GYMNOTUS ELECTRICUS. 419 



to the heart, viz. an auricle and ventricle, answering to the right auricle 

 and ventricle in the animals which have four cavities. It has a bran- 

 chial artery, similar to the pulmonary [in function]. The great artery 

 which arises from the gills runs along the hack-bone, sending out 

 branches as it passes. The great vein runs along the spine in the con- 

 trary direction, collecting the smaller veins as it passes along. 



The respiratory organs are gills : they have no small bones, but two 

 pretty broad ones, acting as ribs for the dilatation of that part which is 

 similar in use to the thorax ; besides the lamina branchiarum, which 

 are so much fixed to the other head-bones, as not to move forwards and 

 downwards. The electrical gymnotus has, in its membrana branchi- 

 ostega, three flat rays or radii, connected by the tough membrane, and 

 moveable forwards and downwards. 



Air-bags. — There are two air-bags, a large and a small one. The 

 large one begins at the termination of the cavity of the abdomen, and 

 passes back along the under surface of the spine, as far as within a few 

 inches of the end of the tail, becoming smaller and smaller towards this 

 part. It has a pretty strong external covering, which appears to be a 

 continuation of the septum which divides the two electrical organs : 

 this is lined with a proper or distinct soft membrane. As these parts 

 are appropriated for the specific gravity of the animal, their size and 

 extent are such as answer this purpose without any connexion with 

 any other known circumstance in the animal economy. 



The small air-bag is placed forwards under the posterior part of the 

 head or beginning of the body ; it is a circumscribed cavity terminating 

 at the fore part in two blind ends ; its substance is of a firm tendinous 

 consistence, lined with a soft membrane like the large air-bladder. 

 These air-bags have each a small duct which unites into one near the 

 oesophagus, into which it opens near its termination in the stomach. 

 The duct of the larger air-bag comes out at the upper or anterior end, 

 and passes along the surface of the kidneys towards the oesophagus. The 

 duct of the small one comes out at the posterior end, and passes almost 

 directly towards the oesophagus, where it joins the large one ; and these 

 two form a common duct, which becomes cellular, and then opens into 

 the oesophagus near its termination into the stomach. These ducts are 

 very small ; not much larger than a large brad-awl. 



The bones of this fish are like those of the eel, cod, and many other 

 fishes. 



This fish abounds with fat, having it everywhere in the interstices of 

 the muscles, and also in other parts of the body. Besides which there 

 is, under the skin of the back, and more particularly near to the end of 

 the tail, a whitish yellow substance of considerable thickness, nearly 



2e2 



