PROSOMATIC SEGMENTS OF LIMULUS 237 
So, also, since Woodward’s monograph, Laurie has discovered in 
Shimonia acuminata a small median pair of chelate appendages 
exactly corresponding to the cheliceree 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 chelicerz of the scorpions. 
In the living scorpion and in Limulus the nerves to this pair of 
Fie. 104.—Hurypterus Fischert. (From Houtm.) 
appendages undoubtedly arise from the foremost prosomatic ganglia, 
and the reason why they appear to belong to the supra-cesophageal 
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 cesophagus during 
development, thus becoming pseudo-supra-cesophageal, though in 
reality belonging to the infra-cesophageal ganglia. This cheliceral 
pair of appendages is, in all probability, homologous with the second 
pair of antenne in the crustacea. 
