1952 J Eisner and Wilson — Formicine Proventriculus 57 
section of the bulb (pi. 7). The walls of the canals are 
constructed along their outer edges of exceptionally thick 
chitin, which cannot easily be folded in. The action of the 
transverse muscles is obviously to decrease the volume of 
the bulb. The first thing that must occur as this constric- 
tion begins is that the opposing chitinous walls immediately 
adjacent to the canals meet, although the canals themselves 
remain open. The point of contact of the walls now pro- 
ceeds toward the center of the bulb, until, at the completion 
of contraction, the bulb cavity is mostly obliterated. 
A fourth misconception, not entirely referable to Emery, 
but partly stemming from other authors such as Janet, is 
that the crop is a passive organ which functions only as a 
storage center. Examination of entire and dissected Camp- 
onotus, the crops of which were distended with stained 
honey, showed that the crop wall is capable of strong and 
almost total contraction, which at the very least would 
suffice for regurgitation by itself. In dissected material 
the movements were most marked in the posterior ring 
muscles, but they often proceeded anteriorly to include 
the entire crop. In fully intact but excited and active 
individuals the crop, when only slightly distended, could 
be seen through the body wall to undergo very swift pul- 
sations, forcing almost its entire contents into the forward 
part of the gut. 
Our interpretation of the action of the proventriculus in 
Camponotus americanus is as follows. The calyx and oc- 
clusory tract are devices for checking the posterior flow 
of liquid as fluid pressure builds up in the crop. They are 
able to do this without muscle contraction, simply because 
more pressure is required to force liquid through the 
filtering slits than is present even when the crop is con- 
siderably distended. Muscle action can have little effect 
on the width of these filtering slits and therefore cannot 
exert a valve-like control per se. In the euformicines the 
muscularis can act as a secondary damming device by 
closing the calyx and preventing liquid from reaching the 
filtering slits. But in dissected individuals with distended 
crops the closure of the calyx was not a necessary device, 
and liquid from the crop failed to reach the bulb even when 
the calyx was open and its cavity filled. The pressure re- 
