220 



SOME PROBLEMS OF CELL-ORGANIZATION 



the chromosomes of the germinal vesicle appear in two distinct 

 groups, and Riickert suggests that these may represent the paternal 

 and maternal elements that have remained distinct throughout the 

 entire cycle of development, even down to the formation of the egg ! 

 When to these facts is added the evidence afforded by Brauer's 

 beautiful observations on Artemia, no escape is left from the 

 hypothesis of the individuality of the chromosomes in one form or 



Fig. 106. Hybrid fertilization of the egg of Ascaris megalocephala, var. bivalens, by the sper- 

 matozoon of var. univalens. [HERLA.] 



A. The germ-nuclei shortly before union. B. The cleavage-figure forming; the sperm-nucleus 

 has given rise to one chromosome (cf ), the egg-nucleus to two (9). C. Two-cell stage dividing, 

 showing the three chromosomes in each cell. D. Twelve-cell stage, with the three distinct chro- 

 mosomes still shown in the primordial germ-cell or stem-cell. 



another, even though we admit that Boveri's statement may have 

 gone somewhat too far. The only question is how to state the facts 

 without introducing obscure conceptions as to what constitutes an 

 " individual." It is almost certain, as pointed out beyond (p. 221), that 

 the chromosomes are not the ultimate units of nuclear structure, for 

 they arise as aggregations of chromatin-grains that have likewise the 

 power of growth and division. The fact remains and it is one of 



