1913 ] 
Pearse: Fauna of the Rock Beaches 
29 
will be found in the annotated list of species. Many species feed 
on the microscopic organisms that swarm in the littoral water 
(sponges, clams, coelenterates, Bryozoa, barnacles, ascidians, etc.) ; 
others devour the algae which grow on the rocks ( Strongylocentro - 
tus, nudibranchs, Idothea); a number of the larger species feed 
on smaller animals (Asterias, pycnogonids, ribbon fish, spiders, 
ants, sandpiper, etc.) ; several are scavengers (beetles, flies, worms, 
crabs, rats). Both plant and animal food are abundant. It is 
interesting to note that at least two of the larger predaceous 
animals ( Pholis , crabs) eat barnacles, which constitute the most 
abundant animal food. 
It is noteworthy that those animals which show the greatest 
development of the characteristics enumerated above have the 
widest distribution in the different zones and occur in the greatest 
numbers. Balanus, which combines with its firm fixation, the 
ability to capture food anywhere that sea water comes, and a 
remarkable resistance to changes in temperature, is everywhere. 
Mytilus and Littorina are almost as ubiquitous. The most abun- 
dant animals are those which feed on microscopic organisms or 
minute organic particles. 
From the foregoing discussion it is apparent that the rock 
beaches at Nahant are a royal battle ground for the lower animals. 
The surface of the rock is a veritable sieve through which the 
microscopic organic content of the water disappears. The barnacles 
sweep it constantly with their fishing nets; the carpets of clams 
siphon food into their depths from the turbid water; Littorinas 
search every square inch and sweep it clean; wherever there is 
sufficient moisture the coelenterates and bryozoans spread their 
delicate tentacles to seize their share. Such abundant inhabitants 
with the algae furnish food for the less common larger animals; 
their refuse supports a host of lowly saprophytic organisms and 
scavengers. The keen competition for place and food, the abun- 
dance of life and its various forms makes one willing to believe 
that here indeed did organic matter have its origin. 
III. THE SAND BEACH 
The sand beach at Nahant (fig. 1, Station 4) was of interest 
because it showed a zonal arrangement in the distribution of ani- 
mals without the presence of large algae, though microscopic 
