300 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



spermatozoa of the frog are first treated for a longer period 

 with a strong radium bromide preparation, so that they are 

 no longer able to fuse with the nucleus of the egg, they can 

 cause the toad egg to develop into tadpoles which are able 

 to live as long as from three to five weeks and which are 

 almost normal. In this case the foreign spermatozoon had 

 only a developmental effect and the resulting larva was prac- 

 tically produced by artificial parthenogenesis. 1 



5. Combination of artificial parthenogenesis and hybridiza- 

 tion by sperm. Herbst has made the very interesting experi- 

 ment of fertilizing eggs with the sperm of a different species 

 after the eggs had been treated with a fatty acid. In this 

 case he obtained eggs in which the maternal characters 

 predominated. 2 He crossed Sphaerechinus ? with Strongyh- 

 centrotus $. The skeleton of the plutei of these two forms is 

 typically different and it is therefore easy to follow the paternal 

 influence in the larvae. Herbst proceeded in the following 

 manner. The eggs of Sphaerechinus were first treated with 

 50 c.c. sea-water +3 c.c. N/10 acetic acid. A large percentage 

 of these eggs formed no typical fertilization membrane. As far 

 as I can learn from his description, the eggs formed, however, a 

 fine gelatinous film around the periphery. These eggs had there- 

 fore undergone a peripheral change which started their develop- 

 ment. If after one and one-half hours sperm of Strongyloce?itrotus 

 lividus was added these eggs could be fertilized. The plutei which 

 were thus produced were, however, much more like the pure 

 Sphaerechinus plutei than those developing from the eggs which 

 had been fertilized with the same sperm but without having 

 undergone the parthenogenetic treatment with the fatty acid. 

 The explanation for this result was found by Herbst from an 

 analysis of the nuclei of these hybrids. At the time he added the 



1 G. Hertwig, "Parthenogenesis bei Wirbeltieren, hervorgerufen durch art. 

 fremden, radiumbestrahlten Samen," Arch. f. mikr. Anat., LXXXI, Abt. 2, 1913 



2 Herbst, " Vererbungsstudien," IV, Archiv f. Entwicklungsmechanik, XXII 

 475; 1906; V, ibid., XXIV, 185, 1907; VI, ibid., XXVII, 266, 1909. 



