CHROMATIN — DEVELOPMENT AND HEREDITY 255 



mitosis (in the cross, Stenotomus 9 X Ctenolabrus d^ , abnormali- 

 ties appear at the beginning of the first cleavage) , it seems that 

 the determining factor must be a quality of the cytoplasm and 

 not a peculiarity of the yolk of the egg. This factor or combina- 

 tion of factors resembles in a general way those which cause the 

 spermatozoon to enter the egg. Of the latter process Loeb 

 ■ ('16) says, "We reach the conclusion therefore that the speci- 

 ficity which allows the sperm to enter an egg is a surface effect 

 which can be increased or diminished. . . ." As the role of 

 surface tension phenomena in both fertilization and cell division 

 has been given attention by many investigators, the special 

 views concerning this need not be considered here. It may be 

 pointed out, however, that, in fishes, the normal division of chro- 

 mosomes in the environment of a foreign cytoplasm, as well as 

 the penetration of an egg by a spermatozoon of a different 

 species is the result of a chance fitness due to physical characters, 

 such as viscosity, surface tension, permeability, structure, etc. 

 of the combining or reacting agents. This may be more profit- 

 ably discussed in connection with another topic. 



The behavior of the chromatin of the spermatozoon during the 

 cleavage of the egg, then, is independent of the degree of relation- 

 ship existing between the species which are crossed. 



2. The relation of normal mitotic behavior to development 



Normal mitotic division in the early stages of cleavage is not 

 closely correlated with normal development. Although we may 

 reasonably expect normal chromatin distribution to be the 

 necessary accompaniment to normal development, the preceding 

 observations show clearly that the regular behavior of chromatin 

 cannot be taken as a criterion of harmony existing between the 

 germ plasms of the egg. The natural cycle of mitosis may 

 take place if certain physical requirements of the chromatin of 

 the sperm and the cytoplasm of the egg be fulfilled. It is in- 

 dependent of the relationship of the two species crossed. Having 

 favorable cytoplasmic environment and compatible germ plasms 

 one may expect successful development, but favorable cyto- 



