Fission and Oemmation in the Animal Kingdom. 25 



increase due to growth over and above the limits of the indi- 

 vidual, which separates off from it, that the character of this 

 reproduction as a process of terminal gemmation was made 

 plain. That it is a case of terminal gemmation with which 

 we have to deal is emphasized even more definitely bj the 

 fact that the parent, however many buds it may produce, 

 never decreases in size. On the contrary, the size is always 

 equal to that of solitary individuals, which I have observed 

 before the appearance of any indication of budding, or at the 

 very commencement of it. . . ." 



This view has hitherto met with much approbation. 



Yet opposition, though indeed more of an occasional kind, 

 has also been meted out to von Graff's gemmation theory. 



Thus Count Zeppelin, in his paper on Ctenodrilus mono- 

 slyJos * (1883), observes : — " The erroneous view previously 

 liekl, that reproduction by fission in the Worms depends upon 

 mere gemmation, has been overthrown by O. Schmidt for 

 the Microstomids, which belong to the Rhabdocoele Turbel- 

 laria, since in these animals there takes place an actual sepa- 

 ration of a portion previously belonging to the parent. The 

 incorrectness of this theory is similarly proved by the pro- 

 cesses of fission which are found in Nais^ Choitogaster^ 

 Ctenodrilus, &c., in which the hindmost section of the body 

 passes unchanged into the new creature. In these animals 

 a genuine fission occurs, while in Autolytus, Filograna 

 implexa, F. Schleideni, Mgrianida, and others the young 

 individuals sprout forth as buds upon the parent form without 

 including in themselves integral constituent parts of the latter. 

 In this case therefore a true gemmation takes place." 



Count Zeppelin therefore agrees with O. Schmidt and 

 M. Schultze in regarding the direct transition of a portion of 

 tJie parent into the daughter individual as the crucial test of 

 fission. 



It is essentially from the same point of view that Goette, 

 a. prvpos of his investigations into the ontogeny of Aurelia 

 aurita, pronounces the reproduction of the animals which we 

 are discussing to be a process of " successive fissions " f. 



Claus, too, in the different editions of his well-known 

 manual, always treats the asexual reproduction of Microstoma 

 substantially as (transverse) fission, although it is true no 

 great weight can be attached to this, since this author by no 



* Graf Zeppelin, " Ueber deo Bau und die Theilungsvorgauge des 

 C'fenodrilus vionostylos, nov. spec," Zeitschr. f. wiss. Zool. Bd. 31), p. 645. 



t A. Goelte, * Eutwickluiigsgeschichte der Aurelia aurita und C'otylo- 

 rhiza tuhcrculata^ Leipzig, 1887, p. 48. 



