Powers that are most serviceable--Estimated by Focal length--Length of Body of Microscope and its Effects--Popular Errors about Great Magnification--Modes of Stating Magnifying Power--use of an "Erector"--Power of various Objectives with different Eye-pieces--Examination of Surface Markings--Methods of Illumination--Direct and Oblique Light--Stage Aperture--Dark-ground Illumination--Mode of Softening Light--Microscope Lamps--Care of the Eyes CHAPTER II. JANUARY. Visit to the Ponds--Confervæ--Spirogyra quinina--Vorticella--Common Rotifer--Three Divisions of Infusoria--Phytozoa--Protozoa--Rotifera--Tardigrada--Meaning of these Terms--Euglenæ--Distinction between Animals and Vegetables--Description of Vorticellæ--Dark-ground Illumination--Modes of producing it--The Nucleus of the Vorticella--Methods of Reproduction--Ciliated Protozoa--Wheel-bearers or Rotifers--Their Structure--The Common Rotifer--The young Rotifer seen inside the old one--an Internal Nursery--"Differentiation" and "Specialization"--Bisexuality of Rotifers--Their Zoological Position--Diversities in their Appearance--Structure of their Gizzard--Description of Rotifers CHAPTER III. FEBRUARY. Visit to Hampstead--Small ponds--Water-Fleas--Water-Beetle--Snails--Polyps--Hydra viridis--The Dipping-tube--A Glass Cell--The Hydra and its Prey--Chydorus Sphæricus and Canthocamptus, or Friends and their Escapes--Cothurnia--Polyp Buds--Catching Polyps--Mode of Viewing Them--Structure of Polyps--Sarcode--Polyps Stimulated by Light--Are they Conscious?--Tentacles and Poison Threads--Paramecium--Trachelius--Motions of Animalcules, whether Automatic or directed by a Will--Their Restless Character CHAPTER IV. MARCH. Paramecia--Effects of Sunlight--Pterodina patina--Curious Tail--Use of a Compressorium--Internal Structure of Pterodina--Metopidia--Trichodina pediculus--Cothurnia--Salpina--Its Three-sided Box--Protrusion of its Gizzard Mouth CHAPTER V. APRIL. The Beautiful Floscule--Mode of Seeking for Tubicolar Rotifers--Mode of Illuminating the Floscule--Difficulty of seeing the Transparent Tube--Protrusion of Long Hairs--Lobes--Gizzard--Hairy Lobes of Floscule not Rotatory Organs--Glass Troughs--Their Construction and Use--Movement of Globules in Lobes of Floscule--Chætonotus larus--Its mode of Swimming--Coleps hirtus--Devourer of Dead Entomostraca--Dead Rotifer and Vibriones--Theories of Fermentation and Putrefaction--Euplotes and Stylonichia--Fecundity of Stylonichia