The porifera and coelentera . nt of Bougain-villea may be taken as typical. A rapid proliferation of cells atthe apex of a simple bud (Fig. 27, I) results in the production ofa lens-sh,aped mass of cells ; this sinks below the level of the super-ficial ectoderm, pressing the cndodermal wall in front of it intothe shape of a cup. This mass of ectoderm is termed the ento- THE HYDROMEDUSAE 19 codon, and a cavity which appears in its inteiior is the rudimentof the subumbral cavity (Fig. 27, II). It is followed by an in-vagination of the superficial ectoderm, between which and itselfmesogloea is de
The porifera and coelentera . nt of Bougain-villea may be taken as typical. A rapid proliferation of cells atthe apex of a simple bud (Fig. 27, I) results in the production ofa lens-sh,aped mass of cells ; this sinks below the level of the super-ficial ectoderm, pressing the cndodermal wall in front of it intothe shape of a cup. This mass of ectoderm is termed the ento- THE HYDROMEDUSAE 19 codon, and a cavity which appears in its inteiior is the rudimentof the subumbral cavity (Fig. 27, II). It is followed by an in-vagination of the superficial ectoderm, between which and itselfmesogloea is deposited ; the wall between the two cavities is thefuture velum (Fig. 27, III). Growth of the subumbral cavityresults in an approximation of the endodermal walls of the coelen-teron; they ultimately fuse into an endodermal lamella (Fig. 27, IV)except where the circular and radial canals are to lie (Fig. 6). Anupgrowth of the manubrium from the floor of the subumbralcavity, the formation of the tentacles, and the perforation of. RC
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
