586 The American Naturalist. [July, 
Sameness of environment and lack of competition for space 
have tended to make pelagic plant life retain its primitive 
simplicity, but existing apparently under the same conditions 
is an infinite variety of animal life. How can this be ac- 
counted for? In tracing the phylogeny of Salpa, Mr. Brooks 
finds that the structure which is so well adapted for life on 
the high seas has come to it by the inheritance of peculiarities 
originally acquired by bottom animals in adaptation to the 
needs of a sessile life. In this connection the author states 
that the majority of the present pelagic animals have not been 
produced at the surface of the ocean by gradual evolution 
from a simple pelagic ancestor, but that part of their family 
history has been worked out by individuals who colonized — 
upon or near the bottom, or along the sea shore, or upon the 
land, and the exceptions are all simple animals of minute size. 
He reviews the chief groups of metazoa to demonstrate this 
fact and gives, as notable exceptions, some of the veiled 
meduse, a few of the primitive annelids, possibly, and the 
copepods among the crustacea. Among the higher forms, the 
fishes, which at first sight would seem to have been pelagic 
from the beginning, so admirably are they fitted for life in 
the open water, are found upon examination to be only sec- 
ondarily adapted to a pelagic life, like the sea-birds and the 
cetaceans. 
Mr. Brooks bases these statements on evidence from paleon- 
tology, from embryology, and from the structure and habits 
of living animals. 
In discussing the conditions under which the primitive pe- 
lagic fauna lived, and the comparative results of pelagic and 
bottom environment upon marine life, the author points out. 
that while the animals which first settled on the bottom prob- 
ably did not secure more food than did their floating allies, 
they obtained it with less effort and were able to devote their 
surplus energy to growth and multiplication. The rapid mul- 
tiplication led to crowding and competition, prevented the in- 
flux of newcomers from the open water, and finally resulted in 
the elaboration and specialization of the types of structure al- 
ready established. Evolution was rapid, for life at the bottom 
Wome ia ate dU Y EET ER i a: dba ra METER NE 
