222 Annals Entomological Society of America [Vol. XII, 



is this lateral beat against the water that it swings the anterior 

 end of the larva in the opposite direction, the succeeding stroke 

 swinging it in the reverse direction, thus making the course 

 described by the head a distinct zig-zag, characterized by 

 abrupt rhythmic changes in the lines of progression. While 

 the swimming activities of this larva resemble in many respects, 

 those of the larva of Bellura melanopyga (Welch, 1914, pp. 

 110-112), there is a distinct difference in the swimming move- 

 ments, since in the latter they are of the graceful sinuous type 

 and lack entirely the jerky character of the former. 



As mentioned above, these larvae swim in a surface depres- 

 sion. They have an integument which resists wetting and 

 enables them to utilize the surface film, but experiments showed 

 that if these caterpillars break entirely through it they sink 

 slowly, performing in vain the swimming movements described 

 above. They seem to have no ability whatever to swim in 

 water and individuals which become completely submerged 

 ultimately go to the bottom. The fate of such larvae is not 

 known. It is possible that some may return to the surface by 

 crawling up the stems and petioles of floating and emergent 

 vegetation, since experiments showed that they can withstand 

 continued submergence for at least one and one-half hours. 



Sometimes a larva gets inverted on the surface film and 

 has great difficulty in righting itself. The swimming activities 

 are continued, however, in the regular way, progress being 

 made until contact with some plant or floating object enables 

 the caterpillar to regain its normal position. 



Ordinarily, larvce seem somewhat unwilling to leave a 

 supporting leaf and take to water, but when sufficiently dis- 

 turbed they will voluntarily do so. No doubt new retreats 

 and new feeding surfaces are sought in that way also. 



RESPIRATION. 



Larval Stages. — As mentioned before, the larva has developed 

 no structural adaptations in connection with its aquatic rela- 

 tions. So far as respiration is concerned, it is a typical air- 

 breather and requires direct exposure to the atmosphere. 

 Throughout the whole larval existence, protection against 

 complete submergence is afforded. Certain features of the 

 food-plant aid materially in accomplishing this end. The 

 exposed surface of the leaf is waterproof, due, according to 



