The gemmules are usually fastened together in groups, which may either be free in the sponge or adhere to its support as a "pavement layer"; sometimes, however, they are not arranged in this manner, but are quite independent of one another. The skeleton is usually delicate, sometimes very stout (_e. g._, in _S. nitens_, Carter).

The term _Eunapius_ here used is not quite in the original sense, for Gray included under it Bowerbank's _Spongilla paupercula_ which is now regarded as a form of _S. lacustris_. His description, nevertheless, fits the group of species here a.s.sociated except in one particular, viz., the smoothness of the gemmule-spicules to which he refers, for this character, though a feature of _S. carteri_, is not found in certain closely allied forms. The use of "_Spongilla_" in a double sense may be avoided by the adoption of Gray's name.

The subgenus _Eunapius_ is, like _Euspongilla_, cosmopolitan. It is not, however, nearly so prolific in species. Four can be recognized in India, two of which range, in slightly different forms, as far north as Europe, one of them also being found in North America, Northern Asia, and Australia.

8. Spongilla carteri* _Carter_ (_Bowerbank_, in litt.). (Plate II. fig.

1.)

_Spongilla friabilis_?, Carter (_nec_ Lamarck), J. Bombay Asiat. Soc. iii, p. 31, pl. i, fig. 3 (1849), & Ann. Nat.

Hist. (2) iv, p. 83, pl. ii. fig. 3 (1849).

_Spongilla carteri_, Carter, Ann. Nat. Hist. (3) iii, p.

334, pl. viii, figs. 1-7 (1859).

_Spongilla carteri_, Bowerbank, P. Zool. Soc. London, 1863, p. 469, pl. x.x.xviii, fig. 20.

_Eunapius carteri_, J. E. Gray, _ibid._ 1867, p. 552.

_Spongilla carteri_, Carter, Ann. Nat. Hist. (5) vii, p. 86 (1881).

_Spongilla carteri_, _id._, _ibid._ x, p. 369 (1882).

_Spongilla carteri_, Potts, P. Ac. Philad. 1887, p. 194.

_Spongilla carteri_, Weltner, Arch. Naturg. lxi (i), pp.

117, 134 (1895).

_Spongilla carteri_, Kirkpatrick, P. Zool. Soc. London, 1906 (i), p. 219, pl. xv, figs. 3, 4 (? figs. 1, 2).

_Spongilla carteri_, Annandale, J. Asiat. Soc. Bengal, 1906, p. 188, pl. i, fig. 1.

_Spongilla carteri_, Willey, Spolia Zeyl. iv, p. 184 (1907).

_Spongilla carteri_, Annandale, _ibid._ vii, p. 63, pl. 1, fig. 1 (1910).

[Ill.u.s.tration: Fig. 14.--Gemmule of _Spongilla carteri_ (from Calcutta), as seen in optical section, 140.]

_Sponge_ ma.s.sive, as a rule with the surface smooth and rounded, occasionally bearing irregular ridges, which may even take the form of c.o.c.ks...o...b..; the oscula large, rounded, conspicuous but not raised above the surface of the sponge, leading into broad vertical ca.n.a.ls; the lateral ca.n.a.ls, except in the immediate vicinity of the central vertical ones, not very broad; the oscular collars extending for a considerable distance over the oscula in living or well-preserved specimens, never standing out from the surface; the oscula never surrounded by radiating furrows. The inhalent pores surrounded externally by unmodified cells of the external membrane. Colour greyish, sometimes with a flush of green on the external surface.

The sponge has a peculiarly strong and offensive smell.

_Skeleton_ fairly compact, with well-developed radiating fibres; the transverse fibres splayed out at either end so that they sometimes resemble a pair of fans joined together by the handles (fig. 3, p. 33).

A moderate amount of spongin present.

_Spicules._ Skeleton-spicules smooth, pointed, nearly straight, never very stout but somewhat variable in exact proportions. Gemmule-spicules similar but much smaller. (There are no true flesh-spicules, but immature skeleton-spicules may easily be mistaken for them.)

