It is said, that these animals are never found in males until the age of puberty ; that they decrease as life ad vances, and in old men are altogether wanting. The like is reported of the inferior animals; none could be discovered in very young rams ; they were more nume rous in young bulls, two or three years old, than those of five or six. They have been unsuccessfully sought for in the mule. In the human species, it is also said, that they do not appear during the prevalence of the venereal disease. All these facts perhaps require cor roboration, by a series of more careful experiments, than, we apprehend, they have yet received.
It has been affirmed, that vermiculi are found in the peculiar fluid secreted by feales, as well as in the masculine race. The count Buffon and signor Bono maintain the fact, and Spallanzani declares his belief of it. We have purposely refrained from speaking of the experiments by the first of these naturalists on the male vermiculi, and the conclusions he deduced from them, because the fallacy of both has been amply de monstrated; and this renders us more reserved in ad- mitting his assertions respecting the vermiculi of the female. But, without presuming to deny the fact, which we have certainly no authority to do, we shall content ourselves with observing, that they are sometimes found in the blood of females. This is no doubt a rare oc currence. Spallanzani discovered a number of seminal vermiculi in the mesenteric blood of a frog and three newts, which were all females excepting one newt. Some were seen in the blood of a sucking calf, and se veral among the red globules in that of a ram. Blood is one of the fluids not fatal to their existence, as they survive after its mixture with their native fluid.
The use of the vermiculi is yet unknown. No sooner were they discovered, than various conjectures were formed concerning them, and these stood on plausible grounds, until overturned by more logical reasoning. The most important hypothesis was that which .sup posed them the germs of future animals; that they were transmitted to the female, and expanded into her off spring. Thus, the famous Lecuwenhoek, in particular, maintained, that the human vermiculi would become so many children, those of the bull so many calves, and those of the frog so many tadpoles. Philosophers ea gerly embraced his theory ; instead of finding it repug nant, they rather judged it consistent with external ap pearances. They discovered a great resemblance be tween the vertniculus of the cock, and what is exhibited in the progregS of an impregnated egg during incuba tion; and the likeness of tadpoles to the vermiculi of frogs, they conceived still more minute. But such theories have vanished.—The most enlightened natu ralists consider the germ of the offspring as pertaining to the female alone, though it cannot refold of itself: whence the use of the male vermic mains in its original obscurity.* III. Animalcula arc found in none of the other fluids of animal bodies, if recent ; and, if they have been seen there, probably it was owing to some accidental circum stance, for it does not appear that they have a general and permanent abode. It has been supposed that cer tain diseases originate from animalcula. Nay, some
authors have gone so far as to advance, that every differ ent disease has animalcula peculiar to itself, and that they arc actually exhibited by several in different stages. It is extremely probable, that they harbour in diseased organs, whose particular state may promote their origin : and we doubt not that numbers may at all times be found in neglected ulcers, or in cutaneous disorders, but per haps they are chiefly of species analogous to the infu soria. Those which Lecuwenhoek found inhabiting the teeth of various people were possibly of this description. They resisted the application of salt, but were destroyed by vinegar.
Besides the infusoria, there are many other micros copic animalcula, hitherto reduced under no specific classification. Such is the urslet, so called from its re semblance to a bear, which Goeze and Eichorn discov ered in Germany ; and which also inhabits Denmark and Scotland, though rarely seen in the latter country.
The urslet has been found in greatest abundance among the yellow ochry slime, that in spring covers pools of standing water. It has eight short legs, disposed in pairs, each terminated by three curved nails. The last pair are situated exactly like those of caterpillars. The body of some urslets appears opaque, and covered with a granulated skin; others are quite transparent, and are often observed to contain a number of eggs. Here it is to be remarked, however, that Muller affirms they cast the skin, and, by a singular operation of nature, the exuvix are the depositary of the animals ovary ; whence it is likely, that the transparent urslets are always sloughs. The number of eggs is various; sometimes there is a single one, which is so large as to distend the body ; at other times, it is completely filled from end to end with them.
The urslet is a dull and sluggish animalcule : like Spallanzani's sloth, it is generally found supine. It sel dom appears in motion, and then its progression is slow and languid : a universal torpor seems constantly to affect it, which increasing heat never removes.
Muller, Animalcula Infusoria. Zoologia Da nica, et Kleine Scriften. \Vrisberg, de Animalculis infu .so•lis. Leeuwenhock, Arcana Naturce, et Continuatio. Ledermuller, Amusement Microscopique. Pallas, Elen chus Zoophyto•um. Rocsel, Belustigung des Insecten, vol. iii. Joblot, Observations avec le Microscope. Bonnet, Oeuvres, torn. v. Fuessly, Archives de l'Histoire des In sectes, Winthe•toun, 1794. Vallisneri, Opere fisico Hediche. Gleichen, Sur les Animalcules Spermatiques et ceux d'Infusions. Needham, .Nouvelles Observations Microscopiques, 1750. Journal de Physique, 1775, 1776. Philosophical Transactions, vol. xlii. xliv. Hooke's Philo sophical Collections. Bruigierc, dans l'.Encyclopedie thodique, article (I think) HELMNTDOLOGIE. Baker, Of Microscopes, Haller, Physiologia, torn. vii. Spallan zani, Tracts on Animals and Vegetables, Edinburgh, 1805, et Lettera relativa a diverse Produz:ieni Marine. Philosophical Transactions, vol. xiii. —1045.—xvii. 861.—xix. 254.—xxi. 270,-301.—xxii. 759.—xxiii. 1 1 37,-1304,-1450,-1494.—xxiv. 1784.— xxvii. 516.—xxviii. 138.