Apr. 5, 1924 
Anatomy of the Apple Maggot 
15 
maggot suggest that the anterior parts are extended mostly by blood pressure 
resulting from the constriction of the rest of the body and the retraction of the 
rear parts; but when the head and pro thorax are fully everted the oral hooks 
can be still farther protruded by the pharyngeal protractors. 
The independent up-and-down motion of the oral hooks is accomplished by 
their special extensor and flexor muscles (PL 3, F, EMcl, FMcl ), which lie against 
the sides of the lateral plates of the pharynx ( B ), beneath the lateral pharyngeal 
protractors ( LPMcl ). The two on each side arise posteriorly from the cartilage¬ 
like ridge (b) of the lateral plate ( B ), and are inserted by narrow tendonlike ends 
on the upper and lower lobes, respectively, of the wide bases of the hooks. 
At the end of the third larval instar, when the hardened puparial skin is 
separating from the body of the insect within, the hypoderm and new cuticle 
about the pharyngeal skeleton are loosened and form a sheath over all the external 
parts of the pharynx and upon the inner faces of the wing plates and the upper 
surface of the pharyngeal roof. The muscles are thus detached from their 
skeletal supports. The dilators are retracted from the rear wall of the base of 
the dorsal pouch (PI. 3, C, DP), being now contained in a tongue of the body cavity 
lying like a plug loosely in the space between the wing plates and the roof of the 
pharynx. In this way the cuticular parts are prepared for the final molt, though 
they remain in place until the second stage of the pupa, when the pharyngeal 
skeleton and the oral hooks are finally cast out along with the lining of the 
oesophagus. 
All the pharyngeal muscles go into histolysis during the early period of meta¬ 
morphosis. The protractors and the muscles of the oral hooks apparently have 
no homologues in the adult, but the dilators may be prototypes of those of the 
fly- 
THE ALIMENTARY CANAL AND SALIVARY GLANDS 
The alimentary canal and its convolutions are shown in Plate 4, A. The 
narrow oesophagus ((E) proceeds from the rear end of the pharynx backward 
between the frontal sacs ( FS ) and the brain lobes (PI. 3, F, Br) to the globular 
proventriculus ( Pvent ) in the first abdominal segment. The ventriculus (Vent), 
immediately following, has four short gastric caeca (GC) on its anterior end, and 
is disposed in many loops and coils from the first to the seventh abdominal 
segments, forming most of the length of the alimentary canal. Its final loop 
meets the intestine at about the middle of the body. The latter makes first one 
or two coils and then proceeds as a straight tube (Red) to the anus along the left 
side of the other viscera. 
The salivary glands are two thick cylindrical tubes lying latero-ventrally in 
the front part of the body cavity (PL 3, F, Pl. 4, A, SalGl). Their ducts unite 
into a median one (Pl. 3, F, SalD) which opens on the floor of the mouth in front 
of the ventral bridge (Pl. 3, C, e) of the anterior lateral plate (A) of the pharynx 
and between the imaginal buds of the labium (Pl. 3, F, LbB ). 
The four Malpighian tubules (Pl. 4, A, Mai) arise in pairs from two short 
basal tubes that originate in small ampullae on the anterior end of the intestine 
(Pl. 4, B). In the adult the basal ampullae of the tubules disappear (Pl. 4, Bx). 
In old larvae the terminal parts of the Malpighian tubules are commonly much 
enlarged, often to twice their usual diameter, and are so prominent by their size 
and opaque white color that they show through the body wall of a live maggot as 
conspicuous long white bodies in the rear half of the abdomen. This condition 
of the tubules is due to a great mass of transparent crystals contained in the 
lumina of the swollen parts. The crystals are structureless bodies varying in 
size from minute spherical grains to large irregularly oval or ovate stones, 40 
microns in diameter (fig. 5, A). 
