244 THE APODID^ Part 11 



was, as a sensory limb, richly innervated. The eyes 

 also seem to have been highly developed. 



The following four limbs, which correspond with 

 the second antennae, mandibles, and first and second 

 maxillae of Apus and of the other Crustacea, resemble 

 the ordinary Trilobite limbs. Their dorsal branches 

 probably functioned as palps or tasters, as perhaps 

 was the case in the Trilobites, or perhaps as limbs 

 for holding prey brought by the chelae in the right 

 position for the mandibles to crush, just as the fore 

 legs of a caterpillar hold the leaf in the best position 

 for the jaws to work upon it, only in this latter case, 

 of course, the jaws lie in front of the legs instead of 

 behind them. 



The masticatory ridges of these four limbs probably 

 functioned as maxillae, but, as already mentioned, lying 

 anteriorly to the mandibles, not posteriorly as in all 

 modern Crustacea. 



The first trunk limbs have already been mentioned 

 as large rowing limbs. It was in one sense natural 

 that the powerful limb should also develop a powerful 

 ventral parapodium functional as a jaw, but the union 

 of the two functions is not easily comprehensible, and 

 we are more than ever inclined to think that the two 

 may have been separately articulated with the body. 



The limbs of Eurypterus differ markedly from those 

 of Pterygotus. In front of the large rowing limb, i.c. 

 the first trunk limb, we have only four limbs visible in 

 the figure, all of these appearing, to be sensory, and 

 thus affording a striking contrast to the head limbs of 

 Pterygotus, none of which appear, at first sight, to be 



