42 



SOME ASPECTS OF MORPHOLOGY 



In the Machilidae the second to ninth pairs of coxites each bear 

 styU, but in other famiUes the styh are more restricted, and in the 

 Lepismidse they may be present only in relation with the eighth 

 and ninth pairs of coxites ; in the Japygidae they are borne on 

 the first to seventh coxosterna. 



In the Protura the first three abdominal segments bear greatly 

 reduced appendages, which, in the Eosentomonidae, are two- 

 jointed. These appendages are comparable with coxites which, 

 in the two-jointed condition, include the rudiment of a second 

 leg-segment (Fig. 25). The appendages of the first abdominal 

 segment in the Campodeidae appear to be of a comparable nature. 

 In the CoUembola true abdominal appendages are represented by 



the ventral tube, the hamula 

 and the furcula which are 

 derived by direct conversion 

 from rudiments borne on the 

 corresponding segments in the 

 embryo. 



The morphological signifi- 

 cance of the styli has been so 

 Fig 25. Eosentomon. Third abdominal ^^^^^ discussed that only brief 

 sternum s, showmg| two-segmented / 



appendages^; c, coxite ; c^ second reference to the subject is 



segment of appendage. 

 Berlese.) 



(From required here. It appears 

 probable that the styli which 

 are borne upon a variable number of the abdominal segments in 

 Thysanura (Fig. 24) are homologous with similar organs present 

 in the relation with the limb bases in Symphyla (Fig. 18). In 

 two groups these styli are in similar close relations with eversible 

 sacs. It follows, therefore, from this homology that the styli of 

 Thysanura are not to be regarded as vestiges of true limbs as has 

 often been contended. The styli borne on the ninth sternum of 

 the males of the Isoptera, Ephemeroptera and of many Orthoptera 

 are evidently homodynamous with those just referred to. 



As regards the cerci, it is well established on embryological 

 grounds that they are the persistent true appendages of the 

 eleventh abdominal segment. Each cercus is borne on the 

 membrane between the epiproct and paraprocts, the two latter 



