THE LIFE-CYCLE OF MOINA RECTIEOSTRIS. 
511 
The Life-Cycle of Moina rectirostris. 
By 
'J'lie late G. H. Grosveiior, M.A., 
New College, Oxford, 
and 
Geoffrey Sinitli, Itl.A., 
New College, Oxford. 
In tlie summer of 1904 the late Mr. G. H. Grosvenor began 
some experimental observations on the life-cycle of Moina, 
with the object of testing Weismann’s hypothesis (1) that 
the succession of parthenogenetic and sexual individuals is 
controlled by an internal rhythm independently of external 
circumstances. The species of the genus Moina, as pointed 
out by Weisrnann, belong to the polycyclic group of Cladocera 
which inhabit small ponds and which produce sexual indi- 
viduals with great frequency, and this fact, together with the 
ease with which they can be cultivated, renders them con- 
venient for experimental purposes. 
After cultivating the animals for some time, Grosvenor 
noticed that if the parthenogenetic females were kept isolated 
in separate vessels from the time of their birth to the period at 
which they produced }’oung, they gave rise to a much smaller 
proportion of males than was the case when they were kept 
crowded together in the same vessel. His method of cultiva- 
tion was to place the young newly hatched parthenogenetic 
females, either isolated or together in numbers of about five to 
fifteen, in ordinai-y tumblers three quarters full of tap-water, 
and to add to the water a small quantity of a stock infusion 
