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to account for reversion by bud variation, there yet remain that larger class of bud variations wherein there is no suspicion of reversion.
This latter category, so far as we see, can only be explained by Mr. Darwin's assertion that, in “ cases in which the organisation has been modified by changed conditions, the increased use or disuse of parts or any other cause, the gemmules cast off from the modified units of the body will be themselves modified, and, when sufficiently multiplied, will be developed into new and changed structures."
But before we can, with propriety, avail ourselves of this latter explanation, we have to be satisfied that a change of conditions has really been in operation. And this is too often beyond our ken. The majority of bud variations not distinctly referable to reversion, appear suddenly, without any obvious change of external condition, we know not why or wherefore. Suppose we admit, on the ground of intrinsic probability, the operation of changed conditions, even though we may have no direct evidence on the point, we have yet to explain how and why one particular shoot on one particular part of a plant should be acted on in this way, when there is no appreciable reason why it should be influenced more than the rest.
There is still another way of explaining the phenomena on
the number, arrangement, or position of the gemmules; and this supposition, though plausible, is yet based on a number of mere assumptions, and, moreover, it leaves the cause of the altered condition of the gemmules entirely unexplained.
To sum up, then, we may say that there is no absolute difference between bud variation and seed variation. The changes manifest themselves in the same manner and in the same organs in the case of buds or seedlings respectively. The conditions, so far as we know, that produce variation in the one are the same that are effectual in the other. Lastly, apart from the different mode of origin, there is no essential difference between a bud formed as the result of fertilisation, i.e., an embryo, and one formed without the direct agency of the two sexes, i.e., a bud.
AN ACCOUNT OF A GANOID FISH FROM
BY DR. ALBERT GÜNTHER, F.R.S.
The genus Ceratodus has been established by Professor Agassiz for teeth which are found in strata of Jurassic and Triassic formations in various parts of Europe and India. These teeth (fig. 3), of which there is a great variety with regard to general shape and size, * are much longer than broad-sometimes 2 in. longdepressed, with a flat or slightly undulated, always punctuated crown, with one margin convex, and with from three to seven prongs projecting on the opposite margin. They have always been found isolated, sometimes with a portion of a bony base attached to them. Yet Professor Agassiz pointed out, from their shape, that there must have been only two of them in the upper jaw and the same number in the lower, that the convex margin was directed inwards, and the prongs outwards. No other part of the fish to which they belong has hitherto been found associated with them; but Agassiz considered it to have been a cartilaginous fish, or more especially a shark-a view not so very far from the truth, as we shall see hereafter.
The discovery of a Ceratodont fish in the recent fauna is due to the Hon. William Forster and Mr. Gerrard Krefft, the Curator of the Australian Museum at Sydney. Years ago the former of these gentlemen had informed Mr. Krefft that there existed in the fresh waters of Queensland a large fish with cartilaginous backbone, but he was thought to be mistaken
• Mr. Higgins possesses the largest, and probably most unique, collection of Ceratodont teeth from one locality-viz. from Aust-passage near Bristol. Among some 300 specimens there are scarcely two which are sufficiently alike to be assigned to the same individual.
VOL. XI.—NO. XLIV.
until he succeeded in obtaining for Mr. Krefft a specimen which, although in an imperfect state of preservation, removed all doubts on the matter, and enabled Mr. Krefft to communicate this remarkable discovery to the Zoological Society of London (April 28, 1870). He says : “ The discovery of a species of Lepidosiren in Australia will, no doubt, take the scientific world by surprise—the more so as this newly-found amphibian has a dentition different from that of Lepidosiren, and closely resembling the teeth of certain fossil sharks described by Agassiz under the generic term of Ceratodus. On this ground, and being convinced that the various species of animals classed under the name of Ceratodus were not sharks, but amphibians, I shall adopt Professor Agassiz's name, and describe the Australian amphibian, in honour of its discoverer, as Ceratodus forsteri.”
As soon as Mr. Krefft had recognised the importance of this discovery, the Trustees of the Australian Museum took steps to secure well-preserved examples. They sent a collector into the district where the animal was known to occur; and, with their usual liberality, they despatched to the British Museum for examination the first specimens they could spare, by which I was enabled to work out the details of its structure. Some attempts subsequently made to obtain other examples appear to have been unsuccessful, as the fish is locally distributed, and easy of capture at a certain season or at a certain state of the water only.
