REST OF INSECTS. 405 



be proximately caused by a retarded current of blood. 

 We want data also for determining whether similar 

 effects are produced upon the senses of insects during 

 their quiescence, or apparent sleep, as take place in 

 ourselves. The shutting of the eye-lids, next to 

 motionless rest, is one of the most obvious charac- 

 teristics of sleep in man ; but in insects nothing like 

 this can be observed, because they have nothing 

 analogous to eye-lids. The senses of insects, indeed, 

 may not sleep at all and what renders this the more 

 probable is, that in the case of gnats, crane-flies 

 (Tipulidcc), moths, butterflies, &c, however long they 

 may have been observed to be quiescent, or sleeping, 

 in the same place, they are instantly on the alert at 

 the approach of danger, though no noise be made to 

 alarm them.* It may serve to illustrate this state of 

 wakefulness in the senses of quiescent insects, that 

 the senses in man do not all sleep in the same degree 

 of profundity. This very curious fact was first, we 

 believe, observed by M. Cabanis, who also found 

 that some of our senses and members go to sleep 

 sooner than others in proportion, it may be pre- 

 sumed to their fatigue from their waking exertions, 

 and to the flow of blood through them. According 

 to Cabanis, then, the muscles of the legs and arms 

 are the first to become drowsy, and next those that 

 sustain the head, which, losing its support, falls for- 

 ward ; the muscles of the back follow, and it becomes 

 bent. Among the senses, the eye is the first that 

 goes to sleep ; and after it the smell, taste, hearing, 

 and touch, become drowsy in succession. The sense 

 of touch never sleeps so profoundly as the others, 

 a fact inferred from our frequent change of position 

 during sleep, which must be the consequence of 

 uneasy sensations of touch. Besides this, it is well 

 known that a slight tickling of the soles of the feet 



* J. R. 



