500 PISCES— FISHES. 



Second type of Fishes. The Haddock {Gadus aglefinus) 

 — A type of Teleosteans with closed swim-bladder 

 (Physoclysti). 



Form and external features. — The elongated wedge-like 

 form is well adapted for rapid swimming. The terminal 

 mouth bears a short barbule ; this is long in the cod 

 (G. morrhud), and absent in the whiting (G. merlangus). 

 The nostrils, situated near the end of the snout, have double 

 apertures. The eyes are lidless, but covered with transparent 

 skin. Over the gill-chamber and the four gills lies the 



Fig. 214. — External characters of a Teleostean — 

 a carp. — After Leurtis. 



R., Dorsal unpaired fin ; S., homocercal caudal fin ; A., anal fin ; 

 £., B., pectoral and pelvic paired fins. Note also the lateral 

 line and barbule. 



operculum, supported by several bones. Distinct from one 

 another, but closely adjacent, are the anal, genital, and 

 urinary apertures, — named in order from before backwards. 

 Along the sides of the body runs the dark lateral line con- 

 taining sensory cells. There are three dorsal and two anal 

 fins, and an apparently symmetrical tail fin. 



Skin. — The small scales which cover the body are 

 developed in the dermis, and are without any bone cells. 

 Their free margin is even, a characteristic to which the term 

 cycloid is applied, in contrast to ctenoid, which describes 

 those scales which have a notched or comb-like free margin. 

 Over the scales extends a delicate partially -pigmented 

 epidermis. 



