322 THE LAW OF EVOLUTION. 



The like process, variously exemplified in other organs, is 

 meanwhile exhibited by the body as a whole; which 

 becomes integrated somewhat' in the same way that 

 an outspread handkerchief and its contents become in- 

 tegrated when its edges are drawn in and fastened to make 

 a bundle. Analogous changes go on long after 



birth, and continue even up to old age. In man, that solidi- 

 fication of the bony framework which, during childhood, is 

 seen in the coalescence of portions of the same bone ossified 

 from different centres, is afterwards seen in the coalescence 

 of bones that were originally distinct. The appendages of 

 the vertebrse unite with the vertebral centres to which they 

 belong a change not completed until towards thirty. At 

 the same time the epiphyses, formed separately from the 

 main bodies of their respective bones, have their cartilagi- 

 nous connexions turned into osseous ones are fused to the 

 masses beneath them. The component vertebras of the 

 sacrum, which remain separate till about the sixteenth year, 

 then begin to unite ; and in ten or a dozen years more their 

 union is complete. Still later occurs the coalescence of the 

 coccygeal vertebrae; and there are some other bony unions 

 which remain unfinished unless advanced age is reached. 

 To which add that the increase of density and toughness, 

 going on throughout the tissues in general during life; is the 

 formation of a more highly integrated substance. 



The species of change thus illustrated under several 

 aspects in the unfolding human body, may be traced in all 

 animals. That mode of it which consists in the union of 

 similar parts originally separate, has been described by 

 Milne-Edwards and others, as exhibited in various of the 

 Invertebrate though it does not seem to have been in- 

 cluded by them as an essential peculiarity in the process of 

 organic development. We shall, however, see clearly that 

 local integration is an all-important part of this process, 

 when we find it displayed not only in the successive stages 

 passed through by every embryo, but also in ascending from 



