28 Vertebrata. 



SUB-ORDER i, PHYSOSTOMI, or those in which the 

 swimming-bladder communicates, in the adult, with 

 the digestive canal by means of a duct. In these 

 also all the fin rays are soft and jointed, except 

 perhaps the foremost ray of each fin, which may be 

 spinose from a fusion of its separate elements. In 

 this group are included the pike, carp, goldfish, 

 herring, salmon, trout, and most of our fresh-water 



FIG. 13. 



Viscera of herring. 



a, oesophagus ; b ) c, stomach, with its appendages, d; e, intestine ; 

 /, duct of the swimming-bladder, k ; 7t, ovary. 



fishes, such as the. barbel, tench, roach, ide, minnow, 

 &c. Some of these physostome fishes have no 

 ventral fins for example, the eels, a few of which, like 

 the prettily marked Helen's eel of the Mediterranean, 

 are also devoid of pectoral fins. One genus of eels, 

 the Gymnotus, of the large rivers of South America, 

 has a powerful electric organ, formed of some of the 

 modified body muscles. This apparatus stretches 

 along almost the entire body, and as the fish some- 

 times reaches the length of six feet, the organ is of 

 very considerable size, and is capable of giving violent 

 electric shocks. Two other genera of physostome 



