512 PISCES-SUBCLASS IIL-TELEOSTOML 



length of four-and-twenty feet. The smallest is the sterlet (A. ruthvenus), 

 whose length is only about three feet, while the common species (A. sturio) 

 is intermediate between the other two. The sterlet claims pre-eminence on 

 account of the excellent quality of its flesh, while the roe of all the larger 

 species affords caviare, and the air-bladder isinglass. Frank Buckland writes 

 that " sturgeons seek their food chiefly among the mud at the bottom of rivers, 

 and their head is admirably adapted for the purpose. The elongated 

 snout, protected by broad plates, ploughs up the mud as a hog does the 

 ground ; and it is probably from this habit they got the name of sturgeons, 

 from the German, storen (which means to rake up, poke, or stir). A little 

 way behind the point of the snout, and on the under side, is placed a series of 

 worm-like tentacles, or feelers, the office of .which is to examine the objects 

 turned up by the snout ; and in rear of these comes the sucker-like mouth, 

 ready to receive what is thus provided." In reference to the last sentence, 

 it may be suggested that the use of the tentacles may be to attract other fishes 

 within range of the mouth. 



ORDER II. CROSSOPTERYGII. 



FRINGE-FINNED GANOIDS. 



Africa is a country where several ancient types of animal life that have dis- 

 appeared from other regions of the globe still linger on, and a remarkable 

 instance of this survival is afforded by two fishes from the fresh waters of that 

 continent. One of these is the bichir (Polypterus bichir) of the Nile and its 

 tributaries, as well as the rivers of the west coast, and the other the reed-fish 

 (Calamoichthys calabaricus) of the fresh waters of Old Calabar on the west 

 coast. In the structure of their fins, and likewise in the hard quadrangular 

 ganoid scales with which the body is covered, these strange fishes resemble 

 a host of ancient types which were widely spread over the fresh waters of the 

 globe during the Palaeozoic epoch. Their essential difference from all other 

 living representatives of the sub-class Teleostomi is, however, to be found in 

 the structure of the fins, seeing that scales of a similar nature are met with 

 in the bony pike already described. In all these fishes the pectoral and 

 pelvic fins consist internally of a jointed longitudinal axis, from which pro- 

 ceed a larger or smaller number of divergent rays belonging to the dermal 

 system. On the under surface of the lower jaw there is at least one pair of 

 jugular plates occupying the space left between its two branches. The nerves 

 supplying the eyes when meeting one another in the middle line give off inter- 

 lacing fibres, and another primitive feature is the presence of a spiral valve in 

 the lining membrane of the intestine. The air-bladder is provided with a 

 duct, this being probably likewise a primitive character. Both the living 

 members of the order are included in the family Polypteridce, which is 



characterised by the replacement of the 

 primitive notochord by bony vertebrae, 

 as well as by certain features of the 

 skeleton which need not be noticed 

 here. The tail is very short, and 

 terminates in a diphycercal fin ; and 

 the dorsal fin is peculiar in being split 

 Fig. 35. THE BICHIR. up into a number of finlets, severally 



supported by a spine in front, such 

 finlets varying in the type genus from eight to eighteen in number. 



