Dec, 1916.] Relationships of Apterygotan Insects. 283 



view broader than deep. Eyes, when present, always small and 

 situated on the side of the head, never extending above the antenna; 

 or approximate above. They are composed of relatively few, large, 

 separate ommatidia. Mouthparts of the exposed type. Maxillary 

 palpi usually five-segmented (six-segmented in Thermophila) . Pro- 

 notum usually longer than, or as long as the mesonotum. The 

 thoracic sterna usually in the form of broad plates projecting some- 

 what over the coxse laterally. Coxje usually broad and flattened; 

 those of the meso- and metathorax devoid of styliform appendages. 

 Tarsi usually two-segmented. Abdomen composed of eleven seg- 

 ments, the tergum of the tenth usually partially covering the eleventh. 

 Body usually depressed, or flattened dorso-ventrally, thus differing 

 from the more cylindrical Machilidae, although Ridley describes a 

 specimen of " Lepisma" corticula of which he states that "the chief 

 peculiarity of this Lepisma is its very rounded back, resembling that 

 of a Machilis rather than that of a typical Lepisma." The body is 

 usually scaled, although in such forms as Nicoletia and the Main- 

 droniidae, the scales are absent. Brues and Melander are thus not 

 strictly correct in stating that in the members of this group " the 

 body is always clothed with scales." The number of abdominal 

 ganglia is eight, and there are eight pairs of spiracles in the ab- 

 dominal region. The tracheae anastamose ventrally with those of the 

 opposite side of the body, and those of the same side are connected 

 dorsally by longitudinal trunks. Malpighian tubules six in number. 

 Ovaries with five ovarioles. Heart with nine pairs of ostia. The 

 principal families of this order are the Lepismatidae, Nicoletidae, 

 Maindroniidse, and Gastrotheidse. With regard to the Gastrotheidse, 

 it may be remarked that Silvestri, 19120, has shown that these insects 

 belong to the Lepismid group, and that the supposed springing organ 

 described by Casey is the ovipositor, which is somewhat similar to 

 that of Atelura and related genera. Cook, 1901 (Proc. Ent. Soc. 

 Washington, IV, p. 53) considered it so different from other insects 

 that " he thought it necessary in consequence, to admit at least a new 

 sub-order, which he would call Gastrotheoidea," and Handlirsch, 

 1906, raised it to an order, although he thought this a matter of some 

 doubt. Silvestri, however, has shown that the insect in question is 

 one of the Lepismid group. 



