REINVIGORATION PRODUCED BY CROSS FERTILIZATION 343 
the constant environment of the horse manure food cultures. 
The influence of the environment upon the race will be considered 
in a subsequent paper when certain experiments which are in 
progress now shall have been completed. At present it is useless 
to discuss this point because of the lack of sufficient data. From 
the evidence it is also concluded that race B has’ become the 
weakest or the most exhausted in its general vigor, while race D 
is the strongest and most vigorous. 
After the general vigor or vitality of the parthenogenetic races 
A and B had been ascertained it was decided to determine 
whether fertilization within each race would increase its general 
vitality. Several females from each race were placed in separate 
new cultures made in small battery jars and allowed to live in 
them two to three weeks. During this time males appeared and 
fertilized eggs were produced. After a short time these fertilized 
eggs from both races A and B were hatched and a series of paral- 
lel observations were made upon the rates of reproduction of the 
races, from the fertilized eggs, from the original parthenogenetic 
race, and from the new race D. ‘Tables 2 and 3 show the negative 
influence of inbreeding once in race A. Table 4 shows the same 
result in race B. 
After these results were obtained it was thought best to ascer- 
tain whether or not a second inbreeding of the races which had 
_already been inbred once would reinvigorate them, perhaps by an 
accumulation of stimuli of some sort which were too weak in the 
first fertilization to give apparent results. Table 5 gives the data 
and results of the second successive inbreeding of race 4. The 
new race D was used as the control or normal race as has been 
done in the former experiments. ‘Table 6 shows the results ob- 
tained from fifty-one females each of which developed from a 
different fertilized egg of race B which had already been inbred 
once. In neither table is there found any very marked increase 
of the rate of reproduction. These two races, both of which re- 
sulted from a second successive inbreeding of the original races, 
were continued. Later in the year race A produced fertilized 
eggs which resulted from the third successive inbreeding of the 
race, and race B even was allowed to produce fertilized eggs which 
