rsyclie [Jime 



, The mandibles are articulated at the anterior ends of the man- 

 dibular sulci. There is a thickening of the chitin of the walls of 

 the mandibular sulci from the point of articulation to some dis- 

 tance posteriorly to which the protrvider muscles are partly 

 attached. This thickening we ternl the mandibular pillar (Fig. 

 11, C mdp). It plays an important role and its homology in the 

 more highly modified forms is difficult to recognize, but its origin 

 can be easily discerned in the Cicada nymph. The tendons to 

 which the retractor muscles (Fig. 11, mdt and rjn 1) are attached 

 have a similar origin to that of the maxillary setse, namely, to an 

 invagination and chitinization of the ectoderm at the base of the 

 setae. 



The position of the trophi of the head of the nymphal Cicada 

 is thus seen to be very little modified in position; the tentorium 

 is similar to that of other insects and arises from the usual invagi- 

 nations. The greatest modification is in the shape of the head- 

 capsule, the formation of the three pairs of sulci, the amalgama- 

 tion of the maxillary plate to the head-capsule and the forward 

 position of the labium and phar\aix. The sulci appear to be the 

 outcome of the maxillary plates and head-capsule overlapping 

 and enclosing the setse. 



The Head of Siphanta acuta Walker. 



If we now compare the head of Siphanta acuta (Fig. 12) with 

 that of the nymphal Cicada we can follow their homologies. In 

 Cicada the head-capsule is short and broad, the eyes being nearly 

 on a level with the vertex; in Siphanta the head is long and nar- 

 row and the vertex prolonged far beyond the eyes. Incidentally 

 we may state that a large "food-reservoir" (Fig. 12, /r) (a diverti- 

 culum from the oesophagus and crop) fills the epicranium of Flata 

 in a similar manner to Pyrops candelaria. 



The pharyngeal sulci are near the median line of the clypeal 

 region, short, but project inward as long pharyngeal struts to the 

 antero-lateral edges of the pharynx; the pharyngeal struts also 

 give support to the protractor muscles of the mandibles. The 

 sections (Fig. 14, / pst) show a distinct lumen but actually the 

 walls are so pressed together as to practically form a single plate. 

 The walls do not, however, fuse; the invaginations can easily be 



