CELL MULTIPLICATION IN SUB-CUTICULA. 395 



the manner described, we have here an exceptional method of 

 cell multiplication, unlike anything previously described in 

 Metazoa. 1 Moreover, if future research supports this view, the 

 present theories of the role of the nucleus in heredity will have to 

 be greatly modified at least with respect to cestodes. 



As Young has previously suggested, the explanation of such a 

 method of cell multiplication as this may rest on the fact that the 

 cestode is highly degenerate in most characteristics due to its 

 long period of parasitism. In the development of cells from 

 protoplasmic masses the nucleus passes through a cycle in which 

 occur stages resembling nuclei of lower forms. The protoplasmic 

 mass with its diffused nuclei in the form of chromidia is com- 

 parable to a cell of the Bacteria or of the Myxophycese. In 

 certain Protozoa also, as noted by many observers, the nuclear 

 material at certain periods diffuses throughout the cytoplasm 

 in the form of chromidia which may give origin to secondary 

 nuclei, and these in turn to gametes. It is possible that the 

 cestode nucleus has lost the power of mitotic division, accom- 

 panying the somatic degeneration of the worm due to parasitism. 

 Richards, Harman, and others have shown, however, that we 

 still find cell division taking place by mitosis in the sex cells and 



developing embryos. 



CONCLUSIONS. 



I have made the following conclusions in regard to cell multi- 







plication in the sub-cuticula of Dilepis scolecina. 



1. After a careful examination, and after counting 10,000 of 

 the nuclei in this region, I conclude that the growth of the sub- 

 cuticula cannot be accounted for by mitotic or amitotic division. 



2. Tissue growth is taking place rapidly in this region by the 

 development of protoplasmic masses. My reasons for believing 

 this are the following: 



A. The nuclei in the multinucleate cells are frequently seen 

 crowded together as if they had developed in protoplasmic masses. 



B. In the protoplasmic masses the quantity of cytoplasm is 

 out of proportion to the number of complete nuclei present. 



C. Developing nuclei have been actually observed in the cyto- 

 plasm. The different stages of nuclear formation are shown by 

 the following: 



1 A similar process was suggested long ago by Schleiden and Schwann. 



