382 BRADLEY M. PATTEN 
It is during this stage that the individual variability previously 
alluded to is most conspicuous. The more usual configuration 
of the heart is indicated in the figures referred to in the preceding 
paragraph where the loop is shown as rather closely twisted. 
There were not a few embryos, however, in which the heart stood 
out from the body, and was more loosely twisted than in the 
Length in Millimeters. 
Mee as indicated by oie Hi; en 
Fig.2 Graph to show the rate of heart-tube elongation as compared with the 
rate of elongation of pericardial region. The heart length was measured along 
the original middorsal line of the heart tube from the point of bifurcation of the 
aortic roots to the point of convergence of the omphalomesenteric veins. (In the 
older embryos the omphalomesenteric veins have begun to fuse with each other. 
The caudal point for the measurements had, therefore, to be approximated by 
taking it in a given relation to the point of entrance of the ducts of Cuvier.) As 
an index of the length of the pericardial cavity, the distance between these same 
two points was measured along the middorsal iine of the embryo. All of the 
measurements were taken on models made to the same scale of magnification, and 
then converted to actual size. 
