to her task in about two or three minutes. [Illustration: Mandibles--Jaws of Mason-Wasp.--Greatly magnified.] Within two days the excavation was completed; but it required two other days to line it with a coating of clay, to deposit the eggs, two in number, and, no doubt, to imprison a few live spiders or caterpillars for the young when hatched--a process which was first observed by Ray and Willughby,[O] but which has since been frequently ascertained. In the present instance, this peculiarity was not seen; but the little architect was detected in closing up the entrance, which was formed of a layer of clay more than double the thickness of the interior lining. In November following, we hewed away the brick around this nest, and found the whole excavation was rather less than an inch in depth. [Illustration: Cuckoo-Fly (_Tachina larvarum?_).--Natural size.] Notwithstanding all the precautions of the careful parent to conceal her nest it was found out by one of the cuckoo-flies (_Tachina larvarum?_)--probably a common species very similar to the house-fly, but rather larger, which deposited an egg there; and the grub hatched from it, after devouring one of the wasp-grubs, formed itself a cocoon (_a_), as did the other undevoured grub of the wasp (_b_). Both awaited the return of summer to change into winged insects, burst their cerements, and proceed as their parents did. [Illustration: Mason-Wasp's Nest and Cocoons.--About one-third the natural size.] [Illustration: Mason-Wasp (_Odynerus murarius_).--Natural size.] Another mason-wasp (_Odynerus murarius_, Latr.), differing little in appearance from the former, may often be seen frequenting sandy banks exposed to the sun, and constructing its singular burrows. The sort of sand-bank which it selects is hard and compact; and though this may be more difficult to penetrate, the walls are not liable to fall down upon the little miner. In such a bank, the mason-wasp bores a tubular gallery two or three inches deep. The sand upon which Réaumur found some of these wasps at work was almost as hard as stone, and yielded with difficulty to his nail; but the wasps dug into it with ease, having recourse, as he ascertained, to the ingenious device of moistening it by letting fall two or three drops of fluid from their mouth, which rendered the mass ductile, and the separation of the grains easy to the double pickaxe of the little pioneers. [Illustration: Nests, &c., of Mason-Wasps.--About half the natural size. _a_, The tower of the nest; _b_, the entrance after the tower is removed; _c_, the cell; _d_, the cell, with a roll of caterpillars prepared for the larva.]