Smallwood and Rogers, Molluscan Nerve Cells. ji^ 



the bodies in Planorbis and they are of larger size. When tested 

 with Sudan III and cyanin they give the colors which are charac- 

 teristic for fats. 



The cells o^ Limnea contain granules so closely similar to those 

 of Planorbis that we have yet to find any way of distinguishing 

 them. The pigmented granules are of the same color, size, and 

 position in the cell. They also react in the same way to the 

 various tests. We have not had opportunity to observe any sea- 

 sonal changes in their appearance. 



In the cells of Melantho we find a pigment of a light yellow color. 

 The granules are generally smaller than those found in Planorbis 

 and Limnea. This is evidently a different sort of substance, for 

 it does not give a blue test with sulphuric acid. We have not yet 

 made sufficient study to make a definite statement as to its chem- 

 ical nature. 



VII. THE CENTROSOME IN NERVE CELLS. 



A few years ago the centrosome was all the fashion among bio- 

 logical works. The question of its origin, use and fate furnished 

 the basis for many papers. With the accumulation of a consider- 

 able number of facts, it became evident that no general homology 

 was to be established for the centrosome; nor did its detailed 

 structure permit of reducing all centrosomes to a common form. 

 About the only feature generally agreed upon was that the cen- 

 trosome was at the center of radiation. In order to be sure that 

 the dark staining granule or granules or vesicle when found in 

 various parts of the cytoplasm has any claim to be regarded as a 

 centrosome, it must have astral radiations. The question of the 

 sphere substance which immediately surrounds the centrosome 

 is more indefinite and less clearly defined than that of the centro- 

 some. It may assume a variety of appearances and probably 

 plays an unimportant part. 



While centrosomes were being recognized in a great variety of cells, von Len- 

 HOSSEK ('95) vvas the first definitely to announce the presence of centrosomes in 

 nerve cells. His observations were on the moderate sized spinal ganglion cells of 

 the frog. He found the nucleus occupying in some cells an eccentric position and 

 flattened or slightly concave on the side nearest the cell center. In this larger 

 region of the cytoplasm there was a concentric figure in thecenter in which he located 

 minute granules. 



Lewis ('96) describes in the giant ganglion cells of an annelid centrosomes on 

 one side of the nucleus — the one toward the center and the one which tends to be 



