INTRODUCTION. XV11 



away from a stale Gudgeon, when at the distance of a foot 

 from his nose, as if perfectly aware at that distance of the 

 real condition of the intended prey. Mr. Couch has ob- 

 served in a Fifteen-spined Stickleback of large size, kept in 

 a glass vessel, that the opening and closing of the nostrils 

 was simultaneous with the action of the gill-covers, and he 

 felt convinced from his observations, that the fluid was re- 

 ceived and rejected for the purpose of sensation. Among 

 the ground-feeders in fishes, the various species of Skate are 

 remarkable for the extent of the surface over which the ol- 

 factory nerves are disposed, produced by numerous laminae 

 radiating from a centre, which in appearance may be com- 

 pared in form to the under surface of a mushroom, of which 

 the trunk of the nerve is the stem. In the absence of cirri 

 or feelers in the various Skate, very considerable branches of 

 the fifth pair, the nerve of touch, are distributed over the 

 angular snout with which these fish turn over the sand in 

 search of proper food. It will be recollected that the mouth 

 in this family of fishes is on the under surface. They are 

 probably among the lowest of the ground- feeders. 



Whether fishes possess any high degree of taste is a sub- 

 ject not easily proved. Obliged unceasingly to open and 

 close the jaws for the purpose of respiration, they cannot long 

 retain food in the mouth when quite shut ; the substance if 

 of small size must be swallowed quickly, and without being 

 iuch altered by anything like mastication. From the car- 

 tilaginous hardness of the tongue in many species, more or 

 covered with recurved teeth, which assist in conveying 

 food to the back part of the mouth, the sense of taste may 

 pervade the surface of the soft and fleshy portions of the 

 pharynx. 



The teeth in fishes are so constant as well as permanent in 

 their characters, as to be worthy particular attention. In the 



VOL. i. b 



