487 
the temperature to 5° C. At the latter temperature quite a few eggs at the 
end of six hours of incubation withstood removal and cooling to 5° C. for 
ten days and continued developing when returned to the incubator. Other 
eggs removed after 37 to 42 hours of incubation and cooled for three days 
continued to develop upon reincubation. 
‘ If incubation is interrupted and followed by cooling during the first 
24 to 36 hours, malformations usually occur. When the incubation is inter- 
rupted at six hours, malformations do not occur unless the eggs are kept out 
6 to 16 days. If incubated 7 to 19 hours and cooled 5 to 13 days malfor- 
mations occur. Interruptions after 72 hours cause no malformations. Malfor- 
mations are more frequent in embryos up to 42 hours incubation after having 
been cooled to 5° C. The results of these experiments are quite interesting. 
When the egg is cooled, the yolk rises to the shell and sinks again when 
the egg is warmed. Warynskr ‘7 holds that if the pressure of the embryonic 
area against the shell be sufficiently great, a disturbance will be caused 
in the area leading to malformation. KAESTNER obtained the same results by 
a momentarily strong pressure upon the exposed embryonic area with the 
handle of a scalpel. If the eggs be placed blunt end upwards while cooling 
and then returned to the incubator for a short time in the same position and 
allowed to develop, no malformations occur and the chicks hatched are normal. 
This is due to the fact that the embryonic area impinges upon the yielding 
white membrane of the air chamber and as this membrane thus exerts but 
slight pressure, no disturbances or adhesions are produced in the embryonic 
area during cooling as occurs when cooled in the horizontal position. 
The malformations resulting from these experiments were of various 
kinds. Most of these malformed embryos die shortly after incubation except 
the omphalocephalia which continue to develop to later stages. 
The variety of malformations cannot be predicted. Only one can be 
produced with (near) certainty by incubating 6—12 hours and cooling for 
90—120 hours. Under these conditions malformations of the cephalic end of 
the vascular system occurs, but this does not check continued development. 
This is of interest as Ravn*® states that the proamnion becomes greatly 
enlarged recognized by the fact that the two vitelline veins diverge at an 
obtuse angle. As a result the cephalic amniotic fold is retarded so that in 
extreme cases it is so restricted at the time of its appearance that it is too 
small for the developing head thereby causing constriction of the head. 
When incubation is interrupted late (20 days) and the egg cooled for 
24 hours, KAEsTNER noted a defective resorption of the yolk-sack when the 
chick was hatched at the 22nd day, a complete yolk-sack protruding from 
abdominal cavity. Another egg cooled 6 hours on the 19th day, hatched 
with a closed navel, but died at the 10th day and postmortem revealed a 
tumor 2'/, cm. in diameter that was found to be the yolk-sack filled with 
condensed yolk. The apparent reason that malformations do not occur after 
the middle of the second day of incubation, is that the amniotic folds are 
formed covering the head and so protect it. For this reason For, and Kastner 
do not agree with DarEsteE *° who maintained that amniotic pressure has most 
to do with malformations in the chick. 
