6 Journal New York Entomological Society. tVoi. xxi. 



quart jar and after about two weeks adults emerged from most of 

 them. Some of these adults mated, laid eggs, and larvae are now 

 living (Jan., 1913) in a small dish containing less than one gill of 

 water, which is merely renewed, never changed. 



There is, however, a rather definite relation between the distribu- 

 tion of Trichoptera and the speed of the current, as is shown by the 

 accompanying cut. The vertical divisions indicate the relative speed 

 of the current and the black areas show the conditions in which the 

 various cases (selected as typical forms) are found. The widths of 

 the areas give an approximate idea of the relative abundance of the 

 respective species in the various environments. Probably further 

 study will make some changes in this diagram necessary, but I believe 

 that it is correct in a general way at least. The upper case is that 

 of a net-building Hydropsyche; it is typically found only in very 

 strong currents but occasionally it does occur where the flow is not 

 so rapid. They usually build their cases of sand or small pebbles, 

 cemented together with silk and fastened on or between stones. The 

 larvae are very active, they are able to crawl over the stones and 

 cling fast with their long pro-legs which are provided with strong 

 hooks. The entrance of the case opens into a net with a canopy over 

 it, built of very small pieces of twigs and leaves. The opening of 

 the net faces the current. The pupa, upon leaving the case, crawls 

 over the bottom for a short time, then shoots to the surface, where it 

 immediately sheds its skin and takes flight. I have witnessed this 

 a number of times. They undoubtedly obtain their food by means 

 of the net. 



The next species shown occurs with the net builder. It builds 

 loose cases of small pebbles between or on stones in rapidly flowing 

 water. 



The next three species are found in water which has a fairly 

 strong current but they do not occur in the swiftest streams where 

 the two previously mentioned are at home. The larvce do not fasten 

 down their cases as do the two above mentioned. 



The case of Halcsiis argiis Harr. (the large one in the middle) 

 consists of a tough inner portion surrounded by heavy water-soaked 

 twigs and pieces of bark. The immature larvae occasionally use 

 pebbles also and those about to pupate normally do. 



The cases of the other two species are made of sand and pebbles. 



