FCETAL NUTRITION: THE PLACENTA 449 



allantoic region (Fig. 111). Whether they are maternal or 

 foetal in origin is not yet determined. They persist for a time, 

 but disappear when the endothelial proliferation occurs. Around 

 the groove, the tissue becomes looser by an increase in the size 

 of the newly formed blood-spaces. The endothelium lining 

 them is swollen and deep, and the cells bulge into the lumen. 

 Near the ovum the endothelium proliferates and forms an 

 enormous cell-mass, the trophospongia, 1 interposed between the 

 blastocyst and the unaltered decidua. The trophoblast with 

 its lacunae, and the trophospongia with large blood-sinuses 

 together form the trophosphere, which, along with the maternal 

 blood, represents an effective nutritional arrangement for the 

 embryo before the vitelline or allantoic circulation is estab- 

 lished (Fig. 112). Many of the blood-spaces are ruptured, 

 and the blood pours out into the lacunae of the tropho- 

 blast, and circulates through them before returning into the 

 maternal veins. At this stage the trophospongia is separated 

 from the external decidua by rows of fusiform cells. 



As in the mouse, in which, however, the trophospongia is 

 derived 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 deciduofracts by Hubrecht (Fig. 113). 

 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. These appear- 

 ances indicate an erosion and absorption of the maternal tissue. 

 The deciduofracts are probably derived from the maternal 

 trophospongia (Hubrecht 2 ). After a short life-history they 

 dwindle and are themselves absorbed. 



1 " The trophospongia is a maternal cell -proliferation specially intended 

 for the fixation of the blastocyst. It shows a different histological evolution 

 in different genera" (Hubrecht). 



2 Hubrecht now considers that the deciduofracts are of fostal origin, and 

 represent the outermost layer of the trophoblast. See p. 470, footnote. 

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

 (see p. 444), and Bryce and Teacher's of that of Man (see p. 469). 



2F 



