cells; but in no instance have I seen the former in the gonidial cell, or been able to produce a blue colour in the nucleus of the latter by the application of iodine.

Thus we have followed the contents of the internode of Nitella from the breaking up of the green layer to the development of the gomidia. Let us now direct our attention to the different parts of the gonidial cell analytically, more however with the object of adding to rather than recapitulating what has already been stated respecting it."

We have seen that the mucus-investment, which appears to be derived from the mucus-layer, gives the cell the power, not only of limited polymorphism, but also of locomotion; in addition to this also, the cell possesses for some time the power of projecting thread-like filaments of extreme tenuity from its surface that adhere to neighbouring objects, and thus form a point d'appui towards which the cell can then move itself. Subse quently, however, these processes, apparently following the same law of development as the cell, become stiff, and then stand out like short, straight hairs, more or less thinly scattered over its circumference, and resembling a parasitic growth,which some might consider them, as they do not appear on all the cells, but my impression is that they are what I have stated. I have also seen, now and then, a small gonidial cell in which the hardening process appeared not to be about to take place, but, from the rhizopodous prolongations of a part of its periphery, and its containing nothing besides the gonidial substance, presenting rather the appearance of a polymorphic spore about to germinate than to pass into a fixed cell. Occasionally the gonidial cell, after it has become stiff and transparent, presents itself under a lenticular form; at others, as if a notch had been cut in it, and sometimes with a plane surface, &c., but all these irregularities appear to be caused by objects against which the cell rests while passing from its flexible into its hardened cellulose state. Iodine alone does not appear to impart any colour to the gonidial cell. Immediately within the transparent globular cell is a layer of brown matter, which, as before shown, is composed of the green disks in which the chlorophyll has thus become changed in colour. This layer is also globular, and encloses the circular disk alone or with its vesicle. It often presents a botryoidal surface, which appears to be occasioned by the presence of the gonidia inside or in the midst of its substance; when the gonidia have been developed, this as well as its granular contents disappear, leaving a homogeneous, brown substance, which shrinks up into a more or less defined nucleus of a much darker colour. The brown matter is deepened in colour by the addition of iodine, and extracted by that of alcohol. In the small gonidial

cells there appears to be no brown matter, but from the red granules, which are the equivalents of the green disks in the fanshaped group of cells forming part of the capsule of the globule, being attached singly or in groups to their periphery, it may reasonably be inferred that this is the position of the so-called brown matter in them.

After a certain time, the gonidial substance with its bright refractive granules makes its appearance in different parts of the brown matter, as if it were rising out of it, and then to one side in a distinct mass which acquires a mulberry-form and separates into gonidia; or the gonidia may be fully developed inside or in the midst of the brown matter before they make their appearance. The gonidial substance has already been described, as well as the bright refractive globules, which do not alter in colour by contact with iodine. Making its appearance then in this way, it is not extraordinary that the gonidia, in addition to their own peculiar blue-coloured mucus, which colour, as before stated, appears to depend on its granular contents, should, for the most part, also contain more or less of the refractive globules, and occasionally a fragment of the brown matter, which is the

case.

I have already described the commonest form of gonidium, but there is still another about twice the size, viz. 2150th of an inch in diameter, which although not so frequent, is nevertheless sufficiently so to show, that there are two sizes more common than the rest; for we shall presently see, that the gonidial substance may occasionally come out as a whole, or in gonidia of all sizes below its original bulk. This large gonidium generally presents itself under a circular or globular form, with single cilium, but it is sometimes seen ovate or spindle-shaped like the smaller one. It must be obvious to all, that a polymorphic cell, such as the gonidium is, can have no constant figure while in a state of activity; hence at one time it may be of one shape, and at another of another; but when under polymorphism and the cilium has disappeared, a group of gonidia will evince a strong tendency to assume the same kind of figure generally, whatever that may be. Thus, just after they become stationary, the form of Actinophrys Sol seems to prevail; then the digitated form for progression; then the diffluent form, which appears to be produced by the more internal protoplasm bursting through that which is becoming hardened on the surface; and lastly, the tardy, rhizopodous form which I have mentioned; but I will not vouch for this sequence, and only instance it for example.

I have already alluded to the variety in size of the gonidia, but this is an exception to the general rule, for the smallest gonidial cell, in which only one gonidium is developed, yields a

gonidium equal in size to the one first mentioned. It may however yield a smaller one, and occasionally, in the same mulberry-group, may be seen gonidia of different sizes; again, sometimes a whole group is composed of the same-sized gonidia, which are not more than half the size of the common form, that is 1-8600th of an inch in diameter; while occasionally a large mass is seen creeping about which seems equal in size to the whole of the gonidial substance of a large gonidial cell. Sometimes a compound mass of gonidia, composed of three or more which appear to have flowed into each other, may be seen, with their cilia projecting from different parts of the circumference.

I have already alluded also to the variable contents of the gonidia. In addition to the dull, bluish-green mucus, they also frequently contain more or less of the bright refractive globules, which, when the latter are beneath or in the midst of the mucus, may be mistaken for the transparent vesicles which I shall presently mention.

The gonidium may also contain more or less of the brown matter, and occasionally, when it is unusually large and of a Florence-flask shape, with the vesicle in front and a fragment of brown matter of a bright colour present, it is hardly distinguishable from Astasia.

