56 ALICE M. BORING AND RAYMOND PEARL 



The history of the present investigation is as follows: In 

 1907-08 there was begun in this laboratory by Dr. F. M. Surface 

 and one of the present writers (R. P.) a preliminary stud of the 

 spermatogenesis of the domestic fowl. The inherent difficulties 

 of the material were at once apparent. It seemed clear that 

 with any sort of technique then available it would be literally 

 impossible to make out a definite and connected account of the 

 spermatogenesis, in which the ^objective evidence on essential 

 points would be unequivocal and indubitable. Later the other 

 of the present writers (A. M. B.) took up the work. A great 

 deal of time was spent in the development and experimental ex- 

 tension of technique in an attempt to overcome the inherent dif- 

 ficulty of the material. In 1910-11 the late Dr. N. M. Stevens 

 was interested in the matter, and from then on till the time of 

 her death in 1912 she devoted a very considerable amount of 

 work to this problem, partly with material (both living and pre- 

 served) supplied from this laboratory and partly with cockerels 

 of other breeds. After her death her notes, drawings and 

 preparations were turned over to us. As will presently appear. 

 Miss Stevens was totally unable to confirm Guyer's account in 

 regard to any essential point. At the Cleveland meeting (1913) 

 of the American Society of Zoologists, Professor Guyer announced 

 a demonstration of his chicken preparations showing the X- 

 element. To one of us was given a very full account of the 

 exact technique he had used. It may be said at once that 

 every objective fact described by Guyer in his paper regarding 

 the so-called X-element^ was clearly and successfully demon- 

 strated. There can be no question regarding the existence of 

 bodies which Guyer calls X-chomosomes. It is the chief object 

 of this paper, however, to show that there is at present no valid 

 evidence that any element which may justly be interpreted as 

 an X-chromosome exists in the chicken. 



3 No preparations were at hand for demonstrating the chromosome counts in 

 the different stages of spermatogenesis, so this phase of the matter was not gone 

 into. 



