1916] Biology of Aquatic Lepidoptera 179 



elliptical in outline, the dimensions usually being about 1.25x2 

 cm. The maximum thickness is usually but Httle more than the 

 maximum diameter of the pupa. This silken covering is 

 relatively strong and not easily torn open. 



The case varies to some extent in size and shape. In general, 

 it- is elliptical and has dimensions varying from 1.5x2 cm. to 

 2.5 X 5 cm. The vast majority of the pupal cases are attached 

 to the lower surface of the floating water-lily leaves and are thus 

 constantly submerged. Pupal cases have been found on the 

 upper surface of floating water-lily leaves, a position which 

 minimizes contact with the water. The fate of such pupae is 

 not known. A few pupal cases have also been found on the 

 submerged water-lily leaves, several inches under the surface 

 of the water. 



The external surface of pupae is not easily wetted and they 

 float if removed from the silken coverings and placed in water. 

 The fate of pupae which accidentally become removed from 

 their cases is not known. It is said (Miall, '95, p. 233) that the 

 pupae of certain European species of Nymphida, when removed 

 from their silken coverings and placed in water, live for a time 

 but do not transform into adults. 



Dissemination. — In connection with the discussion of the 

 dissemination of the larvae, mention was made of the fact that 

 an indirect method of distribution occurs, due to the influence 

 of wind and waves, or the work of other insects, or both. The 

 pupae are sometimes scattered in the same way. The work of 

 the larvae of Hydromyza confluens, Bellura melanopyga, and 

 others, frequently bring about the separation of the leaf or 

 portions of the leaf from the petiole, permitting them to float 

 about at random. Such detached leaves often bear pupal cases 

 of N. maculalis and may be carried some distance from the 

 original breeding place. After storms in which portions of the 

 floating water-lily leaves are torn away by wave action, pup« 

 are sometimes found on the opposite shore. 



The Adult. 

 Adults of N. maculalis have been taken about Douglas Lake 

 by the writer from June 28 to August 30 but these limits are 

 probably too narrow. They are normally confined to the region 

 surrounding the food plants of the larva and the few scattering 

 adults which are sometimes found remote from yellow water- 



