388 



Dr. J. C. Ewart. 



[Apr. 27, 



much diminished, as it normally is on the upper side, and it is sug- 

 gested that possibly there is an inverse physiological relation between 

 the formation of guanin and the formation of pigment. 



We conclude that exposure to light does actually cause the develop- 

 ment of pigment in the form of normal chromatophores on the lower 

 side of the Flounder, and also causes the absorption of the argenteum 

 to a great extent. We infer, in spite of the occurrence of congenital 

 abnormalities, that the exclusion of the light from the lower sides of 

 Flat Fishes is the cause of the absence of pigment from that side in 

 normal specimens. We think that the fact that the metamorphosis 

 of the Flounder takes place at first normally, in spite of the light 

 coming from below and being shut off from above, is, in respect of 

 the pigmentation, in favour of the inheritance of acquired characters. 

 When the exposure is continued long enough, the change that has 

 taken place in consequence of heredity is reversed, and pigment 

 appears. 



We have discussed briefly the question of the physiological process 

 of the formation of the pigment, but we have at present no decisive 

 result to offer in this part of the subject, and need not include it in 

 this abstract. 



We consider that these investigations afford support to the view 

 that the incidence of light is the reason why the. upper and dorsal 

 surface of animals is more strongly pigmented than the lower or 

 ventral throughout the animal kingdom, and that the absence of 

 light is the cause of the disappearance of pigment in many cave-in- 

 habiting and subterranean animals. 



III. " The Electric Organ of the Skate : Note on an Electric 

 Centre in the Spinal Cord." By J. C. Ewart, M.D., Regius 

 Professor of Natural History, University of Edinburgh. 

 Communicated by Professor Sir W. TURNER, F.R.S. Re- 

 ceived March 15, 1893. 



Having considered the development and structure of the electric 

 organ of the Skate, it appeared to me desirable, by way of making my 

 work more complete, to reinvestigate the nervous apparatus of the 

 organ, and more especially to ascertain whether, as in Torpedo and 

 Gymnotus, there is an electric centre. In Torpedo the electric 

 organs are developed from a limited number of myotomes, and inner- 

 vated by afferent fibres, belonging to a limited number of cranial 

 nerves, which proceed from two large collections of cells — the electric 

 lobes — situated in the region of the medulla. In Gymnotus the nerves 

 for the electric organs proceed from two well-marked cellular tracts 



