In order to lend itself to the movements of the travelling Caterpillar, and particularly to enable the head and legs to move freely while a new piece is being fixed in position, the front part of this case or sheath must be made in a special way. Here a casing of sticks is no longer suitable, for their length and stiffness would hamper the workman and even make his work impossible. What is required here is a flexible neck, able to move in all directions. The collection of stakes, therefore, ends suddenly at some distance from the fore-part, and is there replaced by a collar where the silk lining is merely hardened with very tiny particles of wood, which strengthen the material without making it less flexible. This collar, which allows of free movement, is so important that all the Psyches use it, however greatly the rest of their work may differ. All carry, in front of the bundle of sticks, a yielding neck, soft to the touch, formed inside of a web of pure silk and coated outside with a velvety sawdust, which the Caterpillar obtains by crushing up any sort of dry straw. The same kind of velvet, but dull and faded—apparently through age—finishes the sheath at the back, in the form of a rather long projection, open at the end. When I remove the outside of the straw casing, shredding it piece by piece, I find a varying number of laths, or tiny sticks. I have counted as many as eighty, and more. Underneath it I find, from one end of the Caterpillar to the other, the same kind of inner sheath that was formerly visible at the front and back only. This inner sheath is composed everywhere of very strong silk, which resists without breaking when pulled by the fingers. It is a smooth tissue, beautifully white inside, drab and wrinkled outside, where it bristles with a crust of woody particles. Later on we shall see how the Caterpillar makes himself this complicated garment, formed of three layers, one placed upon the other in a definite order. First comes the extremely fine satin which is in direct contact with the skin; next, the mixed stuff dusted with woody matter, which saves the silk and gives strength to the work; and lastly the outer casing of overlapping sticks.