Ciiap. IV. 
MANNER OF DEVELOPMENT. 
117 
their lesser height. This shortness of the arms is 
apparently due to their greater use, and is an un- 
expected result ; but sailors chiefly use their arms in 
pulling and not in supporting weights. The girth of 
the neck and the depth of the instep are greater, whilst 
the circumference of the chest, waist, and hips is less in 
sailors than in soldiers. 
Whether the several foregoing modifications w T ould 
become hereditary, if the same habits of life were fol- 
lowed during many generations, is not known, but is 
probable. Rengger 22 attributes the thin legs and thick 
arms of the Payaguas Indians to successive generations 
having passed nearly their whole lives in canoes, with 
their lower extremities motionless. Other writers have 
come to a similar conclusion in other analogous cases. 
According to Cranz , 23 who lived for a long time with the 
Esquimaux, “ the natives believe that ingenuity and 
“ dexterity in seal-catching (their highest art and virtue) 
“ is hereditary ; there is really something in it, for the 
“ son of a celebrated seal-catcher will distinguish him- 
“ self though he lost his father in childhood.” But in 
this case it is mental aptitude, quite as much as bodily 
structure, which appears to be inherited. It is asserted 
that the hands of English labourers are at birth larger 
than those of the gentry , 24 From the correlation which 
exists, at least in some cases , 25 between the development 
of the extremities and of the jaws, it is possible that 
in those classes which do not labour much with their 
hands and feet, the jaws would be reduced in size from 
this cause. That they are generally smaller in refined 
and civilised men than in hard-working men or savages, 
22 * Saugethiere von Paraguay,’ 1830, s. 4. 
23 ‘ History of Greenland,’ Eng. translat. 1767, vol. i. p. 230. 
24 ‘ Intermarriage.’ By Alex. Walker, 1838, p. 377. 
25 4 The Variation of Animals under Domestication,’ vol. i. p. 173. 
