PART III.

FRESHWATER POLYZOA

(CTENOSTOMATA & PHYLACTOLÆMATA).

INTRODUCTION TO PART III.

I.

STATUS AND STRUCTURE OF THE POLYZOA.

The Polyzoa constitute a class in the third great division of the animal

kingdom, the so-called Triploblastea. In this division are included also

the worms, molluscs, insects, crustacea, spiders, vertebrates, etc.; for

heterogeneous as its elements appear, all these animals may be

considered to have essential features in common, in particular a body

consisting primarily of three cellular layers. Most of them also possess

a body cavity distinct from the alimentary canal. Some authors regard

the position of the polyzoa as near that of the higher worms, but the

group is an isolated one.

In considering the anatomy of simple forms of animal life such as the

sponges it is necessary to pay attention mainly to individual cells, but

in discussing more complicated forms our notice is first attracted to

tissues and organs, for the cells of which these tissues and organs are

composed have each a definite position, a definite structure, and a

definite function. The most characteristic feature of the polyzoa,

considered from this point of view, is the fact that most of their

organs fall into one of two categories and are connected either with

what is called the "zooecium" or with what is known as the "polypide."

The zooecium is a cage in which the polypide is enclosed, but it is a

living cage, differing from the shell of a snail or the tubes in which

many worms encase themselves in being part of the animal itself. The

polypide consists mainly of the organs connected directly and indirectly

with nutrition and of part of the muscular system; its name is derived

from the fact that it bears a superficial resemblance to a polyp such as

_Hydra_.

The shape and structure of the zooecium differs greatly in different

groups of polyzoa. In its simplest form it is merely a cylindrical tube

of living matter which secretes an outer horny or gelatinous covering.

It is open at the end furthest from its base, at which it is attached

either to another zooecium or to some kind of supporting structure.

Certain parts of the polypide can always be extruded from the aperture,

which is known technically as the "orifice," or withdrawn through it

into the zooecium. When the polypide is retracted it draws in with it a

portion of the zooecium. The dead outer layer or ectocyst lines part of

the portion thus invaginated and forms the walls of a cavity within the

orifice. The base of this cavity consists in many forms of a transverse

partition pierced in the middle by a circular hole and known as the

"diaphragm." The diaphragm, however, does not constitute the limit of

the invaginated portion of the zooecium, for the living inner wall or

endocyst is dragged in still further and forms a sheath round the

retracted tentacles. When the tentacles are protruded they emerge

through the hole in the diaphragm, carrying with them their sheath of

endocyst. The invagination above the diaphragm, consisting of both

endocyst and ectocyst, is then everted.

The tentacles are a characteristic feature of the polypide. Together

with the base to which they are attached they are known as the

"lophophore"; they surround the mouth, usually in a circle. They differ

widely from the tentacles of _Hydra_ in both structure and function,

although they too serve as organs for the capture of prey; they are not

highly contractile and are not provided with nettle-cells but are

covered with cilia, which are in constant motion. When extruded they

form a conspicuous calix-like crown to the zooecium, but in the

retracted condition they are closely pressed together and lie parallel

to one another. They are capable individually of motion in all

directions but, although they usually move in concert, they cannot as a

rule seize objects between them.

The mouth is a hole situated in the midst of the tentacles. It leads

directly into a funnel-shaped oesophagus, the upper part of which is

lined with cilia and is sometimes distinguished as the "pharynx," while

the lower part, the oesophagus proper, is a thin-walled tube that

connects the pharynx with the stomach, which it enters on the dorsal

side. The stomach is a bulky organ that differs markedly in form and

structure in different groups of polyzoa. It is lined internally with

glandular cells and the inner wall is sometimes thrown into folds or

"rugæ." The part with which the oesophagus communicates is known as the

"cardiac" portion, while the part whence the intestine originates is

called the "pylorus" or "pyloric" portion. The intestine commences on

the ventral side opposite the entrance of the oesophagus and nearly on a

level with it, the bulk of the stomach depending between the two tubes.

This part of the stomach is often produced into a blind tube, the fundus

or cæcum. The alimentary canal may therefore be described as distinctly

Y-shaped. The proximal part of the intestine is in some forms lined with

cilia, and the tube as a whole is usually divided into two parts--the

intestine proper, which is nearest the stomach, and the rectum, which

opens by the anus not far from the mouth.

The nervous system consists of a central ganglion or brain, which is

situated at the base of the tentacles on the side nearest the anus and

gives out radiating nerves in all directions. Close to the brain and

providing a communication between the cavity of the zooecium and the

cavity in which the tentacles are contained (or, in the case of an

expanded polyp, the external world) is a ciliated tube known as the

"intertentacular organ." Apparently it acts as a passage through which

the genital products are expelled; but contradictory statements have

been made regarding it, and perhaps it is present only at certain

seasons or in certain conditions of the polypide.

[Illustration: Fig. 30.--Vertical section through a polypide of

_Alcyonidium_ with the polypide retracted (after Prouho).

A=orifice; B=contracted collar; C=diaphragm; D=parieto-vaginal muscles;

E=tentacles; F=pharynx; G=oesophagus; H=stomach; J=intestine; K=rectum;

L=intertentacular organ; M=retractor muscle; N=testes; O=ovary;

P=funiculus; Q=parietal muscles; R=ectocyst; S=endocyst.]

The muscular system is often of a complicated nature, but three sets of

muscles may be distinguished as being of peculiar importance, viz., (i)

the retractor muscles, which are fixed to the base of the lophophore at

one end and to the base of the zooecium at the other, and by contracting

pull the former back into the zooecium; (ii) the parieto-vaginal

muscles, which connect the upper part of the invaginated portion of the

zooecium with the main wall thereof; and (iii) the parietal muscles,

which run round the inner wall of the zooecium and compress the zooecium

as a whole. The parietal muscles are not developed in the

Phylactolæmata, the most highly specialized group of freshwater polyzoa.

The cavity between the polypide and the zooecium contains a reticulate

tissue of cells known as the "funicular" tissue, and this tissue is

usually concentrated to form a hollow strand or strands ("funiculi")

that connect the outer wall of the alimentary canal with the endocyst.

This rapid sketch of the general anatomy of a simple polyzoon will be

the best understood by comparing it with fig. 30, which represents, in a

somewhat diagrammatic fashion, a vertical section through a single

zooecium and polypide of the order Ctenostomata, to which some of the

freshwater species belong. The polypide is represented in a retracted

condition in which the Y-shaped disposition of the alimentary canal is

somewhat obscured.

In the great majority of cases the polyzoa form permanent colonies or

polyparia, each of which consists of a number of individual zooecia and

polypides connected together by threads of living tissue. These colonies

are formed by budding, not by independent individuals becoming

associated together. In a few cases compound colonies are formed owing

to the fact that separate simple colonies congregate and secrete a

common investment; but in these cases there is no organic connection

between the constituent colonies. It is only in the small subclass

Entoprocta, the polypides and zooecia of which are not nearly so

distinct from one another as they are in other polyzoa (the Ectoprocta),

that mature solitary individuals occur.

As representatives of both subclasses of polyzoa and of more than one

order of Ectoprocta occur in fresh water, I have prefaced my description

of the Indian species with a synopsis of the more conspicuous characters

of the different groups (pp. 183-186).

CAPTURE AND DIGESTION OF FOOD: ELIMINATION OF WASTE PRODUCTS.

The food of all polyzoa consists of minute living organisms, but its

exact nature has been little studied as regards individual species and

genera. In _Victorella bengalensis_ it consists largely of diatoms,

while the species of _Hislopia_ and _Arachnoidea_ possess an alimentary

canal modified for the purpose of retaining flagellate organisms until

they become encysted. Similar organisms form a large part of the food of

the phylactolæmata.

Although the tentacles may be correctly described as organs used in

capturing prey, they do not themselves seize it but waft it by means of

the currents set up by their cilia to the mouth, into which it is swept

by the currents produced by the cilia lining the pharynx. The tentacles

are also able in some species to interlace themselves in order to

prevent the escape of prey. Apparently they have the power of rejecting

unsuitable food, for they may often be observed to bend backwards and

forwards and thrust particles that have approached them away, and if the

water contains anything of a noxious nature in solution the lophophore

is immediately retracted, unless it has been completely paralysed. In

the phylactolæmata the peculiar organ known as the epistome is capable

of closing the mouth completely, and probably acts as an additional

safeguard in preventing the ingestion of anything of an injurious

nature.

In many genera and larger groups the food commonly passes down the

pharynx into the stomach without interruption, although it is probable

that in all species the oesophagus can be closed off from the stomach by

a valve at its base. In some forms, however, a "gizzard" is interposed

between the oesophagus and the stomach. This gizzard has not the same

function in all cases, for whereas in some forms (_e. g._, in

_Bowerbankia_) it is lined with horny projections and is a powerful

crushing organ, in others (_e. g._, in _Hislopia_ or _Victorella_) it

acts as an antechamber in which food can be preserved without being

crushed until it is required for digestion, or rough indigestible

particles can be retained which would injure the delicate walls of the

stomach.

Digestion takes place mainly in the stomach, the walls of which are of a

glandular nature. The excreta are formed into oval masses in the rectum

and are extruded from the anus in this condition.

Although the gross non-nutritious parts of the food are passed _per

anum_, the waste products of the vital processes are not eliminated so

easily, and a remarkable process known as the formation of brown bodies

frequently takes place. This process cannot be described more clearly

and succinctly than by quoting Dr. Harmer's description of it from pp.

471 and 472 of vol. ii. of the Cambridge Natural History, a volume to

which I have been much indebted in the preparation of this introduction.

The description is based very largely on Dr. Harmer's own

observations[AW].

[Footnote AW: Q. J. Micr. Sci. xxxiii, p. 123 (1892).]

"The tentacles, alimentary canal, and nervous system break down, and the

tentacles cease to be capable of being protruded. The degenerating

organs become compacted into a rounded mass, known from its colour as

the 'brown body.' This structure may readily be seen in a large

proportion of the zooecia of transparent species. In active parts of the

colony of the body-wall next develops an internal bud-like structure,

which rapidly acquires the form of a new polypide. This takes the place

originally occupied by the old polypide, while the latter may either

remain in the zooecium in the permanent form of a 'brown body,' or pass

to the exterior. In _Flustra_ the young polypide-bud becomes connected

with the 'brown body' by a funiculus. The apex of the blind pouch or

'cæcum' of the young stomach is guided by this strand to the 'brown

body,' which it partially surrounds. The 'brown body' then breaks up,

and its fragments pass into the cavity of the stomach, from which they

reach the exterior by means of the anus."

Brown bodies are rarely if ever found in the phylactolæmata, in which

the life of the colony is always short; but they are not uncommon in

_Hislopia_ and _Victorella_, although in the case of the former they may

easily escape notice on account of the fact that they are much paler in

colour than is usually the case. When they are found in a ctenostome the

collar-like membrane characteristic of the suborder is extruded from the

orifice (which then disappears) and remains as a conspicuous external

addition to the zooecium, the ectocyst of which, at any rate in

_Bowerbankia_ and _Victorella_, sometimes becomes thickened and dark in

colour.

It is noteworthy that the colouring matter of the brown bodies is

practically the only colouring matter found in the polypides of most

polyzoa. Young polypides are practically colourless in almost all cases.

REPRODUCTION: BUDDING.

Polyzoa reproduce their species in three ways--(i) by means of eggs,

(ii) by budding, and (iii) by means of bodies developed asexually and

capable of lying dormant in unfavourable conditions without losing their

vitality.

Most, if not all species are hermaphrodite, eggs and spermatozoa being

produced either simultaneously or in succession by each individual, or

by certain individuals in each zoarium. The reproductive organs are

borne on the inner surface of the endocyst, as a rule in a definite

position, and often in connection with the funiculus or funiculi. It is

doubtful to what extent eggs are habitually fertilized by spermatozoa of

the individual that has borne them, but in some cases this is

practically impossible and spermatozoa from other individuals must be

introduced into the zooecium.

