10 EVOLUTIONS OF ORGANIZATION. 



position of the digestive system throughout the 

 animal kingdom, the truth at the bottom of Hackel's 

 gastrsea theory; and that he so far appreciated the 

 relation of the segmented invertebrata to the verte- 

 brata as to perceive that, while in certain lower 

 forms the nervous system completed a circle round 

 the mouth, in the invertebrate segmentata the nerv- 

 ous centres were concentrated on the under, and in 

 the vertebrata on the upper side ; seeing in this 

 what Oken had already observed through the 

 organic world, and what so skilled and accurate an 

 observer as Dana 1 has more recently recognized in 

 this very matter, a system of expression in nature, 

 according to which things of highest dignity are 

 placed uppermost. 



In France, Etienne Geoffroy St. Hilaire, claiming 

 to be free from all a priori fancies, but acknowledg- 

 ing the influence which the definition of Leibnitz 

 had on him, that " the order of the universe is variety 

 in unity," was led to the conception of the "unity 

 of organization" by the results of researches into 

 points of detail ; and collecting those detailed 

 researches in one work, his " Philosophic Anatom- 

 ique," he commences by asking, "Can the organi- 

 zation of vertebrate animals be reduced to one 



*J. D. Dana "On Cephalization," &c. Ann. and Mag. Nat. Hist., 

 Sept., 1863. 



