(lii) 



wliich is often soiiipwliaf concave, is more or less regular, especially ventrally, 

 and, surrouucling tlie naked space, forms a kind of cavity (fff, PI. LIX. 

 f. 13. K). 17. 18. 25 ; PI. LX. f. '■]). The naked membrane is doubtless sensory, 

 bnt we conld not fiud 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 regnlar one. This specialisation is found only among 

 Oriental and Aethiopian Sp/nitgifku', not in American ones. The 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 iu shape ; it may be 

 snbcylindrical, 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 

 angolate 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-i)arts are exposed. This is the case when the scaling of the second 

 segment is very short, as in PI. LIX. f. 10. 11. 26. 



The inner surface of the second segment exhibits some remarkable specialisa- 

 tions. It is normally scaled all over, bnt we find the scales very small and 

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

 partly naked. In all the other species of Choerocampinae 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 (piite constant, and 

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

 and of the auteniial end-segment, and form the subfamily ('Iiocrocampinae. The 

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

 either short or form a couspicuous tuft, which projects ventrad (PI. LIX. 

 f. 19—21. 26. 27). This difference is of importance, the absence of the tuft 

 being cbaracteristical for the fifty species of the purely American genus 

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

 Choerocampinae {Rlioilafra and Fergesa excepted), the scaling at the apex of 

 the first segment irregular, as stated above. We 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 

 Psilogramma of the subfamily Achcrontiinae. Here the segment bears a naked 

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

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

 occur in the otherwise very closely allied genus T.eucomonia. 



A third modification peculiar to the Acheronliicae, bnt vestigial also in one 

 genus of Spliingicac, 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 

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



