196 WILLIAM C. YOUNG AND HAROLD H. PLOUGH. 



mal. In other sections from sterile males degeneration is also 

 suggested for the sperms are decidedly reduced in number, have 

 lost their orderly arrangement in masses in the testis, and seem 

 shrunken in compact irregular aggregations. Apparently a few 

 pass down into the vas deferens but these are probably not func- 

 tional. 



Ventral receptacles of females from sterile and fertile cultures 

 respectively were also examined. Actual dissection of such 

 flies in Ringer's solution shows clearly that spermatozoa are 

 present in the receptacles of normal flies, but they can not be 

 found in the females from sterile cultures. The sections simply 

 confirm these findings. Masses of sperm can be seen clearly to 

 fill the lumen of the receptacles of flies from normal cultures while 

 ducts of flies from sterile cultures are empty. These observa- 

 tions prove that even though the male and female flies of sterile 

 cultures copulate no transference of sperm to the receptacles of 

 the females takes place. 



Beyond these facts cytological study reveals little. The testes 

 of sterile flies are smaller on the average, and there is some 

 suggestion of disorganization in the cells in the lower portion, 

 but this is not constant. However it has been shown above 

 that exposure of the adult males to 31 degrees for ten days or 

 more produces sterility from which a certain number do not 

 recover when they are placed at 24 degrees. If only the sperma- 

 tozoa are affected, it is hard to see why this should happen. 

 The data showing the recovery of the male flies suggests a pro- 

 gressive sterilizing effect beginning with the sperms and even- 

 tually reaching cells at earlier stages. Only when the latter 

 occurred would the male fail to recover fertility when placed at 

 24 degrees. 



It is interesting that one pair of testes greatly reduced in size 

 was found in a sterile male and sectioned separately. Both 

 testes appear to have been but empty shells for neither spermato- 

 zoa nor any clear germinal tissue whatever were present. This 

 may have been a degenerative change produced by high tempera- 

 ture, but such testes occasionally appear in normal stock. None 

 did appear among the controls examined, however. 



The cytological observations therefore confirm the breeding 



