THE SENSE OF SMELL IN SELACHIANS 55 



24 feet long, 8 feet wide at one end and 10 feet wide at the other, 

 with normal sea bottom, an irregular stone wall on three sides, 

 and a depth of water of from two to eight feet, depending on the 

 portion of the pool considered and the height of the tide. Tufts 

 of eel grass, together with many other varieties of sessile marine 

 life, grew on the bottom and sides. The pool, therefore, fulfills, 

 to a reasonable degree, the conditions of normal life, so far as the 

 dogfish are concerned. 



The individuals used were those caught in the traps from day 

 to day, and placed in the pool for a period of ten days in order 

 to bring about a state of hunger. 



Experiments with normal fishes 



Spider or blue crabs were first offered the dogfish, but were 

 always left untouched. The rock crab. Cancer irroratus, was 

 next tried with success, and used for all the experimental work. 

 All experiments were conducted at low tide when it was easy to 

 observe the actions of the individual fishes. At first living crabs 

 were used. These are found by the dogfish in from ten to fifteen 

 minutes. Next, crabs were killed and a hole broken in the cara- 

 place, exposing the flesh. Such are found in from two to five 

 minutes. These results suggest, at the start, that food is recog- 

 nized through the diffusion of animal juices into the water. Crabs 

 killed, with the flesh thus exposed, were used for all further work. 



In a total of about forty experiments the method of feeding was 

 the same in all cases. The dogfish spend most of the time swim- 

 ming lazily around the pool, usually close to the sides. Now and 

 then the direction is reversed, but at no time was there observed 

 any search over the bottom or the rocks forming the sides of the 

 pool. When a crab is placed in the pool a few minutes are re- 

 quired, as noted, before any evidence of stimulation is to be seen. 

 Then one of the dogfish, which happens to be swimming within 

 three or four feet of the crab, seems suddenly startled. It 

 turns very suddenly and swimming with quick, nervous motions, 

 instead of the calm, lazj^ movement of the unstimulated fish, be- 

 gins a systematic search over the bottom, investigating particu- 



