222 



BEAN. 



the individual are present. Wliatever further development takes place 

 is caused by the chromosomes acting through the environment. When 

 the first few cell divisions take place there may be little influence from 

 environment, but the greater the number of cells, that is, the further 

 away they are from the original one, the greater is the influence of 

 environment and the greater becomes the differentiation of the individual 

 cells. During a long series of generations of an individual species 

 (type), the changes produced even in the germ cells by division, growth 

 and nutrition must be so great and the ultimate germ cell so far removed 

 from the original one that the supposition of its unaltered condition is 

 untenable, and this is true without considering the manifold influences 

 on the germ plasm during the life of each individual. A germ cell 

 may sej)arate itself from the other cells almost at the beginning of the 

 segmentation of the ovum (fig. 2), and in this way carry on directly 



S 4 



S7 



S8 



Pig. 2. — Segregation of the sex ceUs in the segmentations ot the ovum after fertilization. 

 Ascaris megalocephala var, univalens. (Adapted from Bucli's Reference Handbook 

 of the Medical Sciences, 1902, i, 650. After Boveri.) 



The germ plasm divides by doubling division (growing in bulk and dividing) so 

 that each resulting mass is precisely like the other. One of these may divide 

 repeatedly, always doubling, and remains unaltered germ plasm (G 1—2—3—4—5—6—7) 

 going to that part of the individual from which new organisms arise (ovary in 

 woman, testicle in man.) The germ plasm is thus handed on directly from genera- 

 tion to generation. 



The second portion of the germ plasm (somatic cell) (S 1-2-3-4-5-6-7-8) under- 

 goes differentiation division, and controls the building of the individual. 



