218 EVOLUTION IN BIOLOGY vi 



3. In a remarkable essay 1 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 deduced 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 

 perennibranchiate 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 



" From these lowest Vertebrata to the highest, and to the 

 highest forms among these, the comparison between the embry- 

 onic conditions of the higher animals and the adult states of the 

 lower can be more completely and thoroughly instituted than if 

 the survey is extended to the Invertebrata, inasmuch as the latter 

 are in many respects constructed upon an altogether too dissimilar 

 type ; indeed they often differ from one another far more than 

 the lowest vertebrate does from the highest mammal ; yet the 



1 " Entwurf einer Darstellung der zwischen clem Embryozus- 

 tande der hoheren Thiere und clem permanenten der niederen. 

 stattfindenden.Parallele," Beytragezur Vergleichendcn Anatomic, 

 Bd. ii. 1811. 



