1968] 
Barth — Behavior of Eurycotis 
281 
surface of the paper in a stationary fashion rather than jittering 
them as in Periplaneta , Barth 1968a), but never show any additional 
signs of sexual motivation. Chemoreception of some substance 
present on the body of the virgin female, and also tactile stimulation 
from contact with the female are probably the usual releasers of 
lateral vibration. However as we have seen, it sometimes appears 
in situations lacking certain of these stimuli. Differences in the 
balance of tendencies making up the motivational state of the animal 
concerned may be involved in such cases. 
The fact that lateral vibration appears in so many different situa- 
tions in E. floridana makes it very difficult to make inferences con- 
cerning its motivational basis. It appears to be similar in form to 
the lateral jerking movement of Periplaneta (Barth, 1968a) and 
may well be homologous with it. In Periplaneta , lateral jerking 
appears in agonistic situations and it seems to indicate a fairly high 
level of escape tendency, in addition to a certain level of attack 
tendency. This is based on the observation that P. americana indi- 
viduals showing the lateral jerking movement frequently flee if the 
animal toward whom the display is directed, rather than being 
intimidated, responds with a similar movement or with some higher 
intensity aggressive movement such as lateral kicking or a biting 
attempt. The appearance of this movement in E. floridana in some 
of the situations mentioned above is somewhat clarified by assuming 
a certain underlying level of both attack and escape tendencies in 
the animal performing it. However, in this species, the movement 
has taken on a sexual function, and presumably is indicative of a 
certain level of sexual motivation as well, as it almost always pre- 
cedes copulatory movements in the male. This species may repre- 
sent an intermediate stage in the evolution of the lateral vibration 
display, in which a sexual component has been added to its ancestral 
agonistic motivational basis. However, the possibility that subtle 
differences (perhaps in the nature of the tactile or olfactory stimuli 
presented) exist among vibration displays appearing in different 
contexts, i.e., that two or more distinct displays are involved, can 
not be overlooked. 
In spite of the fact that females fairly frequently mount males 
which are not showing lateral vibration, the major function of this 
display appears to be the release of mounting and feeding behavior. 
Females in antennal or body contact with males showing lateral 
vibration almost invariably mount, and males apparently mount only 
vibrating males. Females have also been observed to mount vibrating 
females. Although tactile stimulation is probably of importance in 
