3 8 4 Morphology. chap. xiv. 



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 physiolo- 

 gists 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 vertebra. 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 

 oan actually see, during the early or embryonic stages of develop- 

 ment 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 vertebra?? As 

 Owen has remarked, the benefit derived from the yielding of the 

 separate pieces in the act of parturition by mammals, will by no 

 means explain the same construction in the skulls of birds and 

 reptiles. Why should similar bones have been created to form 

 the wing and the leg of a bat, used as they are for such totally 

 different purposes, namely flying and walking ? Why should one 

 crustacean, which has an extremely complex mouth formed of 

 many parts, consequently always have fewer legs ; or conversely, 

 those with many legs have simpler "mouths ? Why should the 

 sepals, petals, stamens, and pistils, in each flower, though fitted 

 for such distinct purposes, be all constructed on the same pattern? 



On the theory of natural selection, we can, to a certain extent, 

 answer these questions. We need not here consider how the bodies 

 -of some animals first became divided into a series of segments, 

 or how they became divided into right and left sides, with corre- 

 sponding organs, for such questions are almost beyond investiga- 

 tion. It is, however, probable that some serial structures are 

 the result of cells multiplying by division, entailing the multi- 



