1 
External Factors of Sex Determination (377 
and females. The starved caterpillars gave no special excess of 
males, although there were, it is true, a few more males; but 
Riley pointed out that under natural conditions the females in 
several species take a longer time than do the males to reach the 
pupa stage, undergoing in some cases one more moult, so that, 
if starved, the mortality would therefore probably be greater 
amongst the females, and hence more male than female moths 
might be found. Other observers, Bessels 1868, Briggs 1871, 
Andrews 1873, Fletcher 1874, have also found that an excess or 
diminution of the food does not alter the proportion of the sexes. 
The futility of many of these experiments has now become 
apparent, since it has been shown that the sex of the caterpillar 
is already determined when it leaves the egg. Under these cir- 
cumstances it is not probable that feeding could produce a change 
in the sex. It is much more probable that starvation or over- 
feeding could only effect the proportion of males and females 
by bringing about a greater mortality of the individuals of one 
Sex. 
Kellogg and Bell have studied food conditions in relation to 
sex determination in silkworms (Bombyx mori). They have 
guarded against the possibility of greater mortality of one sex. 
The chief interest of their work is their examination of the pos- 
sible effects of nourishment on the second generation. The 
effects of feeding the caterpillars themselves different amounts 
of food were as follows. Twenty larve were present at first in 
each lot. . 
“Lot I. Fed optimum food; no deaths before emergence of 
moths; produced 8 males, 12 females. 
“Lot II. Fed optimum food; 2 deaths before maturity; 
produced 7 males, 11 females. 
“LotIII. Fed one half (approximately) of optimum of food ; 
4 deaths before maturity; produced 1o males, 6 females. 
“Lot IV. Fed living minimum of food; 3 deaths before ma- 
turity; produced 10 males, 7 females. 
“Lot V. Fed living minimum of food; 6 deaths; produced 9. 
males, 5 females.” 
