Vol. XXXI. October, igi6. No. 4 



BIOLOGICAL BULLETIN 



STUDIES ON THE CHROMOSOMES OF THE COMMON 

 FOWL AS SEEN IN TESTES AND IN EMBRYOS 



MICHAEL F. GUYER, 

 DEPARTMENT OF ZOOLOGY, UNIVERSITY OF WISCONSIN. 



Some years ago ('096) I gave an account of the spermato- 

 genesis of the common fowl insofar as I was then able to interpret 

 it. Since then I have spent much time in further observation, 

 partly on the same but mainly on new and better material. 

 Altogether I have been engaged on the problem at intervals for 

 over ten years. In the aggregate this means many months of 

 continuous work inasmuch as it includes summer months as 

 well as those of the school year. I emphasize the element of 

 time, not because time alone is particularly significant, but 

 rather to show that my problem has not been one worked out 

 as a summer's pastime. And while time is not the chief essential 

 in solving problems in avian spermatogenesis, in my estimation 

 such problems will not be solved without the most painstaking 

 and critical study extending over months of protracted daily 

 observation. The cells are small, the chromosomes tend to 

 mass, and fixation is uncertain. This necessitates the prepara- 

 tion of literally hundreds of slides and then the abandonment of 

 the great majority of these in favor of the few which really show 

 adequate detail upon which it is safe to base conclusions. The 

 latter once secured, however, one has material enough in a single 

 slide to occupy many hours and even weeks of the closest scrutiny. 



My later studies tend in the main to confirm my earlier 

 observations. Chief among the latter was the rinding of a large 

 curved chromosome, comparable to the so-called sex-chromosome 

 of other forms, which typically passes undivided to one pole of 

 the spindle during the division of the primary spermatocyte. 



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