The Life of the Fly 



Land-shells, swept into the ditches by the 

 rains after the inmate's death, are accepted 

 quite as readily. In the work made of the 

 Mollusc's cast-off clothing, I find encrusted 

 the spindle-shell of the Clausilium, the key- 

 shell of the Pupa, the spiral of the smaller 

 Helix, the yawning volute of the Vitrina, 

 or Glass-snail, the turret-shell of the Buli- 

 mus,^ denizens all of the fields. In short, the 

 Caddis-worm builds with more or less every- 

 thing that comes from the plant or the dead 

 Mollusc. Among the diversified refuse of 

 the pond, the only materials rejected are those 

 of a gravelly nature. Stone and pebble are 

 excluded from the building with a care that 

 is very rarely absent. This is a question of 

 hydrostatics to which we will return presently. 

 For the moment, let us try to follow the con- 

 struction of the scabbard. 



In a tumbler small enough to allow of easy 

 and precise observation, I instal three or four 

 Caddis-worms, extracted this moment from 

 their sheaths with every possible precaution. 

 After a number of attempts which have at 

 last shown me the right road, I place at their 

 disposal two kinds of materials, possessing 

 opposite quahties; the supple and the firm, 



^The above are all Land-snails. — Translator's Note. 

 i88 



