172 Harry Lewis Wieman. 



division and not an indication of amitosis or degeneration. This 

 author observed nuclei whose sinuous outlines simulate stages 

 of direct division in the egg of Rhahditis nigrovenosa and Ascaris 

 megacephala, and in the spermatogonia of Rana fusca. These 

 cells in all cases subsequently divide mitotically. 



On the other hand, the work of Gerassimow ('92), Nathanosohn 

 ('00) and Haecker ('00) demonstrate experimentally at least, that 

 mitosis may follow amitosis and vice versa in both plants and 

 animal cells. In these experiments it was found that under the 

 influence of low temperature or narcotics, mitotic divisions cease, 

 and amitosis ensues. When the cells are brought back to normal 

 conditions mitotic divisions reappear. 



Child ('07 c) has reported the occurrence of amitosis in the repre- 

 sentatives of six different animal phyla, in practically all kinds 

 of tissue including the reproductive cells. In general, his observa- 

 tions indicate that amitosis is more frequent than mitosis in con- 

 nection with a rapid cell multiplication which accompanies normal 

 and regulatory growth. Child speaks of mitosis as a cyclic process 

 in that the nucleus, starting from the resting stage, undergoes dur- 

 ing every mitotic division a series of changes and finally returns 

 to a resting stage similar to the starting point. In amitosis there 

 is no such cyclic movement. ''Nothing in the visible phenomena 

 indicates the occurrence of reversal in direction of the processes 

 involved." In other words the nuclei of these cells are not in con- 

 ditions of equilibrium with the cytoplasm. 



The most interesting of his observations (Child '07 a, '07 b) 

 deal with, the development of the ovaries and testes of Moniezia, 

 in which the early divisions of the germ cells are amitotic. Then 

 comes a growth period at the beginning of which a spireme is 

 formed, followed by the maturation divisions, which take place 

 mitotically, as do those of the early cleavage. The remaining 

 divisions are amitotic. 



Patterson ('08), from observations made on the blastoderm of 

 the pigeon's egg, came to the following conclusions. 1. Mitosis 

 may follow amitosis and vice versa. 2. Amitosis is the result 

 of a physiological stimulus which creates a stimulus to growth. 

 3. Amitosis exists in regions of rapid growth. Maximow ('08) 



