KAND: NERVOUS SYSTEM OF LUMBRICID^. 87 



at Harvard University under the direction of Professor Mark and Doctor 

 W. E. Castle, from whom have been received much valuable assistance 

 and many helpful suggestions as to the proper interpretation of the 

 results obtained. 



II. Historical. 



1. The Centrosome in Nerve Cells. 



Previous to von Lenhossek's discovery, in 1895, of the centrosome in 

 the nerve cell, we find in the literatui'e a few references to a fibrillar 

 structure of the cytoplasm of nerve cells and a concentric arrangement 

 about the nucleus. 



Remak ('44, p. 469) described in the nerve cells of Astacus " sehr 

 zarte granulirte, den Kern umkreisende Fasern." In the nerve cells of 

 Raja he ('53) mentions two systems of fibrillse, — peripheral ones 

 extending into the axis cylinder, and deeper ones concentric to the 

 nucleus. 



Walter ('63), Leydig ('64, p. 84), Arnold ('67), and Schwalbe ('68) 

 found a fibrillar structure concentric to the nucleus in nerve cells of 

 vertebrates and invertebrates. 



Arnold ('65, '67), Courvoisier ('66), Sigraund Mayer ('72), Eimer ('77), 

 and other authors speak of fine fibres extending out from the nucleus, or 

 even from the nucleolus, in vertebrate nerve cells, but from the descrip- 

 tions and figures given it is impossible that these structures could have 

 been identical with the exceedingly delicate radiations recently observed 

 in connection with the centrosome. 



Max Schultze ('71) found fibrillse concentric to the nucleus in certain 

 brain cells of Torpedo, as well as fibrill^ which enter the cell from the 

 processes. 



Hans Schultze ('79) described fibrillse concentric to the nucleus in 

 nerve cells of vertebrates. 



Flemming ('82, '82 *) mentioned a " streifige Structur " concentric to 

 the nucleus in the central nerve cells of the pig. In the cells of the 

 spinal ganglion of various mammals he found a fibrillar structure, but 

 it exhibited no concentric or radial arrangement. 



Von Lenhossek ('86) figured and described, in the spinal-ganglion 

 cells of the frog, an arrangement of fibrillae generally, but not always, 

 concentric to the nucleus. In some of his figures the nuclei are very 

 excentrically placed and are flattened or even slightly concave on the 

 side nearest the centre of the cell, agreeing in this respect with the con- 



