membrane which urges the yolk-bag into the cavity of 

 abdomen of the chick. 



INCUBATION. 



gated. It feems likewife to be the contra(Sion of the fame form curves j thefe elongate and expofe the interval of their 



two curvatures. Tiiey break at the end, and the two ends 

 become nearly ftraight, remaining attached to the edge of 

 the valve. The breadth of thefe little membranes appears 

 alfo covered with cylindric tubes, fometimcs branched and 

 feparated by the reticular intervals. The day after, the 

 yolk-bag having been fteeped in water, he faw the appear- 

 ance of cylindric tubes forming a net-work upon the mem- 

 brane which makes the breadth of the valves, and continuous 

 with the vermiform tubes of the edges. He further faw 

 that the vefFels of the valves, having arrived there, were co- 



Thejo/i appears to be fomewhat lefs than in the preceding 

 days ; but on the clofefl examination we have not been able 

 to difcovcr any of it in the inteftinal canal. We have ob- 

 ferved at this period, although it probably exills much fooner, 

 an appearance of yellow vefTcls accompanying on each fide 

 the blood-veffels of the yolk in the fame manner as tiie fmall 

 veins generally attend arteries. We have not been able to 

 determine whether this appearance be caufed by real veflels 



filled with a yellow fluid, or bv the inner coat of the bag ^'^''^^ "'"•' fo™<^ ^'^■'y fine fmall tubes refembhng a powder, 

 being feen throuo-h the outer, p'roducing on the edge of the The following morning, he faw fome of the tubes which 

 traft of the rearblood-veffels an appearance of yellow lines, ascended from the bafe of the valves, and which were con- 



The chkh has now attained nearly the utmoft fize that it ''""^^d with the tubes of the edge. They were cylindric as 

 will polfels while in the egg. Its form is entirely that of the )f' ^^^^ .'^""•'^ perceive, and jouied m form of a net-work. 

 excluded chick, except that its abdomen is enlarged in pro- ^.^'\ ^"'g^' ^fff ^ ^^''="' evidently as tar as the vafcular 

 portion to the quantity of the yolk-bag which is admitted ''"■'-"''' °^ ^^^ yolk-bag. 

 into that cavity. The fourth day many of the tubes had difappeared, and 



The different organs of the chick are very perfed. The ^^^'^'^^ °^h' remained on the edge of the valves the membrane 

 convolutions of the inlejlhiei which were outfide are taken which covered the trunk of the vefl'el. With refpeft to the 

 into the belly with a portion of the yolk-bag, as before men- 'i^turc of the tubes on the fides of the valves, he found it 

 tioned. Maitre Jan Hates that he found about this period difficult to pronounce with certainty. By examination with 

 the tympanum and the labyrinth of the car hard, and nearly of a ftrong lens he perceived that there were fome real tubes 

 their full fize. All the boTus have acquired ofFeous matter "P°" '^^ 



green, 



and 



their full fize. All the bones have acquired 

 and confiderable hardnefs. 



The lilc contained in the gall-bag is an intenfe 

 gives that bag a blue colour. 



The end of the lijth day, or 4J6 hours, the air-cell ex- 

 tends round one-half of the cavity of the egg. 



The amnios is in fome inftances found to be ruptured by 

 the bill of the chick. 



According to Haller, the chick begins to cry about this 

 period. Harvey and Langly alfo heard the piping of tlie 

 chick at this date. Some other authors have not noticed 

 the chick to cry until tlie twentieth day, which agrees witli 

 our obfervations. Still, however, the time at which the 

 chick begins to cry is fubjedl to vary, according to the de- 

 gree of heat to which it is expofed. Thus, in an egg from 

 which no found ifl'ues while it is in the nell, if placed upon 

 warm water the piping of the chick will be heard. 



The chorion begins to appear a little faded, the circulation 

 of blood upon the membrane being carried on more fiug- 

 gifhly. This change feems to be preparatory to the deftruc- 

 tion of that membrane which is about to happen. 



More than two-thirds of the yolk-bag and its contents 

 have been received into the abdomen. If that cavity be 

 opened, it will be feen that the bag is pretFed in aniongft the 

 different vifcera, to which its figure is capable of being per- 

 fectly accommodated in confequpnce of its folds and lo- 

 bules. 



The -white is reduced to a few irregular-fhaped knots, 

 which generally contain fome calcareous matter that appeai 



fides of the valves, which afcended in a ferpe 

 manner; but thofe which are the moll numerous, and which 

 f(n-m the net-work on the breadth of the valves, were not 

 determined to be tubes, although they are moft probably fo, 

 as they appear cylindric under every point of view, and are 

 continuous with the tubes of the edge. 



The fifth day, the veffels of the edge appeared all unco- 

 vered : thefe veffels preferved fome breadth, and a round 

 figure at the edge, and an undulating courfe. It was more 

 eafy to diftinguifh the real veffels which defcend from the 

 edge in a ferpentine manner, and traverfe obliquely the 

 breadth of the membrane, in order to return into the plain 

 between the valves. Haller alfo faw very evidently fome 

 branches whicli proceed from the veffels between the valves, 

 and which afcend in a ferpentine manner by the fide of the 

 valves, and communicate with the trunk which runs along 

 the edge. The remainder of the valve was become an open 

 net-work of extreme beauty. 



The fixth day many of the valves had difappeared, and 

 others prefented only a plaited border, like a mefentery, from 

 which the intefiines had been removed. Mem. r. p. 379. 



The chick at the prcfcnt date is about the fize that it is 

 immediately after exclufion from the fhell. It lies coiled 

 round with its head under the right wing. 



The blood-veJlels in the interior of the chick have attained 

 more of their proper fi/e in proportion to the parts they 

 fupply. The left branch of the aorta, however, which 

 forms the principal umbilical artery, is lUU nearly equal in 

 magnitude to the aorta itfelf. 



Haller obferved at this period the vena cava beat between 



to remain after all the liquid parts of the albumen have been 



removed. The knots are compofed of the chalaz:e, and the the lobes of the liver 



membrane of the white compreffed together. The end of the 20th day, or 480 hours, the Jhell is ex- 



Maitro Jan very readily fucceeded in diftending the yolk- tremely dry, and very fragile, which is occafioned by the 

 bag and the duilus viteUo-intcflinalis, bv blowing air into more extenfive detachment of the membrane which is imme 

 the oefophagus, bat did not yet perceive that any of the diately under it. The brittlenefs of the (hell is a very con- 

 yolk had p.iffed through the du£t into the intelline. vcnicnt circumllance at this period, when it is about to be 



Haller defcribes at this date the effeits produced upon tlie ruptured by the eflbrts ol the chick, 

 valvular ftructure of the yolk-bag by maceration in water It is ufual at the prefcnt date to find the greaternumber of 



for fome days. 



the eggs in a hen's nefl cracked or chipped near tlie gr 



Having firft wafhcd the fac containing the yoik with fe- end. This is attributed by common people to the parent, who 



veral waters, he found the edges of the valves covered with is fuppofed, by a particular inftinft, to know the proper pe- 



the vermiform tubes before defcribed, which ieparatc and riod for the liberation of the young cluck. Malpighi likewife 



Vol. XIX. E fuppofed 



