xxxii THE ANIMAL KINGDOM. 



man cannot read other men's minds ; he judges of their mental processes by their 

 actions and his own mental processes. In the same manner we conclude that animals 

 reasoTi by judging of their acts alone. If human psychology is an inexact science, 

 much more so is comparative psychology, which includes human as well as animal 

 psychology. 



Although the Amceba performs operations which are akin to the instinctive acts 

 of higher animals, it may in general be said that the nervous system is the organ of 

 mind ; not the brain alone, in animals which have a brain, but the entire nervous 

 system. The mental manifestations of animals are not alone physiological, i. e. auto- 

 matic and reflex, but there are, at least in highly organized animals, such as crabs, 

 insects, spiders, and vertebrates, processes which are psychological as opposed to 

 physiological. 



The elementary or root principle of mind, as distinguished from purely ])hysio- 

 logical processes, is the power of making a choice between two alternatives presented 

 to the animal. 



As we have said on another occasion, granted that insects have sensibilities, how 

 are we to prove that they have an intellect ? Simply by observing whether they make 

 a choice between two acts. " On entering a closet, ants unhesitatingly direct their 

 steps to the sugar-bowl in preference to the flour-barrel ; one sand-wasp prefers beetle- 

 grubs to caterpillars, to store up as food for her young. In short, insects exercise 

 discrimination, and this is tlie simplest of intellectual acts. They try this or that 

 method of attaining an object. In fact, an insect's life is filled out with a round of 

 trials and failures." 



While no one would doubt that an insect has the power of choice or discrimination, 

 may this also be said of the lowest organisms, such as the Anaceba ? Mr. Romanes 

 believes that it can. "Amoeba is able to distinguish between nutritious and non- 

 nutritious particles, and in correspondence witli this one act of discrimination it is 

 able to perform one act of adjustment ; it is able to enclose and to digest the nutri- 

 tious particles, while it rejects the non-nutritious." Some proto])lasmic and unicellular 

 organisms are able also to distinguish between light and darkness, and to adapt their 

 movements to seek the one and shun the other; Mr. H. J. Carter thinks that the 

 beginnings of instinct are to be found so low down in the scale as the Rhizopoda. 

 As quoted by Romanes in his Animal Intelligence: "Even Athealium will confine 

 itself to the water of the watch-glass in which it may be placed when away from saw- 

 dust and chips of wood among which it has been living ; but if the watch-glass be 

 placed upon the saw-dust, it will very soon make its way over the side of the watch- 

 glass and get to it." Other facts are cited from Mr. Cai-ter, upon which Mr. Romanes 

 makes the following reflections : — 



" With regard to these remarkable observations it can only, I think, be said that, 

 although certainly very suggestive of something more than mechanical response to 

 stimulation, they are not sufficiently so to justify us in ascribing to these lowest 

 members of the zoological scale any rudiment of truly mental action. The subject, 

 however, is here full of difficulty, and not the least so on account of the Amoeba not 

 only having no nervous system, but no observable organs of any kind ; so that, 

 although we may suppose that the adaptive movements described by Mr. Carter were 

 non-mental, it still remains wonderful that these movements should be exhibited by 

 such apparently unorganized creatures, seeing that as to the remoteness of the end 

 attained, no less than the complex refinement of the stimulus to which their adaptive 



