The life history Diplodiscus tenipoiatiis Staffokd. 629 



The constriction about the middle of the nucleus becomes deeper 

 and deeper involving-, apparently, only a short section of the nuclear 

 membrane. In the last stages of the separation of the daughter 

 nuclei they are connected only b}^ a narrow strand of the membrane, 

 and each half is nearly spherical in shape. When the two sides of 

 the nuclear membrane come together, at the end of the period of 

 constriction, they fuse and the connecting strand of tissue is broken. 



At no time, so far as I have been able to determine, is there 

 an open communication of any appreciable size between the cytoplasm 

 of the cell body and the interior of the nucleus. 



After the daughter nuclei have separated from one another 

 they move to opposite ends of the cell and then the cytoplasm of 

 the body of the parent cell becomes separated into two parts by 

 the ingrowth of a constriction of the cell wall. 



Within the daughter nuclei the chromosomes continue to fuse 

 into a mass until all of them have lost their individuality and they 

 form a body with a regular outline, which is the caryosome. The 

 less densely staining material becomes localized about the caryosome. 

 and we have again a typical resting nucleus of a cell of a germ ball. 



The striking similarity between the late telophase in the 

 mitosis of Diplodiscus and a typical amitotic division suggests a 

 possible explanation of the results which have been obtained by 

 some of the investigators of cell division in Cestodes and Trematodes. 

 In a stage such as is shown in Fig. 30, and as w'ould appear in 

 all later stages of division, we have an appearence which might 

 easily be interpreted as a true amitotic division, since practicallj' 

 all of the evidences of mitosis have dissappeared. The later telophase 

 would present conditions showing all of the usual stages of amitosis, 

 such as have been figured by Child (1905) for the various tissues 

 of Moniezia eximnsa. 



In all of my preparations of Diplodiscus, while there have been 

 many instances of what at first sight seemed to be amitosis, a 

 careful study has shown that there would invariably be some of 

 the characteristics of mitosis by which it could be definitely deter- 

 mined that the division of the nucleus under observation had taken 

 place by the usual method of mitosis as previously described. 



The maturation division. 



The maturation division in the parthenogenetic eggs differs in 

 several respects from a typical segmentation division, as above described. 



