JTTOMAL 

 -OCIETIES 



NDER the sheltering 

 influence of shores the 

 vascular plants may 

 grow. Animals elude 

 the eyes of their ene- 

 mies, not by becom- 

 ing transparent, but 

 by taking on colors and forms in resemblance to their 

 environment. They escape capture, not alone by fleet- 

 ness, but also by development of defensive armor, by 

 shelter-building and by burrowing. 



Large and small and all intermediate sizes occur 

 together along shore, and those that appear betimes in 

 open water make shifts innumerable for place and 

 food and shelter for their young. 



There are many factors affecting the grouping of 

 littoral organisms into natural associations, most of 

 them as yet but little studied ; but the most important 

 single factor is doubtless the water itself. The density 

 of this medium and the consequent momentum of its 

 masses when in motion so profoundly affect the form 

 and habits of organisms that they may be roughly 

 divided into two primary groups for which are sug- 

 gested the following names: 



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