ADVANCE OF ZOOLOGY. 25 



external resemblance are produced over and over 

 again in Nature, and do not always point to phy- 

 letic affinity, while Homology is one of our safest 

 guides. The relations of organs to each other, or 

 the idea that one structure is sacrificed for the 

 development of another, now known as the law of 

 Economy of Growth, was also perceived by Aris- 

 totle, but was first clearly stated by Goethe in 1807, 

 and by St. Hilaire in 1818. Aristotle, following 

 Democritus, was strongly impressed with the law 

 of Adaptation, or the wonderful fitness of certain 

 structures for certain ends, and Adaptation, with 

 all its beautiful manifestations in Nature, has always 

 been the focus of the differences between the 

 Special Creationists and Evolutionists. 



Degeneratioji^ox the gradual decline of structures 

 in form and usefulness, does not appear to have 

 been perceived by Aristotle, although in his analy- 

 sis of " Movement " he employs a very similar idea 

 in connection with development. We first meet 

 with Degeneration as part of an explanation of the 

 origin of species, in the writings of Linnsus and 

 Buffon in the eighteenth century ; but the idea 

 itself was much older, because we find it expressed 

 in a passage of criticism of Sylvius upon Vesa- 

 lius. Vesalius (15 14-1564) had brought the charge 

 against Galen (a.d. 131-200) that his work could 

 not have been founded upon the human body, be- 

 cause he had described an intermaxillary bone. 

 This bone, Vesalius observed, is found in the lower 



