PARTS OF INSECTS, AND MISCELLANEOUS OBJECTS. 139 



Fig. 238. 



tion, and to mark its course as it speeds along through the arteries and veins. 

 The globules are very abundant in the blood, each drop being filled with many 

 thousands, and yet, small as they are, they have been accurately studied and ex- 

 amined. They are divided into three kinds, the red and white globules, and other 

 smaller atoms, which have received the name of molecules. The red globules far 

 excel the white in number, and appear, as they roll through the centre of the blood- 

 vessels, to constitute the greater portion of the fluid. 



In man and in most Mammalia, these atoms possess a round, flattened form, 

 like that of a coin, with a slight depression towards the centre. The position 

 of this depression is indicated by a dark spot, and its depth depends upon the 



