94 SECTIONAL ADDRESSES 



in consequence of some stimulating factor, would account for the later 

 step in the colour scale being so often obtained. This phenomenon is 

 so frequently observed that one expects every red-coloured species at 

 least occasionally to produce yellow specimens. According to the 

 combined experiences of many observers, there is undoubtedly this 

 tendency of a development from red in the direction to white, and if we 

 find that in one species the male is orange and the female yellow (or 

 white) (as, for instance, in some Colias and Soritia), there is reason for 

 considering the female the more advanced sex, and vice versa. Now there 

 is a curious discrepancy in the frequency of occurrence between red and 

 yellow (or orange, yellow and white) in species where only occasional speci- 

 mens bear the different colour , being so-called aberrations among a normally 

 coloured population. To ascertain the frequency of a comparatively rare 

 occurrence of this kind requires large collections brought together over a 

 long period. Collectors, as a rule, are very keen on such aberrant speci- 

 mens, and what we see therefore in collections is a disproportionately 

 large number of aberrants among the normals. There is a collection of 

 Lepidoptera at Cologne (Dr. Philipps), consisting almost entirely of 

 aberrants ; a madhouse the late Prof. Study, of Bonn, called the collection. 

 The discrepancy alluded to is this : whereas the number of yellow 

 aberrants among red normals (and white among yellow) is large, the 

 change in the opposite direction from white to yellow and from yellow 

 to red is excessively rare. I have in my collection only two instances of 

 such inverse aberrants : an orange male of the yellow {^) and white (?) 

 Dercas verhuelli Hoev. from China, and an Indian specimen and a Javan 

 one of Troides helena L., with the abdomen and hindwings partly reddish 

 instead of yellow. If the yellow aberrants of red species are due to 

 accelerated development in the chrysalis, the red or orange aberrants of 

 yellow species must be considered the result of retarded development. 

 But why this enormous difference in frequency ? As a systematist I 

 can only present the riddle and must leave it to the experimentalist to 

 find the solution of this contradiction. 



Besides colour and pattern, the size and shape of the specimens and 

 their appendages and the structure of the secondary sexual characteristics of 

 many kinds are found to be of great help in species classification, but 

 experience has shown that none can be relied on unreservedly any more 

 than colour or pattern. The comparison of the frequently exaggerated 

 distinctions of the males, such as the horns of stags and beetles, the long 

 forelegs of beetles, the stalked eyes of certain flies, etc., has led to the 

 discovery that the size of these organs is not always proportionate to the 

 size of the body, but that the ratio in the development of such appendages 

 increases disproportionately with the size of the specimens ; in a small 

 male of a species of Longicorn beetle the antenna may be a little longer 

 than the body, while in a large specimen of the same species it may be 

 several times longer than the body. Collections bear out this law of 

 growth almost completely, but only almost. The Stag-beetles are one of 

 the families that have early drawn attention to the remarkable develop- 

 ment of their mandibles, which are sometimes so large, and the point 

 of gravity therefore placed so far forward that the specimen has to assume 



