lated at an early stage
of embryonic growth. Furthermore, behind the legs of the last pair two
pairs of appendages are present. The second of these persists as the
gonopods of the adult, but the first is suppressed. Possibly, however,
it is represented in the male of _Scutigera_ by the anterior branches
of the gonopods. The cerebral or cephalic portion of the nervous
system consists of a quadrilobate mass. From the two upper lobes,
which are set transversely, arise the ocular nerves; from the two
lower lobes, which are united by a transverse commissure, spring the
antennal nerves in front and the chords which form the oesophageal
collar behind. These chords unite below the oesophagus to form the
compound suboesophageal ganglion, whence the nerves for the four pairs
of jaws arise. The ventral system consists of a double chord uniting
in each of the leg-bearing segments in a ganglionic swelling which
gives off four pairs of nerves to the limbs and tissues of the somite.
There is a single ganglion in the genital segment.

[Illustration: Modified from Heymons, _Bib. Zool._, 1901, by
permission of E. Nagele.

FIG. 1.

A, Diagram of anterior extremity of an early embryo of
_Scolopendra_, ventral view; cl, clypeus; lb, labrum; m, mouth; p.a,
preantennal appendage; a, antenna; int, premandibular rudiment; mdl,
mandible; mx, maxilla; p.g, palpognath; t.g, toxicognath; lg. 1,
first pair of walking legs.

B, Posterior end of a later embryo of _Scolopendra_, ventral view,
showing the anal segment or telson (t); the legs of the last pair in
the adult (lg. 21) and the two rudimentary pairs of legs (lg. 22,
lg. 23).]

Eyes are frequently absent. When present they may be either simple or
compound, i.e. consisting externally of a single lens (monomeniscous)
of or an aggregation of lenses (polymeniscous). Simple eyes vary in
number on each side of the head from one, as in _Henicops_, to many as
forty, as in some species of _Lithobius_. In _Scolopendra_, where
there are four, the corneal lens is a biconvex thickening of the
cuticle. The soft or retinal portion of the eye beneath the lens
consists of an aggregation of large cells forming a single layer
continuous with the epidermic cells of the circumocular area. Thus the
eye is monostichous. The arrangement of the cells, however, is
peculiar. They are invaginated to form what may be descr