258 Hominoxious Arthropods 



ARACHNIDA 



In this class the antennae are apparently wanting, wings are never 

 present, and the adults are usually provided with four pairs of legs. 

 Scorpions, harvest-men, spiders, mites, etc. 



HEXAPODA (Insects) 



True insects have a single pair of antennae, which is rarely vestigial, 

 and usually one or two pairs of wings in the adult stage. Familiar 

 examples are cockroaches, crickets, grasshoppers, bugs, dragonflies, 

 butterflies, moths, mosquitoes, flies, beetles, ants, bees and wasps. 



ORDERS OF THE ARACHNIDA 



a. Abdomen distinctly segmented. A group of orders including scorpions, 

 (fig. n), whip-scorpions (fig. 10), pseudo-scorpions, solpugids (fig. 12) 



harvest-men (daddy-long-legs or harvestmen), etc ARTHROGASTRA 



aa. Abdomen unsegmented, though sometimes with numerous annulations 



SPKEROGASTRA 



b. A constriction between cephalothorax and abdomen (fig. 7). True Spiders 



ARANEIDA 



bb. No deep constriction between these parts. 



c. Legs usually well developed, body more or less depressed (fig. 49). Mites 



ACARINA 



cc. Legs stumpy or absent, body more or less elongate or vermiform, or if 



shorter, the species is aquatic or semi-aquatic in habit, 

 d. Four pairs of short legs; species inhabiting moss or water. Water- 

 bears TARDIGRADA 



dd. Two pairs of clasping organs near the mouth, instead of legs, in the 

 adult; worm-like creatures parasitic within the nasal passages, 

 lungs, etc. of mammals and reptiles (fig. 148). Tongue worms. 



. .LlNGUATULINA 



148. Linguatula, (a) larva; (enlarged). (b) adult; (natural size). 



