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.! 
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.” He crossed Sphaerechinus 2 with Strongylo- 
centrotus 2. 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 Strongylocentrotus 
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 
1G. Hertwig, ‘‘Parthenogenesis bei Wirbeltieren, hervorgerufen durch art. 
fremden, radiumbestrahlten Samen,” Arch. f. mikr. Anat., LXXXI, Abt. 2, 19135 
2 Herbst, ‘‘ Vererbungsstudien,’’ LV, Archiv f. Entwicklungsmechanik, X X11 
475; 1906; V, ibid., XXIV, 185, 1907; VI, ibid., X XVII, 266, 1909. 
