184 INTRODUCTION TO CYTOLOGY 



amitosis as well as deranged mitosis and nuclear fusion may sometimes 

 occur in such cells and the periplasmodia they form. 



Another very prevalent opinion regarding the significance of amitosis 

 is that expressed by Flemming (1891), namely, that the process is 

 primarily a degenerative phenomenon, since it is so frequently observed 

 in pathological tissues. In the words of vom Rath (1891), "when once 

 a cell [nucleus] has undergone amitotic division it may indeed continue 

 to divide for a time by amitosis, but inevitably perishes in the end." 

 That this interpretation cannot be of universal application has been 

 contended by those who have found amitosis or amitosis-like appearances 

 in cells which show no other sign of degeneration. ^ It is probably 

 significant, however, that most if not all of the observed cases of amitosis 

 in living tissues have occurred in cultures which were growing old or 

 showing distinct signs of degeneration, or in which the medium was 

 unfavorable for normal growth.^ It is the opinion of Kofoid (1923) that 

 the supposed amitosis in Protozoa is a degenerative or pathological 

 phenomenon, or in some cases a special form of mitosis which has been 

 incorrectly interpreted. Conklin (1917) was able to show that the 

 amitosis-like appearances in Crepidula eggs and embryos were all instances 

 of abnormal mitosis and cytokinesis. He observed that the chromosomes 

 might scatter and fail to unite in a single nucleus; or mitosis might occur 

 without cytokinesis, giving cells with two or more nuclei; or certain 

 chromosomes might fail to separate in the anaphase, leaving a bridge 

 between the sister nuclei; or the nuclear membrane might persist through- 

 out mitosis and finally constrict at the middle. As a result of his many 

 observations and an examination of the evidence offered by others he 

 concluded that there is not a single case of true amitosis known in nor- 

 mally differentiating cells. 



The literature contains conflicting opinions on the question of whether 

 or not a portion of a nucleus resulting from amitosis can subsequently 

 divide by mitosis. The observation of amitosis under abnormal con- 

 ditions followed by mitosis after the tissue has been restored to a normal 

 environment is not conclusive evidence on this point unless it is shown 

 that the mitotically dividing nucleus is actually a product of amitosis. 

 Chambers (1917a) observed that after a nucleus is pinched in two with 

 the micromanipulator the parts may reunite and undergo mitosis. In 

 wound tissue of the stem of Tradescantia, Conard (1926a, 1928) has 

 shown that markedly lobed nuclei may enter mitosis while in this form, 

 also that they sometimes become constricted into two separate portions 

 while in the metabolic or prophase stage. Two such portions may then 



2 Des Cilleuls (1914) on rabbit cells; Saguchi (1917) and Helvestine (1921) on 

 ciliated cells of animals; Bast (1921) on bone; Kisser (1922), Conard (1926rt, 1928) and 

 others on vegetative tissues of plants; F. E. V. Smith (1923) on Saprolegnia. 



3 Lewis and Lewis (1924), Drew (1923). 



