508 ¢ Charles Zeleny 
at the same time, it is obvious that only a very careful control of 
these factors can give results showing any uniformity. In dealing 
with a factor like level of the cut, the difference in rate with level 
is greater than differences due to variation in the other factors and 
a more uniform result can obviously be obtained. 
4 The literature of the subject does not take into consideration 
these subsidiary factors and accordingly cannot be used ina general 
statement. ‘he age factor has been shown to indicate an increase 
in rate of regeneration with age in certain species in opposition 
to the general rule of decrease with age. ‘The results so far 
obtained therefore show that it is at present unsafe without 
further evidence to say that the age factor is a minus or plus or 
negligible quantity. ‘“[he statement in the literature that the rate 
of regeneration is uninfluenced by successive removal is unreliable 
as far as pure effect of removal is concerned. It is, however, prob- 
able that Vanlair’s data would remain unchanged even with the 
elimination of the age factor, though his data are too meager for 
this purpose. 
Taking the present data into consideration and making a com- 
parison with former data, the following general statement of the 
facts seems warranted. 
Among species without a molting habit the subsidiary factors 
are more readily eliminated than among those with a molting habit. 
The former show an increase in rate with successive removals 
(Vanlair, sciatic nerve-dog; Zeleny, tail-salamander and margin of 
disk—Cassiopea). Furthermore, the meager data from Cassiopea 
indicate that this effect is both constitutional and local. 
Among species with a molting habit the complex molting factors 
are hard to eliminate and may yield some factors as yet wholly 
unknown. Eliminating sources of disturbance as far as possible 
it is found that successive removal of the chelz causes little or no 
change in the rate of replacement. 
The data as a whole therefore make it highly probable that the 
pure effect of successive removal 1s either no change in rate of regener- 
ation or an increase in rate. 
