THE ANTENNA OP LEPIDOPTERA. 263 



taste, but the evidence previously offered is of the most unsatisfactory 

 character. 



The evohition of the antenna is a comprehensive, but interesting 

 subject. The antenna of Mkropterijx (PL II., fig. 1) is probably the most 

 generalised form now existing among Lepidoptera, and Bodine thinks 

 that " the primitive antenna was made up of a scape large enough to 

 afford room for the strong muscles to provide for the movement of the 

 pedicel, and also to contain the large trunks of trachea3 and nerves 

 which supply the parts distad ; of a pedicel large enough to provide 

 space for the nervous apparatus previously described (and numbered 

 6, ante^. 227), of a clavola composed of numerous segments, probably at 

 least a score, all of them very much alike. What was the character of the 

 chitinous surface we cannot say. Doubtless there were hairs of the 

 first type. There may have already been specialised hairs of the second 

 type." 



As may be expected in the evolution of any complex organ, modifi- 

 cation of various parts may progress together. This has happened in 

 the case of the antenna, and, although it is convenient to consider the 

 modifications separately, it must be understood that the same antenna 

 may present more than one modification. 



The variation of the scape and pedicel is usually dependent on the 

 changes of the clavola. The scctpc has become modified in two direc- 

 tions : (1) Increase in diameter and relative shortening, as in the 

 Papilionids (PI. II., fig. 2), Hesperids, etc. (2) Lengthening without 

 marked increase in diameter, as in the Adelids. The first tends to 

 produce exact and definite movement. The second, more indepen- 

 dent movement. The jJCf/trcZ shows but little variation, although it 

 is relatively larger in those families which are highly specialised. 

 Its development is probably correlated with that of the contained 

 nervous apparatus. 



The clavola is the part of the antenna that has undergone most 

 variation. The primitive form of the segments of the clavola was 

 probably cylindrical, probably covered with hairs having the double 

 function of protection and sense-perception. Differentiation of the 

 hairs into different types was accompanied by their concentration in 

 particular areas, and hence those connected with sense-perception 

 became localised on the ventral, those for protection on the dorsal, 

 aspect. Since the chief function of the antenna is sense-perception, 

 specialisation in the direction of enlarging that part which bears the 

 sense organs, as well as an increase in the efficiency of the organs, 

 went on side by side. 



The enlargement took place in two ways : (1) By the formation of 

 a ventral ridge, as in r>jrausta, Crambus, Sphingidae, etc. (2) By the 

 projection of small portions of the segments to form pectinations, as 

 in the Saturniids, Bombycids, etc. In many Lepidoptera the pectina- 

 tions are more marked in the male than in the female. Poulton,*'- 

 argumg from the similarity of the pupal antennae in both sexes, con- 

 siders that the difference has been produced by a degeneration of these 

 organs in one sex, and a corresponding development in the other. 

 Woodf has suggested that sexual functional stimulus causes the 

 development to take place in both sexes alike at the comihencement of 



* Trans. Linn. Soc. Lond., 1890, p. 247 et seq. 

 t Entom. Rec, vol. iv., pp. 237-238. 



