Studies in heredity. II.—Further experiments in crossing British species of sea-urchins

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-urchinEchinus esculentus andEchinocardium 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 ofEchinocardium fertilised by the sperm ofEchinus 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 ofEchinus fertilised by the sperm ofEchinocardium 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, now my colleague at the Imperial College, and he obtained different results. According to him the eggs ofEchinus fertilised by the sperm ofEchinocardium gave rise to hybrid larvæ which were maternal in character, whilst the eggs ofEchinocardium fertilised by the sperm ofEchinus gave rise to hybrids of two kinds, some purely maternal in type and some resembling those which I had obtained.