1912] Muir and KersJiaic — Development of Mouthparts in Homoptera 



83 



a large cross-bar. The second invagination arises from the pos- 

 terior end of the mandibular sulci and, amalgamating with one 

 from the antennal ring, joins the cross-bar near its origin. 



The maxillary setse arise from the liase of the inner surface of 

 the maxillary plate, a position they liold in the embryo after their 

 division into two parts. The tendons (Fig. 11, 7nxt.) which sup- 

 port the retractor and protractor muscles (Fig. 11 rm 2, pm 2) arise 

 as all such internal chitinous structures arise, by the invagination 



JjiTTT^ 



11a. Internal view of right side of head of nymphal Cicada. 



lib. Horizontal section through head above pharynx. 



lie. Attachment of mandibles to head-capsuie. 



lid. Attachment of maxillary seta to head-capsule. 



lie. Sectional diagram of maxillary seta showing nature of chitinous "tendon." 



of the ectoderm at the base of the setee which becomes solid or 

 partly solid by deposits of chitin (Fig. 11, e). These are often 

 described as the basal parts of the maxillary setae and have led 

 to the idea that the setse are drawn back into the head and have 

 partly Ijecome internal organs. 



