Fission and Gemmation in the Animal Kingdom. 49 



to the mass of the original individual ' before the commence- 

 ment of the visible changes by which the process was ushered 

 in ; " because every instance of fission in the ]\letazoa is, and 

 must be, inevitably combined with regenerations or new 

 formations of another kind. But these just as necessarily 

 entail an increase in organic substance. 



Now it is certainly no reason for claiming a process as an 

 instance of fission to say that if we did not fission would 

 entirely disappear as a method of reproduction in the Metazoa. 

 But von Kennel himself designates as fission the asexual 

 reproduction of Planaria snbtentaculata, which lias been 

 described, it is true only imperfectly, by Zacharias *, and 

 has moreover acquainted us with the interesting multiplica- 

 tion of a freshwater Triclad, which he terms " transverse 

 fission," although in both cases, having regard to the regene- 

 rative processes which ensue, an increase in organic substance 

 is undeniable t- 



Fundamentally von Kennel's conception of fission is 

 exhausted with the bare process of separation, therefore with 

 that which I have termed " dissection " within a case of 

 paratomy. It is therefore postulated by this investigator 

 that, when we would speak of fission in animals, the process 

 in question must be identical with the splitting of a block of 

 stone. This, however, according to animal organization is 

 impossible. 



' Von Kennel's conception of gemmation is in no better case. 

 If, as we have seen, practically nothing remained for fission, 

 gemmation, according to von Kennel, includes all instances 

 of asexual reproduction in Avhich any sort of growth appears. 

 It is consequently a matter of complete indifference whether 

 the particular process of growth takes place in the animal as 

 a speciality, leaving the individual manifestation thereof 

 unaft'ected, or whether it coincides with the normal increase 

 in size of the creature, as we also meet with it in the animal's 

 nearest allies, which, however, lack the faculty of asexual 

 reproduction. 



The gemmation of a Salp or Bryozoon, the formation of 

 Ephyrffi in the Medusge, the processes of strobilation in the 

 Worms, the gemmation of Hydroids and Corals, &c., are 

 accordingly the same in principle, so much so indeed that, as 

 V. Kennel % in the first instance, and, independently of him, 



* 0. Zacharias, " Ergebuisse eiuer zoolog. Excursion in das Glatzer-, 

 Iser-, und Riesengebirge," Zeitsclir. £ wiss. Zool. Bd. 43, pp. 271 et sqq. 



t J. Kennel, " Unlersuchungen an neuen Turbellarien," Zool. Jalirb. 

 Bd. 3, Abth. f. Anat. u. Ont. der Tliiere, pp. 407 et sqq. 



\ J. V. Kennel, ' Ueber Theiluuguud KnospuugderTliiero,' pp. \7 et sqq. 



Ann, (& Mag. N. Hist. Ser. 6. Vol. x. 4 



