Fission and Gemmation in the Animal Kingdom, 53 



The second point, whether fission and gemmation may be 

 conceived in a general sense, is in no better case. No one 

 will wish to maintain that the various kinds of fission as well 

 as the manifold cases of gemmation have been inherited 

 through the animal series from their first appearance, and 

 should consequently be regarded as phyletic units. But 

 also as regards their origin fission and gemmation cannot 

 have proceeded from the same causative conditions. 



From the facts which we have before us an origin of the 

 same kind cannot be exhibited for the series of those modes 

 of reproduction which are to be designated as cases of gemma- 

 tion ; on the contrary, it is in the highest degree probable 

 that the gemmation of the Salps and that of the Bryozoa 

 represent specific acquisitions within the respective phyla. 

 Although at the present time no certain decision is possible 

 as to the way in which these acquisitions were developed, 

 nevertheless the wide-reaching investigations of Seeliger 

 have sufficiently demonstrated that the formative laws of 

 gemmation in the Bryozoa are of an entirely different 

 character from those which have had effect among the 

 Tunicata *. 



With reference to the quite aberrant gemmation of Syllis 

 ramosa, I have already remarked above that the active causes 

 of its origin may well be sought without hesitation in the 

 specialities of its peculiar mode of life. 



The cases of gemmation among the Cnidaria are in no way 

 lacking, as it appears, in a more homogeneous character, 

 which may well indicate a common originating cause. 



Although it follows that the conditions under which the 

 manifold instances of gemmation may have arisen in the 

 various animal phyla are at present in a great measure still 

 an object of pure conjecture, nevertheless that which is actually 

 known about them in the several cases or series presents 

 results of so heterogeneous a nature that tlie justification for 

 generalizing about gemmation is at least not proved. 



The same applies to fission. 



The strobilation-forms of this process in the Cnidaria and 

 Worms, which are usually selected for comparison, have in 

 truth a mere external similarity only. Owing to the great 

 agreement which is exhibited in essential features by all 

 cases of fission in the Worms, we shall have to consider them 

 as a development pointing to a common basis ; for this deve- 

 lopment the conditions of the origin of those modes of rej)ro- 



* O, Seeliger, " Die imgescbleclitlicbe Vermehrung der eudoprocten 

 Bryozoen," Zeitsclir. f. wiss. Zool. Bd. 49, p. 204. 



