588 The American Naturalist. [July, 
life was represented only by simple and minute pelagic organ- 
isms.” 
Mr. Brooks’ point of view, then, is that marine life is older 
than terrestrial; it has shaped itself in relation to its food 
supply; this food supply, the microorganisms referred to 
above, is the only form of life which is independent and it 
therefore must be the oldest; from these simple types the pe- 
lagic ancestors of all the great groups of metazoa were slowly 
evolved until the colonization of the bottom, when a rapid ad- 
vancement took place; the present highly differentiated 
forms which constitute the ocean fauna are the descendants of 
the colonizers, while the lower pelagic forms are the lineal rep- 
resentatives of the primitive forms, some of which are slightly 
modified by the influence of the emigrants from the shore and 
bottom. 
