there are some eye-bearing monades" in diameter. Thus the traces of a nervous system descend to the monades.

I have extended farther my first endeavour to class the Infusoria according to their internal organization. The digestive system furnishes, in each of the two classes, only four differences. The Polygastrica fall under the Anentera, those without intes tine; the Cyclocæla, those with a circular intestine; Orthocæla, those with a straight intestine; and Campylocæla, those with a curved intestine. The Rotatoria fall under the Trachelogastrica, long-throated without stomach; Cælogastrica, long intestine without a stomach, and with a short throat; Gasterodela, those with a stomach; Trachelocystica, those with bladders. The intestine of the latter is very peculiar.

The Rotatoria alone, from my further observations, have been capable of being divided according to their dentary organs. They fall first under three groups: Agomphia, toothless, they are few in number; Gymnogomphia, free toothed, they are the most numerous; Desmogomphia, hook-shaped teeth. Those with free teeth fall under two great natural divisions, viz. the Monogomphia with one tooth in each jaw, and the Polygomphia, with many teeth. The Desmogomphia, whose teeth are not free but inserted into a cartilaginous plate, fall also into two natural subdivisions, the Zygogomphia with teeth disposed in pairs, and Lochogomphia, with teeth in rows, so that the fol lowing scheme may be formed

Marvellous Multiplication of the Infusoria.-I have also made some observations on the development and multiplication of the Infusoria, which I deem among the most im portant of all my researches. I have observed for eighteen days successively a single Hydatina senta, and as it was perfectly grown when I singled it out, and did not die of old age, being accidentally destroyed, the life of this animal must be more than twenty days. Such an individual, when circumstances are favourable, is capable of a fourfold propagation every twenty-four-thirty hours. It can in this time bring forwards

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four eggs from the embryo state to the exclusion of the young. But this fourfold increase in the space of a day, when no ob stacle intervenes, and the same individual gives, in ten days, forty eggs, and raised to the tenth power (therefore on the 10th day) a million of individuals from one mother; and on the 11th day four, on the 12th sixteen, millions, &c. Although this productive power is the greatest which has been yet observed in nature, far exceeding that of insects, it is far from attaining that of the Polygastrica. In the Paramecium aurelia, which is "in size, and which has been ascertained to live several days, a doubling of each individual by transverse division has been observed within twenty-four hours, its rate of increase is therefore double that of the preceding. But as these animals, besides division, also propa gate by eggs, and these eggs are not separated from the parent singly but in masses, and as they also form gems, the possible increase within forty-eight hours becomes quite innumerable. Who can wonder that, under such circumstances, fluids should, with the brood of two or three days only, swarm with these ani-malcules ?

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Estimate of the relative Value of the Microscopes of Chevalier, Ploessel, and Schiek.-The following are my individual views regarding the microscopes of Chevalier, Ploessel, and Schiek, which are the best of the present day. The advantages of all these instruments rest upon the discovery of Selligue, and the most important advances upon this basis have been certainly made by Chevalier.

The chief practical advantages of the microscope of Chevalier are,-extent of field of vision, distinctness of outline, even with the highest powers, high magnifying power, a sufficient distance of the object-lens from the object, which amounts to a line even with the highest powers, simplicity of apparatus, and, conse quently, a very moderate price.

Ploessel's microscope, compared with that of Chevalier, is distinguished by the following properties. With as extensive a field of vision, it has still greater, perhaps too great, light, it magnifies nearly double the diameter with great distinctness of outline; its use is more convenient under high powers, from the employment of several eye-glasses, instead of the elongation of

the tube required by the former. The inconveniences of Ploessel's microscope are,-its almost entire uselessness for the observation of fluids, on account of the small distance of the object lens from the object under the high powers, and the impossibility of employing apparatus for pressure, not even mica. It is also, on account of its varied adjustments, and particularly a very fine screw-micrometer, twice the price of Chevalier's; therefore only half as useful considered in the abstract. Its form is much handsomer than that of Chevalier, and more convenient for use.

Schiek's microscope unites the advantages of both of the others. Its field of vision is extensive, extremely sharp and clear illumination, even to the highest powers, appearing to me much clearer than either of the others when I compared them together. Its magnifying powers equal the highest of Ploessel's, therefore twice that of Chevalier's, accompanied with considerable focal distance, permitting of the use of water and pressure for the most minute objects. Its size is smaller, and form more convenient and handsomer than the others without being weaker. From the simplicity of its arrangements, the price is very moderate, and therefore particularly adapted for the working naturalist.

