434 MISS A. M. EVANS ON THE STRUCTURE AND OCCURRENCE 



of Hemimerus, although eacli is considerably shorter in proportion (o its 

 width than are the corresponding organs in this latter genus. In one adult 

 specimen they measured -02 mm. in length and their width at the base was 

 •02 mm. The hypopharynx extended beyond the level of their buses to a 

 distance of "03 mm. and its greatest breadth was '07. 



Proximally the floor of the mouth bears the pair of asymmetrical 

 sclerites (n.) from the side of which the plates (e.) extend downwards to 

 be closely associated, at their ventral extremities, with the inner angle of 

 the mandible. These sclerites have an exact counterpart in H. liqvseni, Sharp, 

 although in the latter case there is no sign of asymmetry. Anteriorly we 

 find in Forficula a chitinous arch consisting of two asymmetrical sclerites (p.), 

 the small piece (s.), and the curious setiferous median sclerites (6.;, which will 

 be referred to when we come to consider the Psocida? and Mallophaga. In 

 this position in II. hqnseni, Sharp, however, we find only a single slender 

 arch of chitin immediately above which the maxillulas arise. 



In all the specimens examined the dorsal wall at the base of the hypo- 

 pharynx exhibited a tendency to form the curved fold (/.) whose apex lay 

 considerably to the left of the median line. A similar fold at the base of the 

 left maxillula gave this organ a bilobed appearance. 



The ventral surface of the 'tongue is stiffened by a continuous plate of 

 yellow chitin. This plate extends forwards to a short distance behind the 

 base of the hypopharynx. It is associated at its anterior lateral corners 

 with a slender chitinous rod (p.m.) which supports the external wall of the 

 maxillula. In this position I found a more plate-like sclerite in H. hanseni, 

 Sharp. 



It is probable that Forficula is derived from a form in which the 

 hypopharynx and its lateral appendages originated as far back as the 

 transverse sclerite. Such a condition would resemble more closely that of 

 Hemimerus. This supposition is supported by the presence of a faintly 

 marked suture (y.) extending back from the inner angle of the left maxillula 

 to this skeletal bar. 



ORTHOPTERA. 



Folsom (17. p. 115) gives an account of the hypopharynx of Orthoptera. 

 The lingua he says " corresponds exactly with the lingua of Apterygota." 

 He finds that the chitinous supporting stalks described by Miall and Denny 

 are comparable to those in Apterygota. In Melanopus femoratus, Folsom 

 discovered " superlinguas " as " large dorso-lateral rounded lobes intimately 

 united with the lingua." He notes the evidence of the presence of lingua 

 and superlingiue in Packard's figure of Anabrus, Packard (36). The tongue 

 of Blattidre is described by Mangan (29. p. 3, pi. i. fig. 1). "The free tip," 

 he says, " is furnished at the sides with a pair of elongate plates (Z) which 



