600 THE REPRODUCTIVE FUNCTIONS 



clmnges which constitute the metamorphoses of 

 winged insects,* and of Batrachian reptiles, 

 phenomena which are too striking to have 

 escaped the notice of the earliest naturalists : 

 but the patient investigations of modern inquirers 

 have led to discoveries still more curious, and 

 have shown that all vertebrated animals, even 

 those belonging to the higher classes, such as 

 birds, and mammalia, not excepting man him- 

 self, undergo, in the early stages of their deve- 

 lopement, a series of changes fully as great and 

 as remarkable as those which constitute the 

 transformations of inferior animals. They have 

 also rendered it extremely probable that the 

 organs of the system, instead of existing simul- 

 taneously in the germ, arise in regulated succes- 

 sion, and are the results not of the mere expan- 

 sion of pre-existing rudiments, but of a real 

 formation by the union of certain elements ; 

 which elements are themselves successively 

 formed by the gradual coalescence or juxta- 

 position of their constituent materials. On con- 

 templating the infinitely lengthened chain of 

 means and ends, and of causes and effects, 

 which, during the construction and assemblage 

 pf the numerous parts composing the animal 



* The researches of Nordmann, on different species of Zerw^a, 

 have brought to light the most singular succession of forms 

 during the progress of developement of the same individual 

 animal. 



1 



