PRESIDENTIAL ADDRESS. 3 



animal passes in its progess from the egg to the adult are no accidental 

 freaks, no mere matters of developmental convenience, but represent 

 more or less closely, in more or less modified manner, the successive 

 ancestral stages through which the present condition has been acquired. 



Evolution tells us that each animal has had a pedigree in the past. 

 Embryology reveals to us this ancestry, because every animal in its 

 own development repeats this history, climbs up its oavii genealogical tree. 



Such is the Recapitulation Theory, hinted at by Agassiz,and suggested 

 more directly in the writings of von Baer, but first clearly enunciated 

 by Fritz Miiller, and since elaborated by many, notably by Balfour 

 and by Ernst Haeckel. 



It is concerning this theory, which forms the basis of the Science of 

 Embryology, and which alone justifies the extraordinary attention this 

 science has received, that I venture to address you this morning. 



A few illustrations from different groups of animals will best explain 

 the practical bearings of the theory, and the aid which it affords to 

 the zoologist of to-day ; while these will also serve to illustrate certain 

 of the difficulties which have arisen in. the attempt to interpret 

 individual development by the light of past history — difficulties which 

 I propose to consider at greater length. 



A very simple example of recapitulation is afforded by the eyes of the 

 sole, plaice, turbot, and their allies. These ' flat fish ' have their bodies 

 greatly compressed laterally ; and the two surfaces, really the right 

 and left sides of the animal, unlike, one being white, or nearly so, and 

 the other coloured. The flat fish has two eyes, but these, in place of 

 being situated, as in other fish, one on each side of the head, are both 

 on the coloured side. The advantage to the fish is clear, for the 

 natural position of rest of a flat fish is lying on the sea bottom, with 

 the white surface downwards and the coloured one upwards. In such 

 a position an eye situated on the white surface could be of no use to 

 the fish, and might even become a source of danger, owing to its 

 liability to injury from stones or other hard bodies on the sea bottom. 



No one would maintain that flat fish were specially created as such. 

 The totality of their organisation shows clearly enough that they are 

 true fish, akin to others in which the eyes are symmetrically placed 

 one on each side of the head, in the position they normally 

 hold among vetebrates. We must therefore suppose that flat fish are 

 descended from other fish in which the eyes are normally situated. 



