172 Annals Entomological Society of America [Vol. IX, 



mechanical stimuli by immediate retraction into the case, a 

 reaction which probably plays an important part in escaping 

 enemies. Under normal conditions, the larva is apparently 

 very shy, never, according to the observations of the writer, 

 emerging completely from the case except in connection with 

 the construction of a new one. At times, the anterior two-thirds 

 of the body is projected from the case but such periods of 

 partial emergence are of short duration, except when engaged in 

 a special form of locomotion to be described later. Larvae, 

 removed from their cases and placed in aquaria provided with 

 yellow water-lily leaves, very soon begin the construction of 

 a new case. 



The second function of the case — that of support in the 

 water — is vitally connected with an interesting form of locomo- 

 tion. The specific gravity of the older larvae is greater than that 

 of water and, unless supported, they will sink. The leaf tissue of 

 the yellow water-lily has a specific gravity distinctly less than 

 that of water and the oblong pieces cut out by the larva in 

 case-making are always buoyant enough to easily support it. 

 Therefore, all detached cases float at the surface and no effort 

 on the part of the larva is required to support itself in the 

 medium. Where larvae are numerous, individuals are often 

 found crawling over the top of the water-lily leaf, carrying the 

 cases with them. To accomplish this form of locomotion, the 

 larva extends the anterior part of the body from the case, uses 

 the true legs as locomotor organs, and holds the case with the 

 prolegs. When detached cases are dropped in the water, the 

 larva performs certain movements which result in a change of 

 position in space. As mentioned before, no evidence of an abiHty 

 to swim was observed when larvae were isolated from their cases. 

 However, they do possess a form of locomotion in water in con- 

 junction with their cases. The anterior portion of the body is 

 projected from the case into the water and vigorous, horizontal, 

 side to side motions are executed which result in the propulsion 

 of both larva and case. It does not constitute a very efficient 

 form of locomotion but is effective enough to bring the larva in 

 contact with other water-lily leaves. If the horizontal move- 

 ments are equal on either side of the long axis of the body, the 

 result is a backward movement approximately in a straight 

 line. If, as is often the case, the strokes are stronger on one 

 jside than the other, the result is an irregular rotation. 



