DEPARTMENT OF EMBRYOLOGY. 



Ill 



oughly fixed — that is, until a misplaced photograph could be replaced 

 in its group with ease and until all the duplicates fell together. At 

 first some of these duplicates fell two stages apart, showing that not 

 all the stages fixed at first were reliable. Finally, when the arrange- 

 ment had been rendered as satisfactory as possible, we found that 14 

 stages remained, 6 having been eliminated. This arrangement is given 

 in the accompanying table, in which photographs from illustrations in 

 the literature, photographs of embryos in other collections, and those 

 from our own collection are blended. When there are photographs 

 of both sides of an embryo they are counted as one. 



The various stages have been arbitrarily marked with letters of the 

 alphabet, beginning with H, reserving the letters A to G for younger 

 stages like that of Bryce and Teacher. When the mean measurements 

 are taken it is found that Stage H is 2 millimeters long, the embryo 

 increasing a millimeter in length for each stage from H to L and 2 milli- 

 meters from L to U. 



The gap between stages over 25 millimeters long and those measured 

 by Dr. Reicher is yet to be filled in, but the material is at hand for this 

 work and many new data which have been secured will enable us to 

 construct a new and more satisfactory curve of growth for all stages of 

 development. 



