60 ANATOMY OF THE LYMPHATIC SYSTEM. 



capillaries. But on closer observation another much more important 

 fact is brought to light ; namely, that the branched cells of the 

 matrix stand in direct continuity with the protoplasmic wall of these 

 young capillaries, by their processes. From the extraordinarily com- 

 mon occurrence of the above fact in various modifications, and from 

 the clearness with which it may be observed, no error is possible. I 

 must especially insist upon this now, because in any figure, however 

 successful, apart from the suspicion one may always feel of a drawing, 

 this can never be so clearly recognised as it appears de facto under 

 the microscope. 



We need not seek long in a patch in which the number of such 

 young capillaries is considerable in order to come upon a capillary 

 which ends csecally. This is either a short lateral branch or a longer 

 capillary which makes a loop-like bend. At the csecal end we can 

 recognise very clearly the protoplasmic character of the wall. The 

 lumen becomes more or less suddenly narrowed, the wall finally 

 becomes solid, and passes into a perfectly ordinary nucleated branched 

 cell of the matrix. We find all forms of this hollowing out of the 

 branched cells ; at one time only in a thicker process of a cell, at 

 another even in the body of the cell itself. 



A very common occurrence is, further, that the branched cells, as 

 we have already had occasion to state, show vacuoles, both in the 

 body and also in thicker processes. The vacuole^ -become elongated 

 towards a capillary branch which is being hollowed out, and finally 

 fused with it. Capillaries, therefore, are not only formed from pre- 

 viously existing capillaries by continuous excavation of the branched 

 cells connected with their walls, but are also formed isolated in the 

 branched cells themselves, becoming ultimately united with the 

 former. Isolated vacuolation for the purpose of the formation of 

 blood-capillaries is a perfectly distinct process from vacuolation for 

 the purpose of the development of lymphatic capillaries ; for in the 

 latter case vesicles are developed whose wall almost immediately 

 shows an endothelial differentiation, even when these vesicles have not 

 yet come into communication with lymphatic vessels ; in the former 

 case, on the contrary, this differentiation into endothelial plates does 

 not take place for a considerable time. 



