6 PROFESSOR A. M. MARSHALL. 



and gradually acquiring the adult peculiarities as it approaches the 

 surface, through removal of the cells lying above it. 



The above examples, selected almost haphazard, will suffice to 

 illustrate the Theory of Recapitulation. 



The proof of the theory depends chiefly on its universal applicability 

 to all animals, whether high or low in the zoological scale, and to all 

 their parts and organs. It derives also strong support from the ready 

 explanation which it gives of many otherwise unintelligible points. 



Of these latter a familiar and most instructive instance is afforded by 

 rudimentary organs, i.e., structures which, like the outer digits of the 

 horse's leg, or the intrinsic muscles of the ear of a man, are present in 

 the adult in an incompletely developed form, and in a condition in 

 which they can be of no use to their possessors ; or else structures which 

 are present in the embryo, but disappear completely before the adult 

 condition is attained, for example, the teeth of whalebone whales, or 

 the branchial clefts of all higher vertebrates. 



Natural selection explains the preservation of useful variations, but 

 will not account for the formation and perpetuation of useless organs ; 

 and rudiments such as those mentioned above would be unintelligible 

 but for Recapitulation, which solves the problem at once, showing that 

 these organs, though now useless, must have been of functional value 

 to the ancestors of their present possessors, and that their appearance 

 in the ontogeny of existing forms is due to repetition of ancestral 

 characters. Such rudimentary organs are, as Darwin pointed out, of 

 larger relative or even absolute size in the embryo than in the adult, 

 because the embryo represents the stage in the pedigree in which they 

 were functionally active. 



Rudimentary organs are extremely common, especially among the 

 higher groups of animals, and their presence and significance are now 

 well understood. Man himself affords numerous and excellent 

 examples, not merely in his bodily structure, but by his speech, dress, 

 and customs. For the silent letter b in the word doubt, or the w of 

 answer, or the buttons on his elastic-side boots are as true examples of 

 rudiments, unintelligible but for their past history, as are the ear 

 muscles he possesses but cannot use, or the gill-clefts, which are 

 functional in fishes and tadpoles, and are present, though useless, in 

 the embryos of all higher vertebrates, which in their early stages the 

 hare and the tortoise alike possess, and which are shared with them by 

 cats and by kings. 



