14 
descriptions in Professor Westwood’s ‘ Introduction to 
Entomology ’ rather than enlarge further on this 
order now. 
It is of great importance to us to he able to distinguish 
the injurious insects in their larval conditions, as it is in 
this stage that they commonly do us the most harm, and 
also from peculiarities in their constitution fall from 
time to time within our power. The larva usually eats 
voraciously and grows fast, hut the skin does not stretch 
beyond a certain point, and, when this is reached, the 
tight-fitting covering splits, and the larva emerges in a 
new coat from its cast skin, and when this operation is 
about to happen, it is particularly susceptible of injury. 
In the case of the Turnip Sawfly, for instance, the cater- 
