598 



GENERATION AND DEVELOPMENT. 



of the heart shortly assumes the characters of blood. At the 

 same time the cavity itself forms a communication with the 

 great vessels in contact with it, and the cells of which its wall 



FIG. 232. 



Capillary bloodvessels 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 concealing 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. 



are composed are transformed into fibrous and muscular tis- 

 sues, and into epithelium. 



Bloodvessels appear to be developed in two ways, according 

 to the size of the vessels. In the formation of large bloodves- 



