506 REIGHARD—MAST. [VoL. XIX. 
lieve that we are justified in saying that the differences be- 
tween Prather’s results and ours are due to the insufficiency of 
the methods used in the preparation of his material. His Fig. 
1 shows that in the material used by him, the egg membranes 
had not been removed from the eggs before preserving them. 
The figure shows also that in this case the membranes had 
shrunken down close against the embryo. The result of 
this is that the tissues of the embryo are pressed together and 
the limits between adjacent tissues are frequently obliterated. 
The hypophysis is not then visible in its early stages, and in 
the stages some time before hatching it is so pressed into the 
entoblast of the dorsal foregut wall as to be scarcely distin- 
guishable. Such a condition is shown in Prather’s Fig. 3. 
At the time of hatching or upon removal of the egg mem- 
branes the pressure from them is, of course, removed, and the 
hypophysis, being no longer pressed into the dorsal foregut 
wall, becomes visible and appears to be differentiated in situ 
out of the entoblast. 
We have tried every feasible method of preserving these 
eggs without shrinkage of the membranes and have not found 
any method hitherto in use that accomplishes this. One of 
us has, however, devised a fluid, consisting of a five per cent 
formalin solution (i. e., containing two per cent of formalde- 
hyde) to which is added two or three per cent of potassium 
bichromate and ten per cent of glacial acetic acid. This fluid 
used for eight hours or longer causes not more than a very 
insignificant shrinkage of the membranes or none at all. It 
is not stable and should be used fresh. Eggs are transferred 
from it to four per cent formalin which is changed until no 
longer discolored by the bichromate, and are then preserved 
permanently in the formalin. The histological results are 
similar to those obtained from Flemming’s or Hermann’s fluids 
and are excellent, as may be judged from the figures of cell 
divisions visible in Fig. 2. In spite of the results obtairied from 
this fluid we have made it a rule, before preserving the eggs, to 
remove the membranes from them in the earliest stages prac- 
ticable. This may be done in the stage represented by Fig. 
