416 pisces. 



motion of what may be called its body ; for the real body, or tbat part 

 where the viscera and parts of generation he, is situated with respect to 

 the bead as in other fish, and is extremely short, so that, according to 

 the ordinary proportion, this should be a very short fish ; therefore the 

 tail, or that part which is extended beyond the cavity of the abdomen, 

 is much longer than what is absolutely necessary for the progressive 

 motion of the body, or fore part of the animal, as it is much longer 

 than what is to be found in fishes in general, which have no other use 

 for this part ; therefore we may reasonably suppose it was extended 

 out for the purposes of this organ only. However, it is still adapted 

 for progressive motion and the specific gravity [of the fish] ; for there 

 is a continuation of the spine, medulla spinalis, muscles, fin, and air- 

 bladder, through its whole length. Its great length, therefore, seems 

 chiefly to afford a surface for the support of the peculiar organ ; how- 

 ever, the tail part is adapted to the progressive motion of the whole, 

 and to preserve the specific gravity ; for, besides the above parts, there 

 is a membrane passing from the spine to the fin which runs along the 

 belly. This membrane is broad at that end next to the belly, termi- 

 nating in a point at the tail. It is a support for the belly-fin, gives a 

 greater surface of support for the [electric] organ, and makes a septum 

 between the organs of the two opposite sides. 



The gymnotus has three fins ; two of them are pectoral, situated one 

 on each side, just behind the posterior openings of the gills, very much 

 like those called the pectoral fins of an eel. The third is the anal fin, 

 and is continued along the lower surface of the fish, almost its whole 

 length. It begins upon the belly, and is continued to the tail, being 

 narrowest forwards, and becoming broader towards the tail : it consists 

 of small bones laid close to one another, and placed a little obliquely, 

 pointing backwards towards the tail. These are articulated to another 

 row of small bones, but rather longer bones, within the body of the 

 animal. These again are fixed to the edge of a pretty strong tendinous 

 membrane or septum, the upper part of which, after enclosing the 

 large air-bag, is fixed to the thinnest. This septum is broadest at the 

 anterior end, towards the abdomen, where it begins and terminates in a 

 point, at or near the end of the tail. All this part of the fish is divided 

 into a right and left side ; each of the bones of the fins have four mus- 

 cles, two lateral and two interstitial ; the lateral muscles are immedi- 

 ately under the skin and arise from it ; tbe others are between the 

 bones of the second row. The lateral muscles give the fin its lateral 

 motions, and the interstitial ones give each bone more or less obliqiuty, 

 which may be called flexion and extension. 



The Shin. — The skin is smooth, and in general pretty strong and 



