216 



A. RICHARDS AND DONNELL J. GOOD. 



TABLE IV. 



irradiation is behind the 3-minute exposure. The same handicap 

 is present here as in the two previous series; there being no 

 samples after this period until the free-swimming larval stage is 

 reached. Results of development, 381 minutes after fertilization, 

 however, show that the effect is quite similar to the series where 

 the egg only has been irradiated. 



It is worthy of note that here, as in the cases reported by the 

 Hertwigs and by Packard, that the rays produce more effect 

 upon the fertilized eggs than upon the unfertilized. (Compare 

 Tables I. to IV., the A and the B, C, D series.) In general the 

 effect of a short irradiation of the fertilized egg of Cumingia is a 

 stimulation in the rate of cell division through the first and 

 second cleavage divisions, after which time there is a retardation. 

 A longer irradiation causes a less acceleration than the shorter 

 treatment and markedly greater retardation and inhibition of 

 growth. In the case of a short irradiation of the sperm (B series) 

 no change whatever can be noted in the rate of division. In the 

 C series where the unfertilized egg is subjected to a short irradia- 

 tion, the effect after fertilization is a direct retardation of de- 

 velopment and a complete inhibition of growth by the time the 

 free-sw T imming larval stage is reached. There is apparently 

 only a difference of degree in the extent of the injuries due to 

 the two strengths of exposure. 



The result of the D series is quite similar to that of the C 



