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II. — On the vascular arrangement of the Capillary Vessels of the 

 Allantoid and Vitelline Membranes in the Incubated Egg. By 

 J. Dalrymple, Esq. (See Plate I. figs. 1 & 2). 



Read July 22, 1840. 



Some weeks since I was induced to attempt the injection of the in- 

 cubated egg, with a view, if possible, of determining the type of ar- 

 rangement in the capillary vessels of the different membranes proper 

 to the embryo. Having procured some eggs from the Eccaleobion at 

 the 19th day of the artificial process of incubation, I placed a small 

 pipe in the omphalo-mesenteric vein, and threw in, towards the chick, 

 a minute injection composed of parchment size and vermilion. I had 

 the satisfaction of seeing the bird immediately become red, and, short- 

 ly, the coloured fluid returning by the arteries, the allantois and vitel- 

 line sac became beautifully injected. Having thus succeeded beyond 

 my expectations, I carefully separated the allantois from the mem- 

 brane of the shell, and placed it in water beneath the field of the 

 microscope. 



Many large trunks of a somewhat tortuous character were observed 

 giving off smaller lateral branches, which, frequently subdividing and 

 inosculating, presented a beautiful appearance even to the naked eye. 

 These vessels are constantly seen injected with blood, on opening an 

 egg some few days prior to the completion of the process of incubation. 



It is this vascular membrane to w r hich has been attributed, by nearly 

 all the most celebrated physiologists, the function of respiration dur- 

 ing the embryonic life of the chick : but at various times, and even 

 very recently, doubts have been thrown upon the truth of this theory 

 of the function of the allantois, by reports of eggs hatched in various 

 irrespirable gases, or when the atmosphere has been excluded by 

 various coatings applied to the shell. I was anxious, therefore, to 

 attempt to obtain, by artificial injection, a view of the capillary ar- 

 rangement of these vessels, having been much shaken in my previous 

 belief as to the respiratory nature of this surface by the late ingenious 

 experiments of Mr. Town, published in the Guy's Hospital Reports : 

 — experiments, I must be permitted to say, suggested to that gentleman 

 by the truest principles of inductive reasoning, and executed with 

 a tact and delicacy that do him infinite honor. It has subsequently 

 appeared, however, by the experiments and tests of our President,* 



* Professor Owen. 



