50 Annals Entomological Society of America [Vol. VIII, 
the relaxation of the dilating muscles the elastic membrane forces 
the food dorsad thru the open valve (v.) into the oesophagus. 
A more detailed account will be given of this process in the 
discussion of the pharynx of Cephalothrips. 
Cephalothrips yucce.—In a similar manner, as with Helio- 
thrips, figures 48-57 and 59 show the chief characteristics of 
the pharynx of the Tubulifera. In its main features it cor- 
responds with the general description of the pharynx but in a 
few details it shows a greater degree of specialization than the 
pharynx of Heliothrips. In the first place it is strikingly ham- 
shaped and comparatively smaller. This difference in size 
is probably due to the reduction of the mouth-cone. Trans- 
verse sections show that the maxillary guides (mx. g.) unite 
with the pharynx for a short distance, and the extension over 
which the left mandible passes is the cephalic margin of the 
left, maxillary guide. The right, rudimentary mandible (r. md.) 
is not as large asin Heliothrips, however, it still retains its con- 
nection with the right side of the pharynx. The lumen (1.) 
of the pharynx is straight. The most striking difference between 
the pharynx of Heliothrips and Cephalothrips is in the arrange- 
ment of the dilating muscles. 
A lateral view and transverse sections of the pharynx 
show a distinct chitinized plate (pt.) standing on edge along the 
meson of the elastic membrane (e.).. The muscles are confined 
to the ventral and dorsal ends of this plate and the majority 
of them are connected to the chitinous tendon (c. t.) at the 
ventralend. These muscles, so-called ventral dilators (v. d. m.), 
extend into the head and unite with the vertex. There is a 
small band of muscles, the so-called dorsal dilators (d. d. m.), 
which extend between the dorsal end of the plate and the caudo- 
ventral area of the front. This arrangement of muscles is 
easily derived from the more generalized type found in Helio- 
thrips. On the whole the form and arrangement of the parts 
in the pharynx of Cephalothrips would suggest that it is a 
more efficient organ than that of Heliothrips. 
The lumen (1.) of the alimentary canal is cut off by a valve- 
hike structure at the dorsal end of the pharynx (fig. 58a.). A 
prominent projection (p.) extends from the caudo-dorsal end 
of the pharynx into the lumen. This projection fits into a 
pocket (po.) on the opposite side. Under normal conditions 
