1190 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
third of that of the nuclei of the mid-intestinal epithelium. The cells forming 
the walls of the silk gland are like those of the mid-intestine in the deeply- 
staining character of their cytoplasm, which usually stains so densely in com¬ 
parison with the other tissues as to be almost totally opaque, as shown in Plate 
5, A, SlkGL Other points of similarity are the form of the cells, whose breadth 
and height are approximately equal, the striated or fibrillated aspect of the 
eytoplasm, noted also in the cells of the silk gland of Lepidoptera and Trichop- 
tera (12), and the spherical nuclei, each containing a compact mass of chromatin 
granules. Near their anterior ends the character of the cells forming the wall 
changes somewhat. Here the walls are thicker, the cells composing them being 
smaller and long-columnar in form. The cytoplasm stains less deeply and no 
longer shows well-marked fibrillae. The lumen of this portion of the gland 
shows within it coagulated secretion, although the larva in question was scarcely 
mature. 
The ducts of the silk glands are thin-walled and otherwise histologically pre¬ 
cisely similar to the tracheae, this similarity extending to the possession of a 
chitinous intima, thickened spirally to form taenidia. 
MUSCULAR SYSTEM 
MUSCLES OF THE HEAD 
The muscles of the bee larva may be divided for descriptive purposes into 
muscles of the head and muscles of the trunk, since these two sets are totally 
different. The principal muscles of the head are as follows: 
MANDIBLES 
Each of these is provided with an extensor and a flexor muscle. The extensor 
(PI. 6, C and D, EMd) is inserted on the inner surface of a papillate elevation 
of the hypodermis located on the ectal side of the base of the mandible. From 
this point it passes directly caudad to its origin on the fold of hypodermis sepa¬ 
rating the head and trunk (neck fold) close to the outer end of the transverse 
arm of the tentorium. The flexor muscle (PI. 6 , C and D, RMd), which is the 
largest in the head, is inserted on a long and pointed hollow spine, the mandi¬ 
bular apodeme (PI. 1, A, and 6, D, RAp), which arises from the mesial side of 
the base of the mandible ( Md ). From this a stout bundle of muscle fibers 
passes caudad parallel to the fibers of the extensor muscle to an origin just 
dorsad of them. Another and larger group of fibers breaks up into small sub¬ 
equal bundles, passing behind the brain. These are attached at regular inter¬ 
vals along the neck fold between the point of origin of the extensor muscle and 
the mid-dorsal line of the head (PL 6, C, RMd). 
MAXILLAE 
Mesiad and dorsad of the base of each maxilla, below the apodeme for the 
extensor of the mandible, there is a papillate elevation of the hypodermis, on 
the inner surface of which is inserted the flexor muscle of the maxilla. This is 
of small size (PL 6, C, RMx ), and originates on the neck fold, just ventrad of the 
origin of the extensor muscle of the mandible. The maxillae have no extensor 
muscles corresponding morphologically to those of the mandibles. They are, 
however, provided with a pair of strong muscles which appear to be functionally 
extensor muscles. Each of these takes its origin as a broad band from the 
ventral surface of the anterior arm of the tentorium of the corresponding side, 
close to the posterior end of the arm, and from here passes ectad and ventrad 
