496 HISTORY OF PHYSIOLOGY. 



Another application of the principle, according 

 to which creatures the most different are develope- 

 ments of the same original type, may be discerned 12 

 in the doctrine, that the embryo of the higher 

 forms of animal life passes by gradations through 

 those forms which are permanent in inferior ani- 

 mals. Thus, according to this view, the human 

 foetus assumes successively, the plan of the zoo- 

 phyte, the worm, the fish, the turtle, the bird r the 

 beast. But it has been well observed, that " in these 

 analogies we look in vain for the precision which 

 can alone support the inference that has been de- 

 duced 13 ;" and that at each step, the higher embryo 

 and the lower animal which it is supposed to re- 

 semble, differ in having each different organs suited 

 to their respective destinations. 



Cuvier 14 never assented to this view, nor to the 

 attempts to refer the different divisions of his system 

 to a common type. " He could not admit," says his 

 biographer, "that the lungs or gills of the verte- 

 brates are in the same connexion as the branchiae 

 of molluscs and crustaceans, which in the one are 

 situated at the base of the feet, or fixed on the feet 

 themselves, and in the other often on the back or 

 about the arms. He did not admit the analogy 

 between the skeleton of the vertebrates and the 

 skin of the articulates ; he could not believe that 

 the tsenia and the sepia were constructed on the 



12 Dr. Clark, Report, Ib. iv. 113. " Dr. Clark, p. 114. 



14 Laurillard, Elog. de Cuvier, p. 66. 



