800 



COMPARATIVE ANATOMY 



The lymph glands (Fig. 453) are made up of a network of connec- 

 tive tissue in which the lymph leukocytes (lymphocytes) are formed. 



The function of lymph glands, therefore, seems to be that of de- 

 stroying foreign bodies and to add white blood corpuscles to the general 



Ant. cardinal vein- " 



Right 



lymphatic duct 

 Subclavian vein 



Ant. lymph heart 



Post, cardinal vein -I 



'V /? 



*;r -t 



B. 



Post, lymph heart 



Fig. 453. 



A, Diagram showing arrangement of lymphatic vessels in a 20 mm. pig 

 embryo. (After Sabin.) 



B, Diagram illustrating a stage in the development of a lymph gland. (After 

 Stohr.) 



circulation. The lymph itself bathes all the cells of the body. There are 

 no red blood corpuscles in lymph. 



The lymphatics of the intestine are called lacteals and perform the 

 important function of absorbing fats from the ingested food. These 

 lacteals combine with the lymphatic vessels from the hind limbs and 

 body to form a receptacle known as the receptaculum chyli, from which 

 a tube (thoracic duct) passes cephalad to open into one of the large veins 

 of the precaval system by a valvular opening. The thoracic duct is often 

 double. 



In mammals the lymphatic system ramifies throughout all portions 

 of the body. The lymphatic system is too delicate to be worked out by 

 the ordinary laboratory dissection. 



SUMMARY OF THE CIRCULATORY SYSTEM 

 AMPHIOXUS (Fig. 444) 



The blood vessels are all of one kind, but due to various homologies 

 with the more complex vessels of higher animal forms, some are called 

 arteries and others veins. 



The circulatory system consists of a ventral pulsating vessel, with- 

 out a specialized heart enlargement. This pulsating vessel pumps the 

 colorless blood forward and through the branchial arches to be aerated. 

 The blood then collects in paired dorsal aortae which unite back of the 

 pharynx into a single dorsal aorta. Branches are sent from this dorsal 

 aorta to the walls of the intestine where they break up into capillaries. 



