1898] . I XX I 'LA TE ANCESTR Y OF THE \ 'Ell TEH1L I 7\ I 1 U 



of any group of animals, we must, if possible, discover the method 

 <»f feeding which caused the ancestral form to depart from its 

 congeners. Strong in this conviction, therefore, I made a special 

 comparative study of the Arachnida, extending over tour years, and 

 ultimately endeavoured to show 1 that their peculiar morphology could 

 be explained in detail as an adaptation to their method of feeding. 



It was therefore only natural that any suggestion, even the 

 faintest, as to what might have been the primitive method of feeding 

 of the ancestors of the vertebrates should lead me at once to see 

 whether the same principle could not be made to apply again. 

 Was it not possible to deduce the typical low vertebrate from a 

 hirudinean by a series of structural modifications resulting from a 

 further development of the leech-method of feeding ? Xo one will 

 deny that such a possible solution was worthy of investigation, 

 even though he may not be so convinced as I am that morphology 

 is an aimless pursuit unless it go hand in hand with physiology. 

 Although most zoologists admit this latter as a pious opinion, in 

 practice it is too often ignored, as may be gathered from the fact 

 that every attempt to discover the ancestry of the Yertebrata, 

 with which I am acquainted, has been based solely on structural 

 similarities, while the functions of the structures themselves have 

 been treated in a most arbitrary fashion. For example : the 

 central nervous system of the Arachnida is said to have be- 

 come the central nervous system of the Yertebrata, with an 

 entirely different organism to be innervated. The intestine of the 

 king-crab is said to have been lost in the spinal cord of the 

 Yertebrata, and a new one has been provided ; the sheath of a 

 protrusible proboscis is turned into the vertebrate notochord ; old 

 mouths may close and new ones open, and so on. Continuity of 

 function is apparently of very secondary importance, while similarity 

 of structure or of mere position relative to other organs is of prime 

 importance. I do not call this physiology and morphology going 

 hand in hand. It seems to me more like physiology being dragged 

 by the neck, while the morphologist demonstrates the perfection of 

 his structural resemblances. Hence, all the arguments to which we 

 have hitherto been accustomed have seemed to me from the first to 

 be hopeless. It is not alone to the discovery of similarities of 

 structure that we must look for clues to evolutionary progress, but 

 rather to the development of new functions in response to some 

 probably gradual change in the environment, these new functions 

 leading, whether by selection or inheritance, or both together, to 

 modifications of structure, subject always to the physical laws of 

 the environment. 



1 "Comparative Morph. of the Galeodidae. " — Trans. Linn an Soc, vi., pp. 30r>- 117. 

 1S96. 



