THE BLOOD AND ITS CIRCULATION. 



461 



mals chiefly throuarli the lacteals and veins of the stomach : secondly, 

 from the waste of the body received through the lymphatics and tho- 

 racic duct ; and, thirdly, through respiration, which supplies oxygen. 

 The amount of solid matter seems to bear a proportion to the amount 

 of flesh in the diet and to the temperature of the animal, being greater 

 in the carnivorous and warm-blooded animals. 



In color, the blood of all vertebrates is red, excepting that of the 



Fig. 1. Human Blood-Corpuscles ; maguified 370 diameters. 



amphioxus, the lowest animal of the sub-kingdom, which is colorless. 

 In the muscles of fishes it is also white. In the invertebrates the 

 blood is of various colors, but commonly white, on account of which 

 fact they were formerly supposed to be destitute of blood. 



Microscopic examination of the blood of a vertebrate animal shows 

 that the color is due to an im- 

 mense number of red particles 

 floating in a watery fluid. But 

 the shape and size of these corpus- 

 cles vary in the different groups 

 of vertebrates, and in different 

 species. In man, and all mam- 

 mals excepting the camel tribe, 

 the red corpuscles are biconcave 

 disks. In the camel they are ellip- 

 tical. The corpuscles in all other 

 vertebrates are nucleated, or have ^^^- 2. Blood-Corpuscles (relative size) 



, 1 1 T m-, Man : b, Blenuy ; c, Frog ; d. Newt. 



a thickened center. Those of >..-. 



birds, reptiles, and amphibians are elliptical, while those of fishes are 



discal, ellij^tical, or angular. 



The size of the red blood-corpuscles bears little relation to the size 

 of the animal, except within the natural groups, as the orders of mam- 



a. 



