THE LYMPHATIC SYSTEM. 171 



the majority of cases the black spots are formed by the albu- 

 minous serum which these openings retain by capillary attrac- 

 tion, having been coagulated and stained by the nitrate of 

 silver, producing a plug. In other cases, a globular cell re- 

 sembling a lymphoid corpuscle occupies the stoma, surrounded 

 by a black margin due to the action of the silver. Other cells 

 have a greater resemblance to small endothelial cells than to 

 lymphoid corpuscles. The irregularity of their distribution in 

 different membranes, in different animals, and at different 

 ages, seems to favor the idea of such an accidental manner of 

 formation. 



Klein on true and false stomata. Klein divides the sto- 

 mata vera, or true stomata, into two classes : a, those which 

 form the mouth of a vertical lymphatic channel leading to a 

 superficial vessel (they have a 

 special endothelial lining) ; and 

 &, those formed by discontinuity 

 between the endothelium of the 

 surface leading into a simple 

 lymphatic sinus near the sur- 

 face, and lined only on the lower 

 surface with endothelium. Pseu- 

 do-stomata, or false stomata, may 

 be produced, according to this 

 observer, by the prolongations of 

 the sub- endothelial branched cells 



-, /. , ,. FIG. 76. Frond of fern (Osmtmda Clayto- 



beCOimng free by projection OUt- niana), under-surface showing stomata. 



ward between the endothelial 



cells. In pathological conditions he has seen an extensive 

 cell-proliferation going on from one of these projecting pseudo- 

 stomata. Ranvier accounts for the origin of the fenestra 

 of the omentum in a similar manner, as for the stomata. It 

 is of interest to know that the openings do not exist before 

 birth, but increase in size and number as age advances. 

 Klein, on the other hand, considers that the openings in the 

 omentum are produced by a process of vacuolation. The 

 arrangement of the connective-tissue fasciculi around these 

 openings is not that of complete rings, but is such that each 

 opening is bordered by several fibres which take part in the 

 formation of other openings in consequence of the irregularity 

 in their arrangement. The endothelial cells may form a com- 



