The Caddis-Worm 



lowing facts are a refutation of any such hy- 

 drostatic calculations in the animal. 



I remove a number of Caddis-worms from 

 their sheaths and submit these, as they are, to 

 the test of water. Whether formed wholly of 

 fibrous remnants or of mixed materials, not 

 one of them floats. The scabbards made of 

 shells go to the bottom with the swiftness of a 

 bit of gravel; the others sink gently. I experi- 

 ment with the separate materials one by one. 

 No shell remains on the surface, not even 

 among the Planorbes, which a many-whorled 

 spiral ought, one would think, to keep afloat. 

 The fibrous remnants must be divided into two 

 categories. The first, darkened by time and 

 soaked with moisture, sink to the bottom. 

 These are the most plentiful. The second, 

 considerably fewer in number, of more recent 

 date and less saturated with water, float very 

 well. The general result is immersion, as in 

 the case of the intact scabbards. I may add 

 that the animal, when removed from its tube, 

 is also unable to float. 



Then how does the Caddis-worm manage 

 to remain on the surface without the support 

 of the grasses, considering that itself and its 

 sheath are both heavier than water? Its secret 

 is soon revealed. I place a few high and dry 

 205 



