PROC. ENT. SOC. WASH., VOL. 23, NO. 1, JAN., 1921 11 



insects. The Corrodentia and some of the Mallophaga, both 

 possessing strong biting mandibles and simple, one-lobed 

 maxillae have also a pair of short mouth rods, one on each side, 

 issuing from pouches entad to the bases of the maxillae. Each 

 rod has an internal apodemal prolongation of its shaft to which 

 are inserted retractor muscles attached to the epicranium and 

 protractor muscles attached to the base of the maxilla. The 

 distal ends of the rods are usually forked. Some writers explain 

 these rods as being the modified inner lobes of the maxillae which 

 are otherwise one-lobed. Since the embryologists have shown 

 that the lower end of sclerite B of the Hemipteran head is formed 

 from the body of the maxilla, and that the second seta is formed 

 from a maxillary lobe, we can trace here such a clear analogy 

 with the maxillary structure in the Corrodentia and the Mallo- 

 phaga as to suggest that these insects present a more primitive 

 condition of the Hemipteran maxilla than does the Hemipteran 

 embryo itself. It would be a great relief if the supposed man- 

 dibular seta of the Hemiptera could be so easily compared with 

 some other known structure. In any case it should prove highly 

 interesting if we can find in the Corrodentia and Mallophaga a 

 suggestion of the link between the Hemipteran mouth parts and 

 those of biting insects. But the relationship of these orders and 

 the homologies ot the mouth rods and the setae have already been 

 discussed by Borner (1904) in a paper on insect phylogeny. 

 This author would derive the Hemiptera and the Corrodentia, 

 including the Mallophaga, from a common stem, with the 

 Thysanoptera intermediate but related rather to the Hemip- 

 teran branch, while the Siphunculata are doubtfully connected 

 with the Mallophaga. 



LIST OF SYMBOLS AND LETTERING USED ON PLATES i AND II. 



A, anterior lateral head sclerite. 

 , lateral wing of hypopharynx. 

 .//, antenna. 



_''.//>, apodeme of second seta. 



B, posterior lateral head sclerite. 

 b, free lower end of B. 



C, side of epicranium 



f, soft appendicular lobe of b. 

 Clp, clypeus. 



d, swelling below salivary pump. 

 , compound eye. 



e , invaginated roof of pharynx. 

 EpAy, epipharynx. 



/, outer edge of protractor apodeme of first seta. 



Ft, front 



g, attachment of protractor apodeme of first seta to C. 



