50 Br. F. von Wagner on 



Lang *, almost simultaneously endeavoured to render probable , 

 all these processes are referable to one and the same starting- 

 point — the regenerative faculty of animals \. 



Nothing appears to me to be so characteristic of vou 

 Kennel's view of gemmation as the following statements by 

 him % : — " There appear .... in many Annelids, such as 

 'Nais^ Chaitogaster^ ^olosoma, Si/llis, &c., new structures 

 nearly in the middle of the segmented body, owing to which 

 the anterior and posterior halves of the body are pushed away 

 from one another. If this newly intercalated region of the 

 body differentiates into a larger number of young segments, 

 which further develop partly into new cephalic somites for 

 the section of the body which lies behind them, and partly 

 into new trunk-segments for that which lies in front — it is 

 manifest that a formation of buds is thereby constituted^ for 

 in the original individual a new formation has appeared 

 which is at first small, but is nourished by the original form 

 and increases in size. If this bud subsequently constricts 

 more and more about at its middle until complete separation 

 takes place, we can scarcely be contradicted if we term it a 

 case of reproduction by gemmation." 



Here, therefore, v. Kennel designates as a bud the " new 

 formation^ which is at first small, but is nourished by the 

 original form, and increases in size." This supposed bud, 

 which in truth represents nothing else than the so-called zone 

 of gemmation (zone of regeneration), is no individual at all, 

 no organic person, but a mixtum compositum, formed from 

 the posterior and anterior halves of two different animals, 

 attached together by their opposite ends ; and for the origin 

 of these two there finally remains no other method after all, 

 except — fission. 



Moreover it is at once evident that v. Kennel is here con- 

 sidering cases of fission which, as we are wont to express it, 

 depend upon processes of gemmation, and, designating the 

 special kind of definite regenerative processes as processes of 



* A. Lauo', ' Ueber den Einfluss der festsitzenden Lebensweise auf die 

 Thiere &c.,' Jeua, 1888, pp. 108 et sqq. 



t From my standpoint I am naturally unable to assent to this view, 

 especially in this generalization. The faculty of reproduction by 

 gemmation and fission and the power of regeneration may 

 certainly depend upon the same general primary causes ; 

 but with this nothing is stated as to the special causes, in consequence 

 of which fission has been developed in one case and gemmation in another. 

 The cutting off of a tentacle is, it is true, the external stimulus for its 

 regeneration, but it is not the cause of the power to replace the lost part. 



X Op. cit. p. 13. 



