358 DAVID DAY WHITNEY 
Later this assumption was doubted and the possibility was 
recognized that this reinvigoration might be due to external con- 
ditions. Consequently further experiments entailing great care 
were carried out in which every fertilized egg obtained was known 
for a certainty to have been fertilized by the sperm of the other 
race. Separate new cultures of the two races were made in 
several battery jars at the same time. After a few days many 
males appeared in both races. Then several thousand females 
of each race were isolated in separate watch glasses and soon 
produced both female and male parthenogenetic eggs. These 
eggs were transferred to other watch glasses containing food 
culture water and allowed to hatch. At this period of hatch- 
ing the eggs of both races were continuously watched and the 
young females and the young males were isolated as soon as 
they left the egg membrane thus preventing any fertilization by 
males of the same race. Scores of young females and dozens 
of young males were isolated from each race and then the young 
males of one race were placed in the dish containing the young 
females of the other race. Copulation soon took place and later 
some of the females at maturity produced the thick-shelled con- 
spicuous fertilized eggs. Such females were readily distinguish- 
able, by the general appearance of the enclosed eggs, from the 
parthenogenetic females, and were isolated in separate dishes 
containing food and allowed to produce as many fertilized eggs 
as possible. By this method several dozens of cross fertilized 
eggs were obtained. Eggs of race A were fertilized by the sperm 
of race B and eggs of race B were fertilized by the sperm of race A. 
Twenty-four of these cross fertilized eggs were hatched thus 
starting twenty-four separate races. The immediate offspring 
of each of these races consisting of parthenogenetic females were 
cared for and the reproduction rates of eighty-four parthenoge- 
netic daughter-females from these were determined. At the same 
time the rates of reproduction of the A and B race after the third 
and fourth successive inbreeding respectively were determined 
and also that of the control race, E. All fertilized eggs in these 
reciprocal crossbreeding and the third and fourth successive 
inbreeding experiments of races A and B were produced in the 
