302 EVOLUTION IN BIOLOGY. [LECT 



besoin d'aucune hypothese ni d'aucune supposition pour cela: j'en 

 atteste tous les 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, espe- 

 cially 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 



"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 dis- 

 similar type j indeed they often differ from one another far 

 more than the lowest vertebrate does from the highest mammal; 

 yet the following pages will show that the comparison may also 



1 " Entwurf einer Darstellung der zwischen dern Embryozustan.de 

 der hoheren Thiere und dem permanenten der niederen stattfindenden 

 Parallele," " Beytrage zur Vergleichenden Anatomie," Bd. ii. 1811. 



