The few experiments on the hybridisation of the Echinoderms of which I am now giving the results were commenced on the advice of Professor MacBride, who himself had made similar experiments on other species. At his suggestion I chose Echinus miliaris, Echinus esculentus and Echinus acutus, in order to verify the interesting results obtained by Shearer, De Morgan and Fuchs (‘ll) in their experiments on these species. I should like in the first place to express my thanks to Professor Sedgwick, who so kindly received me at his institute, and to Professor MacBride, who has helped me so much by his valuable advice and has placed at my disposal material which he had himself collected.