6o 'Journal of Comparative Neurology and Psychology. 



in the minds of the various workers who have coined these terms 

 as to their significance and relationship. 



It is rather hard to make a classification of these structures as 

 described by the various authors because in most instances the 

 cytological study was not followed or preceded by an examination 

 of living nerve cells. Our results have been so clear and satis- 

 factory that we are tempted to try to correlate some of the pre- 

 vious facts with them. Probably the commonest structure present 

 in the cytoplasm of the invertebrate nerve cells is the vacuole. 

 These vacuoles are present in all of the great groups already cited, 

 although usually described under the terms "lymph space," 

 "Netzapparate," "Saftkanalchen, " "Trophospongien, " etc. The 

 vacuole can be determined in the following manner in the living 

 cell: Isolate a nerve cell and study it in a 1-500 solution of methylene 

 blue or neutral red in normal salt solution under the oil immersion 

 lens. At first, but little can be determined; but as the stain pro- 

 gresses the vacuoles become more distinct and their contents often 

 take on a differential stain. The experienced worker can make out 

 these vacuoles without any stain. The time that it takes to stain 

 these vacuoles will vary; but usually from 5 to 20 minutes will be 

 the limit, as after that time the nerve cell is apt to become over- 

 stained and undergo some changes in its general appearance and 

 the character of its parts. This gives about 15 minutes when a 

 critical study may be made. During this time the vacuoles are 

 readily made out as isolated spherical bodies containing a fluid. 

 It is impossible to trace any connection between vacuole and vacu- 

 ole. The size is also further evidence of their individuality, for 

 they range from the very minutest bodies recognizable with the 

 oil immersion lens to structures a third the size of the nucleus. 

 Studying these vacuoles in Planorbis and Limax for two years, in 

 which we examined almost weekly the living nerve cells from 

 hundreds of specimens, we are convinced that these vacuoles are 

 transitory structures, that they vary in number from time to time, 

 and that they are not limited by a distinct wall. The vacuoles 

 move about in the cytoplasm when the nerve cell is put under pres- 

 sure, which would be impossible if they were part of lymph spaces 

 that had grown in from the surrounding neurogha tissue. 



The Chronodromiten and Mitrochondrien of Rhode, the Tro- 

 phospongien of Holmgren as interpreted by Bergen, present 

 in Helix but not figured by McClure, the chromophilic corpuscles 



