Life-cycle of the Lower Crustaceans 343 
composed of 70 broods. There were about 500 individuals 
produced. All were parthenogenetic, and no males and no 
sexual females appeared. In another similar series a few males 
and sexual females developed, but the tendency seemed to be to 
produce purely parthenogenetic forms. When kept at room 
temperature, 16° C., an isolated parthenogenetic female pro- 
duced from February 6 to April 15 two generations, and 13 
broods in all, composed of about 100 individuals. The first 
brood consisted of females and 5 males. The sixth brood was 
composed of parthenogenetic females which brought forth males, 
etc. Another culture under the same conditions gave 30 broods 
of 250 individuals, Again there was observed a transition from 
females to males through an intermediate mixed brood. In both 
cultures the females of the first generation produced the shell 
for the winter egg —the so-called ephippium. This was then 
thrown off because the egg was not fertilized. The next brood 
of the same individuals consisted only of parthenogenetic fe- 
males, but the next brood after this was made up either entirely 
of males or else another ephippium was formed. When a 
female produces the ephippium with the winter egg in it, the 
sexual condition is present, and therefore it will be observed 
that the same individual may function at one time as a partheno- 
genetic and at another time as a sexual female. In the case last 
mentioned where another ephippium is produced this may be 
thrown off and the following brood will be again males or an- 
other ephippium develops. When kept in the cold, 6° C., there 
is a still stronger tendency to produce sexual forms. This is 
shown in the two following experiments. All the offspring of 
one female were taken from the warm culture and separated 
into two groups. One set was kept at 24° and the other at 8°. 
The results for the two cases are shown below :— 
24° 8° 24° g° 
2 2 2 winter egg 
2 $ 9 winter egg 
fe) winter egg 2 died 
died winter egg died 
