There are few fresh-water animals more commonplace and apparently uninteresting when observed casually than the pond sponge and the river sponge. Yet, if we take either of them home and examine them with the aid of our microscope, we shall be delighted with our specimens. In reality they are of absorbing interest and, at certain times of the year we may easily obtain young sponges, and capital objects they make for the microscope. [Illustration: _Photos by Flatters & Garnett_ 1. STARCH GRAINS OF POTATO Starch is largely used as an adulterant of various foods. The Potato starch grain resembles a miniature oyster shell. 2. PHOSPHORESCENCE ANIMALCULAE These minute animals, occurring in millions, render sea water beautifully phosphorescent. 3. PROTEUS ANIMALCULE The lowliest of all animals. It is a jelly-like animal which changes its shape from hour to hour. 4. CYCLOPS A common one-eyed water animal. The female, illustrated, carries her eggs in a pair of relatively large bladder-like sacs. ] Before we describe our two specimens let us try to explain what manner of creature a sponge really is. If we examine any bath sponge, we notice that it is perforated with many small holes and some larger ones. Some sponges show this better than others. The small holes are pores, the large ones mouths, but, as we shall see in a moment we must not run away with the idea that they in any way resemble our familiar idea of a mouth. These large holes are called oscula by scientists, but we wish to avoid scientific words as much as possible. The simplest sponge of all, consists of a little bag, which remains affixed by its base to a seaweed. All over its sides there are many pores and at its tip there is a single osculum; it is known as the Purse Sponge and is common round our coasts. The inside of the purse sponge is lined with cells, each one of which is tipped with a little whip which waves about unceasingly. The waving of the whip causes water to flow through all the pores into the hollow bag and out again by way of the osculum. Although most sponges, including our fresh-water forms, are much more complicated than the purse sponge, the same thing happens in them all, water is drawn in by way of the pores and forced out by way of the oscula. The best place to seek for the fresh water sponges is on the under sides of floating wood, broken tree branches and the like. Their appearance depends upon whether they have been growing in a well-lighted spot or in darkness; they contain chlorophyl as do the higher plants, and sponges grown in the light are green, those which the light has not reached are buff-coloured or corn-yellow. The pond sponge is brighter green than its river frequenting relative and is a coarser creature altogether. It often forms little finger-like outgrowths, whereas the river sponge is more leaflike.