Lixternal actors of vex Determination 379 
provided, of course, that it is not in reality already determined, 
since the absence of differentiation of the sex cells does not neces- 
sarily mean that the sex may not have been previously settled. 
Lowne had found that flies from large larve are almost always 
females, and those from small larve males; but Lowne himself 
doubted the value of his observations, and Cuénot says his con- 
clusion from them is erroneous. Weismann fed one lot of Cal- 
liphora vomitoria abundantly, and starved another lot from time 
to time. Both lots produced males and females. Cuénot’s ex- 
periments were as follows: — 
Experiment I. The larve after hatching were fed abundantly 
on putrefying flesh, and produced large flies. ‘The proportion of 
females to males is given in the next table. pea CeweGe 
FEMALES 
Lucilia cesar... . . . . 293 females 281 males 49.0 
Calliphora vomitoria . . . . 224females 215 males 51.0 
Sarcophaga carnaria . . . . . g6females go males 51.6 
Experiment II. The larve were given as little nourishment 
as possible; they. often were entirely without food, and the mor- 
tality was very great. The flies were small. The proportion 
of females to males was as follows: — ben Genrer 
FEMALES 
Lucilia cesar. . . . . - - + 95 females 69 males 57-92 
Calliphora vomitoria . . . . . 93 females 91 males 50.05 
Curtonevra pabulorum. . . . . 26 females 17 males 50.50 
Experiment III. The larve were kept under varied condi- 
tions, being fed on brain, suet, and a little meat. They were 
in a starved condition at first and were then abundantly fed or 
were fed at first and then starved. Several species were reared 
together. 
Calliphora vomitoria (April19) . . . . 185 females 166 males 
Lucilia cesar (Aug.Sept.). . . . . . 143 females 141 males 
The normal proportion of males to females in these species 
of flies is approximately equal. This relation is also found in 
those kept under the different conditions of the other experi- 
