THE FISHES, MOLLU8CA. AND OTHER OBJECTS. 41 



the body. The head and the first three segments of 

 the body are hard and horny a most useful fact 

 in the economy of these creatures, seeing that these 

 are the parts necessarily required to be thrust forth 

 in obtaining food. The rest of the body is soft, and 

 at the extremity are a series of hooks, by means of 

 which the caddis-worm can take firm hold of its 

 dwelling. The swellings or humps, on the body, 

 which fill the case, help also to prevent the body 

 being forcibly dragged out. In looking out for 

 these interesting objects, you will not fail to find 



Fig. 25. 



Case of Phryganea grandis. 



one species, the Phryganea grandis (Fig. 25), whose 

 case is invariably formed, not of shells, but of pieces 

 of leaves and other vegetable matters so cemented 

 together that they form a cylindrical tube. You will 

 notice that the pieces are arranged spirally, either 

 from left to right, or from right to left, generally the 

 former. The tubes are of nearly equal diameter 

 throughout, and the larva of this species has the 

 power of turning itself inside, and thus of presenting 

 its head at either end as it may wish. Not less 

 common than this species of caddis-fly, are the larvae 

 of another genus, named Limnepliilus, or " pond- 

 lover." One of them (L. rhombicus, Fig. 26) uses 

 pieces of moss, cut lengths of rushes, grass, &c.. and 



