HISTORY OF GEOLOGY. 



[2nd Ed.] [The hypothesis of the progressive developement of 

 species has been urged recently, in connexion with the physiological 

 tenet of Tiedernann and De Serres, noticed in B. xvn. c. vii. sect. 3 ; 

 namely, that the embryo of the higher forms of animals passes by 

 gradations through those forms which are permanent in inferior ani- 

 mals. Assuming this tenet as exact, it has been maintained that the 

 higher animals which are found in the more recent strata may have 

 been produced by an ulterior development of the lower forms in the 

 embryo state ; the circumstances being such as to favor such a deve- 

 lopement. But all the best physiologists agree in declaring that such 

 an extraordinary developement of the embryo is inconsistent with phy- 

 siological possibility. Even if the progression of the embryo in time 

 have a general correspondence with the order of animal forms as more 

 or less perfectly organized (which is true in an extremely incomplete 

 and inexact degree), this correspondence must be considered, not as 

 any indication of causality, but as one of those marks of universal ana- 

 logy and symmetry which are stamped upon every part of the creation. 



Mr. Lyell 11 notices this doctrine of Tiedemann and De Serres ; and 

 observes, that though nature presents us with cases of animal forms 

 degraded by incomplete developement, she offers none of forms exalted 

 by extraordinary developement. Mr. Lyell's own hypothesis of the in- 

 troduction of new species upon the earth, not having any physiological 

 basis, hardly belongs to this chapter.] 



Sect. 5. Question of Creation as related to Science. 



BUT since we reject the production of new species by means of external 

 influence, do we then, it may be asked, accept the other side of the 

 dilemma which we have stated ; and admit a series of creations of 

 species, by some power beyond that which we trace in the ordinary 

 course of nature ? 



To this question, the history and analogy of science, I conceive, 

 teach us to reply as follows : All palretiological sciences, all specula- 

 tions which attempt to ascend from the present to the remote past, by 

 the chain of causation, do also, by an inevitable consequence, urge us 

 to look for the beginning of the state of things which we thus con- 

 template ; but in none of these cases have men been able, by the aid 

 of science, to arrive at a beginning which is homogeneous with the 



11 Principles, B. m. c. iv. 



