J. W. Jenkinson 
445 
And thirdly Boas has urged and brought forward evidence to support his 
contention that the value of the coefficient of correlation between various organs 
diminishes with the diminution of the growth-rate. The data are taken from 
human growth and it appears that the correlation coefficient, like the variability, 
falls after birth, but rises again at about the time of puberty, thereafter decreasing 
once more. 
All these points are of so much general interest and importance that it 
appeared to me to be worth while to endeavour to secure further data for an 
enquiry into the same three problems, and the animal that soon suggested itself 
for the purpose was the trout. 
The trout is eminently suitable since a large number of parts can be readily 
and fairly accurately measured. Moreover there is fortunately, at Bibury in the 
Cotswolds, not more than thirty miles from Oxford, an excellent hatchery owned 
and superintended by Mr A. Severn. Here the young trout live under very 
favourable conditions. The temperature, a most important matter of course, is 
practically constant, for the hatchery is supplied directly from a spring that rises 
on the spot, and the temperature of this spring does not vary more than a degree 
the whole year round. The animals are kept free from disease, are abundantly 
supplied with food and their death-rate is very low; 75°/ 0 > often more, come to 
maturity; 80°/ o of the eggs of the American Rainbow trout hatch out, 90°/ o of 
those of the English brown trout. While of those Rainbow trout that hatch out 
less than 10°/ o as a rule die within three months after hatching. There is 
however far more loss at this period amongst the English fish. 
I accordingly requested Mr Severn to be good enough to supply me with some 
young trout at different stages after hatching, and he has very kindly provided me 
with the necessary material for my work. I should like to take this opportunity 
of thanking him for the trouble he has taken in the matter. I have used the 
American Rainbow trout. All the young whose measurements are given in this 
paper were the offspring of one pair of parents. The fish were spawned and the 
eggs fertilized on February 14th, 1910. In the hatchery they were kept in a 
separate box. The young alevins, with the yolk-sac still large, hatched out about 
the 19th of March ; all did not hatch on the same day. The young were sent in 
to Oxford as follows : 
I. April 4th . . 200 
(These still had the yolk-sac.) 
II. April 18th . . 209 
III. May 2nd . . 198 
IV. May 17 th . . 200 
V. May 31st . . 161 
Immediately on their arrival the fish were killed in formol. 