The specimens hitherto obtained have come from the Burnett, Dawson, and Mary Rivers, some from the fresh water of the upper parts, others from the lower brackish portions. The fish is said to attain to a “ weight of twenty pounds," and again to a “ length of six feet," the largest example sent to the British Museum being about three and a half feet long. Locally the settlers call it “Flat-head," “ Burnett-," or “ Dawson-Salmon," and the aborigines “Barramunda," a name which they appear to apply also to another similar fish, the Osteoglossum leichardti. I found the intestinal tract crammed full of more or less masticated leaves of various plants (Myrtacea and Graminec ; they had lost the green colour entirely, being of a uniformly deep black, as if they had lain in water for some time, and were eaten when in a decomposing condition. The quantity of these vegetables is enormous, and there is no doubt that they constitute the principal food of the fish. Shells, fragments of which have been found in the stomach, may have been swallowed accidentally; however, it has been stated repeatedly that the fish can be caught with a hook baited with a worm. The flesh is salmon-coloured, and much esteemed as food.
The Barramunda (we will use this probably oldest name) is said to be in the habit of going on land, or at least on mudflats; and this assertion appears to be borne out by the fact that it is provided with a lung. On the other hand, we must recollect that a similar belief has been entertained with regard to Lepidosiren, of which now numerous examples have been kept in captivity, but none have shown a tendency to leave the water. I think it much more probable that the Barramunda rises now and then to the surface of the water in order to fill its lung with air, and then descends again until the air is so much deoxygenised as to render a renewal of it necessary. It is also said to make a grunting noise, which may be heard at night for some distance. This noise is probably produced by the passage of the air through the esophagus when it is expelled for the purpose of renewal.* As the Barramunda has perfectly developed gills, besides the lung, we can hardly doubt that, when it is in water of normal composition and sufficiently pure to yield the necessary supply of oxygen, these organs are sufficient for the purpose of breathing, and that the respiratory function rests with them alone. But when the fish is compelled to sojourn in thick, muddy water charged with gases which are the product of decomposing organic matter (and this must be the case very frequently during the droughts which annually exhaust the creeks of tropical Australia), it commences to breathe air with its lung in the way indicated above. If the medium in which it happens to be is perfectly unfit for breathing, the gills cease to have any function; if only in a less degree, the gills may still continue to assist in respiration. The Barramunda, in fact, can breathe by either gills or lungs alone, or by both simultaneously. It is not probable that it lives freely out of the water, its limbs being much too flexible for supporting the heavy and unwieldy body, and too feeble generally to be of much use in locomotion on land. However, it is quite possible that it is occasionally compelled to leave the water, although I do not believe that it can exist without it in a lively condition for any length of time.
Of its propagation or development we know nothing except that it deposits a great number of eggs of the size of those of a newt, and enveloped in a gelatinous case. We may infer that the young are provided with external gills, as in the African Lepidosiren and Polypterus.
Before I proceed to the description of the Barramunda, it
* Gurnards (Trigla) and Bull-heads (Cottus) are well known to produce a similar noise when drawn out of the water, by the air rushing from the air-bladder through the oesophagus
will not be out of place to refer here to a remarkable fact in geographical distribution which I have omitted in my previous communications on Ceratodus. The division of fresh-water fishes offers not a few instances in which two or more natural families, much differing in their structural characters, have exactly the same geographical distribution. We shall see subsequently that Ceratodus, Protopterus, and Lepidusiren, are members of the same natural Ganoid family (Sirenido). Now this family coincides in respect of its geographical range with a Teleosteous family which I have called Osteoglossidae, and which comprises the genera Osteoglossum, Arapaima, and Heterotis, as will be seen from the following table :
Thus it is only in the East Indian archipelago that we have not yet found the Ganoid representative of the Teleosteous Osteoglossum formosum. That it will be found there I have no doubt. 0. formosum has hithertu been obtained in Sumatra, Banka, and Borneo ; and of the inland fishes of the latter island scarcely anything is known at present.
The body of the Barramunda (fig. 1) is eel-shaped, but considerably shorter and thicker than a common eel, and covered with very large scales. The head is nearly entirely naked, covered with a porous skin, flattened and broad, the eye lateral and small, the mouth in front of the broad snout comparatively narrow, and provided with thick and soft lips. The gill openings are a narrow slit on each side of the head, immediately in front of the fore.paddle. There are no external nostrils. The foremost portion of the trunk is depressed like the head, but it soon passes into the compressed remaining portion, the boundary between trunk and tail being externally indicated by the vent only, which is situated between the hindpaddles. The tail varies in length; it is sometimes shortened, aud it appears that mutilations of this part, particularly when