74 'Journal of Comparative Neurology and Psychology. 



flattened or concave. The sphere varies somewhat in size, but its diameter is 

 approximately one-third that of the cell. In some cases it is quite sharply marked 

 off from the surrounding protoplasm of the cell; in other cases the transition to the 

 surrounding protoplasm is so gradual that it is impossible to define its limits with 

 precision. In the center of the sphere there is a highly refractive body, or occasion- 

 ally two or three such bodies. From this central corpuscle there are in many prep- 

 arations radiations which transverse the whole sphere. The rays are due to the 

 close arrangement in radiating lines of granulations of the ordinary size. Some of 

 the rays are very distinct, others much less clear. They are few in number, usually 

 separated by rather uniform intervals, but often interrupted over an arc of many 

 degrees. The central corpuscle (or corpuscles) is very distinct. It is sometimes 

 spherical, sometimes elongated so as to look like a short rod. It shows a remark- 

 able affinity for stains, being always colored much more deeply than any other 

 part of the sphere. 



McClure ('97) finds in certain cells in the ganglia of Helix structures which 

 he has been pleased to designate as centrosomes. In certain unipolar cells of Helix 

 which have a transverse diameter ranging between 17 and 22 ,«, the nucleus was 

 found in longitudinal sections to have an eccentric position. In addition to this, 

 in such cells the side of the nucleus directed toward the axis cylinder pole of the 

 cell was often flattened, or more frequently invaginated, so that the nucleus pre- 

 sented a kidney-shaped appearance. The flattened or invaginated side of the 

 nucleus was never found to be directed exactly opposite to the base of the axis cylin- 

 der process, but always to a point one side of it. In the body of the cell, directly 

 opposite the invagination, a disk-shaped structure was found. The contents of 

 the disk was finely granular but so far as could be determined there was no evidence 

 of radiation. At about the center of the disk two or three small granular bodies 

 were present which stained much deeper than the surrounding granules and which 

 are taken to be centrosomes (Mikrocentrum). 



Hamaker ('98) described in the nerve cells of Nereis structures to which the 

 term centrosome was given. He found from two to as many as ten in a single cell, 

 each one consisting of a deeply stained granule. No radiations were seen. 



KoLSTER ('00) represents in Cottus scorpius deeply stained granules with no 

 radiations, which are designated as centrosomes. 



Rand ('01) states that there is commonly present in the nerve cells of Lumbri- 

 cidas a centered system consisting of centrosome and radiations. The single cen- 

 trosome (or rarely two, or even three, small granules lying close together) is found 

 in the axis of the cell, on the side of the nucleus opposite the nerve process, and 

 therefore on the side of the greatest cytoplasmic mass. It is generally not far from 

 the nucleus and approximately at the center of the cell as a whole. Radiations 

 consisting of fibrils bearing minute granules extend from the centrosome toward 

 the periphery of the cell. Calling these- "primary radiations," there may also be 

 distinguished secondary radiations, which arise from certain of the large granules 

 in the course of the primary radiations. In rarer cases tertiary radiations may be 

 found arising from granules in the secondary radiations. The centered system is, 

 therefore, a complex one, consisting of a chief center or centrosome, and numerous 

 inferior centers situated throughout the cytoplasm, all with their corresponding sets 

 of radiations, the whole system forming a network whose complexity increases 

 toward the periphery of the cell. In most cases no structure which could be called 



