Experiments in Rhythmetic Periodicity 165 
between cecropia and cynthia is closer, for there was an inter- 
specific attraction and on one oceasion a mating. Other investi- 
gators have found it possible to cross cynthia and cecropia and 
get fertile eggs. 
Exp. 12. Everything so far points to the probability that the 
males find the females through odor perception. The problem 
whether certain females are more attractive than others to the 
males remains open. If odor is the medium of attraction, it 
seems to me that the degree or intensity of odor would be to a 
great extent regulated by the age of the female. With this in 
mind, the following tests were made on cecropia: 
Six cages were arranged in a row (see figure 1); each con- 
tained 10 females, whose ages were as follows: . 
Cage 1, 1%4 day old. Cage 4, 4 days old. 
Cage 2, 1 day old. Cage 5, 5 days old. 
Cage 3, 3 days old. Cage 6, 6 days old. 
The cages were placed in the path of the wind, and be- 
tweeen 10 p. m. and 4:30 a. m., 26 males flew to them. They 
did not always remain on the cage which first attracted them, 
but they were counted as being attracted to the cage upon which 
they finally rested. The following table shows how many males 
were attracted to each cage: 
Cage Age Males Cage Age Males 
1 Vy, 3 4 4 6 
2 1 i 5 5 4 
3 3 2 6 6 0 
Thus the males clearly decreed that in their estimation the 
females which were one day old were the most attractive, while 
the antiquated females were spurned entirely. In some of the 
earlier experiments some of the old females still attracted males, 
but on these occasions no younger rivals were present. 
While the majority of the males flew direct to the cage from 
Which they were recorded, several flew to various cages, testing 
out, as it were, the qualities of the inmates before alighting. 
If an adherent of the theory of chemotropism still thinks that 
the males are drawn to the females as iron filings are drawn to 
a magnet, let him weigh and consider some instances which I 
observed in detail. 
