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January 13, 1859. 

 SIR BENJAMIN C. BRODIE, Bart., President, in the Chair. 



I. " On the Embryogeny of Comatula Rgsacea (Linck)." By 

 WYVILLE THOMSON, Esq., Professor of Geology in Queen's 

 College, Belfast. Communicated by Dr. CARPENTER. 

 Received December 7, 1858. 



(Abstract.) 



The author briefly described the male and female reproductive 

 organs of Comatula. When the ova are mature, and before impreg- 

 nation, they are protruded and remain hanging from the ovarian 

 orifice, entangled in the areolar tissue of the everted ovary. In 

 this position impregnation appears usually to take place. 



After segmentation of the yelk, a solid nucleus is formed in the 

 centre of the mulberry yelk-mass. This nucleus becomes invested 

 in a special membrane, and into this embryonic mass the remainder 

 of the yelk is gradually absorbed. Ciliary motion is observed at 

 various points on the surface of the inclosed embryo, which finally 

 assumes its characteristic form. The young larva, on escaping from 

 the egg, consists of a homogeneous mass of pale-yellow granular 

 matter, with scattered nuclei, cells, and oil-globules. It is barrel- 

 shaped, and girded at intervals with about five broad ciliated bands. 



As development proceeds, one of these belts becomes depressed at 

 a certain point ; and within the loop thus formed, an inversion of the 

 integument indicates the position of the rudimentary mouth. 



A distinct oesophagus and stomach are rapidly differentiated, and 

 a short intestine, ending in a large anal orifice, near the posterior 

 extremity of the animal. The larva at the same time becomes 

 lengthened and vermiform ; the girding ciliated bands resolve them- 

 selves into a single transverse band, encircling the body near the 

 anterior extremitv, and a band passing below the mouth and longi- 

 tudinally down either side to the tail. 



Large lobulated masses of fine granular tissue occupy the cavity 

 of the body on either side of the alimentary canal. 



The echinoderm-zooid originates, apparently, beneath the integu- 

 ment of the larva, but perhaps in an inversion of that integument, 



