386 



Four black spots, seen in the course of the vessel, are blood- 

 corpuscles much out of focus. 



HI. rhotfgraph representing the stomata between the 

 epithelial cells of a vein l-50th of an inch in 

 diameter in the mesentery of the frog. Nega- 

 tive No. 40, New Series. From preparation 

 No. 3276, Microscopical Section. Magnified 

 400 diameters by Wales's ^th objective. The 

 preparation was made by myself. 



Owing to the curved form of the vein, but 

 a small portion of its surface is in focus. In 

 this portion the silver stained boundaries of 

 several of the epithelial cells of the vein are 

 visible, and display in their course certain re- 

 markable forms, which maybe compared to the 

 Wormian bones of the cranial sutures. These 

 are the so-called stomata. They are irregu- 

 larly rounded in form, and vary from the 

 1 -10000th to the l-4000th of an inch in long diameter. 

 Those shown in the photograph present a clear central space, 

 bounded by a sharp blatk outline, which is sometimes even 

 thicker than the boundaries of the cells themselves. The 

 nuclei of the epithelial cells are not shown. The cut ex- 

 hibits one of these cells, a, with portions of the boundaries 

 of adjacent cells, b, b, b, and the stomata, c, c, c. 



IV. Photograph representing the stomata between the 

 epithelial cells of a vein, 1-1 00th of an inch in diameter, in 

 the mesentery of the frog. Negative No. 224, New Series. 

 From preparation No. 3062, Microscopical Section. Magni- 

 fied 400 diameters by Wales's ith objective. The prepara- 

 tion was made by Dr. Kennon. 



The vein having collaj^sed, the epithelial cells of the lower 

 wall come into focus in places, and so somewhat complicate 

 the representation. The stomata are abundantly present, but 

 none of them equal in size the largest shown in the last photo- 

 graph ; in several places, moreover, black spots, similar to the 

 other stomata in shape and size, may be observed in the cell 

 boundaries. 



V. Photograph representing the stomata of a vein, 1-lOOOth 

 of an inch in diameter, in the mesentery of the frog. Nega- 

 tive No. 194, New Series. From preparation No. 3276, 

 Microscopical Section. Magnified 400 diameters by Wales's 

 -ith objective, illuminated by the Magnesium lamp. The 

 small vein represented comes well into view, while the nuclei 

 of the surrounding tissue are seen out of focus on each side of 

 it. Several of the stomata present clear centres, while others 



