INTRODUCTION. 9 



Still our classification would most certainly be imperfect, and 

 in some cases altogether incorrect. In some instances the 

 parts of the machine would be so complex as to be utterly in- 

 comprehensible, and in many cases our ignorance of what 

 each was intended to effect would be an insuperable bar to 

 our arriving at any arrangement. Suppose now, however, 

 that all the machines were suddenly set in motion, so that we 

 could see not only the manner in which they were constructed 

 and the materials of which they were composed, but could 

 also see what they could do — could see, in fact, for what work 

 each is intended. The task of arrangement now becomes im- 

 mensely easier. Our previous classification, founded simply 

 upon the structure of the machines, is now supplemented and 

 rectified by our knowledge of what each is able to efiect. 

 One machine is found performing one set of actions,«another a 

 diflerent set ; and in this way not only is our classification 

 rendered much easier, but we now get an insight into the 

 meaning and nature of many points of structure which were 

 formerly obscure. 



To make this illustration fully meet the case of the natu- 

 ralist who deals with living beings only, we have simply to 

 suppose that the machines to be examined are reasonably per- 

 fect in their parts and fit for work, and that our imaginary 

 workshop is supplied with a reasonable amount of light, not 

 very brilliant, perhaps, and striking upon some objects more 

 sharply than on others, but still upon the whole moderately 

 steady and uniform. Far worse, however, is the case of the 

 naturalist who has to deal with the remains of extinct gen- 

 erations of animals and plants, whose work lies among those 

 relics of a by-gone world which are known as " fossils " or 

 " petrifactions " — objects in many cases more wonderful and 

 more perplexing and more beautiful than the most ornate and 

 elaborate productions of human skill. In his case the work- 

 shop is a vast and gloomy vault or charnel-house, with no in- 

 ternal source of light, and but fitfully illuminated by uncer- 

 tain gleams from the world without. And what is worse than 

 this, his machines are mutilated and defaced, in many cases 

 wanting their most important parts, in all cases destitute of 

 life and motion, and usually very unlike any thing visible at 

 the present daj'. Nevertheless it is almost incredible with 

 what certaintj' and precision a mere fragment of a fossil, a 

 single tooth or bone, can be referred by a skilled worker in 

 this field of science to its proper place in the animal kingdom 

 — with what exactitude the missing parts can be restored — 



