« ElőzőTovább »
small and weak, and not provided with a web; the claws are strong, and well adapted for digging, but not equal to those of the hind feet. The hind feet and legs are enormously strong, the fingers united by a strong broad web, the claws excessively developed, and each in the form of a strong gouge. The combination of machinery in the fore and hind legs and feet thus corresponds with what we know of the habits of the animal so far as that can be observed; and the structure of that portion whose working is difficult to be observed in action, or has not been noticed sufficiently, shows what its real working is. Those who have observed the animal in its native haunts, tell us that it uses the fore paws for carrying the mud and stones used in its constructions, and that it carries this stuff between them and its breast, which quite corresponds with their attitude in my dead specimen. It no doubt uses the fore paws for other purposes, as digging, swimming, and walking (for nature seldom or never creates an organ merely to fulfil one purpose). As clearly, the hind paws are much used in digging, but most in swimming ;-the powerful hind leg, enormous web foot, and strong claws, would prove this although no one had ever seen the animal using them. Combine these different actions of the fore and hind feet together and see what would be the result. Suppose the animal swimming across its pond or river with a burden of heavy materials clasped to its breast by its fore paws, and powerfully propelled by its hind legs, and that it had no tail or only a common tail—what must inevitably be the consequence? The hind feet would propel the animal rapidly enough—no doubt about that_but where to ?—why, to the bottom, for, being overloaded in front, it would be top heavy, and its head becoming directed obliquely downwards the more violent the exertions of the hind feet, the sooner it would reach the bottom, and the deeper its head would be buried in the mud. That this is the necessary and inevitable consequence of the want of the action of the fore paws, will be evident to every one if they will merely fancy what would be the result of their trying to swim with their arms folded; of course, if there is not only the inaction or abeyance of the fore arms to be conquered, but also the weight of a load of mud or stones to be counteracted, a counterpoising lever of more than ordinary power will be ne
cessary, and this is supplied by the broad flat horizontal tail, which is constructed on the best principles for attaining such an object. Were it different or differently placed, the end would not be answered; suppose it vertical like a fish's tail, it would
counterpoise. It must be powerful, and it must be horizontal, so as to press broadly downwards, and as the purpose here is to increase resistance and friction, and not to diminish it, it is denuded of hair, or nearly so, and covered with polygonal scales. A few scattered hairs occur, interspersed between them, but these are not abraded as they would have been had the tail been used as a trowel. That this is the interpretation of the structure and purpose of the tail is I think self-evident from its fitness. The habit of flapping the tail on the ground before plunging into the water is probably only the mechanical repetition of the action with which it habitually starts into motion, and which in the water is essential to its progress.
The teeth of the beaver are often quoted as good examples of the mode in which rodent teeth grow from the pulp at their base, with a hard enamel-like steel on the outer edge, and softer material on the inner side, and thus have their sharpness and chisel-like form always kept up by the very thing which at first sight would seem to be likely to make them blunt-viz., their constant use. The incisor teeth in the fætus are conical, thus showing that the chisel form in the adult is the result of abrasion. The specimens sent me are from the neighbourhood of Moose Factory.
I have adopted the specific name Americanus given to this species by the Russian naturalist Brandt, who has separated the American animal from the European and Asiatic (the true Castor fiber) on osteological grounds, chiefly drawn from the skull. For the reason alluded to above (want of specimens for comparison), I can give no opinion as to the propriety of this separation.
Mus leucopus, Rafin.-In his description of this species, Sir John Richardson says,—" The tail is thickly clothed with short hairs, lying pretty smoothly, no scales whatever being
visible.” In my specimen it is not thickly clothed with hairs ; it is rather sparingly clothed with hairs, and the scales are very apparent under them. He also says that “its” (the tail's) “upper surface is of a hair-brown colour, considerably darker than any other part of the animal, and contrasts strongly with the inferior surface, which is white.” The upper surface of the tail in my individual is not nearly so dark as the back of the body; still, however, as it agrees in all other respects with Mus leucopus, I have no doubt that it is that species, and that these differences are only accidental variations in my specimen.
