580 



GENERATION. 



[CHAP. XL. 



The tufts or villi of the chorion, each of which consists of a col- 

 lection of nucleated cells within a delicate membrane, are the 

 organs by which this nutriment is at first absorbed, just as the col- 

 lections of cells at the terminations of the minute divisions of the 

 root of the plant absorb and appropriate nutriment from the soil. 

 Soon, however, vessels are prolonged from the foetus into these tufts, 

 and thenceforward it continues to be nourished from the vascular 

 system of the mother ; but the nutrient matter is still transmitted 

 through the layer of cells covering the vascular maternal surface, 

 as well as that covering the foetal tuft. The precise nature of this 

 arrangement we shall have to consider when discussing the mode 

 of formation of the placenta. 



Upon the subjects discussed in chapter xl., the reader is referred to the 

 following works and monographs, besides those mentioned in the notes : 

 Mr. Newport, "On the Impregnation of the Ovum in Amphibia," Phil. Trans. 

 1851-53 ; Dr. Barry's "Kesearches in Embryology," Series I., II., Ill,, in Phil. 

 Trans., 1838-40 ; Dr. Sharpey, " On the Structure and Functions of the Mem- 

 brana Decidua and the Uterine Glands," in Miiller's Embryology, translated 

 by Dr. Baly ; " De Evolut. Strongyli Auric, et Ascarid. acum. Vivip.," Diss. 

 Inaug. Erlangse, 1841 ; BischofF, "Entwickel. des Hundeeies " ; Vogt, "Unter- 

 suchungen iiber die Entwickelung der Geburtshelfer-krote Solothurn," 1841 ; 

 Goodsir's "Anatomical and Pathological Observations ;" M. Coste, "Comptes 

 Reudus,'' 1847; Dr. Ransom, "On the Impregnation of the Ovum in the 

 Stickleback," in the Proceedings of the Royal Society, vol. vii. No. 7, 1854 ; 

 Leuckart, "On the Micropyle and Minute Structure of the Egg-shell in Insects," 

 Miiller's Archives, 1855. 



