658 



CLASS IV. INSECTA. 



consists of ten visible segments and the last bears a pair of many 

 segmented cerci which superficially resemble antennae. Certain 

 of the abdominal segments bear on the hinder edge of their sterna 

 i small appendages ar- 



ticulated with the ven- 

 tral surface. They 

 consist of a single seg- 

 ment provided with 

 muscles. By many 

 authorities these ap- 

 pendages are regarded 

 as homologous with 

 the legs, but it must 

 not be forgotten that 

 both legs and processes 

 exactly similar to those 

 borne by the abdomen 

 co-exist on the meso- 

 and meta-thorax of 

 Machilis. Close to the 

 insertion of some of 

 these processes are one 

 or two retractile 

 vesicles which can be 

 protruded by the in- 

 trusion of blood or re- 

 tracted into the body 

 by muscular action. 

 They appear to function as accessory respiratory organs. What 

 are regarded as a fourth pair of jaws (maxillulae) are present 

 as in Collembola. In Japyx * they are described as being 

 very primitive and divisible into galea, lacinia and a three- 

 jointed palp (Fig. 372). 



There are four families, in two of which the mouth is pushed 

 into the head carrying the mouth-parts with it. These two 

 families, the Campodeidae and the Japygidae, are sometimes 

 classed together as the Entotrophi, and the remaining families, 

 the Machilidae and the Lepismidae, in which the mouth parts are 

 prominent are grouped as Ectotrophi. 



* Hansen, loc. tit. 



FlQ. 412. a Campodea staphylinus (after J. Lubbock). 

 b anterior half of the body of G. fragilis (after Pal- 

 m6n) ; Tr trachea ; S stigmata ; P legs ; P' rudi- 

 mentary abdominal feet ; A antennae. 



