FOSSIL PEDIGREES 81 



and simultaneous appearance of numerous new and allied types 

 unheralded by transitional forms. Since Darwin had stressed 

 the gradualness of transmutation, the investigators expected 

 to find the transitional means more numerous than the terminal 

 extremes, and were surprised to find, in the real record of the 

 past, the exact reverse of their anticipation. They found that 

 the classes and families of animals and plants had always been 

 as widely separated and as sharply differentiated as they are 

 to-day, and that they had always formed distinct systems, un- 

 connected by transitional links. The hypothetical "generalized 

 types," supposed to combine the features of two or three fam- 

 ilies, have never been found, and most probably never will be; 

 for it is all but certain that they never existed. Occasionally, it 

 is true, palaeontologists have discovered isolated types, which 

 they interpreted as annectant forms, but a single pier does 

 not make a bridge, and only too often it chanced that the 

 so-called annectant type, though satisfactory from the mor- 

 phological standpoint, was more recent than the two groups, 

 to which it was supposed to be ancestral. But it will make 

 matters plainer, if we illustrate what is meant by the discon- 

 tinuity or incompleteness of the fossil record, by reference to 

 some concrete series, such as the so-called Pedigree of the 

 Horse. 



Whenever a series of fossils, arranged in the order of their 

 historical sequence, exhibits a gradation of increasing resem- 

 blance to the latest form, with which the series terminates, 

 such a series is called a palaeontological pedigree, and is 

 said to represent so many stages in the racial development 

 or phylogeny of the respective mx)dern type. The classical 

 example of this sort of "pedigree" is that of the Horse. It is, 

 perhaps, one of the most complete among fossil "genealogies," 

 and yet, as has been frequently pointed out, it is, as it stands, 

 extremely incomplete. Modern representatives of the Equidaey 

 namely, the horse, the ass and the zebra, belong to a common 

 genus, and are separated from one another by differences 

 which are merely specific, but the differences which separate 



