1916] Biology of Aquatic Lepidoptera 171 



movements are often performed, consisting chiefly of an 

 apparent testing of the lower epidermis with the mandibles, 

 before the larva settles down to the work of removing the piece. 

 It works by using most of the length of the body as a radius and 

 bending the anterior region as the incision is extended. After 

 the initial incision is made, the head is held into the cut and a 

 little to one side, thus placing the cutting plane of the mandibles 

 at approximately right angles to the surfaces of the leaf. One- 

 third of the complete incision may be made without changing 

 the position of the posterior part of the body. Occasionally, a 

 larva takes advantage of the overlapping margins of con- 

 tiguous leaves. Since such a space is usually filled with water, 

 the larva crawls into it, begins work, and in due time cuts an 

 elliptical piece from one or both of the leaves. 



The older larvae utilize the excised pieces in making cases in 

 several ways: 



(1) A single piece may be cut out and tied flatwise against the lower side of 



the leaf. 



(2) Two similar pieces may be cut out, forming a lens-shaped case, which 



is then tied flatwise to the leaf, or else becomes independent. 



(3) Several pieces may be cut out, tied together into a case, and attached to 



the lower surface of the leaf. 



(4) Two pieces may be cut out, tied together flatwise, and then attached 



endwise to the leaf. 



The majority of the cases are placed on the lower, submerged 

 surfaces of the floating leaves. Occasionally, cases containing 

 larvas are found on the dry, upper surfaces, a fact which suggests 

 the possibility that the larvae are not entirely dependent upon 

 respiration by tracheal gills. It is a common thing to find 

 numerous cases of various sizes attached to both surfaces of the 

 submerged leaves of Nymphcea amcricana. How these larvae 

 get on the submerged leaves is not definitely known but it is 

 possible that some of them, by wave action or other mechanical 

 means, are dislodged from the floating leaves and sink to the 

 submerged leaves, or else to the bottom from whence they crawl 

 up the petioles to the leaves. The presence of young larvas in 

 such situations is discussed later. 



The chief functions of the case appear to be (1) protection, 

 and (2) support in the water. The protective function plays 

 an important part in the life of the larva. These caterpillars 

 occur in an environment where predaceous enemies are common 

 and obviously the case is a rather efficient protection. The 

 larva shows a very distinct tendency to respond to slight 