Budding as a rule does not result in the formation of independent

organisms, but is rather comparable to the proliferation that has become

the normal method of growth in sponges, except of course that

individuality is much more marked in the component parts of a polyzoon

colony than it is in a sponge. In the genera described in this volume

budding takes place by the outgrowth of a part of the body-wall and the

formation therein of a new polypide, but the order in which the buds

appear and their arrangement in reference to the parent zooecium is

different in the different groups. In the freshwater ctenostomes three

buds are typically produced from each zooecium, one at the anterior end

and one at either side, the two latter being exactly opposite one

another. The parent zooecium in this formation arises from another

zooecium situated immediately behind it, so that each zooecium, except

at the extremities of the zoarium, is connected with four other zooecia,

the five together forming a cross. The two lateral buds are, however,

frequently suppressed, or only one of them is developed, and a linear

series of zooecia with occasional lateral branches is formed instead of

a series of crosses. In the phylactolæmata, on the other hand, the

linear method of budding is the typical one, but granddaughter-buds are

produced long before the daughter-buds are mature, so that the zooecia

are frequently pressed together, and lateral buds are produced

irregularly. In _Victorella_ additional adventitious buds are produced

freely near the tip of the zooecium.

Reproduction by spontaneous fission sometimes occurs, especially in the

Lophopinæ, but the process differs from that which takes place when a

_Hydra_ divides into two, for there is no division of individual zooecia

or polypides but merely one of the whole zoarium.

The production of reproductive bodies analogous to the gemmules of

sponges appears to be confined in the polyzoa to the species that

inhabit fresh or brackish water, nor does it occur in all of these.

All the phylactolæmata produce, within their zooecia, the bodies known

as statoblasts. These bodies consist essentially of masses of cells

containing abundant food-material and enclosed in a capsule with thick

horny walls. In many cases the capsule is surrounded by a "swim-ring"

composed of a mass of horny-walled chambers filled with air, which

renders the statoblast extremely light and enables it to float on the

surface of the water; while in some genera the margin of the swim-ring

bears peculiar hooked processes, the function of which is obscure. The

whole structure first becomes visible as a mass of cells (the origin of

all of which is not the same) formed in connection with the funiculus,

and the statoblast may be regarded as an internal bud. Its origin and

development in different genera has been studied by several authors,

notably by Oka[AX] in _Pectinatella_, and by Braem[AY] in _Cristatella_.

[Footnote AX: Journ. Coll. Sci. Tokyo, iv, p. 124 (1891).]

[Footnote AY: Bibliotheca Zoologica, ii, pt. 6, p. 17

(1890).]

The external form of the statoblasts is very important in the

classification of the phylactolæmata, to which these structures are

confined. In all the genera that occur in India they are flattened and

have an oval, circular, or approximately oval outline.

In temperate climates statoblasts are produced in great profusion at the

approach of winter, but in India they occur, in most species, in

greatest numbers at the approach of the hot weather.

[Illustration: Fig. 31.--Part of the zoarium of _Victorella bengalensis_

entirely transformed into resting buds, × 25. (From an aquarium in

Calcutta.)]

In the family Paludicellidæ (ctenostomata) external buds which resemble

the statoblasts in many respects are produced at the approach of

unfavourable climatic conditions, but no such buds are known in the

family Hislopiidæ, the zoaria of which appear to be practically

perennial. The buds consist of masses of cells formed at the points at

which ordinary buds would naturally be produced, but packed with

food-material and protected like statoblasts by a thick horny coat. It

seems also that old zooecia and polypides are sometimes transformed into

buds of the kind (fig. 31), and it is possible that there is some

connection between the formation of brown bodies and their production.

Like the statoblasts of the phylactolæmata the resting buds of the

Paludicellidæ are produced in Europe at the approach of winter, and in

India at that of the hot weather.

DEVELOPMENT.

(a) _From the Egg._

Some polyzoa are oviparous, while in others a larva is formed within the

zooecium and does not escape until it has attained some complexity of

structure. Both the ctenostomatous genera that are found in fresh water

in India are oviparous, but whereas in _Victorella_ the egg is small and

appears to be extruded soon after its fertilization, in _Hislopia_ it

remains in the zooecium for a considerable time, increases to a

relatively large size, and in some unknown manner accumulates a

considerable amount of food-material before escaping. Unfortunately the

development is unknown in both genera.

In the phylactolæmata the life-history is much better known, having been

studied by several authors, notably by Allman, by Kraepelin, and by

Braem (1908). The egg is contained in a thin membrane, and while still

enclosed in the zooecium, forms by regular division a hollow sphere

composed of similar cells. This sphere then assumes an ovoid form,

becomes covered with cilia externally, and breaks its way through the

egg-membrane into the cavity of the zooecium. Inside the embryo, by a

process analogous to budding, a polypide or a pair of polypides is

formed. Meanwhile the embryo has become distinctly pear-shaped, the

polypide or polypides being situated at its narrow end, in which a pore

makes its appearance. The walls are hollow in the region occupied by the

polypide, the cavity contained in them being bridged by slender threads

of tissue. The larva thus composed makes its way out of the zooecium,

according to Kraepelin through the orifice of a degenerate bud formed

for its reception, and swims about for a short time by means of the

cilia with which it is covered. Its broad end then affixes itself to

some solid object, the polypide is everted through the pore at the

narrow end and the whole of that part of the larva which formerly

enclosed it is turned completely inside out. A zoarium with its included

polypides is finally produced from the young polypide by the rapid

development of buds.

(b) _From the Statoblast and Resting Buds._

There is little information available as regards the development of the

young polyzoon in the resting buds of the freshwater ctenostomes. In

_Paludicella_ and _Pottsiella_ the capsule of the bud splits

longitudinally into two valves and the polypide emerges between them;

but in _Victorella bengalensis_ one of the projections on the margin of

the bud appears to be transformed directly into the tip of a new

zooecium and the capsule is gradually absorbed.

Contradictory statements have been made as regards several important

points in the development of the statoblast and it is probable that

considerable differences exist in different species. The following facts

appear to be of general application. The cellular contents of the

capsule consist mainly of a mass of cells packed with food-material in a

granular form, the whole enclosed in a delicate membrane formed of flat

cells. When conditions become favourable for development a cavity

appears near one end of the mass and the cells that form its walls

assume a columnar form in vertical section. The cavity increases rapidly

in size, and, as it does so, a young polypide is budded off from its

walls. Another bud may then appear in a similar fashion, and the

zooecium of the first bud assumes its characteristic features. The

capsule then splits longitudinally into two disk-like valves and the

young polypide, in some cases already possessing a daughter bud, emerges

in its zooecium, adheres by its base to some external object and

produces a new polyparium by budding. The two valves of the statoblast

often remain attached to the zoarium that has emerged from between them

until it attains considerable dimensions (see Plate IV, fig. 3 _a_).

What conditions favour development is a question that cannot yet be

answered in a satisfactory manner. Statoblasts can lie dormant for

months and even for years without losing their power of germinating, and

it is known that in Europe they germinate more readily after being

subjected to a low temperature. In tropical India this is, of course, an

impossible condition, but perhaps an abnormally high temperature has the

same effect. At any rate it is an established fact that whereas the

gemmules of most species germinate in Europe in spring, in Bengal they

germinate either at the beginning of the "rains" or at that of our mild

Indian winter.

MOVEMENTS.

[Illustration: Fig. 32.--Zoarium of _Lophopodella carteri_ moving along

the stem of a water plant, × 4. (From Igatpuri Lake.)]

In the vast majority of the polyzoa, marine as well as freshwater,

movement is practically confined to the polypide, the external walls of

the zooecium being rigid, the zooecia being closely linked together and

the whole zoarium permanently fixed to some extraneous object. In a few

freshwater species belonging to the genera _Cristatella_, _Lophopus_,

_Lophopodella_ and _Pectinatella_, the whole zoarium has the power of

progression. This power is best developed in _Cristatella_, which glides

along with considerable rapidity on a highly specialized "sole" provided

with abundant mucus and representing all that remains of the ectocyst.

It is by no means clear how the zoaria of the other genera move from one

place to another, for the base is not modified, so far as can be seen,

for the purpose, and the motion is extremely slow. It is probable,

however, that progression is effected by alternate expansions and

contractions of the base, and in _Lophopodella_ (fig. 32), which moves

rather less slowly than its allies, the anterior part of the base is

raised at times from the surface along which it is moving. The whole

zoarium can be released in this way and occasionally drops through the

water, and is perhaps carried by currents from one place to another in

so doing.

So far as the polypides are concerned, the most important movements are

those which enable the lophophore and the adjacent parts to be extruded

from and withdrawn into the zooecium. The latter movement is executed by

means of the retractor muscles, which by contracting drag the extruded

parts back towards the posterior end of the endocyst, but it is not by

any means certain how the extrusion of the lophophore is brought about.

In most ctenostomes the action of the parietal muscles doubtless assists

in squeezing it out when the retractor and parieto-vaginal muscles

relax, but Oka states that protrusion can be effected in the

phylactolæmata even after the zooecium has been cut open. Possibly some

hydrostatic action takes place, however, and allowance must always be

made for the natural resilience of the inverted portion of the ectocyst.

Even when the polypide is retracted, muscular action does not cease, for

frequent movements, in some cases apparently rhythmical, of the

alimentary canal may be observed, and in _Hislopia_ contraction of the

gizzard takes place at irregular intervals.

When the lophophore is expanded, the tentacles in favourable

circumstances remain almost still, except for the movements of their

cilia; but if a particle of matter too large for the mouth to swallow or

otherwise unsuitable is brought by the currents of the cilia towards it,

individual tentacles can be bent down to wave it away and similar

movements are often observed without apparent cause.

In the cheilostomes certain individuals of each zoarium are often

profoundly modified in shape and function and exhibit almost constant

rhythmical or convulsive movements, some ("avicularia") being shaped

like a bird's beak and snapping together, others ("vibracula") being

more or less thread-like and having a waving motion.

DISTRIBUTION OF THE FRESHWATER POLYZOA.

Fifteen genera of freshwater Polyzoa are now recognized, one

entoproctous and fourteen ectoproctous; five of the latter are

ctenostomatous and nine phylactolæmatous. Of the fourteen ectoproctous

genera seven are known to occur in India, viz., _Victorella_,

_Hislopia_, _Fredericella_, _Plumatella_, _Stolella_, _Lophopodella_,

and _Pectinatella_. Except _Stolella_, which is only known from northern

India, these genera have an extremely wide geographical range;

_Victorella_ occurs in Europe, India, Africa, and Australia; _Hislopia_

in India, Indo-China, China, and Siberia; _Fredericella_ in Europe, N.

America, Africa, India, and Australia; _Plumatella_ in all geographical

regions; _Lophopodella_ in E. and S. Africa, India, and Japan;

_Pectinatella_ in Europe, N. America, Japan, and India.

Two genera, _Paludicella_ and _Lophopus_, have been stated on

insufficient grounds to occur in India. The former is known from Europe

and N. America, and is said to have been found in Australia, while the

latter is common in Europe and N. America and also occurs in Brazil.

Of the genera that have not been found in this country the most

remarkable are _Urnatella_ and _Cristatella_. The former is the only

representative in fresh water of the Entoprocta and has only been found

in N. America. Each individual is borne upon a segmented stalk the

segments of which are enclosed in strong horny coverings and are

believed to act as resting buds. _Cristatella_, which is common in

Europe and N. America, is a phylactolæmatous genus of highly specialized

structure. It possesses a creeping "sole" or organ of progression at the

base of the zoarium.

The other phylactolæmatous genera that do not occur in India appear to

be of limited distribution, for _Australella_ is only known from N. S.

Wales, and _Stephanella_ from Japan. The ctenostomatous _Arachnoidea_

has only been reported from Lake Tanganyika, and _Pottsiella_ only from

a single locality in N. America.

As regards the exotic distribution of the Indian species little need be

said. The majority of the _Plumatellæ_ are identical with European

species, while the only species of _Fredericella_ that has been

discovered is closely allied to the European one. The Indian species of

_Lophopodella_ occurs also in E. Africa and Japan, while that of

_Pectinatella_ is apparently confined to India, Burma and Ceylon, but is

closely allied to a Japanese form.

