38 Dr. F. von Wagner on 



the less importance, since the various processes themselves are 

 the same in all cases. 



This conception of the reproduction of the Naids applies 

 in corresponding fashion to the asexual reproduction by fission 

 not only of the Annelids, but of the Worms in general, for 

 there is no room for doubt that those modes of propagation 

 are essentially of the same kind. 



Now if an animal begins to divide and the regenerative 

 processes in the zooids thus produced are quickly completed, 

 and if, moreover, fission again sets in in the zooids themselves 

 before they have attained their independence by means of the 

 separation which is the concluding stage of the primary fission, 

 the result naturally is a formation of temporary colonies, 

 or, to speak more precisely, chains, since we are dealing 

 with the transverse fission of animals which grow in their 

 longitudinal axis. The precocious commencement and retarded, 

 conclusion of fission^ concurrently with rapid growth of the 

 dividing animals, are the circumstances which are chiefly 

 responsible for the complicated and often very peculiar mani- 

 festations which are exhibited in the course of the asexual 

 reproduction of many Metazoa. It is true that secondary 

 causes are often added to these, since reproduction by tission 

 may combine with transformations of the fission-products 

 (strobilation of the Medusae) or become more or less subser- 

 vient to favourable sexual reproductive conditions ; this may 

 result in the omission of regenerative processes and the occur- 

 rence of effective new formations which did not belong to the 

 original animal, but are of great service for the special pur- 

 poses of the fission-products. An example of this is presented 

 by, among others, the swimming zooids of the already 

 mentioned Ilaj^losyllis, which, in order to ensure the widest 

 possible distribution of the sexual products, have equipped 

 themselves with an exquisite locomotor apparatus *. 



With regard to gemmation a few words only are necessary, 

 for its character lies exclusively in the peculiarity of differen- 

 tial growth, so that all instances of gemmation, no matter 

 whether we have to deal with a Polype, a Bryozoon, or a 

 Salp, agree in this, though diverging widely in the details of 

 the process. It is in consequence of this simplicity in the 

 nature of gemmation as opposed to fission, which in many 

 respects is subject to manifold changes, that the very different 

 phases of development in which gemmation confronts us 

 nevertheless invariably exhibit tlie same characteristic of 

 special growth. 



* F. Albert, " Ueber die Fortpflanzung von Haplosyllis spongicola, Gr.," 

 Mitth. a. d, zool. Stat, zu Neapel, Bd. 7, pp. 12 et sqq. 



