11. Of the Walking Motions of Flies, and other Crea∣tures.
WHat Experimental Writers mention concern∣ing the feet of Flies, and their structure, to wit, that they have two claws or talons, and two palms or soles, by the help of which they can walk on the sides of glass, or other smooth bodies perpendicularly upwards; If this be the onely reason they can give, then certainly a Dormouse must have the same stru∣cture of feet; for she will, as well as a flie, run streight upwards on the sharp edg of a glazed or well-polished Sword, which is more difficult then to run up the sides of Glass: And as for Flies, that they can suspend themselves against the undersurface of many bodies; I say, not onely Flies, but many other Creatures will do the same; for not onely great Caterpillers, or such worms as have many leggs, as also Spiders, but a Page 29 Neut, which is but a little Creature, will run up a wall in a perpendicular line; nay, walk as Flies do with its back down, and its leggs upwards. Wherefore it is not, in my opinion, the Pores of the surface of the body, on which those Creatures walk; as for example, that a Flie should run the tenters or points of her feet, which some have observed through a Microscope, in∣to the pores of such bodies she walks on, or make pores where she finds none; (for I cannot believe, that in such close and dense bodies, where no pores at all can be per∣ceived, a small and weak legg of a Flie should pierce a hole so suddenly, and with one step) Nor an Ima∣ginary Glue, nor a dirty or smoaky substance adhe∣ring to the surface of glass, as some do conceive; nor so much the lightness of their bodies that makes those Creatures walk in such a posture; for many can do the same that are a thousand times heavier then a little Flie; but the chief cause is the shape of their bodies; which being longer then they are deep, one counterpoises the other; for the depth of their bodies has not so much weight as their length, neither are their heads and leggs just opposite: Besides, many have a great number of feet, which may easily bear up the weight of their bo∣dies; and although some Creatures, as Horses, Sheep, Oxon, &c. have their leggs set on in the same manner as Mice, Squirrels, Cats, &c. yet they cannot run or climb upwards and downwards in a perpendicular line, as well as these Creatures do, by reason of the depth Page 30 of their bodies from the soles of their feet to the surface of their back, the weight of their depth over-power∣ing the strength of their leggs. Wherefore the weight of a Creature lies for the most part in the shape of its body, which shape gives it such sorts of actions as are proper for it; as for example, a Bird flies by its shape, a Worm crawls by its shape, a Fish swims by its shape, and a heavy Ship will bear it self up on the surface of water meerly by its exterior shape, it being not so much the interior figure or nature of Wood that gives it this faculty of bearing up, by reason we see that many pieces of Timber will sink down to the bottom in water. Thus Heaviness and Lightness is for the most part caused by the shape or figure of the body of a Creature, and all its exterior actions depend upon the exterior shape of its body.