its peduncle, leaving a small hole through which the seeds are expelled with such violence as sometimes to be shot off to a distance of fifteen feet, the fruit at the same time undergoing a marked diminution in size. Mr. Yule found that, in most cases, the breech of the fruit, or the end farthest from the peduncle, was positive to the centre-so that the direction of the current is precisely opposite to that of a muscle -and that a very considerable negative variation took place at the moment of dehiscence.

The Foraminifera-those favoured organisms which, next to Diatoms and Podura scales, have always been among the most cherished objects of worship with the believing microscopist-have had a zoological history almost as chequered as that of the sponges and zoophytes. From having been looked upon by Ehrenberg and D'Orbigny as minute cephalopods, they have come to take the lowest room in the animal series, as Protozoa of the simplest type. So simple indeed is their structure that Haeckel denies them altogether a place among animals, and relegates them to his no-man's-land, the Regnum Protisticum.

But, notwithstanding the extreme simplicity of their structure, and the fact that it has been investigated by such men as Max Schultze in Germany, and Carpenter, W. K. Parker, and Rupert Jones in England, certain important points in their morphology have been overlooked, and their true place in the scale of being has consequently been mistaken. It has, in fact, been hitherto considered that these fabricators of the exquisite shells, by which alone the group is usually known, have not attained to the complexity of a simple cell, but consist of a mere lump of protoplasm devoid of even a nucleus, and hence simpler, in a morphological sense, than an amoeba or a colourless blood-corpuscle. But, by the judicious use of reagents, especially of chromic acid and carmine, two German observers, Franz Eilhard Schulze and Hertwig, have, independently, discovered in many forms undoubted nuclei, and have thereby raised the Foraminifera from the group of Monera, or animals wholly devoid of an internal structure ascertainable even by the highest power of the microscope, to that of Endoplastica, or creatures in which the first indication of visible structure, the nucleus, has appeared. In other words, a single Foraminifer is not a cytode, but a cell. This, however, is not all. In some species several nuclei were found; sometimes each of the constricted masses into which the animals are divided, and which correspond with the chambers of the shell, was found to have its own

8

Quarterly Journal of Microscopical Science, January 1877. Schulze's original paper is in the Archiv für mikr. Anat., Bd. xiii.; Hertwig's in the Jenaische Zeitschrift, Bd. x.

nucleus; sometimes, on the other hand, there were two or three nuclei to a chamber. Now it is a well-ascertained fact that the first step in the division of an egg-cell, and therefore in the formation of one of the many-celled higher animals, is the division of the nucleus into two distinct parts, this being followed by the division of the protoplasm into two masses, one corresponding to each nucleus. So that it appears as if the Foraminifera were not only not cytodes, but were even on the very point of becoming multicellular, having taken the first step in the formation of a tissue out of a cell.

Mr. Romanes has recently communicated to the Linnæan Society a further series of his researches on the nervous system of jelly-fish ; his former work has thrown a flood of light on the first beginnings in the animal kingdom, and consequently on the probable phylogenetic origin of the nervous system, and his new results are if possible more remarkable than former ones. In a new species of Medusa, which, in allusion to its habits, he has called Tiaropsis indicans, Mr. Romanes has found that, when any point of the edge of the bell is touched, the manubrium, or long tubular stomach which hangs down from the apex of the bell like a clapper, and bears the mouth at its opposite extremity, moves over to the point touched, and does this with absolute and unvarying certainty, never missing the point to which the stimulus was applied. When a horizontal cut is made in the bell of this Medusa, and the margin of the bell irritated below the point of section, a very curious result follows; the manubrium moves from side to side in an indeterminate way, evidently not knowing where to feel for the irritating body. The reason of this is, that the impulse, being prevented by the cut from travelling directly upwards to the manubrium, is diffused over the surface of the bell, and so reaches the manubrium from many points instead of a single one. This shows conclusively, what the most careful histological investigation fully bears out, that, in the bell of the Medusa, there are as yet no tracks of tissue definitely marked out as nerves, but only certain more or less well-defined lines along which a nervous impulse travels more easily than by any other road, but from which an impediment makes it deviate into other channels.

Another species of Medusa (Tiaropsis polydiademata) was found to be perfectly sensible to luminous impressions. When suddenly exposed to light it underwent a long-sustained spasm of the same nature as was produced by any other form of stimulation. When the margin of the bell, in which nerve-cells are now known to exist, was cut off, the remainder of the animal was perfectly insensible to light, while the excised margin reacted as vigorously as ever. Moreover, Mr. Romanes found that a flash of light must be of at least one second's duration to produce an effect, and that the Medusa, like our

selves, was only affected by rays from the luminous portion of the spectrum; ultra-red and ultra-violet rays were wholly without effect upon it.

9

A curious and interesting set of observations has lately been recorded by Surgeon-Major Day on certain Indian fishes which are truly amphibious-that is to say, possess the means of breathing air direct, and not only air dissolved in water. Every one knows more or less about the climbing perch' (Anabas), which is able to sustain life for a considerable time out of water, and even to traverse considerable tracts of country in search of its native element during the dry season; but the degree of amphibiousness of this and other fish has never been properly appreciated. Mr. Day placed an ordinary carp and an Ophiocephalus, one of the most remarkable of the amphibious fish, in a glass globe together, fixing a net some two inches below the surface of the water, so that the fish were prevented from rising. Under these circumstances the carp swam about as usual for any length of time, but the Ophiocephalus made the most vigorous and frantic efforts to reach the surface, and, if not released, died of asphyxia in from twenty minutes to two hours. Another trial was made by tying a bandage round the head of the same two fish in such a way as to prevent all egress of water by the gill-slits; this time the carp it was that died,' the Ophiocephalus showed no signs of discomfort.

