James George Needham, General Biology, New York, The Comstock Publishing, Ithaca, 1910, pp. 478-479.
Almost any species that makes it cases of pieces of wood (fig. 268), or stones, with or without ballast-pieces attached to the side, will do. For the following experiments, handle the larvae gently, with care not to do them any physical injury, and leave them in clean water and comfortable conditions while waiting the results of the experiments. While cutting cases the larvae may be temporarily removed from them, if this be deemed necessary.
Observe the fitness of the cases for protection of the body and for escaping observation when in the natural environment. Observe the ordinary activities of the caddis-worms; the manner in which they drag their cases about, or retreat into them when disturbed. Drive a worm out of its case (by poking it gently from the rear), and observe the form and structures of the body and its need of protection. Study the case of the species selected for experiment, its materials and construction. Observe the cement-substance which binds the other materials together; this is the hardened secretion from glands that open through the labium of the larva, which exudes as a fluid, and hardens after contact with the water. This secretion is all the equipment the larva needs for building or repairing its cases.
I. To test the adaptability of case building to present physical needs;
1.) Cut a hole in the side of the case, exposing a vulnerable part of the body, and see if it will be repaired.
2.) Slit a case lengthwise, in a narrow opening from end to end and leave it to be repaired.
3.) Cut a case in two crosswise, and leave one part of it only on the larva for repair.
II. To test the adaptability of case building to conditions of environment.
4.) Provide a background of a different color form the natural one, (background may be placed under the bottom of the glass dish), and materials for case building of a suitable size and of a color to match the background (strips and bits of mica, glass, colored celluloid, whitewood, etc.).
Provide also the materials ordinarily used, but which are unsuited to the new background, being there conspicuous when viewed against it. See what materials a larva, removed from its case, uses for making a new one.
5.) Leave a larva, removed from its case, upon the old background, but provide it only with case-building materials that will be conspicuous against that background, and note the result.