_Infusorial Life_, with all its fascinations, was fully unveiled to naturalists by the celebrated Ehrenberg. It was he who termed it infusorial, because he first met with the more interesting forms of minute life in infusions of hay and other vegetable substances. Since his day it is a well-known experience of those who take up the microscope that the most interesting objects to commence with are infusorial living creatures of sufficient dimensions to be easily understood and seen with moderate magnifying powers. Moreover, infusoria are more readily found in almost any pool or running stream of water, either near the surface or clinging to the under surfaces of aquatic plants. At one time all the small shallow pools in the neighbourhood of London--Hampstead Heath, Clapham, Wandsworth, and other commons--abounded in the most interesting forms of life, were famous hunting grounds for the marvellous volvox, the charming dismid and diatom, the wonderful budding and self-dividing hydra. A few hours’ ramble furnished the microscopist with a bountiful supply of these and many other forms of life. Now all is changed; our commons have been devoted to other purposes, and with the general _levelling_ up all the little pools have disappeared, and the microscopist has been warned off and driven further afield, or seeks the good offices of a country friend for an occasional peep into pond life.[48] A teaspoonful, however, judiciously taken from a well-chosen locality will often be found to contain a variety of living forms, every one of which will deserve a careful and patient study. Of the microscopic organisms, the collection of which requires no other methods than those ordinarily pursued by the naturalist, most of them must be sought for in pools or running waters, basking in the sunshine, clinging to leaves and rootlets of all aquatic plants; some freely moving about, others clinging to stones or pieces of wood at the bottom. Dismids congregate in shallow waters or rise to the surface in a quiet nook, while the diatomaceæ are seen covering the bottom of clear water, to which they give a yellowish-brown tinge of colour.