The greater clearness of the image, and sufficiency of light, is a step made by M. Schiek which is a clear gain to optics; which, united to all the other advantages, have appeared to me quite new and surprising.

Outline of the Geology of the Bhurtpoor District. By JAMES HARDIE, Esq. Bengal Medical Establishment. Communicated by the Author.

THIS district may be described as forming a portion of the south-western boundary of the Valley of the Ganges and Jumna. It presents a level platform, elevated about sixty feet above the bed of the latter river, and is in most situations covered with the usual alluvium of the Gangetic provinces. The country is fertile and highly cultivated, and impresses us with a favourable idea of the industry and enterprise of the Jauts, as contrasted with their Rajpoot neighbours of Jeypoor. The lesson

taught them by the fall of their far-famed capital in 1825, has not been thrown away upon the inhabitants; and in no part of India does the English traveller meet with more civility and attention than in this district, where a few years ago he was treated with insult and contempt.

The rocks which immediately underlie the Gangetic deposits in some few situations, appear near the surface, and are quarried for architectural purposes; while strata of an anterior date to these here and there crop out, forming, especially in the northern portion, small detached hills, which are generally topped by a village or stronghold. To the west the Bhurtpoor district is flanked by a belt of rocks of the secondary class, which stretches in a north-easterly direction from the ancient city of Biana, situated on the south-western portion of the district. This belt is interposed between the newer strata just alluded to, and the decidedly primary formations of the Jeypoor and Ajmeer territories: its eastern limit is marked by a low hill range, seen a short distance to the westward of the city of Bhurtpoor.

The sandstone quarries which have for centuries supplied all this portion of India with materials for building, are situated in the Bhurtpoor district, and, as these are important, both in a statistical and geological point of view, I shall, in the first place, communicate what little information. I have been enabled to collect relative to their natural history.

Of the sandstones there are three varieties. No. 1. is a closegrained argillaceous sandstone, more or less slaty; of a uniform dark red colour, so soft as to be scratched by the knife, and apparently composed of small particles of quartz, cemented together by a ferrugino-argillaceous basis: minute scales of mica are distributed through the mass, to which circumstance it apparently owes its slaty texture. No. 2. is also a close-grained argillaceous sandstone. This is a very beautiful variety, its colour is dark red, speckled with white spots, which are generally roundish, and vary from an inch in diameter to the size of a pin's head. This rock is less schistose than No. 1, contains less mica, and, when slabs of it are properly cut and squared, has, at a little distance, exactly the appearance of a fine red porphyry. No. 3. is a rock similar in point of texture and composition to the last, but is of a uniform salmon-colour, passing into

greyish-white. It can with difficulty be obtained in slabs less than four inches thick, while No. 1. may be had in plates less than one-half an inch.

The above rocks are all of them employed in architecture, and are remarkably free working stones. Slabs of the slaty variety, spanning from beam to beam in flat roofs, have been substituted by my friend Lieut. J. T. Boileau of the Bengal Engineers, instead of the bridging joists and tiles in common use; and he has found that the roofs completed upon this principle have, in every instance, proved perfectly water-tight, and that the terrace laid over the stones has invariably dried more uniformly, and freer from cracks, than when bridging joists have been used. By a series of experiments, Lieutenant Boileau has demonstrated that no apprehension need be entertained in regard to the transverse strength of the sandstones, objections on this head having been urged against his plan, while the advantages attending its adoption are invaluable, inasmuch as it secures the buildings against fire, and, what is of still more importance, renders them safe from the attacks of white ants. The annexed Table will shew the results of Lieutenant Boileau's experiments, which are interesting both in a mineralogical and economical point of view.

By a reference to the Table, it will been seen that the redsandstone does not lose much, if any, of its strength by being saturated with water, which renders it particularly fit for the purposes of roofing; and though, in its dry state, it is far infe rior to the salmon-coloured variety, (as 11 to 17 nearly), yet, when wet, it is something superior to it, the latter variety losing about one-half its strength by immersion in water. For the cause we may look to the difference observable in the arrange ment of the component particles of either variety.