418 THE PHYSIOLOGY OF REPRODUCTION 



secrete, the epithelium of the more superficial parts proliferates, 

 and then degenerates and loses its secretory function ; finally 

 it forms a symplasma which plugs up the lumen of the 

 glands. 



On the other hand, the amount of nutriment furnished 

 directly from the maternal blood is increased. It is found in 

 the extravasations already described, and as individual blood 

 corpuscles and droplets of haemoglobin or its derivatives in the 

 lumina of glands. Leucocytes are found during the whole of 

 pregnancy, but in less abundance than in the sheep. They do 

 not act to the same extent as store-houses of fat, but some of 

 them, the siderophores, contain granules which give an iron 

 reaction. In the course of pregnancy they disappear com- 

 paratively early, with the exception of a few in the deep 

 glandular layer. Fat is found in the intact epithelium of the 

 glands, and in the lumen after desquamation of the cells. It 

 appears in the epithelium partly as an infiltration and partly as 

 a degeneration product of the protoplasm. 



In the Carnivora, the fcetal ectoderm of the zonular band 

 of attachment attacks the uterine mucosa more strongly than 

 in the Ungulata. As a result, the maternal tissues, with the 

 exception of the septa containing the placental vessels, disappear 

 down to the middle of the spongy layer, and the tissue which is 

 destroyed serves as pabulum for the developing embryo. Van 

 der Brock l suggests that the general oedema of the uterine 

 mucosa may lead, as elsewhere, to its malnutrition and de- 

 generation, and thus it may fall an easy prey to the trophoblast. 

 Others maintain that the degeneration is brought about by a 

 trophoblastic influence, perhaps of the nature of an enzyme 

 action. The result is a transformation of all the elements to a 

 symplasma. In the cat the connective tissue cells may form 

 large decidual cells before their final destruction. 



As in the Indeciduates, there is strong histological evidence 

 that the trophoblast is actively phagocytic, and takes up, as it 

 meets them, the constituents of the prochorion, and later the 

 degenerated tissues and extra vasated blood. In the neighbour- 

 hood of the extravasations active absorption is indicated by the 



1 Van der Brock, "Die EihiiUen und die Placenta von Phoca vitulina," 

 Petrus Camper, D. ii. Quoted by Kolster (Ergebn. d. Anat., vol. xvi., 1906). 



