I 



( xcii ) 



Altli(iu;;ii ])li_vl(ig('iictically closely allieil forms may (lifter from each other j 



in one or more organs to a surprising extent, they are generally similar to one ]' 



anotlier, if not in aspecf, at least in structure, and if not at one stage, at least i 



at others of the metamorjiliosis of the individuals. The same kind of similarity V 



or identity we meet again in sjieci.'s or genera which are not nearly related, but A 



have preserved one or more cliaracters of the common ancestor. It is evident I 



that this kind of agreement stands in contraposition to similarities whicli are l 



the outcome of evolution. The preservation of four wings in Lepidoptera, J 



Orthoptera, Hemiptera, etc., aud of six fully developed legs in most insects, i 



the occurrence of ocelli in many Heterocera and other insects, of filiform or J 



setiform antennae in most orders of Arthropoda, and the retention of a pad to i 



the claw-segment of the tarsus in many Butterflies, Moths, and other insects, ,■ 



or of a frenulum in one Butterfly and the greater proportion of Moths, etc., »: 



etc., establish a similarity in respect to the said characters which is manifestly i 



of quite a difterent kind from the similarity established by the acquisition of i 



clubbed antennae or of a sucking-apparatus, or by the loss of the wings or \ 



the mouth-])arts, or by the adajjtation to bark in colour and pattern, or to leaves • 



and sticks in shape. j 



Though the distiuctiou between a resemblance preserved and a resemblance | 



acquired is obvious, it is not so sharp as it appears to be at first sight, I 



since the two kinds of similarity are connected to a certain extent by that i 



acquired resemblance whicli is the direct outcome of inherited community of « 



characters. We find, for instance, that the distribution of pale and dark ] 



colours on the legs of Arthropoda stands normally in close cjunection with the i 



articulation, the segments being very generally pale-coloured at the joints. | 



White-tipped tarsal segments, and tibiae with three pale rings are of common % 



occurrence among insects, as are white-ringed antennae and white-ringed abdomina. ] 



Where there is a break in the surface of the skeleton of insects, there is normally ' 



also a break in the coloration. Thus we find a stripe along the eye aud lines t 



at the edges of the thoracical plates in members of nearly all orders of insects. | 



The wing is perhaps the best example of a conspicuously coloured, regularly ^ 

 interrujited surface, wliere the connection between the pattern on the one hand 

 and the outline and the division of the surface by the veins on the other is 



very obvious in a great many insects. The original pattern of the insect-wings \ 

 (outstretched) is symmetrical to the body and symmetrical to the veins. On the 

 triangular wings of Liqjidoptera the modifying influence of the cross-veins and 

 the oblique distal margin is especially conspicuous. The position of new markings 



is dependent on the position of the old ones, new lines appearing often along i 



tiie old ones and rings around spots. The external lines of a vast number of \ 



Heterocera are distally concave between the veins according to the undulation i 



of the distal margin of the wing, while the proximal lines are distally convex j 



(respectively dentate) between the veins. The median space of the forewing j 



extending from the costal to the inner margin and including the cross-veins j 



seems to be greatly influenced in its pattern by these veins, a large number i 



