464 MARIE A. HINRICHS. 



Discussion. The differential modification of development pro- 

 duced in Arbacia eggs by radiation resembles so closely that 

 produced by chemicals and other agents (Child, '16, '24, Mac- 

 Arthur, '24, Hinrichs, '26), that a lengthy discussion appears 

 unnecessary here. Since the effect is differential, we may infer 

 that a difference in susceptibility relations is established at an 

 early stage along the axis of the egg. The results are the same 

 whether the egg is fertilized or unfertilized at the time of radi- 

 ation. Those regions of the egg which have the highest rates of 

 physiological activity and are consequently the most intimately 

 dependent on the continuance of normal conditions, or as R. S. 

 Lillie puts it ('23, p. 39), on a proper "cooperation of external 

 and internal factors," are naturally the first to show failure of 

 equilibrium or incompatibility in their relation to their environ- 

 ment. (See also L. Loeb, '22.) The result is an interference, 

 temporary or permanent, with the normal development of these 

 regions, the degree of interference for a given dosage of radiation 

 being in general proportional to the intimacy of dependence of 

 the region on its environment. Such regions of high activity are 

 also the first to acclimate or recover, provided the degree of 

 inhibition has not been such as to produce permanent injury. 



In the cases where normal eggs are fertilized by radiated sperm, 

 the injurious action of the radiation on the sperm prevents 

 normal development of the egg. Whether this is due to the 

 bringing in of the toxic sperm protoplasm alone, which may be 

 conceived of as acting in the same manner as other agents which 

 interfere with normal development, or whether the abnormal 

 development is an expression of incomplete fertilization bordering 

 on parthenogenesis, as suggested by P. Hertwig, '13, is an open 

 question which these experiments have raised but not answered. 

 (In this connection, see also Lillie and Baskervill, '220, F. R. 

 Lillie, 'i i, '12, Oppermann, '13, and Dungay, '13.) I am inclined 

 to believe that the toxic action of the radiated sperm protoplasm 

 (after its incorporation with the egg protoplasm to form the 

 zygote), induces abnormal development of the zygote in the 

 same manner as do other toxic agents. There seems to be a 

 certain analogy between this type of abnormal development and 

 that resulting from hybridization (Newman, '17). 



