PIONEER COMMUNITIES 



Ecologically one of the most interesting insects is a caddis-worm 

 (Leptoceridae), which creeps over the Char a and submerged wood. 

 It (Fig. 93) has a case made of the minutest sand grains and pieces of 

 humus, such as are stirred up by the waves and which are to be found 



86 



REPRESENTATIVES OF A YOUNG POND COMMUNITY 



FIG. 86. The shell of a mussel (Anodonta grand is footiana) that has been broken 

 open by a muskrat; slightly enlarged. 



FIG. 87. The burrowing dragon-fly nymph (Gomphus spicatus), with the mask 

 extended. 



FIG. 88. Some fishes of the pond. The dark fish which rests near the bottom is 

 the mud minnow (Umbra limi). The fish swimming about is the golden shiner 

 (Abramis crysoleucas) ', 1/5 natural size. 



among the chara. This species is the successor of the bottom species 

 (Goera). It belongs to a different group and has structural characters 

 which distinguish it from Goera, but which probably have no relation 

 to its habitat or habits. On the other hand, the mores as indicated by 

 case-building is also different but is related to the environment. The 



