HABITS OF THE LARVA OF BELLURA MELANOPYGA. 1 07 



the entrance hole and other openings which usually occur are 

 sufficient to provide the necessary air. 



The Petiole Period. When the larva deserts the leaf and 

 becomes a borer in the petiole new conditions are encountered 

 and new provisions must be made. The leaves of Nymphcea 

 americana are never normally held above the surface of the water 

 by the petiole as in the case of N. advena but the emergent leaves 

 float on the surface. This means that the burrow in the petiole 

 is filled with water and that the larva is submerged. When the 

 length of the burrow increases to such an extent that it is longer 

 than the body of the larva which is making it, the latter is 

 compelled to resort to other means of getting air. To do this the 

 larva makes periodic trips to the surface where the fresh air is 

 drawn into the tracheal system in sufficient quantity to allow 

 a sojourn of several minutes under water at the bottom of the 

 burrow. 



As stated previously, the larva lies in the petiole with the 

 posterior end towards the top of the burrow. This position 

 eliminates the necessity for the larva to come out of the burrow 

 when taking air, and to turn around when starting on its trip 

 to the top. When at the bottom of the burrow the larva feeds 

 (or in some cases merely rests) until the need for air stimulates 

 it to return to the surface. Then it backs up to the top of the 

 burrow, stopping when the large pair of spiracles on the posterior 

 margin of XI is just pushed above the surface film. It remains 

 in that position until sufficient air has been taken into the trachea 

 to permit a return to the bottom of the burrow again. This 

 alternate sequence of feeding and breathing goes on continuously 

 so long as the larva remains in the burrow. In this form of 

 respiration it appears that the other spiracles are not needed since 

 only the posterior pair is pushed above water. 



Frequency of Trips to the Surface. A number of observations 

 were made on various larvae in order to determine what is the 

 normal period of time spent under the water and likewise the 

 normal period spent at the top. The records were made by 

 means of a stop-watch and the observations on each larva were 

 carried on long enough to secure data showing the range of 

 variation in each case. The average of 128 observations involv- 



