1188 
Journal of Agricultural Research 
Vol. XXVIII, No. 12. 
smaller than those of the adjacent epithelium. The muscular investment of the 
mid-intestine ( MclEnt ) ceases abruptly at the margin of the “ stalk. ” As already 
stated, the enlarged anterior end of the hind-intestine is closed by a thin layer of 
minute cells, forming a circular structure ( dph ) which may conveniently be 
termed “the diaphragm. ” The central part of the diaphragm is closely adherent 
to the stalk, as described by Rengel. In larvae of Vespa and of ants the dia¬ 
phragm is relatively much thicker than in those of the honeybee, judging from 
the figures given by Rengel (44), Karavaev (22) and Perez (40), but otherwise 
the relations are essentially similar. 
MALPIGHIAN TUBULES 
The Malpighian tubules are four in number and lie, two on each side, between 
the lateral faces of the mid-intestine and the body wall (PI. 4, A and 5, A, Mai). 
They pursue a winding course, being thrown into numerous loops and folds, and 
extend from about the last thoracic to the 9th abdominal segment. In the newly 
hatched larva the tubules are slender and of nearly uniform diameter throughout; 
in the mature larva their anterior ends only are slender, the tubules widening 
gradually caudad, reaching their maximum diameter, which is about one-half that 
of the mid-intestine, in the region of the 7th abdominal segment (PI. 4, A, Mai). 
From this point they taper rapidly to their caudal (or central) ends, which are 
inserted, two on each side, between the mid-intestine and hind-intestine where the 
two latter have their junction. These central ends are exceedingly slender and 
pointed, composed of relatively small cells, and become closely attached to the 
thin epithelium closing the anterior end of the hind-intestine, with their tips 
abutting on the stalk of the hind-intestine (PI. 6, A, Mai). The lumen of the 
Malpighian tubules becomes greatly reduced here and finally ceases, the central 
ends of the tubules therefore ending blindly, contrary to the statements commonly 
found in the literature on this subject ( 44 ) • The writer (36) stated that in 
the newly hatched larva the Malpighian tubules open into the mid-intestine, but 
renewed investigation shows that there is no basis for the statement, since in all 
the sections examined, both cross and sagittal, the central ends of the tubules 
disappear in the relatively thick layer of cells closing the anterior end of the 
hind-intestine. Sections of a larva two days old also fail to disclose any con¬ 
nection between the lumen of the Malpighian tubules and that of the hind- 
intestine. 
The walls of the Malpighian tubules consist of a single layer of epithelial cells. 
In very young larvae the wall of the tubules is relatively thick and the centrally 
placed lumen correspondingly small. In mature larvae the cells composing the 
walls are flat, thin, and pavement-like in character (PI. 5, A, Mai, and PL 4, 
B and D). This condition exists even in the slender anterior ends, clearly 
indicating that the tubules are distended by internal pressure. The nuclei are 
discoid (PI. 4, D, Nu), being flattened in a plane normal to the surfaces of the 
tubules, and contain abundant chromatin in the form of subequal spherules. 
The cytoplasm of the cells displays no fibrillae, as in the case of the cells of the 
mid-intestine and silk glands, and appears to be finely granular. The margins 
of the cells at the point of junction with one another are uniformly vacuolated, 
as shown in Plate 4, D, thus giving the tubules, stained or unstained, a character¬ 
istic mottled appearance in surface view (PL 4, B). The tubules are lined within 
by a cuticular intima, possibly chitinous, which stains much less densely than the 
cytoplasm (Pl. 4, D, Int). 
The condition just described is characteristic of larvae shortly before the 
capping of the wax cell. Younger larvae show intermediate conditions, that is, 
the diameter of the tubules is relatively smaller and the walls thicker. The 
