RADIATION AND FERTILIZING POWER. 485 



When fertilization is incomplete or partial, abnormal cleavage 

 and abnormal development follow. (See Table IV ; also previous 

 paper, Hinrichs, '266.) F. R. Lillie, 'n, 'i2rt, '19, in analyzing 

 the fertilization reaction in Nereis, divided it into two phases, 

 external and internal. The former concerns itself with membrane 

 formation and needs only the contact of sperm for its initiation. 

 Other investigators have obtained similar results; thus, Just, '19, 

 found that although sperm entry may initiate cortical changes, 

 it is no criterion of fertilization, and further development does 

 not necessarily follow. Loeb, '13, states that cortical changes in 

 the sea urchin are not dependent on the penetration of sperm. 

 Dungay, '13, found that injury of sperm may prevent its entry 

 into the egg, and maturation may go on, but cleavage fail to 

 follow. (See also the recent paper by O. Hyman, '25.) 



In the experiments with ultraviolet radiation, membrane 

 formation is usually less interfered with than cleavage. There 

 may be an advance of from .5-5 per cent, in the number of eggs 

 having membranes only, over those cleaved. This seems to be 

 an indication that the fertilization reaction was initiated but not 

 completed. 



Complete internal fertilization involves compatibility of ger- 

 minal nuclear material, and forms the basis for normal develop- 

 ment. When either sex component has been injured, e.g., by 

 ultraviolet radiation, development becomes abnormal, particu- 

 larly in the regions of the organism which normally have a 

 relatively high rate of physiological activity. (See also Hinrichs, 

 '26^.) Such a result is comparable to that reported by Newman, 

 '17, for teleost hybrids, where incomplete fertilization resulting 

 from the incompatibility of germ plasms produces differentially 

 modified embryos. 



It would be difficult to explain so complete a series of differ- 

 entially inhibited forms as those shown in Plates I. and II. of a 

 previous paper (Hinrichs, '266) on the assumption of partheno- 

 genetic development of the egg induced by injury to the sperm 

 nuclear material. Also, the fact that the degree of effect (as 

 measured by the percentage of eggs cleaved and the type of 

 cleavage) is proportional to the dosage of radiation to which the 

 sperm is subjected, can hardly be satisfactorily explained in 

 this way. 



