134 
Psyche 
[December 
liams (’30-b) gives the results of counts made to determine 
the frequency with which butterflies in migration passed a 
given point. Observations of this kind on C. florella show 
that its migrations are indeed similar to the one observed 
by the writer in C. eubule. The large number of migration 
records in this genus are evidence of the frequency of its 
occurrence, and indicate that such behavior is no small fac- 
tor in the biology of its species. 
There is no evidence that a return flight takes place in 
eubule. The repopulating of the northern part of its range 
may be accomplished by a gradual dispersal northward dur- 
ing the summer, or through the increase in numbers of the 
few that manage to survive the winter. Of interest in this 
connection are the many records of individual northern oc- 
currences of various southern species of this genus; for 
some recent records, reference is made to Galkins (’32), on 
C. philea L., agarithe Bdv. and statira in western Kansas, 
and citations by O’Byrne (’32) of some northern occur- 
rences of C. philea. Such records refer to them as “strays,” 
and indicate a possible way in which a northward spread 
of eubule could take place without attracting attention. 
The foregoing data on C. eubule have important bearing 
on the nature of migration in insects. The question, 
whether insect migration is purposive, or is merely the re- 
sult of their being blown about by the wind, is answered by 
the fac? that the butterflies continued their flight day after 
day in the same direction, despite changes in the direction 
of the wind, and regardless of the contour of the ground 
and presence of obstacles. This has been fully discussed 
by Williams (’26), but the question still keeps bobbing up. 
The fact that the manner and speed of flight differed some- 
what from the usual behavior indicates that the butterflies 
were in an abnormal physiological or mental state. The re- 
sults of dissections of migrating females of C. florella by 
Williams (’30 -a) give further weight to this suggestion, for 
they indicate that flight starts during a condition of sexual 
immaturity, and ceases when oviposition is ready to begin. 
It may be that the climatic changes of a temperate autumn 
are accompanied by internal changes in the butterflies. 
This is reasonable in view of the fact that the genus Catop- 
silia is almost exclusively tropical; eubule itself is most 
