186 



C. M. CHILD. 



TABLE II. 



Series 64, I., II. KCN o.ooi mo!. 



In this series also the younger worms show less resistance, 

 which signifies a higher rate of metabolism, but a comparison of 

 Table II. with Table I. shows that Lot i of Table II. has a longer 

 survival time than Lot I of Table I., i. e., w r orms of 5-6 mm. in 

 length have a low r er rate of metabolism than worms recently 

 emerged from cysts. These facts show that a progressive de- 

 crease in the rate of metabolism occurs during the growth of the 

 animals. Those newly emerged from cysts have the highest 

 rate, those which are full-grown and nearly ready to fragment 

 and encyst have the lowest rate, w^hile intermediate stages show 

 rates between these two extremes. 



These results have been confirmed by various other series with 

 both KCN and alcohol. The small newly emerged worms die 

 much earlier in all cases than the large worms. The differences 

 in resistance to KCN, alcohol, etc., between young and old 

 animals are the same in animals freshly collected from their 

 natural habitat as in animals bred for one or more generations 

 in the laboratory'. 



