PRESIDENTIAL ADDRESS. 47 



It would be easy to point out difficulties in the way of the theory. 

 The omission of historic stages in the actual ontogenetic development, 

 of which almost all groups of animals supply striking examples, is one 

 of the most serious; for if these stages are necessary as stimuli for 

 the succeeding stages, then their omission requires explanation ; while, 

 if such stimuli are not necessary, the theory would appear to need 

 revision, 



Such objections may, however, prove to be less serious than they 

 appear at first sight \ and in any case Kleinenberg's theory may be 

 welcomed as an important and original contribution, which deserves — 

 indeed demands — the fullest and most careful consideration from all 

 morphologists, and which acquires special interest from the explanation 

 which it offers of recapitulation as a mechanical process, through 

 which alone is it possible for an embryo to attain the adult structure. 



That recapitulation does actually occur, that the several stages in 

 the development of an animal are inseparably linked with and 

 determined by its ancestral history, must be accepted. ' To take any 

 other view is to admit that the structure of animals and the history 

 of their development form a mere snare to entrap our judgment.' 



Embryology, however, is not to be regarded as a master-key that 

 is to open the gates of knowledge and remove all obstacles from our 

 path without further trouble on our part ; it is rather to be viewed 

 and treated as a delicate and complicated instrument, the proper 

 handling of which requires the utmost nicety of balance and adjust- 

 ment, and which, unless employed with the greatest skill and judgment, 

 may yield false instead of true results. 



Embryology is indeed a most powerful and efficient aid, but it will 

 not, and cannot, provide us with an immediate or complete answer to 

 the great riddle of life. Complications, distortions, innumerable and 

 bewildering, confront us at every step, and the progress of knowledge 

 has so far served rather to increase the number and magnitude of 

 these pitfalls than to teach us how to avoid them. 



Still, there is no cause for despair — far from it ; if our difficulties 

 are increasing, so also are our means of grappling with them ; if the 

 goal appears harder to reach than we thought for, on the other hand 

 its position is far better defined, and the means of approach, the lines 

 of attack, are more clearly recognised. 



