14 NATURAL HISTORY. 



fishes are not only still valuable, but they embrace certain 

 points which have only been verified and thoroughly 

 elucidated within the present century. 



Not only was Aristotle an admirable observer, but he 

 often exhibits a remarkable power of generalisation. 

 Hence he recognised in various instances the existence 

 of biological laws, which have been firmly established 

 only in quite modern times. Thus, he recognised that 

 there often exists a real relationship what is now called 

 a relationship of 'homology' between apparently dis- 

 similar parts or organs in different animals. For example, 

 he points out that there exists an agreement of this kind 

 between a claw and a nail, or between the feather of a 

 bird and the scale of a fish. Again, he clearly divined the 

 law of what is now known as the law of the * correlation 

 of organs' namely, that certain organs, which are not 

 necessarily in obvious connection with one another, are 

 only found in association with one another, or that certain 

 other organs which, for aught we see, might quite well 

 coexist, are never found in the same animal. Thus, he 

 points out that no quadruped possesses both horns and 

 tusks, and that most animals with horns are two-hoofed ; 

 while he adds that a one-hoofed animal with horns (such 

 as the unicorn of heraldry) had never been observed. 

 Similarly he points out that all winged insects which have 

 stings at the fore part of the body (what he calls the sting 

 in these cases consists really of pointed or lancet-like 

 jaws) are two- winged, while those which have the sting 

 at the hinder end of the body are four-winged. 



It should be said that Aristotle was essentially what we 

 should now call a * teleologist ' that is to say, he generally 



