PRELIMINARY ESSAY ON GENERATION, 
exqulfite degree of feeling. If a fmall worm happens to get within the fphere of their aclivity, it is quickly entangled 
bv one of thefe arms ; and foon after, the others being drawn in the fame direftion to it's aid, the worm is brought to 
the mouth of the animal, and fpeedily devoured, colouring the body as it is fwallowed. Thus much is neceffary to be 
obferved of this animal's mode of living, to evince that it is a real exillence, and not of the vegetable tribe ; but more 
extraordinary circumftances ftill remain to be unfolded concerning it. If examined with a microfcope, there are feen 
feveral little' fpecks , like buds, pullulating from different parts of it's body; and thcfe foon after appear to be young po- 
lypi, which, like the larger fort, begin to cafl their little arms about for prey, in a fimilar manner. 
Thus every polypus has a new colony fprouting from it's body; and thefe nafcent ones, even Vv'hile attached to the 
parent animal, become parents themfelves, having a ftill fmalk-r colony budding from thern: all, at the fame time, bufiiy 
emoloyed in fearching for their prey; and the food of any one of them ferving for the nourifliment, and circulating 
through the bodies of all the reft. This fociety, however, is every hour difTolving; thofe newly produced are feen at 
intervals to quit the body of the large polypus, and become, fiiortly after, the head of an incipient colony themfelves. 
After this manner, the polypus multiplies in a natural courfe ; but it may be increafed by a much {horter and expe- 
ditious wav. Thousrh cut into a thoufand pieces, each part ftill retains it's vivacious principle, and each fhortly be- 
comes a di'ftinft and compleat animal. Whether cut longitudinally or tranfverfely, it is all the fame: it gains by our 
endeavours, and multinlies by apparent deftruition. The experiment has been fo repeatedly tried, that nothing can be 
better confirmed than this method of generation, which may be ftridlly called philofophical. The famous Sir Tiiomas 
Brown hoped one day to be able to produce children by the fame means as trees are produced: the polypus is certainly 
multiplied in the manner related; and every philofopher may thus, if he pleafes, boaft of a numerous, though ufelefs 
progeny, without being accufed of cruelty in his experiments, as he will be encreafing aninaal life, inftead of de- 
Itroying it. 
This mode of generation, from cuttings, may well be confidered as the fimpleft of all poffible kinds ; and may ferve to 
Ihew how little pains Nature takes in the formation of her lower and humbler produftions. As the removal of thefe 
from inanimate into animal exiftence is but fmall, few preparations are either made or become neceffary for their journey. 
No organs of generation feem provided, no womb to receive, no covering to protedt them in their Hate of tranfuion. 
The little reptile is quickly equipped for all the functions of it's humble fphere; and, in a fliort time, arrives at the 
fummit of it's contemptible perfection. 
The generation of animals from an egg conftitutes the next fuperior degree of generation. In this manner all birds, 
the o-enerality of fifties, and many of the infed tribes, are produced. An egg may be confidered as a womb, detached 
from the body of the parent animal, in which the embryo is but juft commencing to be formed : it may be regarded as a 
kind of imperfeft delivery, in which parturition takes place before the ofi^spring has attained it's compleat formation. 
Fifties and infefts, indeed, moft ufually commit the care of their eggs to hazard; but birds, which are more perfeftly 
organized, are found to hatch them into maturity by the warmth of their bodies. However, any other heat, of the fame 
temperature, would anfwer the purpofe as efieclually; for either the warmth of the fun, or of a Rove, is equally power- 
ful in bringing the animal inclofed in the egg to a ilate of perfeft exillence. Nature has taken care of the viviparous 
animal in every ftage of it's being. That force which feparates it from the parent, feparates it from life ; and the em- 
bryo is ftiielded with unceafing proteftion, till it arrives at exclufion. 
It is far otherwife with the little animal in the egg: often totally ncglefted by the parent, and always feparable from 
it, every accident may retard it's growth, or even deftroy it's exiftence. Befides, art, or even chance, may alfo bring 
thi? animal to a ftate of perfeftion ; fo ttiat it can never be confidered as a compleat produdion of nature, in which fo 
much is left for accident to accomplifli or retard. 
