellular lens, the posterior, a several-layered
retina of ordinary structure. The arrangement, however, of the rods
and cones is the reverse of that found in the cephalic eyes of
Molluscs, as they are here turned away from the light and are under-
laid by a pigmented layer. Again fibres from the optic nerve
form a layer anterior to the other retinal layer, so that light must
traverse this nervous layer before it can reach that of the rods and
cones. The plan of structure is therefore practically identical with
that found in the Vertebrate eye save that the optic nerve does not
pass through the retina, but attains its connection with the rods and
cones by passing around one side of this layer and thence spreading
out over the distal surface.

Very curiously nearly similar eyes are found upon dorsal processes
in a peculiar Gastropod, Onchidium, and here even closer approxi-
mation is made to the plan of the Vertebrate eye. Instead of the
optic nerve turning the flank of the rods and cones, it passes through
at one point, thereby producing a blind spot exactly analogous to
that found in the Vertebrate eye. This eye of Onchidium constitutes

DIVERGENT ORIGINS OP MOLLUSC AN EYES. Ill

the fifth and perhaps the most interesting of the types of Molluscan
eye — for, standing as it does alone, it furnishes us with one of the
most remarkable instances of independent evolution that we are at
present aware of.

And in this connection it is important to notice that no other
organ has had so many. -independent evolutions as has the eye.
Nothing could so strongly emphasize the supreme importance of
sight to the majority of creatures. Here, within the types referred
to above, four distinct evolutions of ocular organs undoubtedly took
place. No one can for a moment deny that the cephalic eyes of
Cephalopods and of Vertebrates have had independent and conse-
quently dissimilar origin. Embryology at once marks out this
divergence ; while the peripheral position of the eyes of Lamelli-
branchs is sufficient to separate them from each of the former.
Again one cannot gainsay divergence of origin to the dorsal eyes of
an aberrant Gastropod and the pallial eyes of the Lamellibranchs.
If only our knowledge of the homologies of the more obscure
organs were on a par with that of the eye— though much remains to be
done even here — our attempts at constructing phylogenetic tables or
trees of descent, would be infinitely simplified. Indeed, it may be
considered a biological axiom that no reliable phylogenetic tree can be
constructed till the homologies of individual organs have been exhaus-
tively made known.

EXPLANATION OF PL. VII. Figs. 1. TO XI.
The Gephalopod Eye.

Fig. I. Section through eye of Sepia officinalis. ae. argentea
externa ; ey. eyelid ; c. cartilages of optic bulb ; cc.
cephalic cartilages ; ci. ciliary body ; co. cornea ; gn.
optic ganglion ; ir. iris, showing a thin plate of
strengthening cartilage ; /. lens ; on. optic nerve ; p.
retinal layer of pigment ; r* internal layer of retina ;
r" external layer of retina ; wb. white body. (Original).

Figs. II. to V. Diagrams of the chief phases in the development of
the Cephalopod eye. III. represents that stage which
in Nautilus is the permanent condition ; IV. is prac-
tically a diagram of the eye in Helix ; e. unmodified
epidermis ; /. lens ; r. retinal layer; a thick black layer
denotes the position of the distal margin of the layer of
rods and cones.

Figs. VI. to VIII. Diagrams illustrative of the development of the
Vertebrate eye. b. represents a hollow outgrowth from
the brain which eventually form the retina and the

112 MICROSCOPICAL STUDIES.

optic nerve. In Fig. VII. the epidermis is sinking
downwards to meet this hollow outgrowth, while in
VIII. it has become pinched off and forms now the
basis of the future crystalline lens. e. epidermis.

(Figs. II. to VIII. are after Carriere, "Die Sehorgane der Thiere,"
Miinchen and Leipsig, 1885).

Fig. IX. Diagram of the structure of the eye in Nautilus ; on.
branches of the optic nerve ; r. retina.

Fig. X. Diagrammatic representation of the eye structure in Cepha-
lopods, to show the arrangement of the retinal elements
in relation to the optic nerves. (After Graber).

Fig. XI. A similar representation of the retinal arrangement, &c..
of the Vertebrate eye. (After Graber).

September 10th, 1896.

113

NOTE ON THE
PROTECTIVE DEVICES OF THE GENUS HIPPOLYTE

a. The colour adaptability of the adult H. varians to the hue of its
environment.

b. The significance of the plumose hairs of H. fascigera is mimetic
and not primarily sensory.

DURING the past summer (1897) I took advantage of an unusual
abundance in the Jersey rock-pools of the little ^sop's Prawns, Hippolyte
(Virbius) varians, Leach, and II. fascigera, Gosse, to carry out some
experiments I had long contemplated relative to the protective coloura-
tion of these crustaceans.

That the former species is very variable in colour and that the
colours are plainly of protective value are well-known facts ; thus
Professor Herdman in 1893 described in the " Sixth Annual Report of
the Liverpool Marine Biology Committee," four variations of H. varians,
each agreeing in hue with the colour of its special habitat. He put
forward four alternative possibilities to account for such variability,
thus : —

1. The colours noted may represent four distinct varieties which do
not interbreed, keep to their own special habitat, and produce young
of their own colours.

2. Or, there may be no permanent varieties, but the young may
have great adaptability and assume the hue of the habitat they find
themselves in and keep to this for the rest of their lives.

