The sea mat and bird’s head, two common animal colonies of the sea-shore, possess pond-dwelling relatives of the greatest interest to the microscopist. Like the seaside forms they dwell in colonies. One of the commonest is known as _Lophopus Crystallinus_ and it may be found attached to duckweed, the curious little plant whose tiny leaves float upon the surface of the water. _Lophopus_, when at rest, resembles a little piece of jelly. If we are patient and watch it under our microscope we shall see it expand, sending forth a number of stalks, each one tipped with a horse-shoe shaped feathery tentacle. Each of these tentacles belongs to a separate animal which with its fellows forms a colony. Not so interesting are the branched, threadlike colonies of _Plumatella Repens_ which may be sought upon the leaves of water plants. Our ponds can furnish no more extraordinary object for our microscope than a colony of _Cristatella Mucedo_; it is curious in appearance and still more curious from the fact that though a colony of animals it acts like a single individual in crawling over the weeds and stones in shallow, sun-kissed water. The _Cristatella_ colony is jelly-like and greenish in colour, in length it may grow to a couple of inches. Its under surface is flat, whilst from its upper, convex surface the little animals forming the colony wave their brush-like tentacles in the water. In searching the various pond weeds for specimens we are sure to meet with various jelly-like masses; these must always be examined carefully. They may be the egg-masses of interesting water creatures; various water-snails, for instance, protect their eggs with a jelly-like covering. If we meet with any large fresh-water mussels, sometimes called swan mussels, we shall probably find the fleshy parts of the molluscs swarming with minute creatures, which we may conclude are parasites. Mussels, like nearly all living creatures, have their parasites it is true, but what we have discovered will almost certainly prove to be young mussels. We must examine them under the microscope to make sure. Then we shall see, if young mussels they be, very minute and very thin-shelled little creatures; the edges of their shells are armed with teeth and are quite unlike the highly polished and smooth shells of the parent mussel. We shall also see a long thread issuing from the animal within the shell. If we are examining the young mussel in water we shall notice that it is constantly snapping its two shells together.