1915] The Head and Mouth-Parts of Thysanoptera 51 
this valve is closed, consequently the lumen of the oesophagus 
is cut off from the pharynx while the elastic membrane is dilated. 
In suction the ventral dilating muscles (v. d. m.) contract and 
pull out the ventral portion of the elastic membrane. This 
results in the formation of a partial vacuum, and into this space 
the liquid food is drawn. The dorsal dilators (d. d. m.) now 
contract and dilate the dorsal end of the elastic membrane 
(e.). This dilation opens the valve separating the lumen of the 
pharynx and the oesophagus. While the dorsal dilators are 
contracting the ventral dilators relax and the ventral portion 
of the elastic membrane presses upon the enclosed food. This 
pressure forces the food dorsad in the lumen and then on the 
relaxation of the dorsal dilators the elastic membrane falls 
back into its normal position and the food is.forced on and into 
the oesophagus. This completes one stroke or dilation of the 
pharynx of Cephalothrips. 
The dilating muscles of the pharynx (d. m.) of Heliothrips, as 
before noted, are arranged along the meson of the elastic mem- 
brane (e.). This fact, along with the large size of the pharynx 
and its peculiar bent condition, would indicate that the elastic 
membrane does not have as distinct a ventro-dorsal dilation 
as that of Cephalothrips. Possibly the entire central portion 
of the membrane is dilated at one time and then as the large 
muscles relax the few strands of muscles uniting with the 
pharynx in the region of the valve contract and open the lumen. 
With the valve open and the elastic membrane pressing upon 
the enclosed food, the plant juice is forced into the oesophagus. 
SALIVARY GLANDS. 
Two or three kinds of salivary glands (fig. 15, 16, 23, 24, 
30, 31, 38-44, 45, 49 and 51-55) are present in thrips and 
these are all located in the thorax and abdomen. Uczel has 
figured the glandular portion of the salivary glands located 
in the thorax and abdomen but does not figure the course 
of the ducts. In Uzel’s figures two kinds of salivary glands are 
present in the thorax of Aeolothrips fasciatus, a form belonging 
to the suborder Terebrantia, and three kinds of salivary glands 
are found in the thorax of Trichothrips copiosa, a form belonging 
to the suborder Tubulifera. The species figured in this paper 
have only two kinds of salivary glands, which extend into the 
thorax and abdomen. These two kinds are paired and distinct. 
