114 



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 m 

 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, mctaphase 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 d and 9 gametes still separate, showing the five chromosomes of the one and 

 the six of the other. 



0, 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 



