130 



most important of which we arrive by an analysis of the conditions 

 of existence,* is the object of Comparative Anatomy : a science 

 indispensable to General Physiology and Natural History. 



11 we confine our observations to the structure of the different 

 varieties of the same species, or even to the organization of the 

 same individual under different circumstances, we shall also ob- 

 serve the same kind of organs subjected to perpetual varieties ; 



for, 



1st. Every organic body is destined to undergo, during the 

 progress of its natural existence, a series of changes more or 

 less remarkable ; losing certain parts, and developing others, which 

 were either much less considerable, or did not exist. The meta- 

 morphose of the caterpillar into the butterfly, and of tlie tadpole 

 into the frog, &c. are obvious and striking in the extreme; but 

 the changes, which the higher or more complicated animals under- 

 go, though not so remarkable, are nevertheless as real. The 

 infant, at birth, loses its placenta and coverings ; at a certain 

 period, is nearly deprived of its thiuuis and renal capsules ; and 

 acquires, by degrees, its hair and its teeth. Moreover, the rela- 

 tive magnitude, and intimate structure of the different tissues and 

 organs, undergo perpetual changes, from conception to the latest 

 moment of a protracted existence ; so that no being is possessed 

 of an organization, exactly tlie same, at any two different periods 

 of life.* 



• " Comme rien ne peut exister s'il ne rcunit les conditions, qoi rendent son existence 

 •' possible, les differentes parties de chaque etre doivent etre coordonnees de maniere a 

 " rendre possible I'etre total, non-seulement en lui-uieme, inais dans ses rapports arec 

 " ceux qni I'entourent; e\. I' analyse de ces conditions coniiuit souvent a des lois generulea 

 '< tout aussi diimontrces que celles qui derivent du calcul, ou de I'experience-'' Cuvier, Regn* 

 Animal disltibue d'apris son Organisation, Paris, IS 1 7. Introduction, p. 6. 



* Cuvier Regne Adimal. 



