MUSEUM OF COMPARATIVE ZOÖLOGY. 147 
25. The nuclei finally become reduced to uniformly staining, irregu- 
lar masses of chromatin, which has partly entered into solution. Such 
nuclei are found in all stages of division. 
%6. In binucleate cells of the ovarian epithelium the nuclei become 
dimorphic. 
27. The chromatic substance of one of the nuclei enters into solution 
in the karyoplasm, and the nucleus becomes reduced in size. 
28. The other nucleus loses its stainability, and increases in size. It 
finally disappears. 
V. Discussion of Amitosis. 
As long as karyokinesis was supposed to be a uniform process, all the 
complicated details of which were carried out with the greatest exact- 
ness and in the same sequence, wherever it occurred, no one sought to 
homologize it with the little known and far simpler “direct” division. 
The latter had, apparently, so restricted a range, and had received so 
little attention, that its very existence was denied ; and it was generally 
anticipated that, in the few kinds of cells in which it was stated to oc- 
cur, a better technique and more careful study would reveal mitotic 
phenomena. This opinion seemed to receive confirmation by the dis- 
covery of mitotic division in leucocytes and the Protozoa, thus carrying 
mitosis back to the simplest types of cells and to the lowest forms 
of life. The ascertainment of two facts has brought about a radical 
change in our views regarding amitosis : (1) the variability of karyo- 
kinesis, including, in some cases, the omission of apparently essential 
steps ; and (2) the wide occurrence of amitosis, new instances of which 
are constantly coming to light in various parts of the Animal Kingdom. 
Inasmuch as it became necessary to recognize the existence of direct 
division, efforts were naturally made to find links connecting it with 
mitosis; the variability of both mitosis and amitosis seemed to lend 
strength to the theory which refers them to a single fundamental plan 
of division. In this scheme, amitosis is considered either as a primitive 
method from which mitosis was evolved, or else is looked upon as a 
degenerate form of mitosis, occurring in nuclei which, from their patho- 
logic or exhausted condition, have lost the power of dividing by the more 
complicated process. By fixing epithelium of the salamander larva with 
osmic acid, then treating it with Miiller’s fluid, and finally staining with 
hematoxylin, Pfitzner (’86") has shown conclusively that, even in cases of 
very perfect mitosis, the karyoplasm maintains its integrity, and divides 
