A represents the upper part of the reservoir or vessel which contains the silk in a liquid state, B B are the muscles which contract the reservoir and force the liquid matter out. It will be seen that both these vessels terminate in a delivery tube, identical in office with that of the bullet-making machine. As soon as the liquid silk passes into the air it is hardened, and is formed into a silken rod, C, just as is the lead in the machine. The only difference between the two, if it can be called a difference, is, that in the silkworm the rod is double, whereas in the machine it is single. The principle, however, is identical in both cases. The webs of spiders, and the threads by which so many caterpillars suspend themselves, and with which they make their nests, are all formed on the same design, namely, a reservoir containing a liquid which is squeezed through a tube, and hardens when it comes in contact with the air. ARCHITECTURE. CHAPTER I. THE HUT, TROPIC AND POLAR.--PILLARS AND FLOORING.--TUNNEL ENTRANCE OF THE IGLOO.--DOORS AND HINGES.--SELF-CLOSING TRAP-DOORS. Primitive Architecture evidently borrowed from the Lower Animals.--Roof Hut of the Nshiego Mbouvé of Western Africa.--Platform Hut of the Orang-outan of Borneo.--Lake Dwellers and their Huts.--Tree-huts of Southern Africa, and their Uses.--Ascendancy of the Wild Beast over Man.--Snow-hut of the Seal copied by Esquimaux, and its Value shown.--Pillars and Flooring.--Crypt and Cathedral.--The Cuttle “Bone” and its many-pillared Structure.--The Wasp-nest, its Pillars and Floors.--Tunnel Entrances to Igloo.--Sudden Formation of Snow.--Nest of the Fairy Martin.--The Sand-wasp and its Mode of Building.--Doors and Hinges.--Eggs of the Gnat and Rotifer.--Cocoons of Ichneumon-flies.--Habitations of Microgaster.--Trap-doors in Nature and Art.--Habitation of the Trap-door Spider.--A Nest upon a Pillar. THE HUT. There can be little doubt that mankind has borrowed from the lower animals the first idea of a dwelling, and it is equally true, as we shall presently see, that not only primitive ideas of Architecture are to be found in Nature, but that many, if not all, modern refinements have been anticipated. To begin at the beginning. The first idea of a habitation is evidently a mere shelter or roof that will keep off rain from the inhabitant. When Mr. Bowdich was travelling in Western Africa, he was told that the Njina--another name for the Gorilla--made huts for itself from branches, the natives also saying that it defended these huts with extemporised spears. A more truthful account is given of the Mpongwe and Shekiani, namely, that the animal builds a hut, but lives on the roof, and not under it.