EAND : NERVOUS SYSTEM OF LUMBRICIDiE. 95 



varying position of the centrosomes, Hunter says : " These facts can 

 only be explained on the supposition that the centrosome does not exert 

 any decided mechanical influence on the cell protoplasm." 



Hunter found individual variation as to the frequency of the presence 

 of the centrosome in the nerve cells of different animals killed at the 

 same time, the preparations being subjected to exactly the same treat- 

 ment throughout. 



Rohde ('98) finds that certain " Nebennucleolen " wander out from 

 tlie nuclei into the cytoplasm of nerve cells of the frog, and come to 

 resemble closely the sphere described by Dehler. In the cytoplasm of 

 the nerve cells of the dog he found bodies of nucleolar origin. 



In nerve cells of the frog, Rohde commonly finds structures that 

 resemble a " centrosphere." They consist of a central dark body in a 

 clear area, which lies within a sphere exhibiting a radial arrangement. 

 The whole structure suggests the centrosome and sphere described by 

 von Lenhossek. Rohde, however, maintains the existence of such 

 structures in all the cells of the ganglia, — not merely in cells of a 

 certain size, as described by von Lenhossek, — and in any region of the 

 cell whatever, even within the nucleus, or immediately outside the cell 

 body. Moreover, as many as eight of them may occur in one cell. 

 They were not found in the cells of mammals. Rohde thinks they are 

 not artifacts. As regards the existence of the centrosome in the nerve 

 cells of either invertebrates or vertebrates, he says, " Ceutrosomen kom- 

 men also bei Ganglienzellen nicht vor." 



Hamaker ('98) found structures in the nerve cells of Xereis which 

 he considered to be comparable to the centrosomes described for nerve 

 cells by other authors. Often two or three of these structures and 

 sometimes as many as ten were found in a single cell. Each one con- 

 sisted of a deeply stained granule in a clear space enclosed within a 

 hollow sphere of coarse granules. No radiations were seen. The nuclei 

 were excentric and often flattened. The " centrosomes " lay at the centre 

 of the cell body. 



Holmgren ('99) occasionally finds sections of cells which exhibit a 

 central structure very similar to the sphere of von Lenhossek. He 

 describes a system of fibres which sweep in from the periphery of the 

 cell to form a " Spiralfigur." Similar conditions are described by 

 Btihler ('98). Among the generally hyaline fibres of this system are 

 some more deeply staining fibres. Holmgren thinks certain favorable 

 sections through this spiral system give the appearances interpreted by 

 von Lenhossek as a sphere, his *' centrosomes " being simply sections 



