COM 



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From the fourth day, when the chicken 

 has attained the length of four lines, and 

 its most important abdominal viscera, as 

 the stomach, intestines, and liver, are visi- 

 ble, (the gall bladder, however, does not 

 appear till the sixth day,) a vascular mem- 

 brane (chorion, or memhranaumbilicalis) 

 begins to form about the navel, and in- 

 creases in the following days with such ra- 

 pidity, that it covers nearly the whole in- 

 ner surface of the shell within the mem- 

 brana albuminis, during the latter half of 

 incubation. This seems to supply the 

 place of the lungs, and to carry on the 

 respiratory process instead of those or- 

 gans. The lungs themselves begin in- 

 deed to be formed on the fifth day ; but, 

 as in the foetus of the mammalia, they 

 must be quite incapable of performing 

 their functions while the chick is contain- 

 ed in the amnion. 



Voluntary motion is first observed on 

 the sixth day; when the chick is about 

 seven lines in length. 



Ossification commences on the ninth 

 day, when the ossific juice is first secret- 

 ed, and hardened into bony points (punc- 

 ta ossificationis.) 



These form the rudiments of the bony 

 ring of the sclerotica, which resembles at 

 that time a circular row of the most deli- 

 cate pearls. 



At the same period, the marks of the 

 elegant yellow vessels (vasa vitelli lutea) 

 on the yolk-bag, begin to be visible. 



On the fourteenth day, the feathers 

 appear ; and the animal is now able to 

 open its mouth for air, if taken out of the 



egg- 



On the nineteenth day it is able to utter 

 sounds ; and on the twenty -first to break 

 through its prison, and commence a se- 

 cond life. 



We shall conclude with one or two re- 

 marks on those very singular membranes, 

 the yolk-bag and chorion, which are so 

 essential to the life and preservation of 

 the animal. 



The chorion, that most simple yet most 

 perfect temporary substitute for the lungs, 

 if examined in the latter half of incubation 

 in an egg very cautiously opened, pre- 

 sents, without any artificial injection, one 

 of the most splendid spectacles that oc- 

 curs in the whole organic creation. It ex- 

 hibits a surface covered with numberless 

 ramifications of arterial and venous ves- 

 sels. The latter are of the bright scarlet 

 colour, as they are carrying oxygenated 

 blood to the chick ; the arteries, on the 

 contrary, are of the deep or livid red, and 



bring the carbonated blood from the 

 body of the animal. Their trunks are 

 connected with the iliac vessels ; and, on 

 account of the thinness of their coats, 

 they afford the best microscopical object 

 for demonstrating the circulation in a 

 warm-blooded animal. 



The other membrane, the membrana 

 vitelli, is also connected to the body of 

 the chick, but by a twofold union, and 

 in a very different manner from the 

 former. It is joined to the small intes- 

 tine, by means of the ductusvitello-intes- 

 tinalis (pedunculus^ apophysis;) and also 

 by the blood vessels, which have been 

 already mentioned, with the mesenteric 

 artery and vena portae. 



In the course of the incubation the yolk 

 becomes constantly thinner and paler, by 

 the admixture of the inner white. At the 

 same time innumerable fringe-like vessels, 

 with flocculent extremities of a most sin- 

 gular and unexampled structure, form on 

 the inner surface of the yolk-bag, oppo- 

 site to the yellow ramified marks above 

 mentioned, and hang into the yolk. There 

 can be no doubt that they have the office 

 of absorbing the yolk, and conveying it 

 into the veins of the yolk-bag, where it is 

 assimilated to the blood, and applied to 

 the nutrition of the chick. Thus, in the 

 chicken which has just quitted the egg, 

 there is only a remainder of the yolk and 

 its bag to be discovered in the abdomen. 

 These are completely removed in the fol- 

 lowing weeks, so that the only remaining 1 

 trace is a kind of cicatrix on the surface 

 of the intestine. 



COMPARATIVE degree, among gram- 

 marians, that between the positive and 

 superlative degrees, expressing any par- 

 ticular quality above or beneath the level 

 of another. 



COMPARISON of ideas, among logi- 

 cians, that operation of the mind, whereby 

 it compares its ideas one with another, in 

 regard of extent, degree, time, place, or 

 any other circumstance, and is the ground 

 of relations. This is a faculty which the 

 brutes seem not to have in any great de- 

 gree. 



COMPARISON, in rhetoric, a figure that 

 illustrates and sets off one thing, by re- 

 sembling and comparing it with another, 

 to which it bears a manifest relation and 

 resemblance, as the following figure in 

 Shakspeare : 



" She never told her love, 

 But let concealment, like a worm i* 

 the bud, 



