144 HISTORY OF 



the error. Thus it may often happen, that in a 

 lax system of natural history, a creature may be 

 ranked among quadrupeds that belongs more pro- 

 perly to the fish or the insect classes. But that can 

 produce very little confusion, and every reader can 

 thus make a system the most agreeable to his own 

 imagination. It will be of no manner of conse- 

 quence whether we call a bird or an insect a quad- 

 ruped, if we are careful in marking all its distinc- 

 tions : the uncertainty in reasoning, or thinking, 

 that those approximations of the different kinds 

 of animals produce, is but very small, and hap- 

 pens but very rarely ; whereas the labour that na- 

 turalists have been at to keep the kinds asunder, 

 has been excessive. This, in general, has given 

 birth to that variety of systems which we have just 

 mentioned, each of which seems to be .almost as 

 good as the preceding. 



Taking, therefore, this latitude, and using me- 

 thod only where it contributes to conciseness or 

 perspicuity, we shall divide animated nature into 

 four classes ; namely, quadrupeds, birds, fishes, 

 and insects. All these seem in general pretty 

 well distinguished from each other by nature ; yet 

 there are several instances in which we can scarce- 

 ly tell whether it is a bird or quadruped that we 

 are about to examine ; whether it is a fish or an 

 insect that offers to our curiosity. Nature is varied 

 by imperceptible gradations, so that no line can be 

 drawn between any two classes of its productions, 

 and no definition made to comprehend them all. 

 However, the distinctions between these classes 

 are sufficiently marked, and their encroachments 