POLYZOA OF BRACKISH WATER.

With the exception of _Victorella_, which occurs more commonly in

brackish than in fresh water and has been found in the sea, the genera

that occur in fresh water are confined or practically confined to that

medium; but certain marine ctenostomes and cheilostomes not uncommonly

make their way, both in Europe and in India, into brackish water, and in

the delta of the Ganges an entoproctous genus also does so. The

ctenostomatous genera that are found occasionally in brackish water

belong to two divisions of the suborder, the Vesicularina and the

Alcyonellea. To the former division belongs _Bowerbankia_, a form of

which (_B. caudata_ subsp. _bengalensis_, p. 187) is often found in the

Ganges delta with _Victorella bengalensis_. No species of Alcyonellea

has, however, as yet been found in Indian brackish waters. The two

Indian cheilostomes of brackish water belong to a genus (_Membranipora_)

also found in similar situations in Europe. One of them (_M.

lacroixii_[AZ]) is, indeed, identical with a European form that occurs

in England both in the sea and in ditches of brackish water. I have

found it in the Cochin backwaters, in ponds of brackish water at the

south end of the Chilka Lake (Ganjam, Madras), on the shore at Puri in

Orissa, and in the Mutlah River at Port Canning. The second species (_M.

bengalensis_, Stoliczka) is peculiar to the delta of the Ganges[BA] and

has not as yet been found in the open sea. The two species are easily

recognized from one another, for whereas the lip of _M. bengalensis_

(fig. 33) bears a pair of long forked spines, there are no such

structures on that of _M. lacroixii_, the dorsal surface of which is

remarkably transparent. _M. lacroixii_ forms a flat zoarium, the only

part visible to the naked eye being often the beaded margin of the

zooecia, which appears as a delicate reticulation on bricks, logs of

wood, the stems of rushes and of hydroids, etc.; but the zoarium of _M.

bengalensis_ is as a rule distinctly foliaceous and has a peculiar

silvery lustre.

[Footnote AZ: There is some doubt as to the proper name of

this species, which may not be the one originally described

as _Membranipora lacroixii_ by Andouin. I follow Busk and

Hincks in my identification (see Cat. Polyzoa Brit. Mus. ii,

p. 60, and Hist. Brit. Polyzoa, p. 129). Levinsen calls it

_M. hippopus_, sp. nov. (see Morphological and Systematic

Studies on the Cheilostomatous Bryozoa, p. 144; Copenhagen,

1909).]

[Footnote BA: Miss Thornely (Rec. Ind. Mus. i, p. 186, 1907)

records it from Mergui, but this is an error due to an

almost illegible label. The specimens she examined were the

types of the species from Port Canning. Since this was

written I have obtained specimens from Bombay--_April_,

1911.]

[Illustration: Fig. 33.--Outline of four zooecia of _Membranipora

bengalensis_, Stoliczka (from type specimen, after Thornely). In the

left upper zooecium the lip is shown open.]

_Loxosomatoides_[BB] (fig. 34), the Indian entoproctous genus found in

brackish water, has not as yet been obtained from the open sea, but has

recently been introduced, apparently from a tidal creek, into isolated

ponds of brackish water at Port Canning. It is easily recognized by the

chitinous shield attached to the ventral (posterior) surface.

[Footnote BB: Annandale, Rec. Ind. Mus. ii, p. 14 (1908).]

[Illustration: Fig. 34.--_Loxosomatoides colonialis_, Annandale.

A and B, a single individual of form A, as seen (A) in lateral, and (B)

in ventral view; C, outline of a similar individual with the tentacles

retracted, as seen from in front (dorsal view); D, ventral view of an

individual and bud of form B. All the figures are from the type

specimens and are multiplied by about 70.]

II.

HISTORY OF THE STUDY OF THE FRESHWATER POLYZOA.

The naturalists of the eighteenth century were acquainted with more than

one species of freshwater polyzoon, but they did not distinguish these

species from the hydroids. Trembley discovered _Cristatella_, which he

called "Polype à Panache," in 1741, and Linné described a species of

_Plumatella_ under the name _Tubipora repens_ in 1758, while ten years

later Pallas gave a much fuller description (under the name _Tubularia

fungosa_) of the form now known as _Plumatella fungosa_ or _P. repens_

var. _fungosa_. Although Trembley, Baker, and other early writers on the

fauna of fresh water published valuable biological notes, the first

really important work of a comprehensive nature was that of Dumortier

and van Beneden, published in 1848. All previous memoirs were, however,

superseded by Allman's Monograph of the Fresh-Water Polyzoa, which was

issued in 1857, and this memoir remains in certain respects the most

satisfactory that has yet been produced. In 1885 Jullien published a

revision of the phylactolæmata and freshwater ctenostomes which is

unfortunately vitiated by some curious lapses in observation, but it is

to Jullien that the recognition of the proper position of _Hislopia_ is

due. The next comprehensive monograph was that of Kraepelin, which

appeared in two parts (1887 and 1892) in the Abhandlungen des Naturwiss.

Vereins of Hamburg. In its detailed information and carefully executed

histological plates this work is superior to any that preceded it or has

since appeared, but the system of classification adopted is perhaps less

liable to criticism than that followed by Braem in his "Untersuchungen,"

published in the Bibliotheca Zoologica in 1888.

During the second half of the nineteenth century and the first decade of

the twentieth several authors wrote important works on the embryology

and anatomy of the phylactolæmata, notably Kraepelin, Braem, and Oka;

but as yet the ctenostomes of fresh water have received comparatively

little attention from anything but a systematic point of view.

From all points of view both the phylactolæmata and the ctenostomes of

Asia have been generally neglected, except in the case of the Japanese

phylactolæmata, which have been studied by Oka. Although Carter made

some important discoveries as regards the Indian forms, he did not

devote to them the same attention as he did to the sponges. In the case

of the only new genus he described he introduced a serious error into

the study of the two groups by placing _Hislopia_ among the

cheilostomes, instead of in its true position as the type genus of a

highly specialized family of ctenostomes.

For fuller details as to the history of the study of the freshwater

Polyzoa the student may refer to Allman's and to Kraepelin's monographs.

An excellent summary is given by Harmer in his chapter on the freshwater

Polyzoa in vol. ii. of the Cambridge Natural History; and Loppens has

recently (1908) published in the Annales de Biologie lacustre a concise

survey of the systematic work that has recently been undertaken.

Unfortunately he perpetuates Carter's error as regards the position of

_Hislopia_.

BIBLIOGRAPHY OF THE FRESHWATER POLYZOA.

A very full bibliography of the freshwater Polyzoa will be found in pt.

i. of Kraepelin's "Die Deutschen Süsswasserbryozoen" (1887), while

Loppens, in his survey of the known species (Ann. Biol. lacustre, ii,

1908), gives some recent references. The following list contains the

titles of some of the more important works of reference, of memoirs on

special points such as reproduction and of papers that have a special

reference to Asiatic species. Only the last section is in any way

complete.

(a) _Works of Reference._

1847. VAN BENEDEN, "Recherches sur les Bryozoaires fluviatiles de

Belgique," Mém. Ac. Roy. Belgique, xxi.

1850. DUMORTIER and VAN BENEDEN, "Histoire Naturelle des Polypes

composés d'eau douce," 2^e partie, Mém. Ac. Roy. Bruxelles, xvi

(complément).

1856. ALLMAN, "A Monograph of the Fresh-Water Polyzoa" (London).

1866-1868. HYATT, "Observations on Polyzoa, suborder Phylactolæmata,"

Comm. Essex Inst. iv, p. 197, v, p. 97.

1880. HINCKS, "A History of the British Marine Polyzoa."

1885. JULLIEN, "Monographie des Bryozoaires d'eau douce," Bull. Soc.

zool. France, x, p. 91.

1887 & 1892. KRAEPELIN, "Die deutschen Süsswasserbryozoen," Abhandl.

Nat. Vereins Hamburg, x & xii.

1890. BRAEM, "Untersuchungen des Bryozoen des süssen Wassers," Bibl.

Zool. ii, Heft 6 (Cassel).

1896. HARMER, Cambridge Natural History, ii, Polyzoa, chap. xviii.

1899. KORSCHELT and HEIDER, "Embryology of Invertebrates," vol. ii,

chap. xvi. (English edition by Bernard and Woodward, 1899.)

1908. LOPPENS, "Les Bryozoaires d'eau douce," Ann. Biol. lacustre, iii.

p. 141.

(b) _Special Works on Embryology, etc._

1875. NITSCHE, "Beiträge zur Kenntniss der Bryozoen," Zeitschr. f. wiss.

Zool. xxv (supplement), p. 343.

1880. REINHARD, "Zur Kenntniss der Süsswasser-Bryozoen," Zool. Anz. iii,

p. 208.

1888. BRAEM, "Untersuchungen über die Bryozoen des süssen Wassers,"

Zool. Anz. xi, pp. 503, 533.

1891. OKA, "Observations on Freshwater Polyzoa," J. Coll. Sci. Tokyo,

iv, p. 89.

1906. WILCOX, "Locomotion in young colonies of _Pectinatella

magnifica_," Biol. Bull. Wood's Hole, ii.

1908. BRAEM, "Die geschlechtliche Entwickelung von Fredericella sultana

nebst Beobachtungen über die weitere Lebensgeschichte der Kolonien,"

Bibl. Zool. xx, Heft 52.

(c) _Papers that refer specifically to Asiatic species._

1851. LEIDY described _Plumatella diffusa_ in Proc. Ac. Philad. v, p.

261 (1851).

1858. CARTER, "Description of a Lacustrine Bryozoon allied to

_Flustra_," Ann. Nat. Hist. (3) i, p. 169.

1859. CARTER, "On the Identify in Structure and Composition of the

so-called Seed-like Body of _Spongilla_ with the Winter-egg of the

Bryozoa: and the presence of Starch-granules in each," Ann. Nat. Hist.

(3) iii, p. 331. (Statoblast of _Lophopodella_ described and figured.)

1862. MITCHELL, "Freshwater Polyzoa," Q. J. Micr. Sci. (new series) ii,

p. 61. ("_Lophopus_" recorded from Madras.)

1866. HYATT, "Observations on Polyzoa, suborder Phylactolæmata," Comm.

Essex Inst. iv, p. 197. ("_Pectinatella carteri_" named.)

1869. STOLICZKA, "On the Anatomy of _Sagartia schilleriana_ and

_Membranipora bengalensis_, a new coral and a bryozoon living in

brackish water at Port Canning," J. As. Soc. Bengal, xxxviii, ii, p. 28.

1880. JULLIEN, "Description d'un nouveau genre de Bryozoaire

Cheilostomien des eaux douces de la Chine et du Cambodge et de deux

espèces nouvelles," Bull. Soc. zool. France, v, p. 77. ("_Norodonia_"

described.)

1885. JULLIEN, "Monographie des Bryozoaires d'eau douce," Bull. Soc.

zool. France, x, p. 91. (_Hislopia_ assigned to the ctenostomes.)

1887. KRAEPELIN, "Die deutschen Süsswasserbryozoen," Abh. Ver. Hamburg,

x. (_Plumatella philippinensis._)

1891. OKA, "Observations on Freshwater Polyzoa," J. Coll. Sci. Tokyo,

iv, p. 89.

1898. MEISSNER, "Die Moosthiere Ost-Afrikas," in Mobius's

Deutsch-Ost-Afrika, iv. (_Lophopodella carteri_ recorded from E.

Africa.)

1901. KOROTNEFF, "Faunistische Studien am Baikalsee," Biol. Centrbl.

xxi, p. 305. ("_Echinella_" described.)

1904-1906. ROUSSELET, "On a new Freshwater Polyzoon from Rhodesia,

_Lophopodella thomasi_, gen. et sp. nov.", J. Quekett Club (2) ix, p.

45. (Genus _Lophopodella_ described.)

1906. ANNANDALE, "Notes on the Freshwater Fauna of India. No. II. The

Affinities of _Hislopia_," J. As. Soc. Bengal (new series) ii, p. 59.

