32 INTRODUCTION. 



to signs (at times equivocal) of sensibility, that is, to some few slight 

 movements to escape from pain. Between these two extremes, the 

 degrees are infinite. 



In a great number of animals, however, there exists another kind 

 of intelligence, called instinct. This induces them to certain actions 

 necessary to the preservation of the species, but very often alto- 

 gether foreign to the apparent wants of the individual; often also 

 very complicated, and which, if attributed to intelligence, would sup- 

 pose a foresight and knowledge in the species that perform them 

 infinitely superior to what can possibly be granted. These actions, 

 the result of instinct, are not the effect of imitation, for very fre- 

 quently the individuals who execute them have never seen them 

 performed by others: they are not proportioned to ordinary intelli- 

 gence, but become more singular, more wise, more disinterested, in 

 proportion as the animals belong to less elevated classes, and in all 

 the rest of their actions are more dull and stupid. They are so 

 entirely the property of the species, that all its individuals perform 

 them in the same way without ever improving them a particle. 



The working Bees, for instance, have always constructed very 

 ingenious edifices, agreeably to the rules of the highest geometry, 

 and destined to lodge and nourish a posterity not even their own. 

 The solitary Bee, and the Wasp also, form highly complicated nests, 

 in which to deposit their eggs. From this egg comes a worm, which 

 has never seen its parent, which is ignorant of the structure of the 

 prison in which it is confined, but which, once metamorphosed, con- 

 structs another precisely similar. 



The only method of obtaining a clear idea of instinct is by admit- 

 ting the existence of innate and perpetual images or sensations in 

 the sensoriurn which cause the animal to act in the same way as 

 ordinary or accidental sensations usually do. It is a kind of perpe- 

 tual vision or dream that always pursues it, and it may be considered, 

 in all that has relation to its instinct, as a kind of somnambulism. 



There is no visible mark of instinct in the conformation of the 

 animal, but, as well as it can be ascertained, the intelligence is always 

 in proportion to the relative size of the brain, and particularly of its 

 hemispheres. 



Of Method, as applied to the Animal Kingdom. 

 From what has been stated with respect to methods in general, we 



