Surface Fauna of the Bay of Fundy. 609 
In many invertebrate animals the difference in pressure at 
1000 fathoms and at one fathom is endured with impunity by 
the same species. Difference in pressure under which a deep-sea 
animal is placed is not believed to be the influence which is most 
important in the determination of the limitation of deep-sea faunæ 
to certain depths. 
Invertebrate animals, however, which can endure equally well 
enormous pressures or live near the surface without harm, are 
delicately susceptible to a change of temperature of a few degrees. 
Temperature has drawn even in littoral zones invisible limits or 
lines of demarcation, which are partially known to naturalists. 
The laws of the diminution in heat with the depth has also been 
shown. It is known that the bottom temperatures of deep-seas are 
surface temperatures in some parts of the globe. If temperature. 
is an important condition of the environment of deep-sea animals, 
it is significant to discover what the character of the marine life is 
in latitudes where the temperature is that of the deep sea and where 
it is constant. 
The polar oceans show on the surface of the water the low 
temperatures of the deep seas. Those temperatures, to find which in 
tropical oceans the plummet has to go many fathoms below the 
surface here come to the surface, and are its ordinary temperature 
It is interesting to discover whether in places widely separated in 
latitude, but where the temperature of the sea is the same and 
constant, we find any uniformity in the ocean fauna. It must be 
recognized that we have in the great body of water which com- 
poses the ocean a mass of liquid, the temperature of which is 
modified by local currents, vicinity to the land, and other conditions. 
As a general law, to which there are some exceptions, it may be 
said that the temperature of the sea decreases as we sink below its 
surface, Of all places in the ocean, where the limits of variations 
sB temperature are small, none equals the deep water. A maximum 
variation in the tropics may be found on the surface and in the 
neighborhood of the coast line. The minimum is far below the 
surface in the deep water. 
It may readily be imagined that, if there were no distribution of 
heat in the ocean by currents as we go north or south from 
the equator, we should find the isothermobatric lines, or lines 
