32 Dr. F. von Wagner on 



whereby its subordinate importance appears sufficiently esta- 

 blislied (formation of colonies in Metazoa). 



Although I have hitherto spoken of the Protozoa, it was 

 far from my intention in so doing to pronounce judgment 

 upon the forms of reproduction in these animals, which so 

 greatly overlap one another, especially since scarcely anything 

 can be added to the classic statements contained in Biitschll's 

 great work ; it is, on the contrary, more in accordance with 

 the plan of these explanations briefly to consider, by the aid 

 of a few characteristic examples, reproductive conditions of 

 the simplest kind, which are not without value for the com- 

 prehension of the asexual propagation of the Metazoa. The 

 following arguments refer solely to the Metazoa, and claim 

 validity for these alone. I therefore think it desirable, since 

 I consider a sharp separation of fission from gemmation to be 

 possible for the higher animals, and shall exert myself to 

 accomplish the same, to declare emphatically at this point 

 that as regards the Protozoa I side unreservedly with those 

 who hold that fission and gemmation merge into one another 

 in these simplest forms of animals, and who therefore decline 

 to draw a strict distinction between them within this branch 

 of the Animal Kingdom. In this connexion it will be readily 

 understood that in proceeding with the views which we have 

 just acquired to the domain of the Metazoa I do not wish to 

 convey that the fission and gemmation of the higher animals 

 are to be referred phylogenetically to the similarly named 

 processes in the Protozoa. 



At the gate of the Metazoon kingdom stands the so-called 

 process of segmentation (fission of the ovum). Although this 

 has no direct relation to asexual reproduction, it will never- 

 theless be useful for our purpose to bestow a brief considera- 

 tion upon it. 



The segmentation of the ovum has invariably and without 

 contradiction been regarded as fission, even where " so typical 

 a picture of gemmation is exhibited as can only be presented 

 by an Acinetarian among the Protozoa " *. It is clear that 

 " if from certain large cells there actually grow out small 

 portions, which are gradually constricted oiF"^, such a 

 process, provided it really takes place, coincides far more with 

 the idea of gemmation than with that of fission. In spite of 

 this we speak even in such cases, and rightly, of a fission of 

 the ovum, since the growth which thereby appears is the 

 normal growth for the ovum in question, and must indeed be 



* J. V. Kennel, ' Ueber Tlieilung und Knospun^' der Thiere,' Dorpat, 

 1888, p. 11. 



