24 ANIMAL BIOLOGY. [Part I. 



is represented by the dark line in Fig. 8. It secretes a moisten- 

 ing serous fluid. 



The stomach and succeeding (duodenal) portion of the small 



TT.st. 



D.tto 



Sv.l.s 



Pie.-. 



aut.Ab. 



FIG. 8. TRANSVERSE SECTION OF THE POSTERIOR PART OF THE BODY OF A 

 MALE FROG. 



ant. Ab. Anterior abdominal vein. D. ao. Dorsal aorta. Du. Duodenum. 

 H. G. Hip-girdle. I. s. p. Lumbo-sacral plexus. L. Int. Large intestine. 

 I/r. Liver. Pe. Peritoneum. Pn. Pancreas. PL c. Postcaval vein. r. p. 

 Renal portal vein. Ren. Kidney. S. int. Small intestine. Sc. I s. Sub- 

 cutaneous lymph space. Sv. I. s, Subvertebral lymph space. St. Stomach. 

 Sy. Sympathetic nerve chain. Ts. Testis. U. st. Urostyle. Ur. Ureter. 



intestine form a loop united by mesentery. In this loop lies a 

 triangular yellow organ, the pancreas (Pn). Through the midst 

 of it there passes a delicate tube opening into the small intestine. 

 This is the bile duct leading the product of the liver from that 

 organ, and from the gall-bladder (G. Bl.) attached to it, into the 

 alimentary canal, and receiving also the pancreatic fluid secreted 

 by the pancreas. Note how the large liver is attached to the 

 anterior end of the cavity, and how it is divided into lobes. 



2. The Respiratory System. The organs of respiration of the 

 adult frog are the lungs. They lie in the pleuro-peritoneal 

 cavity on either side near its anterior end. The right lung is 

 slightly displaced in the figure (7). The layer of peritoneum 

 reflected on to the lungs is called the pleura. Air passes into 

 them from the glottis, and they may be inflated from that aper- 

 ture. The nares are the external apertures of the respiratory 



