THE ANIMAL KINGDOM 



423 



fever. Trombicula irritans, chigger; Macrobiotics hufelandi, 

 a water bear, .7 mm. in length. 



CLASS III. ONYCHOPHORA. The head bears a pair of sim- 

 ple eyes, a pair of segmented antennae, and a mouth with a pair 

 of hooked jaws. The wormlike trunk is unsegmented and 

 provided with numerous annulated legs (14 to 43 pairs). The 

 body cavity is hemocoel through 

 which the alimentary canal passes 

 as a straight tube. A tracheal 

 respiratory system and a nephrid- 

 ial excretory system are present. 

 There is an opening of a nephrid- 

 ium at the base of each leg. The 

 sexes are separate. In viviparous 

 forms the egg is poor in yolk and 

 is totally divided in cleavage. 

 The embryo in such cases is nour- 

 ished by the walls of the uterus, 

 forming a very primitive sort of 

 placenta. The animals are ter- 

 restrial and feed on insects and 

 other small forms. From the 

 point of view of evolution, they 

 are important as a connecting 

 link between annelids and 

 arthropods (Fig. 246). 



Example: Peripatus eiseni, a 

 viviparous species; habitat, cen- 

 tral South America. 



CLASS IV. MYRIAPODA. The 

 head bears a pair of segmented 

 antennae, 



Fig. 246. — A, ventral view of the 

 head of Peripatus capensis, showing 

 the mouth surrounded by lips 

 raised into large white papillae. 

 B, dorsal view of entire animal. 

 a, antenna, p, oral papilla at the 

 base of which a gland ejects a 

 a pair of mandibles, sticky slime used in capturing food. 

 r .,, (After Leuckart-Nitsche wall chart.) 



and one or two pairs of maxillae. 



The trunk is segmented (11 to 173 segments) and each segment 

 has one or two pairs of legs with claws. The sexes are separate 

 and all are oviparous. Development is direct. There are four 

 orders, of which the Diplopoda (millipedes) and Chilopoda 

 (centipedes) are the more important. 

 Order 1. Diplopoda. A cylindrical body with usually two pairs 

 of legs to a segment. A single pair of maxillae. An anterior 

 genital pore. 



