No. 3.] DEVELOPMENT OF MARINE SPONGES. 367 
mule, in the parenchyma of the mother sponge, and only after 
formation do they get into the peripheral layer of the gem- 
mule. The cells of the latter layer, however, secrete the 
outer cuticle, and subsequently entirely disappear. 
Gemmules fundamentally like those of Spongilla have been 
found in certain marine sponges by E. Topsent (32). The 
sponges in which the gemmules were observed are Chalina 
oculata, Chalina gracilenta (I have seen them myself in Chalina 
arbuscula, Verrill, during the summer at Woods Holl), Cliona 
vastifica, Suberites ficus. The gemmules consist of a mass of 
cells surrounded by an envelope of horny matter (keratode), 
the protoplasm of the cells being full of highly refractive gran- 
ules (presumably yolk). An earlier notice (1880) of the exist- 
ence of such gemmules in marine sponges is contained in 
Claus’s Grundziige, Bd. I, p. 214: “Auch bei den Meeren- 
schwammen ist die Vermehrung durch Gemmulae verbreitet. 
Dieselben entstehen unter gewissen Bedingungen als kleine 
von einer Haut umschlossene Kiigelchen, deren Inhalt im 
Wesentlichen aus Schwammzellen und Nadeln gebildet ist und 
nach langerer oder kiirzerer Zeit der Ruhe nach Zerreissen der 
Haut austritt.” 
In Craniella are found embryos which Vosmaer interprets 
as gemmules (Bronn’s Class. und Ord., p. 428). Sollas has, 
however, seen the same structures and regards them as egg 
embryos (28, pp. 33-39). 
Oscar Schmidt (22) stated it as his opinion that there was no 
true segmentation in the eggs of horny and silicious sponges, 
but that the egg very early lost its cellular character. It 
seems probable that Schmidt had seen cases of gemmule de- 
velopment, more or less like the development of Esperella and 
Tedania, as described by myself. 
The ciliated larvae of species of Esperia (Esperella) have 
been repeatedly seen and studied (Metschnikoff 11, Carter 2, 
Schmidt 22, Maas 16, Yves Delage 36). It has been assumed 
in all cases that the larva observed was an egg larva, and 
of course this may have been true. The close resemblance, 
between the larvae observed by Maas and myself, suggests, 
however, that the former larvae were, like mine, gemmule larvae. 