1906. KRAEPELIN, "Eine Süsswasser-bryozoë (_Plumatella_) aus Java,"

Mitth. Mus. Hamburg, xxiii, p. 143.

1907. ANNANDALE, "Notes on the Freshwater Fauna of India. No. XII. The

Polyzoa occurring in Indian Fresh and Brackish Pools," J. As. Soc. Bengal

(new series) iii, p. 83.

1907. ANNANDALE, "Statoblasts from the surface of a Himalayan Pond,"

Rec. Ind. Mus. i, p. 177.

1907. ANNANDALE, "The Fauna of Brackish Ponds at Port Canning, Lower

Bengal: I.--Introduction and Preliminary Account of the Fauna," Rec.

Ind. Mus. i, p. 35.

1907. ANNANDALE, "The Fauna of Brackish Ponds at Port Canning, Lower

Bengal: VI.--Observations on the Polyzoa, with further notes on the

Ponds," Rec. Ind. Mus. i, p. 197.

1907. ANNANDALE, "Further Note on a Polyzoon from the Himalayas," Rec.

Ind. Mus. i, p. 145.

1907. ROUSSELET, "Zoological Results of the Third Tanganyika Expedition,

conducted by Dr. W. A. Cunnington, 1904-1905.--Report on the Polyzoa,"

P. Z. Soc. London, i, p. 250. (_Plumatella tanganyikæ._)

1907. OKA, "Eine dritte Art von _Pectinatella_ (_P. davenporti_, n.

sp.)," Zool. Anz. xxxi, p. 716.

1907. APSTEIN, "Das Plancton im Colombo-See auf Ceylon," Zool. Jahrb.

(Syst.) xxv, p. 201. (_Plumatella_ recorded.)

1907. WALTON, "Notes on _Hislopia lacustris_, Carter," Rec. Ind. Mus. i,

p. 177.

1907-1908. OKA, "Zur Kenntnis der Süsswasser-Bryozoenfauna von Japan,"

Annot. Zool. Japon, vi, p. 117.

1907-1908. OKA, "Ueber eine neue Gattung von Süsserwasserbryozoen,"

Annot. Zool. Japon, vi, p. 277.

1908. ANNANDALE, "The Fauna of Brackish Ponds at Port Canning, Lower

Bengal: VII.--Further Observations on the Polyzoa with the description

of a new genus of Entoprocta," Rec. Ind. Mus. ii, p. 11.

1908. ANNANDALE, "Corrections as to the Identity of Indian

Phylactolæmata," Rec. Ind. Mus. ii, p. 110.

1908. ANNANDALE, "Three Indian Phylactolæmata," Rec. Ind. Mus. ii, p.

169.

1908. KIRKPATRICK, "Description of a new variety of _Spongilla

loricata_, Weltner," Rec. Ind. Mus. ii, p. 97. (_Hislopia_ recorded from

Burma.)

1909. ANNANDALE, "Preliminary Note on a new genus of Phylactolæmatous

Polyzoa," Rec. Ind. Mus. iii, p. 279.

1909. ANNANDALE, "A new species of _Fredericella_ from Indian Lakes,"

Rec. Ind. Mus. iii. p. 373.

1909. WALTON, "Large Colonies of _Hislopia lacustris_," Rec. Ind. Mus.

iii, p. 295.

1910. ANNANDALE, "Materials for a Revision of the Phylactolæmatous

Polyzoa of India," Rec. Ind. Mus. v, p. 37.

1911. WEST and ANNANDALE, "Descriptions of Three Species of Algæ

associated with Indian Freshwater Polyzoa," J. As. Soc. Bengal

(_ined._).

GLOSSARY OF TECHNICAL TERMS USED IN PART III.

_Brown body_ A body formed in a zooecium by the degeneration

of a polypide as a preparation

for its regeneration.

_Cardiac portion_ (of That part which communicates with the

the stomach). oesophagus.

_Collar_ A longitudinally pleated circular membrane

capable of being thrust out of the orifice

in advance of the lophophore and of

closing together inside the zooecium above

the tentacles when they are retracted.

_Dorsal surface_ (_Of zooecium_ or _polypide_) the surface

nearest the mouth; (_of statoblast_) the

surface furthest from that by which the

statoblast is attached to the funiculus

during development.

_Ectocyst_ The outer, structureless layer of the zooecium.

_Emarginate_ Having a thin or defective triangular area

(of a zooecium) in the ectocyst at the tip.

_Endocyst_ The inner, living (cellular) layer of the

zooecium.

_Epistome_ A leaf-like ciliated organ that projects

upwards and forwards over the mouth

between it and the anus.

_Funiculus_ A strand of tissue joining the alimentary

canal to the endocyst.

_Furrowed_ Having a thin or defective longitudinal

(of a zooecium) linear streak in the ectocyst on the dorsal

surface.

_Gizzard_ A chamber of the alimentary canal situated

at the cardiac end of the stomach and

provided internally with a structureless

lining.

_Intertentacular organ_ A ciliated tube running between the cavity

of the zooecium and the external base of

the lophophore.

_Keeled_ Having a longitudinal ridge on the dorsal

(of a zooecium) surface.

_Lophophore_ The tentacles with the base to which they

are attached.

_Marginal processes_ Chitinous hooked processes on the margin

(of statoblast). of the swim-ring (_q. v._).

_OEsophagus_ That part of the alimentary canal which

joins the mouth to the stomach.

_Orifice_ The aperture through which the lophophore

can be protruded from or retracted into

the zooecium.

_Parietal muscles_ Transverse muscles running round the inner

wall of the zooecium.

_Parieto-vaginal_ Muscles that surround the orifice, running

_muscles_ between the folds of the zooecium in an

oblique direction.

_Polyparium_ The whole body of zooecia and polypides

which are in organic connection.

_Polypide_ The tentacular crown, alimentary canal,

and retractor muscles of a polyzoon-individual.

_Pyloric portion_ That part which communicates with the

(of the stomach). intestine.

_Resting bud_ An external bud provided with food-material

in its cells, with a horny external

coat and capable of lying dormant in

unfavourable conditions.

_Retractor muscles_ The muscles by the action of which the

lophophore can be pulled back into the

zooecium.

_Statoblast_ An internal bud arising from the funiculus,

containing food-material in its cells,

covered with a horny coat and capable

of lying dormant in unfavourable conditions.

_Swim-ring_ A ring of polygonal air-spaces surrounding

the statoblast.

_Ventral surface_ (_Of zooecium_ or _polypide_) the surface

nearest the anus; (_of statoblast_) the surface

by which the statoblast is attached

to the funiculus during development.

_Zoarium_ The whole body of zooecia which are in

organic connection.

_Zooecium_ Those parts of the polyzoon-individual

which constitute a case or "house" for

the polypide.

SYNOPSIS OF THE CLASSIFICATION OF THE POLYZOA.

I.

SYNOPSIS OF THE SUBCLASSES, ORDERS, AND SUBORDERS.

Class POLYZOA.

Small coelomate animals, each individual of which consists of a

polyp-like organism or polypide enclosed in a "house" or zooecium

composed partly of living tissues. The mouth is surrounded by a circle

of ciliated tentacles that can be retracted within the zooecium; the

alimentary canal, which is suspended in the zooecium, is Y-shaped and

consists of three parts, the oesophagus, the stomach, and the intestine.

Subclass ENTOPROCTA.

The anus as well as the mouth is enclosed in the circle of tentacles and

the zooecium is not very distinctly separated from the polypide. Some

forms are solitary or form temporary colonies by budding.

Most Entoprocta are marine, but a freshwater genus (_Urnatella_) occurs

in N. America, while the Indian genus _Loxosomatoides_ (fig. 34, p. 176)

is only known from brackish water.

Subclass ECTOPROCTA.

The anus is outside the circle of tentacles and the zooecium can always

be distinguished from the polypide. All species form by budding

permanent communities the individuals in which remain connected together

by living tissue.

Order I. GYMNOLÆMATA.

Ectoproctous polyzoa the polypides of which have no epistome; the

zooecia are in nearly all cases distinctly separated from one another by

transverse perforated plates.

Most of the Gymnolæmata are marine, but species belonging to two of the

three suborders into which they are divided often stray into brackish

water, while a few genera that belong to one of these two suborders are

practically confined to fresh water. The three suborders are

distinguished as follows:--

Suborder A. _CHEILOSTOMATA._

The zooecia are provided with a "lip" or lid hinged to the posterior

margin of the orifice (see fig. 33, p. 175). This lid closes

automatically outside the zooecium or in a special chamber on the

external surface (the "peristome") when the polypide retracts and is

pushed open by the tentacles as they expand. The majority of the zooecia

in each zoarium are more or less distinctly flattened, but some of them

are often modified to form "vibracula" and "avicularia."

The Cheilostomata are essentially a marine group, but some species are

found in estuaries and even in pools and ditches of brackish water (fig.

33).

Suborder B. _CTENOSTOMATA._

The zooecia are provided with a collar-like membrane which is pleated

vertically and closes together above the polypide inside the zooecium

when the former is retracted; it is thrust out of the zooecium and

expands into a ring-shaped form just before the tentacles are extruded.

The zooecia are usually more or less tubular, but in some genera and

species are flattened.

The majority of the Ctenostomata are marine, but some genera are found

in estuaries, while those of one section of the suborder live almost

exclusively in fresh water.

Suborder C. _CYCLOSTOMATA._

The zooecia are provided neither with a lip nor with a collar-like

membrane. They are tubular and usually have circular orifices.

The Cyclostomata are exclusively marine.

Order II. PHYLACTOLÆMATA.

Ectoproctous polyzoa the polypides of which have a leaf-shaped organ

called an epistome projecting upwards and forwards within the circle of

tentacles and between the mouth and the anus. The zooecia are not

distinct from one another, but in dendritic forms the zoarium is divided

irregularly by chitinous partitions.

The Phylactolæmata are, without exception, freshwater species.

II.

SYNOPSIS OF THE LEADING CHARACTERS OF THE DIVISIONS OF THE SUBORDER

CTENOSTOMATA.

Suborder B. _CTENOSTOMATA._

The suborder has been subdivided in various ways by different authors.

The system here adopted is essentially the same as that proposed in a

recent paper by Waters (Journ. Linn. Soc. London, Zool. xxi, p. 231,

1910), but I have thought it necessary to add a fourth division to the

three adopted by that author, namely, the Alcyonellea, Stolonifera, and

Vesicularina. This new division includes all the freshwater genera and

may be known as the Paludicellina. In none of these divisions are the

tentacles webbed at the base.

The four divisions may be recognized from the following synopsis of

their characteristic features:--

Division I. ALCYONELLEA.

The zooecia arise directly from one another in a fleshy or gelatinous

mass. The polypide has no gizzard. The species are essentially marine,

but a few are found in brackish water in estuaries.

Division II. STOLONIFERA.

The zooecia arise from expansions in a delicate creeping rhizome or

root-like structure, the order in which they are connected together

being more or less irregular. As a rule (perhaps always) there is no

gizzard. The species are marine.

Division III. VESICULARINA.

The zooecia grow directly from a tubular stem which is usually free and

vertical, their arrangement being alternate, spiral or irregular. There

is a stout gizzard which bears internal chitinous projections and is

tightly compressed when the polypide is retracted. The species are

essentially marine, but a few are found in brackish water.

Division IV. PALUDICELLINA, nov.

The zooecia are arranged in a regular cruciform manner and arise either

directly one from another or with the intervention of tubular processes.

If the polypide has a gizzard it does not bear internal chitinous

projections. Most of the species are confined to fresh water, but a few

are found in brackish water or even in the sea.

Although all true freshwater Ctenostomes belong to the fourth of these

divisions, species of a genus (_Bowerbankia_) included in the third are

so frequently found in brackish water and in association with one

belonging to the fourth, and are so easily confounded with the latter,

that I think it necessary to include a brief description of the said

genus and of the form that represents it in ponds of brackish water in

India.

SYSTEMATIC LIST OF THE INDIAN FRESHWATER POLYZOA.

