426 [Feb. 5. 



may exist without the capacity of combining chemically, or, in other 

 words, without chemical affinity. Chemical affinity (a very inap- 

 propriate term) is only known by combination ; the previous attrac- 

 tion has never yet been shown to be of two kinds ; and it seems more 

 in accordance with Nature to diminish than to increase the number 

 of original powers. 



February 5, 1863. 



Major-General SABINE, President, in the Chair. 

 The Earl of Caithness was admitted into the Society. 

 The following communication was read : 



" On the Embryogeny of Comatula rosacea (Linck)." By Pro- 

 fessor WYVILLE THOMSON, LL.D., F.R.S.E., M.E.I.A., 

 F.G.S. &c. Communicated by Professor HUXLEY. Re- 

 ceived December 29, 1862. 



(Abstract.) 



After briefly abstracting Dr. W. Busch's description of the early 

 stages in the growth of the young of Comatula, the author details 

 his own observations, carried on during the last four years, on the 

 development and subsequent changes of the larva. After complete 

 segmentation of the yelk, a more consistent nucleus appears within 

 the mulberry mass still contained within the vitelline membrane. 

 The external more transparent flocculent portion of the yelk liquefies 

 and is absorbed into this nucleus, which gradually assumes the form 

 of the embryo larva, a granular cylinder contracted at either end and 

 girded with four transverse bands of cilia. This cylinder increases 

 in size till it nearly fills the vitelline sac, gradually increasing in 

 transparency, and ultimately consisting of delicately vacuolated sar- 

 code, the external surface transparent and studded with pyriform 

 oil-cells, the inner portion semifluid and slightly granular. 



The vitelline membrane now gives way, and, usually shortly after 

 the escape of the larva into the water, the third ciliated band from the 

 anterior extremity arches forwards at one point ; and in the space thus 

 left between it and the fourth band, a large pyriform depression indi- 



