THYSANURA 



221 



Fig. 222. — Japyx sol 

 ifiigus. (After Lub 

 bock.) 



(Machilis), the eyes are very perfect; for this reason, they are used 

 in Chapter III to illustrate the structure of the compound eyes of 

 insects. In all other Apterygota they are more or less degenerate or are 

 lost entirely. In the Lepismatidas (Lepisma), the degeneration of the 

 eyes has progressed far, they being reduced to a group of a dozen 

 ommatidia, on each side of the head. In the 

 Campodeids and the Japygidas, the eyes have 

 disappeared. The mouth-parts are formed for 

 chewing ; those of Machilis will serve to illustrate 

 their form. The mandibles are elongate with a 

 toothed apex and a sub-apical projection teimi- 

 nated by a grinding surface (Fig. 223, A); the 

 paragnatha are comparatively well developed 

 (Fig. 224); on the outer edge of each there is a 

 small lobe, which Carpenter ('03), who regarded 

 the organs as true appendages, believed to be a 

 vestigial palpus, and at the tip there are two dis- 

 tinct lobes, which this author homologized with 

 the galea and the lacinia of a typical maxilla ; the 

 maxillae (Fig. 223, B) bear prominent palpi. 



In the Campodeidee and the Japygidse, the 

 jaws are apparently sunk in the head. This con- 

 dition is due to their being overgrown by folds of the genas. In the 

 Machilidfe and the Lepismatidas the jaws are not overgrown; these 

 two families are known, 

 on this account, as the 

 Ectotrophi or Ectotro- 

 phous Thysanura; while 

 the Campodeidse and the 

 Japygidae are grouped 

 together as the Ento- 

 trophi or Entotrophous 

 Thysanura. The over- 

 growing of the mouth- 

 parts by folds of the 

 gense is characteristic of 

 the Collembola also and 

 is discussed more fully in 

 the next chapter. 



The three thoracic 

 segments are distinctly 

 separate. There is noth- 

 ing in the structure of 

 the thorax to indicate 

 that these insects have 

 descended from winged 



ancestors. The three pairs of legs are well developed. In the genus 

 Machilis the coxae of the second and third pairs of legs each bears a 

 stylus (Fig. 221, .s). 



Fig. 223. — A, mandibles of Machilis; B, maxilla 

 of Machilis. (After Oudemans.) 



