Ryder.] 544 [Oct. 18, 



grown. It may be shown Ihat traces of the more primitive biconcave 

 matrix of the vertebral bodj' are embtflded within the cartilaginous or 

 even osseous matrix of the later stages as seen in some Batrachia and 

 reptiles. It may also be shown that the epiphyses of the centra of higher 

 types have their cartilaginous bases developed as ingrowing proliferations 

 from the cartilage formed outside of the more primordial calcifying matrix 

 which is broken or interrupted into a regular succession of recurring rings 

 by the flexures of the body induced by the muscles during locomotion. 

 This process of cartilaginous invasion begins to show itself in the very 

 lowest of the true fishes or Lyrifera, viz., CMmmra. 



There has been not even a partial abandonment of the primordial 

 method of development of the vertebral bodies until we meet with forms 

 which undergo a prolonged and complete development in ovo or in iitero. 

 There has, therefore, been no deviation from the primitive method of 

 evolution of the calcified, flexible, jointed vertebral column vintil forms 

 are reached in which specialization is so extreme as to require as an 

 absolute physiological necessity an abbreviation of the processes of develop- 

 ment of the column. Yet even in the most abbreviated form of develop- 

 ment, as seen in Mammalia, including man, unmistakable traces are left 

 over of the once biconcave condition of the vertebral segments. It may 

 be shown that the physiological, histological, chemical, physical and me- 

 chanical conditions render the biconcave vertebral body the only one 

 which is possible in tlie primitive condition ; it therefore follows that there 

 was no natural selection possible after the notocliord was formed. There 

 was only one groove, so to speak, along which the progressive evolution 

 of the segmented, calcified, vertebral axis of vertebrates could proceed. 

 There was no turning back once the notocliord or vertebral matrix had 

 been formed. The advent of the notochord "ordained the becoming," to 

 borrow a phrase from Owen, of the future jointed column, and all the 

 variations of the latter as manifested in species are the mere expressions ot 

 adaptive by-play. The same grounds are taken by Geddes in the discus- 

 sion of tlie evolution of epigyny through perigyny and hypogyny in flow- 

 ering plants. 



Natural selection has therefore had absolutely nothing to do with the 

 genesis of the primordial type from which all vertebral axes are evolved. 

 At most the action of natural selection must be extremely indirect, and 

 could in no way be operative except through the notochord, which may 

 be shown to be a modified derivative of the intestinal wall of the same 

 histological nature as the cellular axial cords of the tentacles of Hydrozoa 

 and Scyphozoa. If it is possible to exclude natural selection it is also pos- 

 sible in a great measure to exclude the eflects of inheritance. If it can be 

 shown that the only thinkable or conceivable method of evolution ot 

 a jointed yet calcified and flexible vertebral axis is that actually realized, 

 how is it possible to prove that inheritance even has anything to do with 

 its development beyond providing for the ontogenetic recapitulation of its 

 cellular matrix, the notochord and the arrangement of the muscles in a 



