^332 CHARLES PACKARD 



scription of such typical abnormalities has been given by Tennant 

 ('10). It is evident from both series of experiments that pro- 

 toplasmic changes in Arbacia are very small, if indeed they 

 occm' at all. 



3. Experiments on Drosophila. The larvae and pupae of 

 Drosophila do not show any external change even after an 

 intense radiation for one hour. It is probable that the rate of 

 development is somewhat retarded, although there is not suffi- 

 cient evidence to prove this point conclusively. When the pupae 

 hatch out, the flies are normally active but are completely sterile 

 inter se and with normal wild stock. The sterility is however, 

 only temporary for after about three weeks the flies become 

 fertile again. The offspring appeared to l3e normal. Apparently 

 only those germ cells which were in advanced stages of devel- 

 opment were destroyed, whilfe the earlier stages were merely 

 retarded. 



Summary 



The gamma rays from 50 mg. of radium bromide bring about 

 some acceleration in the rate of development of the sea urchin, 

 but have no effect on Nereis'. Rapid beta rays, acting at 50 mm. 

 distance exert a retarding efl"ect, most marked in Arbacia, but 

 noticeable in Nereis and Drosophila. Acting at 4 mm. these 

 rays affect the peripheral protoplasm of Nereis. When both 

 rapid and slow beta rays are used there is a marked protoplasmic 

 change in Nereis and an inhibition of development. Under the 

 same treatment Arbacia shows little or no protoplasmic change, 

 but a very abnormal development. The chief efl"ect on Droso- 

 phila is a destruction of the germ cells in the later stages of 

 gametogenesis. 



CYTOLOGY OF RADIATED EGGS 



In a previous paper I described a number of typical abnormali- 

 ties which occur in the radiated eggs of Nereis. The point was 

 made that in these eggs marked protoplasmic changes occur as a 

 result of the treatment with small amounts of radium, and that 

 the nuclear changes, while present, are not always obvious. 



