222 MICHAEL F. GUYER. 



I have found no reason to reverse my opinion on this point since 

 in all of my preparations in which fixation is adequate, I find in 

 abundance a characteristic chromatic element of constant shape 

 and size which behaves in the manner indicated. I have re- 

 corded stage readings of over 900 views of it in my preparations 

 and I have seen and studied many others which it was not 

 deemed worth while to record separately. Although the exist- 

 ence of this element has been called in question (Boring and 

 Pearl, '14), I do not see the least reason to doubt its existence 

 or its constancy. However, as my subsequent account will 

 show, and even as suggested in my earlier report, there is strong 

 reason for doubting that it is a single or univalent element. 

 The outcome of my investigation leads me to believe that it is 

 composed of two curved univalent chromosomes which exist 

 separately in the spermatogonial and somatic cells. 



The present account is based upon a study of testicular 

 materials from two Langshan, four Plymouth Rock, and two 

 Rhode Island Red fowls, together with sections of a number of 

 embryo chicks of 9, 10, 13, and 19 days of incubation respec- 

 tively. Of the embryos, chicks of the 10 and 13 day stage were 

 found to be the most satisfactory and consequently were used 

 most extensively. By the tenth day of incubation the sexes 

 can readily be distinguished and from this time on to the thir- 

 teenth or fourteenth day there seems to be an unusually plentiful 

 division of primitive germ-cells in progress. 



METHODS. 



Materials were fixed mainly in Gilson's, Flemming's, Her- 

 mann's, and Bouin's fluids. The latter, used straight or with 

 various slight modifications, was perhaps the most universally 

 successful fixing agent. When modified, the alteration took 

 the form of reducing the percentage of acetic acid which tends 

 to swell chromosomes and make them agglutinate more than 

 they would do otherwise, or of the addition of chromic acid 

 which in some preparations proved helpful in getting better 

 definition of both chromosomes and cytoplasm. 



In the study of the testicular material, smears were used 

 extensively and as a rule proved more satisfactory than sections. 



