426 THE PHYSIOLOGY OF REPRODUCTION 



gular blood extravasations are formed, and later surrounded by 

 trophoblast'. In the deeper layers of the intermediary region, 

 according to Chipman, capillary haemorrhages occur more 

 slowly, and give rise to a fibrinous tissue with red and white 

 blood corpuscles scattered through it. This is similar to the 

 hsematogenous symplasma of Bonnet. It gradually increases in 

 amount, and extends to the region of the uterine sinuses. 



While the foetal ectoderm advances along the vessels, it 

 remains stationary at the non-vascular parts. Hence there is 

 an interlocking of maternal and foetal tissues, and peninsulse of 

 multinucleate cells come to lie between the projections of the 

 trophoblast. At the same time the intermediary region de- 

 creases in thickness, and the ectoderm reaches the superficial 

 sinuses of the deeper zone. Here the uninucleate decidual cells 

 again become multinucleate, apparently at the expense of the 

 blood symplasma, in the same manner as formerly at the ex- 

 pense of the glandular symplasma. The sinuses enlarge, and 

 their walls proliferate into several layers of degenerated cells, 

 which after mid-term are gradually replaced by lamime of 

 fibrin. 



At a later period the intermediary zone still further de- 

 creases in thickness, and the multinucleate cells gradually 

 " melt to form a granular detritus " (Duval). At the end of 

 pregnancy the maternal placenta consists almost entirely of 

 blood and blood symplasma, except for a thin rim of tissue 

 containing blood-sinuses at the zone of separation. The gesta- 

 tion period is thirty days. 



As compared with the placenta of Carnivora, it is obvious 

 that the dilatation of maternal vessels is much more marked in 

 the rabbit, and throughout the placenta the maternal blood is 

 in direct contact with the trophoblast, and not only at the 

 border or round a blood-pouch. The blood is not degenerated 

 to a sufficient extent to exhibit the varieties of pigmentation 

 found in the zonary placenta. Chipman does not state whether 

 the maternal blood circulates in the trophoblastic tubes, but 

 Maximow * says that it does. Similarly Duval says : " The 

 maternal blood circulates from the foetal extremity towards the 



1 Maximow, " Die ersten Entwicklungsstadien der Kaninchenplacenta," 

 Arch./, mikr. Anat., vol. lvi. f 1900. 