But, inferior as this fpecies of generation unqueftionably is, it's confideration will aftord great infight into that of 
nobler animals, as we can here watch the progrefs of the growing embryo in every period of it's exiftence, and catch it 
in thofe very moments when it feems ftarting into motion. Malpighi and Haller have exerted particular induilry on 
this curious fubjedl; and, with apatience almofl: equal to that of a fitting hen, have attended incubation through all it's 
feages. From them, therefore, we have a wonderful hiftory of the chicken in the egg, and of it's gradual advances to 
compleat exiftence, 
It would be tedious and uninterefling to defcrlbe thofe parts of the egg which are well known and obvious, fuch as 
it's ihell, it's white, and it's yolk; but the difpofition and ufes of thefe are not fo apparent. Immediately under the 
fhell lies that common membrane, or fkin, which lines it internally, every where adhering to it very clofely, except at 
the broad end, where a fmall cavity is left, which is replete with air, and which encreafes as the inclofed animal be- 
comes larger. Under this membrane are contained two whites, though feemingly only one, each wrapped up in a mem- 
brane of it's own, one white within the other. In the centre of all this is the yolk, wrapt round, likewife, in it's own 
membrane. At the end of this are two ligaments, denominated chalaza-, forming, as it were, the poles of this micro- 
cofm ; being denfe white fubftances, made from the membranes, and ferving to keep the white and the yolk in their 
natural places. 
It was the opinion of Mr. Derham, that thefe ligaments anfwered likewife another purpofe : for a line being drawn 
from one ligament to the other, would net pafs diredlly through the middle of the yolk, but rather towards one ftde; 
and would divide the yolk into two unequal parts, by which means the chalazE ferved to keep the fmalleftfide of the yolk 
always uppermoft ; and in this part he fappofed the cicatricula, or firft fpeck of life, to refide ; which, by being upper- 
inoft, and confcquently next the hen, would thus enjoy the warmeit fituation. ^ 
But this is rathar ingenious than real ; the incipieni animal being found in all fituations, and appearing uninfluenced 
by any. This cicatricula, wliich is the part where the animal firft begins to fhew figns of life, is not much unlike a 
vetch or hntil, !yi»ig on one fide of the yolk, and within it's membrane. All thefe contribute to the convenience or fup- 
port of the iiitle animal ; the exterior membranes and ligaments preferve the fluids in their proper places ; the white 
ferves as nourifliment; and the yolk, with it's membranes, after a due fpace, becomes a part of the animal's body. 
Such is the nature of the egg of an hen; and the fame defcription applies to thofe of birds of every fize. 
Previous to their placing the eggs under the hen, the naturalifts from whom we derive our principal information on this 
fubjecl, v/ell examined the cicatricula, or little fpot, already m.entioned; which may juftly be confidered as the molt im- 
portant part of the egg. In fuch as were impregnated by the cock, this was found to be large ; but in thofe laid without 
the cock, very fmall. It was found, on a microfcopic examination, to be a kind of bag, containing a tranfparent fluid, 
in the centre of which the embryo was obferved to refide. The embryo refembled a conipolition of little threads, which 
the genial warmth of future incubation tended to enlarge, by varying and liquifying the other fluids contained within the 
Ihell, and thus prefling them either into the pores or the tubes of their fubftance. 
The eggs being placed in a proper warmth, either expofed to the fun, or in a ftove, after fix hours, the fpeck begins to 
dilate, like the pupil of the eye. The head of the chicken Is diftiiidtly feen, with the back-bone, fonieivhat refembling 
a tadpole, fio.iting in it's ambient fluid; but as yet feeming to aiTume none of the functions of animal life. In the fpace 
of fix hours more, the little animal is more diftindly feen ; the head becomes more vifible, and the vertebra: of the back 
more plainly perceptible. All thefe preparatory figns of incipient exillence are encreafed in fix hours more; and, at the 
end of twenty-four, the ribs begin to affume their places, the neck to lengthen, and the head to incline to one fide. 
The fluids in the egg feem alfo at this period to have changed place; the yolk, which was before In the centre of the 
fhell, approaching nearer to the broad end ; the aquatic part of the white is, in fome meafure, evaporated through the 
fhell; and the grofl^er parts fink to the fmall end. The little animal appears to turn towards that part of the broad end, 
in which a cavity has been defcrlbed, and, together with it's yolk, feems to adhere to the membrane there. 
At the end of forty hours, the great work of life feems fully begun, and the animal plainly appears to move; the back- 
bone, which is of a whitifh colour, thickens ; the head is ftill more inclined towards one fide ; the firft rudiments of the 
eyes ftiev/ themfelves; the heart beats, and the blood already commences it's circulation. The parts, however, ftill con- 
tinue fluid; but, by degrees, become more and more tenacious, and harden in to a kind of jelly. 
At the expiration of two days, the liquor in which the chicken fwlms feems to encreafe; the eyes exhibit the ap- 
pearance of two fmall bladders; and the heart palpitates in the manner of every embryo where the blood does not cir- 
b 2 culate 
