PROSOMATIC SEGMENTS OF LIMULUS 235 
away and become insignificant, we still have the muscular, ccelomic, 
and nervous arrangements left to us as evidence of segmentation in 
these animals, just as in vertebrates. 
In this prosomatic region, we find in Limulus the same tripartite 
division of the nerves as in the mesosomatic region, so that the 
nerves to each segment may be classed as (1) appendage-nerve ; 
(2) sensory or dorsal somatic nerve, supplying the prosomatic cara- 
pace; (3) motor or ventral somatic nerve, supplying the muscles of 
the prosoma, and containing possibly some sensory fibres. The main 
difference between these two regions in Limulus consists in the closer 
aggregation of the prosomatic nerves, corresponding to the concentra- 
tion of the separate ganglia of origin in the prosomatic region of the 
brain, 
The number of prosomatic segments in Limulus is not evident 
by examination of the prosomatic carapace, so that the most reliable 
guide to the segmentation of this region is given by the appendages, 
of which one pair corresponds to each prosomatic segment. 
The number of such segments, according to present opinion, is 
seven, viz. :— 
(1) The foremost segment, which bears the chelicere. 
(2, 8, 4, 5, 6) The next five segments, which carry the paired 
locomotor appendages; and 
(7) The last segment, to which belongs a small abortive pair of 
appendages, known by the name of the chilaria, situated between the 
last pair of locomotor appendages and the operculum or first pair of 
mesosoniatic appendages. These appendages are numbered from 1-7 
in the accompanying drawing (Fig. 103). 
Of these seven pairs of appendages, the significance of the first 
and the last has been matter of dispute. With respect to the first 
pair, or the chelicere, the question has arisen whether their nerves 
belong to the infra-cesophageal group, or are in reality supra- 
cesophageal. 
It is instructive to observe the nature and the anterior position of 
this pair of appendages in the allied sea-scorpions, especially in Ptery- 
gotus, where the only chelate organs are found in these long, antenne- 
like cheliceree. In Slimonia and in Stylonurus they are supposed by 
Woodward to be represented by the small non-chelate antennz seen 
in Fig. 8, B and C (p. 27), taken from Woodward. If such is the case, 
then these figures show that a pair of appendages is missing in each 
