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. 221
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