DEFENCE OF COCOONS. 217 



insect be a large or a small one, although it may be accele- 

 rated or prolonged according to the degree of temperature 

 of the atmosphere. 



The envelope of silken or other materials formed by the 

 larvae of many insects, immediately previous to their assum- 

 ing the pupa or chiysalis state, is termed a cocoon ; and per- 

 haps in no department of our knowledge of the lower tribes 

 of animals is there so much skill, or so much of that faculty 

 which we term instinct, displayed, as in the proceedings which 

 characterize the formation of these envelopes. All larvae, 

 however, do not make these coverings, the cause of which is 

 at once obvious ; the pupa of the grasshopper or cockroach, 

 dragon-fly or cimex, is an active animal, continuing to enjoy 

 all the habits of the larvae, and consequently not needing 

 any other defence than it possessed in its former state ; but 

 in other insects the case is entirely different ; the pupa state 

 being one of inactivity and total helplessness, and in which 

 the insect is consequently subject to the attacks of any stray 

 bird or mouse, or not less voracious insect, which would 

 feast with as much avidity upon the soft and creamy sub- 

 stance of the newdy-formed chrysahs, as the Romans did 

 upon the cossus, (which was a large insect in the earlier 

 stage, and which is considered to have been the larva of the 

 goat-moth, Cossus liyniperda). Hence the necessity, not 

 only for retreat to some quiet and unobserved corner or 

 hole, but also for a covering for more complete conceal- 

 ment and defence. At this time many larvae accordingly 

 make their way several inches deep into the earth. Here, 

 or concealed under leaves, moss, or other like matter, many 

 insects become pupae, with the mere precaution of fastening 

 the substances which conceal them together with a gluti- 

 nous secretion from the mouth; but others are far more 

 careful, forming for themselves an entire covering, composed 

 either of silk spun from their own mouths, or of silk united 



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