394 SYNOPTIC COLLECTION. 



the skull by an imperfect articulation and not buried 

 within the cavity of the skull as in Campodea. They 

 consist of a pair of mandibles (PI. 951, fig. i) and two 

 pairs of maxillae (figs. 2, 3) ; the two parts of the second 

 pair are united to form the labium (fig. 3). At the tip of 

 the labial palpi are three sense organs. 



The legs are similar in structure and are flattened, espe- 

 cially the large basal sections, which enables this little ani- 

 mal to glide in and out of crevices. Each leg ends in a 

 pair of claws. The forward abdominal appendages of 

 Campodea are replaced in Lepisma by clusters of stiff 

 hairs, but the seventh, eighth, and ninth segments have 

 abdominal appendages (PI. 951, fig. 4), and the extremity 

 of the abdomen is provided with three long hairy bristles 

 'and a pair of short curved bristles ; hence the name of 

 Thysanura or bristle-tails. In the female there is an ovi- 

 positor (fig. 4) composed of four parts. 



The tracheal system of Lepisma consists of ten pairs 

 of spiracles, and the tracheae are united into one system 

 consisting of two longitudinal trunks and of cross tubes. 1 

 The tracheae are strengthened by delicate spiral threads 

 (Fernald). 



It has been shown that Lepisma is more specialized 

 than Campodea in having a scale-protected body, exter- 

 nal mouth parts, a well developed ovipositor, and a com- 

 plete tracheal system. 



Campodea and Lepisma are representative Thysanuran 

 insects, having the abdominal bristles which give them 

 the name of bristle-tails. In this same order is the sub- 

 order Collembola represented by the Poduridae or spring- 

 tails, some of which have at the posterior end of the 

 abdomen a peculiar spring for leaping. This is seen bent 

 under "the body in PI. 952, which is a side view of Pap- 

 irius fuscus Lubbock. In this genus the leaping organ 

 extends far forward and the tips are white. Besides the 



1 Sharp, Cambridge Nat. Hist., V, 1895, p. 186. 



