428 



INVERTEBRATE MORPHOLOQT. 



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- 



FiG. 195. — Limulus polyphemus, Pbmalb, feom the Ventral Suefacb. 

 ah = abdomen cp = cepbalotbovaxi 



an = amis. ol = olfactory organ. 



all = chelicera. op = operculum. 



chi = chilariura. 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). 



