May, 1916] Ilomopteroiis Studies. Part II 309 



Mandibles— (PI XX, Figs. 6, 16, 2, 4, 3). Viewing the head 

 on the inside from its caudal aspect, the two pairs of setae, viz., 

 the mandibular (m. s.) and maxillary setae, can be seen attached 

 to the head capsule. These two pair of setse are in rather close 

 relationship, but with careful dissection it will be seen that the 

 more dorsal pair are articulated with head-capsule, between 

 the maxillary plate and the clypeus. The posterior end of the 

 mandible is produced into a small tendon (t) to which attach 

 the strong retractor muscles (m. r.) which attach in turn to 

 the head-capsule at the sides of the occipital foramen. A 

 small tendonous rod (m. a.) connects the mandibular seta with 

 the latero-posterior edge of the clypeus. While the mandibular 

 seta is intimately related to the maxillary seta in the labium, 

 the two are separate within the head-capsule. The mandibles 

 are capable of being withdrawn and protruded within limits 

 owing to the muscles, which are connected with the posterior 

 end. The retractor muscles (m. r.) attach to the head capsule 

 on the inner side of the clypeus. The position of the invagi- 

 nation of the anterior arms of the tentorium, which are asso- 

 ciated with the mandibles, enables one to homologise the 

 mandibular setae in the Jassoidea with the mandibles in the 

 Cicadidae and other Homoptera. 



The identity of the mandibular plate or lora, has been well 

 demonstrated by the work of Muir and Kershaw on the develop- 

 ment of the Homopterous head, wherein it is shown that the 

 mandibles become completely enclosed within the head-capsule. 

 Although this question has been much discussed, from various 

 points of view, it seems to the writer clear that the evidence 

 favors the interpretation of the mandibular setae as representing 

 the entire mandible. The articulation of the mandibular 

 set^ viz., between the clypeus and the maxilla is the normal 

 position, and further the invagination of the anterior arms of 

 the tentorium add additional weight to the interpretation. 



The structure and morphology of the mandibular seta 

 resembles very much that of the general Homopteron; the 

 tips are barbed, with the barbs (b. a.) pointing backward. 

 As stated before, their function is probably that of piercing 

 the plant, to enable the maxillae to perform the sucking function. 

 Like the maxillary, the mandibular setae are surrounded for 

 their proximal half with a membranous sleeve. 



