Mode of Life of Orthocladiiis 



17 



but jerks itself forward by a few powerful undulations in 

 which the flexible case participates. It is unlikely that 

 the creature swims by this method, which demands con- 

 siderable effort, and is not continued long at a stretch. 

 When it swims it leaves the case altogether, and loops 

 through the water like a blood-worm. In captivity it 

 has been seen to return to its tube after swimming in 

 this manner. (4) Building. At intervals the larva 

 apparently adds fresh material to its case. It with- 

 draws its head towards the middle, and then works over 

 the inner surface with its mandibles, from behind for- 



FiG. 9. — Egg-mass of Cliironomiis (Ortliocladitis). x lo. 



wards, testing the wall continually with its prothoracic 

 legs. It has not been seen to work in this way on the 

 outer surface. 



' The larva grows rapidly, and pupates in about a fort- 

 night. The cast larval skin is passed out of the pupal 

 tube, which is now attached at one end to some fixed 

 object. The pupa executes respiratory movements inside 

 the tube, and after a short time— two days or less — comes 

 out and floats at the surface of the water, where the fly 

 escapes. 



