H4 CYTOLOGY CHAP. 



(primary oocytes) which will give rise to eggs are indistinguishable from 



FIG. 52. 



Spermatogenesis in Ascaris nigrovenosus. (After Schleip, A.Z., 1912.) A, portion of gonad after the 

 primitive germ-cells have differentiated into oocytes and spermatocytes. In both, note the plasmosome, and in 

 the spermatocytes the single sex chromosome (cf. E). B, oocyte just before synizesis ; C, oocyte during growth 

 period. In both B and C note absence of compact sex chromosome. D, metaphase I., 9 .six bivalents; E, 

 spermatocyte I. ; one sex chromosome has condensed out ; F, later stage, both sex chromosomes condensed ; G, 

 late prophase I. ; H, two secondary spermatocytes ; I, metaphase II. ; J, anaphase II., 5 +X chromosomes 

 passing to each pole ; K, late anaphase II., one X chromosome lagging behind ; L, M, two pairs of spermatids. 

 In one of each the sex chromosome has been left out of the nucleus. N, first cleavage division of an egg 

 fertilized by a spermatozoon, without the X chromosome, and which will therefore develop into a male. The 

 groups of chromosomes from the <$ and 9 gametes still separate, showing the five chromosomes of the one and 

 the six of the other. 



o, primary oocytes ; s, primary spermatocytes ; X, the sex chromosomes ; the distinction between X 

 and Y made in the text is not shown here. 



those (primary spermatocytes) which will give rise to spermatozoa. All 



