On Naked Fresh-Water Radiolaria

Abstract

ABSTRACT The distribution of animals in the older strata of the earth’s crust would lead one to assume that fresh-water lakes could not have been inhabited until a late period, and, indeed,’’the distribution of living beings in fresh and salt waters is now very disproportionate. With regard to many orders of the animal kingdom, nature seems to have made some feeble attempts to populate fresh waters, and then to have given up the matter ; with others the distribution in both quarters is tolerably equal, although no very important physiological differences seem to exist; with the majority the sea presents a most decided predominance. Until recently Radiolaria have been found only in the sea, or at least shell-less free-living forms have never yet been observed in fresh water. In the middle of last summer I, to my great surprise, discovered at the same source · three different kinds of creatures which presented decided characters of Radiolaria. As most of the inhabitants of the sea belonging to this order are enclosed in hard porous shells, the examination of their tissue elements is rendered difficult to a great degree ; consequently, the opportunity of examining these free-living forms from fresh water offer a very desirable facility for making a minute investigation.