lyo The Orders of Insects 



Sub-Order B. Ectotrophi. 



This sub-order includes two families of Bristle-tails, 

 with scaled bodies, and with jaws not withdrawn into 

 the head, but articulated somewhat as in the cock- 

 roach, the maxillae bearing prominent palps. 



Machilidae. — The MachUida are another family with only a 

 single genus (Tkfai:^///^). These insects have compound eyes largely 

 developed, meeting in the central line of the head ; in front of each 

 compound eye is a peculiar elongate simple eye. In the hind-body 

 the tergites overlap the sternites at either side, and limbs are pre- 

 sent on all the segments from the second to the ninth inclusive. 

 There is a prominent ovipositor in the female, while the long 

 paired cercopods are exceeded in length by a similar median 

 appendage borne on the tenth abdominal segment. There are 

 nine pairs of air-openings ; the tubes arising from these do not 

 unite with each other. The Machilida; are world-wide in their 

 distribution. 



Lepismidae. — The Lepismida: are the only family of Thysanura 

 containing several genera. The eyes are less developed than in the 

 Machilids, but the thoracic segments are larger than, and maritedly 

 distinct from, the abdominal ; while the air-tubes, arising from ten 

 pairs of stigmata, are united into one system by longitudinal and 

 transverse connections, as in higher insects. The tergites of the 

 hind-body do not overlap the sternites, and abdominal limbs are 

 present only on the eighth and ninth segments. A many-jointed 

 median tail-appendage is present as in Machilis, its length usually 

 equalling tiiat of the paired cercopods. The family has a most 

 extensive geographical range. Lepisma sacchar'ina (fig. 92), the 

 " silver-fisii insect," is a well-known inhabitant of houses. 



ORDER 3.— DERMAPTERA. 



Structure. — The Earwigs are often included in 

 the next order (Orthoptera) with which they agree in 

 the structure of their jaws. They differ markedly, 

 however, in their wings. Of these the front pair are 

 modified into firm oblong plates serving as covers for 

 the hind pair when at rest. The hind-wing of an 

 earwig consists of an ovoid basal piece of firm texture, 

 whence radiate numerous nervures supporting the 

 spreading delicate membrane of the wing. This 



