Smallwood and Rogers, Molluscan Nerve Cells. 57 



distributed, while in the larger cells it tends to concentrate in regions, giving the 

 cytoplasm a blotchy appearance; (3) rather conspicuous granules or masses staining 

 fairly deeply and often surrounded by an area within which the material of the 

 second class is less dense; (4) a fine fiber irregularly distributed through the cell 

 body, but often appearing to be associated with the more conspicuous granules 

 and sometimes occurring about granules as centers of radiations. 



Hamaker ('93) shows in one type of the nerve cells in Nereis the following: 

 In the posterior half of the brain there are several pairs of very large cells which 

 have a very striking characteristic. The nucleus lies in the narrow end of the cell, 

 and is surrounded by the granular cytoplasm. At the other end of the cell, there 

 is a large vacuolar space containing a number of deeply staining bodies of irregular 

 form, embedded in an indistinct coagulum (Fig. 6). Other cells have very finely 

 granular substance occupying a similar position, the granules being much smaller 

 and staining less deeply than those of the body of the cell. In these cases the 

 nucleus shows no signs of degeneration. 



Lengendre ('05, '06) in a series of short papers during the years 1905 and 1906 

 has given us reports of an investigation on nerve cells of Gasteropods. He has 

 studied the cell from the physiological point of view, with the idea of determining 

 whether the structures described by Holmgren and others are in any way related 

 to the nutritive functions of the cell. He follows the work of Holmgren, 

 BocHENEK, McClure, Rhode, and others. A study is made of the effects of 

 various fixing reagents and he finds that Rabl's solution is a very poor reagent for 

 the study of nerve cells. Consequently many of the results which have been 

 obtained through the use of this fluid are to be considered as artefacts and not as 

 actual structures which exist in the living cell. He questions the work of Rhode 

 and does not believe that the fibrils of the nerve protoplasm are continuations of 

 the processes of the neuroglia cells on account of the difference in size and staining 

 qualities. He finds in the cells of Helix pomatia vacuoles of various sizes, arranged 

 in various ways in the cell. Sometimes they communicate with one another and 

 sometimes open to the outside of the cell. These vacuoles are without definite 

 walls and contain a homogeneous fluid without granules. The chromophile 

 granules are always found in the protoplasm when present at all and never appear 

 in the vacuoles. Legendre does not admit the theories of Holmgren concerning 

 the nutritive functions of the nerve cells. He advocates in his first paper that the 

 vacuoles represent accumulations of excretory products and that they are in no 

 way connected with the constructive metabolism of the cell (Fig. 7). 



In these papers he calls attention to the following points: He describes the 

 appearance of living nerve cells that have been immersed in water for a consider- 

 able time. The result is a rapid increase in size due to osmotic exchange. In the 

 protoplasm of the cells thus treated the meshes of the spongioplasmic net become 

 greatly enlarged and more clearly visible. The nucleus becomes large and numer- 

 ous vacuoles appear in the periphery of the cytoplasm. He also advances the 

 idea that the Holmgren canals in the trophospongium are to be interpreted as 

 pathological rather than nutritive and that they act more like the phagocytes in that 

 they destroy cell substance rather than build it up. 



Pflucke ('95) notes the presence of a few vacuoles in the cell plasma which 

 he does not regard as true vacuoles but as accumulations of unstainable substance. 



Ewing ('98) takes an extreme position in regard to the presence of vacuoles, 

 claiming in the majority of cases that they are cadaveric or artificial products. 



