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system, with the natural characters of the families for the class of mammalia.

The proportion of the spinal cord to the encephalon which we have already found of such value in the primary divisions of the vertebrata, is no less important in their further subdivision. I have found it to correspond with, and to follow, analogous gradations, with the natural characters in the genera and species. Of these dimensions, the most important are the greatest breadths of the two organs, which agrees with their relative weights, and very nearly with the transverse diameters of the cranial cavities, and of the occipital foramen. In the following table, I have brought together several of these relations, and have ranged the species according to their natural affinities. Those marked with an asterisk are taken from Tiedemann's Icones Cerebri Simiarum et quorundam Mammalium Rariorum ; the others are from my own observation. Most of these last depend on immediate measurements of the brain and cord. Those marked with a cross, are the relative breadths of the occipital foramen and of the cranial cavity.

The greatest breadth of the spinal cord immediately behind the pons is to the greatest breadth of the cerebrum,

In Man, as
Simia sphinx,

capucina,
Sabæa,
Resus,
Cynomolgus,

Nemestrina,
Lemur Mongoz,
+ Ursus maritimus,

Canis vulpes,

Mustela Foina, # Felis Leo,

Nasua narica, * Lotor vulgaris, Erinaceus

europæus, Talpa europæa, Vespertilio myotis,

Didelphis virginiana, * Mus alpinus,

Rattus,

Cricetus,
* Hystrix cristata,
* Castor Fiber,
• Cavia Agouti,

Lepus timidus,
Capra ovis,

Sus Scrofa sinensis,
* Phoca vitulina,
+ Monodon Narwhal,

100 : 685

: 470 : 430 : 414 : 365 : 352 to 360. : 357 : 371 : 322 : 278 : 270 to 308 : 275 : 208 to 248 : 248 : 230 : 200 to 265 : 192 : 147 : 227 : 204 : 205 : 200 : 207 : 222 : 230 : 250 : 222 : 352 : 363

We have here.a double series, an increasing and a decreasing. The first ranges from man to the Virginian Opossum; the second continues from the Opossum to the Cetacea. The intermediate members of the first series are, first, the apes, then the makis (Lemur), then the plantigrade or digitigrade carnivora, and, lastly, the insectivorous genera of Erinaceus, Talpa, and Vespertilio. In the second series, the links are filled up by the Rodentia, of which the hare forms the passage to the Ruminantia ; to which follows the Pachydermata, which pass through the Phocæ into the Cetacea. Thus the relations of the spinal cord to the brain in these animals, entirely coincide with their other natural affinities. Some writers, it is true, have regarded their affinities differently, making the bat succeed to the makis, and the phoca to the plantigrades. But, in the determination of these affinities, we must not be swayed by a few of the more obvious external marks, but by the whole internal as well as external conformation. Upon such a basis these animals will assume the order that we have given them above. The only analogy of the bats with the makis is in the pectoral mammæ ; and the phocæ are intimately unconnected with the cetacea through the genus Manatus.

By this, however, I am far from asserting the mammalia can be ranged in an uninterrupted series, according to the proportions of the brain to the cord. Even in the above list, deviations are found from such an order. This is owing partly to the relative breadths of these two organs not being exactly indicative of their relative masses; and to the circumstance of the number of individuals in which the masses are determined with precision being still too small to justify the formation of an exact series. Only, if these defects were supplied, it might be expected that, in order to preserve the scale of natural affinities, the vacuities of the ascending and descending series should be filled

It cannot be doubted, for example, that, in the sloths (bradypus), the brain, compared with the cord, is smaller than in the makis and the uppermost of the carnivora. They are, however, immediately connected with the makis, and must be placed in the series between the lemur and ursus. If the proportional breadths of the organs were as 100 to 300, the descending series from man to the opossum would change into two others, one from man

up.

to the sloth, the other from the bear to the opossum. Farther inquiries would likewise disclose other intermediate series. Such interruptions of the principal series are, however, quite correspondent to the laws of natural affinity. They would only transgress these if interposed members gave rise to recurrent series in one of the two principal ; if, for instance, an animal which, according to its natural affinities, succeeds to the sloth, should, from the proportion of its brain and spinal cord, stand above it. But I do not believe that such a genus can be found.

