of the Vertebrate Skeleton. 27 



each other by close comparison, if they are in the same divi- 

 sion of the body. And there being this sequence, the form of 

 parts only changing with the changed function of different 

 regions of the body, it will be legitimate reasoning, if we can 

 discover a law capable of accounting for a primitive initial 

 segment, to conclude that the continuous operation of that law 

 would eventually segment the entire animal, if an animal 

 capable of being encased in a segmented covering already 

 existed. 



According to the laAvs of growth, we find that differentiation 

 of parts is due to the kinetic energy of the individual or to 

 tlie potential energy of its organization — and that no organic 

 energy is lost, but becomes accumulated in the individual long- 

 after the mobility of the parts ceases, and then is transmitted 

 with and added to the common stock of energy to be inherited. 

 If this inlierited energy is such that it is capable of being- 

 manifested within the mobile period of life, then it will stamp 

 its characteristic marks upon the organism. But if it is too 

 general to be manifested during that period, it takes a poten- 

 tial form, and may even remain latent for several generations 

 and accumulate, and then, instead of being developed kineti- 

 cally in the individual, it at an early period is merged in the 

 common stock, and appears kinetically in the organization, 

 and potentially in the individual, as a new part. 



Thus in Ophidians, which exert continually an intense 

 muscular force upon every joint of the vertebral column, we 

 find that the kinetic energy is manifested in giving to the 

 bones great density, sharpness of definition, and perfect ossifi- 

 cation, but never in the partial formation of a growth like 

 an epiphysis, between vertebra3. Yet, if the views which 

 I urge are true views, there should be some result, in in- 

 creased ossification, of aU this muscular power ; and the 

 result is found in the numerical increase of the vertebrae, so 

 that in Ophidians they sometimes number 400 or 500. But 

 this increase is potential, and takes place at so early a period 

 that the newly added segment (vertebra3, muscles, nerves, &c.) 

 is developed equally with the others. If the increase takes 

 place in the thoracic region, it necessarily elongates the viscera ; 

 if the tail is lengthened, by comparison the body appears to be 

 shortened. 



If we take another type, that of the Anm-ous Amphibia, 

 which do not display muscular power by wrigglings v/hich 

 press and pull the vertebrse, as among serpents, but progress 

 by leaping, and keep the body removed from the ground, ex- 

 cept at the caudal style, the power, both kinetic and potential, 

 acts chiefly on the limbs — kinetically in the elongation and 



