124 A - RICHARDS. 



There are inherent in the very nature of the problem involved 

 in the recognition of cases of amitotic cell division as such certain 

 difficulties which render the study of the question upon fixed 

 material more or less unsatisfactory. Mitoses are, of course, 

 well adapted for such a study, although they may be obscured 

 in various ways. The presence of definite chromatin bodies and 

 the absence of a nuclear membrane at most stages makes their 

 recognition in properly treated material comparatively easy. 

 But positive evidence of amitosis in fixed material is difficult to 

 obtain. One cannot always be sure that a nuclear constriction 

 is not a product of mechanical compression, e. g., by yolk granules, 

 or an artifact due to reagents rather than a stage in division. 

 A strand of linin stretched across a nucleus with chromatin 

 granules upon it often gives the appearance of a membrane 

 dividing the nucleus amitotically (endogenous division?). Nu- 

 clear lobations are frequently seen in cells which are known to 

 multiply by mitosis. Finally, a reduplication of nuclei for any 

 of several reasons disintegration, accessory sperm nuclei in 

 egg cells, the male and female pronuclei themselves, lagging of 

 cytoplasmic division behind nuclear mitosis, incompletely fused 

 chromosomal vesicles, etc., easily presents a simulacrum of 

 amitosis which is quite misleading. These and other factors 1 

 all render the amitosis problem difficult of solution. 



Clearly, however, a definition of what one means by amitosis 

 and of what he will accept as evidence of that process is impera- 

 tive. Dahlgren and Kepner (p. 38) define amitosis as division 

 "by a series of autoconstrictions of first the nucleolus, then the 

 nucleus, and lastly the cytoplasmic body." The nucleus itself 

 divides in three ways: the constriction of its body, the formation 

 of a "nuclear plate" in the plane of division and subsequent 

 separation, and the endogenous method of Child. Wilson (p. 

 114) describes the process as follows: "First the nucleus remains 

 in the resting stage (reticulum), and there is no formation of a 

 spireme or of chromosomes. Second, division occurs without 

 the formation of an amphiaster. . . . The nuclear substance 

 undergoes a division of its total mass but not of the individual 

 elements or chromatin granules." It will be seen that these 



1 Mitosis may be periodic and of very short duration. 



