W. K. BEOOKS ON THE GENUS SALPA. 169 



Colonies which started in shallow water were exposed to accidents 

 from which those in great depths were free, and in view of our present 

 knowledge of the permanency of the sea-floor and of the broad outlines 

 of the continents, it is not impossible that the first fauna which settled 

 in the deep zone around the continents may have persisted and given 

 rise to our modern life. However this may be, we must regard this deep 

 zone as the birthplace of the fauna which has survived ; as the ancestral 

 home of all the improved metazoa. 



The effect of life upon the bottom is more interesting than the place 

 where it began, and we have now to consider its influence in the evolution 

 of animals. 



The effect of the secondary acquisition of a sedentary life by modern 

 animals has been fully discussed by many writers, but no one, so far as 

 I am aware, has ever considered the effect of the first settlement of the 

 bottom by pelagic animals, all whose competitors and enemies had 

 previously been pelagic. 



It is doubtful whether the animals which first settled on the bottom 

 secured any more food than the floating ones, but they undoubtedly 

 obtained it with less effort, and were able to devote their superfluous 

 energy to growth and to multiplication, and thus to become larger and 

 to increase in numbers faster than pelagic animals. 



Their sedentary life must have been favorable to both sexual and 

 asexual multiplication, and the tendency to multiply by budding must 

 have been quickly rendered more active. It is sometimes stated that the 

 capacity for budding has been acquired among the metazoa as the result 

 of a sedentary life, but this view hardly seems to be the true one. Capacity 

 for asexual multiplication is very old, older in all probability than sexual 

 reproduction, and there is no reason to believe that it has ever been lost 

 even by the highest animals, for it must be regarded as nothing more, in 

 ultimate analysis, than discontinuous growth. The tissues of all animals 

 have vegetative power, and external influences determine whether this 

 shall result in continuous or discontinuous growth, and a trace of the 

 power to multiply asexually is retained even among the embryos of 

 mammals. It is therefore wrong to speak of the acquisition of a capacity 

 for budding, and it is not at all improbable that the primitive pelagic 

 metazoa multiplied by buds ; although the tendency to form connected 

 cormi, and to retain the connection between the parent and the bud until 

 the latter was able to obtain its own food and to care for itself, was a 

 result, and probably one of the first results, of life on the bottom. 



