PROGRESS, BIOLOGICAL AND OTHER 19 



organizations; and later evolution consists mainly 

 in the evolution of this ground-plan. 



In other words, we can now pass from the consid- 

 eration of the general plan of life's architecture to 

 that of its details. During the next great tract of 

 time, that which was novel in life (for we must not 

 be guilty of a petitio principii in yet speaking of 

 "advance" or "progress") was brought about in two 

 main ways — by an increase in the size of organisms, 

 and by an increase in the efficiency of their working. 



The simplest Metazoa, such as the polyps, as well 

 as the simplest three-layered forms, such as the free- 

 living flat-worms, are all small, composed of an 

 amount of material comparable with that contained 

 in a single one of our hairs. In every group of Met- 

 azoa, increase of size is one of the main features that 

 accompanies specialization, and the more specialized 

 groups possess a higher average size than the less. 



A jelly-fish against a polyp; a cuttle-fish against a 

 primitive mollusc; a vertebrate against its chordate 

 ancestor; the giant reptiles of the late secondary 

 period against their forbears; a horse against Phena- 

 codus; man against the earliest primates — over and 

 over again does size increase with the march of time. 



Not only this, but when there occurs aggregation 

 of individuals to form units of a higher order, as in 

 bees and ants and termites, and in man himself, 

 there too increase of size in the new units thus pro- 

 duced is one of the most notable features. Is not 



