252 MICHAEL F. GUYER. 



element as large as it is, if one half of the spermatozoa possessed 

 it and one half did not, one would certainly expect to obtain a 

 fairly well marked bi-modal curve in the measurements of such 

 spermatozoa. The presumption is therefore that only a single 

 class of spermatozoa are represented. The probability that 

 this class is the one developed from the five-chromosomed 

 spermatids has already been indicated. While one wishes that 

 the evidence might be more decisive on this point, no more 

 significant facts seem forthcoming under present conditions of 

 technique. What evidence there is points to the interpretation 

 I have given and I have found no facts which indicate the con- 

 trary. 



CONCLUSIONS. 



Many as are the pitfalls and unsatisfactory as are parts of the 

 evidence, I feel that I have examined a large enough number of 

 cases and have studied a sufficient number of interpretable 

 stages in chromosome behavior to proclaim the foregoing account 

 as substantially the ordinary course of spermatogenesis in the 

 common fowl. I feel that the chief hiatus centers about the 

 fate of the one class of spermatids; that is, as to whether the 

 degeneration evinced is confined to the four-chromosomed class, 

 whether this class never forms spermatozoa, and whether all 

 cases I have regarded as abnormal are really conditions of 

 degeneration. But in the light of the fact that as a result of 

 the transformations of spermatids only one class of spermatozoa 

 arises I feel that only one class of spermatids completed the course 

 of final transformation. 



To those who have followed the recent literature on sex-linkage 

 in fowls the significance of the conclusions arrived at in this paper 

 is obvious. The facts of such linkage have been reviewed so 

 often in recent papers and books (e. g., cf. Morgan, "Heredity 

 and Sex," 1913) that it is needless to lengthen my paper by 

 restating them here. It is sufficient to mention that certain 

 characteristics such as color pattern are inherited in a manner 

 to indicate that in fowls the female is heterozygous, the male 

 homozygous, for sex and sex-linked factors. My earlier study 

 in which the X-like chromosome therein described was regarded 

 as an ordinary X-element and therefore presumed to exist as 



