104 Darwin, and after Darwin. 



which, with other objects in view, have incidentally 

 yielded seemingly good evidence of such transmission. 

 The best-known of these researches and therefore 

 the one with which I shall begin is that of Brown- 

 Se*quard touching the effects of certain injuries of the 

 nervous system in guinea-pigs. 



During a period of thirty years Brown-Se*quard 

 bred many thousands of guinea-pigs as material for 

 his various researches ; and in those whose parents 

 had not been operated upon in the ways to be 

 immediately mentioned, he never saw any of the 

 peculiarities which are about to be described. There- 

 fore the hypothesis of coincidence, at all events, must 

 be excluded. The following is his own summary 

 of the results with which we are concerned : 



1st. Appearance of epilepsy in animals born of parents which 

 had been rendered epileptic by an injury to the spinal cord. 



2nd. Appearance of epilepsy also in animals born of parents 

 which had been rendered epileptic by section of the sciatic nerve. 



3rd, A change in the shape of the ear in animals born of 

 parents in which such a change was the effect of a division 

 of the cervical sympathetic nerve. 



4th. Partial closure of the eyelids in animals born of parents 



pigment-cells from the lower side throughout life is due to the fact 

 that light does not act upon that tide, for, when it is allowed to 

 act, pigment-cells appear. It eems to me the only reasonable con- 

 clusion from these facts is, that the disappearance of pigment-cells was 

 originally due to the absence of light, and that this change has now 

 become hereditary. The pigment-cells produced by the action of light 

 on the lower side are in all respects similar to those normally present 

 on the upper side of the fish. If the disappearance of the pigment-cells 

 were due entirely to a variation of the germ-plasm, no external influence 

 could cause them to reappear, and, on the other hand, if there were no 

 hereditary tendency, the colouration of the lower side of the flat-fish 

 when exposed would be rapid and complete." Natural Sfunct, 



