240 DR. E. KI.EIN, 



nucleus. On carefully looking over a portion of the omentum 

 it can be ascertained that the last-named spaces are vacuoles 

 which open completely on one of the surfaces. I presume 

 the only interpretation that can be put on these different 

 appearances is this : there appear smaller or larger vacuoles 

 in the substance uniting the connective-tissue bundles, which 

 ultimately open through the endothelial niembrane first of 

 one then of the other surface. These vacuoles appear not 

 only at those places between the bundles, where there is 

 situated a connective-tissue corpuscle — in this case the vacuole 

 appears to be lined on one side by the cell, — but also 

 independently of these. 



Comparing with the above specimen one that had been 

 stained in the usual manner with nitrate of silver, we per- 

 ceive that the smallest examples of those holes which 

 penetrate completely through the membrane {a in fig. vii) 

 correspond to the interstitial substance of the endothelial 

 cells of the surface ; so that the above holes of the omentum 

 are due to a dehiscence of the interfascicular, and also of the 

 corresponding parts of the interstitial substance of the surface 

 endothelium, viz. two substances which, as is well known, are 

 identical in their chemical characters. That, therefore, the 

 theory of Ranvier, viz. that the holes are caused by migra- 

 tory cells, is to be dismissed need not be specially insisted 

 upon. The absence of migratory cells in many parts where 

 the holes are just being formed — ^judging from the very 

 small vacuoles found in the membrane — confirms this con- 

 clusively. I presume the above vacuolation is due to the 

 presence of fluid in the interfascicular substance, probably 

 liquefaction of part of this substance, and that a similar pro- 

 cess in corresponding portions of the interstitial substance of 

 the endothelium leads to the establishment of complete 

 holes. 



Turning now to the exauiinationof the omentum of young 

 and half-grown dogs and rats we ascertain the following 

 important appearances : 



(a) Apart from the large trabeculse containing large 

 blood-vessels, we find some parts in the fenestrated 

 portion which are of a denser structure; they contain, 

 besides tlie surface endothelium, a considerable number of 

 connective-tissue bundles, arranged parallel with each other ; 

 between these we find the ordinary connective-tissue cor- 

 puscles. 



(b) In some extensive portions, however, the meshes of 

 the fenestrated part are surrounded by tliin trabeculge which 

 are composed of a single connective- tissue bundle, ensheathed 



