98 Trans. Acad. Sci. of St. Louis 
obtained for all alike. I hold that we are logical in assuming 
in all these tests that those which came in one and two days 
late did so only by virtue of their wanderings or of shifting of 
the winds, and hence do not have much weight in the present 
investigations. Out of 72 new males which had flown to the 
root from their wild haunts, 6 came back in this test flight (6 
more came in on following days); out of 7 young bred males 
which had never been out of doors before, none returned; one 
bred male which had made a successful previous flight did come 
back, and out of the lot of 11 which had made two previous 
flights, 5 came in promptly. All that we dare say at this point 
is this: while we have tried as far as possible to eliminate com- 
plicating factors, our problem is still a tangle. In this tangle 
we can from time to time recognize threads of different kinds, 
but the wisest method for us is to follow up and straighten out 
the one thread with which we have begun; in that way the 
others will be more easily disentangled later. The element of 
chance is always present to complicate matters, but here we 
are about to become involved with the factors of profiting by 
experience, and possibly trial and error; later we shall meet 
the more obvious but less knotty obstructions of old age and 
fatigue. The only kink conclusively disposed of here is that 
about 20 per cent of these moths can follow the trail of the 
female for a half-mile when the wind is semi-favorable. 
Exp. 20. May 22. There was a dearth of female cecropias; 
it seems, as Fabre complains, ‘‘when the farmer needs dung, the 
asses become constipated’’; now when I so needed a few females, 
only males emerged. I even went so far as to put cocoons in the 
incubator, but when they came forth, they were males and more 
males. Let us take inventory of our stock of females and esti- 
mate their drawing power. In one cage at the window were 
seven dead females and one feeble one nine days old; this cage 
had not been attractive to the opposite sex for the past two 
nights. In another window were four, aged 10, 8, 8 and 3 days; 
other experiments have shown that 2 and 3 days is the most at- 
tractive age; therefore for the approaching dawn the burden 
of attraction lay with this young moth. I waited with curiosity, 
and at 3:25 the first suitor arrived; they came on constantly ae 
groups or singly until 4:30, the usual time for the procession t 
