98 Miscellaneous. 



lighter than that upon which the animal can see ; the ablation of 

 both eyes restores the equilibrium. 



9. Curare does not act upon the colorator nerves, the excitation 

 of which induces the light tint when the motor nerves no longer pro- 

 duce muscular contraction ; eserine(physostigmine), on the contrary, 

 acts first upon the colorator nerves. 



10. Light gives a dark tint to the portions of the skin that it 



strikes (C. Perrault, Vrolik, Brucke). This action, which 



is exceedingly distinct during sleep, during anaesthesia, and after 

 death, is very manifest even during the waking state. It takes 

 place through dark blue glass, but not through red and yellow 

 glasses.' 



Conchisions. — From the whole of these facts the following con- 

 clusions may be drawn : — 



a. The various colours and tints that chameleons assume are due 

 to the change of position of the coloured corpuscles, which, accord- 

 ing as they bury themselves under the dermis, or form an opaque 

 ground beneath the caerulescent layer, or spread out in superficial 

 ramifications, either leave the skin its yellow colour or give it green 

 and black colours. 



b. The movements of these corpuscles are governed by two kinds 

 of nerves, some of which cause them to travel from the depths towards 

 the surface, while the others produce the opposite effect. In the 

 state of maximum excitation these corpuscles conceal themselves be- 

 neath the dermis ; this is also the case in the state of complete 

 repose (sleep, anaesthesia, death). 



c. The nerves which cause the corpuscles to flow back beneath 

 the dermis have the greatest analogies with the vaso-constrictor 

 nerves. 



Like these, in fact, they follow the mixed nerves of the limbs and 

 the great sympathetic of the neck ; like them they do not intercross 

 in the spinal marrow ; like them they have their origin for the head 

 at the commencement of the dorsal region ; like them they possess a 

 very powerful reflex centre in the medulla oblongata, the entire 

 spinal marrow being another much less energetic centre ; like them 

 they are not afiected by curare and poisoned by eserine. 



d. The nerves which bring the corpuscles towards the surface are 

 comparable to the vaso-dilatator nerves ; but although we are forced 

 to assume their existence, it is difficult to say any thing very distinct 

 as to their anatomical distribution and their relations to the nervous 

 centres ; it is vei-y probable that they traverse nervous cells before 

 passing to the colouring corpuscles. 



e. Each cerebral hemisphere, by the intermediation of the reflex 

 centres, governs the colorator nerves of both sides of the body ; but 

 it acts principally upon the nerves analogous to the vaso- constrictors 

 of its own side, and on the nerves analogous to the vaso-dilatators 

 of the opposite side. 



In the regular condition of things each hemisphere comes into 

 play (besides the excitations arising by general sensibility) under 



