THIRD LECTURE. 



THE CENTROSOMES OF THE FERTILIZED EGG 

 OF ALLOLOBOPHORA FOETIDA. 



KATHARINE FOOT, 



EVANSTON, ILLINOIS. 



BEFORE we discuss the centrosome we must glance at the 

 attraction sphere, the structure of which the centrosome is a 

 part (Fig. 4). 



A typical attraction sphere has at least three essential 

 parts: first, the relatively central, opaque body or bodies, the 

 centrosome or centrioles; second, the less opaque substance 

 which forms a relatively large part of the entire attraction 

 sphere, the archoplasm; and, third, the rays of the attraction 

 sphere, which in some cases extend quite to the periphery of 

 the cell. In addition to these three structures, we often see a 

 lighter area between the centrosome and the archoplasm, the 

 " Hof " of German authors and "zone me"dullaire " of Van 

 Beneden. This appearance has been pronounced by some 

 investigators to be an artifact to be due merely to the fixa- 

 tives and is assumed, therefore, not to be a normal structure. 

 But the centrosome itself has been called an artifact ; and, again, 

 the specific nature of the archoplasm has been denied, while 

 some investigators see spheres or centrosomes without rays. 

 Thus, if we accept all these denials, we shall have no attraction 

 sphere at all. This certainly would simplify the subject; but 

 at the present stage of the centrosome question I believe that 

 we are not justified in assuming that any one of these structures 

 is an artifact. 



