BIOLOGY OF SATURNIID MOTHS—BLEST 461 
cremental course of the rocking response did not differ from that 
found in free-flying moths. If the moths are suspended and receive 
the appropriate stimuli for flight without flight being released (prep- 
arations may, for a variety of reasons, become refractory), the rock- 
ing response does not increase in strength. What is being registered, 
therefore, is the duration of the activity of some part of the central 
nervous system which excites and regulates the flight response. This 
situation is of peculiar interest because the rocking response is stable 
to retesting for periods of at least 90 minutes, and probably for 
longer; hence, the whole process of registration is comparable in some 
respects to a learning process in that a stable change is imposed upon 
the nervous system. It differs from conventional learning processes 
in that there is no problem of perceptual filtering to complicate the 
issue, and the quantitative and qualitative nature of the output is 
rigidly determined. While this simplicity and rigidity may be for- 
mally inconvenient for the learning theorist, it offers experimental ad- 
vantages for an attack on the physiology of learning processes which 
it is hoped may one day be put to proper use. 
However, it is a different aspect of the rocking response which bears 
upon the problem of lifespan. 
A statistical analysis of the relations between rocking pattern and 
other responses has shown that it is linked to a system that exerts an 
inhibitory “brake” action on flight behavior. Apparently the strength 
of the rocking response is in some sense a measure of the strength of 
this inhibitory potential. If the rocking response is strong, then the 
threshold of the flight response tends to be high and its persistence 
poor. Although these parameters of flight performance have not yet 
been placed on a firm quantitative basis in relation to the rocking po- 
tential, it is already apparent that in this respect the quantitative im- 
plications of the rocking response are considerably less strict than in 
the case of the relationship to flight performance per se. Now the 
strength of the rocking potential follows a definite course with age. 
Immediately after hatching from the pupa it is strong; thereafter, it 
falls off, most steeply in the few hours that immediately follow the 
act of eclosion from the pupa. Moreover, the slopes of the regression 
of rocking response on flight time (fig. 1) also fall off (fig. 3). Thus, 
ultimately, an age is reached at which (a) no overt rocking move- 
ment can be performed, and (0) all flight durations would, in princi- 
ple, in any case yield the same rocking strength, for the regression 
coefficients have fallen to zero. Since the rocking potential is held to 
be linked to an inhibitory potential, it may be argued that the conclu- 
sion of these age changes in the rocking response should see the total 
disinhibition of flight. 
Hemileucine moths do not feed, and their mouth parts are, in fact, 
vestigial; they are partially closed metabolic systems, and their life- 
