400 



ARTHROPODA 



The description may be completed by saying that the straight alimentary 

 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 vivipar- 

 ous, 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, Peripatns, Peripatopsis, 

 Opisthopatus, etc. 



Fir,. 436. Anatomy of female Peripatus opened dorsally (from figures of Moseley 

 and Balfour). a, anus; at, antenna;; bm, ventral nerve cords; d, digestive tract; go, 

 genital opening; o, ovary; og, brain; p, pharynx; sd, slime gland; so, nephridia; sp, 

 salivary gland; tr, tracheae; u, uterus. 



Class IV. Insecta. 



The Insecta is a distinct group marked off from all other arthropods 

 by several important characters. The appendages show no signs of a 

 schizopodal condition. The head is always a distinct region, bearing a 

 single pair of antennae, a pair of mandibles, and two pairs of maxillae, the 

 posterior pair often being fused into a lower lip or labium. 



