Fission and Gemmation iii the Animal Kingdom. 43 



sary to bear in mind tlie fact that the regeneration of an 

 Ephyra on the oral disk of the Sc3-phostoma, within the circlet 

 of tentacles belonging thereto, has in no single case been 

 proved. There is no terminal gemmation of Ephyrge on the 

 oral disk of the Scyphostoma-polype ; on the contrary, the 

 rudiments of the disks of the Ephyras are segments of the 

 actual body of the IScyphostoma, which are marked otF outside 

 the circlet of tentacles by constriction of the wall of the cup, 

 and are set free as sections of the body." 



In opposition to Ha^ckel Glaus insists * that " as a matter 

 of fact the terminal portion of the Strobila which becomes 

 the Ephyra — and for the sake of simplicity we will commence 

 with the simplest and most typical form, that of the mono- 

 discous Strobila — is no product of subsequent growth on the 

 part of the Scyphostoma, but rather the anterior l;alf of the 

 body of the latter, which after previous uniform growth of 

 the trunk of the Scyphostoma has marked itself off by con- 

 striction and proceeds to attain its liberty as a segment. 

 Moreover, with the separation of the latter the primary indi- 

 vidual, as such, is destroyed and split up into two new 

 individuals, since the posterior individual also represents only 

 a segment of the parent form. Both fission-products are 

 coordinated to one another, for the basal stump, with or 

 without a circlet of tentacles, nevertheless essentially corre- 

 sponds to a Polype which is equivalent to a Medusa. Both 

 Ephyra and Polype are consequently in their mutual rela- 

 tions comparable to an Infusorian in process of fission, of 

 which only the one segment possesses a mouth and adoral 

 zone of cilia, while the other is as yet without these struc- 

 tures or only exhibits them in course of formation. But 

 should we wish to consider one segment as older than the 

 other, and to subordinate the latter to the former, it would be 

 more just to regard the hinder and less perfect segment as 

 the younger portion, which would then be comparable to a 

 terminal bud. In truth, however, from the point of view of 

 ontogeny, they are both of the same age and equivalent to 

 one another ; yet the anterior segment differentiates sooner 

 into a form which becomes free as a Medusa, while the poste- 

 rior one subsequently undergoes regeneration and comple- 

 tion." 



tioned {vf. note a, p. 2G) ; I quote them, ho-svever, in order to sjiow that 

 even those investifrators who consider it superfluous to discuss whether 

 we are dealing with fission or gemmation, nevertheless in a given case 

 exert themselves dihgently to answer the question, 

 * Op. cit, p. 17. 



