470 THE PHYSIOLOGY OF REPRODUCTION 



cavity, and some wander into the decidua and lie singly or in 

 groups. In their interior degenerating leucocytes are frequently 

 seen. Sobotta also stated that they were festal in origin, and helped 

 to fix the ovum and erode maternal capillaries. More recently 

 Kolster has brought forward evidence from their histological appear- 

 ance that they are transformed decidual cells, and this is strongly 

 supported by Disse's investigations on the field-mouse, 1 in which the 

 giant-cells are found before the ovum has become embedded, and 

 the first to appear are at an appreciable distance beneath the surface 

 epithelium. A second series of smaller size appears later in the 

 lumen and wall of the implantation cavity. Jenkinson also recognised 

 two groups, but assigned to them different origins, fetal in the 

 " Eikammer " and maternal in the decidua. 



All authorities agree that they are phagocytic. The tissue 

 around them undergoes fatty degeneration, and in their interior 

 may be seen remnants of connective tissue and endothelial cells and 

 fat globules. Many capillaries are 'ruptured, and red and white 

 blood corpuscles are also absorbed. Such an absorption of maternal 

 tissue by the giant-cells leads to an increase in the size of the 

 implantation cavity and a thinning of its wall (Disse). In spite of 

 their abundant supply of nutriment, their life-history is short. No 

 cell-divisions occur, and soon they degenerate. Their contents are 

 absorbed by the trophoblast, and their protoplasm shrinks to form 

 a rim around the nucleus. Later still their remnants are also 

 absorbed. 



The allantois in the mouse is a solid mass of mesoderm with no 

 entodermal cavity. Growing out from the posterior end of the 

 embryo, it projects into the extra-embryonic cceloni, and on the 

 eleventh day fuses with the mesoblast of the ectoplacental cone. 

 After this the ovum again becomes spherical. The circulation in 

 the decidua reflexa diminishes, and gradually more and more of the 

 nutriment is conveyed to the embryo by the allantoic vessels. At 

 the same time the allantoic trophoblast increases in thickness, and 

 its lacunae become more numerous and complicated. Into its mass, 

 in which the circulation of maternal blood is now established, the 

 vascular mesoblast projects at intervals, and breaks it up into 

 segments. The glands take no part in the formation of the placenta. 

 Their ducts do not even act as guides to the advancing edge of the 

 trophoblast, as in the rabbit. They are completely displaced by the 

 rapid formation of decidual tissue, and their remnants are absorbed 

 by the giant-cells. Hence the embryotrophe contains no glandular 

 secretion. 



1 Disse, "Die Vergrosserung der Eikammer bei der Feldmaus," Arch. f. mikr. 

 Anat., vol. Ixviii., 1906. 



