FERTILIZATION 



297 



mitosis, a reduction, qualitative as well as numerical, in all respects 

 similar to that accomplished in the regular heterotypic mitosis, would 

 be brought about if the pairing members are qualitatively different. 

 But instead of such a separation, each member of each pair segments 

 transversely, giving 4x segments which are equally distributed to the two 

 daughter nuclei, each of the latter receiving the diploid number. Since 

 the 4x segments become more or less intermingled before their distri- 

 bution it is probably impossible to determine just which ones pass to 

 each pole. If both halves of one transversely divided chromosome pass 

 to one pole (see Fig. 122), that daughter nucleus only, and not the other, 

 will receive the kind of chromatin carried by that chromosome, so that 



CLUWAfrE MITOSIS EQUftTIONAL 



FUSION NUCLEUS 



V 



SEGMENTATION 



FIG. 122. Diagram showing the behavior of the chromosomes in fertilization and the 

 first embryonal mitosis as usually interpreted (upper part) and according to Hutchinson's 

 interpretation (lower part). 



the two nuclei will be qualitatively different. A qualitative reduction 

 will have occurred, but without a change in the number of chromosomes, 

 since each old chromosome has become two new ones. If, on the other 

 hand, the two halves of the transversely segmented chromosome regularly 

 pass to opposite poles, each daughter nucleus will receive a half of each 

 and every parental chromosome: thus if there are just as many kinds of 

 chromatin as there are chromosomes, these nuclei will be qualitatively 

 alike, just as they would be had the division been longitudinal instead of 

 transverse. But, as has been stated in the chapter on reduction and will 

 be developed at greater length in Chapter XVII, there is a considerable 

 body of evidence which indicates that each chromosome is not only 

 qualitatively different from its fellows, but possesses a linear differen- 



