328 HELEN DEAN KING 
five different females, were experimented upon, and in no case 
did more than one-tenth of the eggs segment even when the solu- 
tion used had a strength of only 0.0025 per cent. The failure 
of these experiments cannot be due to the chance selection of a 
particularly bad lot of eggs and sperm, since eggs from two of the 
five females were used for all of the other experiments that were 
made, and the very great majority of them developed normally 
although they were fertilized under very unusual conditions. 
The only explanation that I can offer for this very unexpected 
result is that, when fertilization was attempted, the eggs happened 
to be in a physiological condition that rendered them particularly 
sensitive to the action of acid solutions. This past spring no toads 
were obtained until the seventh of April, and each of the five 
females used for these experiments had already laid a portion of 
her eggs before she was brought into the laboratory; the eggs were, 
therefore, very ripe. In 1910, females were obtained the latter 
part of March, and as none of them had laid any of their eggs when 
captured, the eggs were presumably in an early stage of ripening 
when they were experimented upon. According to Hertwig (06), 
the physiological condition of amphibian eggs varies considerably 
at different phases of their ripening, and it may be, therefore, that 
very ripe eggs are more easily injured by acid solutions than are 
eggs that are in an earlier stage of development. 
The individuals belonging to only one of the acid series were 
saved. In each experiment in the series about 400 eggs, taken 
from female b, were fertilized in solutions of acetic acid and re- 
moved to fresh water at the end of one-half hour. The strengths 
of solutions used, which were the same as those employed last 
year, are shown in table 3. Many eggs that segmented in a more 
TABLE 3 
Eggs fertilized in solutions of acetic acid 
| | | 
NUMBER SEX | | PER CENT NUMBER MALES 
STRENGTHS TOTAL NUMBER 
D8 sae ty ee | asceRTaInED | MALES | BeeaNeaS FEMALES to 100 FEMALES 
— | ae | ~ — —— 
per cent | 
0.01 46 42 22 20 ATE G2 an el OROO 
0.0050 51 42 | 26 16 38.19 | 162.50 
0.0025 7 | 19 [ea sie Be |e Sggrotal T8000 
