DARWIN S LIFE. 1 33 



tion. It is Well known that the islands in the South Seas 

 consist for the most part of coral reefs, and are surrounded 

 by them. Formerly no satisfactory explanation could be 

 given of their different and remarkable forms, and of their 

 relation to those islands which are not formed of corals. 

 It was reserved for Darwin to solve this difficult problem, 

 for together with the constructive action of the coral 

 zoophytes, he assumed geological risings and depressions 

 of the bottom of the sea to account for the orisrin of 

 the different forms of reefs. Darwin's Theory of the 

 Origin of Coral Eeefs, like his later one as to the Origin of 

 Organic Species, is a theory which fully explains the 

 phenomenon, and for this purpose assumes only the simplest 

 natural causes, without hypothetically supporting it with 

 any unknown processes. Among the remaining works of 

 Darwin, I must not pass over his excellent monograph on 

 Cirrhipedia, a curious class of marine animals, which in 

 their outward appearance resemble mussels, and were 

 actually considered by Cuvier as Molluscs possessing two 

 shells, while in truth they belonged to the Crustacea (crabs). 

 The extraordinary hardships to which Darwin had been 

 exposed during his voyage in the Beagle had injured his 

 health to such a degree, that after his return home he was 

 obliged to withdraw from the restless turmoil of London life, 

 and since then has lived in quiet retirement on his estate at 

 Down, near Bromley, in Kent. This seclusion from the rest- 

 less activity of the great city certainly exercised a beneficial 

 influence upon Darwin, and it is probable that we owe to it, 

 at least partially, the formation of the Theory of Selection. 

 Undisturbed by the various engagements which in Londoi^ 

 would have wasted his strength, he was enabled to concen- 



