The porifera and coelentera . .^l. Fio. 63. Tliree stages in tlie development of Axinella cristagalli, Maas. J, longitudinal section of thelarva ; B, early pupal stage soon after fixation ; C, late pupal stage shortly before the formationof the osculum; one half only of the section is represented, , inner mass ; , ciliatedlayer ; , dermal lay^r ; /.?, gastral layer ; , flagellated chambers ; , canal system.(After Maas.) (y) Metaviorjyhosis and Organogeny.—Until the present decade it wasalmost universally supposed that in all sponges except those with anamphiblastula lar
The porifera and coelentera . .^l. Fio. 63. Tliree stages in tlie development of Axinella cristagalli, Maas. J, longitudinal section of thelarva ; B, early pupal stage soon after fixation ; C, late pupal stage shortly before the formationof the osculum; one half only of the section is represented, , inner mass ; , ciliatedlayer ; , dermal lay^r ; /.?, gastral layer ; , flagellated chambers ; , canal system.(After Maas.) (y) Metaviorjyhosis and Organogeny.—Until the present decade it wasalmost universally supposed that in all sponges except those with anamphiblastula larva, such as Sycon, the ciliated layer of the larvabecame the dermal epithelium ( ectoderm ) of the adult, while the furnished the collared gastral epithelium ( endoderm) and theconnective tissue layer ( mesoderm ). The only point at all disputedwas the origin of the flattened epithelium lining the gastral cavity andthe canals. Most authorities agreed with Schulze (1884) in deriving fromthe endoderm the flat epith
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