602 SPECIAL METHODS OF DISCOVEKY. 



By digging in gravel-pits at Abbeville, in Picardy, 

 M. Boucher de Perthes, in 1847, discovered rough stone 

 hatchets associated with relics of extinct animals, and was 

 thereby enabled to infer and discover that man must have 

 existed upon the earth ages previous to the earliest periods 

 of history, or even of tradition; and this inference has 

 since been abundantly confirmed by a number of dis- 

 coveries of a similar kind in other places. 



In the concrete science of biology also, our greatest 

 discoveries have been arrived at by means of inference. 

 Lamarck (born in 1747), by the study of such living 

 things as snails, worms, insects, shell-fish, sea-anemones, 

 sponges (to which he gave the name of ' invertebrate 

 animals,' because they have no backbone), and from the 

 impossibility of determining what were distinct forms or 

 species, was led to infer and discover the defective nature 

 of the theory of distinct species, and to conclude that 

 all the immense variety of animals were not separately 

 created, but were probably evolved by the gradual alteration 

 and differentiation of a few simple forms during a long 

 series of ages ; and that differences of climate and of food 

 formed a part of the cause of their change. Having also 

 discovered, by observation, that the lower animals are 

 more like each other than the upper ones, and that those 

 which are more nearly related to the common stock are 

 more nearly alike than are those more distantly related, 

 he was led to partly discover, by inference, the probability 

 that all animals form a great system of series of living 

 things, springing from a single ancestor, just as the branches 

 of a tree arise from a parent stem. Cuvier also, the great 

 comparative anatomist and osteologist (who was born in 

 1769), was a great collector and classifier of facts in his own 

 particular subject. By inference based upon comparison 

 he discovered that all the different parts of any one animal 



