THE CHROMOSOMES OF 1 HE INDIAN RUNNER DUCK. 



ORILLA STOTLER WERNER. 



During recent years the attention of a number of cytologists 

 has been focused on the problem of the avian sex-mechanism. 

 Their investigations have brought varying results and numerous 

 hypotheses have been advanced to explain the cytological 

 findings in such a way as to bring them into agreement with the 

 genetic evidence which is beyond dispute. 



Cytologists agree that both physiologically and morphologi- 

 cally the character of the chromosomes of the birds is undeter- 

 mined and that up to this time our only method of forming a 

 conception of the activities of the chromatic material is through 

 genetic study. In view of this consensus of opinion it would be 

 a hazardous thing for a beginner in the field to criticize the 

 theories that have been developed around the studies of the avian 

 chromosomes unless he has a sufficient number of properly pre- 

 pared figures for study and has subjected them to a very critical 

 analysis. 



Stevens, Hance, and Schiwago agree that the male chick ap- 

 pears to have two large chromosomes equal in size. These they 

 presume are the X-chromosomes. Guyer claims to have evi- 

 dence to show that in the guinea hen and in the domestic chicken 

 the sperm are of two classes. These are to be distinguished by the 

 presence or absence of an unpaired X-element or accessory chro- 

 mosome. He believes, however, that the sperm which do not 

 possess the X-element degenerate and are, therefore, non- 

 functional. In regard to this Wilson (1925) says: "In view of 

 this fact it is remarkable that the diploid group seems to show 

 in the female but one large curved chromosome (X) while in the 

 male two such elements are present. The diploid group thus 

 seems to show the expected relations, the female being hetero- 

 zygous, the male homozygous; but, per contra, the gamete forma- 

 tion of the male seems to show this sex to be cytologically diga- 

 metic, with one class of gametes non-functional. It is stated, 



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