200 Wisconsin Academy of Sciences, Arts, and Letters. 
posterior end of the crop, lying close to this part of the digestive 
tract are four structures, presumably salivary glands, though it 
is impossible to find an outlet for them. The two of these lying in 
closest proximity to the crop are large and nearly oval in outline 
(fig. 7, l.g.) ; while the others are longer, more slender, and with 
rounded ends posteriorly. Their position is lateral and ventral to 
the larger ones. When studied in microscopic section, there appear 
to be six structures instead of four, for the anterior portion of the 
tubular pair is histologically distinct. The posterior part of each 
tubular organ (figs. 7 and 8, g.r.) has a broad lumen and the cells 
which make up its walls are probably syncitial, since no cell walls 
show, though nuclei are scattered throughout it at intervals. The 
structure of these leads to the conclusion that they are gland reser¬ 
voirs rather than glands. The anterior part (fig. 8, s.g.) has no 
lumen, but is made up of cells which sometimes show droplets of 
secretion in their cyptoplasm. The histological arrangement of 
these cells is similar to that of the large oval bodies mentioned 
above and the two pairs of structures are probably connected. The 
oval bodies have no lumen and are composed of large glandular 
cells, the nuclei of which are large and stain heavily, while the 
cytoplasm stains irregularly. These structures are glands and are 
connected with the reservoirs through their anterior ends, though 
this connection is not discernible. Their appearance. suggests the 
three pairs of glands described by Uzel (22) in the thoracic region 
of the Thysanoptera. He does not show any ducts leading from 
them. 
Faure-Fremiet (13) describes in the Hydrocorises a pair of 
labial glands which lie in the thorax, even extending into the ab¬ 
domen, and are composed of an anterior and posterior lobe uniting 
anteriorly, and, where they come together, joining the excretory 
duct of a gland reservoir. An arrangement similar to this is very 
possible in Troctes, because of the relation the various parts bear 
to each other. 
The fore-intestine with its thin walls and wide channel, narrows 
abruptly at its posterior end to form the cardiac constriction, or 
valve (fig. 15, c.J. 
The mid-intestine (fig. 7, m.) beginning with this valve shows in 
section a sharp transition lo thick glandular walls, markedly folded. 
The content of this part of the digestive tract reveals the food of 
the book louse, for it is often made up of the spores of molds and 
small particles of other organic matter. At times the contents of 
