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