[The types have been examined in the case of all species, etc., whose

names are marked thus, *.]

Order I. GYMNOLÆMATA.

Suborder I. _CTENOSTOMATA._

[Division III. Vesicularina.]

[Genus BOWERBANKIA, Farre (1837).]

[_B. caudata_ subsp. _bengalensis_*, Annandale (1907).

(Brackish water).]

Division IV. Paludicellina, nov.

Family I. PALUDICELLIDÆ.

Genus 1. PALUDICELLA, Gervais (1836).

? _Paludicella_ sp. (_fide_ Carter).

Genus 2. VICTORELLA, Kent (1870).

26._V. bengalensis_*, Annandale (1907).

Family II. HISLOPIIDÆ.

Genus HISLOPIA, Carter (1858).

27. _H. lacustris_, Carter (1858).

27 _a._ _H. lacustris_ subsp. _moniliformis_*, nov.

Order II. PHYLACTOLÆMATA.

Division I. Plumatellina.

Family 1. FREDERICELLIDÆ.

Genus FREDERICELLA, Gervais (1836).

28. _F. indica_*, Annandale (1909).

Family 2. PLUMATELLIDÆ.

Subfamily A. PLUMATELLINÆ.

Genus 1. PLUMATELLA, Lamarck (1816).

29. _P. fruticosa_, Allman (1844).

30. _P. emarginata_, Allman (1844).

31. _P. javanica_*, Kraepelin (1905).

32. _P. diffusa_, Leidy (1851).

33. _P. allmani_, Hancock (1850).

34. _P. tanganyikæ_*, Rousselet (1907).

35. _P. punctata_, Hancock (1850).

Genus 2. STOLELLA, Annandale (1909).

36. _S. indica_*, Annandale (1909).

Subfamily B. LOPHOPINÆ.

Genus 1. LOPHOPODELLA, Rousselet (1904).

37. _L. carteri_* (Hyatt) (1865).

37 _a._ _L. carteri_ var. _himalayana_* (Annandale) (1907).

Genus 2. PECTINATELLA, Leidy (1851).

38. _P. burmanica_*, Annandale (1908).

Order CTENOSTOMATA.

[Division VESICULARINA.

Family VESICULARIDÆ.

VESICULARIDÆ, Hincks, Brit. Marine Polyzoa, p. 512 (1880).

Zooecia constricted at the base, deciduous, attached to a stem that is

either recumbent or vertical.

Genus BOWERBANKIA, _Farre_.

_Bowerbankia_, Farre, Phil. Trans. Roy. Soc. cxxvii, p. 391 (1837).

_Bowerbankia_, Hincks, _op. cit._ p. 518.

_Zoarium_ vertical or recumbent. _Zooecia_ ovate or almost cylindrical,

arranged on the stem singly, in clusters or in a subspiral line.

_Polypide_ with 8 or 10 tentacles.

Bowerbankia caudata, _Hincks_.

_Bowerbankia caudata_, Hincks, _op. cit._ p. 521, pl. lxxv,

figs. 7, 8.

This species is easily distinguished from all others by the fact that

mature zooecia have always the appearance of being fixed to the sides of

a creeping, adherent stem and are produced, below the point at which

they are thus fixed, into a pointed "tail."

Subsp. bengalensis, _Annandale_.

_Bowerbankia caudata_, Thornely, Rec. Ind. Mus. i, p. 196

(1907).

_Bowerbankia caudata_, Annandale, _ibid._ p. 203.

_Bowerbankia caudata_ race _bengalensis_, _id._, _ibid._

ii. p. 13 (1908).

The Indian race is only distinguished from the typical form by its

greater luxuriance of growth and by the fact that the "tail" of the

zooecia is often of relatively great length, sometimes equaling or

exceeding the rest of the zooecium. The stem, which is divided at

irregular intervals by partitions, often crosses and recrosses its own

course and even anastomoses, and a fur-like structure is formed in which

the zooecia representing the hairs become much elongated; but upright

branches are never formed. The zoarium has a greenish or greyish tinge.

TYPE in the Indian Museum.

GEOGRAPHICAL DISTRIBUTION.--_B. caudata_ subsp. _bengalensis_ is common

in brackish water in the Ganges delta, where it often occurs in close

association with _Victorella bengalensis_, and also at the south end of

the Chilka Lake in the north-east of the Madras Presidency. Although it

has not yet been found elsewhere, it probably occurs all round the

Indian coasts.]

Division PALUDICELLINA, nov.

This division consists of two very distinct families, the species of

which are easily distinguished at a glance by the fact that in one (the

Paludicellidæ) the zooecia are tubular, while in the other (the

Hislopiidæ) they are broad and flattened. The anatomical and

physiological differences between the two families are important, and

they are associated together mainly on account of the method of budding

by means of which their zoaria are produced.

[Illustration: Fig. 35.--Single zooecia of _Victorella_ and _Hislopia_

(magnified).

A, zooecium of _Victorella pavida_, Kent, with the polypide retracted

(after Kraepelin).

B, zooecium of _Hislopia lacustris_, Carter (typical form from the

United Provinces), with the collar completely and the tentacles partly

protruded.

A=collar; B=orifice; C=tentacles; D=pharynx; E=oesophagus proper;

F=gizzard; G=stomach; G'=cardiac portion of stomach; H=intestine;

J=rectum; K=anus; L=young egg; M=green cysts in gizzard; N=testes;

O=ovary; O'=funiculus.

The muscles are omitted except in fig. B.]

Family PALUDICELLIDÆ.

PALUDICELLIDÆ, Allman, Mon. Fresh-Water Polyzoa, p. 113

(1857).

HOMODIÆTIDÆ, Kent, Q. J. Micr. Sci. x, p. 35 (1870).

VICTORELLIDÆ, Hincks, Brit. Marine Polyzoa, p. 558 (1880).

PALUDICELLIDÉES, Jullien, Bull. Soc. zool. France, x, p. 174

(1885).

PALUDICELLIDES, Loppens, Ann. Biol. lacustre, iii, p. 170

(1908).

VICTORELLIDES, _id._, _ibid._ p. 171.

_Zoarium._ The zoarium is recumbent or erect, and is formed typically

either of zooecia arising directly in cruciform formation from one

another, or of zooecia joined together in similar formation with the

intervention of tubules arising from their own bases. Complications

often arise, however, either on account of the suppression of the

lateral buds of a zooecium, so that the formation becomes linear instead

of cruciform, or by the production in an irregular manner of additional

tubules and buds from the upper part of the zooecia. A confused and

tangled zoarium may thus be formed, the true nature of which can only be

recognized by the examination of its terminal parts.

_Zooecia._ The zooecia are tubular and have a terminal or subterminal

orifice, which is angulate or subangulate as seen from above. Owing to

this fact, to the stiff nature of the external ectocyst, to the action

of circular muscles that surround the tentacular sheath, and to the

cylindrical form of the soft inverted part, the orifice, as seen from

above, appears to form four flaps or valves, thus [illustration: sketch,

similar to a cloverleaf inside a square with rounded corners].

_Polypide._ The alimentary canal is elongate and slender as a whole, the

oesophagus (including the pharynx) being of considerable length. In

_Paludicella_ and _Pottsiella_ the oesophagus opens directly into the

cardiac limb of the stomach, which is distinctly constricted at its

base; but in _Victorella_ the base of the oesophagus is constricted off

from the remainder to form an elongate oval sac the walls of which are

lined with a delicate structureless membrane. _Victorella_ may therefore

be said to possess a gizzard, but the structure that must be so

designated has not the function (that of crushing food) commonly

associated with the name, acting merely as a chamber for the retention

of solid particles. In this genus the cardiac limb of the stomach is

produced and vertical but not constricted at the base. The tentacles in

most species number 8, but in _Paludicella_ there are 16.

_Resting buds._ The peculiar structures known in Europe as "hibernacula"

are only found in this family. The name hibernacula, however, is

inappropriate to the only known Indian species as they are formed in

this country at the approach of summer instead of, as in Europe and N.

America, at that of winter. It is best, therefore, to call them "resting

buds." They consist of masses of cells congregated at the base of the

zooecia, gorged with food material and covered with a resistant horny

covering.

The family Paludicellidæ consists of three genera which may be

distinguished as follows:--

I. Orifice terminal; main axis of the zooecium

vertical; zooecia separated from one another

by tubules.

[A. Base of the zooecia not swollen; no

adventitious buds POTTSIELLA.]

B. Base of the zooecium swollen; adventitious

buds produced near the tip VICTORELLA, p. 194.

II. Orifice subterminal, distinctly on the dorsal

surface; main axis of the zooecium horizontal

(the zoarium being viewed from the dorsal

surface); buds not produced at the tip of the

zooecia PALUDICELLA, p. 192.

Of these three genera, _Pottsiella_ has not yet been found in India and

is only known to occur in N. America. It consists of one species, _P.

erecta_ (Potts) from the neighbourhood of Philadelphia in the United

States.

_Victorella_ includes four species, _V. pavida_ known from England and

Germany and said to occur in Australia, _V. mülleri_ from Germany

(distinguished by possessing parietal muscles at the tip of the

zooecia), _V. symbiotica_ from African lakes and _V. bengalensis_ from

India. These species are closely related.

_Paludicella_ is stated by Carter to have been found in Bombay, but

probably what he really found was the young stage of _V. bengalensis_. A

single species is known in Europe and N. America, namely _P.

ehrenbergi_, van Beneden (=_Alcyonella articulata_, Ehrenberg).

I have examined specimens of all the species of this family as yet

known.

Genus 1. PALUDICELLA, _Gervais_.

_Paludicella_, Gervais, Compt. Rend. iii, p. 797 (1836).

_Paludicella_, Allman, Mon. Fresh-Water Polyzoa, p. 113

(1857).

? _Paludicella_, Carter, Ann. Nat. Hist. (3) iii, p. 333

(1859).

_Paludicella_, Jullien, Bull. Soc. zool. France, x, p. 174

(1885).

_Paludicella_, Kraepelin, Deutsch. Süsswasserbryozoen, i, p.

96 (1887).

_Paludicella_, Loppens, Ann. Biol. lacustre, iv, p. 14

(1910).

_Zoarium._ The nature of the zoarium in this genus is well expressed by

Ehrenberg's specific name "_articulata_," although the name was given

under a false impression. The zooecia arise directly from one another in

linear series with occasional side-branches. The side-branches are,

however, often suppressed. The zoarium as a whole is either recumbent

and adherent or at least partly vertical.

_Zooecia._ Although the zooecia are distinctly tubular as a whole, two

longitudinal axes may be distinguished in each, for the tip is bent

upwards in a slanting direction, bearing the orifice at its extremity.

The main axis is, however, at right angles to the dorso-ventral axis,

and the dorsal surface, owing to the position of the aperture, can

always be readily distinguished from the ventral, even when the position

of the zooecium is vertical. Each zooecium tapers towards the posterior

extremity. Parietal muscles are always present.

[Illustration: Fig. 36.--Structure of _Paludicella ehrenbergi_ (A and B

after Allman).

A=a single zooecium with the polypide retracted. B=the base of the

lophophore as seen from above with the tentacles removed. C=the orifice

of a polypide with the collar expanded and the tentacles partly

retracted. _a_=tentacles; _c_=collar; _d_=mouth; _e_=oesophagus;

_f_=stomach; _g_=intestine; _k_=parieto-vaginal muscles; _p_=parietal

muscles; _o_=cardiac part of the stomach; _r_=retractor muscle;

_s_=funiculus.]

_Polypide._ The most striking features of the polypide are the absence

of any trace of a gizzard and the highly specialized form assumed by the

cardiac part of the stomach. There are two funiculi, both connecting the

pyloric part of the stomach with the endocyst. The ovary develops at the

end of the upper, the testis at that of the lower funiculus.

_Resting buds._ The resting buds are spindle-shaped.

