MONTHLY 180 OCT 82 MICROSCOPICAL JOURNAL VOL. III. NEW YORK, OCTOBER, 1882. Development of the Planula of BY J. H. PILLSBURY. On the tangled masses of sea-weed (Fucus) which grow in profusion over the rocks of our New England coast between high and low water, may be found little clusters of the orangeyellow polypites of one of our commonest hydroids, Clava leptostyla, Ag. Fig. 1 of the plate represents a portion of the sea-weed with such a cluster of polypites, of natural size. As the incoming or receding tide floats the long stems of the sea-weed back and forth over the rocks, the little animals may be seen gracefully moving with the waves, or suddenly contracting their tentacles on the approach of danger. No. 10. are formed by the outward growth of the body-wall, and at first do not differ in appearance from the general tissue of the body. Usually before the bud has reached its full size, one or two small, transparent spots appear in the outward and larger end of the bud (fig. 3 a and b). These are the germinal vesicles, and each contains a distinct spot called the germinal dot. This I have been able to distinguish only by the aid of carmine staining, but under such treatment it becomes very distinct. As the buds continue to grow the sarcode surrounding this germinal vesicle becomes more dense than that in other parts of the bud, and a little later the ovum separates from the general mass of the bud, which is now called the spadix (fig. 4 a and b). The ovum continues to increase in size at the expense of the spadix until it nearly fills the sac, the spadix shaped termination of the stem of the being meanwhile reduced to a cup All the polypites of the same cluster are connected at the base by minute, thread-like fibres, called stolons, which unite them into a single colony. Each polypite consists of a tube with an oral opening at the free end, which is surrounded for some distance down the slightly swelling body with a number of stout, and somewhat scattered, tentacles (fig. 2). Just below these tentacles the body contracts into a perceptibly narrower stem, which maintains a uniform size until just above its union with the stolon. At the point of contraction just mentioned there will be found in early summer, of various shapes and sizes, clusters of minute buds, which often extend down the stem for a dis tance of 2 mm sporosac. Such of the buds as had When the ovum has reached its full size and fills the whole sporosac, the ovum becomes so opaque as to make the germinal vesicle obscure, and render observation in regard to its changes impossible. The ovum itself, however, soon divides into two cells, the division commencing by a depression at one side, which becomes These buds (fig. 2 a) gradually deeper and deeper until the *Read before the Section of Histology and Microscopy of the A. A. A. S., at Montreal. two cells are entirely separated (figs. 7 and 8). Each of these cells again divides into two, and this is repeated until the ovum passes through the mulberry state and assumes a granular appearance, beyond which time it is impossible to follow the cell-division (figs. 9 to 13). At this stage the coat of the embryo begins to show signs of separating into the two layers which are characteristic of the body-wall of the Cœlenterata (fig. 14), and the body of the embryo shows slight changes of form, from time to time elongating itself into a somewhat worm-like form. It is at this point that the results of my observations differ from those of others who have written upon the development of the hydroids. The elder Agassiz says he has never been able to discover vibratile cilia while the embryo is within the sporosac. I have, however, found not only welldeveloped cilia on the surface of the embryo, while as yet there were no signs of rupture of the sporosac, but I have also found them in motion, producing vortical currents within the sporosac, as shown by the direction of the arrow (fig. 15 a). The embryo assumes an arched position as seen in fig. 14, and seems to be endeavoring thus to burst open its prison wall. In this stage the motion of the cilia becomes very energetic beneath the arch, as if to assist in bursting the wall of the sporosac. After successive and finally successful attempts, the larva comes forth in the planula form, and moves about freely for some time by means of its thick covering of cilia (fig. 16). At this time the planula shows no signs of a mouth, and seems to be moving about in quest of a resting place. In this state the outer layer of the body-wall shows a quite distinct cellular structure under treatment with staining fluids. After moving about freely for a short time, the planula attaches itself to some object by the end which has been posterior in its free motions, a mouth opens into the previously formed body-cavity, and surrounding this mouth a number of tentacles are developed. A New Thuricola. BY DR. A. C. STOKES. In his splendid "Manual of the Infusoria,” Mr. W. Saville Kent has subdivided the genus Vaginicola into several groups, primarily on account of certain structural characteristics, and also, as he expresses it, to "assist the student in his indentification of the numerous species." In the latter he has been eminently successful, for, until he took the matter in hand, we had Vaginicola with a valve and without, Vaginicola upright, decumbent, sessile, and stalked in the most perplexing confusion. One system of classification stated that if the body was pedicellate and the sheath sessile, Vaginicola being in this condition five times out of ten, the specimen was a Tintinnus, and Tintinnus was run down only to find that every known species is free-swimming and marine. Another stated that everything with the lorica fixed by its posterior extremity is a Cothurnia, and still another that the sheath of every Cothurnia is stalked, while one more informed the reader that every Vaginicola has the test adherent by its side. This point reached, although a microscopist soon becomes the most patient of human beings, nothing remained but to follow the advice of Mr. F.'s Aunt, and chuck the thing out o'winder. Kent has righted affairs by directing that both stalked and sessile zooids in an upright, sessile sheath, shall be relegated to the genus Vaginicola, forming for the decumbent lorica a new genus, while the not uncommon valvate species, V. valvata, with two others, he has collated under Thuricola, a new generic title. For two seasons the writer has observed attached to the leaflets of Ceratophyllum, isolated specimens of a loricate and valvate zooid, presenting characteristics which mark it a new species of Kent's Thuricola One of its specific peculiarities, in addition to the valve-like organ closely resembling that of Thuricola (Vaginicola) valvata, consists in a delicate membrane attached to the inner wall of the lorica opposite to the valve, and at a point about midway between the origin of the latter and the orifice of the sheath. It is shown in optical section in figure 38. It extends arcuately upward and inward, and receives the edge of the valve as it descends upon the contracted animal. It is flexible, bending at the touch of the ascending zooid, but is rigidly attached to the lorica, and is stiff enough to make a well-defined indentation in the soft substance of the animalcule. It supports the edge of the closed valve at about the beginning of its middle third. The valve, although the connection could not be demonstrated, FIG. 38. THURICOLA INNIXA, n. sp. is probably attached to a ligamentous prolongation of the body, since it begins to rise before coming in contact with the expanding zooid. Lorica Thuricola innixa, n. sp. sessile, transparent, sub-cylindrical, four to five times as long as broad, truncate, and somewhat tapering posteriorly, bearing at some distance from the orifice an internal valve-like appendage as in T. valvata, and an opposite, rigidly attached, but flexible, membranous organ projecting arcuately inwards, and acting as a support to the edge of the descending valve, the wall of the lorica being dilated laterally immediately behind this, in optical section, bristle-like M FIG. 39. ZEISS' SPECTRAL-OCULAR. solar spectrum far greater dispersion is required, and the light passing through the narrow slit of one of the largest spectroscopes has been spread out into a spectrum over twenty feet in length. The principles of spectrum analy* Read before the New York Microscopical Society. |