has made the effort, we examine its feet with the microscope, we shall perceive that the interspaces between the hairs are filled with dust. After it has rubbed its feet against one another for a short time, and has passed its wings over them, the dust will be found to have disappeared, and it will again be able to walk on glass. The object of this labor, which flies may be observed to be performing at every moment, is not, then, as was once supposed, to cleanse the wings, but to keep the feet in good condition to stick on smooth surfaces. The wings are supplied with a kind of rough hairs that may very well fill the place of brushes.
Blackwall believed that flies cleansed their feet for the purpose of removing the superfluous viscous liquid from their pilæ. If this were the case, all the parts of the insect that touched its feet would shortly be covered with that substance; and, if it does not dry but becomes gelatinous, the fly would collect all the dust with which it comes in contact, and would soon look like a lump of dirt. Contrary to this, we know that flies are always clean.
Other insects that can walk on glass like flies have also, like them, little hairs with club-shaped terminations on the bottoms of their feet, and adhere in the same way. The accompanying illustration (Fig. 3) represents the end of the foot of a beetle (the Polydrosus sericeus), and shows that it is provided with all the appurtenances we have been describing.
I think I have proved by my experiments that the faculty possessed by flies of walking over polished bodies should not be attributed to a viscous liquid, but simply to capillary action. Even if this liquid, which causes the hairs to adhere to the polished surface, were nothing but pure water, the flies would be able to support themselves upon it, whatever position they might be in.—Translated for the Popular Science Monthly from La Nature.
THE subject of the distribution of plants and animals has for a long time engaged the attention of many able, persistent, and discriminating investigators. Much time and effort have been expended in simply observing and describing the various means by which they get about from place to place. The methods and means by which the seeds of plants are carried and deposited in new localities, the agency of insects, birds, and other animals in their distribution, no less than
- Preliminary portion of the author's monograph upon this subject published by Charles Scribner's Sons, New York.