STRUCTURE OF EGGS. 109 



with the pouch) quits the egg-organ, and is laid hold 

 of by the broad extremity of the egg-tube. After 

 this escape of the egg, the pouch or sac which con- 

 tained it very much resembles the bivalve capsule 

 of plants ; and being now no longer of any use, it 

 diminishes rapidly in size, and at last altogether dis- 

 appears. 



When the egg falls into the egg-tube, it is covered 

 only by a single membrane, exceedingly thin, and 

 resembling the scarf-skin in its nature ; but soon 

 after it falls, it exhibits a second covering, a little 

 thicker than the first. This is produced by the irri- 

 tation arising from the presence of the egg exciting 

 the vessels on the interior of the tube to throw out 

 lymph, which by coagulating forms a coating around 

 the egg. This coating juts out into small knobs at 

 each end, which terminate in the feculent extremity 

 of the white, and are termed chalazes, the envelope 

 itself being termed the yolk-bag, or chalaziferous 

 membrane. M. Leveille supposes the chalazes to be 

 absorbing vessels destined to take up the white and 

 mix it with the yolk during incubation * ; but this is 

 only a conjecture. 



Having been thus furnished with this second 

 membrane, the egg advances farther along the egg- 

 tube, and becomes deeply imbedded in the white 

 (albumen) that fills the tube. The white being 

 thence formed, the egg makes a still farther advance ; 

 arid again is furnished from the secreting vessels of 

 the tube with another envelope, constituting the first 

 layer of the membrane of shell which surrounds the 

 white and attaches itself to the loose extremities of 

 the two chalazes. Over this, another covering is 

 formed, being the second layer of the membrane of 

 the shell ; and by this time the egg has got beyond 

 half the egg-tube. In its passage through the re- 

 * Nutrition des Foetus, 8vo. Paris, 1799. 



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