IV 



PHYLUM CCELENTERATA 



173 



manubrium (mnb.) ; and, finally, the ectoderm of the distal surface 

 i.e. the region lying between the mouth and the circlet of tentacles 

 becomes invaginated in each inter-radius so as to produce four 



FIG. 130. Aurelia aurita, development. A, planula, erroneously represented as com- 

 pletely closed ; B, C, formation of stomodseum ; D, transverse section of young scyphula ; 

 E, scyphula ; F, longitudinal section of same : the section passes through a per-radius 

 on the left of the dotted line, through an inter-radius on the right ; G, division of scyphula 

 into ephyrulae ; H, ephyrula from the side ; L, the same from beneath. In A D and 

 F the ectoderm is unshaded, the endoderm striated, and the mesoglcea dotted, a. lobes 

 of umbrella ; mnb. manubrium ; mtk. mouth ; *. /. septal funnel ; st. stomodseum ; f. 

 tentacle ; tn. taenioles. (From Korschelt and Heider's Embryology.) 



narrow funnel-like depressions the septal funnels or infundibula 

 (E and F, s. /.) sunk in the four gastric ridges. 



The outcome of all these changes is the metamorphosis of the 

 planula into a polype (E), not unlike a Hydra or the hydrula-stage 



