TRACHEATA 317 
chambers ; these facts, together with others derived from em- 
bryology, show that each tergum corresponds with two primitive 
somites. The legs have five joints and a terminal claw. 
Segments and Appendages of Julus. 
1. Antennae. 5. One pair of legs. 
2. Mandibles. ‘ : 6. This segment bears no legs. 
3. Maxillae, fused across ae Cra 7. One pair of legs. 
middle line. 8. The succeeding segments bear two 
4, Leg-like appendages, modified in male. pairs of legs. 
The cephalic appendages comprise a pair of antennae, a pair 
of mandibles with broad crushing surfaces, and a pair of 
maxillae which have fused across the middle line and which 
form a bilobed plate. The appendages are borne on the head ; 
the first post-cephalic segment has a broad tergum, and bears 
ventrally a pair of leg-like appendages, which are turned 
forward, and probably assist in the act of feeding; the same 
appendage is in some species modified in the male, and forms 
a blunt hook-like process. The second post-cephalic segment 
bears a normal pair of legs, the third has none, and the 
fourth one pair, the succeeding segments have two. The 
generative orifice in both sexes is on the third segmerit, just 
behind the bases of the second pair of legs. In the male 
the seventh post-oral segment bears only one pair of legs 
and a complex copulatory apparatus not connected with the 
internal organs. This apparatus is of great systematic value. 
The female Julus, like that of Geophilus, watches over its 
eggs. 
Some genera of the Polyzonidae, e.g. Siphonophora (Fig. 
182), have the anterior part of the head and the mouth- 
parts prolonged into a sucking or piercing snout. Most of 
the Diplopoda possess a series of glands which open to the 
exterior by a row of lateral foramina repugnatoria, one on 
each segment; these emit an offensive fluid; in one species, 
Fontaria, this fluid breaks up into prussic acid and _ benzal- 
dehyde (oil of bitter almonds). 
Except in Glomeris, where the tracheae are branched as 
in the Chilopods, the respiratory organs resemble those of 
Peripatus. The stigma opens into a tracheal sac, from which 
a number of short unbranched tracheae arise. There are four 
of these on each segment. The GLOMERIDAE have shortened, 
