SUMMARY OF PART II 227 



a high degree is only rendered possible by the cells in a definite 

 transverse plane of the body being regularly equipped with 

 various groups of suitable supplementary determinants which are 

 capable of acting together as a whole. 



This form of regeneration leads directly to the process of 

 y-eprodiiction by fission, which simply consists in the employment 

 of a marked power of regeneration for the purpose of increasing 

 the number of individuals. 



While the possession of the regenerative power in a low, as 

 well as in a high degree, is due to the equipment of cells with 

 certain larger or smaller groups of determinants in the form of 

 'unalterable' accessory idioplasm, the development of new per- 

 sons by genunation depends either on the fact that a single cell 

 contains all the determinants of the species in an inactive and 

 unalterable condition, in the form of accessory idioplasm ; or 

 else is due to two or three cells in the different layers of the 

 body containing large groups of determinants as accessory idio- 

 plasm, which together constitute all the determinants possessed 

 by the species — i.e., germ-plasm. 



In cases where budding originates in a single cell, as in the 

 Hydroid-polypes, the blastogenic idioplasm concerned in the 

 process must be regarded as a modification of the germ-plasm, 

 which consists of all the determinants of the species, though 

 these have a different arrangement to that which obtains in the 

 germ-plasm proper of the fertilised egg-cell. The fact that a 

 bud may originate in two or three cells does not show that these 

 cells contain exactly those groups of determinants which corre- 

 spond to those of the two or three germinal layers of the Aleta- 

 zoon in question. In fact, the combination of the determinants 

 differs more or less in all known cases, and is adapted to the 

 circumstances under which budding occurs. This proves that 

 in the embryogeny of the species, divisions of the accessory 

 idioplasm occur quite independently of the ordinary divisions in 

 the mass of determinants, and these result in certain cells being 

 provided with a definitely constituted accessory idioplasm. 



The blastogenic germ-plasm must be contained in the germ- 

 plasm of the sexual cells in the form of special ids, for buds can 

 vary independently of the persons which produce them. On 

 the other hand, primary idioplasm must also be supplied to the 

 bud during its development, and this may be effected by means 

 either of special cells which contain the idioplasm in an unal- 



