458 



ARTHROPODA. 



connect dorsal to the anus and are connected in the trunk by 

 numerous non -segmental commissures. 



The description may be completed by saying tliat the straight aliment- 

 ary canal (p and d) bears only salivary glands (sp) ; that it is accompanied 

 throughout by a dorsal heart ; that the gonads (the sexes are separate) 

 open just in front of the anus (go), their ducts being modified nephridia. 

 The animals are viviparous, live in decaying wood, hide by day and hunt 

 their prey at night. The several species have a wide but discontinuous 

 distribution (South America, Cape of Good Hope, New Zealand, etc.), an 

 indication of great antiquity. Recently the forms have been divided into 

 several genera, Peripatus, Feripatopsis, Opdsthopatus, etc. 



Class IV. Insecta. 



The Insecta is a distinct group marlted off from all other 

 arthropods by several important characters. 

 The appendages show no signs of a schizo- 

 podal condition. The head is always a 

 distinct region, bearing a single jiair of 

 antennae, a pair of mandibles, and two j^airs 

 of maxillas, the jjosterior pair often being 

 fused into a lower lip or labium. 



The respiratory organs are tracliew (figs. 

 479, 480), which resemble the trachea of 



Fia. 479. 



Fig. 480. 



Flo. 470.— Tracheal system of Marhili.'i. (From Lai\tr, after Oudemans.) ?;. head; 



I-III, tliiiracic somites: .s-, spiracles: j-Ui^ aiidominal somites. 

 Fia. 4H0.— Portion of trachea of catoi'pillar. (From (Tc^oTiha.ur.) A, main trunk; 



U, C, />, l)ranchcs; a, epithelium witli nuclei, h; ti, air in tracheal tube. 



