244 THE O RIG IS OF Sl'EdElS 



functions of the months of insects. Nevertheless, it is 

 conceivable that the general pattern of an organ niiglit 

 become so much obscured as to be linally lost, by the 

 reduction and ultimately by the complete abortion of 

 certain parts, by the fusion of other ])arts, and by the 

 doubling or multiplication of others — variations which we 

 know to be within the limits of possibility. In the pad- 

 dles of the gigantic extinct sea-lizards, and in the mouths 

 of certain suctorial crustaceans, the general pattern seems 

 thus to have become })artially ol)Scured. 



There is another and equally curious branch of our 

 subject; namel}', 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 tiie si<:ull are homologous — that is, correspond in 

 number and in relative connection — 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 com- 

 plex 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 



