Meeting of May 12, 1898. 231 



yielded only gastmlae. Finally, hybrids, of a presumably inter- 

 mediate character, were obtained from the cross .Echinus microtuber- 

 culatus ? and Echinus acutusg . With the ova of Sphcerechinus and 

 Echinocardium, and the sperm of Echinus acutus, only gastrulae were 

 obtained. 



On performing cross-fertilisations with the colour varieties of 

 Sphcerechinus, there was found to be a distinct diminution of fertility. 

 In the most marked instance, obtained in the experiments made on 

 June 2, it was found that when white-spined varieties were fertilised 

 with white-spined, and violet-spined with violet, 98' 5 per cent, of 

 the ova reached the blastula stage, and 73 per cent, the eight days 

 pluteus stage. But on cross-fertilising white-spined with violet- 

 spined individuals, only 68 per cent, of the ova developed to 

 blastulee, and 15'6 per cent, to plutei. Also these crossed larvae were 

 4'5 per cent, smaller than the uncrossed. Other series of experi- 

 ments were made in July, November, and December, the differential 

 fertility seeming to gradually diminish with the progress of the season. 

 Nevertheless, it was always most distinctly present. On crossing the 

 less definitely marked colour varieties of Strongylocentrotus, a small 

 amount of infertility seemed to be present in one series of experi- 

 ments, but none at all in another. 



May 12, 1898. 

 The LORD LISTER, F.R.C.S., D.G.L., President, in the Chair. 



Professor Dewar made a preliminary communication " On the 

 Liquefaction of Hydrogen and Helium." 



He prefaced his statement by referring to a letter which he had 

 addressed to the President on the lOfch May, announcing to him the 

 fact that he had succeeded in liquefying hydrogen in quantity, and 

 that by means of the liquid hydrogen he had also liquefied helium. 



The following Papers were also read : 



I. " On the Magnetic Susceptibility of Liquid Oxygen." By Pro- 

 fessor FLEMING, F.R.S., and Professor JAMES DEWAR, F.R.S. 



II. "A Study of the Phyto-Plankton of the Atlantic." By GL 

 MURRAY, F.R.S. , and Y. H. BLACKMAN. 



III. " The Electric Response of Nerve to a single Stimulus investi- 

 gated with the Capillary Electrometer. Preliminary Com- 

 munication." By Professor GOTCH, F.R.S., and G-. J. BURCH. 

 VOL. LXIII. s 



