132 INSECT TRANSFORMATIONS. 



than the microscope does in the hands of such ob- 

 servers.'* 



It is apparently a branch of the same untenable 

 theory, which maintains that the fluid termed by 

 Heroldt the blood of caterpillars is the only original 

 portion of them, which, being endowed with a forma- 

 tive power,t produces an envelope for itself of mucous 

 net-work (rete mucosum), and this again, by means of 

 a similar power, is successively transmuted into the 

 caterpillar, the pupa, and the perfect insect ;J in some 

 similar way, we suppose, to the formative power dis- 

 played by water, when, during frost, it shoots into 

 crystals of ice. But the framers of such theories seem 

 to forget that living blood is a very different thing 

 from inanimate water, and the growth and nutrition 

 of animals from the chemical formation of crystals. 

 Kirby and Spence very justly remark, that Heroldt's 

 formative power is only an apology for ignorance, and 

 that his denying the existence. of what he cannot trace, 

 is no proof of his doctrine, but of his mistake in sup- 

 posing the first appearance of the organs of the but- 

 terfly in his microscope to be literally their first 

 existence. To suppose the blood, we may also re- 

 mark, endowed with the power of creating insects, gets 

 rid of no difficulty and explains no phenomenon, while 

 it is altogether a gratuitous assumption, unproved 

 and improbable. c Admirable discovery,' exclaims 

 Virey; ' as if you should affirm that a stone falls 

 because it falls !' We think it is St Pierre who 

 remarks, that Nature seldom permits philosophers to 

 peep to the bottom of her basket ; and we have already 



* Diet. Class. d'Hist. Nat. x, 468. 



t The German term is c Bildende Kraft,' i. e. Vis forma- 

 trix, or JVisus formativus. 



t Heroldt, quoted by Kirby and Spence, hi, 83. 

 Quoted by Kirby and Spence. 



