156 



ZOOLOGY. 



not connected with the gills proper, and receiving their blood-supply 

 from distinct arteries. 



The oesophagus dilates almost immediately to form the stomach 

 (partly concealed in the figure by the liver, Li), which is hardly 

 thicker than the intestine (In). This last is of nearly uniform size 

 throughout, and after making three or four coils terminates at the 

 anus, immediately in front of the urinary and genital apertures. 

 The liver (Li) forms an elongated light-brown mass resting upon the 

 stomach. The elongated gall-bladder lies between the liver and 

 stomach, somewhat imbedded in the substance of the former. There 

 is no pancreas, though it is present in some fishes. The spleen (Sp) 

 lies between the stomach and intestine, in the mesentery; it is dark 

 reddish-brown in color. 



The air-bladder (8) is a single large glistening sac, placed in the 

 dorsal part of the body-cavity. The air-bladder normally contains 

 only gases. It conceals most of the kidneys, which extend the 



whole length of the body-cavity on either 

 side of the middle line, as two long strips 

 of a deep though dull red. They project 

 beyond the air-bladder in front (Ki) and 

 behind (Ki'). 



The ovary is single, and varies greatly in 

 size according to the season. In the male 

 the sexual glands (testes) are double. 



The heart (Ht) lies in the triangular peri- 

 cardial cavity; it consists of two portions, 

 the dark colored venous chamber, or auri- 

 cle, above, and the lighter-colored arterial 

 chamber, or ventricle, below. The auri- 

 cle receives from above two large veins, 

 one from either side; these veins are called 

 the Cuvierian ducts. Furthermore, a large 

 vein, the sole representative of the vena 

 cava of higher vertebrates, passes from 

 the liver, near its anterior end, through 

 the pericardium, and empties into the Cuvierian ducts near their 

 common auricular orifice. 



The brain should be exposed from above by carefully removing by 

 a knife the skin aud thin bones covering the brain-cavity. Begin- 

 ning in front, we notice the minute olfactory lobes and the olfactory 

 nerves proceeding to the nasal cavities. Behind the olfactory lobes 

 lie in succession the cerebral hemispheres (H), optic lobes (Q), the sin- 

 gle cerebellum (Gb), and, lastly, the medulla oblongata (M). 

 A general idea of the two body-cavities, the nervous and visceral, 



Fig. 200.— Transverse section 

 through the middle of the 

 body of a Cunner. Drawn 

 by G. S. Minot. 



