Plate XX 



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Chromosomes in the development of eggs and spermatozoa of the hermaphrodite 

 generation of Rhabdonema nigrofvenosum. (After BOVERI, 1911, reproduced 

 by permission of the Editor, from Quart. Journ. Micr. Science, Lix (1914), 

 p. 50 1 .) Oogenesis on left, spermatogenesis on right. Hetero-chromosomes 

 black, (i, 2) Early stages of first maturation division of egg and sper- 

 matozoon. (3, 4) Daughter groups of first maturation division. (5, 6) 

 Equatorial plates of second maturation division. (7, 8) Diagrammatic 

 side views of same stage. (9, 10) Side views of last stage of second 

 maturation division. 



