DARWIN'S THEORY 75 



if their younger stages were unknown. No naturalist has any 

 doubt that these parasites are the descendants of forms which 

 once swam freely about like other Crustacea, and if so, then 

 undoubtedly they recapitulate in their development the history 

 of the race. 



We might add to the list indefinitely, but one other 

 example must suffice. The beautiful feather-star, one of our 

 less-known Echinodermata, which can be dredged in shallow 

 water all round our coasts, possesses when adult a mere blunt 

 knob in the middle of the back from which rooting processes 

 originate ; it can hold on for a time to a given spot by these 

 processes, and it can also let go and swim about by move- 

 ments of its delicate arms until it finds a more suitable place. 

 When young, however, the feather-star has a delicate stalk 

 springing from the middle of the back, and by this stalk it is 

 permanently anchored to one spot. Now the Carboniferous 

 limestone in some parts of England is in large measure made 

 up of the broken fragments of the stalks of extinct feather- 

 stars, and it is practically certain that amongst these ancient 

 stalked feather-stars the ancestors of our present feather-stars 

 are to be found. Here again the life-history of the individual 

 recapitulates that of the race. Since this principle is found 

 to hold where we have independent evidence as to what the 

 ancestry of a given form has been, it seems justifiable to 

 conclude that it underlies the development of an animal from 

 the egg in all cases, since it seems a reasonable supposition to 

 hold that this development is the same sort of thing wherever 

 it occurs. Hence Haeckel formulated what he called "The 

 fundamental law of biogenesis" in the words which we 

 have just used, viz. : " The individual in its development 

 recapitulates the history of the race." When once the idea 

 was grasped that life-history in general had this meaning, 

 an immensely increased interest was awakened in its study 

 and elucidation, and this interest has lasted in scarcely 

 diminished degree till the present day. The field of research 

 is certainly limitless ; there are at least one million distinct 

 species of animals living at the present day, each with its 

 distinct type of life-history in few cases is the complete life- 

 history known, in a good many more cases only bits and 

 scraps of this history have been made out, but in the vast 



