June, 19 1 2.] 



Webster: Moults of the Pear-Slug. 



127 



wide, clearly belonging to stage V. Again in cage 193/10 stage I 

 moulted twice with a bare increase in width, while there is no 

 measurement which fits stasre IV. 



Measuremexts of Head Widths, 1909-1910. 



Among those larvae that moulted six times similar irregularities 

 may be noticed in nearly every stage. The increase is often very 

 slight, too much so to be considered as a separate stage. 



With the larvae that moulted seven times there are two cases 

 where two successive moults fail to show any increase whatever. 

 The other extra moults are close together. 



In thecase of the single larva that niouUed eight times there was a 

 very slight increase every time, no two measurements being exactly 

 the same. But here also the figures fall rather well into the five 

 stages, as they are given in the table. 



The following table shows the variation under the several stages. 

 The figures at the right of each measurement indicate the numl)er of 

 times that measurement occurred. 