Lastly, we come to the vesicles which are seen in the gonidium. While the gonidium retains its cilium and swimming motion, the vesicle is for the most part single, and though changeable in position with the movements of the cell-wall of the gonidium, does not appear to be endowed with contractility per se; but when it loses its cilium and sinks down to the reptant, polymorphic state, the vesicle becomes distinctly contractile, and the gonidium is then hardly distinguishable from the young Amaba or sponge-cell. Frequently in this state also it presents one or more hyaline vesicles which are not contractile, and only change their position with those parts of the gonidium to which they may be attached.

We now come to the nucleus of the gonidial cell, and of this I can state little more than has already been given. It is evident, that although the larger ones contain a nucleus, the smaller ones do not, unless the irregular body fixed to their periphery is to be considered its equivalent. I have mentioned that the nucleus of the large cells appears to be the circular disk of the mucus-layer, and that the latter is sometimes with and sometimes without its vesicle; also that frequently, under an arrest of development, it is surrounded by a crenulated membrane. The fine granules of which the central part is composed, appear also on these occasions to have become larger and more evident, and in one instance they were replaced by three or four large glo

bules of a faint yellow colour, as if they had run together. In the larger gonidial cells, where a set of healthy gonidia of normal size have been developed, the nucleus shrinks up with the effete brown matter into a common, homogeneous-looking mass, from which it is then undistinguishable.

General Observations.

Having now described the gonidial cell synthetically and analytically, let us for a few moments direct our attention to the offices of the several elements of which it is composed.

The gonidial cell, originally a portion of the mucus-layer endowed with the power of motion, at first appears to gather up a number of the green disks and wrap them round the nucleus; after which it becomes separated from the contents which it has thus enclosed, and passes into a firm, transparent membrane of a globular form, which serves to isolate and protect the materials from which the gonidia are to be developed. Lastly, it frequently assumes a conical form, which bursts at the apex and then gives exit to its gonidia. Whether the bursting is an act of its own, or induced by the distension of the mucus before mentioned, which becomes developed in it immediately after the evolution of the gonidia, and subsequently throughout the internode, I have not been able to determine; but the mucus in question is frequently seen protruding from the ruptured parts of the cell in an organized, transparent, fungoid mass, or in a branched form, as if it had caused the rupture.

This mucus appears to me worthy of notice, from its great resemblance, under the organized forms mentioned, to the gonidial substance. When within the gonidial cells and in the internode, it swarms with vibrios; but when liberated, the vibrios, after moving about for some time in the water, settle down into a form like Bacterium termo. When in the massive or branched form mentioned, bright, refractive, blue-green granules are scattered through it, and there appears to be an abortive attempt at a cellular division of the mass generally. Can this be the remnants of germinating matter which are left about the gonidial cells and the internode?

The power of the green disks, as well as the irregular bodies of the mucus-layer, to produce gonidia, is incontestable, for we have seen gonidia developed in cells where nothing else but the green disk or the irregular body was present.

What is the office then of the circular disk?

This I can only suggest from inference. It is perfectly evident that there are corpuscles in the nucule besides the starchglobules, which corpuscles resist the blue colouring action of

iodine, and it seems equally so, that there are only these two kinds of bodies in the nucule; again, these corpuscles very closely resemble in colour, and in not becoming blue by contact with iodine, the irregular bodies contained in the mucus-layer of the internode, while they bear in other respects also a strong analogy to them. Lastly, we now know, that a gonidial cell having one of these irregular bodies for its nucleus or peripheral appendage can develope a gonidium. Thus then, if the irregular bodies and the corpuscles be identical, we have the germs of gonidial substance and starch-globules as the contents of the mucule, the latter being designed for the nourishment of the former. May not the circular disk contain nutriment for the gonidia ?-while the irregular bodies would seem to be identical with the green disks, and are indeed, in many instances, almost undistin guishable from them, even when both are present among the contents of the evacuated internode.

Thus we see a great resemblance between the formation of the gonidia and the germinating of the nucule, and in the formation of both with that of the "resting spore" of Algæ generally.

As yet, I have never seen a new plant developed from the gonidium of Nitella, nor have I ever been able to identify their germination with that of germinating cells, which I have frequently seen on the surface of an internode containing the gonidia; neither did Pringsheim see those germinate which came from Spirogyra, in which he has carefully described the same kind of gonidial development as that which takes place in Nitella*. But Braun, who has followed the development of gonidia in Hydrodictyon †, states, that the larger gonidia (for there are two distinct sets, which he calls macrogonidia and microgonidia) germinate, that is, form the young water-net, while the smaller ones never do this, but unite into groups, forming a homogeneous green mass, which becomes covered with a distinct cell-membrane. This very much resembles the fungoid growth at the ruptures of and about the internode which follows the disappearance of the gonidia of Nitella, and which I have suggested might be the last efforts to form and to increase of the remnants of gonidial substance left in the gonidial cell and about the internode. Be this as it may, the dividing up of a body formed after the manner of a resting spore into smaller ones, resembling gonidia, which afterwards germinate, is the

* "On the Germination of Resting Spores and one form of Moving Spores in Spirogyra." Ann. and Mag. of Nat. Hist. vol. xi. p. 210, 1853. t Pub. of Ray Society, Botan. and Phys. Mem., Phænom. of Rejuvenescence in Nature. Transl, by Henfrey, p. 261.