204 CxENERAL ORGANIZATION. 



wliicli near their apices each carry two long subuliform 

 setae. 



The three thoracic segments are distinct, and bear 

 each a pair of legs. In some cases, as in Nicoletia, the 

 three segments are similar in form and not very different 

 in size ; in Caw.podea, on the contrary, the prothorax 

 is much smaller than the other two, and the mesothorax 

 is the largest of the three. In Lepisma the thoracic 

 segments are wide and depressed ; the prothorax is 

 excavated for the reception of the head, the metathorax 

 for that of the first abdominal segment. In Machilis 

 the prothorax is compressed and tubular; the meso- 

 thorax is, on the contrary, large, raised, and, as it were, 

 arched. In Lepismina the thorax, and especially the 

 prothorax, is very much enlarged, so that the body 

 becomes almost heart-shaped. 



The leo-s are of moderate leno^th and are clothed with 

 hairs, as also, in certain species, with scales. They 

 are not saltatorial, and the three pairs do not differ 

 much in length, though the posterior pair is generally 

 somewhat the largest of the three. In Machilis and 

 Lepisma the tarsi are biunguiculate ; the claws are horny 

 and terminal, as in true insects. In lapyx ^ (PI. LXV, 

 fig. 12) the claws " are large, foliaceous, but of unequal 

 length. The empodium is well developed and supported 

 by a thin, curved, chitinous piece ; between the claws 

 there is a small cultelliform onychium, which might be 

 described as a third claw, if such a thing was at all 

 possible or reconcilable with the symmetry of the insect 

 body." 



In Machilis the four posterior legs bear on the basal 

 segment a short cylindrical appendage, covered with 

 stiff hairs, and very closely resembling those of the ab- 

 dominal segments. 



The abdomen is cylindrical, with ten nearly equally 

 wide segments, in lapyx, Nicoletia, and Gampodea ; 

 tapering, on the contrary, gradually in Lepisma and 

 Machilis, and rapidly in Lepismina. 



1 Meinert, ' Ann. & Mag. of Nat. Hist.,' 1867, p. 370. 



