Ejfect of Age upon Regeneration 565 
2 The Arms of the Brittle-star, Ophioglypha lacertosa® 
The conditions of the experiment are given in the paper with 
the original data. The data bearing on the effect of age are 
given here in Tables 2, 3, 4 and 5. The disk diameter is taken 
as a measure of age with the reservation mentioned on the preceding 
page. 
An examination of the tables shows that in general the actual 
regenerated arm lengths at any time are the greatest in individuals 
of medium size. Both the smaller and the larger individuals 
show shorter regenerated arms. When the regenerated length 
per unit of disk diameter is taken there is less difference between 
the smaller and medium individuals and more between the medium 
and larger ones. In other words the actual rate of regeneration 
in length is evidently greatest in medium sized individuals with 
a disk diameter of 12.5 to 15.0 mm. Both larger and smaller 
individuals regenerate new material less rapidly. ‘The same is 
true (though not so markedly in the smaller individuals) for the 
specific length of regeneration. ‘The smaller individuals rang- 
ing in size from 4.8 to 12.5 mm. therefore seem to constitute an 
exception to the general rule that the rate of regeneration decreases 
with age. This is true both of actual length and of specific 
length of regeneration. ‘The data are not wholly satisfactory 
because of the large degree of variation and the small number of 
individuals. ‘The larger individuals very evidently follow the rule 
of decrease both in actual length and in specific length of regen- 
eration. 
3. The Tail in Amblystoma jeffersonianum'™ 
The data are taken from 181 individuals reared in the laboratory. 
A comparison is to be made especially between the younger 
individuals (Tables 6, 7 and 8) and the older individuals (Tables 
g, 10 and 11). All the salamanders are still in the larval stage. 
The animals were used for the determination of other factors 
The full data are published in the paper on ‘‘Compensatory Regulation,” Journ. Exp. Zodl., vol. 
li, nO. I, 1905. 
7 Based wholly on new data. 
