STUDIES ON CHROMOSOMES. 245 



and photo 34 show cases in which the chromosomes which have 

 passed to the poles of the spindle in the primary division are in 

 process of rearrangement for the secondary division, the X-like 

 body remains with one group only. The autosomes have fused 

 or are fusing in pairs. 



In a very few instances spindles bearing the same number of 

 chromosomes as occur in the primary spermatocytes were found. 

 The chromosomes were relatively small as if of the univalent 

 type. These are possibly to be interpreted as secondary sperma- 

 tocytes in which the usual fusion has not occurred, but on the 

 other hand the evidence is not clear that they are not primary 

 spermatocytes in which the fixing agent has caused an unusual 

 shrinkage. In any event, supposing these are in reality secondary 

 spermatocytes, out of thousands of secondary spermatocytes 

 examined I have found only fifteen cases of this kind. All the 

 others, even where the exact number of chromosomes could not 

 be determined, showed a chromosome number that was certainly 

 less than that of the primary spermatocyte. 



There has been a disposition on the part of some to question 

 the existence of this second diminution in chromosome number. 

 In my own work I first came across it in studying the spermato- 

 genesis of doves and pigeons (Guyer, 'oo) in which forms its 

 existence has also been confirmed by the more recent work of 

 Geoffrey Smith ('12). Later I described it again in the guinea- 

 fowl ('09-2) and the chicken ('096). A similar occurrence has 

 been recorded for several mammals (e. g., Jordan, 'n, Wodse- 

 dalek '13). In any event, the fact remains that four-groups and 

 five-groups are present in abundance in the testis of the common 

 fowl. They are so obvious indeed at every turn in a good 

 preparation that it has been a long standing puzzle to me why 

 there has been any difficulty on the part of others in demonstrat- 

 ing them. They have become an object of routine demon- 

 stration in my own cytological laboratory which even beginners 

 in the course have little difficulty in finding. 



Photos 36-54 show various groups of four. Photos 47-52 

 represent anaphases where even in a photograph, with its limita- 

 tions as to planes, four chromosomes are revealed at one or both 

 poles. In photos 51 and 52, to show detail at one end the other 



