VIII LARVA AND NYMPH 109 



suspect — though I cannot positively assert it, having 

 several times missed the moment to ascertain it — 

 that the larva disgorges and applies with its mouth 

 the quintessence of the purple pulp in its stomach 

 to make the wash of lacquer. Only after this last 

 piece of work would it eject the remains of 

 digestion in a single mass, and thus is explained 

 the disgusting necessity of storing the excrement 

 within the larva's habitation. 



At all events the usefulness of this layer is clear ; 

 its absolute impermeability protects the larva from 

 the damp which would certainly penetrate the poor 

 shelter hollowed for it by its mother. Recollect 

 that it is buried but a few inches deep in sandy, 

 open ground. To judge how far cocoons thus 

 varnished are capable of resisting damp, I have 

 plunged them in water for several days, yet never 

 found any trace of moisture within them. Let us 

 compare the Sphex cocoon, with manifold coverings 

 to protect the larva in a burrow itself unprotected, 

 with that of Cerceris tuberculata, sheltered by a layer 

 of sandstone, more than half a yard down in the 

 ground. This cocoon has the form of a very long 

 pear, with the small end cut off. It is composed of 

 a single silken wrap, so fine that the larva is seen 

 through it. In my many entomological researches 

 I have always found the labour of larva and mother 

 supplement each other. In a deep well -sheltered 

 dwelling the cocoon is of light materials ; for a 

 surface abode, exposed to wind and weather, it is 

 strongly constructed. 



Nine months pass, during which a work is done 

 which is quite hidden. I pass over this period. 



