44 



fixed, much larger, stoney fragments ; such are common in the 

 Ravensbourne. Very extraordiuary cases are those of Helkopsycke, 

 spread over nearly the whole world, but not occurring in Britain. 

 These are for all the world like small spiral shells formed of 

 sand or gravel, and such is their deceptive resemblance to shells 

 that they were originally described as such, and even a new genus 

 {Thelidomus) was formed for their reception by Conchologists. 

 Their true nature has long been known, but it is only recently 

 that the perfect insects of the species that construct them have 

 been satisfactorily determined. 



Were I to only briefly allude to the many marvellous forms 

 that exist, I should have to occupy your attention for several 

 evenings. Hitherto I have alluded to Caddis- worms as peculiarly 

 aquatic. But there is no rule without an exception, and there 

 exists at least one instance of a species that lives out of the 

 water amongst moss, at the roots of trees {Enokyla) ; it con- 

 structs an ordinary slightly curved tube of sand, and has occurred 

 in one or two localities in this country ; an additional peculiarity 

 in this species, is that the female of the perfect insect has only the 

 slightest rudiments of wings. Mention should also be made of 

 the cases formed by minute insects of the family {HydroiMUdoi) ; 

 these are usually like flattened or kidney-shaped seeds, often 

 without any extraneous materials, or with only a coating of very 

 fine sand, opening by a slit at either end ; recent researches have 

 discovered some extraordinary forms, which time will not permit 

 me to allude to here. 



The constantly fixed cases need little more than passing 

 allusion. They are formed by the families Hydropsychidce. and 

 RhyacophUidcB. 



If we take up a large stone from the bottom of a clear 

 stream, and examine its surfaces, we are pretty certain to find 

 what appear to be little oval masses of agglutinated gravelly 

 fragments, and upon opening them we find Caddis-worms. But 

 many of the larvse of this class live almost free beneath stones, 

 or with the lightest possible covering, and the firm cases are 

 only constructed when the inmates are about to assume the pupal 

 condition. Some of them construct long serpentine mud galleries 

 on stones, &c., in which they live, but a more solid case is 

 formed before metamorphosis. Some insects of this class are 

 extremely abundant, and it has even been suspected that certain 



