178 



(54) has quite recently reviewecl the literature of the hüman 

 placenta. 



a.) Tarsius. 



The placenta is mesometric and discoidal. The changes which 

 take place in the uterus are, firstly, interglandular proliferation 

 of sub-epithelial tissue, and secondly, degeneration of the uterine 

 epitheliuro, a degeneration which advances gradually into the 

 glands. The 'trophospongia', as Hubrecht terms the patch, or 

 patches (as there may be more than one) of proliferated tissue, 

 diminishes and disintegrates as gestation proceeds. It is charact- 

 erized by the disappearance of the endothelium from the blood- 

 vessels, and by the presence of a peculiar 'adenoid' tissue. This 

 tissue is invaded by the trophoblast, which is remarkable for the 

 great development of enornious megalokaryocytes, in which Hu- 

 brecht has described a peculiar process of materual blood formation. 

 Lacunae, containiug maternal blood, are formed in the tropho- 

 blast, and the placenta arises by the vascularisation of this by 

 the capillaries of the allantois. 



b.) Monkeys. 



Turner has described au ad vaneed stage in the placentation of Cer- 

 cocebus cynomolgus. He was able to show that the layer of 'stratified 

 yellowish' cells forniing the 'chorionic epithelium' was continued 

 over the villi, directly bounding the large, anastomosing maternal 

 blood spaces. Turner believed that these blood spaces were derived 

 from enormously dilated maternal capillaries, their cellular lining 

 from 'decidua'. Waldeyer had only one stage in the placentatiou 

 of Tnuus (Macacns) nemestrinus; but he was able to demonstrate 

 a very close similarity between it and the human placenta, parti- 

 cularly in the existence of two layers of cells (or nuclei) in the 

 tissue covering the villi. 



In the two cases just described the placenta is doublé, there 

 being a dorsal and a ventral lobe. 



Selenka has described quite early stages in the placentation of 

 Hylobates (four species), Semnopithecus nasicus, and Cercocebus 

 cynomolgus. 



