50 THE HAUNTS OF LIFE 
of nerve-cells and muscle-cells. So is it in the 
star-fish when it surrenders an arm. We 
know that the star-fish does not do this delib- 
erately, for it has a very poorly developed 
nervous system. There is a strand of nerve- 
cells up the middle line of the under surface 
of each arm, and these are united in a pen- 
tagon around the mouth; there are also many 
scattered nerve-cells; but there is no brain, 
not even a single nerve-centre or ganglion. 
The star-fish does not know what it does, but 
it has somehow in its constitution learned in 
the course of time that it is better that one 
member should perish than that the whole life 
should be lost. Brittle-stars give off their 
arms very readily; sea-cucumbers are less po- 
lite, for they discharge their insides in the 
spasms of capture; sea-urchins have nothing 
that they can give away save their spines. We 
see the same sort of surrender when the lizard 
gives off its tail, and we find many cases 
among insects and spiders. It is very marked 
in the harvest-men, who stalk about in the 
evening among the stubble, with legs over 
twenty times the length of their body. The 
self-mutilation (“autotomy”) is also very 
common among Crustaceans. 
