68 SENSE OF SMELL IN DOGFISH. 



The movements of a dogfish differ from the movements of these lower animals, 

 however, in that they are not pure circus movements. A dogfish with a fully occluded 

 left nostril not only turns to the right but sometimes to the left, and a normal dogfish 

 so often exhibits movements in the form of a figure eight that it is quite clear that the 

 whole figure is a single response rather than two separate acts due to alternate excessive 

 stimulation first on one side and then on the other. Thus, though the responses of the 

 dogfish to the odors of food may be based predominantly on the principle of symmetrical 

 stimulation, it is also clear that odorous material calls forth from this animal what are 

 essentially random movements. 



In consequence, the finding of food or of a bait by a dogfish may, therefore, be 

 described as brought about by a combination of movements, partly random and partly 

 directed, which have resulted from stimulations due to the varying concentrations of 

 odorous. materials in the surrounding sea water. The dogfish, like other elasmobranchs, 

 has a structure especially favorable for this form of stimulation in that its nostrils are 

 wide apart, a condition which is immensely exaggerated in the hammerhead shark, 

 whose nostrils as well as eyes are lodged at the extreme ends of the transversely extended 

 processes of its head. These conditions make it clear why chumming is so eff'ective with 

 mackerel and other fishes. When a fisherman spreads bait to attract such fishes from 

 a distance the response is undoubtedly directive, especially on the part of sharks, 

 which have been seen to come up to food against the tide from as great a distance as a 

 quarter of a mile. Such fish must keep within the stream of odorous substance in the 

 water by responding to the stimulation of their nasal organs in much the same way as 

 the dogfish was found to do in seeking a bait. 



BIBLIOGRAPHY. 

 Aronsohn, E. 



1884. Beitrage zur Physiologic des Geruchs. Archiv fur Anatomic und Physiologic, physiologische 

 Abteilung, jg. 18S4, p. 163-167. 

 Baglioni, M. 



1909. Zur Physiologic dcs Geruchsinnes und des Tastsinnes der Seetiere. Zcntralblatt fiir Physi- 

 ologic, bd. 22, p. 719-723. 

 COPELAND, M. 



1912. The olfactory- reactions of the pufTcr or swellfish, Spheroidcs maculatus (Bloch and Schneider). 



Journal Experimental Zoolog}.', vol. xii, no. 3, p. 363-368. 

 Parker, G. H. 



igio. The olfactory reactions in fishes. Journal Experimental Zoology, vol. vm, no. 4, p. 535-342- 

 1911. The olfactory reactions of tlie common killifish, Fundiilus heteroclitus (Linn.). Ibid, vol. x, 

 no. I, p. 1-5. 

 Parker, G. H., and Sheldon, R. E. 



1913. The sense of smell in fishes. Bulletin V. S. Bureau of Fisheries, vol. xxxii, 1912, p. 33-46. 

 Sheldon, R. E. 



1909. The reactions of the dogfish to chemical stimuli. Journal Comparative Neurology and Psy- 

 chology, vol. XIX, p. 273-311. 

 1911. The sense of smell in selachians. Journal Experimental Zoology, vol. x, no. i, p. 51-62. 



