364 Charles Tjcleny. 



functions of the new buds. Thus each of the new buds grows 

 faster than the single bud of the other animal because each gets 

 more exercise of its parts than does the latter. Unfortunately 

 observations made upon the individuals of the two series did not 

 show any difference between them as regards the activity of either 

 the old or the new parts. It is, however, very hard to judge 

 differences in activity in animals like the crayfish in the present 

 experiment, for the specimens are observed only when disturbed 

 by the presence of the observer. The individuals with one remain- 

 ing chela under these circumstances naturally often put themselves 

 in a defensive attitude threatening the observer with their unin- 

 jured chela. The members of the other series having no chela 

 cannot do this. A strong mdividuality was found m the members 

 of both series. Daily observation of the individuals in the experi- 

 ment for 181 days with but a few gaps enabled me to make out 

 striking differences in the activities of members of a single series. 

 These individual differences in function were not correlated with 

 any differences in the resulting regeneration as far as I was able to 

 decide. Though there is no evidence one way or the other from 

 the present instance, the comparative activities of the organs in 

 future experiments of a similar character should be carefully 

 observed. On the other hand there seems to be great danger in 

 carrying the idea too far for it is inconceivable to me how the 

 attempt of an animal to exercise a function for which it has no 

 morphological background can lead to the formation of a structure 

 furnishing the necessary background. Does not such a state- 

 ment of the case come dangerously near to the other statement 

 that "the cause for the existence of a need is a sufficient cause for 

 the fulfillment of that need?" A mystical attempt to function 

 resulting from the need to function has been supplied, that is all. 

 3. The difference in the mechanical redistribution of food 

 materials which results from the difference in the extent of the 

 injury may be supposed to cause directly the greater rate in the one 

 series. A discussion of the assumptions which must be made in 

 order to explain the facts on this basis will be interesting. Before 

 going on it will be well to recognize the fact that the difference in 

 activity of the parts in the tw^o series as formulated above underthe 

 second suggestion (pp. 363, 364) is supposed to lead to a difference 

 in the distribution of food materials which in turn brings about 

 the difference in rate of growth. The same must be said of all 



