EXPLANATION OF PLATES. 



I have to offer my sincere thanks to the Government Grant Com- 

 mittee of the Royal Society for having furnished the means for the 

 execution of the following plates : 



PLATE I. 



FIG. 1. Germinating Endothelium of tracts freely projecting over the 

 surface of the pleura mediastini of a healthy cat. Preparation stained 

 with nitrate of silver. 



M. p. Hastnark, E. p. No. III. Obj. 7. 



FIG. 2. Surface of a mesentery of frog, stained with nitrate of silver. 

 M. p. E. p. III. Obj. 5. 



a. Common flat endothelial cells of the surface, amongst which six 

 couples of cells are to be found, which have stained deeply with 

 the reagent, and which consist of a granular protoplasm ; these 

 cells are not flat, but more or less polyhedral germinating or 

 young endothelial cells. Between the cells of these couples 

 more or less distinct openings are to be seen stomata vera, 

 which lead into a lymphatic space below ; they are exactly like 

 the stomata of the epidermis of plants. 



FIG. 3. Silver-stained preparation of the septum cysterniB lymphaticae- 

 magnae of frog. 

 M. p. III. Obj. 5. 



A. Peritoneal surface of that membrane. 



B. The surface directed towards the cysterna shows amongst the 

 common flat endothelial cells, the size and shape of which are 

 obviously different on the two surfaces, openings of canals, by 

 which that septum is penetrated. The openings, viz. the 

 canals are lined with a special layer of polyhedral cells, which have 

 the character of young germinating endothelial cells. 



G 2 



