240 



Studies in Heredity. II. — Further Experiments in Grossing 

 British Species of Sea-urchins* 

 By E. W. MacBride, F.B.S. 



(Keceived October 27, — Read November 6, 1913.) 



Two years ago I read a paper before the Society in which I gave the results 

 which I had obtained by crossing the two species of sea-urchin Echinus 

 esculentus and Echinocardium cordatum. The first of these is a regular urchin, 

 the second an enocyclic urchin belonging to the order Spatangoidea. The 

 results recorded in that paper were briefly these : — The egg of Echinocardium 

 fertilised by the sperm of Echinus gives rise to a hybrid which exhibits a 

 mixture of maternal and paternal characters, but only a small proportion of 

 the hybridised eggs develop. The egg of Echinus fertilised by the sperm of 

 Echinocardium, develops a fertilisation membrane, but then breaks up into a 

 heap of globules by the process known as cytolysis, and dies. 



Since writing that paper my experiments were repeated at Plymouth by 

 Fuchs,f now my colleague at the Imperial College, and he obtained different 

 results. According to him the eggs of Echinus fertilised by the sperm of 

 Echinocardium gave rise to hybrid larvae which were maternal in character, 

 whilst the eggs of Echinocardium fertilised by the sperm of Echinus gave rise 

 to hybrids of two kinds, some purely maternal in type and some resembling 

 those which I had obtained. 



As I suspected that some of the divergences between the results of Fuchs 

 and myself might be due to the accidental infection of the sea-water used 

 with the sperm of the species of which the eggs were taken, a circumstance 

 which would produce larvae of purely maternal character, I resolved to 

 repeat my experiments, and accordingly this summer I proceeded to Millport, 

 where my first experiments were performed. I have to thank Mr. Elmhirst, 

 Superintendent of the Marine Biological Station at Millport, for the way in 

 which he aided my efforts. To his kindness I owe the successful issue of my 

 experiments. 



The results which I obtained during this last summer prove that my 

 suspicion as to the cause of the divergence between Fuchs's results and my 

 own was entirely unfounded, for this year I obtained larvae by fertilising the 



* "Studies in Heredity. I. — The Effects of Crossing the Sea-urchins Echinus 

 esculentus and Echinocardium cordatum." 'Roy. Soc. Proc.,' 1911, B, vol. 84. 



t " The Inheritance of the Aboral Process of the Echinocardium Pluteus," ' Arch, 

 Entw.-Mech.,' 1912, vol. 35. 



