444 UNITY OF DESIGN. 



It must, I think, be admittetl that the analogies, on which 

 the hypothesis in question is founded, are numerous and 

 striking; but great care should be taken not to carry it far- 

 ther than the just interpretation of the facts themselves may 

 warrant. It should be borne in mind that these facts are 

 few, compared with the entire history of animal development; 

 and that the resemblances which have been so ingeniously 

 traced, arc partial only, and fall very short of that universa- 

 lity, which alone constitutes the solid basis of a strictly phi- 

 losophical theory. Wliatever may be the apparent simila- 

 rity between one animal and another, during different peri- 

 ods of their respective developments, there still exists spe- 

 cific differences, establishing between ihem an impassable 

 barrier of separation, and elYactually preventing any conver- 

 sion of one species into another, however nearly the two 

 may be mutually allied. The essential characters of each 

 species, amidst occasional varieties, remain ever constant and 

 immutable. Although gradations, to a greater or less ex- 

 tent, may be traced among the races both of plants and ani- 

 mals, yet in no case is the series strictly continuous; each 

 step, however short, being in reality an abrupt transition 

 from one type of conformation to another. In many in- 

 stances the interval is considerable; as, for example, in the 

 passage from the invertebrate to the vertebrated classes; and, 

 indeed, in every instance where great changes in the nature 

 and arrangement of the functions take place.* It is in vain 

 to allege that the original continuity of the series is indi- 

 cated by a few species presenting, in some respects, inter- 

 mediate characters, such as the Ornitfwrhyncus, between 



feet development of some parts of the embryo, while the natural process is 

 carried on in the rest of the system; and thus it happens that a resemblance 

 may often be traced, in these malformations, with the type or the permanent 

 condition of some inferior animal. Hence, all these apparent anomahcs are, 

 in reality, in perfect harmony with the established laws of ort^anic develop- 

 ment, and afford, indeed, striking confirmations of the truth of the theory 

 here cxj^lained. 



• See a paper on tiiis subject, by Cuvier, in the Arm. dcs Sciences Na- 



turcUes, xx. 241. 



