I.] THE FROG. 93 



a. The arteries, running mainly towards the free 

 edge of the web, and constantly diminishing 

 in size as they break up into branches ; the 

 blood-flow, from larger to smaller branches. 



/?. The capillaries, in which the arterial branches 

 end : small vessels forming a close network 

 and frequently branching or anastomosing 

 without much alteration in calibre. 



y. The veins, formed by the ultimate union of 

 the capillaries, and increasing in size as they 

 unite with one another ; the blood-flow, from 

 smaller to larger factors. 



c. The nature of the blood-flow ; the current is 

 marked by the solid bodies {corpuscles) carried 

 along in the blood-fluid : it is most rapid in the 

 arteries ; slowest, and most uniform, in the ca- 

 pillaries. 



iii. Place a small drop of water on a bit of thin mica 

 or of a thin cover-slip, and place the same, water 

 downwards, gently on the web : then examine with 

 •j- or | obj. ; note — 



a. The walls of arteries, capillaries, and veins. 



a. The arterial walls, tolerably thick, seen as a 

 clear well-defined line on each side of the 

 blood-stream. 



/?. The capillary walls ; difficult to see ; apparent 

 as thin slightly transparent boundary lines. 



y. The venous walls ; much like the arterial. 



b. The blood-flow in the small arteries. 



a. The rapid stream in the middle, containing 

 most of the red corpuscles. 



