114 CYTOLOGY chap. 



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



(B 



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m . -0 



* / 



I 



•m} 





• - 









-t: 



^-..*) ^- 



^-5 



v:,_v 



• / 



/®\V 



■^ 



'•/ 



^^J' ' 



fj 



f\> 



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■.- ( 



o *^"tX 



Fig. 52. 



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

 primitive germ-cells have dii^erentiated into oocytes and spennatocytes. In both, note the plasmosome, and in 

 the spermatocytes the single sex chromosome fcf. 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., ?,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 (J and $ gametes stiU separate, showing the five chromosomes of the one and 

 the si.x 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 