These amphibious fish owe their air-breathing power to a pair of large cavities, one on each side of the throat, above the gills; the cavities open into the mouth, and their walls are supplied with impure blood from the arteries immediately connected with the heart; which impure blood, exchanging its waste products for oxygen in the respiratory sac, is taken to the aorta in a purified condition. The sacs, consequently, are, as far as the work they do is concerned, lungs; but in a morphological sense they are not lungs at all, for, in the first place, the purified blood from a lung is always returned directly to the heart, and, in the second place, the study of comparative anatomy clearly shows that the lungs of the higher animals are represented by the swim-bladder of ordinary fish. Two fish, in fact, the mud-fish (Lepidosiren) of Africa and South America, and the Ceratodus of Australia, have an air-bladder, the blood from which is returned in a purified condition to the heart, and which is therefore, morphologically as well as physiologically, a lung.

A sort of hint as to the way in which the specialisation of the airbladder into a lung may have taken place is furnished by an experiment mentioned by Armand Moreau in his elaborate paper on the

In a paper read before the Linnean Society on January 18.

functions of the air-bladder.10 He took a number of perch from the same river, killed some of them at once, and put the rest into a vessel, the water in which was not changed; in the former he found by analysis that the air of the swim-bladder contained 19 to 25 per cent. of oxygen. The fish placed in a small quantity of stagnant water died in less than twenty-four hours, and, in them, the swim-bladder was found to contain 95 per cent. of nitrogen and 5 per cent. of carbonic acid, all its oxygen having been used up for breathing purposes as that in the water became exhausted.

Thus the curious result is arrived at, that Nature has, so to say, tried two distinct plans for converting fishes into air-breathers. The most successful way has been to appropriate the swim-bladder for the purpose of a respiratory organ. We say most successful, because it is by the gradual modification of the swim-bladder that the perfect lungs of the bird and mammal have been produced. But another plan has also been tried; the swim-bladder being left in its usual condition, as in the Ophiocephalus, special offshoots of the throat have been made to perform precisely the same function as the lung of Lepidosiren or Ceratodus. And it is curious to observe to what a marvellous state of perfection this comparatively unsuccessful air-breathing organ has attained, and how, contemporaneously with its perfection, the gills have lost their virtue; for an Anabas or an Ophiocephalus will not only live for days out of the water in half-dry mud flats, but the latter fish, as we have seen, cannot exist for more than an hour or two without a direct supply of air, and Anabas, according to Dr. Dobson, is drowned as easily as a dog.

The stages by which double-breathers may have been converted into true air-breathers by the gradual loss of the gills are exhibited by the life-history of the Mexican gilled salamander or axolotl.

The curious occasional metamorphosis undergone by this animal has been known since 1867, when Duméril communicated to the French Academy the extraordinary fact that, out of the many hundred axolotls in the Jardin des Plantes, thirty had lost their gills, forsaken the water for the land, and assumed the form of what had hitherto been considered the distinct genus Amblystoma, this Amblystoma being a true land salamander, breathing air only by lungs. This announcement naturally created great interest, not because a water-breathing salamander had changed into an air-breather, for this process may be seen any spring in the case of the common newt, but because the gilled larval form was capable of reproduction, and had therefore naturally been considered as an adult.

No cause whatever could be assigned for this sudden assumption of a higher mode of life, for the metamorphosed axolotls had been

1o Annales des Sciences naturelles, ‘Zoologie,' tome iv. 1876.

:

exposed to precisely the same conditions as their unconverted fellows. Duméril tried the experiment of cutting off the gills of an ordinary axolotl to see if this would have the effect of inducing the desired change, but the animal only produced a new set of gill-tufts, and stuck pertinaciously to its old habits.

Lately, however, the attempt has been made again by a German lady, Fräulein Marie von Chauvin," who has overcome all difficulties, and triumphantly evolved Amblystoma out of more than one axolotl. This she accomplished, not by any such violent measures as excision of the gills, but by gradually accustoming the animal to life on land, and by paying the greatest attention, throughout the whole process, to its health and diet.

Five strong and hearty animals were selected for the experiment, and were, at first, not quite covered with water. As they did not thrive under these circumstances, the supply of water was increased, and, after their usual health was restored, they were kept in shallow water during the day and in deep water at night. They now throve perfectly well, but not only showed no disposition to metamorphosis, but actually retrogressed in development. They were therefore put on land as they were, gills and all, but the change seemed to have anything but a favourable effect on them; they lost all appetite; and free cutaneous respiration, so essential to the well-being of an amphibian, was hindered by particles of earth and moss sticking to their slimy skins. A tepid bath twice a day remedied this last difficulty, but then the skin dried so rapidly that the process of casting it was hindered, and eventually they were kept moist with wet moss after their bath. The feeding difficulty Fraulein von Chauvin overcame in a most ingenious way, by thrusting an earth-worm, head first, into the axolotl's mouth, and then pinching the worm's tail until it wriggled so far down that the axolotl was compelled to finish the process. But, even with this assistance, some of the animals proved so refractory as actually to reject the half-swallowed worm, having evidently made up their minds to die rather than submit and improve. Three, out of the five specimens chosen, carried this propensity to fasting to such an extent that the natural result followedthey died after having lived about fifty days on land. At the time of their death, however, the gill-tufts, the tail-fin, and other larval characteristics were already much reduced.

The two remaining specimens were more satisfactory, and showed a marked decrease in the size of the gill-tufts and tail-fin after they had lived a few days on land; before long the atrophy of the gills had gone on to such an extent that the axolotl, when placed in water, displayed his plumes as before, but seemed unable to breathe by their

"Zeitschrift für wissenschaftliche Zoologie, Bd, xxvii. 1876.