Chap. XIV.] MORPHOLOGY. 233 



Geoffroy St. Hilaire has strongly insisted on the high 

 importance of relative position or connexion in homo- 

 logons 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 fore-arm, 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 

 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 ordinary view of the 

 independent creation of each being, we can only say 

 that so it is ; — that it has pleased the Creator to con- 

 struct 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 modifica- 

 tions, — each modification being profitable in some way 

 to the modified form, but often affecting by correlation 

 other parts of the organisation, In changes of this 



