1919] Welch: Pyrausta Penitalis 223 



Pond (1918, p. ISl), to many very delicate hairs which enclose 

 an envelope of air, preventing the water from actually touching 

 the epidermis. Unless the leaf has suffered considerable 

 damage, water thrown upon its upper surface rolls off imme- 

 diately in silvery masses. Some water is occasionally trapped 

 on the surface by upturned margins, but it also fails to wet 

 the surface, and rolls off at the first opportunity. Furthermore, 

 the region of the petiole junction is normally somewhat higher 

 than the surrounding area, thus producing a sloping surface 

 which easily sheds off any water falling upon it. These two 

 features of the plant are effective not only in keeping the 

 exposed surface above water, but in keeping water away from 

 the burrow. Surface feeding ultimately makes the leaf unten- 

 able by the removal of the waterproofing provision and the 

 subsequent wetting and submergence of the surface. Except 

 for short accidental periods of submergence, contact of these 

 larvae with the water is very slight and offers no obstacle 

 to their obligatory holopneustic respiration. Surface swimming 

 also permits dissemination without interference with the 

 usual respiration activities. 



All of the burrows which came under the writer's observa- 

 tion seemed remarkably free from water, in spite of the fact 

 that at least a part of each fully constructed burrow is below 

 the water-level outside. In contrast to the larva of Bellura 

 melanopyga which lives in a water filled burrow in the petiole 

 of the yellow waterlily and secures oxygen only when at the 

 top, the larva of P. penitalis seems to occupy a burrow which 

 is free of standing water and ordinary spiracular respiration is 

 possible at all times. 



Pupal Stage. — Although the exact oxygen demands of the 

 pupa are not known, it is fair to assume that they differ but 

 little from other similar pupae formed in terrestrial environ- 

 ments since the structural features of the respiratory system 

 are the same. Continued submergence of a pupa removed 

 from its silken covering results fatally, indicating that it also 

 must have a certain protection from water. In connection 

 with the field observations, the writer examined many cocoons, 

 none of which contained water. In fact, the pupa appears to be 

 well provided for in this regard. When the full-grown larva 

 begins preparations for pupation, the first activity is the forma- 

 tion of cream-colored, circular, concavo-convex, very closely 



