HEREDITY IN HETEROGENEOUS HYBRIDS' 



JACQUES LOEB 



The Rockefeller Institute, New York 



NINETEEN FIGURES 



1. The study of heredity in embryos offers in one respect a 

 wider field than that in adults inasmuch as heterogeneous hybrids 

 rarely reach the adult stage. Eight years ago I found a method 

 by which the eggs of the sea-urchin can be fertilized by the 

 sperm of starfish, ophiurians and holothurians. The larvae 

 are purely maternal, namely plutei. The results were confirmed 

 by Godlewski for the fertilization of the egg of the sea-urchin 

 by the sperm of the crinoid. It is well known that if we cross 

 two homogeneous forms, e.g., two forms of sea-urchins, the pater- 

 nal influence can be clearly seen in the pluteus stage. Since I 

 have never published the figures of my experiments on hetero- 

 geneous hybridization, I may supplement my former statements 

 with a few drawings. Figs. 1 to 6 are camera drawings of plutei 

 of Strongylocentrotus purpuratus produced by artificial parthe- 

 nogenesis. The plutei are, of course, in every detail identical 

 with the plutei obtained if these eggs be fertilized with sperm of 

 their own species. Figs. 7 to 9 are drawings of five days old 

 plutei of Strongylocentrotus purpuratus 9 and Strongylocentrotus 

 franciscanus &. They differ from the pure breeds of S. purpuratus 

 in several characters of the skeleton which exist in the pluteus 

 of franciscanus but are absent from purpuratus, namely the 

 greater roughness of the skeleton, the presence of cross bars and 

 the greater length of the arms.^ In figs. 10 to 13 are shown the 

 five days old plutei of the egg of S. purpuratus fertilized with 

 the sperm of the starfish (Asterias) . It is obvious that the latter 



1 Prepared for the Whitman Memorial Volume but received too late to be 

 included. 



2 Loeb, King and Moore, Arch. f. Entwicklungsmechanik, vol. 29, 1910. 



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JOURNAL OF MORPHOLOGY, VOL. 23, NO. 1 * 



MARCH 20, 1912 



