6i6 



PHYLUM CHORDATA : CLASS PISCES — FISHES 



in front), which unites with the posterior cardinal sinus 

 at the outer end of the duct of Cuvier. The hepatic portal 

 system opens directly into the sinus venosus by two hepatic 

 veins from the liver. 



Excretory and reproductive systems (see Skate, 

 Figs. 341, 342). — The kidneys are greatly elongated and 

 flattened, lying in the dorsal wall of the coelom on either 

 side of the backbone. 



In the male the paired sperm sacs are long and tapering. 



In the female the lower parts of the oviducts, sometimes 

 termed uteri, may frequently be found greatly distended 

 owing to the presence of developing embryos. 



u.g.a 



-The haddock. 



brm. ^P 



n.a 



Nasal apertures (double on each side) ; d.fA, d.f.^, d.f.'^, dorsal 

 unpaired fins ; c.f., the caudal fin of the homocercal tail. 



b., Barbule ; op., operculum covering the four gills ; br.m., con- 

 tinuation of the gill-cover forming the branchiostegal mem- 

 brane ; pv.f., pelvic fin ( = hind-limb) — note its jugular position 

 in front of p.f., the pectoral fin ( = fore-limb). 



a., Anus; g., genital aperture; u., urinary aperture; a.fA, a.f.^, 

 unpaired anal fins. 



Third type of Fishes. The Haddock {Gadus ceglefinus) 

 — 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 lower 

 jaw bears a short barbule — long in the cod (G. morrhiia), 

 absent in the adult whiting (G. merlangus). The nostrils, 

 situated near the end of the snout, h )ve double apertures. 

 The eyes are lidless, but covered u.th transparent skin. 

 Over the gill chamber and the four gills lies the operculum, 

 supported by several bones. Distinct from one another, 

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



