308 ZOOLOGICAL PHILOSOPHY 



but they suffice at least to constitute feeling, although incapable 

 of producing ideas. 



This state of the nervous system, which gives rise in insects only 

 to these two faculties, is almost the same in the animals of the five 

 following classes, viz. : arachnids, crustaceans, annehds, cirrhipedes, 

 and molluscs ; there are apparently no other differences than those 

 involved by a higher development of the two faculties named. 



I have not a sufficient number of observations to be able to indicate 

 which of the animals possessing a nervous system, capable of support- 

 ing sensations, are Uable to experience emotions of their inner feehng. 

 It may be that as soon as the faculty of feehng exists, that which 

 produces emotions arises also ; but the origin of the latter is so vague 

 and imperfect that I beheve it can only be recognised in vertebrates. 

 Let us then pass on to a determination of the point in the animal scale 

 at which begins the fourth kind of faculty of the nervous system. 



When nature had supphed the nervous system with a true brain, 

 that is, with an anterior medullary swelHng, capable of giving rise 

 immediately to at least one special sense such as sight, and of con- 

 taining in a single nucleus the centre of communication of the nerves, 

 she had not yet completed the development of the system. Indeed 

 she long continued to be concerned with the gradual development of 

 the brain, and started the rudiments of the senses of hearing in the 

 crustaceans and molluscs. But it still continues to be a very simple 

 brain, appearing to be the basis of the organ of feeling, since the 

 sensitive nerves and those of the existing special senses proceed to 

 unite with it. 



Indeed the terminal ganghon, which constitutes the brain of insects 

 and of the animals of the following classes up to and including the 

 molluscs, although as a general rule divided by a furrow and to some 

 extent bilobate, still shows no trace of the two wrinkled hemispheres, 

 so susceptible of development, which in the most perfect animals 

 cover over the true brain, viz. that part of the encephalon which 

 contains the nucleus of the sensitive system ; hence the functions, 

 for which these new accessory organs are adapted, cannot be per- 

 formed in any of the invertebrates. 



The Nervous System m its Complete State gives rise to 

 Muscular Movements, Feeling, the Inner Emotions and 

 Intelligence. 



It is only among the vertebrates that nature has arrived at the 

 completion of every part of the nervous system ; and it is probably 

 in the most imperfect of these animals (viz. the fishes) that she started 

 the rudiments of the accessory organ of that brain which consists 



