THE GERM-PL.\SM 65 



compared to that of a complicated ancient building, the stones 

 of which we may suppose to be alive, so that they can grow and 

 increase, and thus cause displacements and fissures in the walls, 

 in which process the forces of attraction present within these 

 living stones take part. The historical transfuission of the 

 architecture of the i^erni-plas/zi forms the basis of the entire 

 ontogenetic developjnoit of the idioplasm. 



I f how ever the id has a right and left half in bilateral animals, 

 we must not thereby infer that it is merely a miniature of the 

 fully-formed animal, and tliat therefore we are once more deal- 

 ing with the old tlieor}- of preformation. Quite apart from all 

 coniectures as to the detailed architecture of the id of orerm- 

 plasm, it is at any rate certain that the arrangement of the deter- 

 minants in it is quite different from that of the corresponding 

 parts in the fully-formed organism. This is proved bv a study 

 of development, and need scarcely be treated of in detail here. 

 Any one with a knowledge of animal embryology knows how- 

 great a difference there is between the mode of development of 

 the parts from one another in the embryo and their respective 

 relation in the mature organism. The earlv stages of sejrmenta- 

 tion of the ovum show that groups of determinants have been 

 formed in the id of germ-plasm, and that these, moreover, cor- 

 respond to the parts of the body w^hich arise from one another 

 consecutively, though they can have no resemblance to them 

 either in form or in their degree of perfection. 



In some worms the two first blastomeres do not give rise 

 respectively to the right and left sides of the body, but to the 

 entire ectoderm and endoderm. In these cases the id of orerm- 

 plasm must break up into two groups, one of wdiich contains all 

 the determinants of the ectodermal organs, and the other all 

 those of the endoderm : it is evident that this arrangement has 

 no analogy to that which obtains as regards the organs of the 

 fully-formed animal. If in any species we knew the 'value in 

 primary constituents ' (' Anlagenwerth ') — if I may use such a 

 term — of each cell in the ontogeny, w'e could give an approximate 

 representation of the architecture of the germ-plasm : for. begin- 

 ning with the last formed cells, w^e could infer the nature of the 

 determinants which must have been contained in each ]-)revious 

 mother-cell, passing gradually backwards to the ovum ; thus we 

 should reach the tw^o first blastomeres, and finally the egg-cell 

 itself. The groups of determinants which are present at each 



