392 
Journal o f Agricultural Research 
Vol. XXIX, No. S' 
anition series (15 culls or malnourished 
chickens from the same source and 
autopsied in similar manner) show the 
same condition. They are all under 179 
days of age and the sum of the weights 
of the right testes is 83.9 per cent of the 
sum of the weights of the left testes. 
There is a great deal of variation in 
the weight of the two testes from the 
same specimen, for in one male (inani¬ 
tion series) they are identical in weight, 
while in the 179-day-old male the right 
testis weighed 1.685 gm. and the left 
weighed 0.894 gm., or 53 per cent of 
the weight of the right testis. Fur¬ 
ther evidence is needed to show whether 
there is any fundamental relation 
between the development of the left 
ovary and this apparently larger left 
testis up to the time of maturity, and 
then the more rapid growth of the 
The rate of growth is very rapid at 
first and gradually decreases as the 
body weight increases. There is no 
significant sex difference, although 
there is, as in other organs, an ap¬ 
parent difference when the brain 
weight is plotted against age (due to 
the sex difference in gross body weight 
in the later periods). 
The percentage weights of the brain 
show no initial rise but a decrease 
from about 2.7 per cent at time of 
hatching. The decrease is rapid at 
first, or until it reaches about 0.6 per 
cent; then there is a very slow decrease 
until it reaches about 0.15 per cent, 
which continues as the percentage 
weight for the brain of the adult 
chicken. Welcker and Brandt {28) find 
that the brain forms 0.24 per cent of 
the body weight in the two male 
Fig. 29.—The heavy line shows growth oi the brain in grams, and the lighter line shows percentage- 
of the net body weight, plotted on gross body weight 
right testis. Riddle {21) finds the 
right testis larger in both young and 
adult pigeons of pure species. In 
hybrids he more frequently finds the 
left testis larger. 
NERVOUS SYSTEM AND SENSE ORGANS 
Brain.— -The same precocious 
growth which characterizes the de¬ 
velopment of the brain, spinal cord, 
and eyeballs in mammals is found in 
the chick. Figure 29 shows the ab¬ 
solute and relative growth of the brain 
plotted against gross body weight. 
The formula is: 
y = X 0 * 22 - 0.00028X -1.36 
from 40-2,600 gm. gross body weight. 
Y represents the weight in grams of 
the brain and X the gross body 
weight in grams. 
chickens. This is but slightly heavier 
than the relative brain weight for the 
older males of the present series. 
Jackson {8) states that in the rat the 
maximum relative weight of the brain 
is attained at seven days, after which 
it decreases. The curve of brain 
weights in the rat, plotted against body 
weight, as shown by Donaldson {3 ), is 
very similar to that of the chick as 
shown in Figure 29. 
Spinal cord. —Figure 30 shows the 
absolute and relative growth of the 
cord, plotted against gross body weight. 
The formula is: 
Y = X 0 - 14 + 0.00074X -1.62 
from 90-2,300 gm. gross body weight. 
Y represents the weight in grams of 
the spinal cord and X is the gross body 
weight in grams. This curve does no 
