XIl] 



CHILOPODA 



229 



mounted needles these poison claws we shall see attached to the 

 head the fourth pair of appendages, some- 

 times called the second maxillae, though 

 they resemble legs and have undergone 

 little modification. They are reduced in 

 size and each has a blunt functionless 

 gnathobase. In front of these the third 

 pair of appendages or first maxillae take 

 the form of a lobed plate, being united 

 with one another in the middle line. 

 These cover in their turn the second pair 

 of appendages or mandibles which, like 

 those of Insects and unlike those of 

 Crustacea, consist simply of the blade, 

 there being no palp or feeler. 



The fifteen segments which succeed 

 the one carrying the poison claws each 

 bear a pair of seven-jointed running legs 

 ending in a pair of claws. 



Near the base of some of the legs not 

 of all in the soft skin unit- 

 structure! i n & ^ ne narc ^ dorsal an d ventral 

 plates of chitin, is an oral 

 opening. This leads into a chamber from 

 which the tracheae pass off. These tubes 

 divide and subdivide into smaller tubes, 

 which run all over the body and traverse 

 all the tissues, entering even the smallest 

 cell. They are lined with a cuticle of 

 chitin and are kept from collapsing by 

 the presence of a fine spiral thickening of 

 this cuticle which gives them a very characteristic appearance when 

 seen through a microscope. They are full of air and constitute the 

 respiratory apparatus of the Centipedes. 



The existence of such a breathing apparatus, which is confined 

 to Peripatus, the Myriapods, the Insects and certain of the 

 Arachnids, is associated with certain striking features in the in- 

 ternal anatomy of the body. In most animals the oxygen of the 

 air is taken up by the blood and carbon dioxide is given out at 

 certain fixed points called gills or lungs, and the vascular system is 

 arranged so as to drive the blood through these specialised respiratory 



FIG. 94. A Centipede, Li- 

 thobius forjicatus. Dorsal 

 aspect x 12. 



1. Antennae. 2. Poison 

 claws (5th pair of append- 

 ages). 4. First pair of 

 walking legs. 



