96 AMERICAN ENTOMOLOGY. 



cil consists of a silky matter, with various objects attached to 

 the exterior, such as sand gravel, small pieces of wood or reed, 

 &c., so proportioned that its weight exceeds but little that of 

 the water. As the inhabitant increases in bulk, the tube at 

 length becomes too small, and is necessarily abandoned. An- 

 other, of suitable dimensions is, however, soon constructed, and 

 the little animal is again in a state of security. This artisan, is 

 of a cylindrical, somewhat elongated form, consisting of twelve 

 joints or segments; on the fourth joint is generally a conic tu- 

 bercle on each side, and on the ultimate segments are two move- 

 able hooks : these projections from the body, appear to be useful 

 as points of support against the sides of the tube. The head is 

 of firm a consistence, furnished with strong mandibles, and two 

 eyes. The feet are six in number, and are not natatory, the an- 

 terior pair being shorter and thicker than the others, which are 

 considerably elongated, and not dilated, nor deeply ciliated. 

 Thus constituted, the animal crawls at the bottom of the water, 

 with the feet and the anterior part of the body protruded from 

 the tube, in search of food. 



When about to undergo the change into the nymph state, the 

 larva affixes its tube to some permanent object. It then pro- 

 ceeds to close the ends of its dwelling by a silky net, the meshes 

 of which are so small as to prevent the ingress of depredating 

 insects, and yet sufficiently large to admit of a free circulation of 

 water for the purpose of respiration. The head of the nymph is 

 provided with a kind of beak, consisting of hooks, which are 

 used to force a passage through the net-work. At this period, 

 which occurs in fifteen or twenty days after the change from 

 the larva state, its period of immobility ceases : it departs from its 

 tube, and walks or swims with activity, the feet being fringed 

 for the latter purpose. The young animal now, for the first time, 

 emerges from the water, and seeks a dry, secure position for its 

 ultimate change here, after remaining at rest for some minutes, 

 to permit the superfluous moisture to evaporate, it throws oft' its 

 covering, and soon takes wing in search of a mate. Many spe- 

 cies of a smaller size proceed in a difiierent manner ; the nymph 

 ascends to the surface of the water, where it is emancipated from 

 its exuvia, which serves as a boat to support the perfected insect, 

 until its wings are sufficiently developed, dried, and prepared for 

 flight. 



