The spinning of the cocoon, in those species in which the larva is protected in this manner, and its shape, are instinctive. We find that closely allied species in the same genus make very different cocoons, as is seen in T. rubrocinctum and T. bidentatum. Some wasps spin no such covering for themselves. It is a well–known fact that silkworms sometimes omit the spinning of a cocoon; but this does not affect the argument, since the descendants of these individuals make the characteristic covering. Such cases are probably due to individual variation or perhaps to atavism, this throwing back being not uncommon among forms that are well known. Not all of the instinctive acts here enumerated are displayed by each species studied, although they are common to most of them. We have doubtless overlooked some activities that should come under this head, as we have not made a thorough study of any sufficient number of species to make a final settlement of the matter. As we have seen with Ammophila and Pelopæus, faults of instinct are not uncommon, but of all our wasps the one that shows the greatest aberrations is Pompilus biguttatus. The sandy beach of Lake Michigan is a favorite nesting–ground with this species, and is the scene of many a bold robbery, since they are unprincipled little wretches and “... the good old rule Sufficeth them, the simple plan That they should take who have the power And they should keep who can.” We once found an unusually tiny biguttatus vainly trying to drag a large Epeirid which her sting had reduced to helplessness. It was as though a feeble child should try to move the body of an elephant. The little wasp clasped one of the spider’s legs firmly in her mandibles, and then with braced feet and the wildest flutter of wings made gallant but futile attempts to get it started. Now she lost her hold on the ground, and wings and legs were all whirling desperately in the air. Now her feet grasped a loose ball of earth, and, feeling that something was moving, she renewed her efforts. The pellet was drawn nearer and began to rotate around the wasp, while she seemed to be under the impression that she was moving forward. After a few minutes of vigorous exercise, she paused, perhaps to see how she was getting on, and the bit of earth rolled away; so that when the attack was renewed, it was under the old discouraging conditions. She was the impersonation of perseverance and energy; but after half an hour (no one knows how long she had been at it before we came) she gave it up, and with many reluctant circlings flew away. It was probably experiences of this kind that developed in some of her relatives the habit of digging the grave under the victim, and thus saving the trouble of transportation.