

On the Nutrition of the Early Embryo. 165 
probably albumin, comparable to the uterine secretion referred to above; 
when it reaches the water and becomes fertilised, this swells up by absorption, 
‘forming a gelatinous covering. The embryo for nutriment depends upon the 
yolk contained in the ovum before fertilisation, upon the covering of mucus 
and probably albumin, and lastly upon the water in which it hes. In certain 
mammals, as, for example, the rabbit and the mole, a distinct gelatinous 
envelope is described as surrounding the embryo before implantation occurs ; 
this envelope is, I suggest, possibly due to some digestive action of the cells 
of the Trophoblast upon the adjacent medium, producing a form of 
coagulation. 
In a number of mammals during the period of pro-cestrum the secretion of 
uterine glands is supplemented by a pouring-forth of blood, from the simple 
oozing of congested vessels, to that associated with actual exfoliation of 
uterine epithelium. Although there is reason to suppose that the flow of 
blood has practically ceased before the embryo reaches the uterine cavity, 
there is, in all probability, a considerable quantity of blood-serum present, in 
addition to the secretion of the uterine glands. I think it is conceivable, if 
not highly probable, that this process is, in part at least, a preparation on the 
part of the mother for providing a rich pabulum to nourish the embryo until 
such time as it attaches itself to the uterine wall; while, when implantation 
is effected, there is in readiness for the embryo an abundant supply of richest 
nutriment. 
