1912.] 283 



A position in which not only some members of a genus but also 

 some individuals of a species are winged and some not, cannot of 

 course be regarded as static, and since we may assume with some con- 

 fidence that all primitive forms of CnleoiAem were fully wmged, and 

 that such species or groups as are now apterous have become so 

 through some process of atrophy, we may reasonably conclude that 

 certain members of Longitarsus, if not the genus as a whole, are now 

 in process of passing from a fully winged to a completely apterous 

 condition. 



Such being the case, we must necessarily assume that with these 

 insects wings are becoming useless, or at any rate of very subordinate 

 utility to some other organic development with wliich ivitliin the 

 organism wing-development competes, for the atrophy of organs not 

 actively injurious, but only useless, difiicult if not impossible to explain 

 solely on the accepted principles of natural selection and inheritance, 

 becomes clearer if we assume the necessity for economy in the expen- 

 diture of vital energy which the katabolism of the organism demands, 

 and that such necessity would result in an internal competition in the 

 development of separate organs. (i) In this case, then, we would suggest 

 that the very great saltatorial power evinced in Longitarsus has been 

 gained, and is perhaps being increased at the expense of the alar power ; 

 in other words, that as leaping hypothetically serves the needs of the 

 insect better than flying, wing and wing-muscle cellular determinants 

 have been reduced, so that femora and femoral muscle determinants 

 might be increased. 



We must admit that, in the present state of our knowledge of the 

 economy of these insects, we are quite unable to explain why it should 

 be better to jump well than to fly, nor is it any refutation to point to quite 

 other groups such as Orchestes, Scirtes, or other Halticidee, which both 

 possess saltatorial power and are fully winged. As a matter of fact, 

 as most field Coleopterists know, Longitarsi do leap further and with 

 more alacrity than any other beetles, except perhaps Phyllotretse, so 

 much so that their capture is usually considerably more difiicult than 

 is that of species possessed of the most ample wing-development. The 

 suggestion might indeed be made that to facilitate escape from enemies, 



(1) Apropos of this we venture to quote from a recent text book on biology :— " A strengthened 

 representative item or determinant in the germ-plasm will noui-ish itself more abundantly 

 than its neighbours. It may get into a permanent upward movement and attain a degi-ee 

 from which there is no falling liack. On the other hand a weakened determinant will have 

 less power of attracting nutriment and will tend to go downhill. If it be the determinant of 

 something useful, then the ordinary process of natural selection will eliminate the individual 

 that develops from the impoverished germ-cell ; if it be the determinant of something use- 

 less, natural selection will not interfere and the determinant will continue getting weaker 

 every generation."— " Evolution," Geddes and Thompson, j). 174. 



