64 



the primary division of the impregnated germ-cell takes 

 place, it must divide its properties with its matter between 

 the two cells resulting from the spontaneous fission of its 

 nucleus : and this result must follow every subsequent di- 

 vision *. It is scarcely figurative therefore to say that the 

 primary or parent germ-cell has equally divided its sper- 

 matic virtue amongst its countless progeny. 



What has here been propounded of the influence of the 

 spermatozoon is equally applicable to the pollen-filament, 

 and to those organisms in which the spermatic force has 

 not been concentrated in matter presenting the common 

 form of the spermatozoon or pollen-filament. 



In the Polygastria, for example, the condition of sponta- 

 neous fission is due to the previous existence of a spermatic 

 nucleus in each moiety which is about to be individualized. 



* Professor Kolliker (Muller's Archiv fur Physiologic, 1843, p. 137) 

 has summed up the subordinate modifications of this constant and im- 

 portant preliminary process, as follows : 



The germ-cells are developed free in the yelk. 



The first germ-cells are small The first germ-cells are large 



and assimilate the yelk slowly. and take up the yelk quickly. 



Yelk granular. Yelk fluid. 



Bothriocephalus. Ascaris dentata. Cucullanus elegans. 

 Taenia. Oxyurus ambiguus. 

 Distoma tereticolle. 



The germ-cells clothe themselves with the yelk. 



The germ-cells clothe them- The germ-cells clothe them- 



selves with part of the yelk. selves with the whole yelk (as in 



figs. 4-10, PI. I.). 



(Partial division.) (Total division.) 



Coregonus palcea. Rana. Triton. 



Alytes obstetricans. Lepus cuniculus. 



Sepia vulgaris. Canis familiar is. 



Loligo sagittata. Ascarides permultse. 



Strongyli nonnulli. 



Nereis. Botryllus. 



Pycnogonum. jfEolidia. 



