ARTHROPODA — ARACHNIDS. 
87 
body-segments fused under a single shield. On its upper 
surface is a pair of small simple eyes (ocelli) near the centre, Between 
while a nair of compound, facetted eyes is placed on or near Wall-cases 
the front margin. On its under surface is the mouth, with a 
plate in front of it and another behind it, as in the trilobites. 
In front of tlie month is a pair of limbs (i), differing gi'eatly 
