Text-pig. 5. 
ps. 
A represents a coniiiosition of two stages in the development of 
1 lie egg of a sparrow, that is to say, the “liquefaction of the 
yolk ’’ and the enclosure of the yolk liy the epiblast are supposed 
to have taken place several hours earlier than is the case. B 
represents the blastocyst of Ornithorhynchus after Wilson and 
Hill’s desci'iption. It is suggested that the “ primitive knot ’’ 
of those authors represents the final stage in the “liquefaction ” 
of the meroblastic egg. ep., epiblast ; <jw„ junction of hypo- 
blast with yolk-mass — germinal wall of Balfour; hy., hypoblast; 
kt., “ primitive knot ” in B, and ventral pole of yolk-mass in A; 
up., neural plate ; ps., primitive streak. 
