112 



GENERAL PRINCIPLES OF ZOOLOGY. 



the firmer arteries (a) leading to the capillary region, and the 

 thinner- walled veins (v) leading back to the heart. 



Correlation of Respiratory Organs and Blood System. — It is a 



law that in all animals the blood-vascular system has been inilu- 

 enced in its arrangement and structure more by resjoiration than 



Fio. 65.— Scheme of ciroulatinn in a flsh. a', ascending (ventrali aorta; a^ descend- 

 ing (dorsal) aorta; e, carotid , da, intestinal arteries; dc, intestinal capillaries; 

 (Id. intestinal veins; h, auricle; h, ventricle; lia, afferent gill-arteries; hi\ efferent 

 gill-arteries; !c, liver-eapillaries ; tic, body-capillaries ; I'c, cardinal veins ; Wi, 

 hepatic vein ; vj, jugular vein. 



by nutrition in the narrower sense; there exists a correlation 

 between the organs of respiration and of circuhition. A double 

 capillary region must bo distinguished ; besides the bodv capillary 

 system already mentioned there is the respiratory cainUarv region, 

 whose exclusive office is to remove the carbon dioxide from the 