Kraepelin recognized two species in the genus mainly by their method of

growth and the number of tentacles. In his _P. mülleri_ the zoarium is

always recumbent and the polypide has 8 tentacles, whereas in _P.

articulata_ or _ehrenbergi_ the tentacles number 16 and upright branches

are usually developed. It is probable, however, that the former species

should be assigned to _Victorella_, for it is often difficult to

distinguish _Paludicella_ from young specimens of _Victorella_ unless

the latter bear adventitious terminal buds. The gizzard of _Victorella_

can be detected in well-preserved material even under a fairly low power

of the microscope, and I have examined specimens of what I believe to be

the adult of _mülleri_ which certainly belong to that genus.

It is always difficult to see the collar of _Paludicella_, because of

its transparency and because of the fact that its pleats are apparently

not strengthened by chitinous rods as is usually the case. Allman

neither mentions it in his description of the genus nor shows it in his

figures, and Loppens denies its existence, but it is figured by

Kraepelin and can always be detected in well-preserved specimens, if

they are examined carefully. If the collar were actually absent, its

absence would separate _Paludicella_ not only from _Victorella_ and

_Pottsiella_, but also from all other ctenostomes. In any case,

_Victorella_ is distinguished from _Paludicella_ and _Pottsiella_ by

anatomical peculiarities (_e. g._, the possession of a gizzard and the

absence of a second funiculus) that may ultimately be considered

sufficiently great to justify its recognition as the type and only genus

of a separate family or subfamily.

The description of _Paludicella_ is included here on account of Carter's

identification of the specimens he found at Bombay; but its occurrence

in India is very doubtful.

Genus 2. _VICTORELLA_, _Kent_.

_Victorella_, Kent, Q. J. Micr. Sci. x, p. 34 (1870).

_Victorella_, Hincks, Brit. Marine Polyzoa, p. 559 (1880).

_Victorella_, Kraepelin, Deutsch. Süsswasserbryozoen, i, p.

93 (1887).

TYPE, _Victorella pavida_, Kent.

_Zoarium._ The zoarium consists primarily of a number of erect or

semi-erect tubular zooecia joined together at the base in a cruciform

manner by slender tubules, but complications are introduced by the fact

that adventitious buds and tubules are produced, often in large numbers,

round the terminal region of the zooecia, and that these buds are often

separated from their parent zooecium by a tubule of considerable length,

and take root among other zooecia at a distance from their point of

origin. A tangled mass may thus be formed in which it is difficult to

recognize the regular arrangement of the zooecia that can be readily

detached at the growing points of the zoarium.

_Zooecia._ The zooecia when young closely resemble those of

_Paludicella_, but as they grow the terminal upturned part increases

rapidly, while the horizontal basal part remains almost stationary and

finally appears as a mere swelling at the base of an almost vertical

tube, in which by far the greater part, if not the whole, of the

polypide is contained. Round the terminal part of this tube adventitious

buds and tubules are arranged more or less regularly. There are no

parietal muscles.

_Polypide._ The polypide has 8 slender tentacles, which are thickly

covered with short hairs. The basal part of the oesophagus forms a

thin-walled sac (the "gizzard") constricted off from the upper portion

and bearing internally a thin structureless membrane. Circular muscles

exist in its wall but are not strongly developed on its upper part.

There is a single funiculus, which connects the posterior end of the

stomach with the base of the zooecium. The ovaries and testes are borne

on the endocyst, not in connection with the funiculus.

_Resting buds._ The resting buds are flattened or resemble young zooecia

in external form.

_Victorella_, although found in fresh water, occurs more commonly in

brackish water and is known to exist in the littoral zone of the sea.

26. Victorella bengalensis, _Annandale_.

_Victorella pavida_, Annandale (_nec_ Kent), Rec. Ind. Mus.

i, p. 200, figs. 1-4 (1907).

_Victorella bengalensis_, _id._, _ibid._ ii, p. 12, fig. 1

(1908).

_Zoarium._ _The mature zoarium resembles a thick fur_, the hairs of

which are represented by elongate, erect, slender tubules (the zooecia),

the arrangement of the whole being very complicated and irregular. The

base of the zoarium often consists of an irregular membrane formed of

matted tubules, which are sometimes agglutinated together by a gummy

secretion. The zoarium as a whole has a faint yellowish tinge.

_Zooecia._ The zooecia when young are practically recumbent, each being

of an ovoid form and having a stout, distinctly quadrate orificial

tubule projecting upwards and slightly forwards near the anterior margin

of the dorsal surface. At this stage a single tubule, often of great

relative length, is often given off near the orifice, bearing a bud at

its free extremity. As the zooecium grows the tubular part becomes much

elongated as compared with the basal part and assumes a vertical

position. Its quadrate form sometimes persists but more often

disappears, so that it becomes almost circular in cross-section

throughout its length. Buds are produced near the tip in considerable

profusion. As a rule, if they appear at this stage, the tubule

connecting them with the parent zooecium is short or obsolete; sometimes

they are produced only on one side of the zooecium, sometimes on two.

The buds themselves produce granddaughter and great-granddaughter buds,

often connected together by short tubules, while still small and

imperfectly developed. The swelling at the base of the zooecium, when

the latter is fully formed, is small.

_Polypide._ The polypide has the features characteristic of the genus.

The base of the gizzard is surrounded by a strong circular muscle.

[Illustration: Fig. 37.--_Victorella bengalensis_ (type specimens).

A=single zooecium without adventitious buds but with a young resting bud

(_b_), × 70 (dorsal view); B=lateral view of a smaller zooecium without

buds, × 70; C=upper part of a zooecium with a single adventitious bud, ×

70; D=outline of the upper part of a zooecium with adventitious buds of

several generations, × 35; E=remains of a zooecium with two resting buds

(_b_) attached. All the specimens figured are from Port Canning and,

except D, are represented as they appear when stained with borax carmine

and mounted in canada balsam.]

_Resting buds._ The resting buds (fig. 31, p. 170) are somewhat variable

in shape but are always flat with irregular cylindrical or

subcylindrical projections round the margin, on which the horny coat is

thinner than it is on the upper surface. This surface is either smooth

or longitudinally ridged.

TYPE in the Indian Museum.

This species differs from the European _V. pavida_ in very much the same

way as, but to a greater extent than, the Indian race of _Bowerbankia

caudata_ does from the typical English one (see p. 189). The growth of

the zoarium is much more luxuriant, and the form of the resting buds is

different.

GEOGRAPHICAL DISTRIBUTION.--_V. bengalensis_ is abundant in pools of

brackish water in the Ganges delta and in the Salt Lakes near Calcutta;

it also occurs in ponds of fresh water near the latter. I have received

specimens from Madras from Dr. J. R. Henderson, and it is probable that

the form from Bombay referred by Carter to _Paludicella_ belonged to

this species.

BIOLOGY.--In the Ganges delta _V. bengalensis_ is usually found coating

the roots and stems of a species of grass that grows in and near

brackish water, and on sticks that have fallen into the water. It also

spreads over the surface of bricks, and I have found a specimen on a

living shell of the common mollusc _Melania tuberculata_. Dr. Henderson

obtained specimens at Madras from the surface of a freshwater shrimp,

_Palæmon malcolmsonii_. In the ponds at Port Canning the zoaria grow

side by side with, and even entangled with those of _Bowerbankia

caudata_ subsp. _bengalensis_, to the zooecia of which their zooecia

bear a very strong external resemblance so far as their distal extremity

is concerned. This resemblance, however, disappears in the case of

zooecia that bear terminal buds, for no such buds are borne by _B.

caudata_; and the yellowish tint of the zoaria of _V. bengalensis_ is

characteristic. Zoaria of the entoproct _Loxosomatoides colonialis_ and

colonies of the hydroid _Irene ceylonensis_ are also found entangled

with the zoaria of _V. bengalensis_, the zooecia of which are often

covered with various species of Vorticellid protozoa and small rotifers.

The growth of _V. bengalensis_ is more vigorous than that of the other

polyzoa found with it, and patches of _B. caudata_ are frequently

surrounded by large areas of _V. bengalensis_.

The food of _V. bengalensis_ consists largely of diatoms, the siliceous

shells of which often form the greater part of its excreta. Minute

particles of silt are sometimes retained in the gizzard, being

apparently swallowed by accident.

There are still many points to be elucidated as regards the production

and development of the resting buds in _V. bengalensis_, but two facts

are now quite clear as regards them: firstly, that these buds are

produced at the approach of the hot weather and germinate in November or

December; and secondly, that the whole zoarium may be transformed at the

former season into a layer of resting buds closely pressed together but

sometimes exhibiting in their arrangement the typical cruciform

formation. Resting buds may often be found in vigorous colonies as late

as the beginning of December; these buds have not been recently formed

but have persisted since the previous spring and have not yet

germinated. Sometimes only one or two buds are formed at the base of an

existing zooecium (fig. 37 _a_), but apparently it is possible not only

for a zooecium to be transformed into a resting bud but for it to

produce four other buds round its base before undergoing the change.

Young polypides are formed inside the buds and a single zooecium sprouts

out of each, as a rule by the growth of one of the basal projections,

when conditions are favourable.

Polypides of _V. bengalensis_ are often transformed into brown bodies.

When this occurs the orifice closes together, with the collar expanded

outside the zooecium. I have occasionally noticed that the ectocyst of

such zooecia was distinctly thicker and darker in colour than that of

normal zooecia.

Eggs and spermatozoa are produced in great numbers, as a rule

simultaneously in the same zooecia, but individuals kept in captivity

often produce spermatozoa only. The eggs are small and are set free as

eggs. Nothing is known as regards their development.

Polypides are as a rule found in an active condition only in the cold

weather, but I have on one occasion seen them in this condition in

August, in a small zoarium attached to a shell of _Melania tuberculata_

taken in a canal of brackish water near Calcutta.

Family HISLOPIIDÆ.

HISLOPIDÉES, Jullien, Bull. Soc. zool. France, x, p. 180

(1885).

HISLOPIIDÆ, Annandale, Rec. Ind. Mus. i, p. 200 (1907).

_Zoarium_ recumbent, often forming an almost uniform layer on solid

subjects.

_Zooecia_ flattened, adherent; the orifice dorsal, either surrounded by

a chitinous rim or situated at the tip of an erect chitinous tubule; no

parietal muscles.

_Polypide_ with an ample gizzard which possesses a uniform chitinous

lining and does not close together when the polypide is retracted.

_Resting bud_, not produced.

Only two genera can be recognized in this family, _Arachnoidea_, Moore,

from Central Africa, and _Hislopia_, Carter, which is widely distributed

in Eastern Asia. The former genus possesses an upright orificial tubule

and has zooecia separated by basal tubules. Its anatomy is imperfectly

known, but it certainly possesses a gizzard of similar structure to that

of _Hislopia_, between which and _Victorella_ its zooecium is

intermediate in form.

Genus HISLOPIA, _Carter_.

_Hislopia_, Carter, Ann. Nat. Hist. (3) i, p. 169 (1858).

_Hislopia_, Stolickza, J. As. Soc. Bengal, xxxviii (2), p.

61 (1869).

_Norodonia_, Jullien, Bull. Soc. zool. France, v, p. 77

(1880).

_Hislopia_, _id._, _ibid._ x, p. 183 (1885).

_Norodonia_, _id._, _ibid._ p. 180.

_Echinella_, Korotneff, Biol. Centrbl. xxi, p. 311 (1901).

_Hislopia_, Annandale, J. As. Soc. Bengal (new series) ii,

p. 59 (1906).

_Hislopia_, Loppens, Ann. Biol. lacustre, iii, p. 175

(1908).

TYPE, _Hislopia lacustris_, Carter.

_Zoarium._ The zoarium consists primarily of a main axis running in a

straight line, with lateral branches that point forwards and outwards.

Further proliferation, however, often compacts the structure into an

almost uniform flat area.

_Zooecia._ The zooecia (fig. 35 B, p. 190) are flat and have the orifice

surrounded by a chitinous rim but not much raised above the dorsal

surface. They arise directly one from another.

_Polypide._ The polypide possesses from 12 to 20 tentacles. Its

funiculus is rudimentary or absent. Neither the ovaries nor the testes

have any fixed position on the lateral walls of the zooecium to which

they are confined.

