HABITATIONS OF INSECTS. 167 



stances; ami, if tlie cell be too lieav}', glueing to it a bit 

 of leaf or straw; or, if too light, a shell or piece of 

 gravel. It is from this necessity of regulating the spe- 

 cific gravity, that to the cases formed with the greatest 

 regularity we often see attached a seemingly superfluous 

 piece of wood, leaf, or the like. 



A larva of one of the acjuatic TipularicB lives in cases 

 somewhat similar to those of some Phryganecv. Several 

 of these of a fusiform shape and brown colour, composed 

 partly of silk and partly perhaps of fragments of leaves, 

 and inhabited by a red larva apparently of a Cliironoimis, 

 were found by Reaumur upon dead leaves in a pool of 

 water in the Bois de Boulogne^. 



In concluding this head I may observe, that here might 

 have been described the various abodes which solitary 

 larvae prepare for themselves previously to assuming the 

 pupa, and intended for their protection in that defence- 

 less stage of existence ; but as I shall have occasion again 

 to refer to them in speaking of the larva state of insects, 

 I shall defer their description to that letter, to which they 

 more strictly belong. 



From the next division of the habitations of insects — 

 those formed by solitary jperj'ect insects for their own ac- 

 commodation — I shall select for description only two, 

 both the work of spiders, and alluded to in a former let- 

 ter, which indeed, with the exception of the inartificial 

 retreats made by the Grylli, Cicindelcv, and perhaps a 

 few others, are the only ones properly belonging to it. 



The habitation of one of these {Cieniza ccemeniaria) 

 is subterraneous, not a mere shallow cavity, but a tube 

 ' Heaum. iii. 17!'. 

 2 H 2 



