INSECTA.
973
Fig. 430.
Alimentary canal of Sphinx ligustri.
the pollen in the canal leading to the bag, in
the oesophagus, and in the stomach itself. A
gizzard does not exist either in the Diptera or
Lepidoptera, but there is a slight rudiment of
it in the Sphinx (i). The stomach of Lepidop¬
tera is in general short, oval, or a little elon¬
gated (k), and always very muscular, and as
in other insects, the hepatic vessels (p) enter
at its pyloric extremity (q). The ilium (/) is of
considerable length. In the Sphinx it makes
seven folds, and then passes straight to the
Fig. 431.
* Alimentary canal of Pontia brassicce.
colon, which is developed anteriorly into a very
large cæcum (in), and terminates in a narrow
short rectum (n). Throughout its whole course
it is covered by the hepatic vessels. In the
Pontia brassicce (fig. 431), the digestive sto¬
mach is preceded by a very muscular and
transversely banded portion of canal resembling
the stomach of Hymenoptera. It is in the pre¬
cise situation of the gizzard in other orders, and
appears to be the representative of that part in
this insect. The true stomach is long and oval,
and the ilium is longer than in the Sphinx, and
the cæcum, colon, and rectum are all distinct.
In the Diptera the alimentary canal is usually
very long, and is scarcely at all shorter in the
carnivorous than in the omnivorous feeders.
Appendages of the canal.—The first of these,
the salivary glands, are very frequent in most
of the orders, but vary greatly in form and
number. In Lepidoptera they are simple
elongated tubes (A), which extend into the
thorax and are convoluted beneath the oeso¬
phagus and anterior portion of the alimentary
canal. In the larva they constitute the silk
vessels, and empty themselves by a single duct
through the spinneret on the floor of the
mouth. They are formed of three por¬
tions; first, the excretory, which is thin and
transparent, and is gradually enlarged as it
passes backwards along the body ; second, the
apparently secretory portion of the organ, which
is of an elongated cylindrical form, externally
transversely marked as if formed of muscular
fibres, and internally covered with a vast
number of rounded glandular bodies, a§ we