The position of this genus has been misunderstood by several zoologists.

Carter originally described _Hislopia_ as a cheilostome allied to

_Flustra_; in 1880 Jullien perpetuated the error in describing his

_Norodonia_, which was founded on dried specimens of Carter's genus;

while Loppens in 1908 still regarded the two "genera" as distinct and

placed them both among the cheilostomes. In 1885, however, Jullien

retracted his statement that _Norodonia_ was a cheilostome and placed

it, together with _Hislopia_, in a family of which he recognized the

latter as the eponymic genus. Carter's mistake arose from the fact that

he had only examined preserved specimens, in which the thickened rim of

the orifice is strongly reminiscent of the "peristome" of certain

cheilostomes, while the posterior of the four folds into which the

tentacle sheath naturally falls (as in all ctenostomes, _cf._ the

diagram on p. 191) is in certain conditions rather larger than the other

three and suggests the "lip" characteristic of the cheilostomes. If

living specimens are examined, however, it is seen at once that the

posterior fold, like the two lateral folds and the anterior one, changes

its form and size from time to time and has no real resemblance to a

"lip."

That there is a remarkable, if superficial, resemblance both as regards

the form of the zooecium and as regards the method of growth between

_Hislopia_ and certain cheilostomes cannot be denied, but the structure

of the orifice and indeed of the whole organism is that of a ctenostome

and the resemblance must be regarded as an instance of convergence

rather than of genetic relationship.

The most striking feature of the polypide of _Hislopia_ is its gizzard

(fig. 38, p. 201) which is perhaps unique (except for that of

_Arachnoidea_) both in structure and function. In structure its

peculiarities reside mainly in three particulars: (i), it is not

constricted off directly from the thin-walled oesophageal tube, but

possesses at its upper extremity a thick-walled tubular portion which

can be entirely closed from the oesophagus at its upper end but always

remains in communication with the spherical part of the gizzard; (ii),

this spherical part of the gizzard is uniformly lined with a thick

chitinous or horny layer which in optical section has the appearance of

a pair of ridges; and (iii), there is a ring of long and very powerful

cilia round the passage from the gizzard to the stomach. The cardiac

limb of the stomach, which is large and heart-shaped, is obsolete. The

wall of the spherical part of the gizzard consists of two layers of

cells, an outer muscular layer consisting of powerful circular muscles

and an inner glandular layer, which secretes the chitinous lining. The

inner walls of the tubular part consist of non-ciliated columnar cells,

and when the polypide is retracted it lies almost at right angles to the

main axis of the zooecium.

The spherical part of the gizzard invariably contains a number of green

cells, which lie free in the liquid it holds and are kept in motion by

the cilia at its lower aperture. The majority of these cells can be seen

with the aid of a high power of the microscope to consist of a hard

spherical coat or cyst containing green protoplasm in which a spherical

mass of denser substance (the nucleus) and a number of minute

transparent granules can sometimes be detected. The external surface of

many of the cysts is covered with similar granules, but some are quite

clean.

There can be no doubt that these cysts represent a stage in the

life-history of some minute unicellular plant or animal. Indeed,

although it has not yet been found possible to work out this

life-history in detail, I have been able to obtain much evidence that

they are the resting stage of a flagellate organism allied to _Euglena_

which is swallowed by the polyzoon and becomes encysted in its gizzard,

extruding in so doing from its external surface a large proportion of

the food-material that it has stored up within itself in the form of

transparent granules. It may also be stated that some of the organisms

die and disintegrate on being received into the gizzard, instead of

encysting themselves.

So long as the gizzard retains its spherical form the green cells and

its other contents are prevented from entering the stomach by the

movements of the cilia that surround its lower aperture, but every now

and then, at irregular intervals, the muscles that form its outer wall

contract. The chitinous lining although resilient and not inflexible is

too stiff to prevent the lumen of the gizzard being obliterated, but the

action of the muscles changes its contents from a spherical to an ovoid

form and in so doing presses a considerable part of them down into the

stomach, through the ring of the cilia.

[Illustration: Fig. 38.--Optical section of gizzard of _Hislopia

lacustris_, with contained green cysts, × 240.]

The contraction of the gizzard is momentary, and on its re-expansion

some of the green cysts that have entered the stomach are often

regurgitated into it. Some, however, remain in the stomach, in which

they are turned round and round by the action of the cilia at both

apertures. They are apparently able to retain their form for some hours

in these circumstances but finally disintegrate and disappear, being

doubtless digested by the juices poured out upon them by the glandular

lining of the stomach. In polypides kept under observation in clean

tap-water all the cysts finally disappear, and the fæces assume a green

colour. In preserved specimens apparently unaltered cysts are sometimes

found in the rectum, but this is exceptional: I have observed nothing of

the kind in living polypides. Cysts often remain for several days

unaltered in the gizzard.

Imperfect as these observations are, they throw considerable light on

the functions of the gizzard in _Hislopia_. Primarily it appears to act

as a food-reservoir in which the green cysts and other minute organisms

can be kept until they are required for digestion. When in the gizzard

certain organisms surrender a large proportion of the food-material

stored up for their own uses, and this food-material doubtless aids in

nourishing the polyzoon. Although the cysts in the gizzard are

frequently accompanied by diatoms, the latter are not invariably

present. The cysts, moreover, are to be found in the zooecia of

polypides that have formed brown bodies, often being actually enclosed

in the substance of the brown body. The gizzards of the specimens of

_Arachnoidea_ I have examined contain cysts that resemble those found in

the same position in _Hislopia_.

_Hislopia_ is widely distributed in the southern part of the Oriental

Region, and, if I am right in regarding _Echinella_, Korotneff as a

synonym, extends its range northwards to Lake Baikal. It appears to be a

highly specialized form but is perhaps related, through _Arachnoidea_,

to _Victorella_.

27. Hislopia lacustris, _Carter_.

_Hislopia lacustris_, Carter, Ann. Nat. Hist. (3) i, p. 170,

pl. vii, figs. 1-3 (1858).

_Norodonia cambodgiensis_, Jullien, Bull. Soc. zool. France,

v, p. 77, figs. 1-3 (1880).

_Norodonia sinensis_, _id._, _ibid._ p. 78, figs. 1-3.

_Norodonia cambodgiensis_, _id._, _ibid._ x, p. 181, figs.

244, 245 (1885).

_Norodonia sinensis_, _id._, _ibid._ p. 182, figs. 246, 247.

_Hislopia lacustris_, Annandale, J. As. Soc. Bengal (new

series) iii, p. 85 (1907).

_Hislopia lacustris_, Walton, Rec. Ind. Mus. i, p. 177

(1907).

_Hislopia lacustris_, Kirkpatrick, _ibid._ ii, p. 98 (1908).

_Hislopia lacustris_, Walton, _ibid._ iii, p. 295 (1909).

_Zoarium._ The zoarium forms a flat, more or less solid layer and is

closely adherent to foreign objects. As a rule it covers a considerable

area, with radiating branches at the edges; but when growing on slender

twigs or the stems of water-plants it forms narrow, closely compressed

masses. One zooecium, however, never grows over another.

_Zooecia._ The zooecia are variable in shape. In zoaria which have space

for free expansion they are as a rule irregularly oval, the posterior

extremity being often narrower than the anterior; but small triangular

zooecia and others that are almost square may often be found. When

growing on a support of limited area the zooecia are smaller and as a

rule more elongate. The orifice is situated on a slight eminence nearer

the anterior than the posterior margin of the dorsal surface. It is

surrounded by a strong chitinous rim, which is usually square or

subquadrate but not infrequently circular or subcircular. Sometimes a

prominent spine is borne at each corner of the rim, but these spines are

often vestigial or absent; they are rarely as long as the transverse

diameter of the orifice. The zooecium is usually surrounded by a

chitinous margin, and outside this margin there is often a greater or

less extent of adherent membrane. In some zooecia the margin is obsolete

or obsolescent. The dorsal surface is of a glassy transparency but by no

means soft.

[Illustration: Fig. 39.--_Hislopia lacustris._

A=part of a zoarium of the subspecies _moniliformis_ (type specimen,

from Calcutta), × 15; A=green cysts in gizzard; E=eggs.

B=outline of part of a zoarium of the typical form of the species from

the United Provinces, showing variation in the form of the zooecia and

of the orifice, × 15.]

_Polypide._ The polypide has from 12 to 20 tentacles, 16 being a common

number.

TYPE probably not in existence. It is not in the British Museum and

Prof. Dendy, who has been kind enough to examine the specimens from

Carter's collection now in his possession, tells me that there are none

of _Hislopia_ among them.

27 _a._ Subsp. moniliformis, nov.

_Hislopia lacustris_, Annandale, J. As. Soc. Bengal (new

series) ii, p. 59, fig. 1 (1906).

In this race, which is common in Calcutta, the zooecia are almost

circular but truncate or concave anteriorly and posteriorly. They form

linear series with few lateral branches. I have found specimens

occasionally on the shell of _Vivipara bengalensis_, but they are much

more common on the leaves of _Vallisneria spiralis_.

TYPE in the Indian Museum.

The exact status of the forms described by Jullien as _Norodonia

cambodgiensis_ and _N. sinensis_ is doubtful, but I see no reason to

regard them as specifically distinct from _H. lacustris_, Carter, of

which they may be provisionally regarded as varieties. The variety

_cambodgiensis_ is very like my subspecies _moniliformis_ but has the

zooecia constricted posteriorly, while var. _sinensis_, although the

types were found on _Anodonta_ shells on which there was plenty of room

for growth, resemble the confined phase of _H. lacustris_ so far as the

form of their zooecia and of the orifice is concerned.

GEOGRAPHICAL DISTRIBUTION.--The typical form is common in northern India

and occurs also in Lower Burma; the subspecies _moniliformis_ appears to

be confined to Lower Bengal, while the varieties _cambodgiensis_ and

_sinensis_ both occur in China, the former having been found also in

Cambodia and Siam. Indian and Burmese localities are:--BENGAL, Calcutta

(subsp. _moniliformis_); Berhampur, Murshidabad district (_J. Robertson

Milne_): CENTRAL PROVINCES, Nagpur (_Carter_): UNITED PROVINCES,

Bulandshahr (_H. J. Walton_): BURMA, Pegu-Sittang Canal (_Kirkpatrick_).

BIOLOGY.--Regarding the typical form of the species Major Walton writes

(Rec. Ind. Mus. iii, p. 296):--"In volume i (page 177) of the Records of

the Indian Museum, I described the two forms of colonies of _Hislopia_

that I had found in the United Provinces (Bulandshahr). Of these, one

was a more or less linear arrangement of the zooecia on leaves and

twigs, and the other, and more common, form was an encrusting sheath on

the outer surface of the shells of _Paludina_. During the present

'rains' (July 1908) I have found many examples of what may be considered

a much exaggerated extension of the latter form. These colonies have

been on bricks, tiles, and other submerged objects. The largest colony

that I have seen so far was on a tile; one side of the tile was exposed

above the mud of the bottom of the tank, and its area measured about 120

square inches; the entire surface was almost completely covered by a

continuous growth of _Hislopia_. Another large colony was on a piece of

bark which measured 7 inches by 3 inches; both sides were practically

everywhere covered by _Hislopia_."

Major Walton also notes that in the United Provinces the growth of

_Hislopia_ is at its maximum during "rains," and that at that time of

year almost every adult _Paludina_ in a certain tank at Bulandshahr had

its shell covered with the zooecia. The Calcutta race flourishes all the

year round but never forms large or closely compacted zoaria, those on

shells of _Vivipara_ exactly resembling those on leaves of

_Vallisneria_.

In Calcutta both eggs and spermatozoa are produced at all times of the

year simultaneously in the same zooecia, but the eggs in one zooecium

often vary greatly in size. When mature they reach relatively

considerable dimensions and contain a large amount of food material; but

they are set free from the zooecium as eggs. They lie loose in the

zooecium at a comparatively small size and grow in this position.

Nothing is known as regards the development of _Hislopia_.

