SPECIFICITY IN FERTILIZATION 203 



for the experiment was the demonstration that expo- 

 sure of spermatozoa to radium emanations injured the 

 sperm, and that it might be so graded as to leave sper- 

 matozoa with ability to activate the eggs but to transfer 

 no hereditary effect. Paula Hertwig (1913) showed that 

 this was due to failure of the injured sperm nucleus to 

 take part in the cleavage; hence such fertilization is a 

 kind of parthenogenesis, as O. Hertwig had previously 

 assumed. O. Hertwig showed that in the cross Triton 

 ? X Salamandra $ the eggs die in the blastula stage, 

 but if the sperm be first strongly radiated the eggs will 

 produce larvae which possess the haploid number of 

 chromosomes. This shows that egg chromatin alone 

 was concerned in the development and permits the 

 inference that the early death in hybrid fertilization 

 with normal sperm is due to the multiplication of the 

 sperm chromatin. G. Hertwig made a similar deter- 

 mination for the cross Bufo vulgaris $ X Rana fusca $. 

 Bataillon (1909) showed that in fertilization of Pelo- 

 dytes $ by Triton the sperm nucleus takes no part in 

 cleavage; nevertheless the eggs die in the blastula stage, 

 owing, evidently, to some other cause than multiplica- 

 tion of the sperm chromatin. 



2. Self-fertilization. As contrasted with our survey 

 of hybrid fertilization we should next consider the data 

 concerning the self-fertilization of hermaphrodite organ- 

 isms, i.e., the fertilization of the eggs by the spermato- 

 zoa of the same individual. If dissimilarity of gametes 

 is the cause that renders hybrid fertilization difficult, 

 it might be expected that the closest possible relation- 

 ship of gametes, which is found in hermaphrodite indi- 

 viduals, would involve the greatest compatibility of the 



