142 



GENERAL ZOOLOGY 



clavian vein near the heart. The right arm and shoulder, and 

 the right side of the head are drained by a much smaller lymphatic 

 trunk which opens into the right subclavian vein. Lymph nodes 

 lie along the course of the lymphatic vessels, particularly those 

 draining the neck, abdomen, axilla and groin. As the lymph 

 niters through the nodes, lymphocytes from the nodes are added 

 to the lymph stream. The nodes also act as checks to the spread 



of infection along the lymphatic 

 channels. 



From this it should be clear that 

 the lymphatic and blood systems 

 are merely parts of a general cir- 

 culatory system. Each organ 

 receives its primary blood supply 

 from an artery. Most of this fluid 

 leaves the organ by means of cap- 

 illaries which unite to form veins. 

 Some of it, however, mainly 

 plasma, diffuses through the capil- 

 laries into tissue spaces and thence 

 into lymph capillaries. Thus the 

 lymph originates as an overflow of 

 plasma from blood capillaries and 

 accumulates cells as it moves 

 along, in part, by immigration 

 from the capillaries, but mostly 

 from the lymph nodes. Since the 

 cells are bathed by the lymph 

 (tissue fluid), the lymph contrib- 

 utes nutritive material from the blood to the cells and at the same 

 time takes from the cells metabolic products, part of which are 

 carried away by the lymph and part by the venous blood. 



Hemolymph Glands. — These glands resemble lymph glands, 

 except that they have blood vessels in place of lymphatic vessels. 

 Blood filters through the cells of the gland in much the same 

 way as lymph filters through a lymph gland. During its passage 

 through the gland blood loses red corpuscles, engulfed by phago- 

 cytic leucocytes, and gains lymphocytes, formed in the gland. 

 Hemolymph glands occur in certain parts of the abdomen, 

 thorax, and neck of mammals. 



Fig. 90. — Diagram of vascular con- 

 nections in spleen of rat. a, arteriole; 

 c, capillaries passing directly to veins - 

 c.s., conducting sinus, walls con- 

 tracted; pc, peripheral capillaries (no 

 sinuses) ; s, sinus, walls expanded by 

 blood; v, vein; arrows indicate direc- 

 tion of blood flow. {After Knisely.) 



