290 THE SENSORIAL FUNCTIONS. 



indeed, neither the organ of smell nor the olfactory nerves 

 are found.* Some physiologists have gone the length of de- 

 nying the capability of water to serve as the vehicle of odo- 

 rous effluvia. But as water is known to contain a large 

 quantity of air, which acts upon the organs of respiration, it 

 is easy to conceive that it may also convey to the nostrils 

 the peculiar agents which are calculated to excite perceptions 

 of smell. Fishes are, in fact, observed to be attracted from 

 great distances by the effluvia of substances thrown into the 

 water; and they are well known to have a strong predilec- 

 tion for all highly odoriferous substances. Baits used by 

 anglers are rendered more attractive by being impregnated 

 with volatile oils, or other substances having a powerful 

 scent, such as asafoetida, camphor, and musk. Mr. T. Bellt 

 has discovered in the Crocodile and Alligator, a gland, which 

 secretes an unctuous matter, of a strong, musky odour, si- 

 tuated beneath the lower jaw, on each side. The external 

 orifice of this gland is a small slit, a little within the lower 

 edge of the jaw; and the sac, or cavity containing the odo- 

 riferous substance, is surrounded by two delicate bands of 

 muscular fibres, apparently provided for the purpose of first 

 bringing the gland into a proper position, and then, by com- 

 pressing it, discharging its contents. Mr. Bell conceives 

 that the use of this secretion is to act as a bait for attracting 

 fish towards the sides of the mouth, where they can be rea- 

 dily seized in the mode usual to the alligator, which is that 

 of snapping sideways at the objects he aims at devouring. 



The organs of smell in Fishes are situated in cavities, 

 placed one on each side, in front of the head: they are mere- 

 ly blind sacs, having no communication with the mouth or 

 throat, and, indeed, no other outlet but the external open- 

 ings, which are generally two to each sac. The principal 

 entrance is furnished with a valve, formed by a moveable 

 membrane, appearing like a partition dividing each nostril 



* Home; Lectures on Comparative Anatomy, i. 17. 

 f Phil. Trans, for 1827, p. 132. 



