1911.] 



Studies in Heredity. 



403 



In conclusion, I may point out that the types of sea-urchin represented by 

 Echinus and Echinoeardium have been distinct since the beginning of the 

 Secondary epoch and that their common ancestor could not have lived later 

 than a period which a moderate estimate would place at 20,000,000 years 

 ago ; yet the germ-cells of the two types will commingle so as to produce 

 a hybrid in which both paternal and maternal characters are represented. 



LIST OF WORKS REFEREE D TO IN THIS PAPER. 



(1) Doncaster, L. "Experiments in Hybridisation, with Special Reference to the Effect 



of Conditions on Dominance,'' ' Phil. Trans.,' 1904, B, vol. 196. 



(2) Fischel. "Uber Bastardierungsversuche bei Echinodermen," 'Arch, fiir Entw.- 



Mech.,' 1906, vol. 22. 



(3) Godlewski. " Untersuchungen iiber die Bastardierung der Echiniden- und Crinoiden 



familien," 'Arch, fiir Entw.-Mech.,' 1906, vol. 20. 



(4) Hagedoorn. "On the purely Motherly Character of the Hybrids produced by 



crossing the Species Strongylocentrotiis fnaieisranus and iSti'<m<///l<>cr/itrotus pur- 

 puratus" 1 Arch, fiir Entw.-Mech.,' 1909, vol. 27. 



(5) Herbst. " Vererbungs Studien," I— V, 'Arch, fiir Entw.-Mech.,' 1906, vol. 22, and 



1907, vol. 24. 



(6) Kupelwieser. " Entwicklungserregung bei See-igel-eier durch Mollusken Sperm," 



'Arch, fiir Entw.-Mech.,' 1909, vol. 27. 



(7) Loeb. " TJber die Natur der Bastardlarven zwischen Echinodermen- und Mollusken- 



samen," 'Arch, fiir Entw.-Mech.,' 1909, vol. 26. 



(8) Loeb. ' Die Chemische Entwicklung des tierischen Eies,' Jena, 1909. 



(9) Loeb, Redman King, and Moore. " Uber Doniinanz-erscheinungen bei den hybriden 



Pluteen des Seeigels," 'Arch, fiir Entw.-Mech.,' 1909, vol. 27. 



(10) MacBride, E. W. "The Development of Echinoids. Part I. — The Larvte of 



Echinus miliaris and Echinus escidentus," 'Quart. Journ. Micro. Sci.,' 1899, vol. 42 

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(11) Shearer, G, De Morgan, W., and Fuchs, H. M. " Preliminary Notice on the 



Experimental Hybridization of Echinoids," 'Journ. Marine Biol. Assoc.,' 1911, 

 vol. 9, No. 2. 



(12) Tennent, D. "The Dominance of Maternal or Paternal Characters in Echinoderm 



Hybrids," 'Arch, fur Entw.-Mech.,' 1910, vol. 29. 



(13) Vernon, H. "The Relations between the Hybrid and Parent Forms in Echino- 



derm Hybrids," ' Phil. Trans.,' 1898, B, vol. 190. 



