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HANDBOOK OF PHYSIOLOGY. 



the nucleus; at others, the meshwork is more evenly disposed, as in 

 fig. 9. At the junctions of the fibrils there are usually slight enlarge- 

 ments or nodes. 



In some cells, particularly in plants, hut also in some animal cells, 

 there is a tendency toward a formation of a firmer external envelope, 



Membrane of cell 



Reticulum of cell -.. ^ 



^.^ Membrane of nucleus. 



Achromatic substance of 

 nucleus. 



-..Chromatic substance of 

 nucleus. 



j. 8. Cell with its reticulum disposed radially; from the intestinal epithelium of a worm. 



(Carnoy.) 



constituting in vegetable cells a membrane distinct from the more 

 central and more fluid part of the protoplasm. In such cases the reticu- 

 lum at the periphery of the cell is made up of very fine meshes. The 

 membrane when formed is usually pierced with pores by which fluid may 

 pass in, or through which protrusion of the protoplasmic filaments form- 

 ing the cell's connection with other cells surrounding it may take place. 

 It is an exceedingly interesting question whether in cells the one 



Fig. 9. (A.) The colorless blood-corpuscle showing the intra-cellular network, and two nuclei 

 with intra-nuclear network. (B.) Colored blood-corpuscle of newt showing the intra-cellular net- 

 work of fibrils. Also oval nucleus composed of limiting membrane and fine intra-nuclear network 

 of fibrils. X800. (Klein and Noble Smith.) 



part of the protoplasm can exist without the other. Schafer summar- 

 izes the matter thus: "There are cells, and unicellular organisms both 

 animal and vegetable, in which no reticular structure can be made out, 

 and these may be formed of hyaloplasm alone. In that case, this must 

 be looked upon as the essential part of protoplasm. So far as amoeboid 

 phenomena are concerned it is certainly so; but whether the chemical 



