18 DONALDSON BODINE. 



retains in the fullest degree the characters of the stem form. Fig. 

 1 exhibits the general outline of the entire antenna, and Fig. 53 a 

 single segment more highly magnified, showing the finer structure. 

 It will be noticed that the scape is diflferentiated from the other seg- 

 ments by its larger size and different shape ; that the pedicel is not 

 very different from the proximal segments of the clavola, but the 

 whole base is easily distinguished from the other parts by its cover- 

 ing of very generalized scales. These are like long hairs, while 

 those which make a dense covering over the whole clavola are com- 

 paratively specialized, being broad with emarginate apices. The 

 simple, cylindrical segments which compose the clavola show little 

 variation from the common shape and present almost no projections 

 or asymmetrical expansions of the body wall. There are numerous 

 hairs of the first type, especially on the ventral aspect of the distal 

 segments, and a few of the second type. The latter are limited to 

 one, or at most two, on the ventro-distal edge of the segments, and 

 a considerable number in various positions on the apical segment. 

 Other characters appear in the antenna, but for our present purpose 

 those named are the important ones, as indicating what we may 

 fairly predicate of the stem form of the Lepidoptera. We may say, 

 then, that the j)i'ii^iitive antenna of the Lepidoptera 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 tracheae and nerves which supply the parts distad ; 

 of a pedicel large enough to provide space for the nervous apparatus 

 described under section 6 of the preceding chapter ; of a clavola 

 composed of numerous segments, probably at least a score, all of 

 them very nuich 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 specialized hairs of the second type. 



In the evolution of any complex organ, natural selection has acted 

 upon the different component parts and many lines of specialization 

 may have progressed together. This is true of the antcnnte, and in 

 considering them we must necessarily treat of different features sepa- 

 rately. The most striking changes are those of general shape. The 

 variations of the scape and pedicel are for the most part within nar- 

 row limits and are in the direction of changes in their size relatively 

 to that of the clavola, and in the varying proportions of length and 

 thickness. The scape has undergone modification in two directions 

 according as one or the other of its functions has been of predomi_ 



