BIOLOGY.--_L. carteri_ is found on the lower surface of stones and on the stems and leaves of water-plants, usually in lakes or large ponds.
Although the zoaria do not form compound colonies by secreting a common membrane or investment, they are markedly gregarious. The most closely congregated and the largest zoaria I have seen were a.s.sembled amongst a gelatinous green alga of the genus _Tolypothrix_[BM] (Myxophyceae) that grows on the vertical stems of a plant at the edge of Igatpuri Lake; it is noteworthy that in this case the alga seemed to take the place of the common investment of _Pectinatella burmanica_, in which green cells are present in large numbers (p. 237). The zoaria of _L. carteri_ are able to change their position, and I found that if a number of them were placed in a bottle of water they slowly came together at one spot, thus apparently forming temporary compound colonies. Before a movement of the whole zoarium commences its base becomes detached from its support at the anterior end (fig. 32, p. 172), but the whole action is extremely slow and I have not been able to discover any facts that cast light on its exact method of production. At Igatpuri statoblasts are being produced in considerable numbers at the end of November, but many young zoaria can be found in which none have as yet been formed.
[Footnote BM: Prof. W. West will shortly describe this alga, which represents a new species, in the Journ. Asiat. Soc.
Bengal, under the name _Tolypothrix lophopodellophila_.--_April 1911_.]
The larva of a fly of the genus _Chironomus_ is often found inhabiting a tube below zoaria of _L. carteri_. It is thus protected from its enemies but can protrude its head from beneath the zoarium and seize the small animals on which it preys.
Genus 4. PECTINATELLA, _Leidy_.
_Cristatella_, Leidy, P. Ac. Philad. v, p. 265 (1852).
_Pectinatella_, _id._, _ibid._, p. 320.
_Pectinatella_, Allman, Mon. Fresh-Water Polyzoa, p. 81 (1857).
_Pectinatella_, Hyatt, Proc. Ess.e.x Inst. v, p. 227, fig. 20 (1867).
_Pectinatella_, Kraepelin, Deutsch. Susswa.s.serbryozoen, i, p. 133 (1887).
_Pectinatella_, Oka, Journ. Coll. Sci. Tokyo, iv, p. 89 (1891).
TYPE, _Pectinatella magnifica_, Leidy.
This genus is closely allied to _Lophopodella_, from which it is often difficult to distinguish young specimens. Adult zoaria are, however, always embedded together in groups in a gelatinous investment which they are thought to secrete in common[BN], and the statoblasts are entirely surrounded by processes that bear curved spinules at their tips only.
The polypides have the same semi-rec.u.mbent position as those of _Lophopodella_ but are larger than those of any species of _Lophopodella_ or _Lophopus_ yet known. The statoblasts are larger than those of any other Plumatellidae.
[Footnote BN: It is now perhaps open to doubt whether the investment is actually secreted by the polyzoon, for Prof.
W. West has discovered in it the cells of an alga belonging to a genus which habitually secretes a gelatinous investment of its own (see p. 238, _post._).--_April 1911._]
The type-species was originally found in N. America but has since been taken in several localities in continental Europe. Except this and the Indian form only one species is known, namely _P. gelatinosa_ from j.a.pan. _P. magnifica_ has circular statoblasts with long marginal processes, while in _P. gelatinosa_ the statoblasts are subquadrate and in _P. burmanica_ almost circular, both Asiatic forms having very short marginal processes.
The compound colonies formed by _Pectinatella_ are often of great size.
Those of _P. gelatinosa_ are sometimes over 2 metres in length, while those of _P. burmanica_ in the Sur Lake appeared to be only limited as regards their growth by the shallowness of the water in which the reeds to which they were attached were growing. Some were observed that were over 2 feet long.
38. Pectinatella burmanica, _Annandale_. (Plate III, fig. 5.)
_Pectinatella burmanica_, Annandale, Rec. Ind. Mus. ii, p. 174, fig. 5 (1908).
