Fission and Gemmation in the Animal KSngdom. 33 



so, since it does not [)osse3s any other kind. The essence of 

 gemmation, however, lies precisely in this, that the growth 

 peculiar to it is added as a new process to the normal pheno- 

 menon. 



Moreover, no matter what views we may hold as to the 

 evolution of the Metazoa from the Protozoa, we are bound to 

 recognize in tiie fission of the ovum a recapitulation of the 

 typical fission of the Protozoa, which thereby passes from a 

 form of reproduction into a mode of multiplication for tissues. 



The segmentation of the ovum thus teaches us that the 

 expression fission is also applied in the same sense outside the 

 phenomena of reproduction. 



For the investigation of reproduction by fission and gemma- 

 tion in tlie Metazoa tiie course which we adopted in the case 

 of the Protozoa is impracticable for obvious reasons. I shall 

 therefore in the first place attempt to gain standpoints for a 

 general consideration of the question, and in so doing briefly 

 refer to concrete examples only where it is necessary. 



The cases of asexual reproduction by fission and gemmation 

 which have so far been discovered in the domain of the higher 

 animals admit quite well of being connected with the similar 

 conditions which exist among the Protozoa. 



Firstly with regard to fission : the modifications of the 

 original form of fission, architomy, which arise among the 

 lower animals, undergo extensive development in the 

 Metazoa. Tiie higher stage of organization existing in these 

 animals entails the impossibility of architomy in their case ; 

 the processes of regeneration which are connected with almost 

 all cases of fission among the Metazoa cause those modes of 

 reproduction to appear rather as instances of paratoni)^ when 

 contrasted with what happens in the case of Stentor. 



In the fission of the higher animals three stages may be 

 distinguished, which both in themselves, as also in their 

 relation to one another within a case of paratomy, require 

 more detailed discussion. They are, firstly regeneration^ 

 secondly separation [dissection), and \\\\Yd\j growth. ■ 



That the regeneration which in the case of Stentor com- 

 bines with the separation to form an harmonious whole must 

 in the Metazoa advance into the foreground in proportion as 

 the organization of the proliferating animals becomes more 

 complicated, is so natural a circumstance that we should be 

 surprised if it were otherwise. 



Now as the measure of the work to be performed by 

 regeneration in organs and parts of organs, which nmst 

 necessarily be reconstructed, becomes constantly greater, it is 

 self-evident that the process of separation will sink in the 



Ann. & Mag. N. Hist. Ser. 6. Vol. x. 3 



