86 SEX AND HEREDITY 



in equal amounts from the two parents. In later stages, 

 it is true, the double appearance of the nuclei, indicating 

 their origin from the two gametes, disappears (Fig. 46, K) , 

 owing to the two sets of chromosomes having mingled 

 together. The nuclei, however, still contain the six 

 chromosomes, which become visible in certain phases. 



Figs. 46, H-J, show the nucleus and the division of 

 the chromosomes on a larger scale. It can be seen that 

 the chromosomes are not homogeneous, but that each 

 consists of a row of chromatin granules like a string of 

 beads. Fig. 46, H, 1-5, illustrates in detail the process 

 of division of a chromosome, and shows that the splitting 

 of the chromosome as a whole consists in the division 

 of each one of these beads so that two parallel 

 rows of beads are formed. Later, the chromosomes 

 contract so much that the individual beads are no longer 

 visible hence they are not seen in Fig. 46, D, which is 

 the stage shown in Fig. 46, /, on a larger scale. 



These chromatin beads are of course living and 

 growing bodies, and hence the halving of the size of each 

 bead which occurs in each division is compensated by 

 growth in the intervals between divisions. 



This mode of development, and of distribution of the 

 chromatin, is of general occurrence in the animal and 

 vegetable kingdom, though the number of chromosomes 

 varies in different species. The general rule obtains, 

 however, that the gamete has half the number found 

 in the zygote, the former having thrown out half of its 

 chromosomes, as we have seen in Cyclops, in preparation 

 for syngamy. 



Summing up, we are led to identify the chromatin, or 

 some substance intimately bound up with the chromatin, 



