ANTENX.T5 OF LEPIDOPTERA. 19 



nate importance in the action of the antenna. When exact and 

 definite movement became of greater moment, the tendency \va;« 

 towards an increase in diameter and rehitive shortening of the 

 length. This wouhl provide for a nuich more advantageons arrange- 

 ment of the muscuhiture, both as to the direction of tiie axis of the 

 fibres and the securing of a better leverage for their operation. This 

 line of specialization has reached its climax in the Hesperiina and 

 Papilionina. On the other hand, when the direct movement became 

 of less importance than the separation of the two clavolas and the 

 ability to move them from two distinct and widely separated bases 

 somewhat removed from the head, then selection caused a length- 

 ening of the scape accompanied by little increase in diameter. This 

 line of specialization has progressed quite far in certain of the Mi- 

 crofrenatie, especially among the Tineina. 



The pedicel shows but little variation among the moths. In tlie 

 more specialized families it is of greater size, relatively to that of 

 the adjacent segments of the clavola, tlian wouKl l)e necessary, did 

 it serve simply as a socket whose function was to hold the clavohi, 

 while the pedicel itself might be moved by the muscles situated in 

 the scape. It is very probal)le that the degree of its develo})meiit is 

 closely correlated with tliat of tlie contained nervous apparatus 

 al rea( ly described . 



The greatest variation occurs in the clavola. This is the part 

 which more directly bears the sense organs, and therefore is ])ecu- 

 liarly subject to the action of natural selection. We may safely 

 assume that the primitive form of the segments of the clavola was 

 cylindrical, with the whole surface equally provided with hairs, the 

 latter uniting in their function protection and sense- perception. 

 When there came the differentiating modifications of the hairs into 

 difierent types, and the consequent differentiation of the surfaces of 

 the clavola, the organs specialized for sense-perception came to be 

 more or less localized on the ventral aspect, while those for protec- 

 tion were concentrated on the dorsal. It at once becomes evident 

 that, if the chief function of the antenna is sense-perception, spe- 

 cialization would be in the direction either of enlarging that ])art 

 which bears the sense organs and thereby providing for an increase 

 in their number and spread, or of increasing the efficiency of the 

 organs themselves. As a matter of fact, both processes went on 

 together. 



The extent of the ventral surface was enlarged l)y progress along 



TKANS. AM. ENT. SOC. XXIII. JANUARY, 1896 



