THE LIFE-CYCEE OF MOINA RECTIROSTRIS. 
513 
The result of these experiments was to show that Gros- 
venor’s idea as to the factor of isolation and crowding influ- 
encing the life-cycle was well founded^ and also to prove 
that the influence of temperature, especially when combined 
with isolation, was of great importance. We were, in fact, 
able by keeping the parthenogenetic females isolated in an 
incubator at about 28° C. to inhibit absolutely and for an 
indefinite period the production of sexual forms. Although 
this latter result was of a far more definite kiud than could 
be drawn from any experiments published at the time or 
since, we refrained from publishing them, as we hoped to find 
out what the exact nature of the factor of isolation and 
crowding might be, but the experiments which we made to 
settle this point were inconclusive. Owing to other duties aud 
preoccupations the work lapsed, but Mr. Grosvenor’s sudden 
death makes it desirable to publish the results as they stand. 
Before referring to, and explaining, the tabular statement 
of our results, it is necessary to make some general observa- 
tions on the life-cycle of Moin a rectirostris. 
The fertilised egg, after lying dormant, invariably hatches 
out as a female, which reproduces parthenogenetically. The 
parlhenogenetically produced young may be either them- 
selves parthenogenetic females, or they may be males or 
ephippial females. The parthenogenetic females of this 
generation, again, may produce all three kinds of individuals, 
and'so on indefinitely. Schematically we may represent this 
type of life-history as follows : 
Besting egg 
P.? 
/ I V 
P. 2 cJ Ephippial $ 
/ I \ 
P-? df P-2 
etc. 
