20 
Journal of Agricultural Research voi. xxvm, no. i 
Another system of weak, superficial muscles lies close to the skin and consists 
of a few fibers in each segment disposed more transversely as shown in Plate 4, 
C and E. Finally, along the sides of the body, there is a row of slender trans¬ 
verse muscles (PI. 4, E, TMcl) placed on the intersegmental lines entad to the 
attachments of the other muscles attached along these lines. 
This complicated muscular sheath of the maggot is a special feature of the 
larva, since few of its fibers are retained in the adult. Most of the larval muscles 
are either destroyed by histolysis in the pupa stage or form merely a recon¬ 
structive basis for muscles of the imago. Van Rees (47) describes only three 
pairs of muscles in the mesothorax of the larva of the blow fly (Calliphora) as 
persisting into the adult stage, and Breed (10) agrees with him in this, but P6rez 
(89) describes muscles of the abdomen also as going over into adult muscles, 
though with complete reorganization. Most investigators, however, agree that 
in the higher Diptera the majority of the muscles of the adult are built up anew 
from mesoderm cells of the imaginal buds. Whatever may be the truth with 
„ regard to details, however, the musculature of the maggot is a striking example 
of the degree to which organs may be developed for use during one stage of an 
insect's life and then discarded or reconstructed to serve the needs of the next 
stage. The histolysis of larval muscles and the histogenesis of the imaginal 
muscles will be discussed in the section on metamorphosis. 
% 
THE CIRCULATORY SYSTEM 
The heart and aorta are of ordinary tubular form, and are suspended along the 
midline of the back between the dorsal oblique muscles (PL 4, E, Ht) in a delicate 
diaphragm that lies close to the body wall. The writer has not made a detailed 
study of the circulatory organs of the apple maggot, since they apparently do 
not differ from those of other cyclorrhaphus Diptera, and must be studied by 
means of sections. The dorsal vessel of the fly maggot as described by other 
writers, Pantel (37), Wandolleck (52), Lowne (28), and Giacomini (12), consists 
of four parts, a posterior section or ventriculus, a median part, the aorta, and 
an anterior extension of the dorsal wall of the aorta forming an inverted trough¬ 
like tongue. The posterior and median sections are contractile and are suspended 
in the diaphragm, which consists of muscle fibers and the pericardial cells, the 
latter being larger along the posterior section of the tube than along the median 
section. Giacomini describes the muscles as ending mesally in branching fibers 
enclosing the pericardial cells and inserted on the lower lateral parts of the heart. 
The most characteristic feature of the circulatory organs of the maggot is the 
presence of a suspensory ring at the anterior end of the aorta in the neighborhood 
of the frontal sacs and brain lobes. This was first described by Weismann (53) 
in the blow fly, and has been the subject of many complicated descriptions. 
Giacomini (12) says that in Eristalis tenax the ring, or suspensory anellus, is 
composed of epithelial-like cells and slants from above downward and posteriorly. 
At each end there is a core of small, compressed cells. The ring is anchored at 
its lower end by two pairs of tendinous cords. One pair goes back to the dorsal 
wall of the pro ventriculus, and the other goes forward to the anterior tracheal com¬ 
missure and neighboring tracheal branches. The aorta, according to Giacomini, 
penetrates the ring but its lower lip ends immediately in front of it, while its 
upper half is continued forward past the upper end of the ring to the anterior 
dorsal commissure of the tracheal trunk, where it ends in membranous ligaments 
attached to the brain lobes, to the tracheal trunks, to the frontal sacs, and to the 
pharyngeal muscles. The posterior end of the heart is suspended from the dorsal 
wall of the body by delicate tendinous fibers. 
