SECT. XXXIX. 4. GENERATION. 559 



fame time acquire fenfations adapted to their fuua- 

 tions. Thus when the head of a fnail is reproduced 

 after decollation with a fharp rafor, thofe carious 

 telefcopic eyes are alfo reproduced, and acquire 

 their fenfibility to light, as well as their adapted 

 mufcles for retra6lion on the approach of injury. 



With every new change, therefore, of organic 

 form, or addition of organic parts, I fuppofe a new 

 kind of irritability or of fenfibility to be produced ; 

 fuch varieties of irritability or of fenfibility exifl 

 in our adult (late in the glands : every one of which 

 is furnifhed with an irritability, or a tafte, or ap- 

 petency, and a confequent mode of adlion peculiar 

 to itfelf. 



In this manner I conceive the veffels of the- jaws 

 to produce thofe of the teeth, thofe of the fingers 

 to produce the nails, thofe of the (kin to produce 

 the hair ; in the fame manner as afterwards about 

 the age of puberty the beard and other great changes 

 in the form of the body, and difpofition of the 

 mind, are produced in confequence of the new fe- 

 cretion of femen ; for if the animal is deprived of 

 this fecretion thofe changes do not take place. Thefe 

 changes I conceive to be formed not by elongation 

 or diftention of primeval ftamina, but by appofition 

 of parts ; as the mature crab-fifh, when deprived of 

 a limb, in a certain fpace of time has power to re- 

 generate it ; and the tadpole puts forth its feet long 

 after its exclufion from the fpawn ; and the cater- 

 pillar in changing into a butterfly acquires a new 

 form, with new powers, new fenfations, and new 

 defires. 



The natural hiftory of butterflies, and moths, and 

 beetles, and gnats, is full of curiofity ; fome of 

 them pafs many months, and others even years, in 

 their caterpillar or grub flate ; they then reft many 

 weeks without food, fufpended in the air, buried 

 in the earth, or fubmerfed in water ; and change 



themfelves 



