54 MICHAEL F. GUYER 



top consists really of two chromosomes; one, at the base, a deeply- 

 staining, rounded, ordinary chromosome, and the other the 

 curved X-element. In order to show the curve of the latter the 

 camera had to be so focussed as to blend the two images. The 

 X-element of the hybrid, like that of the guinea, is seen to be 

 narrower at one end. 



In my paper on the spermatogenesis of the chicken,^ I noted 

 the fact that it was not uncommon to find what appeared to be a 

 tripartite accessory, but I am now inclined to believe that when 

 such a body exists it is the X-element plus one member of a char- 

 acteristic pair of small chromosomes, the other member of which 

 passes to the opposite pole, either slightly in advance or at the 

 time of the regular division of the ordinary chromosomes. Figs. 

 7, 9, 11 and 12 of that paper ^ show evidence of this condition. 

 In fig. 11 the small element is completely detached. Fig. 10 

 probably represents a condition in which the opposite member of 

 this small pair stands apart from the equatorial plate towards 

 one pole, the accessory being seen on the other side of the equa- 

 torial plate. In the guinea the corresponding pair of small chro- 

 mosomes (see figs. 11 and 12 of my paper^" on the spermatogenesis 

 of the guinea) is considerably smaller than in the chicken. The 

 one which passes to the pole also reached by the X-element shows 

 less tendency to unite with the latter than in the chicken, hence 

 it is only rarely that a tripartite condition of these bodies is ob- 

 served in the guinea. 



In a paper^"^ written in 1909 before I had discovered the pres- 

 ence of an X-element in the common fowl, I suggested that if 

 we assume, as some investigators have done, that increased nutri- 

 tion favors the production of females, diminished nutrition, the 

 production of males, then the excess of males among hybrid birds 

 might be due to the fact that in hybrids, " there would in all proba- 

 bility be more or less default in the metabolic processes because of 

 the incompatibilities which must necessarily exist between two 



* Guyer, M. F. : The spermatogenesis of the domestic chicken (Gallus gallus 

 dom.). Anat. Anz., xxxiv, 22-24, 1909. 



^° Guyer, M. F. : The spermatogenesis of the domestic guinea (Numida mele- 

 agris dom.). Anat. Anz., .xxxiv, 20-21, 1909. 



" Guyer, M. F. : On the sex of hybrid birds. Biol. Bui., xvi, 4; 1909. 



