398 EDWIN G. CONKLIN. 



he finds is actually due to a division, (2) that a portion of the 

 cytoplasm is cut off around each of these nuclei, (3) that the 

 cells arising in this manner again divide mitotically and have the 

 normal number of chromosomes; in his opinion not one of these 

 proofs has been furnished. The binucleate or multinucleate 

 condition, he adds, may be due to an incomplete fusion of chromo- 

 somal vesicles after mitosis, as Rubaschkin (1905) has shown to 

 be true for the blastomeres of Triton. Boveri concludes, there- 

 fore, that the individuality theory has not been shaken by this 

 work on amitosis. There is no doubt that constricted or lobu- 

 lated nuclei are sometimes found in germ cells or embryonic 

 cells; the critical question is whether these are stages in the 

 amitotic division of the nucleus and if so whether the cell bodies 

 divide and are capable of normal development. It is evident 

 from a large number of observations on a great variety of objects 

 that constricted nuclei are not in themselves sufficient evidence 

 that amitosis is occurring, for many such nuclei of living cells 

 have been observed to lose the constriction and later to divide 

 by mitosis. And even if such constricted nuclei actually divide, 

 the chromosomal constitution of the cell could remain normal 

 provided the cell body did not divide following the amitotic 

 division of the nucleus. 



As a matter of fact, amitotic division of the nucleus is rarely 

 followed by division of the cell body. Macklin (1916) has 

 recently studied amitosis in living tissue cells of the embryo 

 chick and, although he was able to follow the process of nuclear 

 division in successive stages in one and the same cell, in no case 

 was such amitotic division of the nucleus followed by division 

 of the cell body. Such amitotic division was sometimes followed 

 by mitosis and in such cases the two or more nuclear vesicles 

 in a cell gave rise to chromosomes which formed a single equa- 

 torial plate. Macklin concludes, therefore, that "there is noth- 

 ing in nuclear amitosis opposed to the chromosome hypothesis" 

 with which opinion I entirely agree. 



Unfortunately it is rarely possible to study all stages of nuclear 

 and cell division in normal living cells, not only because of the 

 indistinctness with which one sees what is going on inside the, 

 cell, but also because of the difficulty of keeping cells alive and 



