162 MR JAMES DEWAR AND DR M‘KENDRICK ON THE 
XJII.—EXPERIMENTS ON THE EYES oF AMPHIBIA AND REPTILES. 
Observations have been made on—(1), the frog (ana temporaria) ; (2), the 
toad (Bufo vulgaris); (3), the newt (Triton aquaticus) ; and (4), a snake (species 
unknown). Those made on the frog have been already fully described. The 
action on the eye of the toad was found to be exactly similar to that of the 
frog, only the variations were much more sluggish. In the case of the newt, 
the eye was found to be sensitive to light to the extent of about 12 per cent. of 
the electro-motive force. It was found also to be sensitive to a flash of light. 
These results were obtained in an eye having the following dimensions :— 
Transverse diameter of eye, 4th of an inch. 
Diameter of the pupil, th of an inch. 
Diameter of the lens, ;5th of an inch. 
The eye of the snake* resembled that of the frog. 
XIV.—EXPERIMENTS ON THE ACTION OF LIGHT ON THE COMPOUND EYE. 
We have examined the eyes of the following crustaceans, namely—(1), the 
common edible crab (Cancer pagurus) ; (2), the swimming crab (Portunus puber) ; 
(3), the spider crab (yas coarctatus; (4), the hermit crab (Pagurus Bernhardus) ; 
and (5), the lobster (Homarus vulgaris). 
1. The Common Edible Crab——In this case it was found that the nerve 
surface was positive to the other parts of the eye, not negative, as had been 
shown in the simple eye of various vertebrate animals. A deflection was 
obtained to the extent of about 300° of the scale of the galvanometer. The 
effect of light was to increase the current from 5° to 10° of the galvanometer 
scale, then to fall slightly. During the action of light the deflection remained 
very permanent, and on the withdrawal of light it fell. 
2. The Lobster.—With this eye the following points were noted :— 
(1.) The direction of the current was reversed, as in the case of the crab, 
that is to say, the corneal surface was negative, not positive, as was observed in 
the simple eye. 
(2.) A deflection of about 600° of the scale were obtained with the smallest 
possible contact of the clay points with the cornea and nerve surface. 
(3.) The action of light was to diminish the current to the extent of 10 per 
cent of the total amount of deflection, and the inductive effect, or effect of 
removal of light, was nearly equal to the depression produced by the impact of 
light. 
* Kindly sent us by Mr Barruert of the Zoological Gardens, Regent’s Park. Genus and species 
not given. 

