28o CHARACTERS OF VERTEBRATE ANIMALS 



on the right side, but its shape is an elongated oval. It is con- 

 fined to European seas. 



Sub-order 5. — Tube-bladdered Fishes (Physostomi) 



This large group (some 2500 species) includes many im- 

 portant food-fishes, and includes both marine and fresh-water 

 forms as well as forms which, like the Salmon, live partly in 

 the one and partly in the other. The fins are supported by soft 

 jointed rays, except, in some cases, the first ray in the dorsal and 

 pectoral, which may be transformed into spines. The pelvic fins 

 are situated far back in what must be considered as the primitive 

 position, judging by other orders of fishes. The air-bladder, 

 which, as previously stated, is an outgrowth from the gut, always 

 retains a connection with it by means of a tube, whence the 

 name of the sub-order. Only the more important families can 

 be mentioned here. 



1. Cat-Fish Family. — The Cat-Fishes or Siluroids include 

 a large number of species inhabiting the fresh waters of tropical 

 and temperate regions, while some of them are estuarine or 

 even marine, though in the latter case they do not go far from 

 shore. The name " Cat-Fish " has reference to the presence of 

 long barbels, suggesting to a lively imagination the " whiskers " 

 of a cat. The scaleless body is sometimes protected by bony 

 plates. There is only one European species, the Wels {Silurus 

 glanis) (fig. 165), and this is limited to the rivers east of the 

 Rhine. Excepting only the Giant Sturgeon, it is the largest 

 of European fresh-water fishes, attaining a maximum length of 

 13 feet and weight of 400 pounds, though average specimens 

 are very much smaller. In this species the skin is soft, and there 

 are six barbels, two very long ones above and four much smaller 

 ones below. 



2. Salmon Family. — The members of this group are in the 

 main either purely fresh - water in habit, or ascend rivers to 

 spawn, and, with the exception of a New Zealand genus, are 

 confined to the northern hemisphere. There are, however, a 

 few purely marine species. The body is of the typical fish-form, 

 and covered with scales, except in the head region. A fairly- 

 large first dorsal is situated about the middle of the back, and 

 much farther back there is a small second dorsal, which, on 



