that decompose water in order to obtain its oxygen. It is obvious that those insects which breathe air immediately, ought to be the only ones in which we find the two kinds of trachea of which we have spoken. The vesicular trachese would not have sufficient elasticity to drive out the superabundant water, which the insect introduces into its tracheæ. Perhaps this elasticity would not even be sufficient for those which live habitually in water, but do not decompose that liquid. In the second place, the insects which decompose water ought to be the only ones that have but one stigma. This stigma ought to be so placed that the animal may receive the water necessary for it; and we see that whenever this disposition exists, it is always at the anus that this opening is found. But before passing to the description of all these different kinds of organization, we shall bere give a table which will render them obvious at one view,

1. Respiration in Air. 1. With tubular Division 1.--Arterial tracheæ. trachea Division II.--Pulmonary and arterial trachea.

With cartilaginous II. With vesicular Always two orders Koops, or a kind of ribs. tracheæ. ? of tracheæ

2. Without cartilaginous

hoops or ribs. II. Respiration in Water.

Breathing by true stigmata, and

Division 1. coming to the surface of the Only with tubu

water to breathe air. lar trachea

Breathing by an opening placed | Division II. at the anus, decomposing

1.

e

fili la

Dr. Prichard, without pledging himself to any opinion, investigates in the first place the criteria by which species are to be distinguished, and after examining those already offered, particularly that of John Hunter, who considered the sterility or fruitfulness of a hybrid the proof of difference or identity of species of the parents, he endeavours to lay down a general rule, derived from analogy, which, although imperfect, yields more satisfaction to the inquirer, than any solitary assumption can do. It has, too, the sanction of two of the most eminent naturalists of the present day. The rule which Dr. Pritchard lays down is, that after having observed a number of the changes produced in living bodies by adventitious causes, when any particular deviation is found frequently to recur, all parallel diversities may be ascribed to analogous causes, although the relations between these latter causes and their effects should not be so distinctly traced as in other more ordinary events. According to this rule, all the remarkable varieties of mankind, when compared with those of the inferior animals, particularly when domestication has displayed its effects, fall within the limits of one species; and Dr. P. makes the inference, that as the strictest analogy exists between the changes which almost the whole of the inferior tribes have a tendency to assume under known circumstances, and those diversities existing among men, it is consistent with the strictest rules of philosophizing to infer, that these changes originate in “ the principle of natural deviation, and furnishing no specific distinction."

The next branch of the inquiry is how far men are to be considered as having all proceeded from one common stock. This question has been treated of by several writers purely on historical evidence; Dr. Pritchard, however, without disregarding the powerful arguments afforded by the historical researches of Sir W. Jones, Bailey, and others, still proceeds on analogy, and endeavours to solve the general problem as it regards all organized tribes, but more particularly animals. With much acuteness he has examined the distribution of animals, more especially in those vast regions of the southern hemisphere, so little known until the important discoveries of Cook, Bougainville, Wallis, Flinders, and others, had reinoved the veil which was spread over Nature; and concludes by inferring, “ that every existing species may be traced with probability to a certain point which appears to have been its original abode; and that few or no species have been found in countries separated from their primary seats by barriers which their locomotive powers and peculiar structure do not enable them to surmount. This inference, if true in general, includes the particular case of the human species.

Having thus established the criteria of species, and rendered it probable that species were originally confined to one point, it is necessary to determine as far as possible, what are the causes that produce the very extraordinary diversities which exist among mankind. The commonly maintained hypotheses of those who adopt

ofi

the opinion of the unity of species among men, that a change
produced in the white European by heat and food becomes here-
ditary, is exceedingly inconsistent with notorious facts. Nor does
it receive any additional weight from its antiquity ; that only affords
an additional proof of the facility with which even absurdity may
be propagated under the sanction of illustrious names. Dr. Pritchard
shows that the previous opinions are irreconcileable with fact, and
supposes that certain causes exist, which, acting on the parents,
“ influence them to produce an offspring endowed with certain
peculiar characters, which characters, according to the law of
Nature, become hereditary, and thus modify the race.” In order
to develope those causes, Dr. P. shows that, although climates
produce very remarkable variations in individuals, both in the
animal and vegetable kingdoms, yet the only permanent effects
seem to be derived from cultivation and domestication. Of these
effects there are ample and apposite proofs in our cultivated fruits,
and among domestic animals. The original stocks remain un-
altered, while the most extraordinary changes are brought about by
culture. Dr. P. institutes a parallel between the culture of plants,
the domestication of animals, and the civilization of man; and,
while he allows that some connate varieties may be produced by
climate, he insists that the condition of man in social life in-
fluences more extensively the physical structure than any variety of
latitude or local temperature: and concludes by ascribing those
remarkable diversities among mankind, not to any moral cause, but
to physical causes connected with a particular mode of life. of
this, several interesting illustrations might be cited, in addition to
those given by Dr. Pritchard.

