rtion or pharynx, which
arises from the stomodaeal invagination in the embryo, is short; a
pair of large, so-called salivary glands open into it. The mesenteric
part of the canal is relatively wide and receives at its junction with
the hind-gut the excretory products of a pair of very long and slender
malpighian tubes of proctodaeal origin. The posterior end of the
canal, arising from the proctodaeum, is relatively short and narrow.

[Illustration: FIG. 3.--Diagram of Alimentary Canal of _Lithobius_.

a, Anus.

mg, Mid-Gut.

hg, Hind-Gut.

mt, Malphighian tubule.

s.gl, Salivary gland.

lg. 1, lg. 15, Legs of first and fifteenth pairs.]

The generative organs vary in structural details in different
centipedes. In the male of _Lithobius_ the testes consist of a single
coiled tube lying above the alimentary canal. The slender vas deferens
which proceeds from its hinder end divides posteriorly into a right
and left branch, embracing the gut and uniting beneath it to form a
common chamber or atrium within the genital orifice. The atrium
receives the secretion of two pairs of large accessory glands; and a
pair of tubes, or vesiculae seminales, open, one on each side, into
the divided sperm ducts close to their point of origin above the
intestine. The organs of the female are very similar. There is a large
median ovary followed by a short oviduct forming a circum-intestinal
collar and a common atrium. Into the latter open a pair of short
receptacula seminis and the slender duct of two pairs of large
accessory glands. There is nothing in the female corresponding to the
supra-intestinal vesiculae seminales of the male. In the male of
_Scolopendra_, on the contrary, there are as many as twelve pairs of
somewhat sausage-shaped testes, approximated two by two. From each
pair proceed two slender ducts which open into a median duct coiled in
the posterior third of the body and much expanded in the last three of
the leg-bearing segments. The right and left portions of the
intestinal ring of the genital duct are unequally developed, and there
are no vesiculae seminales, but two pairs of accessory glands
communicate with the genital atrium as in _Lithobius_. In the female
_Scolopendra_ the right and left portions of the intestinal collar are
also unequally developed, and only a single pair of accessory glands
besides the receptacula semi