THE PRESIDENT'S ADDRESS. 51 



Why should there be a long tactile hair on the front tibia of almost 

 all blind A cart ; it is an excellent place for it, but there are other 

 good places also, and the hair often occurs on the other tibia which 

 are not such good places ? How can such facts as these, and the 

 thousands upon thousands of similar instances, be explained except 

 by community of descent ? An excellent example was pointed out 

 by Professor Flower in his Hunterian lecture on the subject, viz., 

 the reduction in size of the second and third digits in all Australian 

 Marsupials notwithstanding their widely different habits ; it can 

 hardly be supposed that the shortening of these two fingers has 

 arisen separately in all the species. Then, again, the diverse adapta- 

 tions of the same morphological part tell the same story. The oft- 

 quoted adaptation of the fore limbs of Vertebrates, is an admirable 

 example — the leg of a horse, the arm of a man, the wing of a bird, 

 the anterior support of the wing of a bat, and the fin of a fish being 

 different forms of the same part, in one case one portion, in an- 

 other case a different one, being largely developed to meet the wants 

 of the creature ; but almost any other part maybe taken, although 

 perhaps the result may not be quite so striking. For instance, the 

 mouths of insects, the same parts exist in almost all : the mandibles, 

 the maxillae, the mentum and lingua, the labial, and maxillary 

 palpi being present in almost all , but often so profoundly modified 

 that it is difficult at first to recognize that they really are the same 

 parts, so wonderful are the adaptations to the requirements of the 

 insect. What plausible explanation except community of descent 

 can be given for this ? If it did not arise from this cause why 

 should not the sucking mouth of a butterfly or a gnat be formed 

 of totally different parts from those in the mouth of a wood-eating 

 beetle ? Nature does not always utilize the same part for attaining 

 even a similar purpose in allied creatures ; thus, for instance, in 

 insects and Acari parasitic on hairy creatures, the apparatus for 

 holding the hair varies greatly ; in the Pediculus capitis of man the 

 front leg is furnished with a great falx doubling back like the 

 blade of a clasp-knife. In the Dispai-ipes and the Trichodactalus of 

 the humble-bee the same leg has an immense hooked claw, and in 

 the Myobia of the mouse a strange curved lamina folding round a 

 chitinous peg, and holding the hair between the two ; but, on the 

 other hand, in the closely allied Listroplwrus of the mouse it is not 

 the claw, but the greatly-enlarged maxillary lip, which becomes a 

 flexible chitinous organ, to wrap round and hold the hair ; and in 



