at other spots and degenerative processes of the uterine glands which occur with the auxiliary of leucocytes spread throughout in the tissue of the placenta, may contribute to the formation of its spongious structure.
8. The circulation of the maternal blood in the placental region chiefly takes place in the following way: arteries of the muscularis uteri penetrate through the spongious tissue of the placental pad to the top of the trophodermal cone and anastomose with the trophodermic bloodlacunes. The arterial maternal blood, abundant in nutritive substances spreads from the centre to the periphery of the placental cushion and gradually looses its oxygen and nutritive elements in the first stages to the fluid of the exocoeloma, in elder stages to the blood of the foetal capillary system. Having absorbed catabolic material from the foetal liquids the maternal blood becomes venous and flows to the anastomosing spaces of the placental pad which agaiu largely communicate with the venous system of the muscularis uteri and in this manner the catabolic products of the foetal circulation are carriecl away.
9. In the investigated stages the allantois and the allantoic circulation play no part whatever in the formation and function of the placenta. The latter arises under the stimulus of the attachment of the germbladder to the uterine mucosa and consists in the above mentioned stages of a foetal trophodermal ingrowth with a thin covering of exocoelomic mesoblast and of the hypertrophied and altered mucosa uteri i. e. of the maternal trophospongia. The foetal capillary system of the placenta belongs to the outer wall of the exocoeloma. Bloodvessels of the area vasculosa or the allantois do not contribute to this system.