482 Chane 
degree of light, to movements of persons in the room, and to change 
in accuracy of the operation as a result of fatigue of the operator, 
The last is an important item when two hundred or more opera- 
tions are made in a single day. As an example of the second pre- 
caution may be mentioned the mode of procedure in removing the 
tails of salamander and frog larve. ‘The larve that were not to be 
operated upon were put out on the parafiine blocks with the others 
so that any differences due to the mere shock of transference might 
be equalized. : 
Direct sunlight was avoided in all cases, even a few minutes 
was sufficient in the case of salamander larve to seriously disturb 
the ordinary rate of regeneration. 
Differences due to sex were not made out in the present experi- 
ments. In the few sets in which sex records were kept, no notice- 
able difference was made out between males and females. 
Notwithstanding all the precautions that could be taken, individ- 
ual variations in rate were present. ‘The results were freed from 
this source of error in most cases by the use of a large number of 
individuals. In some sets the averages obtained are wholly 
reliable, as shown by the internal evidence of uniformity in the 
data. In other sets, especially those in which accidental death or 
injury has reduced the number of available individuals, the results. 
are not so conclusive. 
III EXPERIMENTS BY THE AUTHOR 
The present paper includes the data on the regeneration of the 
following organs or parts: 
Group A. 1 The tail of the larval salamander, Amblystoma 
jeffersonianum Green. 
2. The margin of the disk in Cassiopea xamachana Bigelow.” 
Group B. 3 The chelz of the crayfish, Cambarus bartoni. 
4. The chelz of the gulf-weed crab, Portunus sayi." 
5 The chelz of the gulf-weed shrimp. Palamon tenuicornis. 
6 The chelz of the Woods Holl shrimp, Palazmonetes vulgaris 
Stimp. 
2 Zeleny ’07. 
13 Zeleny ’08. 
