FCETAL NUTRITION: THE PLACENTA 479 



frniu ciiuiiective tissue cells instead of eiidothelimn, giant-cells 

 appear. Tliey lie lietween the tropliospoiigia and the fusiform cells, 

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

 mesohlast. In their interior are contained fragments of red blood 

 corpuscles and decidual cells. Hence they are called (Iccidtni- 

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

 fusiform cells form sheaths round some of the endothelium-lined 

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

 decidua is irregular, and the decidual tissue is fil)rillar and reticulate. 



/)/. J)' I) 



t'lo. 140. — Tlie extension of the yolk-sac against tlie lacunar trophoblast in 

 Erinu-ceiif. (Hubrecht). The yolk-sac is to the left of the hgure, and its 

 villi ( Fj.) and blood-vessels {P>. I'.) are well seen. 



7V., Trophoblast ; 7V.s'., trophospongia ; T)f., layer of deciduofiucts ; I)., 

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

 aspect ; <S/7., spaces in trophoblast. 



These ajtjieara.nces indicate an erosion and absurjitinn of the maternal 

 tissue. The deciduofracts ai'e prolialjly deri\'ed from the maternal 

 trophos])ongia (Hul)recht ij. After a slKut life-history they dwindle 

 and are themselves al)sorbed. 



With tlie changes in the mucosa, changes also take }ilace in the 

 tropholilast. After the tliinning ali'eady mentioned, its cells increase 

 in number. They grow in strands, leaving sjiaces lietween them like 

 the meslies (if a net, and in the spaces maternal bloml circulates. In 

 this respect the hedgehog differs from the llodents, in which tlie 



' Hulirecht now considers that the deciduofracts are of fietal origin, and 

 represent the onteiiuost layer of the trophoblast. See p. 406, footnote. Also 

 compare (Iraf v. Spee's description of the ti'ophoblast of the guinea-])ig (see 

 p. 473), and Bryce and Teacher's of that of man (see p. 49fi). 



