MODIFICATION OF DEVELOPMENT IN THE FROG 497 
96 hours in HCl. Embryos in advance of control. Heads seem 
relatively larger than in normal embryos (figs. 32, 33, 34). 
Experiment HCI-C. 5. n/5000 HCl. Eggs two to four-cell stage at 
the beginning of the experiment. 
48 hours in HCl. Distinctly accelerated. Blastopore closed and 
medullary folds distinct. Control: advanced yolk plug stages. 
96 hours in HCl. Many hatched. Heads seem relatively large. 
~ None of the control embryos hatched as yet. 
6 daysin HCl. Much accelerated. Tails long and broad. Figures 
35, 36, 87 and 38. The heads of these embryos appear relatively longer 
and broader than controls and the gills are further developed and wide- 
spread. Actively swimming. 
Experiment HCI-C. 6. n/20,000 HCl. Eggs two to four-cell stage 
at the beginning of the experiment. Control same as for the experi- 
ments just described. 
48 hours in HCl. Development accelerated. Blastopore closed. 
Medullary folds distinct and beginning to close. Dorsal region elongat- 
ing. 
96 hours in HCl. Embryos are more accelerated than those in 
n/5000. Nearly all hatched. 
9 days in HCl. Heads relatively large and gills unusually promi- 
nent. The embryos remind somewhat of Amblystoma tadpoles. 
The experiments with NaOH were carried out in the same way as 
those with HCl, and in most cases were ran parallel with eggs from 
the same female and one control for the two series. Save for the slightly 
different concentrations used, there was no particular difference in 
the experiments with the two agents either as regards method or re- 
sults. A single example will suffice here. Eggs in early gastrula 
stages exposed from 1 1/2 to 12 hours to n/300 NaOH and returned to 
water show after several days microcephalic embryos with the bilateral 
sense organs and ventral suckers approximated or ‘fused’ and numerous 
spina bifida forms are present. Figures 24 to 26 represent three em- 
bryos from experiment 125.2 E. The eggs—early gastrula at the 
start of the experiment—were exposed 3 hours to n/300 NaOH and 
removed to water. The camera-lucida sketches were made six days 
later. 
If eggs are taken when the susceptibility is low—early cleavage or 
unsegmented—and somewhat lower concentrations of NaOH used, 
n/400, n/500—n/1000, development is accelerated in much the same 
way asin the HCl experiments described above. Figures 27, 28 repre- 
sent two sister embryos of the same age. Figure 27 is the control and 
28 an embryo exposed 8 days to n/500 NaOH. In this case the solu- 
tion was not changed after the third day. The megacephalic condi- 
tion—differential acceleration—is apparent at once. 
As regard acclimation of the egg or embryo in the various solutions 
my data are incomplete, but a number of the experiments furnished 
conditions where recovery might be expected to take place. Potassium 
permanganate seems to be a favorable agent for the purpose. While 
