PREVIOUS INTERPRETATIONS OF CNIDARIA 151 



by experts in Cnidaria. The gonads have remained in the 

 cnidaria in the intermediate layer and then had developed as 

 such into a corpus separatum. 



We can observe, as a consequence of the progressive retro- 

 gression of sarcosepta (which had been developed from the 

 longitudinal folds of the intestine), as early as in Scyphomedu- 

 sae and quite generally in Hydrozoa, the transition of gonads 

 into the body wall itself, thus into the very narrow area 

 between the skin and the intestine. In the Anlage the gonad 

 comes into the subepithelium either of the skin or of the 

 intestine. In the ripe state the gonad causes a corresponding 

 swelling either of the skin surface (e.g. in Hydra) during 

 which gametes, that had become free, move into freedom 

 through a dehiscence, or the gonad presses in the direction 

 of the intestinal epithelium and passes over into the gastral 

 space, and the gametes finally leave by w^ay of the oral opening 

 (this is the case, for example, in the supposedly primitive 

 Protohydra, Boreo hydra, etc.). The older data, which show the 

 primitive sex cells to have developed out of the functioning 

 skin (or intestinal epithelium cells), need revision during 

 which it wdll be necessary to pay special attention to the 

 subepithelial elements, this data is vaUd for a few species 

 only of the Hydroids. 



In the metagenetic Hydrozoa the gonads were transferred 

 to the medusoid generation after they had been allotted 

 certain areas of the animal body either along the radial canals, 

 or on the manubrium. As a rule, the primitive sex cells become 

 active as early as in the corm-building polyp generation and 

 frequently far from the place where the medusa buds had 

 been formed, so that the primitive sex cells have to move 

 actively over considerable distances, as w^as formerly shown 

 especially by A. Weismann. The same seems to be true, even 

 if to a considerably smaller extent, for those Scyphozoa which 

 have still preserved a corm-forming polyp generation (e.g. 

 Nausithoe), This wandering of the primitive sex cells reminds 

 one of the wandering of cnidocytes. 

 11* 



