108 MORPHOLOGICAL DEVELOPMENT. 



tion no more discloses any such homology than does general 

 appearance. "Bemak," says Prof. Huxley, "has more fully 

 proved than any other observer, the segmentation into ' ur- 

 wirbel,' or proto-vertebroe, which is characteristic of the ver- 

 tebral column, stops at the occipital margin of the skull — 

 the base of which, before ossification, presents no trace of 

 that segmentation which occurs throughout the vertebral 

 column." 



Consider next the evidence supplied by comparative mor- 

 phology. In preceding sections (§§ 206, 208,) it has been 

 shown that among annulose animals, the divisibility into 

 homologous parts is most clearly demonstrable in the lowest 

 types. Though in decapodous Crustaceans, in Insects, in 

 Arachnids, there is difficulty in identifying some or many of 

 the component somites ; and though when identified they 

 display only partial correspondences ; yet on descending to 

 Annelids, the composition of the entire body out of such 

 somites becomes conspicuous, and the homology between each 

 somite and its neighbours is shown by the repetition of one 

 another's structural details, as well as by their common 

 gemmiparous origin: indeed, in some cases we have the 

 homology directly demonstrated by seeing a somite of the 

 body transformed into a head. If, then, a vertebrate animal 

 had a segmental composition of kindred nature, we ought to 

 find it most clearly marked in the lowest Vertebrata, and 

 most disguised in the highest Vertebrata. But here, as be- 

 fore, the fact is just the reverse. Among the Vertebrata of 

 developed type, such segmentation as really exists remains 

 conspicuous — is but little obscured even in parts of the spinal 

 column formed out of integrated vertebra3. Whereas in the 

 undeveloped vertebrate type, segmentation is scarcely at all 

 traceable. The Amphioxus, Fig. 191, is not only without 

 ossified vertebras ; not only is it without cartilaginous re- 

 presentatives of them ; but it is even without anything like 

 distinct membranous divisions. The spinal column exists 

 as a continuous notochord : the only signs of incipient seg- 



