FCETAL NUTRITION: THE PLACENTA 445 



opinion that the epithelium disappears, and the syncytium is formed 

 by the uterine connective tissue. But it is now generally recognised 

 that the syncytium is trophoblastic. It has been proved by Strahl 

 himself, and by Duval, that many of the villi obtain attachment at 

 parts of the surface where there are no gland openings or crypts, 

 and penetrate into the substance of the rnucosa. Before the dis- 

 appearance of the epithelium, the cells lose their outlines and form 

 a homogeneous mass of protoplasm with fragmented nuclei. This 

 degenerated tissue ought not, as Bonnet l emphasised, to be known 

 as syncytium, which represents an active protoplasmic condition (see 

 p. 398). The name which he suggested, symplasma, is very con- 

 venient and is used here. It is not only the surface epithelium 

 which forms a symplasma. The glandular epithelium, the connective 

 tissue cells, and extravasated blood may also give rise to a symplasma 



FIG. 123. Ovum with zonary band of villi. (From Hertwig's Entwicklungs- 

 geschichte des Menschen und der Wirbelthiere, by permission of Gustav 

 Fischer.) 



which may be designated glandular, connective tissue, and hcematogenous 

 respectively. All are formed to a large extent in the placenta of 

 Carnivores, and their resemblance to the trophoblastic syncytium 

 has led to much confusion. 



After the destruction of the epithelium, the villi penetrate into 

 the deeper tissues of the mucosa by gradually absorbing the sym- 

 plasmata, and branch to form secondary and tertiary villi. When 

 the ectoderm reaches the capillary layer, it sends out protoplasmic 

 processes which encircle the dilated vessels. The trophoblast on 

 the sides of the villi becomes syncytial, but retains its cellular 

 character at the tips. Internally the villi contain vascular cores of 

 mesoblast. Hence is formed the angioplasmode of Duval a con- 

 tinuous layer of foetal vascular villi, clad with syncytium, penetrating 

 everywhere into the capillary layer, and leading to a disappearance of 

 all the maternal tissues except the vessels (Fig. 124). By the 

 .epithelial arcades at the tips, the layer of villi rests on the sheet 



1 Bonnet, " Ueber Syncytien, Plasmodien und Symplasma, etc.," Monatsschr. 

 f. Oeburtsh. u. Gynak., vol. xviii., 1903. 