SHREW-MOLE ? (Scalops Canadensis, Cuv.)—I have had no opportunity of comparing this animal with any named specimens, and my determination is made entirely from the description in Sir J. Richardson's “ Fauna Bor. Amer.” My specimen agrees, for the most part, with the description in that work ; but there are one or two points on which I am not quite satisfied. In particular, the whole of the fore foot is said to have a close resemblance to that of the common mole. Now, although this has a general resemblance, it cannot be said to bear a close resemblance. It wants the sabre-shaped bone of the mole, and the nails are greatly smaller. The description of the nails of the shrew-mole is, that they are large, white, and have a semi-lanceolate form, with narrow, but rather obtuse points. These in my specimen can scarcely (according to my ideas) be said to be large ; but large is a word of very doubtful interpretation ; what is large to one person may be very small to another; so that, on this item, I must mark my species with a query.
There is one point in the history of the shrew-mole which I should like to see either confirmed or expunged from our books—yiz., that although a burrowing animal, it has the singular habit of coming daily to the surface exactly at noon.
Sorex parvus, Say. This shrew may be readily distinguished from other American shrews by its tail being rounded instead of being more or less angular. One might be disposed to think that this is a character of little value, depending merely on the greater or less plumpness of the individual; but
it does not appear to be so, and other characters concur with this to establish the species.
This one is certainly not well named ; as, though un. doubtedly a small animal, it is the largest of the North American species.
Sorex Forsteri, Rich.—The tail in this species is quadrangular. It is the smallest quadruped known to the Indians ; and I cannot call to mind any quadruped with which I am acquainted, from any quarter of the world, which is smaller.
Among the specimens which have been sent me is one which differs slightly from the description of S. Forsteri. .Its colour is wholly mouse-dun, whereas that of Forsteri is wholly clove-brown on the back. The specimen is in spirits, however; and the clove-brown being, from what we see in other specimens, a tinge of that colour in certain lights, it is probable that the darker colour is merely owing to the medium in which it has been sent; at all events, that the specimen is at most only a variety.
AMERICAN OTTER (Lutra Canadensis).--I have received a specimen from the York Factory district, in the shape of a medicine-bag, which is a favourite use of it with the natives.
II. On New Protozoa.-(1.) Lagotia producta. (2.) Zooteire areligata.
castaneus. By T. STRETHILL Wright, M.D.
Description of Plate II.
2. Single specimen of do.
ternal and external fleshy coats.
pendage. 9. Summit of “mop”-a, external, and b, internal coat.
10. Summit of Gregarina-like appendage. 11. Salpistos Mülleri, -a, gelatinous lorica.
1. Lagotia producta. (Figs. 1-6.) At our meeting of the 22d April 1857, I described Lagotiu
viridis, which I had discovered some time before, together with two other species, Lagotia hyalina and atro-purpurea. The present species, Lagotia producta, was found in great profusion in the tanks of Miss Gloag of Queensferry, in August last, and resembles Lagotia viridis in its general characters. It has the same long green body, surmounted by a horse-shoeshaped or two-pronged rotatory organ, each prong formed of a membrane folded together, like the ear of a hare, and edged by a muscular band fringed with vibratile cilia. It inhabits also a similar flask-shaped cell, with bent neck and trumpetshaped mouth. But the body of Lagotia producta is greatly prolonged in comparison with that of Lagotia viridis ; the colour nearly black, and the gullet a wide sac, and not a spiral canal. In the present species, the neck of the cell has become a long wide tube, greatly disproportionate to the flaskshaped part from which it projects; the whole bearing some resemblance to a long jack-boot. A careful examination of the anatomy of the cell reveals a structure of singular interest and beauty. It consists of three elements—(1.) a horny or chitinous case, lined with (2.) a layer of dark green sarcode, and covered with (3.) a thin layer of colourless sarcode ; so that the cell is not a mere extraneous house in which the animal lives, but is a quasi-bony framework, buried in an extension of the living flesh of the animal, and growing with its growth. And this, I believe, holds good with regard to the tubes of other genera of Vorticellina. It is especially to be seen in Vagincola valvata, a species which I have described to the Society, and in which the layer of sarcode lining the tube serves to support and partly to form a valve, which rises and falls with the movements of the animal within.
The chitinous case of L. producta, or that part of it corresponding to the body of the flask, resembles that of Lagotia viridis ; but the neck or tube is composed of a spirally-wound ribbon of chitine, the upper edge of each spiral slightly overlapping the lower edge of the spiral arising above and within it, and being slightly everted. The edges have no chitinous connection with each other, but are retained in their places by their fleshy coverings. One might suppose that the tube was formed and gradually increased in length by a continual