The animals are of several kinds. The most numerous is an active little thing of about T^ of an inch in length when extended, though from its extreme versatility it is as difficult to assign to it a definite size as a definite shape. It seems to be the E. sanguinea, so called because it is said to occur sometimes of a deep red hue y and in such vast profusion as to give the waters the appearance of blood. I have never seen it, however, other than as it now appears, rich emerald green in the body, with the two extremities perfectly clear and colourless. I might, perhaps, describe its ordinary form as spindle-shaped, with a pointed tail, and a blunt, rounded head ; but it is remarkable for the variableness of its shape. It is capable of assuming an appearance very diverse from what it had half a minute before, so that you would hardly identify it, if you were not watching its evolutions. Whether this ability to prove an alias be at all dependent on the remarkable clear-headedness of the subject, I leave for those who are skilled in metaphysics to determine. Away they go, tumblingover and over, revolving on the long axis as they proceed, which they do not very rapidly, with the blunt extremity forward.

Here is another kind, a little larger than the former, but much more slender; yet from the slowness and steadiness of its movement more easy of observation. It is named E. acus, or "the Needle Euglena." This is an animalcule of great elegance and brilliancy ; its sparkling green hue, with colourless extremities, and its rich pale crimson eye, are very beautiful. It commonly swims extended, with a slow gliding motion, turning round on its long axis as it proceeds, as may be distinctly seen by the rotation of certain clear oblong substances in its body. These, then, are seen not in the interior, but near the surface, as they would appear if imbedded in the flesh around a hollow centre. The interior is probably not hollow, but occupied with pellucid sarcode. These were assumed by Ehrenberg, but on no adequate grounds, to be organs connected with reproduction. They vary in number in different individuals, and those which contain the greatest number are thereby more swollen. They appear to be separated into two series, one anterior, the other posterior. The animal is capable of bending its head and body in various directions, but is most beautiful when straight. The front is furnished with a slender thread-like proboscis. This species affords us a good opportunity of observing the red spot, which, for convenience sake, we may still term an eye. It seems to be an irregular oblong vacuole, or excavation in the sarcode, tilled with a clear ruby-red fluid. The red spot in the Rotifera is connected with a well-defined crystalline lens, whose definite form and high refractive power may in many cases be distinctly marked ; but here nothing of the kind is seen ; the spot itself has no certain shape, and does not appear to be bounded by a proper wall. Some forms, which are by general consent admitted to be plants, have similar spots ; and hence it has been, rather too hastily, I venture to think, concluded that they have no connexion with vision. I think it still possible that a sensibility to the difference between light and darkness may be the function of the organ.

I have found that this animal, when allowed to dry on a plate of glass, retains its form and colour perfectly ; but in about two days the eye-spot, which at first becomes much larger in the drying, gradually loses all traces of its brilliant colour, probably by the evaporation of the contained fluid.

Another pretty species you see gliding along among the rest, called E. triqrietra, or the Three-sided. It bears a resemblance to a broad rounded leaf, with the footstalk forming a short transparent point, and the mid-rib elevated into a sharp ridge. The under side seams slightly concave. This is equally attractive with the others. It is persistent in form, and appears not to be even flexible. Its motion is slow, and as it goes it rolls irregularly over and over in all directions, THBEE-SIDED EVGLENA. not revolving on its long axis, and thus giving you very satisfactory views, though only momentary, of the keel with which the back is furnished. It is in the turnings of such minute creatures that the microscopist often gets a glimpse of peculiarities of form, which a view of the animal when in repose, however long continued, fails to reveal. Longitudinal interrupted lines

are seen running down the body of this pretty leaf, which do not appear to mark irregularities of the surface, and therefore are probably internal. Ehrenberg calls these and similar collections of granules " ova," or eggs ; but this is to cut the knot instead of untying it. There is no sufficient reason to believe that these animals increase by ova.

About the front of all these Euglence, you may discern now and then a slight nickering or quivering in the water. The power we are using, though best for the general display of the form, is insufficient to resolve this appearance : I will put on a higher objective. You now see that there proceeds from the frontal part of the body a long and very slender filament, which is whisked about in the manner of a whip-lash. This is considered to be the organ of locomotion ; but I rather doubt that such is the function ; the smooth and even gliding, often rotating, action of the creature, seems more like that produced by minute and generally-distributed cilia, than that caused by the lashings of a single long thread.

Yet two more species of this extensive genus we discern in this well-stocked drop of water. They have received the appellations of the Pear (E. pyrum) and the Sloth (E. deses). The former is the most minute we have yet seen and seems to be scarce ; but it is highly curious and interesting in appearance. It much resembles in outline a fish of the genus Balistes ; the muzzle being somewhat protruded and truncate, and the form rhomboidal ; it terminates in a slender pointed tail. The body is obliquely fluted, which gives a very singular effect ; for, from the transparency of the tissues, the lines of the opposite side can be discerned crossing those next the eye, and dividing the animal into lozenge-shaped areas. The colour is sparkling green, but the tail and the edges of the body are clear and colourless, and there is a bright red eye. At other times this Euglena takes the form of a claret-bottle or an oil-flask ; the muzzle being broadly truncate or even indented.

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.

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