150 COMPARATIVE ANATOMY 



7) 



Fig. 32. 



A, encysted _Actinosphaerium, the primary cysts dividing to form secondary cysts. 

 B,a. pair of secondary cysts, more highly magnified, showing the coat of 

 siliceous spicules ; the nuclei are in the resting stage previous to division to 

 form the polar bodies. C, normal mitosis of a non-encysted Actinosphaerium 

 showing the plasmatic cones. D, E, F, successive stages of normal mitosis. 

 G, resting nucleus of a primary cyst, the centrosome dividing preparatory to 

 mitosis, ff, /, successive stages of mitosis in a secondary cyst during the 

 formation of the polar bodies. (After R. Hertwig.) 



