-i I T. 222.] 



FORMATION OF CAPILLAR! KK. 



529 



Fis. 21s. 



vessel. In the next place, delicate, pointed processes bud forth 

 from the walls of these vessels, and these quickly become elongated, 

 and meet with similar pointed processes, derived from stellate cells 

 scattered in the surrounding tissue. These processes coalesce at 

 their point of meeting, and, at the same time, other prolongations 

 of the cells unite with each 

 other, so that a network is pro- 

 duced, consisting of the stellate 

 cells with the already formed 

 capillary tube or tubes. This 

 network, however, is never ex- 

 tensive, for the processes which 

 issue from the perfect capil- 

 laries already formed, as well 

 as from the cells which join 

 them, are always quickly trans- 

 formed into capillaries by the 

 thickening and hollowing out 

 of the prolongations. In this 

 manner vessels are produced 

 which are at first extremely 

 fine, and only receive blood- 

 plasma (genuine rasa plasma- 

 tica s. serosa) ; but they soon 

 become wider, till at last even 

 the blood-globules pass through, 

 and the capillaries are then 

 fully formed. During this en- 

 largement of the processes of 

 the stellate formative cells, the 

 bodies of the cells do not en- 

 large correspondingly, but sim- 

 ply appear as nodular points in 

 the vessels; thus it happens 

 that every trace of the primi- 

 tive network of cells gradually 

 disappears, and the position of the cell-bodies can afterwards only 

 be made out from the situation of the persisting nuclei. When 

 these finer tubes have once been formed from the primitive larger 

 capillaries, the enlargement of the vascular system proceeds further 

 and further from these new vessels, other stellate cells becoming 

 widened to form capillaries, while, at the same time, new material 



M M 



Capillaries from the tail of a tadpole, a. Fully- 

 developed capillaries ; 6. cell-nuclei and remains 

 of the contents of the primitive formative cell ; c. 

 c£ecal processes of a vessel; d. stellate formative 

 cell, connected by these processes with three 

 similar processes of pervious capillaries; e. blood- 

 globules, still containing some granules. Magni- 

 fied 350 times. 



