SEA-SCORPIONS 57 
in the sand by a process of wriggling backwards, as certain modern 
crustaceans do, we may consider to be an open question. 
If only Sea-scorpions had not unfortunately died out, how 
interesting it would be to watch them alive, and to see exactly 
what use they would make of their long bodies, tail-flaps, and 
tail-spikes! Were they nocturnal in their habits, wandering 
about by night, and taking their rest by day? Such questions, 
we fear, can never be answered. But their large eyes would have 
been able to collect a great deal of light when the moon and stars 
feebly illumined the shallower waters of the seas of Old Red 
Sandstone times; and so there is nothing to contradict the 
idea. 
Now, one of the many points of interest in Pterygotus and its 
allies is that they somewhat resemble the crab in its young or 
larval state. To a modern naturalist, this fact is important as 
showing that crustacean forms of life have advanced since the 
days of the sea-scorpions. 
Their resemblance to land-scorpions is so close that, if it were 
not for the important fact that scorpions breathe ai7 instead of 
water, and for this purpose are provided with an air-tube (or 
trachea) such as all insects have, they would certainly be removed 
bodily out of the crustacean class, and put into that in which 
scorpions and spiders are placed, viz. the Arachnida. But, in 
spite of this important difference, there are some naturalists in 
favour of such a change. It will thus be seen that our name 
Sea-scorpions is quite permissible. Insects and Crustacea are 
now included in the term Arthropoda. 
Hugh Miller described some curious little round bodies found 
with the remains of the Pterygotus, which it was thought were 
the eggs of these creatures! 
Finally, these extinct crustaceans flourished in those ages of 
