490 The A)iiiiial Kingdom 



Class X. Chilopoda. Elongate, many segmented animals with a single pair 

 of legs on most segments, reproductive openings on penultimate segment, head 

 with antennae, jaws, two pairs of maxillae, first pair of body appendages hooklike 

 with poison glands, respiration by tracheae, entirely terrestrial forms. Examples : 

 Gcophilus, Lithobius, centipedes. 



Class XI. Pauropoda. Body consisting of twelve segments which are fused 

 in pairs dorsally, nine segments bear legs, no eyes, three-branched antennae, mouth 

 parts consisting of two pairs of jaws and a lower lip. Terrestrial forms, with 

 reproductive organs opening in the anterior part of the body. Example : Pauropos, 

 a pauropod (Fig. 171,/). 



Class XII. Symphyla. Trunk composed of fifteen segments, eleven or twelve 

 bear legs. Head region similar to that of insects, bears antennae, jaws, two pairs 

 of maxillae, entirely terrestrial forms. Example: Scolopcndrella, Scutigcrella. 

 A few are pests in greenhouses where they get in the soil and feed on roots. 

 (Fig. 171,0, 



Class XIII. Insecta. Body divided into head, thorax, and abdomen, three 

 pairs of legs and often wings present on thorax ; head region bearing eyes, antennae, 

 three pairs of mouth parts, respiration by tracheae, excretion by Malpighian tub- 

 ules, may be either terrestrial or fresh-water dwellers. Example: insects. 



THE CLASS ONYCHOPHORA 



While the few wormlike members of this class are known only 

 from tropical rain forests of Mexico, Central and South America, Asia, 

 Australia, and Africa, they are nevertheless of interest to the zoologist 

 (Fig. 160). This interest is due to these onychophorans' possession of 

 many arthropod characters in a primitive condition. In addition they 

 possess many characters in common with the annelids, further demon- 

 strating the common ancestry of these two diverging phyla. The onyco- 

 phorans thus are important far out of proportion to the small number 

 of species, small size, and lack of economic importance. 



Members of the cosmopolitan genus Peripatns are up to 2 inches 

 in length and may be used to illustrate the general anatomy of the mem- 

 bers of this class. 



Externally the only sign of segmentation of the body is the posses- 

 sion of pairs of unjointed appendages or "legs." These are hollow and 

 conical with a distal foot armed with two paired claws. The caterpillar- 

 like body is enclosed in a thin cuticle of chitin. The head is not dis- 

 tinctly separated from the body and consists of but three segments. One 

 of these segments, the preoral, bears a pair of antennae. The two post- 

 oral segments bear jaws and oral papillae ; annelid-like eyes are situated 

 behind each antenna. The mouth is somewhat elongate and surrounded 

 by ridged lips, each ridge being provided with a row of tubercles. Along 



