172 
president’s address. 
its weight by i kilo., and a simple sum shows that to 
perform the same feat on a diet of Daphnias would need 
i.iii.iii individuals. But calculations of this kind are of 
little use for any purpose. 
But apart from countings and calculations of this kind, 
the organisms which compose the plankton association, are 
of great interest in themselves from their structure and adap- 
tation to their surroundings. The following classification has 
been made of them according to their swimming or floating 
apparatus Neidoplankton, possessing active swimming 
apparatus: Morphoplankton, floating in virtue of their shape 
( e.g ., needle or spindle shaped, saucer or disc shaped, or having 
swimming hairs or spines) ; Kollaplankton, surrounded with 
a gelatinous mass ; Hidroplankton, floating by means of 
a secretion of an oil globule or gas vacuole ; and Phlykti- 
plankton, possessing hydrostatic organs. 
The plankton of small lakes is not quite comparable with 
that of large and deep lakes, as it includes a great number 
of forms, which in the latter are confined to the edges ; 
Forel has given the term Heleioplankton to the association 
of floating organisms found in ponds. 
The third or littoral region of lakes is defined by Forel 
as the strip of water bordering the shore down to a depth 
of 20 to 25 m. ; i.e., down to the limit of growth of green 
plants upon the bottom (only Chara and Nitella are found 
at these depths). In this region the greatest variety of life 
is found, and it is distinguished chiefly by its vegetation, 
amongst which the higher plants predominate ; it merges 
on the one hand into the land, and on the other into the 
pelagic region, and partakes of the characters of both. It 
presents an environment much more severe than that of 
the other regions, because it is subject to great vicissitudes 
of temperature and to disturbance by winds and waves. 
It will be clear from what has been said of the physical 
conditions of the larger lakes, which have been studied with 
