ON THE METHOD OF ZADIG. 477 



It might just as well have been like that of some other marsupial ; or 

 even like that of the totally different group of Monotremes, of which 

 the only living representatives are the Echidna and the Orniihorhyn- 

 chus. 



For all practical purposes, however, the empirical laws of coordi- 

 nation of structures which are embodied in the generalizations of mor- 

 phology may be confidently trusted, if employed with due caution, to 

 lead to a just interpretation of fossil remains ; or, in other words, we 

 may look for the verification of the retrospective prophecies which are 

 based upon them. 



And, if this be the case, the late advances which have been made 

 in paleontological discovery open out a new field for such prophecies. 

 For it has been ascertained with respect to many groups of animals, 

 that, as we trace them back in time, their ancestors gradually cease 

 to exhibit those special modifications which at present characterize the 

 type, and more nearly embody the general plan of the group to which 

 they belong. 



Thus, in the well-known case of the horse, the toes which are sup- 

 pressed in the living horse are found to be more and more complete in 

 the older members of the group, until, at the bottom of the Tertiary 

 series of America, we find an equine animal which has four toes in 

 front and three behind. No remains of the horse-tribe are at present 

 known from any Mesozoic deposit. Yet who can doubt that, when- 

 ever a sufficiently extensive series of lacustrine and fluviatile beds of 

 that age becomes known, the lineage which has been traced thus far 

 will be continued by equine quadrupeds with an increasing number of 

 digits, until the horse type merges in the five-toed form toward which 

 these gradations point ? 



But the argument which holds good for the horse holds good, not 

 only for all mammals, but for the whole animal world. And as the 

 study of the pedigrees or lines of evolution to which at present we 

 have access brings to light, as it assuredly will do, the laws of that 

 process, we shall be able to reason from the facts with which the geo- 

 logical record furnishes us to those which have hitherto remained, and 

 many of which, perhaps, may for ever remain hidden. The same method 

 of reasoning which enables us, when furnished with a fragment of an 

 extinct animal, to prophesy the character which the whole organism 

 exhibited, will, sooner or later, enable us, when we know a few of the 

 later terms of a genealogical series, to predict the nature of the earlier 

 terms. 



In no very distant future, the method of Zadig, applied to a great- 

 er body of facts than the present generation is fortunate enough to 

 handle, will enable the biologist to reconstruct the scheme of life from 

 its beginning, and to speak as confidently of the character of long ex- 

 tinct living beings, no trace of which has been preserved, as Zadig did 

 of the queen's spaniel and the king's horse. Let us hope that they 



