86 Psyche [June 



pillars and mandibles. The protractor muscles are attached to 

 the mandibular pillars. 



In the former paper we called the base of the mandibular pil- 

 lar the point of articulation of the mandibles, which is morpho- 

 logically incorrect but functionally correct. The tendons to which 

 the retractor muscles are attached arise as invaginations at the 

 base of the mandibles and are attached by muscles to the occiput; 

 but they are so strongly chitinized in many forms that they ap- 

 j)ear as the basal portion of the mandibles and have led to the idea 

 of the mandibles being drawn into the head-capsule. 



The tentorium is the same as in Cicada. From the end of the 

 maxillary sulcus arises an invagination which meets a similar 

 invagination from the opposite side and forms the cross-bar; a 

 slender invagination from the antennal ring joins the cross-bar 

 near its origin, having just previously joined with the one from 

 the mandibular sulcus. The fact that the principal branch of 

 the tentorium arises from the bottom of the maxillary sulcus, the 

 walls of which are pressed together and appear as one plate, has 

 led to the idea that it (along with the mandibular sulcus) are parts 

 of the tentorium. 



The maxillary plate projects as a free body from between the 

 ends of the maxillary and mandibular sulci, forming a cover for 

 the setse. The maxillary seta arises from the basal inner portion 

 of the plate. A tendon arises from its base in a similar manner 

 to that of the mandible and gives support to the retractor and 

 protractor muscles, the former proceeding to the occupit, the lat- 

 ter to the distal portion of the maxillary plate (Fig. 11, d and e). 



The salivary syringe is attached by a flange to the back of the 

 hypopharynx and opens at the distal end thereof. The syringe 

 is a modified portion of the salivary duct. 



While making the preceding studies it has appeared to the 

 authors that the greatest difl^erence between the head of Homop- 

 tera and the mandibulate insect lies in the amalgamation of the 

 basal part of the maxilla to the head-capsule and its growth 

 over the mandibles, along with the forward growth of the labrum 

 and pharynx. The growth of the head-capsule necessary to bring 

 about this change has resulted in the mandibular and maxillary 

 sulci. The pharyngeal sulci appear to have been formed by the 

 growth of the clypeal region whilst its anterior portion has been 



