^6 Elementary Zoology. 



the cloaca. Into this terminal chamber opens, firstly a large 

 bifid bladder, and just below it the ureters and (in the female) 

 the oviducts. 



Appended to the alimentary canal are two large glands. 

 Of these the liver is much the largest, and is divided into two 

 principal lobes, a right and a left. Attached to the lower 

 surface of the liver is the usually bright green gall-bladder. 

 From this a duct leads through the pancreas, in the substance 

 of which it is joined by the ducts of the pancreas, and finally 

 opens into the duodenum, as is called the first part of the small 

 intestine. 



The circulatory system of the frog consists of a central 

 organ of impulsion, the heart, and of a system of tubes leading 

 to and from the heart. Those conveying blood from the heart 

 are termed arteries, and those returning blood to the heart are 

 termed veins. Peripherally these are united by the minute capil- 

 laries, which permeate all the organs of the body. The vascular 

 system is, as has already been stated, in communication with the 

 ccBlom through the lymphatic vessels. It contains, however, a 

 different fluid. Besides the "white" corpziscles which are 

 common to it and to the lymphatic system and coelom, it has 

 large, red, oval, nucleated discs, the red corpuscles. The red 

 colouring matter of these is due to a substance called haemo- 

 globin, the importance of which will be considered in connec- 

 tion with respiration. The body of the frog is thus permeated 

 by a second system of cavities distinct from the ccelom. 



The heart is a stout muscular organ enclosed in a special com- 

 partment of the ccelom, the pericardium. Its cavity is divided 

 into several chambers, which are in communication with each 

 other. Behind the heart is the sinus venosus, into which the 

 veins bringing back blood from the body generally open. 

 This leads into the right au-ricle, which is separated from the 

 lefc auricle by a septum. Into the left auricle open the pulmo- 

 nary veins. Both auricles lead into the single ventricle by a 

 common aperture, which, however, is divided into two openings. 



further increased, without additional room for storage being required, by 

 villi and folds upon its inner surface. The typhlosole of Lnmhricns and of 

 Anodon is a similar response to a similar need. 



