No. 2.] 



HOMOLOGY OF THE CENTROSOME. 



437 



and vegetable cells. The difference between the microsome 

 and the centrosome according to this view, is merely that of 

 size, and the size taken by itself is no decisive criterion by 

 which we can differentiate one morphological element from 

 another. 



Supposing, then, that the centrosome may be considered as 

 an enlarged form of the microsome, which exists everywhere in 

 the cell-body, it may be further asked, How is it that a certain 

 microsome attains such a gigantic size above all others } Is 



Fig. 4 



Fig. 4. Blastovieres frotn the central part of the blastodisc of Loligo pealii. 

 The segments (i), (2), (3), (4), (5), etc. show different stages in the formation of 

 the spindle from the centrosome. 



there any special arrangement in the cytoplasm which favors 

 the production of such a large microsome at a particular point } 



The problem is a broad one, and involves the discussion of 

 the relation existing between the microsome and the cytoplasmic 

 thread proper. The following is my provisional answer. 



The microsome of the cell-body is more often located at 

 the junction of two or more cytoplasmic filaments. In other 



