1184 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
the external surface. On the other hand, the brain, ventral cord, and ovaries 
are not only penetrated by the tracheoles but not infrequently by the finer 
tracheal branches also, the latter terminating in end cells, which therefore lie 
within the tissues of the nervous system or of the ovaries, as the case may be. 
Anastomosis of the tracheoles to form a meshwork, as reported by Wielowieyski 
(SI), Von Wistinghausen (54), Petersen (41), Williams (S3), and others was 
not observed. 
The tracheal system of the bee larva offers nothing of special interest in its 
general form and relations and conforms to the type usual in the higher insects. 
As compared with the imago the tracheal system is simpler and more generalized. 
In the abdomen of the imago, however, particularly in segments 3 to 7, the 
tracheal trunks and their metamerically arranged commissures and branches 
may easily be recognized, although now enlarged to form air sacs (46 ). The 
posterior commissure is wanting. In the thorax the tracheal system is more 
greatly modified, and the larval type correspondingly obscured. 
ALIMENTARY CANAL, MALPIGHIAN TUBULES, AND SILK GLANDS 
ALIMENTARY CANAL 
The alimentary canal comprises a short and slender fore-intestine (Pl. 4, A, 
Oe), a voluminous mid-intestine (Mint) and a relatively short hind-intestine, 
having a sigmoid flexure (Hint). 
The fore-intestine shows the usual differentiation into three subdivisions, 
mouth, pharynx, and oesophagus. 
The mouth (PI. 2, B, Mth) is a narrow transverse slit bounded above by the 
clypeus, below by the labium, and laterally by the mandibles. It opens im¬ 
mediately into the pharynx. This is a somewhat ill-defined region, comprising 
the anterior end of the fore-intestine and extending caudad to about the point 
where the crura cerebri cross the fore-intestine. The epithelium of the mouth 
and pharynx (with the exception of the roof of the latter) is precisely similar 
to the hypodermis of adjacent parts of the head, being composed of closely 
crowded prismatic cells with flat external ends (PI. 2, B, and 4, C). On the 
roof of the pharynx is a conspicuous and well developed epipharynx (PI. 3, A, 
and 4, C, Ephy), which extends from the mouth well back into the oesophagus. 
It is broad and flat at its anterior end (PI. 3, A, Ephy), scarcely rising above 
the level of the adjacent epithelium of the roof of the mouth, but in the pharyngeal 
region it becomes a highly convex fold of the dorsal wall, projecting ventrad into 
the lumen of the pharynx and giving the latter a crescentic outline in transverse 
section (PI. 4, C, Ephy). The cells constituting this fold are very different 
from those of the remainder of the pharyngeal wall, being of small size and elon¬ 
gated, pyriform or club-shaped in form, their larger ends directed toward the 
lumen of the oesophagus. On the dorsal surface of the pharynx the cavity of 
the epipharyngeal fold is crossed by a large number of muscle fibers which unite 
the two lateral edges of the fold. These are shown in Plate 4, C, and in section 
in Plate 3, A, EphyMcl. Beneath these are a few longitudinal muscle fibers. 
On the floor of the pharynx, at its external end, is a small papillate elevation, 
provisionally labeled the hypopharynx (PI. 3, A, Hyphy). 
In addition to the muscles of the epipharynx, the pharynx is provided with 
other muscles, which are described in this paragraph. In the clypeus a pair of 
small muscles take their origin from the dorsal wall and are inserted on the 
epipharyngeal fold close to the median plane. Some four or five pairs of similar 
muscles are ranged behind one another, having their origin on the dorsal wall of 
the labrum. These are the levators of the epipharynx (PI. 4, C, and 6, C, 
LevEphy). Their action is evidently directly opposed to those crossing the 