3. Or, this adaptability may be retained throughout the rest of their
lives and the adults may change hue upon change of environment.

4. Or, the young may be very variable in tint and then by the
action of natural selection, such as do not agree in hue with the sur-
roundings will be eliminated.

He added that he was inclined to regard the last as the most
probable explanation.

Starting my experiments with these possibilities in view, I collected
a quantity of both our common local species and isolated the individuals
in separate glass vessels, each containing sea-weed of a different hue to
that of the prawn.

The experiments were conclusive and proved Professor Herdman's
third alternative suggestion to be the correct one, namely, that the adults

114 MICROSCOPICAL STUDIES.

retain the power of changing their colour in accordance with that of
their surroundings. Thus a pale olive brown H. varians taken from
amid similarly coloured sea-weed became of a vivid green within an
hour when placed with Enteromorpha, and the same specimen changed
to a pinkish red within three hours when placed amid Delesscria.

Again, red coloured specimens of the same species from amongst
tufts of red weed changed to green during a single night when placed
with Enteromorpha or with Cladophora, and back again to red within
four hours when placed once more amid red weed.

These two instances are representative of a large number of similar
experiments, all having parallel results and demonstrating that the
adult Hippolyte varians has great and rapid colour adaptability.

It is a remarkable fact that this change of hue takes place as
rapidly in the dark as in the light ; thus specimens placed in a dark
cupboard in company with weed of a different colour, will be found to
have assumed the colour of the weed in the course of a few hours. In
the same way individuals left over night exhibit their appropriate
colour change when examined before daybreak on the following morning.
As to Hippolyte fascigera, I find that this species possesses by no
means equal colour adaptability ; this power is much less developed.
Thus it takes considerably longer time to adapt its hue to new colour
surroundings, and the colour is but an imperfect approximation to the
true one. For example, the majority of this species, which are found
living among the mottled pink coarse Corallina of our pools, and have
absolutely similar colouring, take fully twelve to fifteen hours to
approximate partially to the white tint of sun-bleached tufts of weed.

Again, a lengthened sojourn of upwards of a week amid tufts of
Enteromorpha does not effect any well marked assumption of green,
though the pink is decidedly paler and a tinge of green can be made
out without difficulty.

Such marked divergence in this power of colour adaptability between
two species so closely akin* is extremely remarkable, and I had to
make a very careful examination of the natural habitats and habits of
the species in question ere I was able to solve the problem.

I find that H. varians is infinitely more numerous and more widely
spread than is H. fascigera, being found in almost every pool, and

* Indeed, so closely akin that a cursory examination is apt to lead to the belief
that H. fascigera is a mere variety of H. varians. Many points of permanent
divergence are, however, present ; the most marked is that in II. fascigera the only
spines on the upper edge of the rostrum are three placed at the posterior end and
really upon the carapace, while a single sharp tooth is set close to the tip on
the straight under edge. In II. varians, the rostrum above has one tooth set near
the base and another towards the tip, while below there is a well-marked two-
toothed keel.

PROTECTIVE DEVICES OF THE GENUS HIPPOLYTE. 115

haunting tufts of weeds of every hue. In the Zostcra meadows it is
also abundant. No special preference is shown for any particular
colour or species of weed, and it is essentially "cosmopolitan." On the
other hand, H. fascigera is seldom found in any number except among
tufts of coarse Corallina, with which it agrees absolutely in colour, and
where it is often extremely abundant.

Thus we see that the species possessing the greater colour adapta-
bility (H. varians) is much the more numerous, and the more extended
in its range ; we may safely infer that the two latter characteristics are
the direct outcome of the former. H. fascigera, being less "plastic" in
colouring, is on the contrary restricted in habitat to those weeds to
which its colour has become perfectly approximated.

We may note further that the weeds affected by the smooth-skinned
H. varians, in the great majority of cases, are smooth in surface and
not over- grown with foreign matter.

In marked contrast, the body of H. fascigera is ornamented with
tufts of brush-like hairs, especially upon the sides of the carapace, even
invading the surface of the eye-stalks; now if we examine a spray of
the coarse Corallina where this species makes its home, we will find
the stems covered with a multitude of abodes of tiny "messmates" —
porcelain-like coils of the little tube-worm Spirorbis, dull looking
cylinders tenanted by that lovely minature Sabellid, Othonia gracilis, and
crusting colonies of Bryozoa protruding ever and anon circlets of hair-
like tentacles — that impart, when their owners put forth their feathery
crowns, a minutely tufted appearance to the joints of the stem. Hence
when the hairy H. fascigera is at rest on such a weed the mimetic
adaptation is greatly accentuated. The smooth H. varians in a similar
environment is much more easily detected.

As there is no doubt in my mind that the plumose hairs on H.
fascigera are directly useful as aids in protective resemblance to en-
vironment, I believe, as a consequence, that we require no longer to
accord to these hairs any special sensory function. Some authorities
have considered the hairs of this species to be auditory, and while
they presumably must possess a certain amount of tactile appreciation,
their direct utility is, I feel assured, as conducing largely to the
protective resemblance of the prawn to the appearance of its normal
habitat.

