XIPHVXURA 



419 



Nervous System. --The central nervous system consists of a 

 ganglionic mass lying in the cephalothorax and surrounding the oeso- 





\ ^ It 



<L4 



m. 



inn 



an. 



mu. 



PIG. -_^j. Median longitudinal section through a young Limulus polyphemus (after 

 Packard), ctlt, Cephalothorax; tib, abdomen; ss, caudal spine; rm, anterior stomach; m, 

 stomach; Ti, heart; ss, sternal cartilaginous endo-skeleton ; d, intestine; ;/, brain; ug, infra 

 al ganglionic mass; bin, ventral chord; o, operculuin ; rti-a g , gill carrying abdominal 

 's; 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 Avith 

 their transverse commissures, these ganglia lying near each other. 

 The latter yield the nerA r es for the cephalothoracic limbs. The ventral 

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

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

 latter. 



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

 tion. The chitinous cara- 

 pace is thickened over each 

 of the tAvo compound eyes ; 

 outAvardly its surface is 

 smooth, but inwardly, by 

 the formation of conical 

 processes, it pushes in the 

 subjacent hypodermis to 

 form toAvards the interior 

 an equal number of papillae ; 

 each of these chitinous cones 

 may be considered as a 

 lens. A completely 



r CO 



let- 



n. 



Km. 286. Part of a section through the eye of Lirn- 

 Separate retiliula probably ulus. cp, Chitinous carapace; a; papilla-like thickenings 

 consisting Of 10 cells, with * the same over each single eye ; ty, hypodermis ; ret, 



~ retmula- ; n, nerves of the single eyes. 



rhabdom, pigment, and 



nerve, corresponds Avith each of these single lenses. The retinulffi lie 



