SPERMATOGENESIS OF THE CHICKEN 57 



MATERIAL AND METHODS 



The material used in this investigation came from twelve pure 

 Barred Plymouth Rock and crossbred males, raised on the poul- 

 try plant of the Maine Agricultural Experiment Station. The 

 birds varied in age from five months to two years. Those 

 younger than five months had no dividing germ cells. Beyond 

 that time age seemed to have nothing to do with the number of 

 dividing cells present, or the clearness of the mitotic figures. 

 The testes of birds killed in the active breeding period, January 

 to April, may perhaps contain more dividing cells, but no sta- 

 tistics were taken on this point, and those killed in October, 

 November and December contained many such. 



Three general methods of technique have been used in the 

 preparations : stained sections, smears, and aceto-carmine mounts. 

 The latter two give much better results than the first. The 

 difficulties with much vertebrate germ cell material, as compared 

 with insects, have been many times described, and the bird ma- 

 terial is no exception. The chromosomes act as though they were 

 of a sticky nature, and do not separate far apart even in pro- 

 phase. Smears and aceto-carmine preparations both give a pos- 

 sibility of flattening out the cells, and for this reason give greater 

 separation of chromosomes than any of the sections, no matter 

 in what they are fixed. The material for stained sections was 

 fixed mostly in Gilson's, Flemming's or Hermann's solutions. A 

 testis of one bird was found in the laboratory fixed in Zenker- 

 formalin; this was sectioned, but showed rather poor fixation. 

 All possible schemes were tried to keep the cells in as normal 

 condition as possible. The effort was made to transfer small 

 pieces of the testes to the Gilson or Flemming solutions while the 

 testis was still at the body temperature of the bird. For one 

 bird, the Flemming and the Hermann solutions were heated to 

 38°C. when the pieces of testis were added in order to keep them 

 at the normal temperature of the body of the bird until fixed. 

 For two other birds, the whole testis hot from the bird's body, 

 was immersed immediately in Flemming at 38°C., and cut into 

 thin slices while in the hot solution so as to avoid any change 



