8 Journal New York Entomological Society. [Vol. xxi. 



pupae are usually to be found in protected situations. I have found 

 them most often imbedded in soft wood under the bark of decayed 

 logs. As many as twenty-five cases were taken in a piece of white 

 birch 2^ in. in diameter by 6 in. long. 



It will be noted that as far as this material goes and it may be 

 considered typical, the first two species, namely those which live in 

 the most rapid streams, are the only ones among those having ex- 

 posed cases which firmly anchor their larval cases. The last two, 

 namely those characteristic of still water, 'are also the two which 

 build their cases of the lightest, most easily floated material. The 

 species of Polyccntropus build in the mud or sand of the bottom 

 and since there is more loose material, mud, etc., to be found where 

 the current is weakest and since the exposed tips of the cases would 

 be liable to be broken in the swift current, they find their best home 

 in water having slight or no motion. In other words, I believe that 

 the distribution of the larvae of Trichoptera is strongly influenced 

 by the adaptation of their cases to the strength of the current. 



Of course, other factors have influence, but they do not seem to 

 be as important as the strength of the current. As an example of 

 the way these other factors work, it might be noted that although 

 Platycentropiis niaculipennis is typically found in still water, it occurs 

 in even a strong current if there be an abundance of vegetation to 

 which it can cling. 



As another example, Molanna cinerea Hagen is found only where 

 there is slimy ooze on the bottom, but it is not found where there is 

 a slimy ooze if there is no current or if the current be at all strong. 

 As a matter of fact, we can, by a glance at Fig. — , make a fairly safe 

 prediction as to which of these species will be found in a given 

 environment — that is, a given environment in northern New Jersey. 



