4-6 Journal of Comparative Neurology and Psychology. 



later paper we hope to show structural and physiological simi- 

 larities between the nerve cells of invertebrates and vertebrates. 



The various terms employed to describe the stainable and non- 

 stainable substances of the cytoplasm of vertebrate nerve cells have 

 been in large measure carried over to the description of the inver- 

 tebrate nerve cells. Since the Nissl bodies were discovered and 

 known as the visible or stainable part of the cytoplasm, the fol- 

 lowing words have been used for similar structures; the chromatic 

 substance, the chromophile part of the cytoplasm, the chromato- 

 phile elements, the chromophilic particles, the basophile constit- 

 uents, the tigroid substance, the sigroid substance, the collagenous 

 substance, granules or granular substance. The names of most 

 of the authors who have created this confusing and unnecessary 

 terminology may be found in Robertson's review. In a similar 

 manner the non-stainable substance is designated as the achro- 

 matic, fundamental, invisible, not formed, unstainable, acidophile 

 substance, trophoplasm, or kinetoplasm. The fibrillar substance 

 is included in these terms although it is a distinct structure and 

 whether it is considered as a part of the stainable or non-stainable 

 substance depends largely on the writer. 



The pigment found in nerve cells of the central nervous system 

 is deposited in masses distinct from the Nissl bodies and is pale 

 yellow or dark brown. These seem to be unhke, the brown appear- 

 ing early in hfe and ceasing to increase after a few years. It is not 

 blackened by osmic acid. The yellow appears in man during 

 the sixth year, increases with age and is blackened by osmic acid. 

 Some writers maintain that the yellow is not fat, but that it under- 

 goes fatty degeneration. In certain mental diseases there is an 

 accumulation of this pigment and a breaking down of the struc- 

 ture of the cytoplasm. Whether the two processes are related 

 or not is unknown. A golden yellow pigment is found in the nerv- 

 ous system of certain gasteropods and a yellow pigment in other 

 classes of invertebrates, the origin and use of which are somewhat 

 problematic. 



A further modification of the cytoplasm of nerve cells is found 

 in the presence of vacuoles, lymph spaces and the actual though 

 infrequent penetration of nerve cells by capillaries. The vacuoles 

 occur in the cytoplasm, nucleus, and nucleolus and are probably 

 in each case formed in a similar manner even when the exciting 

 cause is different. The vacuoles which occur in the nucleolus 