_Gemmules_ as a rule numerous, spherical or flattened at the base, variable in size, each covered by a thick coat consisting of several layers of relatively large polygonal air-s.p.a.ces. A single aperture surrounded by a crater-like depression in the cellular coat and provided with a foraminal tubule resembling an inverted bottle in shape. (This tubule, which does not extend beyond the surface of the cellular coat, is liable to be broken off in dried specimens.) The spicules variable in quant.i.ty, arranged irregularly among the s.p.a.ces of the cellular coat and usually forming a spa.r.s.e horizontal layer on its external surface. Each gemmule contained in a cage of skeleton-spicules, by the pressure of which it is frequently distorted.

8_a._ Var. mollis*, nov.

This variety is characterized by a paucity of skeleton-spicules. The sponge is therefore soft and so fragile that it usually breaks in pieces if lifted from the water by means of its support. Owing to the paucity of skeleton-spicules, which resemble those of the typical form individually, the radiating and transverse fibres are extremely delicate.

Common in Calcutta.

8_b._ Var. cava*, nov.

This variety is characterized by the fact that the oscula open into broad horizontal ca.n.a.ls, the roof of which is formed by a thin layer of parenchyma and skeleton or, in places, of the external membrane only.

The skeleton is loose and fragile, and the living sponge has a peculiar gla.s.sy appearance. In spirit the colour is yellowish, during life it is greenish or white.

Taken at Bombay; November, 1907.

8_c._ Var. lobosa*, nov.

The greater part of the sponge in this variety consists of a number of compressed but pointed vertical lobes, which arise from a relatively shallow, rounded base, in which the oscula occur. The dried sponge has a yellowish colour.

Apparently common in Travancore.

I cannot distinguish these three "varieties"[AC] from the typical form as distinct species; indeed, their status as varieties is a little doubtful in two cases out of the three. Var. _cava_ appears to be a variety in the strict sense of the word (see p. 18), for it was found on the island of Bombay, the original locality of the species, growing side by side with the typical form. Var. _lobosa_, however, should perhaps be regarded as a subspecies rather than a variety, for I have received specimens from two localities in the extreme south-west of India and have no evidence that the typical form occurs in that part of the country. Evidence, however, is rather scanty as regards the occurrence of freshwater sponges in S. India. Var. _mollis_, again, may be a phase directly due to environment. It is the common form in the ponds of certain parts (_e. g._ in the neighbourhood of the Maidan and at Alipore) of the Calcutta munic.i.p.al area, but in ponds in other parts (_e. g._ about Belgatchia) of the same area, only the typical form is found. It is possible that the water in the former ponds may be deficient in silica or may possess some other peculiarity that renders the production of spicules difficult for _S. carteri_; but this seems hardly probable, for _S. cra.s.sissima_, a species with a rather dense siliceous skeleton, flourishes in the same ponds. I have noticed that in ponds in which the aquatic vegetation is luxuriant and such genera of plants as _Pistia_ and _Limnanthemum_ flourish, there is always a tendency for _S. carteri_ to be softer than in ponds in which the vegetation is mostly cryptogamic, and in Calcutta those parts of the town in which sponges of this species produce most spicules are those in which a slight infiltration of brackish water into the ponds may be suspected; but in the interior of India, in places where the water is absolutely fresh, hard specimens seem to be the rule rather than the exception.

[Footnote AC: The only complete European specimen of the species I have seen differs considerably in outward form from any Indian variety, consisting of a flat basal area from which short, cylindrical turret-like branches arise.

This specimen is from Lake Balaton in Hungary and was sent me by Prof. von Daday de Dees of Buda-Pesth.]

_S. carteri_ is closely related to _S. nitens_, Carter (Africa, and possibly S. America), but differs from that species in its comparatively slender, sharp skeleton-spicules and smooth gemmule-spicules. It may readily be distinguished from all other Indian freshwater sponges by its large, deep, round oscula, but this feature is not so marked in var.

