74 Royal Institution. 



the controversy in the Academie des Sciences — are all these com- 

 mon plans identical, or are they not ? 



Now, if we confine ourselves to the sole method which Cuvier 

 admitted — the method of the insensible gradation of forms — there can 

 be no doubt that the Vertebrate, Annulose and Molluscan plans are 

 sharply and distinctly marked off from one another, by very definite 

 characters ; and the existence of any common plan, of which they are 

 modifications, is a purely hypothetical assumption, and may or may 

 not be true. But is there any other method of ascertaining a com- 

 munity of plan beside the method of Gradation 1 



The Lecturer here drew an illustration from Philology — a science 

 which in determining the affinities of words also employs the me- 

 thod of gradation. Thus unus, uno, un, one, ein, are said to be 

 modifications of the same word, because they pass gradually into one 

 another. So Hemp, Hennep, Hanf, and Cannabis, Canapa, Chanvre, 

 are respectively modifications of the same word : but suppose we 

 wish to make out what, if any, affinity exists between Hemp and 

 Cannabis, the method of gradation fails us. It is only by all sorts 

 of arbitrary suppositions that one can be made to pass into the other. 



Nevertheless modern Philology demonstrates that the words are 

 the same, by a reference to the independently ascertained laws of 

 change and substitution for the letters of corresponding words, in the 

 Indo-Germanic tongues : by showing, in fact, that though these 

 words are not the same, yet they are modifications by known de- 

 velopmental laws of the same root. 



Now Von Bar has shown that the study of development has a pre- 

 cisely similar bearing upon the question of the unity of organization 

 of animals. He indicated, in his masterly essays published five- 

 and-twenty years ago, that though the common plans of the adult 

 forms of the great classes are not identical, yet they start in the 

 course of their development from the same point. And the whole 

 tendency of modern research is to confirm his conclusion. 



If, then, with the advantage of the great lapse of time and pro- 

 gress of knowledge, we may presume to pronounce judgment where 

 Cuvier and Geoffroy St. Hilaire were the litigants — it may be said 

 that Geoffroy' s inspiration was true, but his mode of working it out 

 false. An insect is not a vertebrate animal, nor are its legs free ribs. 

 A cuttlefish is not a vertebrate animal doubled up. But there was a 

 period in the development of each, when insect, cuttlefish, and verte- 

 brate were undistinguishable and had a Common Plan. 



The Lecturer concluded by remarking, that the existence of hotly 

 controverted questions between men of knowledge, ability, and 

 especially of honesty and earnestness of purpose, such as Cuvier and 

 his rival were, is an opprobium to the science which they profess. 

 He would feel deeply rewarded if he had produced in the minds of his 

 hearers the conviction that these two great men — friends as they 

 were to one another — need not be set in scientific opposition ; that 

 they were both true knights doing battle for science ; but that as the 

 old story runs, each came by his own road to a different side of 

 the shield. 



