The peculiar habits of some of the solitary wasps, of stinging the caterpillar or other insect which they store up as food for their young, is often quoted as a wonderful case of adaptive instinct. The poison that is injected into the wound paralyzes the caterpillar, but as a rule does not kill it, so that it remains motionless, but in a fresh state to serve as food for the young that hatch from the egg of the wasp. A careful study of this instinct by Mr. and Mrs. Peckham has shown convincingly that the act is not carried out with the precision formerly supposed. It had been claimed that the sting is thrust into the caterpillar on the lower side, a ventral ganglion being pierced, the poison acting with almost instantaneous effect. But it may be questioned whether this is really necessary, and whether the same end might not be gained, although not quite so instantaneously, if the caterpillar were pierced in almost any other part of the body. Can we be seriously asked to believe that this instinct has been perfected by the destruction of those individuals (or of their descendants) that have not pierced the caterpillar in exactly the middle of a segment of the anterior ventral surface? It seems to me that the argument proves too much from the selectionist’s point of view. If the wasp pierced the caterpillar in the middle of its back, we should have passed over the act without comment; but since the injection is usually made on the ventral side, and since we know that the nervous system lies in this position, it has been assumed that the act is carried out in this way, in order that the poison may penetrate the nervous system more quickly. Yet a fuller knowledge may show that there is really no necessity for such precision. A curious response is the so-called death-feigning instinct shown by a number of animals, especially by certain insects, but even by some mammals and birds. Certain insects, if touched, draw in their legs, let go their hold, and fall to the ground, if they happen to be on a plant. It is not unusual to meet with the statement that this habit has been acquired because it is useful to the insect, since it may often escape in this way from an enemy. This does not appear on closer examination to be always the case, and sometimes as much harm as good may result, or what is more probable, neither much advantage, nor disadvantage, is the outcome. This can, of course, only be determined in each particular case from a knowledge of the whole life of a species and of the enemies that are likely to injure it.