Microscopical Essays. 213 



When the {ilk-worm has attained it's perfect growth, the refer- 

 voirs of filk are full, and it is prefled by it's fenfetions to get rid 

 of this incumbrance, and accordingly fpins a cone, the altitude 

 and fize of which are proportioned to it's wants : by traverfmg 

 backwards and forwards, it is relieved, and thus attains, by an 

 innate defire, the end for which it was formed. 



The fize of the cone is not always proportioned to the fize of 

 the caterpillar ; fome that are fmall conftrucl; larger cones than 

 other caterpillars which are greater in fize. 



There is a caterpillar which forms it's filken cone in the fhape 

 of a boat turned bottom upwards, whence it is called by M. de 

 Reaumur the " coque en batteau ;" the conftruftion is compli- 

 cated, and feems to require more art than is ufually attributed to 

 this infect* It confifts of two principal parts, fhaped like (hells, 

 which are put together with considerable fkill and propriety ; 

 each (hell, or fide, is framed by itfelf, and formed of an innu- 

 merable quantity of minute filk rings ; in the fore part there is a 

 projection, in which a fmall crevice may be perceived, which 

 ferves, when opened, for the efcape of the moth ; the fides are 

 connected with fo much art, that they open and (hut as if framed 

 with fprings ; fo that the cone, from which the butterfly has 

 efcaped, appears as clofe as that which is ftill inhabited. 



Thofe which are not furnifhed with a filky cone, fupply their 

 want with various materials, which they are fufficiently fkilful to 

 form into a proper habitation, to fecure them while preparing for 

 the perfect ftate ; fome conftrucl: theirs with leaves and branches, 

 tying them fail together, and then ftrengthening the connection ; 



others. 



