Setting fire to this, they retired to some distance to await the issue of their experiment. There was unfortunately a cow in the same meadow, and this cow was very much interested in their movements; so when they left the tree the cow approached, its curiosity the more aroused by the smoke rising from the burning fuse. "Now there is an instance of unreasoning curiosity which animals possess. That cow will poke her nose into that tree, and get blown up for her pains if we don't stop her. Let's shy stones at her." But stones in that marshy meadow were not easy to procure, so they tore up clods of earth and threw them at the cow. She scampered away, but went to the other side of the tree and again approached it. The boys dared not go any nearer to the old willow, because they momentarily expected the explosion, and they were in a great fright lest the cow should suffer damage. Just then, with a loud report and much smoke the powder exploded. They threw themselves down to avoid any errant fragments, and the cow scampered off unhurt, but exceedingly astonished and frightened, jumped the ditch which separated the meadow from the next one, and finally landed herself in another ditch, from which she had to be drawn with ropes and a vast deal of trouble by some of the neighbours. The first thought of the boys was to see after the cow, and when they saw she was in a fair way of being pulled out, they returned to their tree, and found it split and torn to pieces and thrown about in all directions. It was quite a chance whether they found any caterpillars in the tree or not, and, to tell the truth, they hardly expected to be successful in their search. What was their delight then to find, that not only were there caterpillars there, but a great number of them. Three or four they found dead and mangled by the force of the explosion, but the many perforations in the wood showed that there were many more caterpillars there. With the aid of a saw and axe they dug out several caterpillars not yet full grown, and also several pupæ which they knew would be out in two months' time. They carried some large pieces of the wood up to the boat-house for living caterpillars to feed on, and reinserted the pupæ in their wooden chambers, where they were safely kept until their appearance in July. The caterpillars of the white butterflies which Dick had collected under Mary's instructions had some time since come out, and it was a very pretty sight to see the chrysalis split at the head and the insect creep out with its wings all wet and crumpled, and then to watch them gradually expand to their full size and dry and harden, until the perfect insect was ready for flight, when with a few flaps of its wings, as if to try them, it would launch into the sunshine with a strong swift flight. CHAPTER VII.