THE SENSE OF SMELL IN SELACHIANS 57 



the baited hook. At length they gradually rise, turning some- 

 what sidewise, as stated by Field, to seize the bait. When the 

 food is lying on the bottom this sidewise turning was never ob- 

 served. 



Observation of the feeding habits of the dogfish would indicate, 

 then, that it recognizes its food through some chemical sense. 

 To test this the following experiments were performed. 



Some fresh eel grass was secured and two packets, closely re- 

 sembling each other were made, one containing a small stone 

 while the other enclosed a crab. Both were so tied that when 

 placed in the water a foot apart, a portion of the grass rose toward 

 the surface giving an appearance similar to the grass of the pool. 

 In three sets of experiments the presence of food was detected 

 in an average time of three minutes, the packet found by the usual 

 procedure, torn apart, and the crab eaten. At no time did the 

 packet containing the stone receive the slightest attention. 



Next two packets of white cheese cloth of a similar size and 

 appearance, were made up. One of these contained a stone, the 

 other a crab. This experiment was repeated four times on differ- 

 ent days. The packet containing the crab was found in each 

 case in from three to five minutes while the one with the stone was 

 never molested. The two packets were placed from ten inches 

 to three feet apart. Once or twice a dogfish which had eaten a 

 crab would return and, circling about the spot where the crab 

 had been found, would approach the packet containing the stone 

 in an inquiring sort of way but at no time touched it. The packet 

 containing the crab was always shaken and bitten until the food 

 could be removed and eaten. 



A crab was killed and a piece of white cheese cloth saturated in 

 its juices- This was then attached to a small stone. In two 

 experiments the presence of a food substance was noted in two 

 minutes. The stimulus was located by the usual circling method 

 and the stone, with its saturated cloth, seized again and again 

 and shaken violently . After a half hour the fish took no further 

 notice of it, probably due to a complete diffusion of the juices into 

 the water. 



