MUSEUM OF COMPARATIVE ZOOLOGY. 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. 



26. 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 karyoplasra, 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 occi;rreuce 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 pi-ocess. By fixing epithelium of the salamander larva with 

 osmic acid, then treating it with MUller's fluid, and finally staining with 

 hsematoxylin, Pfitzner ('86") has shown conclusively that, even in cases of 

 -very perfect mitosis, the karyoplasm maintains its integrity, and divides 



