3O M. LOUISE NICHOLS. 



echinoderms may have eggs of about the same size and shape, 

 but of varying potentialities. Yet here, too, there are peculiar- 

 ities of constitution and behavior characteristic of certain groups 

 rather than of others. There may be as good ground for deter- 

 mining the relationship of organisms by the behavior of chromo- 

 somes as by the character of cleavage in the egg, but in the 

 former case the handicap is severe because of the minute size 01 

 the elements and the fact that changes of important nature may 

 take place in the constitution of the chromosome without pro- 

 ducing any effect tangible for modern microscopic methods. If, 

 however, specific or other differences happen to coincide with 

 visible variations in the chromosomes, such objects form con- 

 venient points of departure for the study of such problems as the 

 determination of sex and the relation of paternal and maternal 

 chromosomes in the cells of hybrid offspring. 



IO 



20 



EXPLANATION OF FIGURES. 



With the exception of 5 and 6, the figures are prophases of the first maturation 

 division of Oniscus asellus Linn. Nos. 5 and 6 are from Porcellio. The drawings 

 were made with the camera lucida, Zeiss oc. 6, obj. T V imm. at the level of the table. 



