1 68 



The Orders of Insects 



are greatly elongated and many-jointed, so that they can be spirally 

 coiled. A well-developed spring is borne on the fifth abdominal 

 segment (in a few species only, on the fourth). Cyplwdcrus (fig. 

 91 16), Tomocerus and Isotoma are typical genera. 



Poduridae. — The PoJm-idie are distinguished from the Entomo- 

 bryidx by the forwardly directed head and the spring when present, 

 being borne on the fourth abdominal segment instead of on the 

 fifth. But in various genera of the family this organ can be traced 

 through all stages of degeneration until it vanishes altogether. 

 The ventral tube is reduced to a small tubercle, and the body is 

 never scaled. Typical genera are Podura, Achorutes, Lipura (fig- 

 91 ^, //, /') and Anur'ida. 



ORDER 2.— THYSANURA. 



Structure. — The Bristle-tails are wingless in- 

 / sects, of small or moder- 



^>- -^"^ ate size, with long, many- 



jointed feelers ; in some 

 cases with compound 

 eyes. The prothorax is 

 often the largest seg- 

 ment of the body, and 

 the legs are provided 

 with tarsal segments. 

 The hind-body consists 

 of ten evident segments, 

 whereof the tenth bears 

 a prominent pair of 

 appendages — usually 

 many-jointed cercopods 

 (fig. 92). The most 

 characteristic structural 

 feature of the family is 

 the presence of small 

 paired limbs on several 

 of the abdominal seg- 

 ments; these are situated 



near the hind margins of the sternites. Associated with 



F1G.92. — Spring-tail ( Lepisma saccharine, 

 Linn.) Europe. Magnified 4 times. 

 From Marlatt, Bull. 4 (n.s.) Div. Ent. 

 U.S. Dept. Agr. 



