360 WILSON. [Vol. IX. 



In young Stellettas (Sollas 28, pp. xvi-xvii) the subdermal 

 cavities seem to arise as lacunae in the parenchyma. And in 

 the external buds of Tethya maza, Selenka (29) believes the 

 subdermal cavities have a similar origin. 



In Spongilla, according to Gotte (6), 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) being produced by the budding of 

 a single large mesoderm cell. This account of the develop- 

 ment of Spongilla is contradicted by Maas (14) who brings 

 Spongilla in line with those forms having a rhagon. Maas 

 describes in the larva a single central cavity from which the 

 chambers arise as diverticula, the central cavity persisting in a 

 modified shape as the efferent system of canals. The sub- 

 dermal 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 afferent 

 system is formed from the ectoderm and the whole efferent 

 system from the endoderm. Ganin's earlier account (7) like- 

 wise makes the chambers originate as diverticula from a main 

 endodermic cavity. 



In the metamorphosis of a larva, which probably belongs to 

 Myxilla, Vosmaer (34) finds the subdermal cavities begin as 

 fissures which gradually become wider, and 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 independent lacunae 

 in the parenchyma. 



Accepting as ancestral the development {i.e. later develop- 

 ment or metamorphosis) of Oscarella and Plakina monolopha, 

 the various coenogenetic modifications which appear in other 

 sponges may be classified as follows : — 



1. The efferent canal system, instead of arising as a single 

 cavity which throws out diverticula, may be formed as so many 

 distinct cavities which subsequently unite (Esperella, Tedania, 

 Esperia [Maas], Halisarca Dujardinii, Myxilla). 



2. The flagellated chambers, instead of arising as endodermic 



