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 i 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. 



)S. The capillary walls ; difficult to see ; apparent 

 as thin slightly transparent boundary lines. 



y. The venous walls ; much like the arterial. 



/a The bloodflow in the small arteries. 



a. The rapid stream in the middle, containing 

 most of the red corpuscles. 



