Apr. 5, 1924 
Anatomy of th e Apple Maggot 
25 
horizontal cleavage lines of the puparium; those from the nine lateral spiracles 
(Sp) form a tangled mass of threads along each side; while those from the hind 
spiracles ( PSp ) are disposed against the dorsal wall of the envelope in the form 
of a double-stalked T, as shown in Plate 6, E ( tra ). The extraction of the anterior 
and the lateral tubes may be accounted for by the contraction of the pupa, 
but it is difficult to understand how the posterior tubes can acquire their curious 
arrangement (PI. 6, E) unless the pupa sways its abdomen sidewise to extract 
them. 
The pupa, now entirely free from its envelopes, retains no connection what¬ 
ever with any of the larval spiracles, and its own spiracles (PI. 6, D, PuSp) have 
no direct access to the outside air. In the Anthomyiidse the hornlike pupal 
spiracles are said to penetrate the pyparium between the first and second abdom¬ 
inal segments. In Rhagoletis , however, as the body of the pupa contracts dur¬ 
ing its transformation, the space about it, within the prepupal skin, becomes 
filled with gas which is visible as a large bubble through the walls of the puparium/ 
and which gives the insect at this stage such buoyancy that it will float on the 
surface of water. This gas is very evidently the respiratory medium of the pupa, 
though it is puzzling at first to account for the presence of air in the pupal cham¬ 
ber. An examination of the molted anterior tracheal tubes, however, will sug¬ 
gest the mode of its ingress. These tubes (PL 6, F, tra), always keep a firm hold 
on the stigmatic chambers of the spiracles ( ASp ), and the walls of their anterior 
parts are so rigid that they remain as open cylinders filled with air as far back 
as the rear margin of the second segment. In the third segment, however, the 
tubes abruptly collapse to flat bands of flabby tissue into which no air pene¬ 
trates; but, just before this point, there is always a rupture ( w ) on the inner 
face of each tube, and these holes establish free passageways from the anterior 
larval spiracles (ASp) of the puparium (pm) into the pupal chamber within 
the prepupal envelope (ppu), evidently the inlet of the pupa’s supply of air. 
The slowly diminishing size of the pupa during the period of its transformation 
may be assumed to suck in the air that forms the first bubble, but subsequent 
renewal must be by diffusion through the spiracles. 
The pupal spiracles differ from the corresponding larval prothoracic spiracles 
in being bilobed (PI. 2, A). The stigmatic chamber of each is elongate and 
forks into the two spiracular lobes where it ends in numerous small papillae that 
press against the cuticle and appear to contain perforations through the latter. 
Each pupal spiracle is developed mesad of the preceding larval spiracle (PI. 5, 
E), and the remains of the larval stigmatic chamber form outer and inner scaLs 
(PI. 2, A, m, n) with a cuticular strand (v) connecting them as in the larval instars. 
After the fifth day the pupa undergoes no further external change. Some 
pupae will transform to adults in the fall of the same year, but the majority 
remain in the pupal stage till the following year, when the flies begin to emerge 
about the first of June, while a few, it is said, do not transform till the second 
year after the end of the larval stage. 
The external forms of the pupa show the progress of the change from the larva 
to the imago; the real activities of reconstruction go on beneath the surface. 
The remaking of the insect is not accomplished in the manner by which a piece 
of clay may be remodelled from one form to another. The processes of meta¬ 
morphosis are physiological and consist of an active metabolism that affects 
nearly all the tissues, but not all in the same way or to the same degree. Some 
parts simply awake from a dormant state and pursue their normal course of 
development by a sudden access of growth; others that were functional in the 
larva are altered by direct growth resulting from the activity of their own cells. 
But the changes most characteristic of metamorphosis are those involving 
coordinated histolyses and histogeneses resulting in the destruction of larval 
