18 Psyche [Fel)ruary 



differ greatly from those of described American Trichopterous 

 larvae. Instead of the usual dwellings of stones or twigs, or tubes 

 of silk, these utilize fallen twigs of wood from the stream-bottom. 

 The twigs are hollowed from end to end, and lined with silk, form- 

 ing portable cases which are a natural part of their surroundings. 

 These belong to an undescribed species, whose larvae abound 

 among the litter of branches and twigs, from the surrounding 

 forest. In spite of their abundance they are most inconspicuous 

 among the debris. They crawl with a jerky motion, as if swayed 

 by the passing current, or rest, as if lodged, on a submerged branch, 

 and when disturbed, let go, drifting down stream with the current. 

 The twigs used as cases vary greatly in length and diameter, 

 apparently being selected at random from the litter on the bottom 

 of the forest stream. Sometimes pieces of heavy bark or frag- 

 ments of broken wood are used. A cylindrical hole always pene- 

 trates the wood from end to end. In some twigs the chamber 

 forks near the anterior end, one outlet curving downward and 

 opening to the exterior at one side, while the other perforates the 

 end of the stick. The side outlet, when present, forms the anterior 

 entrance to the case, the other in the end being plugged with silt 

 or with small pebbles. Sometimes the chamber curves downward 

 without forking, as in Fig. 13. The chamber is always lined with 

 silk. (Fig. 13 represents a case with the silk tube cut away, except 

 around the larva.) Although there is considerable variation in the 

 size of the twigs used their average size increases with the growth 

 of the larvae. To ascertain how the change in cases is made several 

 experiments were made with captive larvae. Some were removed 

 from their cases and put in cages with twigs of appropriate size. 

 These larvae did not attempt to use the wood for making new cases, 

 but merely spun silken tubes to which particles of silt adhered; 

 others, which had one side removed from their cases, repaired 

 the damage with silk and silt. One larva repaired the damaged 

 side with silt and fragments of bark and then proceeded to cut 

 away the two ends of its case. It worked from the damaged side 

 of the case, cutting narrow incisions across the twig until the op- 

 posite side was reached. The operation of cutting the two inci- 

 sions across the twig ten mm. in diameter consumed about 24 

 hours. Two specimens, which were retained in aquaria in the 

 laboratory, attached the anterior ends of their cases securely, by 



