MOnPHOLOGT. 451 



striking by tlie 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 conformity to type, 

 without getting much nearer to an explanation of the 

 phenomenon;" and he then adds '^but is it not powerfully 

 suggestive of true relationship, of inheritance from a 

 common ancestor?" 



Geoifroy St. 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, serving for such widely different purposes, 

 are formed by infinitely numerous modifications of an upper 

 lip, mandibles, and two pairs of maxillae. The same law 

 governs the construction of the mouths and limbs of 

 crustaceans. So it is with the flowers of plants. 



Nothing can be more hopeless than to attempt to ex- 

 plain 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 ordinary view of the independent creation 

 of each being, we can only say that so it is; that it has 

 pleased the Creator to construct all the animals and plants 

 in each great class on a uniform plan; but this is not a 

 scientific explanation. 



The explanation is to a large extent simple, on the theory 

 of the selection of successive slight modifications, each 

 being profitabxo in p/^-^e way to the modified form, but 

 often affecting ly correlation other parts of the organizar- 

 tion. In changes of this nature, there will be little or no 

 tendency to alter the original pattern, or to transpose the 



