Royal Institution. 473 



position to trace a parallelism between the oesophageal nervous 

 centres of these Mollusca and the cerebro-spinal system of the Ver- 

 tebrata, and accordingly they find there is a strict analogy between 

 them, even to the individual pairs of ganglia of which they re- 

 spectively consist, the general result being that the whole of the 

 ganglia, grouped around the oesophagus in these Mollusca, answers 

 to the encephalon, and a small portion of the enrachidion, of the 

 Vertebrate. 



Organs of the Senses. — The auditory capsules are microscopic, 

 composed of two concentric vesicles, the inner enclosing numerous, 

 oval, nucleated otolithes. The eyes are minute black dots, beneath 

 the skin, attached by a pedicle to a small ganglion. They are 

 made up of a cup of pigment, receiving from behind the nerve, and 

 lodging in front a lens, having in advance of it a cornea, the whole 

 enclosed by a fine capsule. The authors believe they have shown 

 the dorsal tentacles to be the olfactory organs. 



The organs of touch are, the general surface of the skin, but 

 more particularly the oral tentacles or veil. Taste is most probably 

 located in the lips and channel of the mouth, the tongue being a 

 prehensile organ, and ill-adapted as the seat of such a function. 



In conclusion, the authors comment on the high organization of 

 the Doridce, and express their belief that the genus, as at present 

 understood, will require to be broken up into several groups. 



ROYAL INSTITUTION OF GREAT BRITAIN. 



Friday, April 2, 1852. — On the Blackheath Pebble-bed, and on 

 certain Phsenomena in the Geology of the Neighbourhood of London. 

 By Sir Charles Lyell. 



There are two kinds of flint-gravel used for making roads in the 

 neighbourhood of London, both of them in certain places superficial, 

 but which are of extremely different ages. The yellow gravel of 

 Hyde Park and Kensington so often found covering the "London 

 Clay " may be taken as an example of one kind ; that of Blackheath, 

 of the other. The first of these is, comparatively speaking, of very 

 modern date, and consists of slightly rolled, and, for the most part, 

 angular fragments, in which portions of the white opake coating of 

 the original chalk flint remain unremoved. The more ancient gravel 

 consists of black and well-rounded pebbles, egg-shaped or spherical, 

 of various sizes, exhibiting no vestige of the white coating of the ori- 

 ginal flints, yet showing by the fossil sponges and shells contained in 

 them that they are derived from the Chalk. In the pits of Black- 

 heath and the neighbourhood, where this old shingle attains at some 

 points a thickness of 50 feet, small pieces of white chalk sometimes 

 occur, though very rarely intermixed with the pebbles. If we meet 

 with thoroughly rounded flints in the more modern, or angular 

 gravel, it is because the latter has been in part derived from the de- 

 nudation of the older bed. 



The researches of the Rev. H. M. De la Condamine have shown 

 that the sand and pebble-beds of Blackheath and Greenwich Park, 

 inclose in some of their numerous layers, freshwater shells of extinct 



