226 



MICHAEL F. GUYER. 



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TEXT-FIG, i. Diagram illustrating the general course of spermatogenesis in 

 the common fowl: a, polar view of spermatogonial metaphase showing sixteen 

 chromosomes, of which two are characteristically curved; b, spermatogonial meta- 

 phase viewed from the side; c, products of spermatogonial division; d, polar view of 

 metaphase in primary spermatocyte showing nine bivalent chromosomes of which 

 one is U-shaped; e,f, g, successive stages in the division of the primary spermatocyte, 

 the curved chromosome passing undivided to one pole and thus producing a di- 

 morphism in the daughter cells; h, secondary pairing of the autosomes at the 

 metaphase of the secondary spermatocytes, the curved element remaining un- 

 affected; i, j, k, stages in the division of the five-chromosomed secondary spermato- 

 cytes, each spermatid (k) receiving five chromosomes, of which four are probably 

 double and therefore equivalent to eight univalent ones; /, secondary pairing of the 

 chromosomes in the secondary spermatocytes which did not receive the curved 

 element ;m,n, o, stages in the division of the four-chromosomed secondary spermato- 

 cytes, the resulting spermatids (o) probably not giving rise to mature spermatozoa. 



