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 Grundzuge, Bd. I, p. 214: "Auch bei den Meeren- 

 schwammen ist die Vermehrung durch Gemmulae verbreitet. 

 Dieselben entstehen unter gewissen Bedingungen als kleine 

 von cincr 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. 



