Its motion is rapid ; a swift gliding in the direction of its long axis : it turns continually on the same axis, which gives a waving irregularity to its course, and has a pretty effect from the continual crossing of the flutings in the revolving. This specimen is about T^ of an inch in length, including the tail.

Euglena deses is much larger, being about ~jj of an inch in length, though the tail is very short. It has a thick body, with a round, blunt head ; it tapers suddenly to the tail. Its colour is bright green with a red eye; but the presence of an infinite number of irregular oblong granules and lines with several globular vesicles, gives an opacity and a blackness to its appearance. In its manners it is sluggish ; it never swims or glides gracefully and swiftly among its playful companions, but contents itself with twining slowly among the downy stems and filaments of the water-plants, or crawls upon the surface of the live-box. It does not appear to change its form, otherwise than its soft and flexible body necessitates, as it twines about.

But enough of the Euglence. For I have just caught sight of a much more curious creature, the Swan Animalcule (Trachelocerca olor). It is reposing on one of the leaves of the MyriophyMum, its long and flexible neck lengthening and contracting at pleasure, the tip thrown about in quick jerks in every direction, somewhat like a caterpillar when it touches several points impatiently with its head.

If we admire the graceful sailing of a swan upon a lake, the swelling of its rounded bosom, the elegant curves of its long neck, we shall be struck with the form and motion of this animal. The form has much resemblance to that of a swan, or still more to that of a snakebird (PloHut) ; the body, swelling in the middle, tapers gradually into a slender pointed tail at one extremity, and at the other into a very long and equally slender neck, which is terminated by a slight dilatation. The whole is perfectly transparent, but the body is filled with numerous minute globular vessels, or temporary stomachs. The grace of its motion, as it glides along with a free and moderately swift progression through the clear water, or winds through the intricate passages of the green conferva, throwing its long neck into elegant curves, is very remarkable. There are, I see, two of them, which, however, take no notice of each other, even when passing close to each other ; the neck of one

SWAN-NECK AND ITS DIVISIONS.

is much longer than that of the other. Now and then, when gliding along, the neck is suddenly contracted, but not wholly, as if something had alarmed or displeased the animal ; the body also can be swollen or lengthened at pleasure ; it can move in either direction, but the neck usually goes foremost, extended in the direction of the motion, and seems to be used to explore the way.

I had once an opportunity of seeing the process of increase by spontaneous self-division in this creature. It was an unusually large specimen, found in an old infusion of sage leaves. When I discovered it, it was darting about its long neck in the most beautiful contortions. As it was partly hidden by the vegetable fibre present, I

turned the glass cover so as to alter the position of the contents. On again looking, the Swan was in a clear part of the field, but in the form of a dark globose mass, the neck being entirely contracted. It was quite still, except a continual slight alteration of the form by the protrusion or contraction of parts of the outline. The body seemed full of minute globules, .set in a granular mass of a blackish hue, and the outline was not a continuous line, but formed a multitude of rounded elevations. Presently it protruded the clear neck, but only for a short distance, and then retracted it as before ; when the only indication of the presence of this organ was a depression in one part of the surface, somewhat like the mouth of a closed Actinia, where there was a slight but incessant working, very much like the irregular motion on the surface of boiling water, in miniature; there was also an indistinct ciliary action at this part, not of rotation, nor of vibration, but a sort of waving. At this point I had occasion to get up from the table, and though I was not away more than a minute, on my return I observed a strong constriction around the middle of the bodv. It was transverse, for the depressed and ciliated mouth was at a point exactly at right angles to the constriction. From the depth to which this latter extended in so few minutes, I supposed the process of separation would be very rapid ; for I could very soon see a line of light all across at intervals, and the two halves seemed to slide freely on each other. Yet they remained long without much apparent progress, or even change, except that the anterior half at one time threw forth its neck a short distance ; at this time it looked extremely like a bird, bridling up its lithe neck and swelling bosom; while, to make the resemblance perfect, it began to imitate the action of a fowl picking up grain, bobbing its head hither and thither : so curious are the analogies of nature ! Along the dividing line there had appeared very early in the posterior half a distinct ciliary action; after a while (how, I do not exactly know), without the general relation of position being changed, the mouth of the anterior (which must now be called the old) animal appeared on the side, and at the point correspondent in the other, a similar ciliary wreath appeared, while the action along the dividing line was no longer seen. So that the division which was at first transverse now appeared longitudinal. I believe, however, the animals were really separated before this, though they remained in contact, for as they slid over each other it was manifest that each had an independent action.

At length, about an hour and a half after the first appearance of the constriction, the new animal threw out its clear neck to a great length, writhing it about with rapid agility, and forming the most elegant curves, like those of a serpent, often completely encircling its own body with it. It still remained, however, in contact with its parent, which after a time also protruded its neck in the same manner. Both then retracted and remained still for a while; and again, almost simultaneously threw out their long necks and then retired to sluggish repose.