As every genus and species, not only of the mammalia, but also of the other vertebrated animals, has a certain proportion between its brain and spinal cord, in the same manner each part of the brain, especially the cerebellum, bears a definite proportion to the other parts. Hence we might deduce further specific and generic marks; and one day we may be able to distinguish the whole of the vertebrata by the numerical masses and dimensions of the parts of the encephalon, and range them from this character according to their natural affinities. The relation, it is true, varies in different individuals of each species, but there are limits which it never exceeds.

Analysis of the Labradorite Felspar found in the Trap-Rocks of Scotland. By Captain LE HUNTE.

By Captain LE HUNTE. Communicated by the Author.

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The specimen analyzed was found near Campsie, in a porphyritic greenstone. It was in the form of long narrow crystals, nearly transparent and colourless, of a foliated structure, and vitreous lustre. Its specific gravity was 2,689. The larger crystals frequently present a flat conchoidal fracture, which first induced me to suspect that it was not felspar. From the great difficulty that I experienced in procuring the mineral in a pure state, the analysis was made upon a small scale; but it was repeated with nearly the same result. It appears, then, that this mineral is labradorite, with the best analysis of which the foregoing nearly agrees. The large crystals of labradorite that are imbedded in trap-rocks are very much cracked, and so impure that they cannot be employed for analysis.

About two miles to the west of the village of Milngavie, near the road between Glasgow and Strathblane, there is a very remarkable brown porphyritic trap, that contains large and beautiful crystals of yellow labradorite. These crystals are cracked, and when heated, present numerous brown spots, which show that they are not pure. The following is their composition :

Silica,
Alumina,
Lime,
Soda,

3.974
Potash,
Perox. of Iron,

52.341
29.968
12.103

0.301
0.866

99.553

All the analyses of labradorite that have hitherto been made differ a little from each other; some agree with my first analysis, while one of Klaproth's differs but little from the last. It is probable, that, owing to its structure, labradorite has seldom been examined in a pure state.

The chemical characters of labradorite enable us to distinguish it from felspar, even when the quantity for examination does not exceed a grain. For this purpose the mineral, in the state of an impalpable powder, is treated with weak muriatic acid in a watch glass, and gently heated for an hour. The solution is then evaporated to dryness, and the saline residue is heated until the excess of acid be expelled when it is redissolved in water. To the clear solution, when warm, a few drops of oxalate of ammonia are added, which produces a precipitate of oxalate of lime if the mineral be labradorite, but does not produce a precipitate if it be pure felspar.

Dr Macculloch mentions, that the glassy felspar which he found

at Sky frequently resembled labradorite. I have seen many specimens from that island to which the latter name must be applied. The mineral, which gives a porphyritic aspect to some of the pitchstone of Arran, appears to be glassy felspar ; as far, at least, as I can judge, from having examined a very small fragment of it. The porphyroidal traps, on the western boundary of the Scotch coal district, more frequently owe their structure to the presence of labradorite than to that of felspar. This last mineral, with its usual characters, very rarely occurs in them. We frequently indeed find a white, opaque, foliated mineral, destitute of lustre, which has generally been called felspar; but I have procured both lime and soda from this substance; therefore it has, in some cases at least, been improperly named. The trap-rocks appear to contain other minerals which resemble felspar in many of their characters, but differ from it in composition. One of these, which I found in the neighbourhood of Stirling, is of a red bright colour, opaque, foliated, and has a silky lustre ; from the small quantity of it which I could procure I could only determine, that it contained a good deal of peroxide of iron, and a little lime. The analysis of another was published some time ago by Dr Thomson, who called it Mornite. It is very remarkable that the composition of mornite is precisely the same as that of the first specimen of labradorite that I examined, excepting that it does not contain an alkali, but it contains a quantity of protoxide of iron, exactly equivalent to the soda in labradorite. The external characters of mornite and labradorite must also be very similar, for the mineral dealer from whom Dr Thomson procured the former, when I showed him my specimens of the latter, immediately called them mornite. I have not seen this mineral, which was found in a trap-rock in the north of Ireland. The granitoidal traps of the Scotch coal district, on the contrary, very frequently present well characterised crystals of felspar, and rarely labradorite. They often, however, contain a white mineral, which, through a great extent of rock, does not present any of the characters of felspar, but rather resembles a zeolite ; and these differ very much, in all their characters, from those which contain felspar. It would be easy to arrange the granitoids, from their external characters, into three

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