350 Dr Barry on the Unity (^Structure in 



When the great Meckel said, " the higher animal in its de- 

 velopment, passes through essentially the lower and permanent 

 grades ; by which periodical differences, and differences between 

 classes, may be brought together ;" * he evidently meant no 

 more, than that there occurred in the development of a single 

 organism, a modified reappearance of structures common to other 

 animals ; and further, that he did not intend to say that all the 

 structures of all " lower" animals reappear in the development 

 of each of the " higher," is evident from a remark he uses in re- 

 ply to one of the objections made by Feiler ;-f- on which occasion, 

 Meckel says, " It is perfectly indifferent, whether the human 

 embryo passes through all, or only some of the grades of forma- 

 tion ; if certainly ascertained facts demonstrate that it passes 

 through many, that it always passes through them, and 

 therefore that the analogies in question are not accidental." j 



It may not be improper, by a few of the facts on which 

 MeckePs proposition appears to have been grounded, to exemplify 

 some of the conclusions at which we arrived when last on this 

 subject ; and by quoting which, we commenced the present paper. 



The uniform appearance first, in the osseous system of the 

 Vertebrata, of what are called the arches of the vertebrae, is re- 

 ferrible at once to the law determining the order in which struc- 

 tures essentially the same in a whole class of animals, manifest 

 themselves in individual development ; and to the law of unifor- 

 mity in the manner of development. If in the Cephalopoda, 

 there is permanently no more than the trace of a spinal column, 

 corresponding to the arches of the vertebrae, it shews that the 

 last degree of development in these animals, is sufficient to pro- 

 duce no more than an approximation to the Vertebrata ; but 

 that, so far as they do go, they proceed, in this respect at least, 

 by nearly the same road. 



If the ilium is the first pelvic bone that becomes ossified in 

 animals possessing a pelvis, || and if there be an animal in which 

 this is the only portion of the pelvis present ; this shews unde- 



* System der Vergleichenden Anatomie ; erster Theil, S. 396. Halle, 1821. 

 f Ueber angeborne menschliche Misbildungen im Allgemeinen und Hor- 

 maphroditen insbesoudere. Landshut, 1820. 



$ L. c. p. 411, 412. Mec-kel, 1. c. p. 399. 



I Meckel, 1. c. p. 400. 



