AGAMIC REPRODUCTION AND REJUVENESCENCE 147 



contraction in cyanide of a particular body region is followed by 

 the death and disintegration of that region before other parts. 

 Evidently motor activity, although slow, increases the rate of 

 metabolism in hydra to a very marked degree. This is perhaps to 

 be expected from the fact that the motor mechanism in this organ- 

 ism is not highly developed, but is merely a part of the ectoderm 

 cell. Motor activity undoubtedly involves the whole cell and at 

 least all the cells of the ectoderm in the region where it occurs. To 

 all appearances it is a very laborious process, and even after the 

 strongest stimulation it is relatively slow and inefficient. In short, 

 the observations made by the susceptibility method indicate that 

 the increased metabolism associated with motor activity is relatively 

 very great. 



The bud in the early stages of development exhibits very little 

 motor activity, and movement does not attain its maximum until 

 separation from the parent takes place. The result of this differ- 

 ence in motor activity between bud and parent is that, even though 

 growth and development are proceeding more rapidly in the bud 

 than in the parent, the rate of metabolism is not greater in the 

 bud where motor activity is slight than in the parent where it is 

 much greater. But as soon as the bud becomes independent, 

 its motor activity is comparable with, perhaps even greater 

 than, that of the parent, and then its susceptibility to cyanide 

 is distinctly greater, i.e., its rate of mefabolism is higher than 

 that of the parent. 



Moreover, the young bud while still attached to the parent 

 grows at the expense of food ingested by the parent body, rather 

 than at the expense of its own tissues. It does not undergo reduc- 

 tion, but grows during its reconstitution from a part of the parent 

 body into a new individual. Since rejuvenescence is undoubtedly 

 associated with reduction, as the following chapter will show, the 

 bud, which receives food and grows rapidly throughout its devel- 

 opment, does not become as young physiologically at any stage as 

 if its development occurred at the expense of its own tissues. 



In the marine hydroid Pennaria tiarella, agamic buds are pro- 

 duced as in hydra but remain permanently in connection with the 

 parent stem or branch, so that a branching tree-like colony with the 



