RELATIONS OF INSECTS TO OTHER ARTHROPODA 15 



there are no pleural pieces or " pleurites," so characteristic of winged 

 insects. 



Perhaps the most fundamental difference between diplopods and 

 insects is the fact that the paired genital openings of the former are 

 situated not far behind the head between the second and third pair 

 of legs. Both the oviducts and male ejaculatory ducts are paired, 

 with separate openings. The genital glands lie beneath, while in 

 chilopods they lie above the intestine; this, as Korschelt and Heider 

 state, being a more primitive relation, since in Peripatus they also 

 lie above the digestive canal. 



The nervous system of diplopods is not only remarkable for the 

 lack of the tendency towards a fusion of the ganglia observable in 

 insects, but for the fact that the double segments are each provided 

 with two ganglia. The brain also is very small in proportion to 

 the ventral cord, the nervous system being in its general appearance 

 somewhat as in caterpillars. 



The arrangement of the tracheae and stigmata is much as in insects, 

 but in the Diplopoda the tracheary system is more primitive than in 

 chilopods, a pair of stigmata and a pair of tracheal bundles occurring 

 in each segment, while the bundles are not connected by anastomos- 

 ing branches, branched tracheae only occurring in the Glomeridse. 

 The tracheae themselves are without spiral threads (tsenidia). It 

 is noteworthy that the tracheae arise much later than in insects, not 

 appearing until the animal is hatched; in this respect the myriopods 

 approximate Peripatus. 



In the Chilopoda also the parts of the head, except the epicranium, 

 are not homologous with those of insects, neither are the mouth - 

 parts, of which there are five pairs. 



The structure of the head of centipedes is shown in part in Fig. 

 12, compare also Fig. 8. It will be seen that it differs much from 

 that of the diplopods, though the mandibles (protomalse) are homolo- 

 gous; they are divided into a cardo and stipes, thus being at least 

 two-jointed. 



The second pair of postoral appendages is in centipedes very differ- 

 ent from the gnathochilarium of diplopods. As seen in Fig. 12 2, 

 they are separate, cylindrical, fleshy, five-jointed appendages, the 

 maxillary appendages of Newport, which are "connected trans- 

 versely at their base with a pair of soft appendages " (c), the lingua 

 of Newport. The third and fourth pair are foot-jaws, and we have 

 called them malipedes, as they have of course no homology with the 

 maxillipedes of Crustacea. The second pair of these malipedes, 

 forming the last pair of mouth-appendages, is the poison-fangs (4), 



