The Recapitulation Theory in Biology 55 



of numerous functionless organs which cannot be explained other- 

 wise than as having been inherited from a previous condition 

 in which they were functional? The answer is that the only 

 organs of this kind which have been retained are organs which 

 have been lost by the adult and have become in this way im- 

 pressed upon development. As an illustration taken from cur- 

 rent natural history of the manner in which larval characters 

 are in actual process of becoming embryonic may be mentioned 

 the case of the viviparous salamander (Salamander atra), in 

 which the gills, etc., are all developed but never used, the animal 

 being born without them. In other and closely allied species 

 of salamander there is a considerable period of larval life in which 

 the gills and gill-slits are functional, but in this species the larval 

 stage, for the existence of which there was a distinct reason, viz., 

 the entirely aquatic habits of life in the young state, has become 

 at one stroke embryonic by its simple absorption into the em- 

 bryonic period. The view, then, that embryonic development 

 is essentially a recapitulation of ancestral history must be 

 given. up; it contains only a few references to ancestral history, 

 namely, those which have been preserved probably in a much 

 modified form by previous larvae. " 91 



This lengthy quotation may be brought to a point by a con- 

 crete application. The traces of gill-slits in the human embryo 

 mean that at a certain period in geological time one of the ances- 

 tors of man was an animal with a larva possessing functional 

 gills of use to it in the water. Later with the extension of the 

 embryonic period this functional condition was rendered use- 

 less by being absorbed, that is, taken into the egg or body of 

 the mother before birth. Its subsequent embryonic history 

 greatly modified it and reduced it to a rudiment. 



It appears, therefore, that with reference to ancestral traces 

 among embryos Sedgwick agrees in the main with Hurst and 

 Morgan. These traces are due to the transmission of similar 

 embryonic forms through successive generations. But Sedgwick 

 differs from these writers in that he does believe there are a 

 few cases of the embryonic retention of functional adult char- 

 acters. And he differs radically in the belief that larvae often 

 retain adult characters in continuing in the life conditions of 

 their ancestors. This however does not happen in a way to 

 show recapitulation. Sedgwick goes beyond Morgan in sug- 

 gesting how the ancestral form originally got the adult char- 



91 Encyclopaedia Britannica, llth ed., art. Embryology, p. 323. 



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