806 The American Naturalist. [October, 
to the corresponding oscillations of the terrestrial fauna and 
flora, and depend on the one side upon climatic and meteoro- 
logical conditions, and on the other upon the varying mode of 
life, particularly upon conditions of reproduction and devel- 
opment. Just as the annual development of most land plants 
is bound up with a definite time of year, as the time of 
budding and leafing, of blooming and fruiting, have in the 
“struggle for existence” become adapted to the meteorological 
conditions, the time of year and other conditions of existence, 
so too the annual development of most marine animals is 
conditioned by definite habits, which have become fixed by 
heredity. The yearly variations may be compared to the 
good and bad fruit years. This yearly variation has been 
noted by many observers in case of many marine animals. 
Our attention is often called to an example of it in the unus- 
ual abundance or scarcity of the catch of certain food fishes. 
Many marine animals, particularly certain meduse, siphon- 
ophores, ctenophores, molluses and tunicates, are found at 
the surface only periodically, in one or a few months of the 
year. This is probably dependent upon conditions of repro- 
duction and development, as well as upon the temperature of 
the season. The daily variations are conditioned by the 
weather and particularly by the wind and rain. A shower 
will very quickly reduce the specific gravity of the surface 
water and thus drive the surface dwelling animals. below. 
Many animals rise to the surface only at a definite time of 
day, some in the morning, others at noon, and yet others only 
towards evening. | 
: Climatic Difference—Prof. Haeckel thinks that the quantity - 
of the Plankton is very little dependent upon the climatic 
difference of the zones, but that the quality is greatly so, and 
indeed in this way, that the number of component species 
diminishes from the equator to the poles. These conditions, 
he believes, are directly referable to the influence of the sun, 
“the omnipotent creator,” whose more direct rays bring about 
an acceleration in the processes which make up the cycle of 
life. As this is true of the Larrea fauna and flora so it, is 
true of the marine. 
