IV. VERTEBRATA: PISCES, TELEOSTEI. 



509 



sphenoid, hyoid, gill arches, superior pharyngeals — the latter alone in 

 Cyprinoids) may bear teeth. Frequently there are present small bones, 

 epipleurals, usually forked, lying in the intermuscular septa above the 

 ribs, which are not preformed in cartilage. In the fins l:)Oth cartilage and 

 dermal rays are ossilied, the former remaining small, the rays forming most 

 of the support. These rays may either be soft and flexible (Malacopteri) 

 or hard and spine-like (Acanthopteri), a matter of classificatory value. 

 In the first case they consist of numerous small threads (fig. 559, Br, 



Fig. 559. — Perca fluviaiilis (from Ludwig-Leunis). A, anal fin; B, ventral fin; 

 Br, pectoral fin; K, operculum; A^, nostrils; R^, R.,, spinous and soft dorsal fins; S, 

 caudal ha; SI, lateral line. 



A , B, R2), in the other the parts of a ray are fused to a spine which, some- 

 times connected with poison glands {Scorpmia, etc.), are good defensive 

 weapons. The tail is usually homocercal ; the diphycercy of eels and other 

 fishes is secondary. The dermal skeleton consists of ctenoid or cycloid 

 scales, sometimes of spines or bony plates, these with true dermal teeth 

 in the armored Siluroids. In rare instances the skin lacks scales. 



The hyoid arch always bears an operculum and branchiostegal 

 membrane; there is no spiracle and the opercular gill is rudimentary or 

 absent. The gills of the comb-like type are confined to the four anterior 

 gill arches, but they may be reduced to two and one-half pairs of demi- 

 branchs. Instead of a conus (present in Butrinus), the bulbus arteriosus 

 is well developed; a spiral valve is lacking, but pyloric appendages are 

 common. A swim bladder is usually present, but its duct is frequently 

 closed. 



The teleosts are distinguished from all vertebrates except the cyclostomes 

 and perhaps some ganoids in that the nephridial system does not form part of 

 the sexual ducts. The eggs and milt are deposited through the abdominal pores 

 or by special canals developed from the body cavity. Copulation occurs in only 

 a few viviparous forms (Embiotocidae, Gambiisia, etc.). The rule is that males 



