COELENTERATA 61 
formed are termed perradii, the next four are situated half- 
way between the perradii, and are known as interradial 
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 bitid lobes have 
grown out, which give to the 
Ephyrae their characteristic eight- 
rayed appearance. ach lobe 
encloses in its notch either a 
perradial or interradial tentacle 
destined to become a tentaculocyst. 
The gastric cavity extends into 
each lobe, and the taeniolae be- 
come detached from the aboral F!- 42:—Strobila of Aurelia aurita. 
: : z : After Haeckel. 
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. 
1. Base of Strobila. 
2. Sense organ. 
3. Marginal tentacle. 
4, Lappet on side of sense organ. 
