SUMMARY OF PART II 229 



take part in the formation of the bud. In any case blastogenic 

 idioplasm and the germ-plasm of the ovum are not identical, 

 even if, as in plants and Hydroid-polypes, the former contains 

 the whole of the determinants of the species. The determinants 

 must at any rate have another arrangement : not infrequentlv, 

 indeed, the blastogenic idioplasm must consist of entirelv dif- 

 ferent kinds of determinants, and in the case of the alternation 

 of generations of the Medusae of far more numerous ones. 



The cells of the germ-tracks are somatic cells ; that is to say, 

 each of them is controlled by a special determinant, and con- 

 tains germ-plasm in an inactive as well as in an unalterable 

 condition. In the latter state, it only again becomes capable of 

 disintegration when the cells in which it is situated give rise to 

 germ-cells, and begin to undergo development into embryos. 

 This germ-plasm, like the unalterable blastogenic idioplasm, 

 may be contained in young cells with only a slight amount of 

 histological differentiation, as well as in cells with a sharply 

 defined histological character. 



We thus see that in many cases the cells of the adult organism 

 contain an accessory idioplasm in addition to the determinants 

 which control their special character, structure, and physiologi- 

 cal activity for the moment : the former may become active in 

 the ordinary course of development, — as occurs in the normal 

 formation of germ-cells and in multiplication by fission and 

 gemmation ; or its activity may be due to abnormal causes only, 

 — such as those resulting from injuries and mutilations, — from 

 which the processes of regeneration or gemmation in the first 

 place originated. 



