STERILIZATION OF DROSOPHILA. 197 



tests by showing that a temperature of 31 degrees sterilizes male 

 flies, with little or no effect on the females. The sterility appears 

 to be caused by some degenerative effect on the spermatozoa, 

 such that all become non-motile, and eventually may be killed. 

 Recovery apparently consists in the formation of spermatozoa 

 anew from cells in the growth period or earlier. 



DISCUSSION. 



These facts are of especial interest when considered with others 

 recently recorded. Cells of the male germ line are here shown to 

 be much more sensitive than eggs or other tissues to a rise of 6 

 or 7 degrees in a cold-blooded animal, the fruit fly. C. R. 

 Moore (4) has given similar evidence of the sensitiveness of the 

 male germinal epithelium in warm blooded animals in his exten- 

 sive studies on experimental cryptorchidism in mammals. He 

 finds that when testes are exposed to the higher temperature of 

 the peritoneal cavity rather than the scrotum there follows a 

 rapid and progressive degeneration of the germinal cells. Such 

 testes show progressive recovery when returned to their normal 

 position. Bluhm (5) has given interesting evidence of the greater 

 sensitivity of spermatozoa of mice to drugs (alcohol, caffein, etc.) 

 since a portion of one class of spermatozoa, the female producing, 

 become non-functional. Further the recent tests of Mavor and 

 DeForest (6) on the sensitivity of eggs and sperm of Arbacia to 

 X-rays show a much greater sterilizing effect on the sperms at 

 all doses. Evidently the male germ cells are much more sus- 

 ceptible than eggs or other cells of the animal body to external 



influences. 



SUMMARY. 



1. High temperature has a differential effect on the germ cells 

 of Drosophila such that males may be rendered completely ster- 

 ile at a point at which females are still completely fertile. 



2. This effect on the males is permanent as long as this tem- 

 perature is maintained, but most males will recover normal 

 fertility after being returned to the optimum temperature. 



3. Exposures to 31 C. of over ten days tend to increase 

 greatly the number of flies which are permanently sterilized. 



4. Examination of the testes of sterile males shows that high 



