( Hi ) 



wliicli is often soiucwliat concave, is more or less regular, especially ventrally, 

 ami, surrounding the naked space, forms a kind of cavity {gr, PI. LIX. 

 f 13. l(i. 17. 18. 25 ; PI. LX. f. 3). The naked membrane is doubtless seusory, 

 but we could not find any external sensory organs in the dry specimens. The 

 long hair-like scales situated in many species on this naked membrane are 

 not of a sensory nature. There is every intergradation between a rudimentary 

 cavity and a large regular one. This specialisation is found only among 

 Oriental and Aethiopian Sphingidae, not in American ones. Tlie joint between 

 the first and second segments is exposed in the species which exhibit the 

 cavity. A naked and exposed joint is also met with among Ambulicinae, but 

 no cavity. 



The second segment undergoes many modifications in shape ; it may be 

 subcylindrical, quadrangular, triangular, ovate ; it may be longer or shorter 

 than broad, or square. In Tinostoma it is three times as long as broad. It is 

 angnlate at the upper outer corner in Aleuron and Unzcla. The scaling of the 

 two palpi generally covers the base of the tongue ; but there are instances where 

 the mouth-parts are exposed. This is the case when the scaling of the second 

 segment is very short, as in PI. LIX. f 10. 11. 20. 



The inner surface of the second segment exhibits some remarkable s])ecialisa- 

 tions. It is normally scaled all over, but we find tlie scales very small and 

 rather dispersed in Euchloron (PI. LIX. f. 24), so that the membrane is 

 partly naked. In all the other species of Choerocnmpinae these small rounded 

 scales have all, or nearly all, disappeared, leaving the segment bare except at 

 the edges (PI LIX. f. 19—21. 26. 27). The character is quite constant, and 

 occurs only in those species which agree also in certain characters of the pilifer 

 and of the antennal end-segment, and form the subfamily Choerocampinae. The 

 scales at the upper apical angle of tlie segment with naked inner surface are 

 either short or form a conspicuous tuft, wliich projects ventrad (PI. LIX. 

 f I'J — 21. 26. 27). This difference is of importance, the absence of the tuft 

 being characteristical for the fifty species of the purely American genus 

 Xylophanes, which has, unlike the Eastern representatives of the subfamily 

 Choerocampinae {Rhodu/ra and Fergesa excepted), the scaling at the apex of 

 the first segment irregular, as stated above. AVo have not ascertained the true 

 nature of the naked membrane, but assume that it serves as an organ of sense. 

 A specialisation reminding one of that just described is found in the genus 

 Pailogvamma of the subfamily Ackerontiinae. Here the segment bears a naked 

 longitudinal stripe not far from the upper edge, the stripe appearing as a 

 jirolongation of the naked part of the first segment. The modification does not 

 occur in the otherwise very closely allied genus Leucomonia. 



A third modification peculiar to the Acherontiicae, but vestigial also in one 

 genus of Spkingicae, is represented by figs. 1 and 2 of PI. LX. Here the 

 second segment is concave on the inner surface ; the scales at the edge of 

 the cavity {c) project over it, forming a kind of roof. The concave part is 

 eitlicr practically naked or scaled. The transition from the vestigial groove of 



