950 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 by inaction. 
