XXXI 
ARTIFICIAL PARTHENOGENESIS AND HEREDITY 
1. The spermatozoon not only induces the development 
of the egg, but it also transmits the hereditary characters of 
the male parent to the offspring. The possibility of artificial 
parthenogenesis makes it certain that the two processes are 
not determined by the same substances, since the methods of 
artificial parthenogenesis are analogous for very diverse species, 
while the hereditary characters are very different. 
When closely related species are crossed the hereditary 
characters of the male are of course recognizable in the off- 
spring. The question arose: What would happen if widely 
divergent species were crossed, such as sea-urchin and starfish ? 
The writer found a method of bringing about this hybridization. 
The main interest was whether or not a sea-urchin egg fertilized 
with the sperm of starfish wou!d produce the skeleton typical 
for the pluteus stage of the larva. As mentioned above, the 
hybridization between purpuratus 2 and Asterias ¢ could be 
accomplished in 50 ¢.c. sea-water +0.6¢.c. N/10 NaOH. These 
hybrid eggs segmented at the same rate as the eggs fertilized 
with sperm of their own species, and the development was 
normal up to the gastrula stage. Then the eggs began to die 
in large numbers and those which survived were sickly and 
developed at a much lower rate than the eggs fertilized with 
purpuratus sperm. But the small number of eggs which lived 
long enough developed into plutei which were in every point 
identical with the pure breed of purpuratus. In the case of 
heterogeneous hybridization the spermatozoon produces only 
the developmental but not the hereditary effect.! 
1 Loeb, ‘“‘Ueber die Befruchtung von Seeigeleiern durch Seesternsamen,’’ 
Pfliiger's Archiv, XCIX, 323, 1903; ‘‘ Weitere Versuche ueber heterogene Hybri- 
disation bei Echinodermen,” Pfliiger’s Archiv, CIV, 325, 1904; ‘‘ Heredity in 
Heterogeneous Hybrids,’ Jour. Morphol., XXIII, 1, 1912. 
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