On the Movement of Animals, Part Two

IO. AL. BORELLI

PROPOS. XIII.

Chap. 1. On the mechanical modes and operations by which the contraction of muscles can be effected.

It must now be explained by what mechanical artifice earthworms can crawl, and how that corrugation which we see in earthworms is in truth not the cause, but the effect, of the contraction of the internal muscles of those same earthworms. Tab. 15. Fig. 10.

Let the length of an earthworm be a cylinder AE, consisting of a soft and membranous substance, which is surrounded by short muscular fibers extended along the length of the worm and connected together, such as MK, LI, KH, IG, etc. And because two motions are observed in earthworms: First, with the body ABCD leaning upon D, the posterior part DE is shortened, with the tail E approaching toward D; and then the external skin DE is corrugated with frequent folds. Then, while C is supported by the ground, the following portion DC is contracted in the same way with visible folds and corrugations; from which shortening, the rearmost part is inflated and swells as much as the diminution of its length demands. The remaining length CB is shortened in the same way. Secondly, with the belly BC leaning, the head A is suspended, and when erected, it appears to be elongated somewhat and is moved forward; afterward, the head A leans upon the pavement and is pulled, just as B was toward A, and C toward B before, and so on further.

It must now be shown that such a movement of the earthworm is not caused by those visible folds and corrugations which appear in its skin. Because if the skin,