ENTOMOLOGY. 93 



eye-case is called Ophthalmotheea, tlie antennse-cases, 

 Cerathecse, &c. 



The length of time insects pass in this stage of 

 their existence varies from a few days to nearly two 

 years. Each species, however, has in general a de- 

 finite period assigned it from which there is no mate- 

 al deviation, unless under very peculiar circumstances, 

 'erhaps the most general duration is from two to four 

 feeks, but, even in the same species, this depends 

 pon the season of the year, for a pupa which would 

 isclose the perfect insect in a few weeks during the 

 ummer, will frequently lie dormant throughout the 

 ntire winter. Unless a provision of this kind 

 btained, it is obvious that many insects would in- 

 allibly perish from being brought into existence at 

 time when it is impossible to find the means of 

 aaintaining life. The immediate cause of this pro- 

 ongation of their quiescent condition is to be found 

 Q the effects of the winter's cold, the more remote 

 ne in the wise ordination of providence. Artificial 

 teat, as has been already stated in a former volume, 

 vill mature the perfect insect and make it burst from 

 ts prison at any period of the year; and, in like 

 nanner, artificial cold will retard its birth. From 

 hese considerations, it is obvious that the evolution 

 f the imago depends on the evaporation and assimi- 

 ation of the fluids, and this takes place in a more 

 speedy or tardy manner, according to the greater or 

 ess degree of heat to which the pupa is exposed ; it 

 loes not, however, happen that pupae of the same 

 species, placed in precisely the same circumstanc 



