448 THE PHYSIOLOGY OF REPRODUCTION 



not in the completed placenta. In the otter and badger the effusion 

 takes the form of a large blood-pouch, filled with a great variety of 

 blood derivatives. In the ferret the conditions are similar ; the main 

 effusion occurs at the anti-mesometrial border of the uterus, and 

 divides the zone into two lateral discs. According to Robinson, it 

 lifts the trophoblast from the decidua, and forces it in the form of 

 irregular pouches towards the interior of the ovum. Strahl and 

 Bonnet also state that the blood is effused between the mucosa and 

 the blastodermic vesicle, and thus is contained in spaces whose walls 

 are maternal on the one side and foetal on the other. According to 

 Duval the blood-spaces are entirely lined by trophoblast, and with 

 the advance of the villi other and larger haemorrhages occur, 

 coalescing to form the green border and islands. In either case the 

 trophoblast is in direct contact with maternal blood. There the wall 

 of the blastodermic vesicle is avillous but strongly folded, the ends of 

 the ectodermal cells are expanded like clubs, and their protoplasm 

 becomes coarsely reticular. Into the meshes the constituents of the 

 green pulpy mass, unaltered erythrocytes and haemoglobin or its 

 derivatives, are absorbed by phagocytosis. 



From the preceding account, it is clear that certain resemblances 

 and certain differences exist between Carnivora and Ungulata in the 

 composition of the embryotrophe. The most notable difference hi 

 the zonary placenta is the absence of the large amount of milky fluid 

 which arises in the sheep from the glandular secretion and the 

 transudation of lymph. In Carnivora the gland secretion is less 

 important. Though the deep parts of the glands which lie in the 

 glandular layer may 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 extravasa- 

 tions 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 comparatively 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 foetal ectoderm of the zonular band of 



