PALAEONTOLOGY AS A DISCIPLLNE. 55 



ogies, the determination of relationships, and the estabhshing 

 of classification upon a sound and natural basis, important as 

 these are, are yet only a part of the great task which mor- 

 phology has set before itself. We wish to penetrate more 

 deeply into the mystery of nature, and learn how and why 

 these changes have occurred ; or, in other words, to discover 

 the manner in which, and the efficient causes by which, devel- 

 opment is effected. On these subjects there is, as yet, wide 

 divergence of view among morphologists. The postulates and 

 assumptions upon which morphological discussions are founded 

 are, in great measure, incapable of proof, and appeal with very 

 different degrees of force to different minds. Modes of devel- 

 opment which appear axiomatic to one observer are by another 

 regarded as absurd. All are agreed that there are limits to the 

 possibilities of change ; no one attempts to derive a butterfly 

 from a beetle, or a horse from a cow ; but just how and where 

 these limits should be drawn it is at present impossible to say. 

 It is this uncertainty which refers the question to the individual 

 judgment, and leaves the way open for such radical differences 

 of opinion. 



To the solution of these problems of evolutionary modes 

 palaeontology offers most valuable assistance, drawn from the 

 study of actual phyla. It might seem that this was merely 

 arguing in a circle, because the construction of phylogenetic 

 series involves certain presuppositions as to what changes 

 are and what are not possible, and we then proceed to prove 

 the presuppositions by the phyla thus constructed. But the 

 cautious, step-by-step method, guarded by the order of appear- 

 ance in time, offers a way of escape, and enables us to con- 

 struct phyla in harmonious structural and stratigraphical 

 succession, which must very nearly represent the actual stages 

 of change. Only a beginning has been made in this work, but 

 the results drawn from an examination of widely separated 

 phyla, such as mammals, gasteropods, and cephalopods, are so 

 consistent and harmonious as to be full of promise for the 

 future. 



Limitations of time and space forbid an attempt to fully 

 consider here all the deductions which have been susforested 



