INTRODUCTION. 11 



cell and an organism can be determined only by tracing out 

 the life-history in each. 



DISTINCTIONS BETWEEN VEGETABLES AND ANIMALS. 



Many attempts have been made to separate vegetables from 

 animals. The cell being common to both groups, attempts 

 have been made to separate them by its means. A sphere 

 of homogeneous membrane intervening between nucleus and 

 wall of the vegetable cell, not peculiar to it; an analogous 

 membrane is seen in cartilage cell. 



There is no difficulty in separating high plant from high 

 animal, as, for example, a horse from a tree; but acknowl- 

 edged difficulty in distinguishing low forms, as a sponge 

 from a Protococcus, an Am&ba from an (Ethalmm. But, as a 

 rule, confusion obtains not so much among the very lowest 

 forms of animal and vegetable life, as, for example, between 

 Rhizopoda and Protophytse, as it does between others higher 

 in the scale, as between certain Infusoria and Fungi, as the 

 Myxomycetes. 



Linnaeus' definition: "Stones grow; plants grow and live; 

 animals grow, live and feel." 



Objections. Stones do not grow, but increase in size by 

 accretion. Feeling may be said to exist in the lower classes of 

 both plants and animals, provided that contractility be accepted 

 as a property of sensitive tissue. If it be surmised that pain 

 is a result of feeling (i. e. sensation), it may be attributed to 

 CEthalium with equal propriety as to Amoeba. Were every 

 act of fissuration, evisceration or amputation accompanied 

 with pain, it becomes difficult to understand why self-mutila- 

 tion should be so frequently imposed for the preservation 

 of both individual life and that of the species (see p. 120). It 

 is probable that at such times an organism feels no more 

 pain than is experienced by the contractile contents of an 

 ovum undergoing segmentation. 



Among the attempts which have been made to separate 

 plants from animals, may be mentioned the following 

 placed, for convenience, in the form of propositions and ob- 

 jections: 



