Division in the Radiata. 393 



The transverse division of the Infusoria also is not a true 

 division. As M. Steenstrup has indicated, it results clearly 

 from the beautiful observations of M. Stein that it is not an 

 individual that divides into two, but two young individuals 

 that are developed in the same mother and become free by 

 absorbing her body. We must also join with those naturalists 

 (Boeck, Steenstrup) who maintain, as resulting clearly from 

 observation, that the act by which the Scyphistoma becomes 

 transformed into the Strobila (by multiple transverse scission), 

 and the latter breaks up into, a series of young Medusce^ is only 

 a slightly disguised development of a series of internal germs 

 or buds, accompanied by an absoi-ption of the Medusa-nurse 

 (the Scyjjhistoma) , exactly as in the Infusoria, with the sole 

 difference that the number of germs is much gTcater than in 

 the latter. 



We may also doubt whether a true spontaneous division 

 ever takes place among the Vermes (at all events those of the 

 highest rank) ; it would seem that in most cases it is only a 

 disguised gemmation. To discuss this question thoroughly 

 with regard to the fissiparous Chaetopoda (Naides, Syllidea, 

 Tubicola) would carry me far beyond the limits of this memoir, 

 and would nevertheless throw no light upon the subject ; it 

 will suffice for me to remind the reader that whilst it seems to 

 result positively from some observations that what takes place 

 here is a gemmation, or a successive development of a series 

 of germs or buds in the posterior extremity of the worm, many 

 observers regard it as beyond doubt that there is a pure division 

 followed by a regeneration of the part separated. These 

 questions being in general surrounded by a certain obscurity, 

 observers have probably in most cases not been fully conscious 

 of the distinction to be established, and consequently have not 

 overcome its difficulties. However, as it cannot be doubted 

 that it is always the same phenomenon that takes place here, 

 i. e. either a true division or a true gemmation, the balance in 

 opinion inclines strongly to the latter side. It seems to me 

 that the observations we possess may be readily brought into 

 accordance with the opinion that the so-called scissiparity of 

 theChaetopoda is only a disguised terminal gemmation, precisely 

 as in the Medusa-nurses. 



That the faculty of regeneration is extremely great in the 

 Vermes is a well-known fact. In certain cases, as 0. F. 

 Miiller showed a hundred years ago (by very exact experiments, 

 in Avhich spontaneous division with the regeneration resulting 

 from it is most distinctly separated from natural scissiparity or 

 gemmation), it attains such a development that artificial 

 division is produced with great facility. In the present day 



