THE BUTTERFLY. 67 



Figs. 174-177] I shall call attention to the curi- 

 ous fact that just as the first segment of the 

 thorax becomes less and less developed as the in- 

 sect changes from caterpillar to chrysalis and 

 from chrysalis to imago, so, in passing from the 

 lower to the higher groups, we shall find a grad- 

 ual atrophy of the legs borne by the first segment 

 of the thorax ; first, the different joints contract 

 in size ; next, they lose a part of their armature ; 

 then, adjoining parts become consolidated, imtil, 

 finally, the tarsus forms only a single piece, 

 spines, spurs, pad, paronychia, and claws all dis- 

 appear, and the whole leg becomes so shrunken 

 as to be utterly useless and readily overlooked ; 

 practically, the animal has passed from a six- 

 legged to a four-legged condition ; in this instance 

 we can trace every step in the change ; and al- 

 though, in the extremest case of atrophy, the 

 front legs have not reached so low a stage as to 

 be classed with wholly rudimentary organs, yet 

 it is plain both that they are well on the way and 

 that their original condition that is, the condi- 

 tion of their ancestors was one in which the 

 front legs were fully developed, like the others. 

 How far back in time this would lead us, we can- 

 not guess ; the geological record now carries but- 

 terflies back toward the end of the lower terti- 

 aries ; but some of the earliest fossil butterflies 

 belong to the highest portion of the highest 



