Page:Proceedings of the Royal Society of London Vol 60.djvu/51

Rh and of L. coriacea, Mont, sp., in Septem ber. Owing to th e inexperienee w ith w hich I approached the difficult task of rearing these larvae, my results are not so complete in all details as I could wish, but in the case of L. variabilis I was able to obtain a more or less perfect developmental series, and in the other three species I was able to make out satisfactorily the m ain points in the m etam orphosis, especially the important question of the relation between the celllayers of the larva and those of the adult. I hope to bring my investigations to completion during the present year, but, in the meantime, the results obtained seemed to me of sufficient im portance to form the subject of a prelim inary note. The material which I collected and preserved was fu rth e r studied at M unich, in the laboratory of Professor Richard Hertwig, to whom I am indebted for much kind help and advice, as well as hospitality.

The larvee of L. variabilis are of the so-called am phiblastula type, but in many respects more primitive than the am phiblastula larva hitherto described in other Calcarea. The minute larvae (70—80 in length, 50—60 p in breadth) leave the m other sponge by the osculum, and at once rise to the surface of the w ater, w here they swim for about tw enty-four hours. They then sink to th e bottom, where, after swimming about slowly for tw elve to tw enty-four hours more, they fix them selves and undergo m etam orphosis. The larval life thus lasts for thirty-six to forty-eight hours.

The oval larva (figs. 1 and 2)* is divided into an anterior region composed of ciliated cells and a posterior region composed of nonciliated granular cells. The centre of the transparent larva is occupied by a conspicuous mass of yellowish-brown pigm ent. The ciliated cells are slender and elongated, reaching from the pigm ent to the surface of the body. Each cell bears a single flagellum, and the body of the cell is divided into an internal refractile portion and an external granular portion. These two portions of the cell are so distinct in the living object th at a superficial exam ination gives the impression of an internal layer of refractile cells covered by an external granular layer, b u t by more careful investigation it is easy to make out th at these two apparent layers are merely parts of a single layer of cells. The ciliated cells situated more posteriorly entirely lack the refractile inner portion, and appear granular throughout. They are also slightly broader, and have more convex outer surfaces than the other ciliated cells, form ing an equatorial zone of intermediate cells, not very distinct in the living object. The

but 1 and 2 are semidiagrammatic and combined from different preparations.
 * Figs. 1—6 represent tlie development of L. variabilis, x 1000 diameters. All