METHOD OF CELL DIVISION IN MONIEZIA. l6l 



as seen in the female reproductive apparatus. Such wide vari- 

 ations from a common type are not usually found within a single 

 family of animals. In both the uterus is single 1 and median but 

 the other organs are arranged in pairs, there being two ovaries 

 and two sets of auxiliary glands and ducts as well as two genital 

 pores in each proglottid in Moniezia while in Tcenia the ovaries 

 are double but they discharge into a common duct and the other 

 parts of the reproductive organs are single. 



But the most interesting comparison of the two forms for 

 present purposes is that regarding cytological characteristics. 

 In both the anlagen of the organs arises as a thickening of the 

 parenchyma cells and the period of cell proliferation is strictly 

 comparable on the two. In Tcenia, however, it is of less duration 

 as seen by the fact that it extends over fewer proglottids. The 

 method of yolk formation is dissimilar in appearance only, for 

 if the yolk granules of Moniezia were to accumulate on one side 

 of the nucleus and fuse the condition would be exactly that of 

 Tcenia. I have not discovered that there is any difference in 

 the principles of division operative in the two forms. 



Between the types of cleavage and early development of the 

 embryos of the two forms there are some noteworthy differences 

 but as they are embryological in character they may not properly 

 be included here. It will be seen from this comparison that 

 there are sufficient differences between Tcenia and Moniezia, 

 although they are members of one family, to justify the claim 

 that observations on the former cannot be used a priori as 

 evidence against the latter; but that actual study does not 

 disclose any real differences in the principles of growth and 

 development in the two cases. 



CONCLUSIONS. 



In conclusion, the evidence presented in this investigation goes 

 to show: (i) that it cannot now be positively affirmed whether 

 mitosis or amitosis is the method which obtains in the develop- 

 ment of the vitellarium and female genital ducts of Moniezia ; 

 (2) that in the early stages of sex cell development mitosis un- 

 questionably occurs (probably periodically), while amitosis is not 



1 Stiles and Hassal state that the uterus of Moniezia is ontogenetically double. 



