162 



ESSENTIALS OF ZOOLOGY 



tissues where they engulf bacteria and foreign matter. Upon ex- 

 posure to air the dissolved fibrinogen in the blood becomes fibrin and 

 forms a clot which is semisolid and blocks flow of blood from most 

 wounds. The remaining fluid after the blood clots is called serum. 

 Lymph is a fluid similar to plasma which has seeped through the 

 walls of the capillaries in the various organs, and it carries amoeboid 

 white corpuscles. 



Veins from uppGP_ 

 part of Body 



Lymphatics 



Thoracic duct - 



Oupcnop vena cava 

 Pulmonary/ artery 



lii^ht aupicla — 

 Infepiop vena cava- 



/ 



ISi'^hl' vcntpiclc 



tactcab — 



Hepatic vcirL 



Vcini from Iowcp 

 part of Body 



Artcploa to uppcp* 



papt of Body 



Pulmonapy vein 



— Left auricle 



- Left vcntplclc 



ArtGPJGS to lov/ep 

 part of Body 



. ^.;/mpBati«--A^•■r^^;^\V^HopatlcaptGl^ 



Fig, 53. — Diagram of circulation of a mammal. The oxygenated blood is shown 

 in black • the venous blood in white. The lymphatics are black irregular hnes. 

 (From P'ettibone, Physiological Chemistry, The C V. Mosby Company.) 



The excretory system of vertebrates consists of kidneys, excretory 

 ducts, and often a urinary bladder. The kidneys serve to remove 



