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THE SENSE OF SMELL IN SELACHIANS 53 



when two packets of similar appearance, one containing minced 

 earthworm, the other empty, are placed in a jar containing catfish, 

 these invariably seek and tug at the one with food. Fishes with 

 the olfactory tracts cut never respond in this manner. Observa- 

 tions by Dr. Parker,- on the sense of smell in Fundulus, give sim- 

 ilar results and show also that the failure of the fishes to respond 

 after section of the olfactory tracts is not due to the shock of 

 the operation. In Fundulus, however, the eyes are also used in 

 the recognition of food substances. 



II. THE NASAL APPARATUS OF THE DOGFISH 



This consists of a pair of large capsules, partially divided into 

 two parts by means of a superficial and an enclosed flap of skin 

 rostrad, and a fleshy ridge caudad. There are thus two incom- 

 pletely separated external apertures, a rostro-lateral and a caudo- 

 median, the latter the closer to the mouth (see Sheldon, '09, fig. 

 3). These capsules contain a double row of lamellae extending 

 laterad from a median ridge, much as do the barbs from the rachis 

 of a feather. This median ridge extends from the more lateral to 

 the more medial opening. The lamellae are innervated by an 

 enormous number of short olfactory nerve fibers which terminate 

 in the large olfactory bulbs, closely apposed to the capsules. 

 The nervus terminalis of Locy also sends a few fibers into the 

 lamellae, while the capsules, in general, are innervated for tactile 

 and general chemical sensation by the nervus maxillaris trigemini. 



During the ordinary movements of respiration, as water is 

 taken into the mouth, a current is, by suction, drawn through 

 the nostrils, entering at the more rostral and leaving at the more 

 caudal aperture to be drawn farther, to some extent, into the 

 mouth. This may be easily demonstrated by fastening a dogfish 

 on its dorsum and expelling, from a pipette, a colored solution 

 rostral to the nostrils. The current then follows the median 

 ridge, a part being diverted laterad between the lamellae. The 

 shape and position of the fleshy ridge and flaps of skin are such, 



2 See this number of the Journal, page 1. 



