CH. m] AMITOTIC DIVISION 27 



amitotic nuclear division only occurs in cells which are be- 

 coming rather highly differentiated, and which are losing 

 their power of division and approaching a condition of de- 

 generation, but according to CHILD and others amitotic 

 division may occur in such cells as those of the testis from 

 which germ-cells will be produced. It should be mentioned, 

 however, that other observers have not always succeeded in 

 confirming these observations. And it must always be re- 

 membered that in tissues satisfactory observations on ami- 

 totic division are by no means easy to make. The tissue 

 must be fixed, sectioned and stained, and the occurrence of 

 amitotic division inferred from the series of figures observed. 

 In a number of instances there is no reason to doubt the 

 correctness of the inference; nuclei in all stages of division 

 are found and no other interpretation seems possible. But 

 in other cases it is not easy to decide, in interpreting the 

 figures, whether what is observed is a process of nuclear 

 division or of nuclear fusion, for if, as may happen in certain 

 rather abnormal cases, nuclei come together and then fuse 

 into one, the series of stages in a fixed preparation may be 

 hardly distinguishable from those seen in amitotic division. 

 It may also happen that in some tissues badly preserved 

 mitotic division figures have the appearance of amitosis. 

 Although, therefore, the process is well known in the Pro- 

 tozoa, and certainly occurs here and there in the Metazoa, 

 in the latter animals it has been only insufficiently investi- 

 gated, and at the present time it is hardly known how fre- 

 quently it occurs or whether it is to be regarded as normal 

 or abnormal. 



In all the higher animals and plants the common and regular 

 method of nuclear division is that known as mitotic or karyo- 

 kinetic, or sometimes as indirect, division (PL II). It is a 

 complicated process, involving a complete transformation 



