FtETAL NUTRITION: THE PLACENTA 427 



maternal extremity of a lobule " (i.e. the series of tubules de- 

 rived from one tube). According to Masius, 1 " the maternal 

 blood circulates in an ectodermal mass of foetal origin." Herein 

 lies a great difference between the placentae of Rodents and 

 Carnivores or Ungulates. In the sheep the main nutriment is 

 furnished by the glands ; the maternal blood which is in contact 

 with foetal ectoderm is stationary and small in amount, and 

 serves chiefly as a supply of iron ; the exchange of gases takes 

 place through foetal and maternal tissues. In the dog the 

 gland secretion is less important ; the blood is again stationary 

 and restricted to certain situations, and it shows markedly 

 degenerative appearances, but it is greater in amount, and 

 probably furnishes other substances besides iron for the foetus ; 

 in the angioplasmode the maternal blood circulates and here the 

 exchange of gases is effected, but again both maternal and 

 foetal tissues intervene between the two blood-systems. In the 

 rabbit the glandular secretion is still less important after attach- 

 ment, and even the blind ends do not secrete ; throughout the 

 placenta there is normal circulating maternal blood in direct 

 contact with foetal tissues, and it serves both as nutriment and 

 for the exchange of gases. In addition, there are stationary 

 blood extravasations which are engulfed by the trophoblast, but 

 they are subsidiary. Both in the dog and the rabbit there is a 

 marked formation of symplasma which may be connected, as 

 Bonnet suggested for the dog and Maximow for the rabbit, with 

 the slowing of the circulation in the placenta, or may be the 

 result of a trophoblastic influence. 



In the placenta of the rabbit there is one other difference 

 which marks it off from the placenta of Carnivores and links it 

 with Insectivores and Man the connective tissue cells of the 

 mucosa form decidual cells. They assist to an important degree 

 in the preparation of nutriment for the embryo. They exercise 

 a phagocytic action on the neighbouring degenerated maternal 

 tissues, glandular remnants and fibrin, and so attain their 

 greatest development, while at the same time they become 

 store-houses of foetal nutriment. At a later period they de- 

 generate and are absorbed by the trophoblast. Their possible 



1 Masius, " De la Genese du Placenta chcz le Lapin," Arch. de. Biol., 



1889. 



