144 PROTOPLASM 



be seen to have a reticular structure, and to consist only of 

 a single layer of meshes. Correspondingly, the walls of 

 the meshes are placed perpendicularly to the inner and 

 outer limiting lamellae of the wall. At the nucleus, the 

 layer of meshes splits into two, so as to surround it both 

 externally and internally by a thin layer of protoplasm, 

 the meshes of which are placed vertically with regard to the 

 nucleus and to the limiting lamella. If the surface of the 

 wall of the capillary be focussed (o), a confirmation of the 

 meshed structure is obtained, which, of course, can be seen 

 in this aspect also. The result is that, corresponding 

 to its extension in a longitudinal direction, the capillary 

 consists of a meshwork modified into a fibrous structure. 

 Whether or not the protoplasm belonging to the individual 

 nuclei is separated by cell boundaries I was unable to 

 determine in preparations of this kind, and I have not 

 followed up this point more thoroughly. 



Ley dig has noticed quite correctly, as far back as 1885 (p. 15), 

 that the cells of the blood capillaries (gills of Salamandra) consist 

 in section of a single layer of alveoli, and hence appear striated. 

 Only he draws the dark wall of the alveoli very thick, and the 

 clear intervening spaces very narrow. From this observation, 

 however, he wishes to infer that the thin plate-like body of these 

 cells is porous. "Under some circumstances the fine pores 

 might widen into larger openings, and thus permit the passage 

 through of blood corpuscles." That this view, which would lead 

 to consequences physiologically untenable, is also unjustifiable 

 anatomically is evident from the description given above. 



12. Connective Tissue Cells between the Nerve Fibres of the 

 Ischiadic Nerve of Rana escidenta 



In teased - up preparations of the ischiadic nerve, 

 numerous elongated spindle-shaped connective tissue cells 

 are obtained isolated, which are interpolated between the 

 nerve fibres. By successful isolation it can frequently 

 be seen that these cells are connected lengthways like a 

 chain, as is shown in Fig. 4, a, Plate VIII., the protoplasm 

 passing directly from one into the other. The cells have a 

 somewhat different aspect, according to the view in which 



