Effect of Successive Removal upon Regeneration 483 
The non-molting and molting animals require fundamentally 
different methods of treatment and are separated in the following 
account. 
Experiments on Non-Molting Animals 
The experiments upon the non-molting animals are simpler 
than those upon the others, because the rate of regeneration in 
animals with a definite molt varies according to the time within 
the period. ‘The present experiments are therefore simpler than 
the others and less liable to danger from disturbing factors. The 
animals are, however, more subject to variation in the location of 
the plane of removal since the chelz in the other groups have 
definite breaking joints. 
1 The Tail of the Larval Salamander, Amblystoma jeffersonianum 
Method. A large number of egg-masses in early cleavage 
stages were collected in a single pond on January 20, 1907 (except 
egg-mass J which was collected on January 8). These were 
brought to the laboratory and were put into separate dishes on 
January 25. The young when hatched were thus separated into 
groups, all the members of a group coming from one mass and 
presumably from the same female. The eggs began to hatch 
on January 31. On February 2 the hatched young were put into 
individual dishes and given egg-mass as well as individual num- 
bers. Unhatched and deformed embryos were not used. One 
hundred and eighty-five larvze belonging toegg-masses A, B, C, D, 
E, F, G, H, I and J were used in the experiment. 
The general method consisted in the comparison during a defi- 
nite period of the third or fourth regeneration of the tail of one 
set of salamander larve with the first regeneration of another set 
otherwise similar. 
Sources of Error. 1 Age. ‘Theage factor was eliminated by 
making comparisons not between the successive regenerations of a 
single individual but between two sets of animals of the same age. 
2 Periodic Physiological Changes. No special precaution 
apart from that used in connection with other factors is necessary 
in the case of salamander larve. 
