368 C. M. Child 
the same position and form in the five groups indicates that it is 
not merely some chance irregularity of growth, but rather a struc- 
ture correlated in some definite way with the others. In the first 
place it indicates the formation of a region of growth in the middle 
of the disc. In normal and regulating individuals such a region 
of growth forms at this point and gives rise to the cesophagus. It 
JO 
Fics. 28-30 
seems not improbable that this outgrowth may represent the 
cesophageal region, which is evaginated instead of invaginated. 
But in no case could any trace of an opening be found at the tip 
of the outgrowth, though such an opening might have been formed 
if the specimen had lived longer and undergone further growth. 
If this outgrowth does represent an evaginated cesophagus certain 
factors existing in this case must determine the peculiar method 
