THE LIFE OF THE SEA-SHORE. 135 
hope to find such a number and variety of animals within a 
limited area. It is, perhaps, remarkable therefore, that in 
spite of our extensive coast line, and of our national love of 
the sea, relatively so few people are interested in the life of 
the sea-shore, even though many of the problems with which 
modern biological science is most closely concerned are 
perhaps more vividly illustrated there than anywhere else. 
We have learned to believe that one of the most striking 
characteristics of living things is the fact that they are 
adapted to their surroundings, and change in harmony with 
changes in their surroundings. But while in the case of 
terrestrial animals there often seems to be great constancy of 
environmental conditions, on the shore the changes are con- 
spicuously vivid. Not only have we the periodical move- . 
ments of the tides, and the less constant changes of storms, 
but a careful study of any area shows that variation in the 
physical conditions is always going on. Rocks which sup- 
port an abundant fauna are overwhelmed by drifting sand, 
and again new rock surfaces are uncovered. The currents 
at the mouths of rivers are perpetually changing, and as 
they change, the relative position of beds of mud and sand 
change also. Though such changes may be sudden, at times 
they are slow and gradual, and must give time for the 
organisms to adapt themselves to the new conditions. The 
shore is thus admirably adapted for the study of many 
biological phenomena, especially those which can be investi- 
gated without elaborate apparatus, and which are readily 
accessible to all. 
Without stopping to strictly define the meaning of the 
word ‘shore, we may conveniently begin with that common- 
place of observation which shows that all parts of the shore 
area are not equally productive of life. It is true that 
wherever the ebbing tide leaves bare long stretches of sand, 
there will be found some of the inhabitants of the shore 
waters, living or dead, according to the force of the waves 
which have torn them from their rocky homes. But to find 
these creatures in their natural condition we must forsake 
the sandy beach for the weed-covered rocks left bare by the 
tide. This is a very familiar fact, but the reason is perhaps 
not altogether obvious. Consider for a moment what 
