nil'. m.ooi> 



hut tubes having walls of their own. The walls of the 

 capillaries arc, however, very thin, and in them the corpuscles 

 of the blood can be seen as they arc carried along-. In some 



FIG. 8. Blood-vessels of the web of a frog's foot seen by a low magnifying power. 

 ., small arteries ; -, small veins. The minute tubes joining the arteries to the veins 

 arc the capillaries. The arrows show the direction of the circulation. In the 

 small portion marked off, the pigment cells, which occur throughout the web, are 

 also represented. 



places the current will be too swift for the corpuscles to be seen 

 distinctly. The red corpuscles of the froj; are, as we have said, 

 o\;d in shape, and are about three times as lur^e as those of 



D 



