SARGENT : THE OPTIC KEFLEX APPARATUS OF VERTEBRATES. 229 



mouth and firmly held there, a stream of sea-water was kept flowing 

 through the gills. In a few seconds the animal began to respire regu- 

 larly, and ceasing its struggles, which were due to partial asphyxiation, 

 remained quiet upon the table during the operation. If, however, tlie 

 tube became displaced, or the flow of water was interrupted, it struggled 

 violently. Pressure applied to the snout will call forth similar reac- 

 tions. Aside from these regions, the shark seemed utterly devoid of any 

 sense of feeling, and I have been unable to observe the slightest reaction 

 to the knife. In the operation aseptic precautions were used as far as 

 possible, thougli it is doubtful if they were efficient enough to be of 

 value. All instruments and materials used were kept in a I to 2 per 

 cent solution of carbolic acid. An incision, Z- or L-shaped, was made 

 through the skin in a region previously determined upon, above the 

 fourth ventricle. A triangular bit of cartilage was then removed, exposing 

 the vascular tela. Through this a fine cambric needle, curved at the 

 point as before described, was inserted and drawn several times trans- 

 versely across the ventricle to insure breaking the fibre. At the point 

 where the tela was punctured, there was a slight hemorrhage. The 

 wound was then washed with 1 per cent carbolic acid, and closed with 

 a cotton plug saturated in carbolated vaseline. The integument was 

 then drawn together and closed by a number of sutures, and the 

 wound rubbed over with vaseline to render it as nearly as possible 

 waterproof. 



The animal was then tagged for identification, and returned to the 

 water, after having been out of water some ten to twenty minutes. 

 Some of the sharks were put in ' The Pool,' a shallow enclosure 20 

 by 30 feet, others in the floating cage before-mentioned. Their be- 

 havior was closely watched for the first few hours, and observations 

 made several times a day for a number of days, or until death ensued. 

 Their general behavior and reactions to optical stimuli were compared 

 with those of normal animals which had not been operated upon, but 

 were confined in the same enclosure. 



3. Experiments. 



Six spiny dog-fish (Squalus), three smooth dog-fish (Mustelus), and 

 two sand sharks (Charcharias) were experimented upon in this way. 

 Squalus j^fo. 1, during the first ten minutes after the operation, swam 

 about sluggishly on its back, head downward, or rested upon the bottom. 

 In half an hour it had partially, and in two hours wholly, recovered 

 from the operation, and swam about quite normally, keeping near the 



