428 



INVERTEBRATE MORPHOLOGY. 



as King-crabs or Horseshoe-crabs. They are large forms 

 measuring a foot or so in diameter, and the body is composed 

 of three portions. The anterior is a broad semicircular ceph- 



oh 



FIG. 195. Limulus polyphemus, FEMALE, FROM THE VENTRAL SURFACE. 



ab = abdomen cp = cephalothorax, 



an = amis. ol = olfactory organ. 



ch = cbelicera. op = operculum. 



chi = cbilarium. sp = spiue. 



alothorax (cp), prolonged backwards into sharp points at its 

 posterior angles and bearing upon its dorsal surface a pair of 

 compound eyes towards the sides and near the median line 

 two simple eyes. The middle region is the abdomen (ab), 



