CELL DIVISION IN T/ENIA. 



319 



no sign of cell division although mitosis is almost complete. 

 This is not an infrequent occurrence ; actual nuclear division and 

 certainly cell division may lag well behind spindle and chromo- 

 some division. Herein lies a fruitful cause for misinterpretation. 

 A nucleus in which chromosome division has been completed 

 would give every appearance of direct division upon constriction 

 and subsequent division. Two nuclei in a single cell which had 

 not begun to form a cell plate would also be misleading. 



No true case of amitosis has been observed in the egg cell 

 formation of the Tienias upon which I have worked. 



Somatic Tissues. The somatic tissues of tape-worms inside 

 the cuticle include muscle fibres, excretory and genital organs, 

 and a primitive nervous system. Surrounding all of these organs 

 and filling all interstices is a large mass of parenchyma. A de- 

 tailed study of all of these structures has been made by Child 

 for Monieza. He reports that many cases of amitotic division 

 occur and that illustrations of this fact might be multipled in- 

 definitely. 



I have made no investigation of the method of cell division in 

 the excretory or nervous systems of Tcenia. There is no reason 



FIG. 13. First oocyte ; late metaphase. 



FIG. 14. Second oocyte ; equatorial plate stage, first polar body dividing. 



to believe, however, that the method of division in those organs 

 differs from that of the genitalia or of the muscle fibers. We 

 have in all of these systems cells that are specialized to a high 

 degree. Even if amitosis be found here where rapid growth may 

 be taking place that fact loses significance when the degree of 

 specialization is considered. The various cell generations of a 

 differentiating tissue differ from earlier generations only in a gain 



