Nor is this all: the manner of working helps the general
arrangement considerably. When the bricklayer is building the
narrow shaft of a factory chimney, he stands in the center of his
turret and turns round and round while gradually laying new rows.
The caddis worm acts in the same way. It twists round in its
sheath; it adopts without inconvenience whatever position it
pleases, so as to bring its spinneret full face with the point to
be gummed. There is no straining of the neck to left or right, no
throwing back of the head to reach points behind. The animal has
constantly before it, within the exact range of its implements, the
place at which the bit is to be fixed. When the piece is soldered,
the worm turns a little aside, to a length equal to that of the
last soldering, and here, along an extent which hardly ever varies,
an extent determined by the swing which its head is able to give,
it fixes the next piece.

These several conditions ought to result in a geometrically ordered
dwelling, having a regular polygon as an opening. Then how comes
it that the cylinder of bits of root is so confused, so clumsily
fashioned? The reason is this: the worker possesses talent, but
the materials do not lend themselves to accurate work. The
rootlets supply stumps of very uneven shape and thickness. They
include big and small ones, straight and bent, simple and ramified.
To combine all these dissimilar pieces into an orderly whole is
hardly possible, all the more so as the caddis worm does not appear
to attach very much importance to its cylinder, which is a
temporary work, hurriedly constructed to afford a speedy shelter.
Matters are urgent; and very soft fibers, clipped with a bite of
the mandibles, are more quickly gathered and more easily put