THE naturalist's OCCUPATION. 39 



at the head of which stands man himself. We do not 

 know when nor how this metamerism of the vertebrate 

 arose ; but, both embryology and paleontology afford 

 ample evidence that it existed long before it took the 

 form of vertebrae. Among the earlier and extinct forms 

 of fishes are found some without bony vertebrae, but still 

 divided into segments ; and in the development of the 

 fishes and other vertebrates of to-day, we find that the 

 vertebrae are preceded and predetermined by a primor- 

 dial division of the trunk into a series of uniform seg- 

 ments. This division appears very early in the embryo, 

 long before there is any cartilage or bone, and before 

 there is any trace of limbs, or indeed of any distinctive 

 vertebrate organ, except the cordal axis referred to in 

 speaking of the ascidian larva. Now this primordial 

 segmentation carries us back to a stage in the evolution 

 or phylogeny of vertebrates, so full of meaning that its 

 contemplation would seem to be enough to arouse the 

 interest of the most worldly-minded. 



This is a stage through which every vertebrate passes 

 on its way from the ^^^ to the adult, a stage in which 

 the fish, the amphibian, the reptile, the bird, the beast, 

 and man find a common level, and in which every title 

 to superior rank lies in unexpressed potentialities. But 

 more than this ; for it is here that the vertebrate is an 

 invertebrate, and stands beside its prototype, the seg- 

 mented worm. On the same metropolitan plain, the 

 lobster, the crab, the insect, in short all the members 

 of the great arthropod group, meet and acknowledge 

 their community of descent. Thus, the great branches 

 of the genealogical tree represented in the higher types 

 first defined by Cuvier converge and unite in a common 



