PREFACE. Xlll 



of known developmental facts ' (or, as Professor 

 Haeckel would call them, Ontogenetic facts) that a 

 ' three-toed Hipparion form, which lived in the Mio- 

 cene epoch, gave rise by suppression of the phalanges 

 of its rudimental toes and other slight modifications, 

 to the apparently one-toed later tertiary horse is 

 satisfactory to my mind as satisfactory,' Mr. Huxley 

 continues, as the evidence based on the analogy 

 of known structural facts (that is, the known correla- 

 tions of anatomical structure) which leads him to 

 entertain no doubt that the said extinct Hipparion 

 had a simple stomach and a certain kind of heart. 



The two classes of facts here referred to, the 

 structural or anatomical facts, and the developmental 

 or ontogenetic facts, do not equally warrant by analogy 

 the inferences which Mr. Huxley would respectively 

 draw from them.. To infer from an examination of 

 two given skeletons of extinct animals, the anatomical 

 characters of the soft parts of their bodies, which have 

 disappeared from decay, is a simple matter of com- 

 parison and induction. It is, in fact, no more than 

 saying that the fossil bones and teeth before you, 

 present, the one. set, the peculiarities of the bones 

 and teeth of a horse or ass, for example ; and 

 the other set the peculiarities of those of a rumi- 

 nating animal, such as a sheep, or ox ; and that 

 therefore, it is in the highest degree probable that the 



