16 CALIFORNIA ACADEMY OF SCIENCES. [3D Ser., 



that no other stain does. This differentiation is nearly always 

 the same, and we may readily recognize each zone by the 

 coloring alone. Thus it will be seen that while the long 

 sides of the nucleus are covered with two of these cytoplasmic 

 zones or spheres, the poles contain six distinct zones, the 

 two outer being the only ones which continue all around 

 the corpuscle. The polar accumulations must, therefore, 

 be considered as something entirely separate from the bal- 

 ance of the cytoplasm ; they, in fact, give rise to the plas- 

 mocytes, and may, therefore, appropriately be called plas- 

 mocytoblasts, or for the sake of brevity, plasmoblasts. 



VI. The Plasmocytoblasts. 



In a general way it may be said that plasmocytoblasts 

 are found at each one of the poles of a fusiform cor- 

 puscle; that they stain much darker in the center or at 

 the base, the apex and outside margin being much lighter. 

 Thus with the toluidine stain the margin is always pale blue, 

 while the central or basal part is more violet. At the very 

 base or in the center are generally seen one or more dark 

 dots which are readily identified with the centrosomes of 

 other cells. Instead of remaining in the non-nucleated 

 parts of the erythrocyte when the nucleus is ejected, as is 

 supposed by Heidenhain to be the case in the erythrocyte 

 of the rat, they continue to remain attached to the cyto- 

 plasmic envelope of the nucleus, only later on to separate 

 from it. 



As might be expected, we meet with some variation in 

 the form, size, and staining properties of these respective 

 zones, but in the main they are very constant and can nearly 

 always be recognized at once. There are two differently 

 appearing kinds of plasmocytoblasts, but between them are 

 numerous gradations showing that the two extremes cor- 

 respond, one to a stage that is dormant, the other to one 

 that is highly active. In the former, the dark staining 

 part with the centrosomes is situated at the base, close to 

 the nucleus, while in the latter, the dark staining part 



