;66 



GENERATION AND DEVELOPMENT. 



external layer of cells is converted into the walls of the 

 vessel. 



In the development of capillaries, another plan is pur- 



Fig. 226* 



V 



* Fig. 226. Capillary blood-vessels of the tail of a young larval 

 frog. Magnified 350 times (after Kolliker). a, capillaries permeable 

 to blood ; b, fat-granules attached to the walls of the vessels, and con- 

 cealing the nuclei ; c, hollow prolongation of a capillary, ending in a 

 point ; d, a branching cell with nucleus and fat-granules ; it communi- 

 cates by three branches with prolongation of capillaries already formed ; 

 e, e, blood-corpuscles still containing granules of fat. 



