FCETAL NUTRITION: THE PLACENTA 479 



from connective tissue cells instead of endothelium, giant-cells 

 appear. They lie between the trophospongia and the fusiform cells, 

 and they are first seen at the time of the appearance of the embryonic 

 mesoblast. In their interior are contained fragments of red blood 

 corpuscles and decidual cells. Hence they are called deciduo- 

 fracts by Hubrecht (Fig. 140). Externally the circular layers of 

 fusiform cells form sheaths round some of the endothelium-lined 

 vessels. The line of union between the giant-cells and the external 

 decidua is irregular, and the decidual tissue is fibrillar and reticulate. 



TV. TV*. Df. 



**;''& '*?'>.'* >' ** " -' 



*t\f<( V'.UNk 



> V:-v ;'> 



Df. I)' I) 



FIG. 140. The extension of the yolk-sac against the lacunar trophoblast in 

 Erinacctis (Hubrecht). The yolk-sac is to the left of the figure, and its 

 villi ( Vi.) and blood-vessels (/). V.} are well seen. 



TV., Trophoblast ; TV,?., trophospongia ; Df., layer of deciduofracts ; />., 

 decidua, of which the inner layer (//) has assumed a more reticulate 

 aspect ; Sp., spaces in trophoblast. 



These appearances indicate an erosion and absorption of the maternal 

 tissue. The deciduofracts are probably derived from the maternal 

 trophospongia (Hubrecht : ). After a short life-history they dwindle 

 and are themselves absorbed. 



With the changes in the mucosa, changes also take place in the 

 trophoblast. After the thinning already mentioned, its cells increase 

 in number. They grow in strands, leaving spaces between them like 

 the meshes of a net, and in the spaces maternal blood circulates. In 

 this respect the hedgehog differs from the Eodents, in which the 



1 Hubrecht now consider that the deciduofracts are of foetal origin, and 

 represent the outermost layer of the trophoblast. See p. 496, footnote. Also 

 compare Graf v. Spee's description of the trophoblast of the guinea-pig (see 

 p. 473), and Bryce and Teacher's of that of man (see p. 496). 



