The same may be said of many of the subordinate groups, or orders, into which these great classes are divided.  At the present time, for example, there are numerous forms of non-ruminant pachyderms, or what we may call broadly, the pig tribe, and many varieties of ruminants.  These latter have their definite characteristics, and the former have their distinguishing peculiarities.  But there is nothing that fills up the gap between the ruminants and the pig tribe.  The two are distinct.  Such also is the case in respect of the minor groups of the class of reptiles.  The existing fauna shows us crocodiles, lizards, snakes, and tortoises; but no connecting link between the crocodile and lizard, nor between the lizard and snake, nor between the snake and the crocodile, nor between any two of these groups.  They are separated by absolute breaks.  If, then, it could be shown that this state of things had always existed, the fact would be fatal to the doctrine of evolution.  If the intermediate gradations, which the doctrine of evolution requires to have existed between these groups, are not to be found anywhere in the records of the past history of the globe, their absence is a strong and weighty negative argument against evolution; while, on the other hand, if such intermediate forms are to be found, that is so much to the good of evolution; although, for reasons which I will lay before you by and by, we must be cautious in our estimate of the evidential cogency of facts of this kind.

It is a very remarkable circumstance that, from the commencement of the serious study of fossil remains; in fact, from the time when Cuvier began his brilliant researches upon those found in the quarries of Montmartre, palaeontology has shown what she was going to do in this matter, and what kind of evidence it lay in her power to produce.

I said just now that, in the existing Fauna, the group of pig-like animals and the group of ruminants are entirely distinct; but one of the first of Cuvier’s discoveries was an animal which he called the Anoplotherium, and which proved to be, in a great many important respects, intermediate in character between the pigs, on the one hand, and the ruminants on the other.  Thus research into the history of the past did, to a certain extent, tend to fill up the breach between the group of ruminants and the group of pigs.  Another remarkable animal restored by the great French palaeontologist, the Palaeotherium, similarly tended to connect together animals to all appearance so different as the rhinoceros, the horse, and the tapir.  Subsequent research has brought to light multitudes of facts of the same order; and, at the present day, the investigations of such anatomists as Ruetimeyer and Gaudry have tended to fill up, more and more, the gaps in our existing series of mammals, and to connect groups formerly thought to be distinct.