INTERNAL ANATOMY OF INSECTS. 199 



to its head : and if after having apparently ceased to 

 move for three or four hours it be merely touched, it 

 will again begin to move and resume the same action. 

 This surprising irritability and contractility of muscle 

 doubtless depends upon the peculiar structure of the 

 antlia, which is composed of an infinite number of horny 

 rings, acted upon by muscles, more numerous probably 

 than those which move the trunk of the elephant. The 

 motion only ceases when the muscles become dry and 

 rigid. 



1 hatfe already, under another head a , considered the 

 annual sleep, or winter state of torpidity of insects, during 

 which an intermission for the most part of muscular mo- 

 tion and action takes place. I shall now make a few 

 observations with respect to their diurnal sleep, which 

 may very properly have its place in the present letter. 

 That insects, usually so incessantly busy and moving in 

 every direction, require their intervals of repose, seems 

 to call for no proof. We see some that appear only in 

 the day> and others only in the night, others again only 

 at certain hours; which leads to the conclusion, that 

 when they withdraw from action and observation, it is 

 to devote themselves to rest and sleep. The cockchafer 

 flies only in the evening ; but if you chance to meet with 

 it roosting in a tree in the earlier part of the day, you 

 will find it perfectly still and motionless, with its antenna; 

 folded and applied to the breast: we cannot indeed say 

 that its eyes are shut; for as insects have no eyelids, that 

 sign of sleep can never be found in them. Again, if a 

 Lepidopterist goes into the wood to capture moths in 



a VOL. II. LETTKR XXVI. 



