Organic Evolution. 179 



the clubbed whip in the ant-lion and the butterfly; the 

 feathered form in certain moths and flies ; the hooked form 

 characteristic of the sphinx-moths; the many-leaf form 

 in the lamellicorn beetles, like the cockchafer; and the 

 feathered plate of other beetles. Equally wonderful are 

 the diverse developments of the mouth-organs of insects, 

 the spiral tube of the butterfly or moth, the strong jaws of 

 the great beetles, the lancets of the gnat, the sucking-disc 

 of the fly, all of them special modifications of the same 

 set of structures. Then, in the same bay, note some of 

 the striking differences between the males and females 

 of certain insects. In some there is an extraordinary 

 difference in size (e.g. the locust Xiphocera, and the moth 

 Attacus) ; in others, like the stag-beetle, it is the size of 

 the jaws that distinguishes the males ; in others, again, 

 the most notable differences are in the length, development, 

 or complexity of the antenna, or feelers ; in some beetles 

 the males have great horns on the head or thorax ; while 

 in many butterflies it is in richness of colour that the 

 difference chiefly lies the brilliant green of the Ornithoptera 

 there exhibited contrasting strongly with the sober brown 

 of his larger mate. 



The fact that the special characteristics of the male, 

 which we have seen to be variable in the ruff, are also 

 variable among insects, is well exemplified in the case of 

 the stag-beetle, in some males of which the mandibles are 

 far larger than in others. This is shown in Fig. 22, which 

 is copied from the series displayed in the British Museum, 

 by the kind permission of Professor Flower. 



Crossing the hall to where the vertebrate structures are 

 displayed, the development of hair, of feathers, of teeth, 

 the modifications of the skull and of legs, wings, and fins 

 are being exemplified. Note here and elsewhere the special 

 adaptations of structure, of which we may select two 

 examples. The first is that seen in the Balistes, or trigger- 

 fish. The anterior dorsal fin is reduced to three spines, of 

 whick that which lies in front is a specially modified 

 weapon of defence, while that which follows it is the so- 