_Pectinatella burmanica_, _id._, _ibid._ v, p. 56 (1910).
_Pectinatella burmanica_, _id._, Spol. Zeyl. vii, p. 63, pl. i, fig. 3 (1910).
_Zoarium._ The zoaria are circular or nearly so except when about to undergo division, in which case they are constricted in the middle. As a rule they measure nearly an inch (2 cm.) in diameter. The polypides have a definite arrangement in each zoarium, being divided into four groups, each of which has a fan-like form. In the first place they are separated into two main divisions in a line running through the centre of the zoarium, and secondly each main division is separated into two subordinate ones in a line running across the other at right angles. The number of zoaria joined together in a single compound colony is very variable; sometimes there are only about half a dozen and sometimes several hundreds. The common investment in living colonies is often as much as two inches thick and has a translucent dark greenish colour due to the presence in it of green cells.
[Ill.u.s.tration: Fig. 47.--_Pectinatella burmanica._
A=polypide with the lophoph.o.r.e expanded, 15; _a_=oesophagus; _b_=cardiac limb of stomach; _c_=stomach; _d_=r.e.c.t.u.m; _e_=a.n.u.s; _f_=funiculus. [The muscles are omitted and the external tubercles are only shown on part of the polypide. The specimen is from the Sur Lake, Orissa.] B=statoblast from Ceylon, 35.]
_Polypide._ The polypide can be extruded for a distance of at least 5 mm. Its whole external surface is covered with minute tubercles. There are about 90 tentacles, which are long and slender, the velum at their base being narrow and almost straight. The stomach is of considerable stoutness.
_Statoblast._ The statoblasts are of large size, measuring from 1 to 1.75 mm. in diameter. In form they are almost circular, but one side is always slightly flattened. The marginal processes are very short and bear a single pair of hooks at the tip. The capsule is circular and small as compared with the free part of the swim-ring.
TYPE in the Indian Museum.
_P. burmanica_ is evidently a near relation of _P. gelatinosa_, Oka, from j.a.pan, differing from that species in the shape of the statoblasts and in having much longer tentacles. The arrangement of the polypides in the zoarium and the general structure of the statoblasts are very similar in the two species.
GEOGRAPHICAL DISTRIBUTION.--_P. burmanica_ was originally described from a swamp at k.a.w.kareik in the Amherst district of Tena.s.serim but has also been found in the Sur Lake near Puri in Orissa. Dr. A. Willey obtained specimens from a pool by the roadside between Maradankadewela and Galapitagala, at the foot of Ritigala, N. Central Province, Ceylon.
BIOLOGY.--The first specimen obtained was a statoblast fixed to a tube of the oligochaete worm _Aulophorus tonkinensis_ taken at k.a.w.kareik in March. At the same time young zoaria, which did not yet possess a common investment, were found on a leaf growing on a twig which drooped into the water. Large compound colonies were taken in Orissa in October. They completely encased the stems of reeds, thus forming hollow cylinders, but slipped from their supports when the reeds were pulled out of the water. In life they resembled gelatinous algae rather than animals and exhibited a striking similarity to ma.s.ses of zoaria of _Lophopodella carteri_ surrounded by such algae. Some of the colonies were evidently dying and contained few polypides in a living condition, but many statoblasts; others were in a flourishing condition and were producing larvae and statoblasts simultaneously.
A piece of a colony full of larvae was placed before midday in an aquarium, which was kept in a shady verandah. Large numbers of larvae were set free almost immediately. They measured about 2 mm. in length and were distinctly pear-shaped; each contained a pair of polypides, which occupied a comparatively small part of the interior, the whole of the broader half being hollow. The larvae swam slowly, broad-end-first, by means of the cilia with which their surface was covered, occasionally gyrating on their long axis and always adopting an erratic course.
