RED GURNARD. 41 



in the outline ; in other Gurnards it is bilobed, but not very 

 deeply cleft at the anterior part : the common Red Gurnard, 

 the subject of the present notice, and the Grey Gurnard, are 

 instances. In the Salmon, the Herring, and the Eel tribes, 

 it is one elongated cylindrical tube, lying close to the under 

 surface of the backbone. In the Sciaena aquila, the edges 

 of the single-chambered swimming-bladder of that fish are 

 fringed all round, of which a representation will be added ; 

 but in the Carp, this organ is formed of two oblong cavities, 

 the larger one lying behind the other, and communicating by 

 an aperture in the neck or narrow portion connecting the two 

 parts. From the anterior surface of the posterior lobe in the 

 Carp, (a section of the whole subject reduced in size from 

 Monroes Anatomy of Fishes being here added, with a probe 

 introduced through the aperture in the neck, to show the 

 communication between the two chambers,) a tube is given 

 off, which, passing forwards, opens into the oesophagus, but is 

 closed against the admission of any extraneous bodies by a 

 delicate valve, which can only be passed in the outward 

 direction. 



The air-bladders are usually made up of two membranes. 

 The inner one has a moist, smooth, and, apparently, a se- 

 creting surface ; the outer membrane is fibrous in its struc- 

 ture, and a portion of the bladder is in some species invested 

 by a fold of the peritoneum : the three coats, when present, 

 are nourished by blood-vessels, which are very apparent. 



The air-bladder does not occur in all fishes : some fishes, 



