XX] MAIN DIVISIONS 491 



in the sea but periodically ascend rivers. Classed with Salmon 

 as anadromous fish, the Eels in reality form a complete con- 

 trast to them for they ascend the rivers to feed and return to 

 the sea to spawn. They lay their eggs on the Atlantic slopes, 

 i.e. where the drop from shallow depths to abysmal depths begins. 

 The egg develops into an extraordinary larva termed Lepto- 

 cephalus, in some ways resembling Amphioxus, and like it 

 devoid of red blood corpuscles. These larvae change to minute 

 Eels termed Elvers as thin as a wire and a few inches long, and 

 in this condition they ascend the rivers. They leave the water 

 and wriggle over damp grass at night in order to reach isolated 

 ponds. It has been plausibly suggested that the Eels were origin- 

 ally estuarine fish and spawned close to the coast ; but as the coast 

 subsided under the sea, their original spawning place to which 

 they have remained faithful has been buried far out under the 

 Atlantic. 



The sub-order OSTARIOPHYSI is characterised by having ab- 

 dominal pelvic fins, an air-bladder with a duct, and a remarkable 

 chain of bones on each side of the vertebral column connecting the 

 anterior end of the air-bladder with the auditory capsule. This 

 chain is termed the "Weberian chain and it consists of a triangular 

 bone, the "tripus," probably a modified rib, which impinges on 

 the air-bladder, of a Y-shaped "intercalare," and finally of a 

 cylindrical " scaphium " which rests against a membranous window 

 in the periotic capsule. The scaphium is supposed to be the neural 

 arch (basidorsal) of the first vertebra. The coracoid has a meso- 

 coracoid branch and the pelvic fins are abdominal in position. 

 This remarkable group of fish includes the families Cyprinidae 

 (Carp, etc.) and Siluridae (Cat-fish). The former family is charac- 

 terised by the presence of normal scales, and the protrusibility of 

 the premaxilla, but the protrusibility is not effected by the motion 

 of the maxilla. The Cyprinidae include the Carp, Cyprinus (species 

 of which constitute the "gold" and silver fish), and the Roach, 

 Loach, Gudgeon and Minnow in fact the majority of the fish 

 which inhabit our rivers and lakes. The Siluroids or Cat-fish derive 

 their name from the numerous tentacle-like appendages (barbels) 

 which adorn their mouths. One specially long one is borne by the 

 maxilla. Certain of the fin rays of the dorsal and anal fins are 

 developed into spines. As in Eels the brain case is unconstricted 

 between the orbits and the symplectic is absent. Ordinary scales 

 are never present. Either as in the Cat-fish of North America the 



