And habits op the Yellow dung-fly. 



641 



are to be contrasted with the spines covering the remainder of 

 the body, which also help to give the segments a grip on the sides 

 of the larval burrow, but, being fixed, prevent a backward move- 

 ment. If the anterior segments were covered with these, the 



Text-figure 9. 



Larva of S. sterc.^raria. 3rd instar. 



Text-figure 10. 



Posterior spiracles. 3rd instar. 



larva, once having pushed its head in one direction, would be 

 obliged to continue whether it wanted to or not. The hinged 

 plates give it a chance to make a second investigation in another 

 direction provided that it has not gone too far. 



