26 CHARLES F. W. MC CLURE, 



SO actively controverted by the earlier investigators, is generally con- 

 ceded by the more recent workers as an established fact. It is further 

 seen that the main diflerences of opinion, that exist in the minds of 

 these investigators, relate chiefly to the manner in which the fibrils 

 are arranged in the cell, and to the functional character of these fibrils. 



My own observations have led me to the conclusion that fibrils 

 form a constituent element in the structural make up of the nerve 

 cells of Invertebrates , and that they are in no way connected with 

 the neuroglia in Rohde's sense. 



In addition to the presence of fibrils, a substance, apparently 

 granular in character and differing morphologically as well as chemi- 

 cally from all other observable structures within the cell (as fibrils 

 and ground-substance), must likewise be regarded as a constituent of 

 the cells structure; unless in the case of these cells, as opposed to 

 those of Vertebrates, its exclusive affinity for certain dyes, notably 

 methylen blue, is entirely disregarded as a diagnostic character. 



We pass now to the detailed consideration of the nerve cells of 

 certain Gastropods, with special reference to the arrangement therein, 

 of their chromophilous and fibrillar elements. 



The Structure of the Nerve Cells of Grastropoda. 



(Helix pomatia, Arion empiricorum and Limax maximus.) 



The majority of the nerve cells in the ganglia of these Gastro- 

 pods are of unipolar type, although, as is well known, bi- and multi- 

 polar cells are also present. 



One remarkable feature which characterizes these cells, parti- 

 cularly the unipolar, is the enormous size which some of them attain. 

 Any well chosen section through the infra-oesophageal ganglion not 

 only shows these large cells, but also the marked variation in size 

 which the nerve cells in general present. This variation has been 

 commented upon particularly by Buchholz (2), who describes them 

 as possessing diameters varying between 3 and 240 u ; by Solbrig (41) 

 who mentions the largest cell observed by him as possessing a 

 diameter of 220 /< ; and finally, H. Schultze (40) describes one as 

 having a diameter of 320 (.t. 



The nuclei are also large in proportion to the size of the cell. 

 In the largest cell described by Schultze, the nucleus is figured as 

 having a diameter of 260 ^<. 



It may be said, in general, that the size of the nuclei is large 

 in proportion to the size of the cell, and normally, the nuclei are 

 usually spherical in form. 



