550 Charles Zeleny 
ance of vitality, to infection, and to other means of lessening 
the rate of regeneration. The accidents of the experiments in 
other words are all in the direction of an apparent lesser rate for 
the higher injury. These facts have already been sufhciently 
discussed under the heading of sources of error (pp. 514-518). 
The above considerations seem to be a sufficient answer to 
the recent criticisms by Emmel, Scott, and Stockard. Stockard 
states (1) that the individual variation is sufficient to cause an 
overlapping of the rates in the two compared groups. (2) that 
in the case of animals with the molting habit this habit consti- 
tutes a serious source of error. (3) That even neglecting these 
difficulties the influence .of degree of injury is small in amount 
as compared with such evident factors as the level of the cut. 
The difficulties connected with the molting habit have already 
been mentioned on pp. 534-535, above and a paper dealing with 
several of the molting factorsis in preparation. ‘The other criti- 
cisms have been considered in discussing the sources of error. 
In a general way these criticisms are directed against the view 
that increase in injury brings about a decided increase in rate 
of regeneration. No special arguments against them are needed 
to support the statement that our evidence at present favors 
the view that increase in degree of injury to the individual within 
moderate degrees increases rather than decreases the rate of regen- 
eration of a part. 
The comparison that has been made between the effect of level 
of the cut in an organ and the degree of injury to the individual 
needs further attention. As stated above (p. 515), the level of 
the cut is not of much value for the determination of the effect 
of degree of injury to the individual because it involves changes 
in local conditions. Nor can the increase in rate of regeneration 
with a lowering of level be compared with the other increase. If 
the rate of regeneration of a chela for instance is unchanged by the 
simultaneous removal of the other one there is still twice as much 
regeneration being accomplished by the individual after a double 
removal as after a single one, just as in the case of a cut at a 
deeper level of the tadpole’s tail proportionately more new tail 
is formed than at a higher level. The increase in rate dis- 
