ELISHA MITCHELL SCIENTIFIC SOCIETY. 43 



as lacunae in the parenchyma. And in the external buds 

 of Tethya maza'^^ Selenka believes that the subdermal cavi- 

 ties have a similar origin. 



In Spongilla, according to Gotte'^, the subdermal cavities 

 and canals are formed as independent lacunae in the 

 parenchyma, and the flagellated chambers are formed from 

 groups of cells, each group (and chamber 1 being produced 

 by the budding of a single large mesoderm cell. This 

 account of the development of these structures in Spongilla, 

 which is not very different from my own for Esperella and 

 Tedania, is contradicted by Maas,J who brings Spongilla 

 in line with the forms having a rhagon. Alaas describes 

 in the larva a central cavity from which the chambers arise 

 as diverticula, the central cavity persisting in a modified 

 shape as the efferent system of canals. The subdermal 

 spaces arise as ectodermal invaginations, from which the 

 afferent canals are formed as ingrowths. Thus, according 

 to Maas in the ontogeny of Spongilla, the whole afi'erent 

 system is formed from the ectoderm and the whole efferent 

 system from the endoderm. Ganin's earlier account§ like- 

 wise describes the chambers as diverticula from a main 

 endodermic cavity. 



In the metamorphosis of a larva which probably belongs 

 to Myxilla, Vosmaer finds that the subdermal cavities 

 begin as fissures which gradually become wider, and that 

 the canals and chambers likewise appear as intercellular 

 spaces. Finally in the gemmule development of Esperella 

 and Tedania, I find that subdermal cavities, both sorts of 

 canals, and the flagellated chambers, all arise as inde- 

 pendent lacunae in the parenchyma. 



Accepting as ancestral the development of Oscarella and 



*Zeit. f. Wiss. Zool. Bd. XXXIII. 



tUntersuchungen zur Entwicklungs-geschichte von Spongilla fluviatilis, 1886. 

 iUeber die Entwicklung des Sursswasserschwamms. Zeit. fur Wiss. Zool. Bd. 

 §Zur Entwicklung der Spongilla fluviatilis. Zool. Anzeiger. 1878. 



