Microscopical Essays. 



235 



that amongft infe&s of the fame kind fome individuals mould be 

 transformed, while others are not at all changed : thefe infecls 

 will be confidered more fully in another part of this chapter. 



Mr. Reaumur * has {hewn that the fpider fly (hyppobofca 

 equina/ Lin.) lays fo large an egg, that the fly which proceeds 

 from it is as big as the mother, though the egg does not increafe 

 the leaft in fize from the time it is Hi ft laid. The infecl pro- 

 ceeds alfo from the egg in the imago, or fly ftate ; it is probably 

 transformed in the egg, for Mr. Reaumur has found it in the 

 pupa flate therein, and having boiled fome of their eggs which 

 had been laid for fome days, he found the infeft in the form of 

 an oval ball, fimilar to that the pupa of flies with two wings are 

 generally found in. De Geer thinks that the egg itfelf is a true 

 larva, which, when it. is born, has nothing elfe to do but to dif- 

 engage it's limbs, &c. from the (hell which covers it ; and he 

 thinks this the more probable, becaufe there is no embryo 

 feen in this egg, but it is entirely filled with the infecl ; 

 he has alfo perceived a contracting and dilating motion in 

 the. egg, while it was in the .belly of the mother, and imme- 

 diately after it was lain ; circumftances which do not agree with 

 a fimple egg. 



As Mr. Bonnet + has attempted to give a theory of thefe various 

 changes, the following extract from it will, I hope, prove agreeable 

 to the reader; it will at leaft tend to render his ideas of this won- 

 derful fubjecl clearer, and will probably open to his mind many 

 new fources of contemplation. 



F f 2 An 



* Reaumur, torn. 6, mem. 14. 



t Bo'inet Conilderations fur les corps organifes. 



Contemplation of Nature, &c. 