Both forms of the species appear to be confined to water that is free

from all traces of contamination with brine.

Order PHYLACTOLÆMATA.

The polypide in this order possesses a leaf-like ciliated organ (the

epistome) which arises within the lophophore between the mouth and the

anus and projects upwards and forwards over the mouth, which it can be

used to close. The zooecia are never distinct from one another, but in

dendritic forms such as _Plumatella_ the zoarium is divided at irregular

intervals by chitinous partitions. The lophophore in most genera is

horseshoe-shaped instead of circular, the part opposite the anus being

deeply indented. There are no parietal muscles. The orifice of the

zooecium is always circular, and there is no trace of any structure

corresponding to the collar of the ctenostomes. The tentacles are always

webbed at the base.

All the phylactolæmata produce the peculiar reproductive bodies known as

statoblasts.

The phylactolæmata, which are probably descended from ctenostomatous

ancestors, are confined to fresh or slightly brackish water. Most of the

genera have a wide geographical distribution, but (with the exception of

a few statoblasts of almost recent date) only one fossil form

(_Plumatellites_, Fric. from the chalk of Bohemia) has been referred to

the order, and that with some doubt.

It is convenient to recognize two main divisions of the phylactolæmata,

but these divisions hardly merit the distinction of being regarded as

suborders. They may be called Cristatellina and Plumatellina and

distinguished as follows:--

Division I, PLUMATELLINA, nov.--Ectocyst well developed; zoaria without

a special organ of progression; polypides contained in tubes.

Division II, CRISTATELLINA, nov.--Ectocyst absent except at the base of

the zoarium which is modified to form a creeping "sole"; polypides

embedded in a common synoecium of reticulate structure.

The Cristatellina consist of a single genus and probably of a single

species (_Cristatella mucedo_, Cuvier), which is widely distributed in

Europe and N. America, but has not been found in the Oriental Region.

Eight genera of Plumatellina are known, and five (possibly six) of these

genera occur in India.

Division PLUMATELLINA, nov.

The structure of the species included in this division is very uniform

as regards the internal organs (see fig. 40 opposite and fig. 47 _a_, p.

236). The alimentary canal is simpler than that of the Paludicellidæ. A

short oesophagus leads directly into the stomach, the cardiac portion of

which is produced as a vertical limb almost cylindrical in form and not

constricted at the base. This limb is as a rule of greater length than

the oesophagus. The pyloric part of the stomach is elongated and narrow,

and the intestine short, straight, and of ovoid form. There are no cilia

at the pyloric opening. A single funiculus joins the posterior end of

the stomach to the wall of the zooecium, bearing the statoblasts. Sexual

organs are often absent.

[Illustration: Fig. 40.--Structure of the Plumatellina (after Allman).

A=a zooecium of _Fredericella_ with the polypide extruded. B=the

lophophore of _Lophopus_ (tentacles removed) as seen obliquely from the

right side. C=larva of _Plumatella_ as seen in optical section.

_a_=tentacles; _b_=velum; _c_=epistome; _d_=mouth; _e_=oesophagus;

_f_=stomach; _g_=intestine; _h_=anus; _j_=retractor muscle;

_k_=parieto-vaginal muscles; _l_=funiculus.]

Two families may be recognized as constituting the division, _viz._,

(_a_) the Fredericellidæ, which have a circular or oval lophophore and

simple statoblast without a swim-ring, and (_b_) the Plumatellidæ, in

which the lophophore is shaped like a horseshoe and some or all of the

statoblasts are provided with a ring of air-spaces.

Family 1. FREDERICELLIDÆ.

FREDERICELLIDÆ, Kraepelin, Deutsch. Süsswasserbryozoen, i,

p. 168 (1887).

_Zoaria_ dendritic; _zooecia_ distinctly tubular, with the ectocyst well

developed; _statoblasts_ of one kind only, each surrounded by a

chitinous ring devoid of air-spaces; _polypides_ with the lophophore

circular or oval when expanded.

The Fredericellidæ consist of a single genus (_Fredericella_) which

includes several closely-allied forms and has a wide geographical

distribution.

Genus FREDERICELLA, _Gervais_ (1838).

_Fredericella_, Allman, Mon. Fresh-Water Polyzoa, p. 11

(1857).

_Plumatella_, ("arrêt de développement") Jullien, Bull. Soc.

zool. France, x, p. 121 (1885).

_Fredericella_, Kraepelin, Deutsch. Süsswasserbryozoen,

i, p. 99 (1887).

_Fredericella_, Goddard, Proc. Linn. Soc. N. S. Wales,

xxxiv, p. 489 (1909).

This genus has the characters of the family. Its status has been much

disputed, some authors regarding the shape of the lophophore as of great

morphological importance, while Jullien believed that _Fredericella_ was

merely an abnormal or monstrous form of _Plumatella_. The latter belief

was doubtless due to the fact that the zoaria of the two genera bear a

very close external resemblance to one another and are sometimes found

entangled together. The importance of the shape of the lophophore may,

however, easily be exaggerated, for, as both Jullien and Goddard have

pointed out, it assumes an emarginate form when retracted.

The best known species is the European and N. American _F. sultana_

(Blumenbach), of which several varieties or phases have been described

as distinct. This form is stated to occur also in S. Africa. _F.

australiensis_, Goddard[BC] from N. S. Wales is said to differ from this

species in having an oval instead of a circular lophophore and in other

small anatomical characters; but it is doubtful how far these characters

are valid, for the lophophore appears to be capable of changing its

shape to some slight extent and has been stated by Jullien to be

habitually oval in specimens from France. _F. cunningtoni_,

Rousselet[BD] from Lake Tanganyika has stout zooecia encrusted with

relatively large sand-grains.

[Footnote BC: Proc. Linn. Soc. N. S. Wales, xxxiv, p. 489

(1909).]

[Footnote BD: Rousselet, Proc. Zool. Soc. London, 1907 (1),

p. 254.]

The zoaria of _Fredericella_ are usually found attached to solid objects

in shallow water, but a form described as _F. duplessisi_, Ford has been

found at a depth of 40 fathoms embedded in mud at the bottom of the Lake

of Geneva. _F. cunningtoni_ was dredged from depths of about 10 and

about 25 fathoms.

The statoblasts of this genus do not float and often germinate in the

parent zooecium after its polypides have died. They are produced in

smaller numbers than is usually the case in other genera of the order.

The polypides sometimes undergo a process of regeneration, but without

the formation of brown bodies.

[Illustration: Fig. 41.--_Fredericella indica._

A=statoblast, × 120. B=outline of expanded lophophore and adjacent

parts, × 75; a=anus, r=rectum. C=outline of zoarium on leaf of

water-plant, × 3.

(A and B are from specimens from Igatpuri, C from specimen from

Shasthancottah).]

28. Fredericella indica, _Annandale_.

_Fredericella indica_, Annandale, Rec. Ind. Mus. iii, p. 373,

fig. (1909).

_Fredericella indica_, _id._, _ibid._ v, p. 39 (1910).

_Zoarium._ The zoarium is of delicate appearance and branches sparingly.

It is often entirely recumbent but sometimes produces short, lax

branches that consist of two or three zooecia only.

_Zooecia._ The zooecia are very slender and almost cylindrical; they are

slightly emarginate and furrowed, the keel in which the furrow runs

being sometimes prominent. The external surface is minutely roughened

and apparently soft, for small grains of sand and other débris cling to

it, but never thickly. The ectocyst is practically colourless but not

transparent.

_Statoblasts._ The statoblasts are variable in size and form but most

commonly have a regular broad oval outline; sometimes they are

kidney-shaped. The dorsal surface is covered with minute star-shaped

prominences, which sometimes cover it almost uniformly and are sometimes

more numerous in the centre than towards the periphery. The ventral

surface is smooth.

_Polypide._ The lophophore bears about 20-25 tentacles, which are very

slender and of moderate length; the velum at their base is narrow; as a

rule the lophophore is accurately circular.

TYPE in the Indian Museum.

The most definite character in which this species differs from _F.

sultana_ and _F. australiensis_ is the ornamentation of one surface of

the statoblast, both surfaces of which are smooth in the two latter

species. From _F. cunningtoni_, the statoblasts of which are unknown, it

differs in having almost cylindrical instead of depressed zooecia and in

not having the zooecia densely covered with sand-grains.

GEOGRAPHICAL DISTRIBUTION.--Western India (the Malabar Zone): Igatpuri

Lake, W. Ghats (alt. ca. 2,000 feet), Bombay Presidency, and

Shasthancottah Lake near Quilon, Travancore.

BIOLOGY.--In both the lakes in which the species has yet been found it

was collected in November. The specimens obtained in Travancore were

found to be undergoing a process of regeneration due at least partly to

the fact that most of the polypides had perished and that statoblasts

were germinating in the old zooecia. Specimens from the Bombay

Presidency, which were obtained a little later in the month, were in a

more vigorous condition, although even they contained many young

polypides that were not yet fully formed. It seems, therefore, not

improbable that _F. indica_ dies down at the beginning of the hot

weather and is regenerated by the germination of its statoblasts at the

beginning of the cold weather.

At Shasthancottah zoaria were found entangled with zoaria of a delicate

form of _Plumatella fruticosa_ to which they bore a very close external

resemblance.

Family 2. PLUMATELLIDÆ.

PLUMATELLIDÆ, Allman (_partim_), Mon. Fresh-Water Polyzoa,

pp. 76, 81 (1857).

Phylactolæmata which have horseshoe-shaped lophophores and a

well-developed ectocyst not specialized to form an organ of progression.

Some or all of the statoblasts are provided with a "swim-ring"

consisting of symmetrically disposed, polygonal chitinous chambers

containing air.

It is convenient to divide the Plumatellidæ as thus defined into

subfamilies (the Plumatellinæ and the Lophopinæ), which may be defined

as follows:--

Subfamily A. PLUMATELLINÆ.

Zoarium dendritic or linear, firmly fixed to extraneous objects; zooecia

tubular, not fused together to form a gelatinous mass.

Subfamily B. LOPHOPINÆ.

Zoarium forming a gelatinous mass in which the tubular nature of the

zooecia almost disappears, capable to a limited extent of progression

along a smooth surface.

Both these subfamilies are represented in the Indian fauna, the

Plumatellinæ by two of the three genera known to exist, and the

Lophopinæ by two (or possibly three) of the four that have been

described. The following key includes all the known genera, but the

names of those that have not been recorded from India are enclosed in

square brackets.

_Key to the Genera of_ Plumatellidæ.

I. Statoblasts without marginal processes.

A. Zooecia cylindrical, not embedded in a gelatinous

investment (Plumatellinæ).

_a_. Zooecia arising directly from one another;

no stolon; free statoblast oval PLUMATELLA, p. 212.

_a'_. Zooecia arising singly or in groups from

an adherent stolon; free statoblasts oval. STOLELLA, p. 229.

B. Zooecia cylindrical, embedded in a structureless

gelatinous investment.

Zooecia arising from a ramifying stolon;

statoblasts circular [STEPHANELLA.]

C. Polypides embedded in a hyaline synoecium

that conceals the cylindrical form of the

zooecia (Lophopinæ).

_c_. Polypides upright, their base far removed

from that of the zoarium when they are

expanded LOPHOPUS, p. 231.

_c'_. Polypides recumbent for the greater

part of their length at the base of

the zoarium [AUSTRALELLA[BE].]

II. Statoblasts armed (normally) with hooked

processes (Lophopinæ).

A. Processes confined to the extremities of

the statoblast; zoaria remaining separate

throughout life LOPHOPODELLA, p. 231.

B. Processes entirely surrounding the

statoblast; many zoaria embedded in a

common gelatinous investment so as to

form large compound colonies PECTINATELLA, p. 235.

[Footnote BE: See Rec. Ind. Mus. v, p. 40, footnote (1910).]

Subfamily A. PLUMATELLINÆ.

Of the two Indian genera of this subfamily, one (_Plumatella_) is almost

universally distributed, while the other (_Stolella_) has only been

found in the valley of the Ganges. The third genus of the subfamily

(_Stephanella_) is only known from Japan.