360 MORPHOLOGY. [CHAP. XIV. 



to serve as a fin ; or a webbed hand might have all its bones, or 

 certain bones, lengthened to any extent, with the membrane 

 connecting them increased, so as to serve as a wing ; yet all these 

 modifications would not tend to alter the framework of the bones 

 or the relative connexion of the parts. If we suppose that an 

 early progenitor the archetype as it may be called of all 

 mammals, birds, and reptiles, had its limbs constructed on the 

 existing general pattern, for whatever purpose they served, we 

 can at once perceive the plain signification of the homologous 

 construction of the limbs throughout the class. So with the 

 mouths of insects, we have only to suppose that their common 

 progenitor had an upper lip, mandibles, and two pairs of maxillae, 

 these parts being perhaps very simple in form ; and then natural 

 selection will account for the infinite diversity in the structure 

 and functions of the mouths of insects. Nevertheless, it is con- 

 ceivable that the general pattern of an organ might become so 

 much obscured as to be finally lost, by the reduction and 

 ultimately by the complete abortion of certain parts, by the 

 fusion of other parts, and by the doubling or multiplication of 

 others, variations which we know to be within the limits of 

 possibility. In the paddles of the gigantic extinct sea-lizards, and 

 in the mouths of certain suctorial crustaceans, the general pattern 

 seems thus to have become partially obscured. 



There is another and equally curious branch of our subject; 

 namely, serial homologies, or the comparison of the different parts 

 or organs in the same individual, and not of the same parts or 

 organs in different members of the same class. Most physiologists 

 believe that the bones of the skull are homologous that is, 

 correspond in number and in relative connexion with the 

 elemental parts of a certain number of vertebrae. The anterior 

 and posterior limbs in all the higher vertebrate classes are plainly 

 homologous. So it is with the wonderfully complex jaws and legs 

 of crustaceans. It is familiar to almost every one, that in a flower 

 the relative position of the sepals, petals, stamens, and pistils, as 

 well as their intimate structure, are intelligible on the view that 

 they consist of metamorphosed leaves, arranged in a spire. In 

 monstrous plants, we often get direct evidence of the possibility 

 of one organ being transformed into another ; and we can actually 

 see, during the early or embryonic stages of development in 

 flowers, as well as in crustaceans and many other animals, that 

 organs, which when mature become extremely different are at 

 first exactly alike. 



How inexplicable are the cases of serial homologies on the 

 ordinary view of creation ! Why should the brain be enclosed 

 in a box composed of such numerous and such extraordinarily 

 shaped pieces of bone, apparently representing vertebrae? As 



