VII 



CHROMIDIA IN PROTISTA 



207 



Another example of multiplication of nuclei by chromidia fonnatiou 

 alternating with multiplication by mitotic division, though attended by 

 more complications, is afforded by Arcclla (Fig. 88), the life history of 



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Fig. 87. 



stages in the formation of macrogainetes in Masligdla viirea. (After Goldschniidt, A T.K., iqoy.) A. 

 niacrogametocyte nucleus surrounded by extruded chromidia. B, a later stage. As tho rhromidi.i get 

 further away from the nucleus they are formed into the macrogamcte nuclei. C, gamctooylc full of n..ii-n>- 

 gametes. Some are undergoing the (? reduction) division. D, four of the macrogameti-s from C on .i larRrr 

 scale. Three are in mitosis, and the fourth has completed the mitosis and contams the mature gamete nucleus 

 and the polar body-like " reduction body." , , ,, 



ch, chromidia ; m, macrogamete nuclei ; /-, " reduction body. 



which has been studied by many workers. The essenti.il features from 

 our present point of view are as follows. At the beginning of tlie asexual 

 cycle the young Arcella consists of a minute unimicleated cell. Soon 

 the nucleus divides into two, by mitosis. At about the same time a 

 great number of chromidia are emitted from the nuclei. These become 



