THE LARGH LARCH SAWFLY. 149 
is single, but the saw of the Tenthredo is double, and consists of 
two distinct saws with their backs. The insect, in using them, 
first throws out one, and, whilst it is returning, pushes forward 
the other; and this alternate motion is continued until the 
incision is effected, when the two saws, receding from each 
other, conduct the egg between them into its place. In the 
artificial saw the teeth are alternately bent towards the sides, so 
that the fissure or ‘skerf’ may be made sufficiently wide for 
the blade to pass easily. To answer this purpose in some 
measure in the Tenthredo the teeth are a little twisted, so as to 
stand obliquely with respect to the right line, and their points 
of course project a little beyond the place of the blade without 
being laterally bent; all those in each blade thus project a 
little outwards. But the ‘skerf’ is more easily procured and a 
free range effected by small teeth placed on the outer side of 
each saw, so that whilst the vertical effect is that of a saw, the 
lateral effect is that of arasp. The teeth point inwards towards 
the ‘handle’ and their outer edge is beset by smaller teeth 
which point outward..... Now it is well known that all 
wounds caused by a rough or blunt tool are more difficult to 
heal than those which are clean cut. This holds good in the 
vegetable as well as in the animal kingdom, and it is here, pro- 
bably, that the final cause of the complicated structure of this 
beautiful little instrument may be sought. It is not desirable 
that the wound should heal. The fissure in which the egg is 
inserted is not a mere resting-place, but is designed to afford 
nourishment to the eggs, which, absorbing the juices of the 
plant, actually grow, between the time of their exclusion and 
their hatching. A supply of nourishment is thus produced and 
maintained by the stoppage of circulation consequent on the 
opening of this wound, which, in some cases is further irritated, 
at the time of oviposition, by the introduction of a drop of 
poisonous fluid, which in some cases results in the formation of 
an excrescence or ‘ gall.’”’ 
Owing to the irregular emergence of the adults, larve of all 
sizes may be found on the same tree at one time. They are to 
be found in a normal year up to the end of August, but in the 
past summer (1911) I could not find any remaining on the trees 
three weeks prior to this, the brilliant weather with which we 
