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 would produce the skeleton typical 

 for the pluteus stage of the larva. As mentioned above, the 

 hybridization between purpuratus ? and Asterias $ could be 

 accomplished in 50 c.c. sea-water +0 . 6 c.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 



1 Loeb, "Ueber die Befruchtung von Seeigeleiern clurch Seesternsamen," 

 Pflilgers 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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