THYSANURA. 



659 



Fam. 1. Campodeidae. Delicate, white insects with long cerci ; 

 blind ; mouth-parts concealed ; abdominal appendages on the second to 

 the seventh segments. Authorities differ as to whether there is more 

 than one genus Campodea and as to whether that genus contains more 

 than one species C. staphylinus (Fig. 412). This is a widely distributed 

 insect, not uncommon in Britain ; it well withstands heat and cold but 

 variations in humidity seem to affect it and it soon dies in captivity. It 

 is so delicate that it breaks at the slightest touch. Many of the features 

 of this insect are archaic in character. The thorax has three pairs of 

 stigmata, each leading into a separate system of tracheae, which systems 

 do not communicate with each other or their neighbours. There are 

 sixteen very short malpighian tubules. The appendages of the third true 

 segment, the intercalary, are said to persist as tubercles in the adult. The 

 ovaries and testes are two simple tubes one each side of the body. 



Fam. 2. Japygidae. The abdomen bears a 

 pair of forceps instead of long multi-segmented 

 cerci ; abdominal appendages on first to seventh 

 segment (Fig. 369^4) ; mouth parts concealed. 

 The single genus Japyx with several species is 

 widely distributed in the warmer parts of the 

 globe. There are four thoracic and seven ab- 

 dominal pairs of stigmata and the tracheal system 

 of one segment opens into that of the others. 

 No malpighian tubules. The female generative 

 organs are metamerically repeated, the ovaries 

 uniting into a common oviduct on each side. 

 The testes however have lost this segmental 

 arrangement. Only one pair of abdominal 

 vesicles have been described. Japyx is usually 

 found in shady places on the edge of woods, 

 etc., but it does not occur so far north as 

 Britain. 



Fam. 3. Machilidae. The tergites arch over 

 and overlap the ventral sternites in the abdomen 

 much as in Astacus ; compound eyes are present ; 

 the female has an ovipositor and the tenth ab- 

 dominal segment bears a long median structure 

 resembling the cerci and projecting between them. 

 There is again but one genus Machilis with two pair of thoracic and seven 

 pair of abdominal stigmata, which open into nine isolated tracheal systems . 

 There are twenty long malpighian tubules and also diverticula which 

 open anteriorly into the stomach. The seven ovarian tubules on each 

 side are not very definitely segmental. The abdominal appendages are 

 found on segments two to nine inclusive. The body bears numerous 

 scales very easily displaced. Machilis is cosmopolitan in distribution. 

 M. maritima is common, running about the rocks on the south ofJSngland, 

 and M. polypoda lurks under leaves in the New Forest and elsewhere. 



Fam. 4. Lepismidae. The thorax well marked off from the abdomen ; 

 tracheal systems all intercommunicate ; the tergites do not overlap the 

 sternites ; abdominal appendages on eighth and ninth segments only ; 

 a median " tail " as in Machilis between, and as long as, the cerci. The 

 Lepismidae have ten pair of stigmata and the tracheae communicate one 

 with another. The number of malpighian tubules is small. There are 



Fm. llS.Lepisma sac- 

 charina 



