58 EVOLUTION AND DISEASE. 
described to demonstrate the increase in the size of 
dermal organs when disuse and irritation from dirt, &c., 
were combined. A few specimens will now be con- 
sidered in which disuse alone seems responsible for the 
mA 
FIG. 30.—The head of a Parrot with overgrown beak. 
overgrowth. The first is the foot of a two-toed sloth 
which lived for many years in the Zoological Gardens, 
London. One of its claws, or nails, whereby it hangs 
suspended from the branches, is very long and has 
almost described a circle. As far as I could learn, the 
j 
