THE ORGANIC AND THE INORGANIC 291 



of consciousness, in so far as we can say that other 

 animals than ourselves possess it, is no distinction 

 between the two kingdoms of life. Consciousness, 

 judged by the degree of development of motility, must 

 be supposed to be absent or very dim in the extreme 

 cases of parasitism attained by some animals ; on the 

 other hand, we may assume that it is present, to some 

 extent at least, in the highly motile zoospores of the 

 Algae. Thus some lower organisms, the Peridinians 

 and the algal spores, exhibit all the characters which 

 we utilise in separating animals from plants — the 

 chlorophyllian apparatus, by means of which the 

 kinetic energy of solar radiation becomes transformed 

 into the potential energy of organic chemical com- 

 pounds ; the apparatus of receptor and motile organs, by 

 means of which the potential energy of stored chemical 

 compounds passes into the kinetic energy of bodily 

 movements ; and the existence (so far as we can say 

 that it exists in organisms other than ourselves) of 

 some degree of consciousness. 



Neither do those morphological schemata which we 

 construct as diagnostic of phyla, or classes, or orders, 

 etc., separate these groups from each other so clearly 

 and unequivocally as our classifications suggest. It 

 might seem for instance that the presence or absence 

 of a notochord would sharply distinguish between the 

 vertebrate and invertebrate, but structures which 

 suggest in their development the true notochordal 

 skeleton of the typical vertebrate animal are to be 

 traced in animals which exhibit few or none of the 

 characters which we regard as diagnostic of the Verte- 

 brate. Typical Arthropods and typical Vertebrates 

 seem to be distinct from each other, but the extinct 

 Ostracoderms of Silurian times may have been animals 

 which possessed an internal axial skeleton, and which 



