LIBRARY

DIPTERA 735
Malpighian tubes - two, four, or five pairs; normally four.
Hind intestine - tubular and but slightly convoluted; divisible distally into
the ileum and colon and posteriorly into the rectum which is furnished with
two, four, or sixpapillce.
Circulatory System.
Not well known for the order as a whole. In higher groups the heart is composed
of four large chambers, each with two posterior ostia and prolonged
anteriorly into a narrow tube. Circulation is also through the wings of some
flies.
Tracheal System.
Well developed and permitting great activity. Special air sacs are present in
the head, thorax, and abdomen and are particularly large in the latter.
Usually two thoracic and seven or eight abdominal spiracles are present.
Nervous System.
Variable. The head ganglia are intimately fused, and the arrangement of the
number of thoracic and abdominal ganglia includes such combinations as
1-0,1-1,1-2,2-0,2-4,2-6,3-5,3-7.
FIG. 266. The larva or maggot and pupa or pupatium of the blowfly, Sarcophaga cistudinis
Aldrich. (After Greene. 1925.)
Reproductive System.
The reproductive system is well developed, and flies are among the most
prolific of insects. In view of the many different methods of bringing forth
young, the systems are greatly modified and specialized.
Female. - Otlarioles - polytrophic, variable in number; one or two or from
five to 100 on each side or a number enclosed in a membrane, Spermatheca
- present. prominent, pigmented, globular, chitinous-lined sacs; onethree
in number.
Accessory glands - paired or single, small or large, tubular; emptying into
upper part of the vagina; furnish excretions to fasten eggs or to nourish
intrauterine larvre.
M ale-Testes - oviod, pyriform, usually pigmented. Vasa deferentia - short,
united into a common ejaculatory duct. Ejaculatory sac and paired accessory
glands present in many species (Imms, 1934).