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 sh.e.l.l 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_ sh.e.l.ls 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 Ca.n.a.l (_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 sh.e.l.ls 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 sh.e.l.l covered with the zooecia. The Calcutta race flourishes all the year round but never forms large or closely compacted zoaria, those on sh.e.l.ls 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 PHYLACTOLaeMATA.
The polypide in this order possesses a leaf-like ciliated organ (the epistome) which arises within the lophoph.o.r.e between the mouth and the a.n.u.s 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 part.i.tions. The lophoph.o.r.e in most genera is horseshoe-shaped instead of circular, the part opposite the a.n.u.s 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 phylactolaemata produce the peculiar reproductive bodies known as statoblasts.
The phylactolaemata, 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 phylactolaemata, 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 ca.n.a.l is simpler than that of the Paludicellidae. 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. s.e.xual organs are often absent.
[Ill.u.s.tration: Fig. 40.--Structure of the Plumatellina (after Allman).
A=a zooecium of _Fredericella_ with the polypide extruded. B=the lophoph.o.r.e 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_=a.n.u.s; _j_=retractor muscle; _k_=parieto-v.a.g.i.n.al muscles; _l_=funiculus.]
Two families may be recognized as const.i.tuting the division, _viz._, (_a_) the Fredericellidae, which have a circular or oval lophoph.o.r.e and simple statoblast without a swim-ring, and (_b_) the Plumatellidae, in which the lophoph.o.r.e is shaped like a horseshoe and some or all of the statoblasts are provided with a ring of air-s.p.a.ces.
Family 1. FREDERICELLIDae.
FREDERICELLIDae, Kraepelin, Deutsch. Susswa.s.serbryozoen, 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-s.p.a.ces; _polypides_ with the lophoph.o.r.e circular or oval when expanded.
The Fredericellidae 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_, ("arret de developpement") Jullien, Bull. Soc.
zool. France, x, p. 121 (1885).
_Fredericella_, Kraepelin, Deutsch. Susswa.s.serbryozoen, i, p. 99 (1887).
_Fredericella_, G.o.ddard, Proc. Linn. Soc. N. S. Wales, x.x.xiv, p. 489 (1909).
This genus has the characters of the family. Its status has been much disputed, some authors regarding the shape of the lophoph.o.r.e 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 lophoph.o.r.e may, however, easily be exaggerated, for, as both Jullien and G.o.ddard have pointed out, it a.s.sumes 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_, G.o.ddard[BC] from N. S. Wales is said to differ from this species in having an oval instead of a circular lophoph.o.r.e and in other small anatomical characters; but it is doubtful how far these characters are valid, for the lophoph.o.r.e 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, x.x.xiv, 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.
[Ill.u.s.tration: Fig. 41.--_Fredericella indica._
A=statoblast, 120. B=outline of expanded lophoph.o.r.e and adjacent parts, 75; a=a.n.u.s, r=r.e.c.t.u.m. 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 rec.u.mbent 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 debris cling to it, but never thickly. The ectocyst is practically colourless but not transparent.