of the artery, a microfcope is applied, the whole extent of the membrane of the gills is feen covered with a beautiful net work of exceedingly minute veffels.'

In the obfervations on the circulation of the blood we find remarks both of a trifling and an important nature, Dr. Monro thinks, that the thick coats of the bronchial veins really poffefs a mufcular power; in proof of this opinion, he alleges, that in the mefenteric veins, and vena portarum of an ox, he can demonftrate a truly mufcular coat. Mr. Hunter, we are told, has been fuccefsfully employed in fome experiments, to afcertain the real mufcular power of the blood-velfels, independent of their elasticity; and we hope he will en able us to resume the fubject by their publication. Confiderable dilatations in the abdominal veins, are owing, in Dr. Monro's opinion, to the temporary retardation of the blood, by the fuperior weight of water; but, as they occur in the lymphatic fyftem alfo, it is probable that they accomplish fome other and more latent purpose.

The last remark I fhall make is, That, the circulation of the blood being carried on in the cartilaginous fishes in the fame manner as in the offeous or pifces of Linnæus, and the whole mals of blood paffing through their gills, they must breathe regularly and uninterruptedly to furnish blood to the brain and other organs, or they cannot poffefs the pulmo arbitrarius as is fuppofed by Linnæus: fo that there appears no just reason for claffing them with the amphibia.

In the animals which are commonly reckoned amphibious, to wit, the tortoife, the frog, the lizard, and the ferpent, a part only of the mafs of blood paffes through the lungs. In the frog and common fmall lizard, branches are fent off from the aorta, which, if we may judge from their fize, convey about one-third part of the whole mafs. In the tortoise, the ferpent, and fuch of the lizard tribe as have two auricles and ventricles, a greater proportion paffes through the lungs. In the fea tortoile, the blood from the lungs paffes into the left auricle, and from it into the left ventricle. From the left ventricle it is tranfmitted, by tranfverfe canals or holes in the feptum between the ventricles, into the right ventricle, where it is mixed with the blood which is fent from the venæ cavæ through the right auricle. All the arteries, therefore, take their rife from the right ventricle; and the pulmonary arteries are confiderably fmaller than thofe which fuppiy the place of

our aorta.

In all these animals, therefore, every part of the body may receive a confiderable portion of blood, although the refpiration and free paffage of the blood through their lungs be interrupted. Hence they are not under the fame neceffity with the mammalia birds, and fifhes, of breathing frequently, regularly, or alternately; or they enjoy the pulmo arbitrarius.'

Dr.

Dr. Monro next defcribes the mucous ducts which are very beautiful they are attended by very numerous nerves; and, in one inflance, the nerve becomes pellucid, so that the author thinks its nature is alfo changed.

The watery liquors in the head, pericardium, and peritonæum of fishes, next claim his attention. They are falt, but contain only about half the quantity of salt ufually found in the fame bulk of fea-water: in fome inftances, much lefs. There are paffages in fome fishes, from whence the water may pass out; but a valve feems to be interpofed to exclude the entrance of any. In the skate too, the pericardium opens into the abdomen; but, from the ftru&ture of the duct, nothing can pafs from thence into it. Dr. Monro thinks that fluids may pass the valve, and that thefe liquors are derived from the fea; but they are lefs falt than fea-water; and befides, in that way, they cannot get into the head or the pericardium. The reafon, which he appears to have overlooked, is probably the following; fishes, though they live in falt water, have no falt in their compofition; and their abforbent veffels feem to feparate the pure water from the element in which they live; yet, in different circumftances, this operation is not fo perfectly performed as may be neceffary for the prefervation of the animal; fo that another outlet is neceffary for the deleterious fubftance. It is, therefore, separated by the veffels of the pericardium and abdomen, and from thence paffes out. That the liquor is recrementitious is evident from its being in fome inftances connected with the urinary organs; and it is by no means certain, that it has not fome outlet from the head. In man we find there are fecretory organs, to throw out what may have been abforbed by the indifcriminate operation of other veffels; fo that our opinion is fupported by analogyThe other fecreted organs, and their liquors, afford nothing which deferves attention, or that we can abridge.

The most curious organ of fishes is the fwimming bladder. Dr. Monro defcribes its various appearances, and the communications, in fome genera, between it and the ftomach: he Tenders it probable, that the air either paffes from the ftomach, or is produced by fecretion. This fubject, however, is left in a very imperfect ftate we shall supply the imperfection by a few facts, and fome conjectures. It is highly probable that, in fame inftances, this bag leffens the fpécific gravity of the fish, and contributes to raise it in the water; but this is not always the cafe, for the bag is very fmall, in proportion to the fize of the animal, and not capable of any very great enlargement. This effect is therefore a fecondary one, and does not merit much confideration. The primary one is probably

to prevent bad air from mixing with the fluids, or as a receptacle for that which has been admitted. We know that phlogisticated air is deleterious to fifhes, and that they die if they have not a fupply of this element, in a proper state. At the fame time, they cannot always discharge the foul air, con taminated by their bodies, or fupplied from their food; fo that in fome inftances they drive it into this receptacle from the stomach; in others, it is fecreted into it from the blood. Dr. Monro has not examined the nature of the air in the bladder; but we know it to be noxious, and it gives probability to our accounts. On every fuppofition, fome excretory duct is neceffary; though none has been yet discovered, and no one has thought of the means by which it is to be discharged. We would fuggeft, though with great diffidence, that from the addition of phlogifton, in confequence of its being confined within an animal body, it may be changed to water, and exude through the pores into the abdomen, from whence there is a ready discharge. We know that water, in an attenuated ftate, will pervade much closer membranes.

