438 ZOOLOGY. 



extends straight along the median ventral line. 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 (S) is a single large sac, placed in the dor- 

 sal part of the body-cavity. Its glistening walls are com- 

 posed mainly of tough fibrous tissue. The pneumatic duct, 

 by which the bladder communicates with the oesophagus in 

 many fishes, is wanting in the perch as in nearly all other 

 Teleosts. 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 (AY). Their an- 

 terior ends are somewhat separated from one another by the 

 intervening pharynx. The ureters open into a urinary 

 bladder (U) behind the anus. 



The ovary is single and varies greatly in size according to 

 the season. In the male the sexual glands are double. Each 

 testis ( r i ) is an elongated, whitish, lobulated organ, placed im- 

 mediately below the swimming-bladder, and continues pos- 

 teriorly with the spermiduct, which opens immediately be- 

 hind the anus. 



The heart (Ht) lies in the triangular pericardial cavity ; it 

 consists of two portions, the dark-colored venous chamber, 

 or auricle, above, and the lighter-colored arterial chamber, or 

 ventricle, below. The auricle receives from above two large 

 veins, one from either side ; these veins are called the ducti 

 Cuvieri. Each Cuvierian duct, as can be seen in the figure, 

 ascends beside the oesophagus, and there receives a large jug- 

 ular vein from in front, and a large cardinal vein from be- 

 hind. 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. 



