Many muscles are inserted into diflerent parts of these organs, and into the walls of the inastax, which impart various and complex motions to all the parts. Thus, as we have seen, they are adapted to the various functions of mouth-organs, those of grasping, holding, bruising, and chewing food.

The mallei correspond with the mandibles of Insects ;

The uncus of the malleus must not be confounded with the incus.

and the rami of the incus with the maxilla? ; while the walls of the mastax with the two edges of its orifice correspond with the mouth, with its labrum and labium.

It is true we are somewhat startled to find a mouth placed far down within the cavity of the breast ; but there are other forms in this class, some of which I may be able to show you, where the mastax has essentially the same structure, in which it is placed at the front margin of the body, from which SIOUTH OF BKACHIONUS. the jaws can be freely protruded. The difficulty will seem less if you weigh the following considerations :—

The integument in the Rotifera is very flexible, and, especially in the frontal regions, is extremely invertible. In those genera in which the mouth-apparatus can be brought into contact with the external water, it is ordinarily, to a greater or less degree, retracted within the body, by the inversion of the surrounding parts of the exterior ; while, in those genera in which it is permanently inclosed, analogy requires us to consider the condition as induced by a similar inversion, but of permanent duration. If we imagine the head of a softbodied Insect-larva retracted to a great degree (as is done partially by many Dipterous larva?), the skin of the thoracic segments would meet together in front, around a purse-like opening, which would be the orifice of such a buccal funnel as exists in most Rotifera. In the latter, it is the normal, or proper condition ; in the former, it is merely accidental and temporary.

We need not devote any more minute consideration to the digestive apparatus in our little Brachion, but there

are some other points in its structure which are worth noticing. In the central line of the body, just above the mouth, as you see the animal in a dorsal view, there is a square speck of a rich crimson hue, the edges of which, when we view it under reflected light, glitter and sparkle like a precious stone. But when we obtain a perfectly lateral view, we perceive that the situation of this gemlike speck is considerably nearer the dorsal side of the shell than the mouth, and that it forms a wart-shaped prominence on a large turbid mass which occupies the whole front portion of the animal. By comparison of this organ with the corresponding parts in other genera, there is every reason to infer that this turbid mass is an enormous brain, the nervous matter being in a very diffuse condition ; and that the ruby seated on it is an eye, consisting of a crystalline lens, and a layer of crimson pigment beneath it.

The oval bodies that you see attached to the hinder part of the shell are eggs. Most of the females that we meet with carry one or more, sometimes to the number of six or seven. The specimen we are examining had two at first, one on each side the foot-orifice ; but just now a* third was excluded,—an operation which occupied but an instant,—and this took its place besides the former two, so that we now see three. These eggs are generally carried by the parent until the young are hatched. The oldest of these three is nearly ready for hatching ; and if you watch awhile you will see the birth of the young. At the first exclusion, the egg, which was seen sometime before in the ovary, as a semi-opaque mass, of well-defined but irregular shape, immediately assumes a form perfectly elliptical, and its coat hardens into a brittle shell. This is so transparent that the whole process of maturation can be watched within the shell. The yelk is at first a turbid mass, in which are many minute oil-globules. Soon it divides into two masses, then into four, then into eight, sixteen, and so on, by the successive cleavage of each division, as fast as it is made, till these divisions are very numerous. Then we begin to see spontaneous movements ; the outline of the young separates in parts from the wall of its prison ; folds are seen here and there, and litful contractions and turnings take place. Soon an undefined spot of red appears, which gradually acquires depth of tint and a definite form, and wre recognise the eye. Slight waves are seen crossing one end of the egg ; these become more and more vigorous and rapid, and at length we see that here is the situation of the frontal cilia. The mastax appears, and the jaws, and soon the latter begin to work ; though it must be only by w ray of practice, for it is hard to imagine what they can yet find to masticate.

All these phenomena have successively appeared in the egg we are now watching ; and at this moment you see the crystalline little prisoner, writhing and turning impatiently within its prison, striving to burst forth into liberty.

Now a crack, like a line of light, shoots round one end of the egg, and in an instant the anterior third of the shell is forced off, and the wdieels of the infant Brachion are seen rotating as perfectly as if the little creature had had a year's practice. Away it glides, the very image of its mother, and swims to some distance before it casts anchor, beginning an independent life. At the moment of the escape of the young, the pushed-off lid of the egg resumes its place, and the egg appears nearly whole again, but empty and perfectly transparent, with no evidence of its fracture except a slight interruption of its outline, and a very faint line running around.