In a future number I hope to recur to this subject and to give further
details regarding the habits of these interesting Crustaceans.

116

Series vi

STUDY XXIV.— FAMILIAE BRITISH BKYOZOA.

THE Bryozoa — better known in this country under the name of
Polyzoa — often constitute a source of delight at meetings of our
Microscopical Societies ; seldom, indeed, is a microscopical conver-
sazione complete without at least one such exhibit set out proudly in
all the glory of parabolic or spot-lens illumination. The beauty of
the pellucid zooids in the full expansion of their glorious crowns of
elegantly tapered tentacles, sentient and responsive to the slightest
alarm, and the ceaseless lashing of the cilia clothing these tentacles
and creating vortices big with fate for many a tiny organism swimming
hard by, make up a picture wherein loveliness and interest chain the
attention alike of the greybeard in microscopy and of the tyro in the
science.

As a rule, the fresh-water Bryozoa are the forms thus exhibited,
being the easier to procure in inland towns. The marine forms, how-
ever, are fully as beautiful, and in some respects are much more
interesting as diversity of form is infinitely greater. If anything, the
marine forms are even hardier than the fresh-water ones, and in these
days of rapid postal communication and of Marine Biological Stations,
inland microscopists have no difficulty in studying living marine
species, and of thus comparing them with those they obtain from
adjacent pond or sluggish canal.

The Bryozoa are colonial in habit of life, except one minute form,
Loxosoma, found parasitic in multitudes of separate individuals upon
the hinder end of the great Spoon-worm (Phascolosoma). The colonies,
or zoaria, may be slender and branched (Botvcrbankia), broadly folia-
ceous (Flustra), massive and calcareous (Lepralia), coiled in elegant
spirals (Bugula), gelatinous as Lophopus and Alcyonidium, horny, hispid,
smooth, or crusting. Almost all live attached, usually to stones or
seaweeds, and often enough we find them growing in profusion upon
the carapace and limbs of crabs. One form, Cristatella, crawls freely,
with slug-like motion, over and amongst the weeds of its pond home,
while others, the Selenarida, swim by the oar-like paddling of giant
bristles — the vibracula. Can diversity be greater? Well might the
earlier naturalists consider the slender forms to be zoophytes, and the
massive ones to be coral growth.

Later, their affinities were recognised as apart from the zoophytes
by the possession of a well-developed alimentary canal. Now they are

THE SIMPLEST BRYOZOA. 117

accorded a place among that heterogeneous assemblage, the "Worms,"
and their closest relationship is undoubtedly with Phoronis, the
Sipunculid worms, and the Brachiopods. These agree in having
tentacles round the mouth ; an alimentary canal more or less U-shaped
— the anus placed far to the front and often approximated to the
mouth ; nephridia (kidneys) reduced in number and rarely more than
a single pair ; the body unsegmented and often secreting a horny or
calcareous covering ; the nervous system greatly reduced ; parapodia
and setae absent.

Two popular names are in use, "Corallines" and "Moss-polyps,"
the latter being the translation of the term Bryozoa.

Simplest of all the Bryozoa are the Pedicellinidce ; the typical
species, P. cernua (Pallas) grows luxuriantly in Jersey rock-pools,
clothing the stems of such algae as small Fucoids, the pink Corallina,
and the green Cladopliora. The individuals or zooids are stalked,
rising at short intervals along the creeping stem or stolon ; in form
they have a superficial resemblance to the Bell-animalcule (Vorticclla),
both having the shape of a wine-glass. Pedicellina is coy of full
expansion, and the ordinary illustrations of text-books never do it
justice ; fig. 10, pi. ix., drawn from a zooid just taken from a rock-pool,
gives a better though still inadequate idea of the graceful outward
curve of the tentacles under natural conditions. The stalk is con-
tractile and flexible and as we watch a group scarcely a moment passes
without we see one or another bob the body almost down to the base
of the stalk or maybe give a sweeping curtsey from side to side. At
another time the whole cluster may bow in unison — a most comical
sight, and one that caused me instinctively to christen it the Bobbing
Coralline when first I made its acquaintance.

The stalk is usually spinous, but all gradations to a perfectly
smooth condition are to be met with.

The tentacles are solid and are arranged in a circlet around the rim
of the cup-shaped body. Such rim is the lophophore or tentacle-carrier.
The lophophore is not retractile as in those forms yet to be named,
but at will the tentacles can be folded inwards to form a rafter-like
roof to the vestibule or depression found in the centre of lophophore.

A diaphragm separates the body from the stalk, and when, as some-
times happens, the former breaks off, it is not unfrequently replaced by
budding from the summit of the stalk. This tendency of the body to
break off is often very troublesome when one is endeavouring to stupefy
a colony preparatory to fixing.

Within the depression (vestibule) enclosed by the ring of tentacles
are two openings, the mouth and the anus. Between the two rises a
small lobe, the epistome. Food is directed to the mouth by means of

118 MICROSCOPICAL STUDIES.

the currents set up by the cilia that clothe the inner or adoral surface
of the tentacles. The alimentary canal is of the typical U shape, and
is of the most primitive description.

A very curious point is the absence of any body-cavity (coelome). Its
place is taken by gelatinous tissue lying between the alimentary canal
and the body- wall. Muscular fibres are present in the stalk, and others
control the movements of the tentacles.

