198 PROCEEDINGS OF THE AMERICAN ACADEMY. 



progressively backward in successive operations; the light reactions 

 being tested at each step. On account of the large size of their 

 brains, Necturus and Cryptobranchus were used for these experiments. 

 The individuals were wrapped in a damp cloth, the head being allowed 

 to protrude ; and a T-shaped incision was then made in the skin on the 

 dorsal side of the head, the stem of the T being toward the anterior 

 end ; after this the muscles were cut away and the bony roof of the 

 cranial cavity carefully picked away with a pair of strong forceps. 

 The brain was then cut across with a pair of scissors or a sharp 

 scalpel and the parts anterior to the cut removed. The flaps of skin 

 were drawn over the wound and stitched together with silk thread. 

 The success of such operations was verified by subsequent dissection. 

 The method used in testing photic reactions was to throw a vertical 

 band of light (which had an intensity of about 220 candle-meters at the 

 point where the animals were placed) upon the anterior or posterior end 

 of an individual, and to observe the responses which took place. As 

 such responses were like those previously described (p. 169), they need 

 not be discussed in detail. 



For a preliminary test as to the effect of such an operation as has 

 just been described, aside from the actual cutting of the brain itself, 

 the roof of the cranial cavities was removed from four individuals and 

 the brain was left exposed to the water in which they were kept. These 

 individuals seemed to be little affected by the operation, as they swam 

 and walked in a normal manner ; and when (twenty-four hours later) 

 light was thrown on the anterior or posterior end of any one of them, 

 it reacted in the same manner as an individual in which only the eyes 

 had been excised. The exposure of the brain had, then, no obvious 

 effect on the photic reactions of Necturus. 



The eyes and telencephalon were next removed from six individuals, 

 and five of them gave marked responses to light on the day after the 

 operation. The other individual, which lived for fifteen days, gave no 

 photic responses until the third day after the cerebral lobes had been 

 excised, though it had apparently recovered from the operation before 

 that time. These animals could doubtless have been kept alive for a 

 long time if it had not been for the Saprolegnia which grew abundantly 

 around the cut surfaces, and, even with this handicap, one of them 

 lived for fifty days. The cerebral lobes are not, then, essential for 

 the photic reactions of Necturus. 



Owing to the scarcity of material, the number of operations had to 

 be limited in the remaining experiments. The portions of the brain 

 anterior to the mesencephalon were, therefore, excised in only one 

 Necturus. This individual lived for twelve days and gave character- 



