COELENTERATA 



6i 



formed are termed jperradii, the next four are situated half- 

 way between the perradii, and are known as inferradial 

 tentacles ; and eight more may be added, one between each 

 perradius and interradius, and these are called adradial. The 

 same convention is made use of in describing the position of 

 the various organs in medusae of other classes. 



The most striking features in the Scyphistoma are the 

 taeniolae, which project into the enteric cavity and divide its 

 outer portion into four chambers (Fig. 39, 13). The taeniolae 

 are four in number, and are inter- 

 radial in position. They are 

 comparable with the mesenteries 

 in the Actinozoa. 



Towards the end of spring the 

 Scyphistoma passes into the Stro- 

 bila stage, it then becomes con- 

 stricted on the aboral side of its 

 tentacles, and thus a disk is partly 

 cut off, behind this a series of 

 furrows arise, cutting the Scyphi- 

 stoma into a series of segments 

 (Fig. 42). These separate off and 

 form the immature medusae or the 

 Ephyrae. Eight bifid lobes have 

 grown out, which give to the 

 Ephyrae their characteristic eight- 

 rayed appearance. Each lobe 

 encloses in its notch either a 

 perradial or interradial tentacle 

 destined to become a tentaoulocyst. 

 The gastric cavity extends into 

 each lobe, and the taeniolae be- ,.,..,. 



-, , 1. J j^ ™ +1,0 alinral PiQ. 42. — Strobila of ^«reZia attnto. 



come detached from the aboral After Haeckei. 



1. Base of StroHla. 



2. Sense organ. 



3. Marginal tentacle. 



4. Lappet on side of sense organ. 



side of the disk and give rise to 

 gastric filaments. The same pro- 

 cesses of growth go on in each of 

 the segments of the Scyphistoma. 



The Ephyra becomes a medusae chiefly by the filling out of 

 the adradial spaces, and it thus acquires a circular outline. 



