155 



lastly, from this time onwards till the moment of parturition. 



Before it comes to be fixed in ifcs depression in the uterine 

 wall the embryo^ floats freely in the lumen of the uterus, into 

 which is poured the secretion of the epithelium and glands. 



Besides the coagulable, presumably proteid-containing fluid 

 which the glands secrete, they also secrete fat. Both proteids and 

 fat are known to be secreted by the uterus in other Mammals 

 (uterine milk in Ungulata, albumen in Lepus and Talpa for 

 example). I have not found fat, as such, in the lumen of the 

 uterus before the degeneration of the epithelium, not, that is to 

 say, in the period before the fixation of the embryo; and it has 

 occurred to me that, by the action of a fat-splitting ferment in 

 the cells of the epithelium and glands, the fat might be dis- 

 charged into the lumen as a soap. However that may be the 

 trophoblast of the embryo at this time certainly contaius fat 

 globules. 



In the next period the trophoblast continues to absorb fat, the 

 fat in this case being set free by the degeneration of the uterine 

 epithelium. Although the trophoblastic cells are soon to become, 

 even if they already are not phagocytic, I do not suppose that 

 the fat is ingested as such but rather absorbed, as in the intes- 

 tine, in the form of a soap, and reconverted into fat within the 

 cells themselves. Fat globules are also to be found in other 

 cells of the embryo, notably in the proximal epithelium of the 

 yolk-sac. 



During the present period the embryo must be entirely depen- 

 dent on its trophoblast; the megalokaryocytes, as well as the 

 cells of the trophoblast which are not so transformed, I have 

 shown to be phagocytic. The cellular débris and blood corpuscles 

 which are so ingested, undergo a process of intra-cellular digestion, 

 as is shown by the presence of fat and other granules, which 

 latter I have compared to the granules in the endosarc of an 

 actively feeding protozoon. The products of their metabolism 

 would then be handed on to the cells of the embryo. In their 

 large size the megalokaryocytes resem ble osteoclasts, while the 



