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THE SENSE OF SMELL IN SELACHL\NS 59 



were made, also, in which there were no normal fishes in the pool. 

 In these cases the crabs were left untouched for twenty-four hours, 

 although the dogfish on the opposite side of the screen became 

 much excited. 



Three of the dogfish, all of which had eaten readilj^ before the 

 use of the cotton, but which had refused to do so thereafter, al- 

 though tested for three successive days, were removed from the 

 pool and the cotton withdrawn from the nostrils. These were 

 returned to the pool which now contained no normal fishes. The 

 following day one of these ate readily in the usual manner, al- 

 though there seemed to be slightly more difficulty than usual in 

 finding the crabs, both in the first place and after one had been 

 dropped. A day or two later all three ate as usual. This experi- 

 ment was repeated twice with the same results. 



These experiments indicate that the dogfish normally recognizes 

 the proximity and location of food through the use of the olfac- 

 tory apparatus. It may be argued, of course, that the mere 

 presence of the cotton in the nostrils renders the fish so uncom- 

 fortable that it refuses to eat, even though it acts otherwise in 

 a perfectly normal manner. To obviate this objection four dog- 

 fish were removed and one nostril onl}^ stuffed rather tightly with 

 cotton. These four were now placed by themselves in the pool. 

 One of them, within an hour thereafter, caught a crab, after the 

 usual preliminary procedure, but lost it and seemed to take no 

 further interest in the matter. The following da}- all four ate as 

 usual. It was noticed in this experiment also, that the dogfish had 

 rather more difficulty than was normally the case in finding the 

 food, but that this wore off in a couple of days. These four fish 

 were removed after four days and seven others, treated in the same 

 way, were substituted. The results were the same. These tests 

 show that the presence of the cotton is not sufficiently irrita- 

 ting to interfere seriously with the normal feeding habits of the 

 dogfish. As remarked, earher individuals with the nostrils plugged 

 act, except in so far as the feeding habits are concerned, just as 

 do the normal fishes; as both kinds swim about the pool, such could 

 not be identified by an uninformed observer. 



