A82 A. W. BELLAMY 
any substances save the ones mentioned in connection with the 
figures which illustrate this type of modification—figures 27 to 
38. 
Differential acclimation and differential recovery. Both aecli- 
mation, which oecurs while the egg or embryo is still exposed to 
the experimental conditions, and recovery, which occurs after 
the egg or embryo is removed to water, involve the same regions 
of the developing organism that suffer distortion in inhibition or 
acceleration. Both are differential. These two conditions are 
to be distinguished from acceleration in that embryos produced 
under conditions that accelerate development are always in ad- 
vanee of the controls, while the differential acclimations and 
Figs. 27 to 29 Differential acceleration. 27, control; 28, embryo same age as 
control after 8 days’ continuous exposure to n/500 NaOH (solution not changed 
after third day) from an early gastrula stage. Exp. NaOH 2. 29, embryo after 
96 hours’ exposure to m/100,000 KNC. Eggs unsegmented when placed in the 
solution. Hxrp. KNC-C.4. v.s., ventral suckers. 
recoveries are usually smaller than controls and differentiation 
has not proceeded as far. Indeed embryos that show acclimation 
or recovery or both may at the same time show a differential in- 
hibition due to an earlier treatment. This is more especially 
true of the differential recovery forms. 
As regards acclimation of the egg or embryo in the various solu- 
tions used, my data are not complete. Such data as have been 
obtained are brought out incidentally in connection with other 
experiments. A number of experiments, however, furnish con- 
ditions where recovery might be expected to take place (pp. 486, 
491). 
Among the more conspicuous features which mark recovery 
forms differentially are: relatively large tail buds on otherwise — 
differentially inhibited embryos and a marked dorsal convexity 
is characteristic. 
