EXPLANATION OF PLATES. 97 



processes which project from the reticulated-branched cells 

 of the matrix up to the free surface between the endothelium 

 of the latter (Pseudo-stomata). 



c. Branched cells of the reticulum, which form, so to speak, the 



matrix of the chord. 



d. Lymph-corpuscles occupying the meshes of the reticulum. 



FIG. 52. From a fresh mesogastrium of rana temporaria. 

 M. p. III. 8. 



A. A knob freely projecting over the surface of the membrane, con- 

 sisting of a clear matrix, in which some granular cellular ele- 

 ments are to be seen ; the knob is covered with an endothelium 

 c, which is not so flat as the endothelium in general. 

 a. The root of the knob. With the endothelial covering of this 

 knob there are in direct continuity four cells, which spring 

 from a common protoplasmic peduncle by means of long 

 thin protoplasmic filaments. 

 The cells 6 have shown for a considerable length of time active 



amoeboid movements. 

 The cell d was also in continuity with the endothelium a of a fold 



of the membrane. 



There cannot be any doubt that these cells are endothelial 

 cells, and consequently that they are in a state where they 

 are already amoeboid cells (lymph corpuscles), although they 

 have not yet perfectly separated from the endothelial 

 matrix. 



FIG. 53. From a fresh mesogastrium of rana temporaria. 

 M. p. III. 7. 



1, 2, and 3. Vesicles of the tissues, the interior of which is lined 

 with ciliee ; the wall consists of a nucleated protoplasm ; 

 each of these vesicles develops from one cell of the tissue 

 by vacuolation ; in 3, three granular cells are to be seen 

 two of which are provided with cilias. These could only 

 have been brought into the cavity of the vesicles from 

 outside, because some of the germinating endothelial cells of 

 the surface are provided with cilise. 



In 4 the summit of such a vesicle is adjusted, which shows 

 a stoma ; so that the interior of the vesicle communicates 

 with the free surface of the mesogastrium. This stoma is 

 H 



