( xcii ) 



Although phylogenetiially closely allied forms may differ from each other 

 iu one or more organs to a surprising extent, they are generally similar to one 

 another, if not in aspect, at least in structure, and if not at one stage, at least 

 at others of the metamorphosis of the individuals. The same kind of similarity 

 or identity we meet a^^-ain in species or genera which are not nearly related, hut 

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

 that this kind of agreement stands in contraposition to similarities which are 

 the outcome of evolution. Tin- preservation of four wings in Lepidoptera, 

 Orthoptera, H-miptera, etc., and of si.\ fully developed legs in most insects, 

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

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

 the claw-segraent of the tarsus in many Biitterfiies, Moths, and other insects, 

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

 etc., estahlish a similarity iu resiiect to the said characters which is manifestly 

 of quite a different kind lioiu the similarity established by the acquisition of 

 clubbed antennae or of a sucking-a]iparatus, or by the loss of the wings or 

 the mouth-jiarts, or by the adajitatiou to bark in colour and pattern, or to leaves 

 and sticks in shajie. 



Though the distinction between a resemblance preserved and a resemblance 

 acquired is obvious, it is not so sharj) as it appears to be at first sight, 

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

 acquired resemblance which 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 c junection with the 

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

 \Vhite-tiii[)ed 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 and lines 

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

 The wing is pcrhajis tiie best example of a conspicuously coloured, regularly 

 interrujjted surface, where the connection between the pattern ou the cue hand 

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

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

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

 triangular wings of Li'i)idoptera the modifying influence of the cross-veins and 

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

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

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

 Heterocera arc distally conc.ave between the veins according to the undulation 

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

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

 extending from the costal to the iunei' margin and including the cross-veins 

 seems to be greatly influenced in its ])attern by these veins, a large number 



