392 MORPHOLOGY. Ciiai-. XIII, 



ineinl)rane connectin*^ them increased, so as to serve as a wing; 

 yet all this modification would not tend to alter the framework 

 of the lx)nes or tlie relative connection of the parts. If wo 

 suppose that an early progenitor — the archetype as it may be 

 called — of all mammals, had its limbs constructed on the ex- 

 isting general pattern, for wliatever puq->ose they served, we 

 can at once perci'ive the plain signification of the homologous 

 construction of the limbs throughout the class. So ^vith the 

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

 }>rogeiiitor had an upper lip, mandibles, and two pair of max- 

 illiT?, these i>arts being jjerhaps very simple in form; and then 

 natural selection will account for the infinite diversity in the 

 structure and functions of the mouths of insects. Neverthe- 

 less, it is conceivable that the general pattern of an organ 

 might become so much obscured as to be finally lost, by the 

 redaction and ultimately by the complete abortion of certain 

 jKirts, by the fusion of other parts, and by the doubling or mul- 

 tii)li('ation of others — variations which we know to be within 

 the limits of possibility. In the paddles of the gig-antic ex- 

 tinct sea-lizards, and in the mouths of certain suctorial crusta- 

 ceans, the general pattern seems thus to have been partially 

 obscured. 



There is another and equally curious branch of our present 

 subject ; namely, the comparison, not of the same parts or or- 

 gans in different members of the same class, Init of the differ- 

 ent parts or organs in the same individual. Most physiologists 

 believe that the bones of the skvill are homologous with — that 

 is, correspond in number and in relative connection with — the 

 elemental parts of a certain number of vertebnv. llie anterior 

 and pt)sterior limbs in all the higher vertebrate classes are 

 ])lainly 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 ]x>sition of the sepals, petals, 

 stamens, and pistils, as well as their intimate structure, are in- 

 telligible on the view that they consist of metamorphosed 

 l(\ives, 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 em- 

 bryonic stages of development in flowers, as well as in crusta- 

 ceans and many other animals, that organs, which when mature 

 become extremely different, are at first exactly alike. 



How inexplicable are these facts on the ordinary view of 

 creation ! Why should the brain be enclosed in a box com- 



