124 RAYMOND PEARL AND MAYNIE R. CURTIS 
4. At the same time, and during the sojourn of the egg in the 
uterus, it receives its outer layer of fluid or thin albumen which 
is by weight 50 to 60 per cent of the total albumen. 
5. This thin albumen is taken in by osmosis through the shell 
membranes already formed. When it enters the egg in this 
way it is much more fluid than the thin albumen of the laid egg. 
The fluid albumen added in this way dissolves some of the denser 
albumen already present, and so brings about the dilution of the 
latter in some degree. At the same time, by this process of dif- 
fusion, the fluid layer is rendered more dense, coming finally 
to the consistency of the thin layer of the laid egg. The thin 
albumen layer, however, does not owe its existence in any sense 
to this dilution factor, but to a definite secretion of a thin albu- 
men by the glands of the isthmus and uterus. 
6. The addition of albumen to the egg is completed only after 
it has been in the uterus from five to seven hours. 
7. Before the acquisition of albumen by the egg is completed 
a fairly considerable amount of shell substance has been deposited 
on the shell membranes. 
8. For the completion of the shell and the laying of the egg from 
twelve to sixteen, or exceptionally even more, hours are required. 