Towards evening they showed signs of settling down, frequently touching the gla.s.s of the aquarium with their broad ends and sometimes remaining still in this position for some minutes. Many attempts were, however, made before fixation was completed, and this did not occur until after nightfall. By next morning every larva was fixed to the gla.s.s and had everted its two polypides. Unfortunately I was not able to trace the development further, but young compound colonies were found in which the secretion of the common investment had just commenced. The zoaria in these colonies measured about 1 cm. in diameter and already contained many polypides each.
Oka has described the development from the statoblast of the allied j.a.panese species. He found that each statoblast produced in the first instance a single polypide, and that the statoblasts, which were produced in autumn, lay dormant through the winter and germinated in spring. As the Sur Lake begins to undergo desiccation as soon as the "rains" cease, the statoblasts in it probably do not germinate until the break of the next "rains" about the middle of June. I have had dried statoblasts in my possession for over two years. Their cellular contents appear to be in good condition, although the cells show no signs of development; but they have not germinated in my aquarium, in which some of them have now been kept for more than six months.
The green cells of the common investment are peculiar bodies that deserve further study than it has yet been possible to devote to them.
Each cell is of ovoid form, varying somewhat in size but as a rule measuring about 0.03 0.008 mm. There can be no doubt that these bodies represent a stage in the life-history of an alga[BO]. Diatoms, bacilli and other minute plants are often present in the membrane as well as the characteristic green cells, but do not form a constant feature of it.
[Footnote BO: Professor W. West identifies this algae as _Dactylococcopsis pectinatellophila_, new species. It will be described, before the publication of this book, in the Journ. As. Soc. Bengal (1911). Prof. West has found, a.s.sociated more or less fortuitously with _P. burmanica_, another alga, namely _Microcystis orissica_, also a new species.--_April 1911._]
APPENDIX TO THE VOLUME.
HINTS ON THE PREPARATION OF SPECIMENS.
_To preserve Spongillidae._--Spongillidae must be preserved dry or in very strong alcohol. Formalin should not be used.
_To clean siliceous sponge spicules._--Place small fragments of the dried sponge (if alcohol is present, the reaction is apt to be violent) in a test tube, cover them with strong nitric acid and boil over the flame of a Bunsen burner or small spirit lamp until the solid particles disappear. Add a large quant.i.ty of water to the acid and filter through pure cellulose filter-paper, agitating the liquid repeatedly. Pa.s.s clean water in considerable quant.i.ties through the filter-paper and dry the latter carefully; place it in a spirally coiled wire and ignite with a match, holding the wire in such a way that the spicules released by the burning of the paper fall into a suitable receptacle. They may then be picked up with a camel"s-hair brush and mounted in Canada balsam.
_To examine the skeleton of a Spongillid._--Cut thin hand-sections with a sharp scalpel, dehydrate if necessary, and mount in Canada balsam.
_To prepare gemmules for examination._--Place the gemmules dry in a watch-gla.s.s with a few drops of strong nitric acid. When gas is given off freely add water in considerable quant.i.ties. Remove the gemmules with a camel"s-hair brush to clean water, then to 50%, 70%, 90% and absolute alcohol in succession, leaving them for an hour in each strength of spirit. Clear with oil of cloves and mount in Canada balsam.
_To ascertain the presence of bubble-cells in the parenchyma of a Spongillid._--Tease up a small piece of the sponge with a pair of needles, mount under a thin cover-slip in strong spirit, and examine under a high power of the microscope.
_To preserve Hydra in an expanded condition._--Place the polyp in a watch-gla.s.s of clean water and wait until its tentacles are expanded.
Heat a few drops of commercial formaldehyde and squirt the liquid while still hot at the _Hydra_, which will be killed instantaneously. Remove it to a solution of formaldehyde and spirit of the following formula:--
Commercial formaldehyde 1 part.
Absolute alcohol 3 parts.
Distilled water 7 parts.
Then pa.s.s the _Hydra_ through 50% and 70% alcohol and keep in 90%.