XIPHOSURA 



419 



Nervous System. The central nervous system consists of a 

 ganglionic mass lying in the cephalothorax and surrounding the ceso- 



ft 



feU cffi. A 



C 



fe 



FIG. 285. Median longitudinal section through a young Limulus polyphemus (after 

 Packard), cth, Cephalothorax ; ab, abdomen ; ss, caudal spine ; vm, anterior stomach ; m 

 stomach; 7i, heart; ss, sternal cartilaginous endo-skeleton ; d, intestine; g, brain; itg, infra 

 oesophageal ganglionic mass ; &m, ventral chord ; o, operculum ; i-5, gill carrying abdominal 

 appendages ; mu, mouth ; an, anus. 



phagus ; it is continued into the abdomen as a ganglionic ventral chord. 

 The circular ganglionic mass of the cephalothorax is found to consist 

 of the brain, which lies in front of the oesophagus, and gives off nerves 

 to the lateral eyes and the ocelli, and of 7 postoral pairs of ganglia with 

 their transverse commissures, these ganglia lying near each other. 

 The latter yield the nerves for the cephalothoracic limbs. The ventral 

 chord of the abdomen consists of 6 ganglia, the last of which is the 

 largest. The nerves to the leaf -like feet are given off by these 

 latter. 



The compound eye of Limulus (Fig. 286) deserves special descrip- 

 tion. The chitinous cara- 

 pace is thickened over each 

 of the two compound eyes ; 

 outwardly its surface is 

 smooth, but inwardly, by 

 the formation of conical 

 processes, it pushes in the 

 subjacent hypodermis to 

 form towards the interior 

 an equal number of papillae ; 

 each of these chitinous cones 

 may be considered as a 

 single lens. ^ A completely FlG> 2 S6.-Part of a section through the eye of Lim- 

 Separate retinula probably Ulus. cp, Chitiuous carapace ; cv, papilla-like thickenings 



conm'stinp- of 10 rells with of the same over each single eye: hy ' hv P d ermis; ret, 

 us, \A iLn retinul8e . %j nerves of the single eyes> 



rhabdom, pigment, and 



nerve, corresponds with each of these single lenses. The retinulae lie 



