218
FIILARY B. MOORE
The present study arises from the observation that it is much more
difficult to keep organisms alive in the laboratory in the tropics than it
is in temperate climates. I n general, departure from optimal conditions
for one environmental factor tends to reduce the tolerance range of a
species for other factors. Mayer (1914) says . . . “ In marine animals of
the temperate or arctic regions a considerable range of temperature
above or below the normal produces relatively little difference in
their activities, but in tropical forms even a few degrees of heat or cold
cause a marked depression in movement.’’ It seemed possible that some
condition in the tropics was less than optimal, even under natural
conditions and that an animal brought into the laboratory was therefore
less tolerant of the unnatural conditions it encountered there than a
comparable temperate species would be. Before examining evidence
for conditions, being other than optimal in the tropics, we have
assembled data on the trend of some of the environmental conditions
with latitude. We must emphasize that throughout these studies we
are showing s i g d c a n t general trends, but that exceptions to the trends
can always be found if we consider isolated species or localities.
11. ML~TERIALS m METHODS
In almost all cases these analyses are based on published data,
although some information from current work at this laboratory has
been included. All the source references are included in the bibliography,
but their inclusion in the individual sections would involve unjustifiably
lengthy tables. For the same reason, graphs would be too complicated
if they indicated the particular species and locality to which each point
referred. Only particularly important sources are mentioned in the
various sections. Throughout this paper, the terms polar, temperate ,
and tropical have been used to refer to cold, intermediate, and warm
seas without implying correspondence with more exactly defined
zoogeographic regions. “ Barnacles ” implies balanoid barnacles only
and “ molluscs ” includes only gastropods and bivalves.
111. PHYSICAL ASPEOTS
A. Temperature
Most comparisons are made with the annual mean sea temperature,
but in aome cases we have made use of the mean maximum and mean
minimum and of the mean seasonal range. Many of the organisms whose
characters we consider live on or close to the shore. For much of the
world, temperatures for shallow waters are not available and we have
been forced to draw on the extensive data from offshore sea surface
FIILARY B. MOORE
The present study arises from the observation that it is much more
difficult to keep organisms alive in the laboratory in the tropics than it
is in temperate climates. I n general, departure from optimal conditions
for one environmental factor tends to reduce the tolerance range of a
species for other factors. Mayer (1914) says . . . “ In marine animals of
the temperate or arctic regions a considerable range of temperature
above or below the normal produces relatively little difference in
their activities, but in tropical forms even a few degrees of heat or cold
cause a marked depression in movement.’’ It seemed possible that some
condition in the tropics was less than optimal, even under natural
conditions and that an animal brought into the laboratory was therefore
less tolerant of the unnatural conditions it encountered there than a
comparable temperate species would be. Before examining evidence
for conditions, being other than optimal in the tropics, we have
assembled data on the trend of some of the environmental conditions
with latitude. We must emphasize that throughout these studies we
are showing s i g d c a n t general trends, but that exceptions to the trends
can always be found if we consider isolated species or localities.
11. ML~TERIALS m METHODS
In almost all cases these analyses are based on published data,
although some information from current work at this laboratory has
been included. All the source references are included in the bibliography,
but their inclusion in the individual sections would involve unjustifiably
lengthy tables. For the same reason, graphs would be too complicated
if they indicated the particular species and locality to which each point
referred. Only particularly important sources are mentioned in the
various sections. Throughout this paper, the terms polar, temperate ,
and tropical have been used to refer to cold, intermediate, and warm
seas without implying correspondence with more exactly defined
zoogeographic regions. “ Barnacles ” implies balanoid barnacles only
and “ molluscs ” includes only gastropods and bivalves.
111. PHYSICAL ASPEOTS
A. Temperature
Most comparisons are made with the annual mean sea temperature,
but in aome cases we have made use of the mean maximum and mean
minimum and of the mean seasonal range. Many of the organisms whose
characters we consider live on or close to the shore. For much of the
world, temperatures for shallow waters are not available and we have
been forced to draw on the extensive data from offshore sea surface