THE PECULIAR FACULTIES 279 



Intelligence. Of all the faculties peculiar to certain animals, this is 

 the one that is the most limited as regards the numbers which possess 

 it, even in a very imperfect form ; but it is also the most wonderful, 

 especially when highly developed ; and it may then be regarded as 

 the high- water-mark of what nature can achieve by means of organisa- 

 tion. 



This faculty arises from the activities of a special organ which can 

 alone produce it, and which is itself highly complex when it has acquired 

 all the development of which it is capable. 



As this organ is actually distinct from that which produces feeling 

 although unable to exist without it, it follows that the faculty of 

 performing acts of intelligence is not only not common to all animals 

 but is not even common to all those that can feel ; for feeling may 

 exist without intelUgence. 



The special organ in which are produced the acts of the under- 

 standing appears to be only an accessory of the nervous system ; 

 that is, a part added on to the brain, and containing the nucleus or 

 centre of communication of the nerves. The special organ in question 

 is thus adjacent to the nucleus ; the nature of the substance of which 

 it is composed appears moreover to differ in no way from that of the 

 nervous system ; in it alone, however, acts of intelligence are performed ; 

 and it is a special organ, for the nervous system may exist without it. 



In the third part I shall take a general survey of the probable 

 mechanism of the functions of this organ. In vertebrates it is con- 

 fused with the medullary mass under the name of brain, although it 

 only consists of the two wrinkled hemispheres which cover it over. 

 It is sufficient here to note that of those animals which have a nervous 

 system, it is only the most perfect that actually possess the two cerebral 

 hemispheres ; probably all invertebrates, except perhaps some of 

 the last order of molluscs, are destitute of it, although a great many 

 of them have a brain to which run directly the nerves of one or more 

 special senses, and although this brain is generally divided into two 

 lobes separated by a furrow. 



In accordance with this view the faculty of performing acts of 

 intelligence has only just begun in the fishes or, at the earliest, in 

 the cephalopod molluscs. It is in these animals in a state of extreme 

 imperfection ; some development has been achieved in the reptiles, 

 especially in the later orders ; much more has been made in the birds, 

 and the faculty reaches its highest point in the latest orders of 

 mammals. 



Intelligence is then a faculty Umited to certain animals which are 

 able to feel ; but the faculty is not common to all those that possess 

 feeling : indeed, as we shall see, among the latter, those that have no 