Having established the probability of these opinions, he proceeds-
to determine whether the original race were white or black; and
having shewn that black, or at least a very dark brown, in all the
inferior tribes, is the primitive colour; and that the same com-
plexion prevails among all savages, and a gradual change towards
white occurs through successive races of semi-barbarians to perfect
civilization, he infers that the prototype of the human race was a
Negro. However satisfactorily this conclusion may be drawn, it is
necessary to afford some proof, and accordingly the author adduces
numerous illustrations calculated to give considerable force to his
argument. He urges with much force the singular varieties in
form and complexion among the widely scattered nations of the
Pacific Ocean, who exhibit almost every variety, from the savage
Papuan to the highly refined European. He proves, by similarity
of language, of religious rites, and other points of coincidence,
their common origin; and then applies the results obviously oba
tained from these individuals to the whole of the human race.

The outline then of these Researches into the physical history of man, is, that as uniform diversities are produced by certain known causes ; so, all similar or analogous diversities should be ascribed to analogous, causes. That as an analogy does actually

' ..

organization which apinals present. We may very well suppose that the insects which decompose water in order to take possession of its oxygen, have only a demi-respiration, while those that receive air immediately, have a complete respiration. Those which receive air immediately, and have very considerable vesicular tracheæ, with an apparatus intended to keep them always full of air, ought to have a respiration still more complete. And to adopt the ratio

. which we have already pointed out, though far from exact, the respiration may be very well doubled by that complication of means. At least it is certain that the cartilaginous hoops which we have compared to the ribs of animals with vertebræ, do not exist along with vesiculary trachea, except in those species which have occasion for a great muscular power, from the great distances which they are destined to travel. Such, for example, are the locusts (criquets), as famous for their einigrations, as for the ravages which they commit in those countries where they stop in order to feed. Finally, the ordinary vesiculary tracheæ, or those which, not being very large, do not require a particular apparatus for moving them, are found only in species which require great muscular exertion, or which, flying a great deal, ought to be able to diminish their specific gravity. The caleopteres lamellicornes, and the lepidopteres and dipteres, are the işsects in which this arrangement is most evident. Before passing to the particular description of the respiratory organs of insects, we ought to explain what we mean by arterial tracheæ and pulmonary trachea. Insects exhibit in general two orders of tracheze, the uses of which not being the same (though their organization is not very different) deserve to be distinguished. * The one goes directly to the stigmata, takes air immediately, and distributes it to the different parts of the body. The other does not receive air immediately. It only communicates with the external air by means of the first order, and generally, being larger than the arterial tracheæ, serves as a reservoir of air. Their direction, in general, is more regular, and their ramifications much less numerous. These two orders of tracheæ having then a different object to fulfil, I thought that in order to render the description of these vessels the clearer, it would be advantageous to distinguish them. I have called the one arterial tracheze, because they are branched like these vessels, and carry air to all parts of the body, as the arteries distribute blood in those animals that have a real circulation. But to perceive how far this analogy is well founded, we must recollect, that in insects air is the only fluid that is really circulated. As to the pulmonary tracheæ, as they serve as reservoirs of air to enable it to act on the different parts of the body, this name was the most suitable that offered itself. The two orders of tracheæ in insects were recognized by Swammerdam, and, in

general, he calls those tracheæ arteries, which we have distinguished by the name of pulmonary tracheæ. The arterial tracheæ of Lyonnet are the same as ours, and, in fact, no others exist in caterpillars. It may be proper to observe, that the two orders of tracheæ do not always exist; but the arterial are never wanting. Perhaps in the species in which we see only arterial tracheæ, the parts require a speedy impression from the air.

(To be continued.)

ARTICLE XI.

ANALYSES OF Books, I. Researches into the Physical History of Man. By James Cowles Pritchard, M.D. F.L. S. of Trinity College, Oxford; Fellow of the Wernerian Natural History Society of Edinburgh, and of the Medical Society of London; and extraordinary Member of the Royal Medical Society of Edinburgh. London, J. and A. Arch, 1S13.

The physical history of man presents a field not less interesting than unexplored, yet Ds. Pritchard is the first who has exhibited it in a connected shape. By assembling together the most important facts he has been enabled to deduce general conclusions of considerable moment, some of which are so very remarkable as to excite something more than common surprise. The naturalists of all times have overlooked, whimsically enough, the history of our own species, and have devoted the whole of their attention to inferior animals. Yet in the course of their researches they have developed certain general principles, which may be applied to all parts of animated nature. The particular application of these principles to the human race appears to have been first made by Dr. Pritchard, although the subject has occasionally and casually engaged the attention of speculative philosophers, from the days of Aristotle to those of M. de Buffon. As it might naturally be expected, a thousand crude conjectures have supplied the place of accurate observations and reasonings. It it needless to repeat them here; it may suffice that, in general, the ancients considered the human race to be of one species, and ascribed every variation in point of form and colour to the effects of climate, the particular examples of which are abundantly ludicrous. The same opinion, variously modified, bas been maintained by many moderns; but with most remarkable eloquence by Count de Buffon, in his Histoire Naturelle. This last named naturalist, however, did not possess a storé of facts to resolve the difficulties that press on his peculiar modification of this hypothesis. Lord Kames stands at the head of another set of philosophers who maintain that mankind have sprung from various stocks, and that each particular race is especially adapted by Providence to the region in which they exist.