CHROMOSOMES OF INDIAN RUNNER DUCK. 33! 



further, that the X-chromosome of the spermatocyte division is a 

 bivalent body (representing the large pair in the spermatogonia) 

 which passes as such to one pole. If these facts be correctly 

 determined they offer a cytological puzzle with which it is not 

 possible to deal without additional data." 



For some time (June 1925 to June 1926) I have been engaged on 

 a study of the chromosomes of the Indian runner duck and I offer 

 the following data as a partial solution of the avian sex-chromo- 

 some problem. 



MATERIAL AND METHODS. 



The material used for giving mitotic figures consisted chiefly of 

 the embryonic membranes of both sexes and to some extent, the 

 germ cells of the male. In most cases the cells of the amnion 

 afforded the best examples, although the cells of the chorion and 

 the allantois gave good results; but such material is more difficult 

 to prepare. 



Tissues were obtained from individuals at different stages of 

 incubation ranging from five to twenty-one days. However, 

 those from eight to eleven days were found most suitable for the 

 purpose. Before the eighth day stage it is difficult to determine 

 sex and after the eleventh day the amnion has so completely 

 formed that few dividing cells can be found. 



Four general methods of technique \vere employed; whole 

 mounts from embryonic membranes, stained sections of the 

 embryos, sections of the testes, and smears of the testes. 



Membrane Technique. Of the embryonic membranes the am- 

 nion was found to give the best results. This is a very delicate 

 tissue resembling a silk chiffon veil. Because of its delicate 

 structure it was found best to keep it as nearly intact as possible. 

 In this way the pressure of the amniotic fluid kept it stretched 

 while being fixed and thus most of the tissue could be saved. Of 

 the allantois only parts could be used. This was especially true 

 of embryos of longer incubation, for the heavy blood vessels 

 catch and hold the stain and the tissue is thick and becomes hard. 



Great care was taken that the eggs should not become chilled 

 while being removed from the incubator. The embryo within its 

 amnion, and sometimes a part of the allantois, was removed from 