Dr. Monro next defcribes the abforbents of fishes, with great accuracy; he has traced them to the furface, and demonftrated that they are a diftinct fyftem of vessels, with the fame properties as the human lymphatics. As thofe of fishes have, however, no valves, it is probable that their coats, though thin, are really mufcular. Our author then attempts to refute Mr. Hewfon's opinion relating to the fpleen, by fome obfervations on the spleen of fishes, and to eftablish his own title to the discovery of the lymphatic fyftem, in thefe animals. The refutation is very fuccefsful; but we believe it is now unneceffary: we are forry fo much has been faid about the discovery, by men of abilities; for, in the state in which this branch of anatomy then was, it lay ready for the firft and moft fuperficial enquirer.

Our author proceeds to the brain, and organs of sense in fishes. The organs of feeing and fmell have been often described: those of herrings have been already defcribed by Mr. Hunter, who is not, however, once mentioned by our author, It must be acknowledged, that the defcription of the ear, in this volume, is more full, particular, and difcriminated, than that of Mr. Hunter, in the Philofophical Tranfactions. We made large extracts from that paper, in our fifty-fifth volume, page 410, and need not now enlarge on the subject, or compare the accounts..

The experiments on hearing in water, are very inftructive, We find that the tremors of the air are communicated readily to the water, and those of water to air; so that tremors, ex

cited

cited by percuffion, can be heard when the head is either above or under water. When a bell is plunged in water, the found is more grave than in air; the bell, which in air founded the highest G of a common harpfichord, in water founded a fifth falfe lower, or the C fharp under G.

From the account of the eyes of fishes, we shall select the following remarks.

Upon the whole, therefore, we are led to the conclufion, that the primary ufe of the almost completely spherical figure of the crystalline lens of fifhes, or great convexity especially of the anterior part of their lens, which I find projects in the cod about feven fortieths of an inch beyond the iris, is to take in a large field of the objects around them; which was particularly neceffary, as the motion of their neck is inconfiderable.

To enable them, with the fame length of the axis of the eye as in the quadruped, to collect into a focus on the retina the rays of light coming from the denfe medium of water, four chief circumitances concur.

In the first place, we obferve that their cryftalline lens is more convex, or compofed of portions of smaller fpheres, than in land-animals.

In the next place, we have found that their crystalline lens is, in correfponding parts, much more denfe than in animals which live in air.

Thirdly, that the lens in fifhes poffeffes powers of refracting light far beyond what have been calculated by authors, who have proceeded on the fuppofition that these powers were proportioned nearly to its fpecific gravity.

In the last place, the vitreous humour of fishes being lighter than that of land-animals, the rays of light iffuing from their lens will be refracted in a greater degree, or brought fooner to a focus."

The next fubject of enquiry is the anatomy of the fepia loligo, the ink-fith. Our author fufpects the black fluid to be the bile of the animal; and to be merely a recrementitious liquor.

The defcription of the anatomy of the echinus marinus, was read to the Philofophical Society, at Edinburgh, in the year 1761. We are forry that we can neither analyse or abridge it; for it is extremely curious: we can only hint, that the perforations in the shell of this animal are intended for the paffage of abforbents; and that abforption seems to be carried on by means of muscular action. With this account the volume concludes.

This work contains fifty tables, fo that it would lead us too far, even with the utmost conciseness, to explain their fubjects. It is enough to remark, that they are intended to illuftrate every part of the description; and, if properly executed,

would

would have been very valuable: at prefent, they fupply the neceffary defects of language very imperfectly.

If we examine this work as a whole, we fhall find great reafon to commend the industry and attention required in fo many laborious diffections; we cannot praise the author very highly: for acute comprehenfion, or penetrating fagacity. His inductions are, however, generally clear; and, fo far as they extend, always accurate. We wish him to purfue the fubject; for much remains to be examined, and many doubts, parti cularly in the phyfiology of fishes, to be elucidated.

A new Syftem of Modern Geography: or, a Geographical, Hif torical, and Commercial Grammar; and prefent State of the feveral Kingdoms of the World. By William Guthrie, Efq The Aftronomical Part by James Ferguson, F. R. S. The Third Edition, with great Additions and Improvements, and a copious Index. Illuftrated with a Set of large and accurate Maps. 4to. 17. 155. in Boards; the Maps half-bound. Dilly and Robinfon.

WE

E have feldom examined a work fo useful in its original form, and fo much improved in the fubfequent editions, as the Syftem now before us. It contains fuch a fund of information, drawn from various fources, that it has a powerful claim to be confidered as a repofitory of valuable knowledge. Of the improvements in the prefent edition, a general account is given in the following advertisement.

The original Preface fo fully explains the general plan of the work, that it feems only neceffary to give fome account of thofe additions and alterations which the fluctuation of states and of human affairs renders unavoidable.

Since the last quarto edition came from the press, the flock of geographical and political knowledge has been much increased, by the publication of fome valuable accounts of travels and voyages. Thefe have been carefully perused; and from them are now added many interefting particulars relative to Ruffia, Poland, Sweden, Denmark, Spain, Switzerland, the two Sicilies, the East Indies, the islands in the Pacific Ocean. the western parts of North America, Hudfon's Bay, and other places.

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