EPITHELIAL CELLS GAMMARUS 131 



plasm, just as in plant cells. That my description is not 

 exhaustive in the latter respect is obvious from the fact that 

 the nucleus must, in any case, be marked off from the 

 central cavity by a delicate layer of protoplasm, although I 

 have not been able as yet to observe any such with cer- 

 tainty. 



6. Observations on some Epithelial Cells 



Since it was known to me from former experience that 

 the epithelial cells of the gill lamellae of Gammarus pulex 

 show a protoplasm very distinctly striated longitudinally 

 even in the living condition, I chose this object in order to 

 obtain further light upon the nature of its minute structure. 

 Both the investigation of freshly cut off gill lamellae, as well 

 as of small and unhurt living animals, showed that the 

 structure is not made up of fibrils, but is a distinctly reticulate 

 meshwork. Fig. 5 on Plate VI. shows the optical section 

 through the epithelium of a freshly cut off gill lamella, 

 such a section as can be well seen at the edge of a 

 lamella. Externally there is the relatively thin cuticle (c). 

 Under this comes a delicate pale border, the significance of 

 which was not clear to me. Then comes finally the pro- 

 toplasm of the epithelial cells, with a very beautiful reticu- 

 late meshwork structure. As has been said, it can be 

 clearly made out that the striation only depends upon the 

 arrangement of the framework of the meshes. The cell 

 boundaries were not to be made out distinctly in the optical 

 section, while they were most conspicuous in the surface view 

 of the gill lamellae. Immediately round the nuclei of the 

 epithelial cells there can be seen fairly distinctly a modifi- 

 cation of the striated structure caused by the layer of 

 meshes directly surrounding the nucleus being arranged 

 radially to the surface of the nucleus. 



In surface views, also, of the epithelial cells the net-like 

 structure can be observed very beautifully during life ; but 

 from this aspect it naturally does not appear striated but 

 irregularly reticular. The two epithelial layers of the 

 two surfaces of the gill lamella are connected with one 



