154 Prof, J. Wood-Masou's Morphological Notes 



two parts, a long and broad distal one — the true coxa — 

 and a short proximal one, divided by an evident suture 

 into two. It is clear that these answer to the distal of 

 the two sclerites which are interposed between the 

 coxa and the sternum in Blatta, and which, in my 

 opinion, are both basal joints of the leg. In Machilis, 

 owing to the softness and delicacy of the integument at 

 the setting-on of the legs, and to the presence of the 

 long pleural prolongations of the thoracic terga, a third 

 sclerite, answering to the basal one in Blatta, is difficult 

 of demonstration ; but in Lepisma, a leg, when torn from 

 its attachment, carries away with it three short joints, the 

 basal one of which, as it lies in situ, is overlapped by the 

 triangular part of the sternum. Some of the least modi- 

 fied of Blatticl(B have preserved almost perfectly the con- 

 dition of things seen in Lepisma ; but in the more 

 modified forms, such as Panesihia, the basal sclerite of 

 the legs is, as often happens in arthropods, immovably 

 articulated, though not confounded, Avith the sides of the 

 sternum, while the two distal sclerites are ankylosed together 

 and show a tendency to become united to the coxa ; the 

 consequence is, that the leg bends at its base, not between 

 the sternum and its true basal joint, but between this 

 latter and the following joint. The appendage, then, in 

 Machilis is articulated to the outside of the limb at the 

 junction of the three-jointed basal with the five-jointed 

 apical portion ; it has, in fact, the same relation of 

 position to it as has the precisely similar, and, as I 

 believe, morphologically identical, exopodite to the five- 

 jointed endopodite and to the protopodite in such a 

 crustacean as Peneus ; the only difference being that 

 Machilis appears to have one more joint in its proto- 

 podite — a difference which may be accounted for on 

 the supposition that Machilis is descended from some 

 crustacean form* in which a three-jointed protopodite is 

 found. 



" The basal segment [of the maxillary ]mlpi] has a 

 process regarded by Latreille as representing the cylin- 

 drical appendage of the posterior legs."t I cannot, how- 

 ever, regard this as anything but a mere process of the 

 basal joint ; a comparison of the two posterior gnathites 



* The Phyllopoda, some of the existing members of which have a 

 distinct head like the insects and myriopods. 



f Lubbock, ' MonograjDh of the Collembohx and Thjsanura,' 1873, 

 p. 202. 



