366 THE PHYSIOLOGY OF REPRODUCTION 



But though maternal leucocytes do not pass as such straight 

 into the foetal blood, they may be important in another way. 

 In Ruminants, Bonnet ^ has drawn attention to the enormous 

 number of degenerated leucocytes in the uterine milk, and 

 demonstrated their absorption by the ectoderm, and similar 

 observations have been recorded in Carnivores. In these orders 

 leucocytes undoubtedly form a part of the embryonic nutriment. 

 In the rest of the deciduate Mammals they seem to play a less 

 important part. 



III. The Decidua 



In the uterine mucosa during pregnancy the most noticeable 

 change occurs in the interglandular tissue of discoid placentas, 

 in which decidual cells are formed. Variovis opinions have been 

 held regarding their origin. Langhans, Hennig,^ and others 

 held that they were enlarged and modified leucocytes, but they 

 could not support their theory by direct observation. Overlach ^ 

 and Frommel * described them as modified glandular cells, but 

 there is no doubt that the true origin is, as Creighton ® first 

 suggested, from the interglandular tissue of the mucosa. This 

 consists of connective tissue of an embryonic type, which 

 allows of a rapid transformation of its cellular elements. 

 Masquehn and Swaen ® demonstrated this mode of origin in 

 Rodents, and were supported by Minot, and Hart and Gulland.' 

 Leopold's studies of early ova showed that the same origin 

 was most probable in Man, and Peters described in the mucosa 

 next the ovum connective tissue cells undergoing a decidual 

 transformation. Their fiist appearance in the superficial layers 



' Bonnet, " ^ber Enabryotrophe," Deuts. med. Woch., 1899. 



' Hennig, Stuiien iiher den Bau der menachlichen Placenta, <fcc.,' Leipzig, 

 1872. 



3 Overlacb, "Die pseudomenstruirende Mucosa Uteri naoh akuter Phos- 

 phorvergiftung," Arch. f. mikr. Anat., vol. xxxv., 1885. 



* Frommel, " Beitrag zur Frage der Wachstumsrichtung der Placenta," 

 Zeits. f. Geburtsh. u. Oynak., vol. xxxvl. 



' CreigBton, " The Formation of the Placenta in the Guinea-pig," Joitr. 

 of Anat. and Phys., vol. xii., 1878. 



^ Masquelin and Swaen, " Premieres phases du d^veloppement du placenta 

 chez le lapin," Bull, de I' Acad. roy. de Belg., 1879. 



' Hart and Gulland, " On the Structure of the Human Placenta," &o., 

 Labor. Rep., Roy. Coll. of Phys., Edinburgh, vol. iv., 1892. 



