MORPHOLOGY. 428 



subordinate though striking instance, that the hind feet of 

 the kangaroo, which are so well fitted for bounding over 

 the open plains — those of the climbing, leaf-eating koala, 

 equally well fitted for grasping the branches of trees — 

 those of the ground-dwelling, insect or root eating, bandi- 

 coots — and those of some other Australian marsupials — 

 should all be constructed on the same extraordinary type, 

 namely with the bones of the second and third digits 

 extremely slender and enveloped within the same skin, so 

 that they appear like a single toe furnished with two claws. 

 Notwithstanding the similarity of pattern, it is obvious that 

 the hind feet of these several animals are used for as widely 

 different purposes as it is possible to conceive. The case is 

 rendered all the more striking by the American opossums, 

 which follow nearly the same habits of life as some of their 

 Australian relatives, having feet constructed on the ordinary 

 plan. Professor Flower, from whom these statements are 

 taken, remarks in conclusion : " We may call this conform- 

 ity to type, without getting much nearer to an explanation 

 of the phenomenon ; " and he then adds, "but is it not power- 

 fully suggestive of true relationship, of inheritance from a 

 common ancestor?" 



Geoffroy Saint-Hilaire has strongly insisted on the high 

 importance of relative position or connection in homolo- 

 gous parts ; they may differ to almost any extent in form 

 and size, and yet remain connected together in the same 

 invariable order. We never find, for instance, the bones of 

 the arm and forearm, or of the thigh and leg, transposed. 

 Hence, the same names can be given to the homologous 

 bones in widely different animals. We see the same great 

 law in the construction of the mouths of insects : what can 

 be more different than the immensely long spiral proboscis 

 of a sphinx-moth, the curious folded one of a bee or bug, 

 and the great jaws of a beetle ? Yet all these organs, serv- 

 ing for such widely different purposes, are formed by in- 

 finitely numerous modifications of an upper lip, mandibles, 

 and two pairs of maxillae. The same law governs the con- 

 struction of the mouths and limbs of crustaceans. So it is 

 with the flowers of plants. 



Nothing can be more hopeless than to attempt to explain 

 this similarity of pattern in members of the same class, by 

 utility or by the doctrine of final causes. The hopelessness 

 of the attempt has been expressly admitted by Owen in his 

 most interesting work on the " Nature of Limbs." On the 



