EVOLUTION IN BIOLOGY. 309 



forment une s6rie tres-simple et partout e"galement nuanc6e ; mais 

 je dis qu'ils forment une s6rie rameuse, irre"gulierement gradue et 

 qui n'a point de discontinuity dans ses parties, oa qui, du moins, 

 n'en a toujours pas eu, s'il est vrai que, par suite de quelques 

 especes perdues, il s'en trouve quelque part. II en resulte que les 

 esp&ces qui terminent chaque rameau de la se>ie ge"nerale tiennent, 

 au rnoins d'un c6te, a d'autres especes voisines qui se nuancent avec 

 elles. Voila ce que 1'etat bien connu des choses me met main- 

 tenant a port6e de demontrer. Je n'ai besoin d'aucune hypothese 

 ni d'aucune supposition pour cela: j'en atteste toute naturalistes 

 observateurs." 



3. In a remarkable essay * Meckel remarks 



" There is no good physiologist who has not been struck by the 

 observation that the original form of all organisms is one and the 

 same, and that out of this one form, all, the lowest as well as the 

 highest, are developed in such a manner that the latter pass through 

 the permanent forms of the former as transitory stages. Aristotle, 

 Haller, Harvey, Kielmeyer, Autenrieth, and many others, have 

 either made this observation incidentally, or, especially the latter, 

 have drawn particular attention to it, and drawn therefrom results 

 of permanent importance for physiology." 



Meckel proceeds to exemplify the thesis, that the 

 lower forms of animals represent stages in the course of 

 the development of the higher, with a large series of 

 illustrations. 



After comparing the Salamanders and the perenni- 

 branchiate Urodela with the Tadpoles and the Frogs, 

 and enunciating the law that the more highly any animal 

 is organised the more quickly does it pass through the 

 lower stages, Meckel goes on to say 



* " Entwurf einer Darstellung der zwischen dem Embryozustande der 

 boheren Thiere und dem permanenten der niederen stattfindenden Paral- 

 lelc," "Beytrage zur Vcrglcichenden Anatomic," Bd. ii. 1811. 



