HABITATIONS OF INSECTS. 4-67 



stances; and, if the cell be too heavy, 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 aquatic Tipularice lives in cases 

 somewhat similar to those of some Phryganece. 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 Chironomus^ 

 were found by Reaumur upon dead leaves in a pool of 

 water in the Bois de Boulogne 3 . 



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 perfect 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^ Cicindelce, and perhaps a 

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



The habitation of one of these (Cteniza cccmentarid) 

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

 a Reaum. iii. 17^. 

 2 H 2 



