86 SECRETS OF ANIMAL LIFE 
therefore flourish so abundantly that the supply of 
available nitrogenous food for the Phyto-plankton 
is greatly lessened. According to Sir John Murray 
and Professor Jacques Loeb, the reason is rather 
that low temperature slows the vital processes and 
increases the length of life, so that several gener- 
ations of Plankton organisms are living at the same 
time in the colder waters. It is probable that both 
views are correct. 
It is hardly necessary to say that the analogy of 
producers, consumers, and middlemen should not 
be pressed too hard. Thus it is quite useful to 
follow a recent investigator, Dr. Blegvad, in regard- 
ing the detritus-eating animals as producers in 
relation to the carnivores, just as fishes are pro- 
ducers in relation to the supreme carnivore Man. 
Bivalves and other animals which feed at a low 
level on minute débris are making available to any 
creature that can eat them supplies of energy which 
would otherwise be wasted. Plaice in the Kattegat 
are very fond of lancelets, which subsist on detritus 
particles; so that in respect to the plaice the 
lancelet is a producer or a middleman. The main 
idea is that of the circulation of matter, or of what 
Sir John Murray, who did so much to make Oceano- 
graphy a science, called “the never-ending cycle.” 
The Algze find nourishment mingled with the water 
that bathes them, and, using chlorophyll to “ con- 
jure with the sunbeams,” they build up organic 
compounds from inorganic constituents. Vegetable 
proteins are thus formed, and when these are eaten 
