31 
lion is supposed to maintain the vigour and stamina of the antelope by 
making prey of those that are in some way below concert pitch, 
whether in intelligence, senses, activity, strength, endurance, or what 
not. 
It seems very likely, if this hypothesis of a healthy plant being 
unattractive to its lepidopterous enemies be sound, that some failures 
we meet with in rearing them, may be due to our falling into the 
very natural and almost inevitable error, of selecting for our flocks, 
what we think to be very good, fine, and nourishing material. 
I satisfied myself many years ago that such destructive beetles as 
Hylurf/us pinrperda and Scolytus destructor are quite harmless to healthy 
trees, attacking usually fallen ones, and of standing timber only such 
trees as have been damaged in health in some way. Once I saw some 
elm trees attacked that had suffered from a severe drought, possibly 
assisted by a circumstance that rarely occurs and makes the only 
exception to the general law of their harmlessness to healthy trees. 
When a large quantity of fallen timber is collected together, as at the 
timber yard of a railway station, the beetles may appear in immense 
swarms, and eating into the bark in great numbers to feed themselves, 
may so weaken the trees as to enable some to successfully oviposit. 
This, however, certainly is a rare occurrence. 
Again, returning to Cannes for an illustration, I have several times 
noticed that Cnethocampa pityocaiupa had strongly attacked certain 
trees to the neglect of others. On one occasion I found two young 
trees, one of which had some thirty batches of eggs laid on it, and the 
other nearly as many, whilst all round were hundreds of apparently 
similar trees without one, and it is very usual with small trees, and 
even with large ones, to see a good many nests of the larva in one 
tree and few if any on those near. At Locarno, I once found a tree 
some twelve or fifteen feet high that had had a number of nests of 
the larva the previous autumn, so that when I saw it in April it was 
without a leaf, and the damage so done enabled a weevil (Pissodes 
nntatus I think) so to attack it, that its death was certain ; whatever 
was the inherent peculiarity of this tree that made the moth approve 
of it, it certainly led to its destruction, a consequence that tended to 
the elimination of that peculiarity from the race of pines in that 
locality. If we may assume that the peculiarity amounted to an 
aberration broadly undesirable foi the well being of the race, then we 
may also assume that the attack of the processionary moth was bene¬ 
ficial. 
Such benefit as this, whatever it amounts to, is of a very different 
character from that that leads the host to invite the attack of the guest, 
because of a very direct and definite advantage. This is such a widely 
known agency that I almost fear to touch on it, lest you accuse me of 
telling a thrice-told tale. Still, as this is the form of relationship that 
I think exists in the case of the Asphodel and Tortrix unicolorana, and 
which, I suggest, may exist in the case of many other lepidopterous 
larvae, if we only fully understood them, I must make some references 
to it. Probably, most cases of Symbiosis are examples of this relationship 
that have reached their full development. As such a case I may instance 
the nitrogen fixing bacilli of the Leyiuumosae. 
It is difficult from one point of view to believe that lepidopterous 
larvae can fall quite outside the action of this relationship, when we 
