^ 82 Erste Sektion: Cytologie und Protozoenkunde. Erste Sitzung. 



Limulus, figs. 22, 23, and also in that of Clemmys, fig. n. This 

 appearance seems to be due to a regulär System of concentric 

 fibers connecting the radial fibers at regulär intervals. Occasio- 

 nally this system of concentric zones is so marked, the limits 

 between the zones so sharply defined, as to suggest the presence 

 of concentric membranes, as in fig. 23. However that may be, 

 it seems clear that this concentric arrangement is the same as 

 that which appears so conspicuously in the concentric arrange- 

 ment of the yellow and white yolk in the hen's egg. The latebra 

 of the birds egg seems to be the original center of the astral System 

 of rays, and its position is evidently determined by the original 

 aster and centrosome, as in the pigeon's egg, fig. 31. It may be 

 reasonable to expect that some day we shall find the egg-centro- 

 some of the hen's egg in the latebra. 



The concentric arrangement is evident also in the reptilian 

 ovum, even after yolk bodies have formed, fig. 33, e, pl. Ia. 

 which I have shown more fully in my work on Clemmys. 



The arrangement of the radial and concentric fibers is illu- 

 strated in the diagram, fig. 33, a, pl. Ia. The number of radial 

 and concentric fibers is, of course, vastly more numerous than 

 those shown in the diagram, which is drawn solely with a view 

 to clearness. 



It is conceivable that this system of radial and concentric 

 fibers may be compacted into a very small body; and that the 

 whole system, when the granulär inclusions are absent might 

 occupy a space like the vitelline body, fig. 25, or even be reduced 

 to the size of a centrosome. Would it be permissible, then, to 

 suggest that the structural elements of the cytoplasm might be 

 contained in the body called the centrosome; and that this may 

 grow, when food is supplied, by a process of expansion, as is 

 apparent in the growth of the sperm center, on entering the egg? 

 In that case, we might say that the centrosome is the cytoplasm 

 in miniature. The history of the vitelline body in the egg of 

 Limulus sustains such a hypothesis. 



III. 



Polarity of the Egg. 



In the typical cell, the center of the astral system, the centro- 

 some, occupies the geometrical center of the cytoplasm. But 

 owing, doubtless, to difference in tension of the astral rays and 

 the accumulation of amorphous substances, flowing to different 

 parts of the cell between the fibers, the center is often eccentric. 

 It nevertheless determines a fixed point in the cytoplasm, which 

 together with the nucleus, or germinal vessicle, fixes the egg 

 axis. A line drawn through the latebra and the germinal vesicle 



