The Florence tribune., 1897-09-11
NEED NO EYES.
Creatures That See Through Their
 Skins.
Some Curious Facts Concerning the Lower Orders of Animal Life -snaiIs, s1ugs and Bi-
 valves.

Eyes are popularly considered to be quite necessary to sight, but this is an error, if we are to believe Dr. Nagel, recent German experimenter. Many creatures without eyes can see, at last they can distinguish perfectly well be- tween light and darkness, and even be- tween different degrees of light. This is the lowest degree of seeing, to be sure, but still il is really sight, and dif fers scareeiy mora from the visions cf some insects that possess eyes than this does from our own clear sight.
 Creatures that see without eyes see by means of their skins. All skins. says Dr. Nagel, are potential eyes; that is, they are sensitive to light In an- imals that have eyes the sensitiveness has been highly localized and greatly insreased-so that man, for instance, has Q retina very sensitive to light, and en expanse of ordinary skin which possesses a sensitiveness to light so slight that it is hardly conscious of it. Yet the s.el is sensitive in some de- gree, as is proved by the fact that it sunburns is, light may cause disturbance in the pigment of the skin just as it does in that of the eye. In the eye the disturbance is accompanied by nervous change which sends telegraphic message along the optic nerve to the brain. In the skin, too, there are nerves, and there are mes sages, also, but their tidings imprint no image on the mind; they simply express discomfort cry out ''sun- burn"
 But in many eyeless creatures the lack of eyes IS in part made up by in- creased sensitiyeness of the whole skin surface to light. Darwin long ago noticed that the earthworms, although they have no eyes, will suddenly with draw into their holes on the approach of . lighted candle. Some creatures seem more sensitive to suddenly increased light, others to sudden diminuticn. If a number of oysters, kept in vessel together, are found to be open, they will shut all at once if a dark object comes between them and the light. Another bivalve called Psammodia. has long, whitish, transparent tubes which protrude from the sand in which it lies buried If they are suddenly H. luminated, they contract. and the brighter the light the greater the con traction. If q number of them be car ried into direct sunlight, they hasten to bury themselves in the sand; or, if there is no sand, they move restlessly to and fro in the water until they are exhausted.
 Iii general, Dr. Nsgel finds that creatures which respond to sudden shadows are those that live in strong shells, while those affected by sud- den increase of light live in sand or mud, from which they emerge occasion ally. In both eases the sensitiYeness of the skin to changes of light serves to protect the animal.
 How does the skin acquire this pc culiar sensitiveness? It will be best for the non-expert to suspend judg- ment, since even the scientists do not agree on this point. It may be that ii is a universal and rudimentary prop erty of all skin, and that animals with eyes have lost it in greater or less de gree, because they have no further need for it. This is one view. Or it may be that this property has been devel- oped in eyeless creatures just because they are eyeless and need it. That is another view. Those who favor the lat ter opinion point to the fact that some of the creatures which now have slin' sensitive to the light are probably de | scendants of creatures with skins no so sensitive; in these instances thC sensitiveness must have been recently developed. Snails are sensitive, bu their relatives, the siugs, are not; thi looks as if the former had acquired th' faculty. However this may be, DT Nagels study of these curious and out of-the-wsy facts is certainly interest ing. and may lead in the future to an ad vance in our knowledge of the mechau