Fission and Gemination in the Animal Kingdom. 41 



in possession of the most important primary organs (central 

 organ of the nervous s}'stem &c.) ; for the proportion of the 

 original reUitions which are dissoluble is indeed limited by 

 the conditions of the permanence of the common life, but 

 within these limits is free, now greater, now smaller. 

 Whether the posterior half or the posterior quarter or eighth 

 of a Alicrostoma forms a new individual of itself is a matter of 

 complete indifference for the character of the entire process. 

 In other words, the division of a Microstoma into two equal 

 halves is fundamentally the same process as its fission into 

 two products, one of which consists of three quarters and the 

 other of one quarter of the original animal, and so on. 



A series of separate acts of fission, as exhibited by the 

 species of Microstoma for instance, is in ordinary terminology 

 usually referred to one animal as the mother-individual 

 ("ancestress" (" Stammmutti^r ") of von GrafFj ; and if a 

 number of units has been developed we are accustomed to 

 say that the " ancestress " has given rise to so many daughter 

 individuals. We are the more inclined to do this since 

 separation sets in very late, so that the zooids remain for a 

 time in connexion with one another and form temporary 

 chains of individuals. 



This view is, however, strictly speaking erroneous, for the 

 ostensible " ancestress " is destroyed by the very first fission, 

 and for the following one the two zooids which resulted from 

 the first paratomy behave to their products as " ancestresses," 

 precisely in the same way as their parent form did to them, 

 and so on. 



If therefore we say that the il/«'cros^o??za-chains have arisen 

 simply through fission we must be understood only to mean 

 that these chains owe their origin to a series of paratomies, 

 in which the final acts, the separations, appear postponed in 

 regular sequence to relatively late periods. The reproduction 

 of Microstoma therefore represents a combination of successive 

 acts of fission, each separate one of which constitutes a para- 

 tomy. 



From the standpoints which have been developed in the 

 foregoing paragraphs, I would define fission and gemmation 

 in the Metazoa as follows : — 



Fission is api-ocess of separation of parts wliicli originally 

 belonged to an integral lohole, and have arisen or are in process 

 of origin hy normal growth^ wherein new individuals are 

 formed hy supplementary new formations ^ with destruction of 

 the original unit. 



Gemmation J on the contrary , is a process of new formation 



