214 
Psyche 
[December 
roaches with simply the antennae amputated. They did not 
perceive the cheese until it was placed under their mouth parts, 
when they carefully tasted it before eating. 
Another experiment appears significant. If the end of a 
stick is smeared with cheese and held at a distance of about one 
inch from the head of roaches with amputated antennae nothing 
occurs. When the same stick is held at the same distance from 
the head of the normal roaches the antennae follow the move- 
ments of the stick until they touch it, much like the pursuit of a 
magnet by a piece of iron. If one antenna is removed and the 
other left intact and the contaminated stick is held alternately 
on the right and left side of the head, the response occurs in about 
half the time on the unoperated side than on the other. 
Naturally cheese is not the only substance that produces the 
above reactions. Dog biscuit will cause an identical response in 
starved roaches, but more tardily due to the much slighter odor 
emanating from this food. 
Roaches are gregarious animals and are often found huddled 
together in enormous numbers. These insects emit a strong 
species odor rather disagreeable to humans. This odor is probably 
responsible for their gregarious habit. During the course of our 
experiments, it was noticed that those insects with the antennae 
removed did not huddle as readily as was the case with the un- 
operated ones. After huddling the roaches with antennae were 
separated by disturbing them with a prod. In approximately 
one-half minute they were usually found together again. Those 
with amputated antennae remained separated until they accident- 
ally ran into one another. 
All of the roaches operated upon are alive up to the present 
(six weeks after the experiments). They behave perfectly nor- 
mally in so far as their appetite is concerned and the females 
have deposited several egg capsules. That they are abnormal 
with respect to the function of smell is a foregone conclusion, but 
it would certainly require a stretch of the imagination to assert 
that they were abnormal in all their behavior. 
3. Conclusions. 
Chemoreceptors are located on the antennae, maxillary and 
labial palps of Periplaneta americana. The antennae are the most 
