144 COMPARATIVE ANATOMY 



Fig- 30- 



^, Encysted ActlnosphErium, the primary cysts dividing to form secondary cysts 

 B a pair of secondary cysts, more highly magnified, showing the cost 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 Actinosphairium 

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

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

 mitosis H I successive stages of mitosis in a secondary cyst durine the 

 . formation of the. pplar.hodies.. ^After R. Hertvvig) ■ •>''■•''■' """"K ">« 



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