112 bulletin: museum of comparative zoology. 



in some places in Figures 2 and 3. It is possible that the granules 

 of the third class may be due simply to concentration of the finely 

 granular material of the second class. 



To what extent these appearances in the fixed cell correspond to 

 structure in the living cell cannot be said. The occurrence of the 

 larger granules or masses within clearer areas suggests coagulation 

 effects, the substance of the clearer area having been massed at the 

 centre of it by the action of the fixing fluid. It is quite likelv, how- 

 ever, that there may be some structural basis for this effect. The 

 occurrence of fibres radiating from these larger granules suggests that 

 they may mark the more important centres of a cytoplasmic network. 



In some cells, especially in certain ones of the brain, a system of 

 fibres could be detected lying at the periphery of the cell and extending 

 out into the nerve process. 



In the larger cells no definite, sharply outlined cell membrane is ever 

 seen. The cells appear to be enclosed by fine connective-tissue fibres, 

 which form more or less of a capsule about them. Small nuclei, doubt- 

 less of non-nervous nature, often occur about the nerve cells^ as seen in 

 the regenerated cell of Figure 11 (Plate 2). 



c. The Centred System. 



Evidences of concentric and radial structure are commonly seen, but 

 the exact nature of this structure would be overlooked except in the 

 most careful study, with the aid of oil immersion lenses. 



Cells of the first type. — The conditions represented in Figure 1 may 

 be considered typical for a large number of cells. This cell is from a 

 section 6§ ^ thick. In focussing up and down upon the section the 

 eye is caught by a granule which is conspicuous by its size, sharpness 

 of outline, and depth of stain. If it were a matter of a few cells or a 

 single one, this might be a chance condition, but when a similar con- 

 dition is commonly found in the observation of a large number of cells^ 

 we must conclude that we have not to do with an accidental granule. 

 Moreover, when such a conspicuous body is found to occupy a definite 

 and constant position in relation to other parts of the cell, and when it 

 is found to be the centre of a system of radiating fibres, it is evident 

 that the whole structure is one of importance. In speaking of the 

 centre of this structure as a " conspicuous granule," it is not meant 

 that it is the first thing that catches the eye in a casual glance at 

 the cell. Many of the granules or masses, which have been described 



