3. Monas Punctum.
M. nigra. A black mona.
A very minute point, solid, opake and black, round and long. They are dispersed in the infusion, and move with a slow wavering motion; were found in a fetid infusion of pears.
4. Monas Ocellus.
M. hyalina puncto centrali notata. Transparent like talc, with a point in the middle.
The margin black, and a black point in the middle; it moves irregularly, is found in ditches covered with conferva, and frequently with the cyclidium milium, see [No. 84].
5. Monas Lens.
M. hyalina. Transparent mona of the appearance of talc.
This is among the number of the smaller animalcula, nearly of a round figure, and so pellucid, that it is not possible to discover the least vestige of intestines. Though they may often be seen separate, yet they are more generally collected together, forming a kind of vesicular or membranaceous mass. Contrary to the custom of other animalcula, they seek the edges of the evaporating water, the consequence of which is almost immediate death. When the water is nearly evaporated, a few dark shades are perceived, probably occasioned by the wrinkling of the body. A slow tremulous motion, confined to one spot, may be perceived at intervals; this in a little time becomes more lively, and soon pervades the whole drop. Its motions are in general very quick: two united together may sometimes be seen swimming among the rest; while in this situation, they have been mistaken by some writers for a different species, whereas it is the same generating another by division. It is to be found in all water, though but seldom in that which is pure; they are in great plenty in the summer in ditch water, also in infusions of animal or vegetable substances, made either of fresh or salt water, myriads being contained in a drop; numbers of various sizes are to be found in the filth of the teeth.[123]
[123] The circumstance of animalcula being found in the teeth is mentioned with confidence by various authors; some doubts may, however, still remain of the fact. Mr. Willughby detected a woman, who pretended to take worms out of the teeth with a quill, having forced the quill, from her just as she was putting it into his mouth, and found small worms in it; see Birch’s History of the Royal Society, vol. iv. p. 387. I am inclined to think that the accounts usually met with in authors have no better foundation. It has also repeatedly happened, that ingenious men, from their anxiety for discovery, have imagined that objects have appeared to their view, which, having related as facts, themselves or others have afterwards found to be nothing more than a deceptio visus; and thus they have been, at least for a time, the unintentional promulgators of error; considerable caution is therefore necessary on these occasions, see [p. 132], [133].