72 



GENERAL EMBRYOLOGY 



short of this, if the fact of continuity of organized chromatic structure 

 be accepted to begin with. 



On the other hand, those who adhere to the continuity hypothesis 

 find many supporting facts in the phenomena of fertilization and 

 maturation, the importance of which can be appreciated more fully 

 after our consideration of these subjects. They assume, from the con- 

 sideration of the behavior of the chromosomes, that they only apparently 

 lose their structural and functional identity during the interkinesis, 

 and that something directly representative of the chromosomal structure 



FIG. 36. Indications of the individuality of the chromosomes in the cleavage 

 of the egg of Ascaris. From Wilson, "Cell," after Boveri. E. Anaphase of first 

 cleavage. F. Two-cell stage with lobed nuclei, the lobes formed by the ends of the 

 chromosomes. G. Early prophase of next division. Chromosomes reforming, 

 centrosomes dividing. H. Late prophases of same division, the chromosomes 

 lying with their ends in the same position as at the close of the preceding division. 



is present in the resting nucleus, invisible directly and known only from 

 its consequences. There are, it is true, a few instances in which the 

 chromosomal arrangement is said really to be visible in the interkinesis 

 (Figs. 36, 37), but these cases are not very clear, except in the maturation 

 divisions leading directly to the formation of the specialized germ cells, 

 where the chromosomes are definitely known to be directly continuous. 

 The remarkable constancy of form, volume, and number of chromosomes 

 throughout the cells of a given organism and species, is important evi- 

 dence favoring the hypothesis under consideration. The probability 

 is so high as to amount almost to certainty, that if the chromosomes 



