54 RALPH EDWARD SHELDON 



also, that a fish in forward locomotion forces water through the 

 nostrils. A dogfish is, therefore, whether in motion or at rest, 

 constantly receiving through its nasal capsules, a current of water. 



in. THE REACTIONS OF THE DOGFISH TO OLFACTORY STIMULI 



The experiments here recorded were performed on the smooth 

 dogfish, Mustelus canis (Mitchell). This was selected owing to 

 its great abundance in Buzzard's Bay near Woods Hole, and also 

 because previous experimentation (Sheldon, '09) rendered many 

 of its habits and reactions familiar. 



Feeding habits 



Bateson, Nagel, and others believed that Selachians recognize 

 their food through the sense of smell ; their evidence, as has been 

 noted is valueless, however, in this connection. Mr. Vinal 

 Edwards, Collector at the Woods Hole Station of the Bureau 

 of Fisheries, states that it is the custom, in fishing after dog- 

 fish, to throw out in the tide lines baited with menhaden or ale- 

 wives. For a time no dogfish will be seen, then they will appear 

 in numbers, swimming aroimd the bait in graduall}^ diminish- 

 ing circles until finally it is seized. Field ('07), finds that the 

 dogfish carefully search the bottom for crabs. Finding one, they 

 turn on their sides to seize it, then dart off swiftly, shaking the 

 crab as a terrier would a rat. After swallowing the food. Field 

 states that the dogfish keeps up its active swimming, often re- 

 turning to the place where the crab was found. 



Some experiments on the relation of the olfactory apparatus of 

 the dogfish to its feeding habits were undertaken in the summer of 

 1908 but failed owing to the fact that the fishes refused to eat in 

 captivity. These experiments and those of Field show that dog- 

 fish will not eat if kept in large tanks or even in the large cod cars 

 of the Station, even though they are kept in captivity to the point 

 of emaciation. In order, therefore, to give them a habitat com- 

 parable to the normal, a portion of the large observation pool of 

 the Station was fenced off with meshed wire. This gave a pool 



