ORDER THYSANURA. 57 



etc., though the bristle-tails prefer warm and dry situations, 

 and either, as in the Cinura, run swiftly, or, as in the 

 Poduridae, vigorously leap by means of a long appendage at 

 the end of the body, which on being released throws 

 the insect high in the air. The higher members of the 

 order, as Carnpodea and Scolopendrella, are connecting 

 links between the true insects and the centipedes (Myrio- 

 poda). In many Podurids the tracheae are wanting. 



Sub-order 1. Collembola. The spring-tails are degraded 

 forms, with the mouth-parts quite rudimentary, and re- 

 tracted within the head, only the ends projecting. What 

 correspond to the anal stylets of Campodea and Lepisma 

 are in the Podurids united at the base and bent under the 

 hind body to form the spring, which is held in place by a 

 hook or tenaculum ; on the under side of the hind body is 

 a sort of sucker (colloplwre) , and as no other insects pos- 

 sess this singular apparatus, the group is named from it 

 Collembola, which means to throw out a sucker, so as to 

 adhere to surfaces. Their bodies are covered with scales. 



These spring-tails occur everywhere under leaves, the 

 bark of trees, etc., and rarely live except in moist or shaded 

 places, where their eggs are deposited. The snow-flea 

 (Achorutes nivicola) is sometimes seen in 

 great numbers leaping on snow. They 

 should be preserved in vials of alcohol, and 

 can be collected by placing an ether vial over 

 them and allowing the creatures to spring 

 into it, or the finger wet with the saliva can 

 be lightly laid on them, when they can be 

 transferred to a vial of alcohol. They can 

 also be mounted in balsam on glass slides. 



Family Poduridae. Body long and slender, Lead small, Tomocerus 

 plumbeus (Linn.); or body short, Smynthurus elegans Fitch. 



Sub-order 2. Symphyla. A remarkably composite type, 

 having the head of a Campodea, while the abdomen has 

 a pair of legs to each joint, like the centipedes. 



Family Scolopendrellidae, with the characters of the sub-order. 

 Scolopendrella, immaculate Newport. 



