458 OSCAR RIDDLE 
water it was easy to measure the distance between the innermost 
borders of two such rings of Sudan, and thus to identify this 
amount of growth with the time which was known to have inter- 
vened between the two feedings. 
Having thus discovered a method! (described in detail by me 
elsewhere, ’10) of measuring the rate and time of growth of ova, 
many data were collected on this point; the distance between the 
normal strata (layers of white and yellow yolk) of the egg was 
carefully measured; later the problems and considerations grow- 
ing out of the results were further followed up. We give here the 
following short statement of the observations and conclusions: 
The radius of the hen’s egg increases during the last few days of 
its growth by about 2.0 mm. per twenty-four hours. The thick- 
ness of a layer of white yolk and a layer of yellow yolk taken to- 
gether is usually about 2.0 mm. Our conclusion is that in the 
fowl a layer of white and another of yellow yolk are laid down 
each twenty-four hours. Other facts at hand indicate that the 
yellow yolk is laid down under the best nutritive conditions, 
while the white yolk is a sort of growth-mark left by poorer nu- 
tritive conditions. 
THE RATE OF GROWTH OF THE OVUM OF THE COMMON FOWL 
1. Ova of more than 6.0 mm. in diameter 
Table 1, section A, and plates 1 and 2 have been prepared to 
show the rate of growth of the larger ova as this is indicated by 
the Sudan method. The reader is referred to the table and plates 
in order to learn the kind of evidence on which the first conclu- 
sion is based. The amount of this evidence could be increased 
several times. It will be seen that the radius of the larger ova 
contained in the ovary of a fowl may increase by rather more than 
2. mm. during twenty-four hours; also that this rate of growth 
is quite variable and may often fall to one-half the above amount. 
Other data in our possession show that this rate not only varies 
for the eggs of different ovaries, but for different eggs of the same 
1 First announcement of the method, and of some of the present results, Riddle 
(07). 
