FCETAL NUTRITION: THE PLACENTA 413 



not so widely dilated and the connective tissue is more 

 abundant (Fig. 96). 



The embryotrophe at this stage differs from that in Un- 

 gulates. The glandular secretion is less fluid, perhaps because 

 the lymph transudate is less abundant (Kolster *). It sur- 

 rounds the ovum to form the prochorion or " Gallertschicht," 

 and is, according to Bonnet, 2 absorbed by the trophoblast. 



When the prochorion disappears, the foetal ectoderm already 

 has proliferated over a broad zone of the citron-shaped ovum 

 (Fig. 97), to form villosities which attack the surface of the 

 mucosa, and obtain an attachment to it about the twentieth 



FlG. 97- Ovum with zonary band of villi. (From Hertwig's Entwicklunga- 

 geschichte des Menschen und der WirbeUhiere, by permission of Gustav 

 Fischer.) 



day in the dog (Duval 3 ) and the twelfth day in the cat 

 (Robinson). Vascular processes of the allantois grow into the 

 centre of the trophoblastic villi, first over a limited discoid area, 

 and later over the whole zone as the allantois spreads round 

 the wall. Hence the rudimentary placenta is discoid, and the 

 completed placenta zonary. 



In procuring attachment to the uterus many of the villi 

 project into glands and crypts. According to Strahl, 4 the 

 epithelium lining the ducts and the surface of the uterine cavity 



1 Kolster, " Ueber die Zusammensetzung der Embryotrophe der Wir- 

 belthiere," Ergebn. d. Anat., vol. xvi., 1906. 



2 Bonnet, " Ueber das ' Prochorion ' des Hundekeimblase," Anat. Anzeig., 

 vol. xiii., 1897. 



3 Duval, " Le Placenta des Carnassiers," Journ. de VAnat. et de la Phys., 

 1893. 



4 Strahl, " Die histologischen Veranderungen d. Uternsepithel. in d. 

 Raubthierplacenta," Arch.f. Anat. u. Phys., Supplement, 1890. 



