152 



PHYLUM C(ELENTERA. 



probably persist as the sub-genital pits, the gastric filaments sprout out 

 from the remains of the septa, and so mark the place where the ecto- 

 dermal gullet passed into the endodermal cavity. 



The first Ephyra differs from those which come after it in bearing the 

 original tentacles of the Hydra-tuba. From its margin eight bifid lobes 

 grow out, each embracing the base of a perradial or interradial tentacle. 

 The bases of these eight tentacles become the sense organs or rhopalia. 

 The other eight adradial tentacles atrophy. On the Ephyrae which 

 follow there are at first no tentacles, only the eight bifid marginal lobes 

 which bear the sense organs in their niches. 



This development illustrates alternation of generations. From the 

 fertilised ovum a fixed asexual Scyphistoma results. This grows into a 

 Strobila, from which transverse buds or Ephyroe are liberated. Each of 

 these grows into a sexual jelly-fish, producing ova or spermatozoa. The 



rarer modes of development (a and 

 />), mentioned on the preceding 

 page, show how readily this 

 alternation might pass into a 

 "direct" development. 



Relatives of Aurelia. 

 The Medusa.-, or true jelly-fish, 

 include forms which agree with 

 the Anthozoa, in relative com- 

 plexity of structure as compared 

 with Hydromedusre, and in the 

 possession of an ectodermal gullet, 

 but differ in possessing ectodermal 

 septal muscles and in some histo- 

 logical features. If Goette's dis- 

 covery of rudimentary ectodermal 

 muscles in the larvie of certain 

 sea-anemones be confirmed, however, it would greatly increase the 

 probability of a close relationship between the two sets. Among the 

 ScyphomedusiTe closely allied to Aurelia some, e.g. Pelagia^ have a 

 direct development without the intervention of Scyphistoma or Strobila 

 stages, but this may occur exceptionally in Aurelia. Cyanea is often 

 very large, "it may measure 7^ ft. across the bell, with tentacles 120 

 ft. long." Chrysaora is hermaphrodite, and has diffuse sperm sacs 

 even upon the arms. In the Rhizostomre, e.g. Cassiopeia and Pilet/ta, 

 the mouth is obliterated, and replaced by numerous small pores on the 

 four double arms. Lucernaria and its allies are interesting sessile 

 forms which have been compared to sexual Scyphistomas, that is, are 

 regarded as persistently larval forms. 



FIG. 70. L^ice>na Ha . A f ter 

 Korotneff. 



