STERILIZATION OF DROSOPHILA. 



The experimental data apparently demonstrate that high 

 temperature has a differential action on the germ cells of Droso- 

 phila such that males are rendered completely sterile at a point 

 at which females are uninjured. This effect is permanent as 

 long as the temperature is maintained, but male flies will recover 

 normal fertility if returned to the optimum temperature for a 

 variable period. Longer exposures, however, tend to greatly 

 increase the number of male flies which are permanently sterilized. 

 Apparently raising the temperature still higher eventually 

 sterilizes the females as well, and finally kills the flies. 







CYTOLOGICAL OBSERVATIONS. 



Sections of testes and of ovaries from flies which failed to 

 produce offspring at 31 degrees were made, and compared with 

 similar sections from normal flies of the same age. In addition 

 the spermathecae and ventral receptacles of females of the two 

 sorts were examined both whole in Ringer's solution and in 

 stained sections. 



Study of these preparations adds very little to the facts al- 

 ready shown by experiment, though it confirms these. In none 

 of the sections is it possible to discover any difference in the 

 cytological picture between normal ovaries and ovaries of females 

 from sterile cultures, except that the latter appear to be smaller, 

 with fewer eggs at similar stages. Sections of the widened end of 

 the testis just about at the point where it joins the vas deferens 

 were studied in a sterile male and in a normal male respectively. 

 The testes were taken from flies one group of which had been 

 hatched and kept at 31 degrees for twelve days and the other at 

 24 degrees for the same time. The spermatozoa in the latter 

 completely fill and distend the surrounding membrane. The 

 same region in a sterile male is partially collapsed, and contains 

 only a few scattered sperm. In other sections even these are 

 absent. In portions of the testis slightly further up one can see 

 a few cells which are probably spermatocytes together with 

 some spermatozoa. At about the same place in testes from ster- 

 ile flies only masses of spermatozoa appear. These seem to be 

 shrunken away from the wall in masses and appear to be under- 

 going degeneration for neither their size nor arrangement is nor- 



