d INTRODUCTORY LECTURE. 



are not explicable on any known chemical or mechanical principles, 

 they are called "vital" acts, and so long as they are continued the 

 plant or animal is said to " live." A mineral or unorganised body can 

 undergo no change save by the operation of mechanical or chemical 

 forces ; and any increase of its bulk is due to the addition of like 

 particles to its exterior: it augments not by "growth" but by 

 " accretion." 



Organised beings differ so much more from the unorganised than 

 they do from each other, that the co-equality of the three Linnaean 

 kingdoms of nature is no longer admitted, and the primary division 

 of natural bodies is into " organic" and " inorganic," the former being 

 collectively designated " organisms." For the distinction of these into 

 two kingdoms, moreover, the Linnasan diagnosis no longer suffices. 

 Nothing seems easier than to distinguish a plant from an animal, and 

 in common practice as regards the more obvious members of both king- 

 doms no distinction is easier; yet as the knowledge of their nature has 

 advanced the difficulty of defining them has increased, and seems now 

 to be insuperable. Not that the lack of such power of definition is 

 any loss to the Naturalist, if he has gained, instead, a truer conception 

 of the fundamental unity of all organic nature. 



Any circumscription of the Animal Kingdom must, therefore, be 

 arbitrary, as will, I think, be evident from the following consider- 

 ations. 



Linnosus was not aware that many movements in unquestionable 

 animals, that seem to be " spontaneous," are not so. Experiment had 

 not proved that all those of Hartley's first class * depending on 

 nervous influence, " which is detached down the motory fibres before 

 reaching the brain," are unaccompanied by sensation, and inde- 

 pendent of volition. f It has, indeed, been remarked Avith regard to 

 this difficulty, that " if we always possessed the means of determining 

 where consciousness and spontaneity do and do not exist, we should 

 have comparatively little difficulty in drawing a definite line of demar- 

 cation between " plants and animals." J Yet, in point of fact, we should 

 then have merely a psychical character, which, in reference to other 

 characters purely physiological, anatomical, and chemical, might 

 prove after all to be an artificial one, drawing the boundary-line as 

 arbitrarily as would be done by any other single character. But 

 taking the power of self-motion, irrespective of its cause in living 



* n. Vol.i. p. 97. 



f III. p. 190, where the author, after detailing certain experiments, concludes 

 from them, '* that thei'c is a property of the sentient and motory system of nerves, 

 which is independent of sensation and volition." 



X IV. p. 182. 



