I6O A. RICHARDS. 



observational evidence not the least of which is Child's young 

 worm in which almost every nucleus is in mitotic division. The 

 fact that I am unable to convince myself that amitosis occurs 

 and the fact that mitosis does occur in some specimens in 

 greater abundance than in others (this applies to Tcenia as well 

 as to Monlezia) and even some organ systems show more figures 

 than others (I have one specimen in which the majority of the 

 testes cells are in mitosis) point strongly to periodicity as a 

 factor in growth. The arrangement of nuclei in pairs may be 

 regarded as a point in favor of this view. That the scolex of 

 this worm should be in division is of no significance for even if 

 it takes no part with the neck region in the formation of new 

 proglottids, and this is not demonstrated, its own growth must 

 be accounted for. The scolex of a young worm is smaller than 

 that of an older one. 



Furthermore, if it can be shown that the eggs pass through 

 any one stage periodically it becomes all the more probable 

 that they also pass through others periodically. The evidence 

 is strong that the eggs undergo maturation in this manner, and 

 that fact is most easily explained by periodicity of oogonial 

 divisions. 



Child holds that mitoses decrease in frequency with increasing 

 age. Let me suggest that perhaps that factor, whatever it may 

 be, that operates to free the intestine of adult sheep from tape- 

 worms may also operate to check mitotic division during the 

 latter part of the period in which the worms can yet live there. 



The evidence, I believe for the various reasons given, strongly 

 favors periodic mitoses as an important factor in the growth 

 of the cestode, Moniezia. 



COMPARISON OF Tcenia AND Moniezia. 



Throughout the course of this discussion it has been made 

 clear that Moniezia differs from Taenia serrata in numerous 

 details, both anatomical and cytological. Yet it is also clear 

 that the differences, while often striking, are differences not of 

 physiological activites and principles but of structural features 

 and structural differentiation. 



Most striking of all the differences is that of gross structure 