The nervous system is little developed, consisting of a single gang-
lion lying beneath the oesophagus, and from which nerves proceed to the
tentacles. Sensory cells are found on the outer surface of the tentacles.

The excretory organs consist of two ciliated tubes opening close to
the central ganglion.

The zooids are hermaphrodite, but it is probable that the reproduc-
tive products ripen at different periods. The larvae are Trochospheres
— tiny swimming spheres characterised by a circlet of cilia around the
body anterior to the mouth (preoral) — as in the Polychaetes, and the
adults themselves retain a majority of the essential features distinctive
of this larval form in the persistence of the simple alimentary canal
of the latter, of a ciliated ring surrounding the mouth and anus (the
tentacles are simply elongated processes of an encircling band), of the
two ciliated canals of the larva as nephridia ; the epistome is present in
the trochosphere as a tufted eminence, and other minor common
characteristics can also be traced.

The larvae pass a considerable period of their development within
the vestibule, which, with the tentacles protectingly overarched, forms
an efficient incubatory pouch.

The higher Bryozoa fall naturally into two divisions according as
the habitat is marine or fresh-water. The former are distinguished by
the lophophore being circular and are termed Gymnolaemata ; the latter,
the Phylactolaemata, by the lophophore being horse-shoe shaped. In
all, the anus lies outside of the lophophore, and this is the great
distinguishing characteristic.

Of the fresh-water forms, Lopliopus and Plumatella are typical, and
resemble one another closely in all essential features. Plumatella, often
found attached to water-weeds in canals and pools, has a creeping
chitinoid stolon from which the zooids rise at short intervals. In
Loplwpus, the zooids are crowded into dense tufts and enclosed in a
gelatinous matrix. In both, the zooids are capable of being wholly
retracted within the zooecia or cell-like cuticular envelope, chiefly by
means of a powerful strand of muscular fibres (retractor muscle, r.)
attached at one end to the anterior portion of the oesophagus and at
the other to the lower inner surface of the resistent stolon-tube.
Besides this, the zooid can be partially retracted by a set of small

Jotirn. of Mar. Zool. & Microscopy.

VOL. 2, PI. I

(Fics. IV., V.. & VII. EXCEPTED).

TYPES OF BRITISH BRYOZOI

125

EXPLANATION OF PLATE IX.

Fig I. — Portion of a colony of Plumatella repens, sketched from life,

showing zooids in various states of expansion. (Original.)
Figs. II. and III. — Statoblasts of Plumatella, surface and edge view.

(Original.)
Fig. IV. — Edge view of a statoblast of Cristatella mucedo, showing the

projection of numerous barbed spines. (After Alhnan.)
Fig. V. — Anterior part of the body of Lophopus, seen from the right

side. The free ends of the lophophore and of the tentacles are cut

off. (After Allman.)
Fig. VI. — Life appearance of a colony of Bowerbankia imbricata, nat.

size. (Original).
Fig. VII. — A cluster of zooids of the same, fully expanded. (After

Hincks.)
Fig. VIII. — A calcareous colony of Lichenopora hispida, showing two

ooecia in the centre. Drawn from Nature. (Original.)
Fig. IX. — Two colonies of the same, nat. size.
Fig. X. — Pedicellina cernua, showing the full expansion of the tentacles.

From life. (Original.)
Fig. XI. — A cluster of Pedicellina cermta on a filament of seaweed, nat.

size. (Original.)
Fig. XII. — Diagram of the structure of a Bryozoon zooid in attracted

condition. (Original.)

Fig. XIII. — The same in a state of expansion. (Original.)
LETTERING : — a. anus ; ep. epistome ; /. funiculus ; g. nerve ganglion ;

i. intestine ; m. mouth ; o. ovary ; oe,. oesophagus ; r. retractor

muscle ; s. statoblasts ; st. stomach ; t. testis ; v. cesophageal

valve.

CLASSIFICATION : —

CLASS.— BEYOZOA ( = POLYZOA).
Sub-Class I.— ENTOPEOCTA ; Anus opening within the lophophore ;

no body cavity ; tentacles non-retractile.
Family a. — Pedicellinidse — colonial.
Family b. — Loxosomidae — solitary.

Sub-Class II.— ECTOPEOCTA ; anus opening outside the lophophore

area ; well-developed body-cavity (coelom) ; tentacles retractile.

Order 1. — Phylactolaemata. Lophophore horseshoe-shaped ; with

epistome ; membrane supporting bases of tentacles ; all

fresh-water in habitat.

Order 2. — Gymnolaemata. Circular lophophore ; no epistome ; no
membrane round bases of tentacles ; all marine except
Paludicella.

126

EXPLANATION OF PLATE X.

Fig. I. — Sapphirina Edtvardsii, Haeckel, viewed from the ventral
surface, and showing the course of the alimentary canal, the dis-
position of the dermal glands, fat spheres, eyes, and ramifications
of the nervous system. (Note : The muscles, genital organs and
swimming feet, etc., are omitted.)

Fig. II. — Anterior portion of cephalic region of same species, showing
in greater detail the arrangement of the eyes, fat-body, dermal
glands and nerve connections.

Fig. III. - Posterior "maxilliped" (really a branch of the second
maxilla) ; same species.

