432 FISHES. 



I Acanthopteri. Example— Perch. \ 



Dorsal, anal, and pelvic J 1 



fins in part spiny. ) Pharyngognathi. Example — I 



( Wrass. 1 Physoclisti, — duct 



> of swim-bladder is 



IAnacanthini ; the pelvic fins are / closed, 

 situated far forward. Examples I 

 -Cod, Flounder. I 



/ 

 Physostomi ; duct of swim-bladder remains open. Ex- 

 amples — Herring, Salmon, Carp, Eel. 



The Haddock {Gadus aglefinus) — A type of Teleosteans 

 with closed swim-bladder (Physoclisti). 



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. 

 morrhua) 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 oper- 

 culum, 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 black 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 de- 

 veloped 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 pig- 

 mented epidermis. 



Appendages. — The pectoral fins are attached to the 

 shoulder girdle just behind the branchial aperture. The 

 pelvic or ventral fins, attached to what is at most a rudi- 

 ment of the pelvic girdle, lie below and slightly in front 

 of the pectorals — far from the normal position of hind limbs. 



Muscular System. — The main muscles of the body are 

 disposed in segments, — myotomes or myomeres, separated 

 by partitions of connective tissue. 



Skeleton. — The Vertebral column consists of biconcave or 

 amphiccelous bony vertebrae. Each centrum in the trunk 



