56 ANATOMY OF THE LYMPHATIC SYSTEM. 



Further, it is easy to make out that the endothelial vesicles whose wall 

 shows distinct endothelial plates after treatment with silver occur 

 chiefly in the immediate neighbourhood of lymphatic capillaries, and 

 not only solitary, but sometimes scattered in groups, and sometimes 

 arranged in a linear series, close behind each other. It is already 

 probable, from what has preceded, that the endothelial vesicles finally 

 communicate with each other either by fusion, or by extension of the 

 vacuoles through the protoplasmic processes which connect their 

 walls ; and also that they communicate in a similar manner with the 

 lumen of neighbouring lymphatic capillaries, because, as we already 

 know, the endothelium of the lymphatic capillaries is in direct com- 

 munication with the lymph-canalicular cells. It is therefore only 

 necessary that the vacuole of the lymph-canalicular cell should extend 

 along the process which connects it with the endothelial cell in order 

 that it should open into the lymphatic capillary. In this manner, 

 first, a lymphatic capillary may become longer, and secondly, lateral 

 sinuses or dilatations may be formed. I have not observed these pro- 

 cesses in the normal omentum of the rabbit, because, as may be easily 

 conceived, they do not occur with sufficient frequency ; but in chronic 

 inflammation, on the other hand, I have followed them out in all 

 serous membranes to so great an extent, and with such intensity, that 

 I do not hesitate to accept them also as the final result in the case of 

 the above-described endothelial vesicles. 



These endothelial vesicles show a peculiar relation in the mesogas- 

 trium of the frog. I have described their development in the ' Quarterly 

 Microscopical Journal,' and have there stated that in female frogs, 

 in winter, they may be sometimes observed in a very considerable 

 number, owing to the presence of slight chronic peritonitis. I have 

 also said that the young vesicles bear cilia, which are directed to 

 their interior, and that this is sometimes still the case when their 

 wall is already distinctly differentiated into endothelial plates. So 

 far as their development is concerned, I have nothing to add to what 

 I have already said. In many vesicles the development of young cells 

 towards the lumen is very marked, while in others nothing is to be 

 seen of this process. I have also shown that these vesicles are not 

 simple cysts, as stated by Eemak, but that they stand in the closest 



