HEREDITY 



FIG. 46. 



Syngamy and early development in the Crustacean, Cyclops (diagrammatized 

 from Hacker and Amma) ; /, nucleus of macrogamete or egg ; g, primitive germ 

 cells ; m, nucleus of microgamete or spermatozoon ; p, rejected portion of female 

 nucleus ; A , immediately after entry of microgamete into the egg, female nucleus 

 dividing into two ; B, having thrown out half of its substance, (p) the female 

 nucleus is moving in towards the centre of the egg to meet the male nucleus; 

 C, the male and female nuclei, now alike in size and constitution, have met in the 

 centre of the egg to form the zygote nucleus ; D, first division of the zygote 

 nucleus. The six chromosomes (three derived from each gamete) have each 

 divided into two V-shaped bodies ; E, two sets of six chromosomes separating. 

 Division of the cell body beginning ; F, division complete, the new nuclei recon- 

 stituted and the egg divided into two cells ; G, the zygote nucleus in C shown under 

 a higher magnification. Three chromosomes, in the form of long beaded threads 

 are seen in each portion ; H, 1-5, stages in the division of a single chromosome ; 

 /, a dividing nucleus (as in D), at a higher magnification ; K, a later stage of 

 development. The two cells with large nuclei, and granules in the cell body 

 are the primitive germ-cells of the young Cyclops ; L, a much later stage, at a 

 lower magnification. Stomach, muscles, etc., now developed. 



