10 EVOLUTIONS OF ORGANIZATION. 
position of the digestive system throughout the 
animal kingdom, the truth at the bottom of Hackel’s 
gastrea 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! 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 griorz 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 “ Philosophie Anatom- 
ique,’ he commences by asking, “Can the organi- 
zation of vertebrate animals be reduced to one 
1J. D. Dana ‘‘On Cephalization,”” &c. Ann. and Mag. Nat. Hist., 
Sept., 1863. 