Fig. IV. — Caudal plate ; same species.

Fig. v. — Combination of a single-celled dermal gland and a terminal
ganglion cell with its sensory bristle ; same species.

Fig. VI. — Sapphirina Gegenbauri, Haeckel, ventral view to show the
eyes, alimentary canal, liver lobes and reproductive system.
(Nerves, muscles and most appendages are omitted.)

Fig. VII. — Posterior "maxilliped" (branch of the second maxilla);
same species.

Fig. VIII. — Caudal plate ; same species.

Fig. IX.— Caudal plate of S. Clausi, Haeckel.

Fig. X. — A swimming foot of S. Clausi from the fourth segment,
showing the two nearly equal branches.

Fig. XI. — A similar foot from S. Darwinii, Haeckel, showing how the
inner branch is here almost suppressed.

Fig. XII.— The medium eye-spot in S. Darwinii, greatly magnified.

LETTERING.— a. anterior antenna; c. corneal lens; d. chitinous cuticle ;
/. fat sphere, secreted by the " Fat-body " ; g. central ganglionic
mass penetrated by the oesophagus (oe) ; h. branch of that peculiar
form of connective tissue know as the " Fat-body " ; i. intestine ;
k. stellate branches of the " Fat-body"; I. liver lobes lying
around the stomach; Is. crystalline cone ; m. muscles; me. median
unpaired eye; n. nerve; o. anus; ce. oesophagus ; p. pigment body
of the paired eyes; pa. posterior antenna; pg. peripheral ganglion
cell with its sensory bristle ; r. spermatophore pouch ; s. vas
deferens ; st. stomach ; t. testis ; y. dermal gland ; yg. double-cell
consisting of a dermal gland and a ganglion cell ; x. problematical
organ (sensory?).

(All figures after Haeckel.)

Journ. of Mar. Zool. & Microscopy.

VOL. 2, PL X.

x.

J. HORNELL, DEL. (AFTER HAECKEL).

STRUCTURE OF SSPPMIRIM,

STATOBLASTS. 119

muscles causing a folding in that forward part of the body- wall called
the tentacle sheath, as seen in the 2nd, 3rd, and 5th zooids counting
from the left in Fig. I., PI. IX.

A thin membrane protects the bases of the tentacles, which are
ciliated on both surfaces. A well- marked ciliated lobe, the epistome,
overhangs the mouth (cp.).

The alimentary canal hangs as a Y-shaped bag, suspended freely in
the body cavity, and in all the fresh-water forms except Paludicella, the
body cavity (coelome) is common to all the zooids — no partitions are
found anywhere — and cilia cover the whole coelomic surface. The
O3sophagus is straight. Notice, as it enters the stomach, how it is
furnished with a valvular arrangement (v.) projecting downwards and
designed to prevent any backflow from the stomach. The latter has
a great pendant bag-like region, the glandular caecum, forming the
straight part of the Y-shape. A strong cord, the funiculus, attaches
the caecum to the outer wall or ectocyst. The intestine is short and
straight and lies parallel with the oesophagus ; the anus (a.) opens close
to the base of the lophophore.

The food consists of microscopical organisms, chiefly infusoria, spores
and the like, swept into the mouth by the currents produced by the
waving of the tentacular cilia.

The nervous system is again confined to a small double ganglion
lying between the oesophagus and the anus and giving off branches
to the lophophore. A delicate commissure surrounds the oesophagus.
No special sense organs are known.

No heart is present ; the coelomic fluid, wherein corpuscles float,
courses freely through all parts of the colony, kept continously in
motion by the cilia of the internal surface. Aeration is secured in the
thin-walled tentacles which are hollow, branches of the coelom being
continued into them.

EEPBODUCTION. — The fresh-water bryozoa are hermaphrodite.
Usually the testis is situated on the funiculus (/.), while the ovary is
placed towards the forward end of the body (o.), and derived from the
endocyst or lining of the ectocyst or cuticle.

In addition to this, the fresh- water Bryozoa are remarkable for an
asexual reproduction by means of winterbuds or statoblasts. Upon
the approach of winter, the era of dissolution for the adult colony,
buds are formed on the funiculus ; the cells at one end of the bud
grow round the remainder and form two convex horny plates attached
by their margins to one another, and with air cells arranged in a
marginal ring. In Plumatclla, which we are now describing, the
statoblast is plain, but in Cristatella it is an exceedingly beautiful
object, studded with minute knobs and provided with barbed spines

120 MICROSCOPICAL STUDIES.

designed to aid in the dispersal of these resting buds. The marginal
air-cushion found both in this genus and also in Pliimatclla and other
fresh-water Bryozoa, has obviously a similar duty. In Fig. 1, PI. IX.,
a string of statoblasts in various stages of development is seen upon
the funiculus of each zooid ; while Figs. 2 and 3 give side and face
views of a single statoblast. The marginal air-cushion in mature buds
shows under the microscope as a broad black border. The statoblasts
becomes free upon the death and decay of the parent, rising to the
surface and floating at the mercy of the currents. In some genera, as
Pcctinella and Cristatella, the whole parent stock breaks free and floats
freely hither and thither — an additional help in the dispersal of the
statoblasts. The latter remain without change during winter. In
spring, under favourable conditions, the valves open, and a tiny mina-
ture of the parent zooid emerges. It floats passive for a while, then
makes fast to some object, generally a water-weed, and soon by active
budding becomes a colonial parent.

