168 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



II. OBSERVATIONS. 

 A. The Photic Reactions of Normal Amphibians compared 



WITH THOSE FROM WHICH THE EyES HAVE BEEN REMOVED. 



In order to compare the reactions of amphibians in which both the 

 skin and eyes acted as photoreceptors with those in which only the 

 skin was open to stimulation, individuals were tested both in normal 

 condition and after the eyes had been excised. The eyes were usually 

 removed by making a single transverse cut as near the anterior edge 

 of the ear drums as possible. The whole front of the head, including 



the olfactory lobes and a 

 part of the cerebral hemi- 

 spheres, was removed by 

 this method of procedure 

 (Figure 1). In Necturus 

 and Cryptobranchus, how- 

 ever, only the eyes were 

 excised. All the species 

 stood the operation well 

 and subsequently gave typ- 

 ical reactions, except Pleth- 

 odon and Diemyctylus, 

 which were apparently much 

 weakened by it and were 

 indifferent to light after the 

 eyes had been removed. As 

 a rule individuals were not 

 used for experimentation 

 until the day after the oper- 

 ation. 

 The species studied fall naturally into two groups, aquatic and 

 terrestrial. The former group included Necturus maculosus and Cryp- 

 tobranchus allegheniensis, and the terrestrial species studied were 

 Amblystoma punctatum, Plethodon cinereus, Diemyctylus viridescens, 

 Ran a clamata, R. sylvatica, Bufo fowleri, "and B. americanus. The 

 reactions of each species will be considered separately. 



(a) Necturus maculosus. 



The first experiments with this species were intended to show what 

 influence light had upon its movements. Four individuals were 

 placed successively in the centre of a large aquarium, which was illu- 



Figtjre 1. Dorsal view of toad's head 

 showing the position of the brain. The dotted 

 line indicates the plane of the cut used in 

 removing the eyes, e, eye; r, ear. 



