THE NUCLEUS 



93 



hardly likely that the basal granules would be of a different nature 

 in the two cases. The whole question of the nature of the basal 

 granules has been discussed in a recent memoir by Erhard (54). 



FIG. 48. Wagnerdla borealis, Mercschk. A, Whole specimen 

 seen under a low magnification: //., head containing 

 the central grain ; P, stalk ; N., nucleus contained in 

 the basal plate of attachment. B, Enlarged view of 

 the head, after fixation and staining with iron-haema- 

 toxylin : c., cuticle of the stalk ; p*., pseudopodia ; 

 ax., axial filaments of the pseudopodia, each arising 

 from a ba^al granule ; c.y., central grain. After 

 Zuelzer (86). 



Few problems in cytology have been more discussed than the 

 question of the nature and origin of the centrosome, and three 

 opposed views have been put forward which may be termed, re- 

 spectively, the achromatinic theory, the nucleolo - centrosomic 

 theory, and the nuclear theory. 



