MORPHOLOGICAL COMPOSITION OF THE NUCLEUS 



217 



These remarkable observations show that whatever be the number 

 of cJiromosomes entering into tJie formation of a reticular nucleus, tJie 

 same number afterwards issue from it a result which demonstrates 

 that the number of chromosomes is not due merely to the chemical 

 composition of the chromatin-substance, but to a morphological organ- 

 ization of the nucleus. A beautiful confirmation of this conclusion 

 was afterwards made by Boveri ('93, '95, i) and Morgan ('95, 4) 

 in the case of echinoderms, by rearing larvae from enucleated egg- 



Fig. 104. Evidence of the individuality of the chromosomes in the egg of Ascaris. [BOVERI.] 

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

 the ends of the chromosomes. G. Early prophase of the ensuing division; chromosomes re-form- 

 ing, centrosomes dividing. H. Later prophase, the chromosomes lying with their ends in the 

 same position as before ; centrosomes divided. 



fragments, fertilized by a single spermatozoon (p. 258). All the 

 nuclei of such larvae contain but half the typical number of chromo- 

 somes, i.e. nine instead of eighteen, since all are descended 

 from one germ-nucleus instead of two ! 



Van Beneden and Boveri were able, furthermore, to demonstrate 

 in Ascaris that in the formation of the spireme the chromosomes 

 reappear in the same position as those which entered into the forma- 

 tion of the reticulum, precisely as Rabl maintained. As the long 



