METHOD OF CELL DIVISION IN MONIEZIA. 135 



entire process of development from primitive germ cells to fully 

 formed embryos is one of comparative simplicity and is quite 

 easily followed with the exception of the cleavage stages. These 

 are difficult to understand in section, and whole mounts of them 

 are not readily prepared. 1 



The vitellarium arises from the middle part of the primary 

 indifferent an age, and in its early stages cannot be distinguished 

 from the ovary other than by its position. But its growth is 

 of a different character and soon permits of a distinction between 

 the cells of the two regions. It acquires the character of a gland 

 and thereafter its activities are those connected with secretion. 



The development of the various female organs will now be 

 considered in detail. 



The Primary Anlage. The indifferent or primary anlage be- 

 gins merely as a thickening of cells median and slightly ventral 

 to the longitudinal nephridial canals. This thickening is not 

 marked off in any way from the surrounding parenchyma; in 

 fact there is a gradation from one into the other. There is a 

 slight difference in the character of the cells of the an'age and, 

 of the adjacent parenchyma but it is only slight. The cytoplasm 

 is perhaps a little more dense in the anlage, and the nuclei show 

 evidence of greater activity. The cells of the parenchyma are 

 clear and usually have but one nucleus. The cells of the anlage 

 stain darker, and their nuclei frequently possess two or more 

 nucleolus-like bodies, of which probably only one is a true nu- 

 cleolus, and show a more or less distinct reticulum, except when 

 fixed with chrom-acetic. The ratio of nucleus to cytoplasm is 

 at first somewhat greater but soon becomes less in the case of .the 

 anlage than of the parenchyma. Nuclei in the former are often 

 somewhat smaller than in the latter. 



To avoid confusion with regard to my use of the term "cell," 

 I will here state my view of the cellular nature of the parenchyma. 

 I do not consider the parenchyma to be a syncytium as that term 

 is generally interpreted. Nuclei are always surrounded by a 

 definite amount of cytoplasm, but that cytoplasm is lacking in 

 a definite limiting membrane or cell wall. 2 The remainder of 



J Cf. for this general development photomicrographs I. to IV. 



2 My former statement that "the parenchyma cells of Tcenia have definite cell 

 boundaries" was not intended to mean that they have cell walls; I have not observed 

 that the two genera differ in this respect. 



