METHOD OF CELL CIVISION IN MONIEZIA. 147 



Although the vitellarium and the ovary arise from the same 

 anlage and at first are distinguishable only by their position they 

 soon acquire histological differences. The nuclei of the former 

 contain very lightly staining chromatin in the form of a reticulum 

 but there is a large nucleolus. It frequently occurs that there 

 are two or more nucleolar-like structures, karyosomes, in a 

 nucleus. The appearance of the nucleus itself is that of an 

 almost empty court surrounding the nucleolus or nucleoli. The 

 nuclei of the oogonia, on the other hand, do contain a reticulum, 

 rather lightly staining, it is true, but consistently present. While 

 the cytoplasm is more indefinite in amount in the vitellarium it 

 can be seen that the ratio of nucleus to cytoplasm, if the inclusions 

 are not taken into consideration, remains much more constant; 

 if the yolk mass be considered the second term of the ratio is 

 much increased. At no time after they become clearly dis- 

 tinguishable are the cells as large as the oogonia, and at matura- 

 tion the oocytes are more than twice their size. 



As to cell multiplication I am convinced that after a com- 

 paratively early period division ceases. During this early period 

 clear cases of mitosis are to be seen, but, it is true, as Child says, 

 less frequently than in the ovary. On the other hand, the ar- 

 rangement of nuclei in pairs is, perhaps, more in evidence here 

 and indented nuclei are somewhat more numerous. The in- 

 dentations do not, however, give a series of autoconstrictions 

 from slight indentation up to complete division. If mitosis is 

 not clearly proved as the sufficient cause of cell multiplication 

 amitosis is certainly less so; for there is positive evidence that 

 some mitoses do occur, but for amitosis there is only negative 

 evidence. 



The Female Genital Ducts. From the same anlage which gives 

 rise to the ovary and the vitellarium, the female 1 genital ducts 

 develop. Therefore, although they are strictly speaking somatic 

 structures, their cells will be considered here, with regard to the 

 method ot cell division, as derivatives of the female anlage. 

 Their early history, therefore, is the same as that of the ovary 

 and vitellarium. A thickening of nuclei appears median to the 

 longitudinal excretory tubes and gradually extends itself both 



!The development of the male ducts will not be touched upon here. 



