52 
Psyche 
[June 
attachment on each sepal is a pair of external epithelioid 
cells of unknown function. Internally the calyx wall is 
lined with a chitinous intima, which is continuous with 
the intima of the crop wall proper. Scattered in the inter- 
sepalary folds are slender longitudinal muscle cells; these 
are few in number and have no obvious function. They 
are inserted on the anterior face of the bulb and are con- 
tinuous with the muscularis of the crop. 
The occlusory tract, or valve of the previous literature, 
is formed posteriorly by a coalescence of the sepals in the 
following manner. As the calyx narrows, the sepals are 
brought closer together. Their wings shorten, the inner 
chitinous zone grows progressively thinner, and the outer 
zone expands toward the center, extending with it the 
filter area. Finally the inner zone disappears altogether; 
the sepals curve together and fuse medially. The filter 
area, seen in cross section of the sepal as a narrow zone 
separating the canal from the calyx cavity, has now 
elongated to form one of the filter slits of the occlusory 
tract (pi. 6, fig. B). The tract is thus a solid chitinous 
structure having in the center a single united cruciform 
slit, the arms of which are expanded at their tips into 
four canals, which are in turn continuous with the sepal 
canals in front and the bulb canals behind. It is of in- 
terest to note here that the arms of the cross are densely 
covered with chitinous hairs, whereas the canals are bare. 
The wall of the tract, external to the chitinous cross, is 
similar to that of the calyx. The longitudinal muscles are 
more concentrated due to convergence, and the external 
pairs of epithelioid cells are no longer evident. 
The occlusory tract merges into the bulb by a thinning 
of the intercanal chitin and an expansion of the cruciform 
slit into the bulb cavity. The outstanding feature of the 
bulb is the powerful development of its circular muscles, 
which are five or more fibers thick in cross section. 
Explanation of Plate 7 
Fig. A, cross section of the bulb at approximately the level of trans- 
ection shown in plate 6. Fig. B, cross section of the cylinder. Fig. C, 
cross section of the cylinder at the level of the cylinder valve. M. g. 
epth.. midgut epithelium. (360X) 
