250 PHILOSOPHY OF ZOOLOGY. 



connection, without perceiving that it is the imagination 

 chiefly that is in exercise. However confused the limits 

 between the ideas of recollection and imagination, the at- 

 tention seems sufficiently active to enable the memory to 

 treasure up the distorted images. 



The recollection of the efforts of our instinctive powers 

 is likewise a common employment of the mind during this 

 state of dreaming, and in some cases, in consequence of these 

 instincts being in part awake, partial action is produced. 

 This is exemplified in Somnambulists, or those who rise 

 and walk during sleep, or those who speak. The former 

 will sometimes rise out of bed and move from one room to 

 another, or even go into the open air, without becoming 

 awake ; and the latter, while talking, if cautiously spoken 

 to, may be made to keep up an irregular conversation. Som- 

 nambulism exhibits, however, this very singular character, 

 that the memory retains no traces of the actions which 

 were performed, or the feelings in which they origina- 

 ted. 



That the same causes operate in producing imperfect 

 sleep, in other animals, may, with considerable property, be 

 inferred, even in the absence of direct proof. Indeed we 

 can have no proof of such a state, unless the instinctive 

 powers have been so far awake as to produce action. This 

 proof, however, has been obtained in the case of the dog. 

 This animal, during sleep, may sometimes be observed 

 moving his limbs and tail with considerable velocity, and 

 even uttering low and imperfect sounds, as if barking. 



In preparing for sleep, some animals assume particular at- 

 titudes, such as we have already noticed, but remain in the 

 open air. Others retire to shaded places or caves. Some 

 sleep without any covering : others prepare for themselves 

 a bed in order to keep up their standard of heat, which 

 would become diminished bv inaction. 



