.((>(> MARIK A. HtNRICllS. 



1 . In order that visible radiation following sensitization may be 

 (.furtive, the sensitized system, in this case eggs or sperm before 

 fertili/ation. must be exposed to radiation of sufficient intensity 

 and duration whose wave-length range includes that absorbed by 

 the particular sensitizer used. 



2. I'ltraviolet radiation is effective without the aid of a 

 sensiti/er, by virtue of its direct absorption by protoplasm. 



3. Susceptibility to sublethal doses of radiation in these two 

 spectral regions is a differential one, i.e., regions of high physio- 

 logical activity an- the first to be modified in their development. 

 They are also the first to recover when the injurious effect is 

 slight. 



4. Modification of development by means of radiation pro- 

 duces results essentially similar to those obtained by other 

 means. 



5. Development may be modified by subjecting fertilized eggs, 

 soon after insemination, to the action of intense radiation as in 

 previously reported experiments. Modification of development 

 may also be obtained by exposure of either sex component of 

 the zygote to intense radiation previously to fertilization. 



6. A differentially modified larva resulting from the union of 

 radiated eggs and normal sperm is evidence that differences in 

 the susceptibility of the various regions already exists in the 

 unfertilized egg. 



7. A differentially modified larva developing from a zygote the 

 sperm component of which has been injured by radiation may 

 be either differentially inhibited or differentially acclimated. 



8. Since the developing embryo becomes differentially modified, 

 it appears that the egg at the time of fertilization already shows 

 a difference in susceptibility of its various regions to the injurious 

 action of the radiated sperm. 



9. Radiation of sperm reduces its motility, delays cleavage, 

 and interferes with normal development of the zygote. 



10. Radiation of sperm inhibits its fertilizing power. (See 

 later paper.) 



LITERATURE CITED. 

 Bardeen, C. R. 



'07 Abnormal Development of Toad Ova Fertilised by Spermatozoa Exposed 



to Roentgen Rays. Jour. Exp. Zool.. Vol. 4. pp. 1-44. 

 '09 Variations in Susceptibility of Amphibian Ova to X-rays at Different 

 of Development. Anat. Rec. .Vol. 3. pp. 163-165. 



