THE CHROMOSOME THEORY OF HEREDITY 295 



of stored food. It is developed to an extreme in the eggs of birds, 

 in which the yolk is the true ovum but the active cytoplasm is 



Fig. 170. — Spermatogeneses in Ascaria megalocephala. A-G, suece.ssive 

 stages in the division of the primary spermatocyte. D shows the two 

 tetrads in profile and E shows an end view of them; F, G, H, division of 

 the primary spermatocyte to form two secondary spermatocytes, each con- 

 taining two dyads; /, secondary spermatocyte; /, K, the same dividing; 

 L, spermatids, each with two chromosomes and a centrosome. The normal 

 diploid numl^er of chromosomes in this .species is four. (From Wilson, 

 after Brauer.) 



restricted to a small mass on one side. The remainder is yolk 

 in the strict sense, and is food for the developing (Miibryo. The 

 white is an env(>lope of albumen of similar importance outside 

 of the cell. 