The asexual reproduction of the fresh-water Sponge by similar
resting buds should be remembered — evidently a method towards
the perpetuation of the species induced by similarly exceptional
requirements.

The Gymnolsemata, which are all marine, save Paludicella, are
infinitely more numerous and in form more diverse. Fig. 13 gives a
fair diagrammatic idea of their structure, while Fig. 12 shows the same
in a state of retraction. They differ from the fresh- water forms in the
lophophore being circular and not crescentic, in frequently having the
sexes separate, and in having no asexual reproduction by statoblasts.

Bowcrbankia imbricata is a typical species, often cast up on our coast
attached to the brown-podded sea-weed Halidrys. Fig. 6 shows a
branch, natural size, while Fig. 7 shows a cluster of individuals. The
cuticle is chitinous, and the zooids are very similar to the diagram
given, save that they have a well-marked gizzard at the fore part of
the stomach.

Figs. 8 and 9 show the calcareous framework of a pretty little
Bryozoon called Lichenopora hispida (Fleming), often found in caves at
extreme low-water mark within the Laminarian zone. It may also
be procured in dredging over coralline bottom, attached to the great
massive Lcpralia, another calcareous Bryozoon.

Lichenopora^ the Cup-Coralline, as it may be appropriately named,
is about | in. to £ in. in diameter ; a snowy-white fragile porcelain
cup, from whose hollow arise tubular columns, each the home of a
delicate zooid. The calcareous wall of this tube is equivalent to the
horny or gelatinous ectocyst or cuticle of Plumatella or Lopliopus. In
the centre of cup are usually one or two elevated trumpet-shaped
openings, the ooecia or receptacles for the ova.

AVICULARIA AND VIBEACULA. 121

In both Bowerbankia and Lichenopora the zooids of each colony are
very similar one to the other ; in other genera, however, especially in
Bugula, a distinct polymorphism seems to take place. Bugula lives in
the Laminarian and Coralline Zones and except at very low spring
tides can only be taken in the dredge. It is fairly abundant in British
waters, and grows in loose spiral coils of great elegance. Examining
a spray, we find the zooecia or cells are arranged in tabular manner,
edge to edge, the apertures all on the inner surface. The normal
zooids approach closely to the form of those of Bowerbankia, but what
arrests the attention at once is the presence of peculiar beak-like bodies
scattered over the surface. Each is a small rounded object provided
with a curved upper beak, to which is hinged a movable jaw-like
mandible, constantly snapping viciously. The whole so closely re-
sembles a bird's head and beak that it has received the name of
avicularium. The only internal organs are two powerful muscles used
to set the mandible in motion. According to many authorities, these
avicularia are believed to be zooids modified for a highly specialised
function, but this point is not assured. What the exact function is, is
also doubtful. The more likely theory is that they are protective,
scaring minute predatory creatures away by the constant gnashing of
the jaws ; some, however, have argued that they assist in procuring
food. Thus they may sometimes be seen holding some minute worm
or crustacean in their grip and while such object is useless, from its
size, as food, yet if held till decay begins, the disintegrated particles
may be swept into the mouth by the waving of the tentacular cilia.
Among my microscopical preparations I have now one wherein an
avicularium is holding the limb of a small Amphipod.

Whip-like organs, called Yibracula, are also seen in Scrupocdlaria,
and other Bryozoa, and again are thought by many to be modified
individuals bereft of alimentary, reproductive and other organs except-
ing muscles. The vibracula most probably also subserve a protective
function, their constant lashing keeping unwelcome visitors at a
respectful distance and also freeing the surface of the colony from
decaying or otherwise undesirable matter. It may also be that the
lashing serves to keep the water around in healthful motion and so to
bring new food particles within reach of the ciliary vortices.

DIVISIONS OF THE GYMNOL^MATA : —

Sub-Order a. — Cyclostomata. Zooecial orifaces round, without avicu-
laria or vibracula or opercular apparatus, e.g., Crisia, Lichenopora.

Sub-Order b. — Ctenostomata. Zooecial orifaces closed upon retraction
by folds of the tentacular sheath or by a circlet of spines, e.g.,

122 MICROSCOPICAL STUDIES.

Alcyonidium, and Bowcrbankia (marine) and Paludicella (fresh-
water).

Sub-Order c. — Cheilostomata. Zooecial orifaces furnished with a
movable thickened lip or operculum, or with a sphincter muscle ;
vibracula and for avicularia usually present, e.g., Actca, Buyula,
Flustra, Scrupocellaria, Lcpralia.*

STUDY XXV.— THE SAPPHIRINIDJS.

The Sapphirinidae are Copepoda of large size found in warm seas.
The males are free-swimming and pelagic, captured usually in the tow-
net, whereas the females are seldom taken free, as they pass their life
as commensals or messmates in the branchial cavities of such pelagic
Ascidians as Salpa.

The females differ considerably from the males in form, as is usual
with species where the sexes have divergent habits. In this article we
shall confine attention to the males.

