26 PATTEN. MOL ex is 
The eggs left in jars that had been running from ten to fourteen 
weeks were finally treated with hardening fluids, making the 
shape of the embryos very conspicuous. The whole collection 
could then be examined under a dissecting microscope, and 
the most important forms picked out and shelled at once. 
As many embryos were already far advanced (six to nine 
weeks) when placed in the hatching jar, it is evident that the 
remaining abnormal forms were at least ten to fourteen weeks 
old, and some may have been even more than twenty, although 
as seen by the figures, many of them appear to be not more than 
from ten days to two weeks old. Most of the monstrosities are 
apparently the result of retrogressive development, rather than 
of a slow, progressive one. That is, embryos normal in out- 
ward appearance may develop up to stage #, Pl. I. They then 
appear to develop less rapidly, or they may remain for a long 
time practically stationary. But they finally become smaller, 
and by the fusion and complete atrophy of their various organs, 
dwindle to some insignificant remnant which is in turn absorbed. 
Thus a once well-grown embryo may disappear completely, 
leaving a healthy-looking egg behind, but one which consists 
of nothing but yolk. 
I was able to confirm the above statement by selecting a 
dozen or more abnormal embryos and keeping them under 
observation for four or five weeks. It is difficult to make out 
details on living eggs, but enough could be seen to prove 
beyond any doubt that in each case the characteristic abnor- 
mality, such as asymmetry, fusion, or reduction of appendages, 
etc., became more and more marked from day to day, until my 
observations were brought to a close by the complete disap- 
pearance of the embryos, due to the increasing opacity of the 
chorion. On killing and staining these eggs, the embryos 
could be easily distinguished again, in advanced stages of 
degeneration. 
In other instances I have kept large numbers of the residual 
eggs in open dishes, for five or six weeks after they were taken 
from the hatching jars. In such cases, the number of indi- 
viduals showing extreme median fusion, or atrophy, or general 
degeneration, seemed to be greater than before. The number 
