1894.] Embryology. 73 
EMBRYOLOGY.’ 
Embryology of Sponges.’—Mons. Yves Delage in an interesting 
paper describes discoveries, the acceptance of which implies the over- 
throw of our present ideas of sponge morphology. The post-larval 
development of three silicious sponges, Spongilla, Esperella, Reniera 
and of a horny sporge, Aplysilla, was followed, and it was found that 
in the essential features of development all the forms agreed. 
Larva.—The larva in all four sponges is a solid larva, the superficial 
layer of which is composed of slender ciliated cells. The inner one 
contains, except in Aplysilla, three distinct kinds of cells, each kind 
destined to form a particular part of the adult body. Just beneath or 
scattered between the basal parts of the superficial elements, is a dis- 
continuous layer of rounded or irregular cells, which the author claims 
form the definitive epidermis, and which he, therefore calls epidermic 
cells. Internal to this layer is a mass composed of ameeboid and 
“intermediary ” cells, the former characterized as well by the nucleus 
as by the power of throwing out pseudopodia, while the latter are 
immobile cells of rather a negative nature. In the Aplysilla larva the 
two latter classes cannot be distinguished. 
While in Spongilla the ciliated cells form a continuous covering for 
the larva, in the larvæ of the three other sporges they are absent over 
one of the poles, posterior in Esperella and Reniera, anterior in Aply- 
silla. Here the epidermic cells lie at the surface. (Against this inter- 
pretation of the cells covering the non-ciliated pole may be urged the 
observations of the reviewer on Esperella and Tedania, in which sponges 
it was found that the cells in question and the ciliated cells of the larva 
are differentiated portions of an external homogenous layer, repre- 
senting the ectoderm of the embryo.*) 
The large cavity which, as is well known, occupies the anterior por- 
tion of the Spongilla larva has, according to the author, no morpholog- 
ical significance. It is only a magnified lacuna, such as is found here 
Edited by E. A. Andrews Baltimore Md: to whom contributions may be 
addressed. 
2 Embryogénie des Eponges. Yves Delage. Archives de Zoologie Expérimentale 
et Génerale. Année, 1892. » 3. 
3 Notes on the Development of Some Sponges. Journal of Morphology. Vol. V, 
No. 3, 1891. 
