538 ROSS G. HARRISON 



the main mass the membrane from the two adjacent sides has 

 united, leaving a large hole, and there are also several smaller 

 spaces left uncovered. A considerable number of isolated 

 branched mesenchyme cells are to be found outside the area 

 covered by the membrane. All of these structures are fixed to 

 the cover-slip. The cells forming the membrane are one layer 

 thick. -^ Those near the periphery of the membrane have the 

 greatest superficial area, and there is a general decrease in their 

 dimensions as the tissue mass is approached, though there are 

 irregularities in this respect. There are no mitoses present, 

 which indicates that membrane formation is due to movement of 

 cells and not to growth.-^ There is no way of ascertaining whether 

 this particular membrane is endothelial or from the epithelium 

 lining the intestinal tract. 



The third culture (fig. 10) was supported upon spider web in 

 the manner described above. It does not show such extensive 

 cell wandering as some other preparations but it is very char- 

 acteristic. A membrane (m) has been formed on the cover 

 glass at one side of the preparation, and at another place, quite 

 detached from the main mass, there is a small group of cells 

 (a) which have moved out along the web fibers. On the opposite 

 side of the tissue a considerable mass of cells (b) projects sharply 

 outward and is firmly attached to the web. What is most inter- 

 esting in this case is the banding together of spindle cells upon 

 bundles of web fibers or upon single threads to form structures 

 which closely simulate embryonic nerves with their sheath cells 

 (c). In several places web fibers covered with such cells cross 

 one another and here there is some accmnulation of cells. Spindle 

 shaped cells are also found singly (e). Some necrotic tissue (d) 

 is present at places around the periphery of the main mass. The 

 arrangement of these structures is shown in figure 12, which 

 represents part of the preparation under higher magnification. 



2" Cf. M. R. and W. H. Lewis, Anat. Rec, vol. G, 1912. Also Burrows, 17th 

 International Congress of Medicine, London, 1913; Section General Path, and 

 Path. Anat., p. 225. 



2^ This is in harmony with the observations of many authors on the covering 

 of wound surfaces by epithelium. 



