LEPISMA. 219 



of each thoracic segment is a sort of flap, beauti- 

 fully covered with scales. That of the prothorax is 

 very large ; the other two are smaller, particularly the 

 one belonging to the metathorax. 



The abdominal appendages are confined to the two 

 posterior segments. They are represented, however, 

 on the anterior ones by a groujD of stiff yellow set^e. 

 There is moreover a second, similar group nearer to 

 the median line, which appears to represent a second 

 process, formed by a prolongation of the ventral margin 

 of the penultimate segment. 



Gervais^ considers that these appendages should be 

 compared to the branchial appendages in Neuroptera 

 rather than to true legs ; he observes, " Cette maniere 

 de voir, que nous avons proposee pen de temps apres, 

 rend egalement compte de I'absence de tracbees deja 

 constatee par plusieurs observateurs chez les veritables 

 Thysanoures, c'est a dire, chez lafamille des Lepismes." 

 The branchial appendages of Neuroptera, however, are 

 dorsal, while those of the Lepismida3 are ventral ; 

 moreover, in opposition to the above assertion, the 

 Lepismidce undoubtedly have tracheae, although the 

 system is not very largely developed. It seems 

 to me curious that there should be any difference of 

 opinion on this point, because, from the transparency 

 of the creature, the tracheae in the legs are visible 

 without dissection. It is true that Treviranus" was 

 unable to satisfy himself as to the presence of tracheae ; 

 but I can only -account for this on the hypothesis that 

 he did not examine freshly killed specimens. 



The egg-tubes and the formation of the ovum 

 resemble those of Machilis, as already described.^ 



The posterior abdominal dorsal plate has a squarish 

 termination. 



Common throughout the greater part of Europe. 



This is the only species which as yet has been found 

 in Great Britain. 



' ' Yermisclite Scliriften,' vol. i, p. 16. 



^ Suites a Buflfon. ' Insectes Apteres,' vol. iii, p. 446. 



5 Ante, p. 209. 



