366 ZOOLOGICAL PHILOSOPHY 



reproducing, those bodies which were endowed by her with organisa- 

 tion and Ufe could have no other organs than those necessary for the 

 maintenance of Ufe. This fact is confirmed by observation of the 

 most imperfect animals, such as the infusorians and polyps. 



But when she subsequently complicated the organisation of these 

 earliest animals and created, with the help of long periods of time 

 and an infinite diversity of circumstances, the multitude of different 

 forms which characterise the later classes, nature formed successively 

 the various organs which animals possess and the different faculties 

 to which these organs give rise. She produced them in an order that 

 I have determined in Part I., Chapter VIII., and from this order it 

 may be seen that the hypocephalon, consisting of the two wrinkled 

 hemispheres covering the brain, is the last organ which she brought 

 into existence. 



Long before creating the hypocephalon, or special organ for the 

 formation of ideas and of all the operations carried out upon them, 

 nature had established in a great number of animals a nervous system, 

 which gave them the faculty of exciting muscular activity, and after- 

 wards of feeling and acting by the emotions of their inner feeling. 

 Now although for this purpose she had multiplied and scattered the 

 nuclei for muscular movement either by estabhshing separate gangha, 

 or by distributing these nuclei throughout the length of a ganglionic 

 longitudinal cord or spinal cord, yet she concentrated the nucleus of 

 sensation in a special locaUty and fixed it in a small medullary mass, 

 which gives direct origin to the nerves of some special senses and which 

 has received the name of brain. 



It was therefore only after having wrought these various perfection» 

 of the nervous system that nature put the finishing touch on her work 

 by creating, in close proximity to the nucleus of sensations, the hypo- 

 cephalon, that remarkable and interesting organ in which ideas are 

 graven and where all the operations constituting inteUigence are carried 

 out. 



It is exclusively these operations that we shall study, in our 

 endeavours to determine their most probable physical causes, by 

 careful inductions and a knowledge of the conditions required. 



Let us now investigate how an idea comes to be formed, and under 

 what conditions a sensation can produce it ; let us even enquire, at 

 least in outline, in what way acts of the intelhgence are carried out in 

 the hypocephalon. 



It is a very singular circumstance that the special organ now under 

 consideration never exerts any action itself in any of the acts or pheno- 

 mena to which it gives rise, and that it does nothing more than receive 

 and preserve for a longer or shorter period the images transmitted to it 



