1916. Carpenter— -Centipedes and Millipedes. 165 
antenniferous head, distinct from the body, mandibles 
with a conical basal process, two pairs (at most) of 
maxillae, a lower lip, and seven or more pairs of legs. 
To this class he referred not only centipedes and milli- 
pedes, but also the Isopoda— now universally regarded 
as a crustacean order. In most zoological systems the 
" class Myriapoda " has been restricted to Latreille's 
" genera " lulus and Scolopendra, that is to say, the 
millipedes and centipedes — those air-breathing (tracheate) 
arthropods that bear a considerable number of pairs of 
generally similar legs on the body-segments which are not 
differentiated into thoracic and abdominal regions as is 
the case in Insecta, Crustacea, and Arachnida. The 
superficial resemblances between milHpedes and centi- 
pedes — the single pair of feelers on the distinct head, the 
elongate worm-like body with its usually large number 
of segments and similar paired Hmbs — made this association 
easy of acceptance 
Now Pocock, in the paper mentioned above, points out 
that — despite the superficial likeness — centipedes differ 
widely from milHpedes in a very important structural 
feature — the position of the reproductive apertures, which 
in centipedes are situated on the hindmost segment but 
one, and in millipedes only a short way behind the head — 
on the third segment of the body. In this character, 
therefore, centipedes resemble insects, while milHpedes are 
like crustaceans and arachnids. Pocock lays so much 
stress on this character that he proposes a fundamental 
division of the Arthopoda into two great series : (i) the 
Progoneata, including Crustacea, Arachnida and Diplopoda 
(mihipedes), and (2) the Opisthogoneata, including Chilopoda 
(centipedes) and Insecta. Pocock included the Symphyla 
(Scolopendrella, etc.) in the latter group under the erroneous 
belief that in these animals the reproductive apertures are 
far back, whereas they are — as in millipedes — far forward, 
on the third segment of the body. 
Besides the position of the reproductive openings there 
are several other important structural distinctions which 
forbid us to include millipedes and centipedes in a single 
class. Centipedes have segments with extensive sterna 
so that the legs are attached laterally to the body which 
is flattened dorso- vent rally. In millipedes the sternal 