Male individuals of this family are all of comparatively large size,
the body is dorso-ventrally compressed, and these characteristics in
conjunction with the perfect transparency of the chitinous covering
makes the Sapphirinida a splendid type-group wherein to study with
ease the structure of all the internal organs.

The prevailing body-form of the Copepoda is pear-shaped, and the
common Cyclops, abundant in fresh-water ponds, is a good representa-
tive. In the Sapphirinida, as already mentioned, the body is flattened ;
in contour it is oval, showing a large cephalic shield, five thoracic
segments, and an equal number of abdominal segments terminating in
two leaf -like caudal lamellae. Only four of the thoracic segments are
readily distinguishable, the fifth being rudimentary (PI. X., Fig. 1, th.).
The first abdominal is marked by the external openings of the sexual
organs being here placed.

The appendages are of the normal Copepod type, save in the form
of the posterior antennae (p>a.) and of the appendages around the
mouth (maxillae), which terminate in hook -like claws well adapted
both for clinging to the host should the Copepod be sojourning with
one, and for grasping the female during accouplement. A swimming
foot of Sapphirina Clausi of typical Copepod form is shown at Fig. X.,
consisting of an inner and an outer branch (endo- and exo-podite) of

* The marine Bryozoa live well in confinement and several kinds (Pediccllina,
Alcyonidium^ Flustrella, Amathia, &c.) can be supplied living from the Jersey
Biological Station. It is advisable to give, if possible, a couple of days' notice. Full
particulars supplied on application to the Director.

SAPPHIRINE COPEPODS. 123

about equal size, and armed with strong oar-like bristles of great
service in swimming, Sometimes, however, as in S. Danvinii
(Haeckel), the inner branch is atrophied, indicating weaker swimming

powers.
No gills are present; the cuticle is so thin and delicate that the

whole surface of the body functions in breathing.

When seen swimming the Sapphirinids present a magnificent play
of metallic colours — the acme of iridescence — as they drive rapidly
through the water, mere sapphirine glints of darting light ; the reason
for the generic name is obvious. If we examine the cuticle, the cause
of the ever-changing sheen is found to be due to excessively fine
parallel and cross rulings upon the surface that produce the optical
effect of lightning-swift colour change with every alteration in the
incidence of the light.

The cuticle is underlaid and produced by an excessively thin layer,
the hypodermis, in which lie numbers of most peculiar dermal glands.
Their proportion varies greatly in different species, attaining greatest
development in S. Edwardsii (Fig. I.), where they are thickly scattered
over the whole body. Each opens to the exterior by a fine duct
passing through the cuticle. Usually they are unicellular as in the
species named ; more rarely they are multicellular, as in S. Danvinii,
composed of from three to seven or even more cells. Usually each
gland is accompanied by a nerve ganglion giving off a sensory bristle
or seta that projects from the surface of the cuticle. A common nerve
serves each pair, breaking into two branches ere reaching them. The
function of the glands is excretory ; its activity is apparently
controlled from its companion nerve cell, which in turn receives im-
pressions from the surrounding medium through its projecting seta
(see Figs. II. and V., y., pg. and yg.).

A former article in Vol. I., p. 42, described the muscular arrange-
ment of Honstrilla, an allied Copepod. That of Sapphirina is on the
same plan.

The oesophagus passes through the centre of the ganglionic mass,
and leads directly into a dilated stomach provided with glandular
diverticula or pouches that may be considered as acting the parts of
liver and pancreas (L). The form of this " liver " varies with the species ;
note how in S. Edwardsii it forms a collar-like mass around the anterior
end of the stomach, while in S. Gegenbauri it forms four pouch-like
branches. The intestine is straight, ending between the caudal plates.

The Nervous System exhibits great centralization. There is no
distinction into brain and ventral ganglionic chain such as is seen in
the free-swimming Copepods. All are fused into one great ganglionic
mass pierced by the oesophagus. But as a compensation, or indeed as

124 MICROSCOPICAL STUDIES.

a consequence, the radiating nerves are wonderfully numerous and
strong. Anteriorly they branch off to the eyes and head appendages,
while posteriorly two great trunks are given off to supply the swimming
feet and the remainder of the thorax and abdomen. The way these
nerves divide into a network of twigs serving the dermal glands has
already been noticed.

Of Sensory Organs, the chief are the eyes, of which there are
three — two complex lateral eyes lying on either side of a small and
simple median eye. The structure of a lateral eye consists essentially
of a very large globular corneal lens (cl.) lying in front of the true crys-
talline lens or " cone," behind which again is a large pigment body
resting upon the ganglionic mass. The corneal lens is derived from the
cuticle ; in some species, as in S. Edwardsii, it rests directly on the
crystalline lens ; in others, as in S. Gcgenbauri, and especially in S.
Clausi and S. Darwinii, quite a considerable distance separates the two
(Fig. VI.).

The sensory setae of the peripheral nerve cells have already been
referred to ; the only other sensory organ is the frontal sensory organ
of unknown use, seen between the corneal lenses (x). It is noteworthy
that the Nauplius larvae of the higher Crustacea also show similar
organs, from which we may infer that this is an organ present in the
ancestral Crustacean stem.

No heart or blood-vascular system is present. The blood or
coelomic fluid moves freely in the whole of the coelome or body cavity.

