1906.] PLACENTA IN UNGULATES. 85 



in the subepithelial tissvie of the Rodent uterus (Mouse and 

 Rabbit), and in the formei^ animal is absorbed and stored by- 

 special trophoblastic glycogenic cells in much the same fashion as 

 by the amniotic bodies of the Ungulata. 



The glycogen secreted by the Ungulate uterus is, however, not 

 nearly sufficient to account for the very large quantity found in 

 the body and adnexa of the fcetus ; most of this must be formed 

 synthetically. 



Finally, I have ventured to give figui-es (text-figs. 31 a, b) of 

 the stratified epithelium of the amniotic bodies. The lowest layer 

 is cubical ; this is succeeded by sheets of polyhedral cells, which 

 become larger and flatter towards the surface. 



All the cells, even the cubical cells of the bottom layer, are 

 vacuolated Avith glycogen. The vacuoles are separated by ex- 

 cessively delicate walls ; these may break down and the cell thus 

 become converted into a bag containing but one large mass of 

 glycogen. In older stages, when the glycogen is used up, the cells 

 become flattened and the nuclei stain faintly. 



Text-figs. 31 c-e show the glycogenesis in the epithelivim of the 

 allantoic stalk, and in the connective-tissue cells of the coats of 

 the umbilical blood-vessels. 



5. The Pigment of the Placenta. 



Kolster has very rightly emphasised the great physiological 

 importance of the ingestion of exti-avasated maternal red cor- 

 puscles by trophoblastic cells. The heemoglobin so taken up is 

 digested and split into an iron-containing and an iron-free 

 constituent. The former is carried away by the fcetal blood-vessels 

 and stored up in large quantities, principally in the liver of the 

 embryo, as a reserve to be used during lactation*, as the milk 

 contains little or no iron. The latter is deposited in the cells as 

 a pigment, occurring in such quantities as to give — especially in 

 the later stages of gestation — a deep brown colour to the foetal 

 cotyledons. 



The extravasation, and consequently the ingestion, of blood- 

 corpuscles takes place mainly in the cotyledons ; the haemorrhages 

 occur principally at the summit of the walls separating the 

 primary crypts, and the ti'ophoblastic cells, which are actively 

 concerned in the ingestive process, are the long columnar elements 

 which lie at the bases of the large villi. 



The stages of ingestion and digestion of the blood-corpuscles are 



* Bunge has shown that the percentage of iron in the new-born puppy ("72 per 

 cent, of the ash) is six times as great as that in the dog's milk ("12 per cent.), and 

 further that the proportion of iron in the new-born puppj' is five to nine times that 

 in the adult dog. Of the assimilation of iron bj' the foetus Bunge remarks : " If 

 the bulk of the organic compounds of iron were afforded by the mammary gland, it 

 might become a prey to bacteria in the alimentary canal before it had time to be 

 absorbed. But if it enters the infant organism through the placenta its safety is 

 assured." 



