134 



FIRST LESSONS IN ZOOLOGY. 



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 (<S) is a single large 

 glistening sac, placed in the dorsal part 

 of the body-cavity. The air-bladder 

 normally contains only gases. It con- 

 ceals most of the kidneys, which extend 

 the whole length of the body- cavity on 

 either side of the middle line, as two 

 long, wide strips of a deep though dull 

 red. They project beyond the air-blad- 

 der in front (Ki) and behind (AT). 



The ovary is single, and varies great- 

 ly in size according to the season. In the 

 male the sexual glands (testes) are 

 double. 



The heart (Hf) lies in the triangular 

 pericardial cavity; it consists of two 

 portions, the dark-colored venous cham- 

 ber, or auricle, above, and the lighter- 

 colored arterial chamber, below. The 

 auricle receives from above two large 

 veins, one from either side; these veins 

 are called the Cuvierian ducts. Fur- 

 thermore, a lar.f;e vein, the sole repre- 

 tentative of the mu* cam of higher ver- 



ventricle; bur, bulbus arterio- tebrates, passes from the liver, near its 

 sus; no, aorta; ba. one of the . .. 



four branchial arteries which anterior end, through the pericardium, 

 carry the blood to the gills, and and t , mpt i e s into the Cuvierian ducts 

 afterwards unite to torm the . 



descending aorta (da<>) ;pc-,por- near their common auricular orifice. 



^SsS^s^JSSA Thc brain Bliouhl 1)o oxposed frora 



kidney. above by carefully removing by a knile 



the skin and thin bones covering the brain-cavity. Beginning 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 (//), optic lobes (Q), the single 

 cerebellum (Cb), and, lastly, the medulla oblongata (M\ 



