SCORPIONS AND THEIR ANTIQUITY 
To the circumstance that scorpions have their bodies pro- 
tected by a coat of the hard substance technically known 
as chitin, the palaeontologist is indebted for a knowledge 
of their past history and extreme antiquity ; and it is owing 
to the preservation of their remains in the Palaeozoic strata 
of both the Old and New Worlds that we are enabled to 
explain their present geographical distribution, There are 
many other groups of invertebrates that we can have little 
doubt are fully as ancient as scorpions, but which lack a 
hard external investment, and whose past history is accord- 
ingly a blank. One of the most remarkable instances of 
this is afforded by the peculiar creatures termed Peripatus, 
representatives of which are found in countries as remote 
from one another as South Africa, New Zealand, Australia, 
South and Central America, and the West Indies. These 
animals have much the appearance of caterpillars, being 
furnished with a pair of simple antennae, and having a 
large number of short, conical, caterpillar-like feet extend- 
ing along the whole length of the under-surface of the 
body, and each terminating in a pair of hooked claws. 
They breathe by tracheal tubes, after the manner of insects, 
but instead of these tubes opening by a regular series of 
apertures along each side of the body, their apertures are 
scattered in an irregular manner over its whole surface. 
And it has been considered probable that these animals 
368 
