PROS DMA TIC SEGMENTS OF LIMULUS 



?37 



So, also, since Woodward's monograph, Laurie has discovered in 

 Slimonia acuminata a small median pair of chelate appendages 

 exactly corresponding to the chelicerae of Limulus, or of Eurypterus, 

 or of Scorpio. We may, therefore, take it for granted that such was 

 also the case in Stylonurus, and that the foremost pair of proso- 

 matic appendages in all these extinct sea-scorpions were in the same 

 position and of the same character as the cheliceral of the scorpions. 



In the living scorpion and in Limulus the nerves to this pair of 



Fig. 104. — Eurypterus Fischeri. (From Holm.) 



appendages undoubtedly arise from the foremost prosomatic ganglia, 

 and the reason why they appear to beloug to the supra- oesophageal 

 brain-mass has been made clear by Brauer's investigations on the 

 embryology of Scorpio ; for he has shown that the cheliceral ganglia 

 shift from the ventral to the dorsal side of the oesophagus during 

 development, thus becoming pseudo-supra-cesophageal, though in 

 reality belonging to the iufra-cesophageal ganglia. This cheliceral 

 pair of appendages is, in all probability, homologous with the second 

 pair of antennas in the Crustacea. 



