12 BENNET M. ALLEN 
the vitellus, their diameter being from one-quarter to one-half 
of that of the typical spherules to the vitellus. In the latter 
cells are scattered a few of these smaller yolk spherules; but 
the distinction between the first three divisions of the entoderm 
and the vitellus is a very sharp one. 
TEXT FIGURE A 
In connection with this distinction it is interesting to note 
that the yolk spherules along the cleavage planes that cut through 
the vitellus are found to belong to this small type. It is easy to 
see that if the vitellus were cut up into cells as small as those 
comprising portions 1, 2, and 3 of the entoderm, the thickness 
of the layers of small spherules which form merely a border to 
the large cells would be so great as to comprise the entire body of 
the more finely divided ones. This difference in the size of the 
