1. Monas: Punctiformis. A mere point. 2. Proteus: Mutabilis. Mutable. 3. Volvox: Sphaericum. Spherical. 4. Enchelis: Cylindracea. Cylindrical. 5. Vibrio: Elongatum. Long. *Membranaceous. 6. Cyclidium: Ovale. Oval. 7. Paramecium: Oblongum. Oblong. 8. Kolpoda: Sinuatum. Sinuous. 9. Gonium: Angulatum. With angles. 10. Bursaria. Hollow like a purse. II. _Those that have External Organs._ *Naked, or not enclosed in a shell. 1. Cercaria: Caudatum. With a tail. 2. Trichoda: Crinitum. Hairy. 3. Kerona: Corniculatum. With horns. 4. Himantopus: Cirratum. Cirrated. 5. Leucophra: Ciliatum undique. Every part ciliated. 6. Vorticella: Ciliatum apice. The apex ciliated. *Covered with a shell. 7. Brachionus: Ciliatum apice. The apex ciliated. 1. These animalcules are discovered in two or three days in all decompositions of organic matter, whether vegetable or animal, in moderate degrees of warmth with sufficient moisture. 2. They appear to enlarge in a few days, and some to change their form; which are probably converted from more simple into more complicate animalcules by repeated reproductions. See Note VIII. 3. In their early state they seem to multiply by viviparous solitary reproduction, either by external division, as the smaller ones, or by an internal progeny, as the eels in paste or vinegar; and lastly, in their more mature state, the larger ones are said to appear to have sexual connexion. Engl. Encyclop. 4. Those animalcules discovered in pustules of the itch, in the feces of dysenteric patients, and in semine masculino, I suppose to be produced by the stagnation and incipient decomposition of those materials in their receptacles, and not to exist in the living blood or recent secretions; as none, I believe, have been discovered in blood when first drawn from the arm, or in fluids newly secreted from the glands, which have not previously stagnated in their reservoirs. 5. They are observed to move in all directions with ease and rapidity, and to avoid obstacles, and not to interfere with each other in their motions. When the water is in part evaporated, they are seen to flock towards the remaining part, and show great agitation. They sustain a great degree of cold, as some insects, and perish in much the same degree of heat as destroys insects; all which evince that they are living animals. And it is probable, that other or similar animalcules may be produced in the air, or near the surface of the earth, but it is not so easy to view them as in water; which as it is transparent, the creatures produced in it can easily be observed by applying a drop to a microscope. I hope that microscopic researches may again excite the attention of philosophers, as unforeseen advantages may probably be derived from them, like the discovery of a new world. ADDITIONAL NOTES. II. THE FACULTIES OF THE SENSORIUM.