The second species of paste eel is oviparous. It is easily distinguished from the first kind by being much smaller; in Fig. 8, is exhibited a magnified view of this eel. The conformation of the alimentary duct and the intestines are in general nearly the same, though an intelligent observer will find out some specific differences. By the flexion of the intestines c c c, a void space is left a little beyond the middle of the body, where the ovary, d d, is situated. There is no exterior protuberance near this ovary, as in the preceding one.
We meet with another eel in paste, which may with propriety be called the common eel. It is often to be found in grains placed in the earth, in which the germ is destroyed, in the roots and stems of farinaceous plants, in the tremella of Adanson, and in several species of conferva, as well as in several infusions. This eel, when at its full growth is rather longer than the common eel of blighted wheat; one of them is represented at Fig. 11. They are easily distinguished from the eels of blighted wheat, because they have no ranges of globules like it, by the two little protuberances which are near the middle of the body, and by the regular diminution of the tail. It is oviparous.
A very small species, represented at Fig. 9, may also be found in paste; they may be distinguished from the young eels of the larger sort by their vivacity and slenderness.
As the eels in paste are objects which are so often exhibited in the microscope, it will be proper, before we leave this subject, to inform the reader how he may procure the young eels from the parent animalcula; a discovery which was originally made by Mr. Sherwood, but more particularly pursued and described by Baker. Take up a very small quantity of paste where these eels abound on the point of a pin, or with a sharpened quill; lay it on a slip of glass, and dilute it well with water; by these means, many of them will become visible to the naked eye; then with the nib of a pen cut to a very fine point, and shaved so thin as to be extremely pliable, single out one of the largest eels, and insinuate the point of the pen underneath it; remove it into a very small drop of water, which you must have ready prepared on another slip of glass. When thus confined, it may easily be cut asunder transversely, by the help of a good eye and steady hand, with a lancet or sharp penknife; or if the eye be deficient, a hand-magnifier will enable almost any person to perform the operation. As soon as the parts are separated, apply your object to the microscope, and if the division has been made about the middle of the animal, several oval bodies of different sizes will be seen to issue forth. These are young anguillulæ of different degrees of maturity, each of which is coiled up, and included in its proper membrane, of so exquisite a fineness, as to be scarce discernible by the greatest magnifier while it incloses the embryo animal. The largest and most forward break immediately through this delicate integument, unfold themselves, and wriggle about nimbly in the water; others get out, uncoil, and move about more slowly; and the least mature continue entirely without motion. The uterus or vessel that contains all these oval bodies is composed of many annula or ringlets, not unlike the aspera arteria of land animals, and it seems to be considerably elastic; for as soon as the operation is performed, the oval bodies are thrust out with some degree of violence by the spring or action of this bowel. An hundred or upwards of young ones have been seen to issue from one single eel, whereby the prodigious increase of them may be accounted for, as probably several such numerous generations are produced in a short time. Hereby we also learn that these creatures are not only like eels in shape, but are likewise viviparous, as eels are generally supposed to be.
Few experiments are to be found more entertaining, or in which there is so little risk of being disappointed; for they seem, like earth-worms, to be all prolific, and you may be sure of success, unless by accident you cut one that has already brought forth all its young, or make your trials when the paste has been kept a very long time, in which cases they have been found unfruitful.
3. ANGUILLULA AQUÆ DULCIS, OR FRESH WATER EEL.
Corculum vermiculo simile, Linn. Amæn. (Mund. Invis.) Anguille Vulgaire, Rozier Journal Physique, 1775. Mars, Nov. 1776. Ibid. Anguille du Bled Rachitique. Ibid. Anguille du Faux Ergot. Spallanz. Opusc. Phys. part 2, p. 354, pl. 5, fig. 10.
The body of this is exceedingly transparent, with no visible entrails, though a few transverse lines may be discovered on the body. It is sometimes, though rarely, furnished with a long row of little globules, and often with two small oval ones; the tail terminates in a point. Müller says he found these eels in the sediment which is formed by vegetables on the sides of vessels in which water had been kept for some time.
4. ANGUILLULA AQUÆ MARINÆ, OR SALT WATER EEL.
This, when pressed between two plates of glass, appears to be little more than a crystalline skin, with a kind of clay-coloured intestines. The fore-part of the body is truncated, the lower part drawn out to a fine point, the rest of the body is of an equal size throughout. The younger ones are filled with pellucid molecular intestines.