40 WITH HARD CHEEKS. 



tory function, and as being the rudiment of the pulmonary 

 cavity of land animals ; the passage of communication with 

 the oesophagus being conceived to represent the trachea." 



Hervey long ago observed " that the air in birds passed 

 into cells beyond the substance of the lungs ; thus showing 

 a resemblance to the cellular lungs in reptiles, and the air- 

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

 Leptsosteus, a fresh-water fish of the rivers of America, 

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

 proceeding upwards into the pharynx, and ending in an 

 elongated slit, with everted edges, resembling a glottis or 

 tracheal aperture. However obvious may be these relations 

 of structure, 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 cartilagi- 

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

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

 ments. Linnseus called the cartilaginous fishes AMPHI- 

 BIA 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. 