Among the sediment, the grains of which are driven hither and thither by their spasmodic, jerking movements, you see several individuals of another sort of creature,— the Chrysalis Animalcule (Paramcecium aurelia). This is a "Triton among minnows"; for it is greatly larger than any of those we have yet observed, and is just visible to the naked eye, when we hold up the live-box obliquely against the light ; for then the animals appear as the smallest possible white specks.

Bringing them again under the microscope, each presents a pellucid appearance, and an oblong figure, of which the fore part is somewhat narrowed. The back rises in a rounded elevation, and the mouth is situated as far back as the middle of the body upon the under surface, where its position is marked by a sort of long fold, the sides of which are fringed with long cilia, whose vibrations are very marked. The whole surface, on both sides, is covered with minute cilia, arranged in longitudinal rows, of which, according to the great Prussian professor, there are from thirty to sixty on each surface, each row bearing sixty or seventy cilia. This must be considered as an approximation ; for we may well doubt the accuracy of the counting, when the objects are so very evanescent as these vibrating cilia.

The vacuoles, and the temporary stomachs, more or less completely tilled with the brown and green food, which the animals are collecting from the decayed vegetable matters, are sufficiently numerous and conspicuous ; but they may be rendered still more so by the device of mixing a little carmine with the water. The ciliary currents are thus instantaneously rendered strikingly visible. The crimson atoms are attracted from all quarters towards the tail of the animal, whence they are urged in a rapid stream along one side towards the head, around which they are hurled, and then down the other side to the tail, pouring off in a dense cloud in a direction contrary to that in which they originally approached.

But now the gathered currents have produced their expected result ; for many of the globular vacuoles are already become of a beautiful rosy hue, from the minute particles of the pigment which have been whirled to the mouth, and swallowed.

The feature of greatest interest, however, in this animal is the contractile bladder. Two of these organs are usually seen co-existent in each individual, placed, the one on the front, the other in the rear of the mouth, but near the opposite,—i.e., the dorsal,—surface of the body; for as the creature slowly revolves on its longitudinal axis, the line of the vesicles alternately approaches and recedes from that of the mouth. They are remarkable for their structure. Far from the simplicity in which the organ is usually presented to us in the animals of this class, the contractile bladders are here very complex. Each when distended is globular; and it is surrounded by a number of others of much smaller dimensions, and of a drop-like form, so set as to radiate around the principal vesicle as a centre, the rounded portion of each in apparent contact with the vesicle, and the slender extremity running off as an attenuated point till lost to sight in the sarcode. The main vesicles alternately become distended, and suddenly contract to a point ; while the radiating cells are continually varying in size, though in a less degree. It is customary to describe the secondary vesicles as coming into view at the instant of the contraction of the primary

PARAMECIUM.

one, and to suppose that the emptying of the one is the filling of the other, but I have not been able to observe this mutual relation satisfactorily made out. The smaller as well as the larger vesicles are conspicuous from their colourless transparency ; for the general sarcode of the body, though pellucid, is only so in the same degree as glass, slightly smoked; besides that its clearness is often impaired by crowds of granules and minute globules.

You ask what is that comparatively large oval body attached by its side to one of the leaves of the plant. It is the egg of some considerable Rotifer, probably JSuchlanis, which is always glued to some filament or stem of a waterplant. It may interest you to watch the progress of the contained embryo, which you can readily do, since the eggshell is as transparent as glass, and the infant animal already displays the movements of independent life.

Meanwhile I will tell you the tragical and lamentable history of just such an embryo as this, that, was eaten up before it was born, under my own eye. One of the depredators was a very amusing animalcule, which is sufficiently scarce to make its occurrence a thing of interest, especially to a young microscopist, as I was at the time.

A large egg of (as I believe) Eucltlanis dilatata had been laid during the night on a leaf of Nitella, in the live-box. When I observed it, the transparency of the shell allowed the inclosed animal to be seen with its viscera, which occasionally contracted and expanded ; the place of the mastax I could distinctly make out. The cilia were vibrating, not very rapidly, but constantly, on COLEPS AND CHIL01IONAS. the front, where there was a vacant space between the animal and the shell. From seven a.m. when I first saw it, I watched it for about eight hours, without perceiving any change ; but at that hour having withdrawn for a short time, I perceived on my return that a portion of the animal was outside the shell. The appearance was that of a small colourless bladder oozing out at an imperceptible aperture ; and this oval vesicle quickly but gradually increased, until it was half as large as the egg itself. A little earlier than this point, the cilia were seen on the front or lower side of the excluded portion, and these began to wave languidly in a hooked form. They thus seemed much longer and more substantial than when rotating in the perfect animal. When excluded to the extent just named, some little creatures that were flitting about found it, and began to assemble round it. These were far too rapid in their

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