45 6 THE GERM-PLASM 



regeneration, and which always diminishes in correspondence 

 with the degree of organisation. Even if we imagine this 

 'force' to be a mechanico-physiological one, it could not be 

 considered as a primary quality of the organism, and to 

 some extent the inevitable result of life itself, but must be 

 looked upon as an adaptation. 



Reproduction by fission is closely connected with regeneration ; 

 it presupposes the existence of a similar apparatus in the idio- 

 plasm, which, however, has in most cases reached a higher 

 stage of development ; fission must have arisen phyletically from 

 regeneration. 



The origin of multiplication by gemination, and the phe- 

 nomena exhibited by this form of reproduction, are different 

 from those concerned in fission. In plants and Coelenterates, 

 gemmation originates in one cell, which must consequently 

 contain a combination of all the determinants of the species 

 closely resembling that existing in the fertilised ovum. In 

 the Polyzoa, however, this process does not originate in one 

 cell, but in at least two, and probably more, belonging to 

 two different layers of cells (germinal layers) of the body ; 

 and in Tunicata, again, the material for the bud is produced 

 from all three germinal layers. 



The first of these forms of budding must be primarily due to 

 the admixture of ' unalterable ' (' gebundenem ') germ-plasm to 

 certain series of cells in ontogeny in the form of inactive ' acces- 

 sory idioplasm^ or '■ blast ogenic'' idioplasm (' Knospungs-Idio- 

 plasma'). In plants this is contained in the apical cells ; and in 

 hydroid polypes, in the cells of the ectoderm. 



In the second group of animals mentioned above, we must 

 assume that the ' blastogenic ' germ-plasm becomes disintegrated 

 into two groups of determinants at an early ontogenetic stage, 

 and that each of these is passed on in an '• unalterable ' condition, 

 through various generations of cells, until the time and place of 

 its activity are reached. 



In the third group, the inactive ' blastogenic ' idioplasm 

 divides into three groups of determinants, one of which passes 

 into the ectoderm, the second into certain cell-series of the 

 mesoderm, and the third into others in the endoderm, until 

 they reach the part in which they have to become active. 



Gemmation must have originated phyletically by 'a doubling 

 of the germ-plasm taking place in the fertilised ^<gg, so that 



