THE NUCLEUS 



81 



may be present. It is simplest in theory, and probably correct in 

 fact, to regard the centriole as the primary, in many cases the sole, 

 constituent of the centrosome an element which may be capable, 

 to a greater or less extent, of changes in size and structure, and 

 which multiplies by division. To the primary centrosome or 



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FIG. 37. Actinosphcerium eichhorni: formation of the centrosome. A, Concentra- 

 tion of the nuclear reticulum towards one pole of the nucleus, near which 

 the cytoplasm appears free from granulations, forming the archoplasm ; 

 B, G, D, passage of a portion of the nuclear reticulum to the exterior to form 

 the " spongy centrosome " lying in the archoplasm ; E, spongy centrosome 

 with striations passing from it through the archoplasm to the nucleus ; 

 F, G, the centrosome passes back again to the vicinity of the nucleus and 

 undergoes a reduction of substance the archoplasm also diminishes tem- 

 porarily in quantity ; H, division of the centrosome. After Hertwig (64). 



centriole there may be added adventitious elements of protoplasmic 

 or nuclear origin, thus forming a centrosomic complex which may 

 attain a size relatively considerable in some cases. 



So far the centrosome has been discussed only in its relation to 



6 



