Apr. 5,1924 
Anatomy of the Apple Maggot 
3 
and Z). On the lateral lips of the mouth are two pairs of ehitinous teeth which 
appear to serve as guards against the hooks. Immediately later ad of each pair 
of hooks is a third sensory organ (Z), shown more enlarged in Plate 1, E. The 
lips of the mouth, posterior to the teeth, are marked by ridges as shown in Plate 
1, B. In some other species these ridges are more extensive and spread out 
like the ribs of a fan from the angles of the mouth. They perhaps serve to 
conduct the liquid food of the maggot into the oral cavity. 
The oral hooks (PI. 1, A, B, Hk) are strong organs of the mouth formed for 
grasping, clawing, and tearing. The apple maggot uses them for tunnelling 
through the fruit and for breaking down the pulp in order to liberate the juices 
and protoplasm of the apple cells which constitute its food. The hooks move 
up and down on a basal articulation, not sidewise as do mandibles, and they can 
be protruded or withdrawn by an evagination or retraction of the oral cavity. 
When the hooks are very forcibly withdrawn the head itself frequently disap¬ 
pears by inversion into the thorax. The mouth hooks differ characteristically 
in the three larval stages as shown in Plate 1, L, M, and N. In the first instar 
(PI. 1, L) the second or proximal claw is well developed, in the second instar 
(PI. 1, M) this claw becomes reduced, and in the third (PI. 1, N) it disappears. 
The hooks are articulated to a ehitinous framework in the wall of the pharynx 
and are worked by sets of special muscles, but those parts will be described ia 
connection with the pharyngeal skeleton. 
On the body of the maggot the intersegmental lines are marked by circular 
swellings (PI. 1, A) widest on the ventral surface and most pronounced on the 
posterior two-thirds. All but the first of these ridges are covered by minute 
hooklets (PI. 1, G) arranged in several irregular, broken rows, forming bands at 
the junctures of the segments. In the wider bands the hooklets of several ex¬ 
treme anterior and posterior rows are turned fqrward and backward respectively 
(PI. 1, F), while those of the median rows are turned backward and forward 
respectively. That the band of hooklets does not mark the end of either of the 
adjoining segments is shown by the attachment of the muscles of the body wall 
(PI. 4, C, E) along distinct lines between the median rows of hooklets in each 
band. 
Anterior spiracles are present only in the second and third instars of the larva, 
and in the pupa, and they differ in each stage, since each successive pair is newly 
formed and not developed from those of the preceding instar. But the spiracles 
are always located on the pro thorax and, in the larva, project like ears from the 
upper lateral parts of this segment close to the posterior margin (PI. 1, A, ASp). 
Each is a lobelike structure, flattened in a vertical plane, arising from a small 
mound of the hypoderm. The free edge carries many small papillae. The 
spiracle of the second instar (PI. 1, H) is smaller and simpler than that of the 
third. In the third instar the lobe is somewhat subdivided and the papillae are 
longer (PI. 1, J). The papillae are perforated at their ends, though ordinarily it 
is impossible to see the openings. But if a larva is killed in hot water and trans¬ 
ferred immediately to cold water or to weak alcohol, the ends of the papillae will 
be turgid with air, and a high-power objective will often show a slitlike aperture 
gaping wide in the tip of each (PI. 1, K). Pressure on the base of the lobe will 
discharge tiny bubbles of air from these apertures. 
The openings of the spiracle lead into a cavity within the lobe, which is pro¬ 
longed backward like a stalk beneath the hypoderm to meet the end of one of 
the two great dorsal trunks of the tracheal system (PI. 2, G, Tra). This cavity 
is the stigmatic chamber (PI. 1, H, J, SpC ). It is always distinguished from the 
adjoining trachea by its yellow color and the granular texture of its walls, and 
by the lack of spiral thickenings in its lining. In the second instar the stigmatic 
chamber of the anterior spiracle is a simple slender tube (PI. 1, H, SpC ); in the 
