1 82 THE GERM-PLASM 



various cells in the body of the polype must be provided with 

 different groups of determinants of the medusae in the form of 

 inactive accessory idioplasm, and these must become active in 

 the process of strobilation, and cause the development of highly 

 complex medusae with eight or more radii, and provided with 

 eyes, auditory organs, and olfactory pits. The difference between 

 this process and that of simple division followed by regeneration, 

 consists in the fact that in the latter the supplementary deter- 

 minants of the cells of the body are of the same kind as those 

 from which the body was constructed : in strobilation, on the 

 other hand, the germ-plasm of the egg- and sperm-cells, which 

 gives rise to the sexual generation or medusa, must contain not 

 one, but two kinds of ids, viz., those of the polype and those of 

 medusa ; the latter, although they remain inactive during the 

 ontogeny of the polype, and take no part in the control of the 

 cell, are nevertheless not absolutely unalterable, for they break 

 up during ontogeny into many different groups of determi- 

 nants, and at the same time become distributed among different 

 cells in a regular and perfectly definite manner. It is very 

 probable, however, that a/l the cells of the polype — those of the 

 ectoderm as well as of the endoderm — are provided with acces- 

 sory determinants, so that each cell of the polype contains in 

 addition the primary constituents of some cell of the medusa. 

 We have, however, no positive knowledge on this point, for no 

 investigations have as yet been made with regard to the succes- 

 sion of the cells which lead to the formation of the medusa from 

 the polype. 



T/ie basis of the alternation of generations as regards the idio- 

 plasm jnnst therefore in all cases consist of a germ-pias7n com- 

 posed of ids of at least two different kinds, which nltimately take 

 over the control of the organism to which they give rise. 



