44 WITH HARD CHEEKS. 



bladder in fishes." M. Agassiz, in dissecting a species of 

 Lepisosteus, a fresh-water fish of the rivers of America, found 

 the air-bladder composed of several cells, with a canal pro- 

 ceeding upwards into the pharynx, and ending in an elon- 

 gated slit, with everted edges, resembling a glottis or tracheal 

 aperture. However obvious may be these relations of struc- 

 ture, it is still difficult to believe there can be any analogy in 

 function, when it is recollected that one-fourth of the fishes 

 known are entirely without air-bladders, and that two-thirds 

 of the other three-fourths have neither canal nor aperture for 

 external communication, but that all are provided with gills. 



The search for these relations of structure in animals of 

 different classes, is among the most interesting of the inves- 

 tigations of the comparative anatomist. The sexual organs 

 of the Sharks and Rays very closely resemble those of some 

 of the reptiles, and the young of both these families of carti- 

 laginous fishes, as far as they have been examined, are now 

 known to possess, for a short time, external branchial fila- 

 ments. Linnaeus called the cartilaginous fishes AMPHIBIA 

 NANTES. 



The trivial names of cuculus and Cuckoo Gurnard are said 

 to have been appropriated to this species on account of the 

 similarity in the sound which issues from this fish when taken 

 out of the water to the note of the well-known bird. 



