4. A STUDY OF WORMS
To show cells associated even more closely than in cœlenterates, forming tissues and systems of organs.
A Study of Earthworms
The Living Earthworm
Materials.
Living earthworms, some of which are left undisturbed from day to day, in damp earth with leaves of various plants scattered upon it.
Definitions.
Anterior end, the head end, usually the leading end. Posterior end, the end opposite the anterior end. Ventral surface, the lower surface, usually the one which contains the mouth. Dorsal surface, the one opposite the ventral surface. Somites, the rings or segments of which some animal bodies are composed. Bilateral symmetry, the symmetry usually shown by animals which have differentiated dorsal and ventral surfaces, and right and left sides. Animals which do not have such differentiated surfaces are usually radially symmetrical, but sometimes asymmetrical (without symmetry). Girdle, the somewhat transparent band frequently found near the anterior end of an earthworm. Anal opening, the posterior opening of the food canal. Setæ (singular form, seta), small bristles or stiff hairs. In the earthworm these are set in the body wall at definite intervals, and aid in locomotion. Cuticle, in the earthworm a delicate, shining cover over the body. Egg capsules, small, light-colored, spindle-shaped sacks, about the size and somewhat the shape of a grain of wheat, containing the eggs or young of earthworms.
Directions.
Take a living earthworm to your table and keep it damp by placing it in a wet tray or upon moist paper. Identify the anterior and posterior ends, the dorsal and ventral surfaces, and the right and left sides. Identify also the somites and the girdle, the mouth with its projecting lip, and the anal opening.