_lobosa_ as in the other forms. The typical form and var. _mollis_ grow to a larger size than is recorded for any other species of the family. I possess a specimen of the typical form from the neighbourhood of Calcutta which measures 30 27 cm. in diameter and 19.5 cm. in depth, and weighs (dry) 24-3/4 oz. The base of this specimen, which is solid throughout, is nearly circular, and the general form is mound-shaped.

Another large specimen from Calcutta is in the form of an irregular wreath, the greatest diameter of which is 34 cm. This specimen weighs (dry) 16-1/4 oz. Both these specimens probably represent the growth of several years.

TYPES.--The types of the varieties _mollis_, _cava_ and _lobosa_ are in the collection of the Indian Museum. I regard as the type of the species the specimen sent by Carter to Bowerbank and by him named _S. carteri_, although, owing to some confusion, Carter's description under this name appeared some years before Bowerbank's. This specimen is in the British Museum, with a fragment in the Indian Museum.

GEOGRAPHICAL DISTRIBUTION.--The range of the species extends westwards to Hungary, southwards to Mauritius and eastwards to the island of Madura in the Malay Archipelago; a specimen from Lake Victoria Nyanza in Central Africa has been referred to it by Kirkpatrick (P. Zool. Soc.

London, 1906 (i), p. 219), but I doubt whether the identification is correct. In India _S. carteri_ is by far the most universally distributed and usually much the commonest freshwater sponge; it is one of the only two species as yet found in Ceylon. Specimens are known from the following localities:--PUNJAB, Lah.o.r.e (_J. Stephenson_): BOMBAY PRESIDENCY, island of Bombay (_Carter_, _Kirkpatrick_, _Annandale_); Igatpuri, W. Ghats (alt. _ca._ 2,000 ft.) (_Annandale_): UNITED PROVINCES (plains), Agra (_Kirkpatrick_); Lucknow: HIMALAYAS, Bhim Tal, k.u.maon (alt. 4,500 ft.) (_Annandale_); Tribeni, Nepal (_Hodgart_): BENGAL, Calcutta and neighbourhood; Rajshahi (Rampur Bhulia) on the R.

Ganges about 150 miles N. of Calcutta (_Annandale_); Berhampur, Murshidabad district (_R. E. Lloyd_); Pusa, Darbbhanga district (_Bainbrigge Fletcher_); Siripur, Saran district, Tirhut (_M.

Mackenzie_); Puri and the Sur Lake, Orissa (_Annandale_): MADRAS PRESIDENCY, near Madras town (_J. R. Henderson_); Madura district (_R.

Bruce Foote_); Bangalore (_Annandale_) and Worgaum, Mysore State (2,500-3,000 ft.); Ernakulam and Trichur, Cochin (_G. Mathai_); Trivandrum and the neighbourhood of C. Comorin, Travancore (var.

_lobosa_) (_R. S. N. Pillay_): BURMA, k.a.w.kareik, interior of Amherst district, Tena.s.serim (_Annandale_); Rangoon (_Annandale_); Bhamo, Upper Burma (_J. Coggin Brown_): CEYLON, Peradeniya (_E. E. Green_); outlet of the Maha Rambaikulam between Vavuniya and Mamadu, Northern Province (_Willey_); Horowapotanana, between Trincomalee and Anuradihapura, North-Central Province (_Willey_).

BIOLOGY.--_S. carteri_ usually grows in ponds and lakes; I have never seen it in running water. Mr. Mackenzie found it on the walls of old indigo wells in Tirhut.

The exact form of the sponge depends to some extent on the forces acting on it during life. At Igatpuri, for instance, I found that specimens attached to the stems of shrubs growing in the lake and constantly swayed by the wind had their surface irregularly reticulated with high undulating ridges, while those growing on stones at the bottom of a neighbouring pond were smooth and rounded.

Sponges of this species do not shun the light.

In Calcutta _S. carteri_ flourishes during the cold weather (November to March). By the end of March many specimens that have attached themselves to delicate stems such as those of the leaves of _Limnanthemum_, or to the roots of _Pistia stratiotes_, have grown too heavy for their support and have sunk down into the mud at the bottom of the ponds, in which they are quickly smothered. Others fixed to the end of branches overhanging the water or to bricks at the edge have completely dried up.