GENERAL ZOOLOGY 



Fig. 3.3. The capillaries and lymphatics in relation to cells 

 throughout the body; diagrammatic. The arrows indicate the 

 direction of circulation. 



tached to that part which becomes the anterior portion of the small intestine, 

 or duodenum, by way of their ducts, the bile duct and the pancreatic duct, 

 respectively. 



The large intestine is very short in the frog, but it is quite conspicuous in 

 mammals, including man, and is separated into the colon and rectum, which 

 opens externally by way of the anus. In most of the vertebrates, as in the 

 frog, the large intestine is not differentiated into regions. It opens into the 

 cloaca, which is a common passageway for substances coming from the ex- 

 cretory organs and urinary bladder, for germ cells from the reproductive 

 organs, as well as for material from the large intestine. The external opening 

 of the cloaca is the anus. When, in the evolution of mammals, the cloaca was 

 divided into a ventral urino-genital sinus and a dorsal rectum, a new opening 

 was formed ventrally; the term anus is retained for the opening through which 

 materials leave the digestive tract. 



The Circulatory System. All the cells of the vertebrate body have, in 

 spite of its complexity, a common internal environment. This is so because 

 of the circulating fluids of the body, the blood and lymph, carried to all 

 parts of the body by the circulatory system. This system is divided into the 

 blood-vascular system and lymphatic system, depending on the type of fluid 

 carried. 



The blood-vascular system of vertebrates is, with few exceptions, what is 



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