This is a female young : the male is totally unlike the female, and is very much smaller. \Ve can always tell whether an egg is going to produce male or female young, by the great difference in its size, the female being more than twice the bulk of the male egg. All of one brood are of the same sex ; we never see Brachionus with male and female eggs at the same time. "What is very strange, is, that the male has no shell, no spines, no mouth, no jaws, no stomach, no intestines ; no ciliary wheels ; its cilia, which are very long and powerful, being arranged in one circle round the whole front. Its movements are exceedingly fleet.

Perhaps you are tired of Brachionus, and are ready to cry out, " Ohe ! jam satis ! " * Well, then, I will turn him off, and show you another elegant little creature, the Whiptail (Mastigocerca carinata). I have here in a bottle some stalks of the Water-Horsetail (Chara vulgaris) which I obtained from a pond a few weeks ago. These I examine in this way. Taking hold of the Chara with a pair of pliers, I pull it partially out of the water, and allowing it to rest on the neck of the bottle, I cut off with a pair of scissors, or with a penknife on my nail, about one-fourth of an inch of the tips of three or four leaves, which adhere together by their wetness. These tips I place in the live-box, with a drop of water, and having separated them with a needle, I put on the cover, and examine them with a triple pocket lens ; holding up the box perpendicularly, not opposite the light, but obliquely, so that the field is dark ; but the light reflected and refracted by the animalcules shows them out beautifully white and distinct, even the minute ones. The forms and some characters of the middling and larger can be quite discerned thus; for example, the slender tail of the one I am now going to show you, I can thus see. The position of any particular individual to be examined being thus marked, it is readily put under the objectglass of the microscope. I have found these leaves very productive of the more stationary animalcules, the Rotifera especially.

It was in this way I this morning found the pretty and * " dear ! quite enough of tli ; s ! " delicate little "Whiptail, which I am going to make the subject of our evening's study. It is inclosed in a glassyshell (lorica) of a long oval form, from which rises on the front half of the back a thin ridge, which in the middle has a height nearly equal to half the diameter of the body, but tapers off at each end. Its base is corrugated with wrinkles. This is not set on symmetrically, but leans over considerably to the right side. Its basal portion is hollow, and is continuous with the general cavity of the shell, for we sometimes see portions of the viscera in its interior.

WHIPTAIL.

The head of the animal is rounded, and divided into several blunt eminences or lobes, which are set with cilia; these rotate constantly, but irregularly and feebly, and do not make manifest wheels, as Brachionus does. A small antenna projects from the back of the head, capable of being erected or inclined. A long brain descends along the base of the ridge, carrying a bright and rather large crimson eye set like a wart on its interior angle.

Instead of the flexible and contractile foot of Brachionus, the Whiptail has a single horny spine of great slenderness, and exceeding in length" the whole body. This spine probably represents not the foot, but one of the toes at the end of the foot. For it is attached to a very short foot, in the midst of two or three bract-like spines, one of which, longer than the rest, and distinctly movable, probably represents the other toe undeveloped. The long spine is set-on by a proper joint, a globose bulb being inserted into a socket, which allows it free motion in all directions except backward. The socket itself is contained in a second joint, the basal part of which is

inserted at some distance within the aperture of the lorica. This articulation is formed by an infolding of the skin, but is permanent in its position.

The most remarkable circumstance connected with this elegant little animal is the unusual form of the dental apparatus, which differs so immensely from that of Brachionus, that we should never recognise it as consisting of the same organs, if we had not numerous intermediate links, which by insensible gradations connect the two remote forms.

The mastax is a somewhat slender sac, much produced in length, and with the component lobes greatly and irregularly developed. The incus has a fulcrum of great length and slenderness, a straight rod with a dilated foot. The rami are small, and pincer-shaped, but with the angles greatly produced. The mallei have long, slender, incurved manubria, and simple unci.

But the remarkable circumstance is the unsymmetrical character of the apparatus. The left side is much more developed than the right. The left angle of the incus descends to a greater distance than the right ; and its extremity is spread out into a surface with several irregular points, to which muscular threads are attached. The ramus also of the same side is larger than its fellow; so with the mallei. The manubrium of the right is comparatively short, very slender, and of uniform thickness; with a long, slender, rod-like uncus, doubly bent in the middle. The left is much longer, irregularly swollen, clubbed at the articulation, and bearing a thick, curved, knotted uncus, which terminates at a point not precisely opposite the tip of its fellow. These circumstances, combined with the unsymmetrical character of the dorsal ridge, of the foot-spine, and of some other organs, render this genus a highly curious one to the naturalist.

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