IV 



COELENTEKATA 



Podocoryne (see p. 61), the endoderm of the radial pouches flattens 

 out so as to form plates which meet each other in the interspace 

 between two adjacent pouches, and thus form the so-called 

 cathammal plates, or, collectively, the endoderm lamella. In these 

 plates branches of the radial pouches hollow themselves out. Some 

 of these branches, at right angles to the pouches, form a circular 

 canal just as happens in Podocoryne ; others form branches of the 

 per-radial and inter-radial pouches. The last formed adradial pouches 

 do not branch. The numerous small tentacles which fringe the disc 

 of the adult, arise as sprouts from the circular canal (Fig. 56). 



FIG. 52. Two stages in the stabilization of the Scyphistoma of Aurelia aurita. 

 (After Glaus.) 



A, the appearance of the first transverse groove. B, tentacles lost, four transverse grooves. 

 I, lobe of Ephyra ; o, oral cone ; t, taeniola ; ten, tentacle. 



OTHER SCYPHOZOA 



Hein (1903) has investigated the early development of another 

 genus CotylorMza. It agrees very closely with Aurelia, but the 

 original blastopore closes, and the mouth is formed later by the 

 reopening of this orifice. The temporary closure and subsequent 

 reopening of an orifice is to be noted as a phenomenon of very 

 frequent occurrence in development; we interpret it as a sign 

 that the orifice in question is no longer continuously functional. 



Pelagia is an instance of a form modified for oceanic life ; it 

 develops a blastula like that of Aurelia, and a gastrula is formed by 

 iuvagination as in that animal ; but the original blastocoele persists 

 in the aboral end of the larva since the endodermic sac remains 



