BY THE GENERAL SURFACE OF THE SKIN. 205 



anterior extremity of the body, where the cerebral 

 ganglia lie, which is affected by light, and he suggests 

 that the light may pass through the skin and acts 

 directly on the nervous centres. 



Lacaze-Duthiers, Haeckel, Engelmann, Graber, 

 Plateau, and other naturalists have abundantly proved 

 the sensitiveness to light of other eyeless animals. 



There has, indeed, long been a vague idea that blind 

 people have some faint perception of light through the 

 general surface of the skin. So far as I am aware 

 there is not the slightest evidence or foundation for this 

 belief; nor, indeed, has it been advocated by any com- 

 petent authority. It seems a priori improbable that 

 an animal with complex eyes should still retain a 

 power which would be almost entirely useless. 



On the other hand, it is unquestionable that light 

 can, and often does, act directly on the nerve termi- 

 nations without the intermediate operation of any 

 optical-apparatus. 



Some of them might, perhaps, be open to criticism. 

 The effect of heat may not have been always suflSciently 

 guarded against. Again, it is quite true that, as Plateau 

 observes " Lorsque les Myriapodes chilopodes aveugles 

 ou munis d'yeux, deposes sur le sol, s'introduisent avec 

 empressement dans la premiere fente qu'ils rencon- 

 trent, cet acte n'est pas determine par le seul besoin de 

 fuir la lumiere, ces animaux cherchent en meme temps 

 un milieu humide et avec lequel la plus grande partie 

 de la surface de leur corps soit en contact direct." * 

 But though this is no doubt true, and though, perhaps, 

 the moisture may be some help, still, whatever be their 



* Plateau, " Rech. sur la perception de la lumiere par les Myriapodes 

 aveugles/' Jour, de VAnatomie, etc., T. xxii. 1886. 