Lining every part of the body wall is a peculiar stellately-branched
and very delicate form of tissue, called the Fat-body, wherein are
formed oil spheres of wonderfully large size. In some species they are
specially numerous, as, for example, in S. Clausi and S. Edwardsii, and
are symmetrically disposed. The fat-body as a whole serves as a
reserve of nourishment, and is especially useful when the animal
moults and when the reproductive function makes special drain upon
the vitality of the individual.

EEPRODUCTION. — In the males here figured, note the two-lobed
testis (Fig. VI., £.), stretching across the body close to the stomach.
On either side is given off a long tubular vas deferens, glandular at its
further end and then expanding into a wider region, the spermatophore
pouch, wherein numerous spermatozoa lie encased in an envelope or
spermatophore until such time as copulation shall take place, when
the spermatophore being fixed by the male upon the genital segment of
the female, the spermatozoa break through their envelope and pass
individually into the oviducal openings.

The young pass through well-marked Nauplius stages.

CHOICE

MICROSCOPICAL PREPARATIONS IN MARINE ZOOLOGY & BOTANY-

Jl " Micro Studies in Marine Zoology."— Two series of 14 splendid slides (price 1/3
to 21- if sold separately) with 11 plates of original explanatory drawings, and over
100 pages of descriptive letterpress each, post free £± Is.
2 " Micro Studies in Botany."— A series of 20 magnificent slides of Flower-buds, &c.
ILlOrt (difficult and beautiful preparations only>, illustrated with 20 original Photo-
micrographs and descriptive letterpress post free £± Is

3 Set of 48 specially chosen slides illustrative of Elementary Botany.—
Specially suitable for teachers' and students' use post free £1 Is.

V 4 Set of 48 typical slides illustrative of Elementary Zoology.. .post free £1 Is.

Microscopical Studies in Marine Zoology,

SERIES I.

As referred to above consists of the following 14 Slides : —

1 Lamp-Polyp, Lucernaria, showing Gonads, &c. 1/9

2 Pelagic Annelid Tomopteris 2/0

3 Dorsal view of Pelagic Tunicate Salpa 1/6

i Lateral view of Pelagic Tunicate Salpa 2/0

5 Type slide of Sponge anatomy, very fine 2/6

6 Monstnlla, a Parasitic Copepod of strange life-

history 1/6

8 Zoea of Porcellain crab, extremely fine

9 Phyllospma-larva of Crawfish Scyllarus

10 Type slide of Anemone structure

11 Fully extended polyp of Alcyonium ...

12 Medusa of Obelia geniculata

13 Scale-backed worm Polynoe (entire) ...

14 Tadpole larvae of Compound Ascidiau

7 Young Amphioxus, structure perfectly shown J/6

Price £1 Is. post free, inclusive of letterpress and illustrations.

1/3

1/6
2/-
1/6
1/6
1/6
1/6

SERIES II.

The full set of 14 Slides is now complete. Can be supplied by return post. Price, inclusive of four

accompanying parts of descriptive letterpress (110 pages) and 10 full-page plates of original illustrations,

£1 Is. post free ($6.25 post free to U.S.A.).

The Slides are as follows :—

1 Colonial Radiolarian Sphcerozoum 1/6

2 Obelia geniculata, polyps fully expanded 1/6

3 Larval Feather-Star 1/6

4 Entire Pteropod (Creseis) 1/6 to 1/9

5 Coryne vaginata, fully expanded 1/6

(i .SV rtularia pumila „ „ 1/6

7 Nauplii larvae of Rock Barnacle 1/6

8 Pupal larvae of Rock Barnacle 1/6

9 Plumularia, fully expanded 1/6

10 Entire young Cuttlefish, just hatched 1/6

11 Sec. eye of Cuttlefish (specially selected) 1/6

12 Sapphirina, a luminous Copepod (very fine) ... 2/-
1H Polyzoon, Lophopiis, polyps fully expanded ... 1/6
14 Cup Coralline, Lichenopora 1/6

The expanded Zoophytes (Nos. 2, 5, 6, and 9) are exquisite mounts— Specially selected.

The two Series of Slides as above, together with a bound volume of letterpress and

plates, post free for £2 2s.

Museum Preparations,

FISHES:-

British Fishes prepared by my recently perfected method— as supplied to the Brit
Museum — are beyond criticism in the way in which the original contours are retained, while '
colouring is absolutely truthful.

No Marine Fishes have ever been prepared to compare with these, which can be obta
solely from myself. My method, I may say, has absolutely nothing in common with the ;
fashioned ordinary methods of taxidermy, and its products must be seen to be appreciated.

Testimonials, Samples and Price Lists on application.

SKELETONS

Skeleton of Scyllium, fully articulated, in Museum jar, 18 ins. high, as supplied to the
principal Colleges in Britain. £1 10s. complete.

Disarticulated Lobster, every part lettered and numbered after Huxley, with accompanying
index-table, in glass-fronted polished case £1 10s., or on plain wood mount £1 2s. The former
is recommended.

List of Skeletons and Dissections on application.

LANTERN SLIDES, WALL-DIAGRAMS and ZOOLOGICAL SPECIMENS
of all Descriptions. Lists post free.

JAMES HORNELL, The Biological Station, JERSEY,