PRESIDENTIAL ADDRESS. 11 



achievements, and afford a rich mine of carefully recorded facts, the 

 full value aud bearing of which we are hardly yet able to appreciate. 



If further evidence as to the value and importance of the 

 Recapitulation Theory were needed, it would suffice to refer to the 

 influence which it has had on the classification of the animal Kingdom. 

 Ascidians and Cirripedes may be quoted as important groups, the true 

 affinities of which were first revealed by embryology ; and in the case of 

 parasitic animals the structural modifications of the adult are often so 

 great that but for the evidence yielded by development their zoological 

 position could not be determined. It is now indeed generally 

 recognised that in doubtful cases embryology affords the safest of all 

 clues, and that the zoological position of such forms can hardly be 

 regarded as definitely established unless their development, as well as 

 their adult anatomy is ascertained. 



It is owing to this Recapitulation Theory that Embryology as 

 exercised so marked an influence on zoological speculation. Thus the 

 formation in most, if not in all, animals of the nervous system and of 

 the sense organs from the epidermal layer of the skin, acquired a new 

 significance when it was recognised that this mode of development was 

 to be regarded as a repetition of the primitive mode of formation of 

 such organs ; while the vertebral theory of the skull affords a good 

 example of a view, once stoutly maintained, w r hich received its death- 

 blow through the failure of embryology to supply the evidence requisite 

 in its behalf. The necessary limits of time and space forbid that I 

 should attempt to refer to even the more important of the numerous 

 recent discoveries in embryology, but mention may be very properly 

 made here of Sedgwick's determination of the mode of development of 

 the body cavity in Peripatus, a discovery which has thrown most 

 welcome light on what was previously a great morphological puzzle. 



We must now turn to another side of the question. Although it is 

 undoubtedly true that development is to be regarded as a recapitulation 

 of ancestral phases, and that the embryonic history of an animal 

 presents to us a record of the race history, yet it is also an undoubted 

 fact, recognised by all writers on embryology, that the record so obtained 

 is neither a complete nor a straightforward one. 



It is indeed a history, but a history of which entire chapters are 

 lost, while in those that remain many pages are misplaced while others 

 are so blurred as to be illegible ; words, sentences, or entire paragraphs 



