340 SPECIAL HISTOLOGY. 



The former, as Schwann and I have shown, proceed from the 

 coalescence of single cells. At the primary origin of these 

 vessels, tubules of some size are formed, at first by the successive 

 apposition in a straight line and the coalescence of rounded- 

 angular cells, and the subsequent absorption of the septa and 

 of the contents, but not of the nuclei, which remain attached 

 to the former cell-membrane, now become the capillary tunic. 

 Delicate pointed processes then project from the walls of these 

 little vessels, which rapidly elongate, and meeting similar 

 pointed processes of stellate cells dispersed in the surrounding 

 tissue, coalesce with them. At the same time, the other pro- 

 cesses of these cells join, so that there is soon produced a 

 network of stellate cells, continuous with the already formed 

 capillary tube or tubes. This net, however, is never spread, 

 for the prolongations, given off from already formed and per- 

 vious capillaries, and the neighbouring cells connected with 

 them, are constantly and rapidly transformed into fresh capil- 

 laries, by the continual increase in size of the coalescing processes 

 from their point of origin onwards, and their becoming hollow. 

 In this way are produced vessels which are at first extremely 

 fine, and admit only blood-plasma — true vasa plasmatica s. 

 serosa ; but they rapidly enlarge, until at last the blood- 

 globules are transmitted through them, and the capillaries are 

 perfected. Owing to the circumstance, that while these pro- 

 cesses of the stellate formative cells thus enlarge, the bodies of 

 the cells do not expand in a corresponding manner, but appear 

 as simple nodular points in the vessels, all vestige of the original 

 cellular network is gradually lost, and subsequently the situa- 

 tion of the bodies of the cells can only be determined by the 

 position of the persistent nuclei. When finer tubules have 

 once been formed from the previous larger capillaries, the facili- 

 ties for the passage of the blood are continually undergoing 

 augmentation, inasmuch as new stellate cells are constantly 

 enlarging into vessels, whilst, at the same time, fresh vascular 

 material is as constantly furnished by the apposition of new 

 cells. New connexions also are frequently formed between 

 capillaries which are already pervious, partly by the direct 

 meeting of prolongations from them, partly also by the mutual 

 connexion of formative cells lodged in their interstices, 

 whence, of course, the original net is rendered closer. This 



