l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 97 



haps it should he said, increased the extent of the compound eye, yet 

 without sacrificing muscular power. In effect, this muscle is here lo- 

 cated between the anterior arm of the tentorium and the anterolateral 

 surface of the sucking pump, thus utilizing what might be charac- 

 terized as " waste space." At the same time, the development of this 

 muscle is necessarily limited by the sucking pump and its muscles. 



A fourth pair of muscles should now be described. This pair con- 

 sists of one muscle located in each proboscis unit, arising on the stipi- 

 tal ridge and inserting in the proboscis base, and called the proboscis 

 base muscle (FBin). In direction it is a continuation of the posterior 

 tentorial proboscis extensor. Its position in the head of Papilio is 

 indicated in figure 9 B, PBm, also in figure 2 G. 



Hesperiidac: Only two species of skippers have been examined: 

 Epargyrens tityrus and Atrytone zabulon. In this family the probos- 

 cis extensors are short but very well developed. The anterior arms are 

 greatly broadened to provide greater attachment surface, while the 

 cranial proboscis extensors in Epargyreus have invaded the antennal 

 ridge to secure greater attachment surface. 



The remarkable simplicity of the stipital tube in Atrytone is well 

 worthy of note. In figure 2 I it is represented in cross-section under 

 compression. In this type, closure of the pressure chamber is effected 

 directly by the cranial proboscis extensor, as it presses the mem- 

 branous stipital ridge against the recurved flange of the parietal. The 

 membranous fold labeled F2 becomes much larger as it approaches 

 the base of the proboscis unit, at which point its outer portion is firmly 

 sclerotized, while its inner lateral section (that is, its morphologically 

 lateral section) remains membranous. 



III. THE SUCKING PUMP 



Among the orders of insects equipped with sucking pumps, the 

 Hemiptera and the Diptera have received considerable study. Snod- 

 grass (1935) has shown that the pump of the cicada is prepharyngeal 

 in origin and evolved almost entirely from the preoral cibarium. Simi- 

 larly, Jobling (1929) and Snodgrass (1935) have demonstrated that 

 the sucking pump in Diptera is derived from the cibarium. In respect 

 to the sucking pump of the Hymenoptera, Snodgrass (1935) states 

 that " while the morphology of the organ is not entirely clear, .... 

 judging from the musculature, it includes without doubt the pharynx 

 and the buccal cavity and perhaps the cibarium." It is, therefore, of in- 

 terest to determine to what extent the sucking pump of Lepidoptera 

 is preoral in derivation. 



