M. Prevost on the. Generation of 4nimals. 337 



process of the growth of; the foetus of the Mtilus gohio is exhi- 

 bited in a plate containing magnified figures. 



The fourth memoir is a notice on the circulation of the foetus 

 in ruminating animals. From the difference of diameter between 

 the globules of blood in the foetus and those of the blood of the 

 mother, M. Prevost infers, that among the Mammalia there ex- 

 ists no direct communication between the sanguiferous systems 

 of the embryo and the mother. His inference was confirmed 

 by the following observations. The uterus of a sheep newly 

 killed, and in which gestation had not gone far, was brought 

 to him. He opened it in warm water, and withdrew the foetus 

 with its membranes, which was the more easily done, that at 

 this period the chorion presented no adherence to the uterus. 

 He perceived that the heart of the foetus was still beating, and, 

 profiting by the occasion to examine the circulation, he placed 

 the ovum with precaution upon a heated square of glass, and 

 exposed it to the rays of a summer sun. The heat and the 

 contact of the air rapidly quickening the motions of the heart, 

 M. Prevost with a microscope followed attentively the motion 

 of the blood in the vessels. These he found to branch out 

 into a very minute series on certain points of the chorion, des- 

 tined to form at a future period the foetal portion of the coty- 

 ledon or placenta of ruminating animals. After being thus 

 subdivided, the vessels were reunited by innumerable anasto- 

 moses, and formed finally one or two veins, which carried to 

 the foetus the blood which had circulated in the vessels first 

 noticed. This foetal portion of the cotyledon in the rudimen- 

 tary state possessed none of those prolongations or papillae 

 which afterwards are found to be connected with corresponding 

 depressions in the maternal placenta. The transparency of the 

 objects permitted him distinctly to perceive that the minute 

 radiations were prolonged without interruption from the inter- 

 mediate tissue into the minute returning veins. No hemor- 

 rhage in any part took place from the separation of the ovum 

 from the uterus. If the cotyledon was pressed, some drops 

 of a white liquid exuded from the small sieve-like cavities. _ 

 This fluid does not naturally appear till a more advanced pe- 

 riod of gestation ; it is in great quantity ; and it is designed, 

 in M. Prevost's opinion, to nourish the foetus. It is secreted 



NEW SERIES. VOL. I. NO. II. OCTOBER 1829. Y 



