338 Mr John Adie's Account of a 



by the surface of the cotyledon, and taken up by the vessels of 

 the membrane of the chorion, which is prolonged in the form 

 of papillae into the cavities of the cotyledon, as mentioned 

 above. 



The necessary consequence of what he has observed leads 

 M. Prevost to conclude, that the ovum is an isolated body in 

 the uterus, and that the uterus secretes a substance which is 

 absorbed by the vessels of the foetus, and contributes to its 

 growth : And he goes on to show, by analogous facts, the near 

 resemblance of the manner in which the embryo is developed 

 among Mammalia and birds. The difference in this respect 

 between these two classes of animals consists in this, 1. That 

 the ovary in the Mammalia does not contribute in any way to 

 nourish the embryo. 2. That the uterus solely performs this 

 function, and accomplishes it not at once, but by degrees, 

 through the medium of the maternal placenta. " Adopting this 

 view, we may regard," says M. Prevost, " the corpora lutea of 

 the ovary in the Mammalia as analogous to the yolk in the eggs 

 of birds,^r,s^, because the corjms luteum is secreted by the same 

 series of vessels which secrete the yolk in oviparous animals ; 

 and, secondly^ because the colouring matter which tinges the 

 corpus luteum in the cow, comports itself with re-agents pre- 

 cisely as the colouring matter of the yolk of an egg.'''' 



Art. XX. — Account of amew Cistern for Barometers. By. 

 Mr John Adie. Communicated by the Author. 

 Dear Sir, 

 I take the liberty of sending you the description of a new 

 construction of cistern for a barometer, which I conceive has 

 considerable advantages over those generally in use; and it 

 will give me much pleasure should you think it worthy of a 

 place in your very valuable Journal of Science. 



The construction is shown in Plate III. Fig. 10, where C is 

 a cylindrical cistern of cast iron, made as thin and light as 

 possible ; into which A, the barometer, and B, the siphon tubes, 

 are screwed. The iron is coated inside and out with a strong 

 varnish to prevent its rusting. D is a cylindrical plunger of glass 

 moved by the screw F, and passing through the collar of leather 



