Thysanura 169 



these limbs are protrusible vesicles, which probably 

 assist in breathing (3, 98, lOI, 102, 206). 



Habits. — These insects usually occur under stones 

 or in damp earth ; in their manner of life they re- 

 semble the Springtails, but as a rule they are more 

 active and lively. Several species are found in human 

 dwellings, and one is especially partial to bakers' 

 ovens. The sea-shore and the depths of caves are 

 alike inhabited by insects of this order. 



The Thysanura may be divided into two sub- 

 orders. 



Sub-Order A. Entotrophi. 



In this sub-order are included two families of 

 Bristle-tails whose jaws (like those of the Collembola) 

 through a deep inpushing at the mouth (213) seem 

 sunk in the head, and whose bodies are not scaled. 



Campodeidae. — The Campodeidce contain only two genera of 

 small, delicate, white, blind springtails readily distinguished by 

 their long many-jointed feelers and cercopods. There are three 

 pairs of air-openings on the thorax, the tubular system from each 

 remaining distinct. The small abdominal limbs are present on all 

 the segments from the second to the seventh. A remarkable 

 structural feature is the persistence of the tritocerebral appendages 

 (see p. 93) as paired tubercles in the adult (103)- The ovaries in 

 the female are very primitive, consisting of paired, simple tubes, 

 one along either side of the body (lOI, 102). These fragile insects 

 have an exceedingly wide geographical range, occurring both in 

 temperate and tropical countries, at the summit of snow-clad 

 mountains and in the depths of caves (see fig. 65). 



lapygidae. — The lapygidie are a family comprising only one 

 genus (^Lipyx^. These insects are peculiar among the Thysanura, 

 in the modification of their tail-appendages into forceps — like those 

 of earwigs — instead of into cercopods. The small abdominal limbs 

 present on each segment from the first to the seventh are less de- 

 veloped than in Campodea. There are eleven pairs of stigmata, 

 and the air-tubes on either side of the body form a connected 

 system. The species of lapyx are unknown in our islands, 

 being characteristic of the tropical and warmer temperate 

 regions. 



