35 



Enlarging the tube. 



of the enemies, which their neighbours living in the mud and sand so 

 frequently fall a prey to, such as for instance the carnivorous and 

 ubiquitous Tanypiis larva. 



When the larva is full grown, and the thoracic segments are 

 beginning to get swollen on account of the imaginal organs which are 

 forming beneath the skin, it seems to find the end of the tube too 

 narrow for the enlarged part of the body, so it starts again building on 

 to the end of the tube, gradually widening the entrance as it proceeds. 

 The enlarged part when completed is about 1-5 mm. long, and rather 

 less in width. In one larva that I kept under observation the work 

 took four days to accomplish. The ultimate object of the enlarged 

 tube is to make room for the large thorax of the coming pupa. 



The larva is now ready to pupate and starts building a cover or Operculum. 

 operculum to close in the free end of the tube. This is done by 

 building inwards on to the edge of the case, the larva working round 

 and round in an ever diminishing spiral. Earthy particles are collected 

 from the arms, and the arms may themselves be utilized ; sometimes 

 however they are bitten off and at other times twisted round outside 

 the case so as to form a rim surrounding the operculum. The operculum 

 is gradually built in from the circumference towards the centre, the 

 larva always stretching through the central open part for fresh material 

 until the opening becomes too small for it to pass through, after which 

 it finishes the process from within until only a very small hole is left, 

 just large enough to allow the pupal respiratory cones to pass through. 

 This operation takes about one day to finish. 



In one case I removed the operculum as soon as it was finished ; 

 the larva immediately set about building a second, which it completed 

 in the short space of six hours ; this I again removed, but now the 

 larva's energies were exhausted, and it made no further attempt to 

 close the opening ; by the next morning it had passed into the pupal 

 stage. 



In the ordinary course of events the larva remains quiescent for 

 about twenty hours after completing the cover, before casting the 

 larval skin. If after this time the case be opened, and the pupa extracted 



