XVI] THE PROBLEM OF PHYLOGENY 717 



such blood-relationship is lacking. The former fact goes a long 

 way to prove that he used his flippers very much as a whale does ; 

 the latter goes still farther to prove that his general movements 

 and equilibrium in the water were totally diflierent. The whale 

 may be descended from the Carnivora, or might for that matter, 

 as an older school of naturalists believed, be descended from the 

 Ungulates ; but whether or no, we need not expect to find in him 

 the scapula, the pelvis or the vertebral column of the lion or of 

 the cow, for it would be physically impossible that he could live 

 the life he does with any one of them. In short, when we hope to 

 find the missing links between a whale and his terrestrial ancestors, 

 it must be not by means of conclusions drawn from a scapula, an 

 axis, or even from a tooth, but by the discovery of forms so inter- 

 mediate in their general structure as to indicate an organisation 

 and, ipso facto, a mode of life, intermediate between the terrestrial 

 and the Cetacean form. There is no valid syllogism to the effect 

 that A has a flat curved scapula like a seal's, and B has a flat, 

 curved scapula like a seal's : and therefore A and B are related 

 to the seals and to each other ; it is merely a flagrant case of an 

 "undistributed middle." But there is validity in an argument 

 that B shews in its general structure, extending over this bone 

 and that bone, resemblances both to A and to the seals : and that 

 therefore he may be presumed to be related to both, in his 

 hereditary habits of life and in actual kinship by blood. It is 

 cognate to this argument that (as every palaeontologist knows) 

 we find clues to affinity more easily, that is to say with less 

 confusion and perplexity, in certain structures than in others. 

 The deep-seated rhythms of growth which, as I venture to 

 think, are the chief basis of morphological heredity, bring about 

 similarities of form, which endure in the absence of conflicting 

 forces ; but a new system of forces, introduced by altered environ- 

 ment and habits, impinging on those particular parts of the fabric 

 which lie within this particular field of force, will assuredly not 

 be long of manifesting itself in notable and inevitable modifications 

 of form. And if this be really so, it will further imply that 

 modifications of form will tend to manifest themselves, not so 

 much in small and isolated phenomena, in this part of the fabric 

 or in that, in a scapula for instance or a humerus : but rather in 



