524 THE ORIGIN OF VERTEBRATES 



Epithelium cells of Ainmoccetes, 347 



,, of central nervous system of vertebrates, 38, 457 



,, ccelomic spaces in annelids, 421 



,, optic diverticula, 103 



„ peritoneal, pleural, and pericardial cavities, 477 



,, velum of Ammocoetes, 301, 302 



Equilibration, 358 

 Eukeraspis, 326 

 Eurypterus, 26, 150, 191, 237 



,, appendages, 150, 236, 237 



,, classification, 249 



,, comparison with Ammocoetes, 170, 323 



,, diagram of sagittal median section, 240, 245 



,, endostoma, 241, 306 



„ eyes, 275 



,, mesosomatic segments, 192 



,, muscles of carapace, 269 



operculum, 150, 190, 212 

 Evidence of alimentary canal, innervation, 446 



„ auditory apparatus and lateral line organs, 355 



,, ccelomic cavities in Limulus, 251 



,, degeneracy in Ammocoetes, 59, 94, 343 



,, embryology, cartilage, 20, 129 



,, ,, eye-muscles, 263 



,, ,, excretory organs, 390 



heart, 179, 451 



,, ,, nervous system, central, cerebral vesicles, 48, 458 



epithelial tube, 37, 42, 102, 244, 433, 

 455 



,, ,, ,, ,, ,, neurenteric canal, 37 



„ ,, ,, ,, ,, neuropore, 220, 457 



,, ,, ,, ,, ,, optic diverticula, 102 



spinal cord, 46 

 oral chamber, 228, 242, 243, 290 

 olfactory organ, 220, 227 



,, ,, palseostoma or old mouth, 317 



,, ,, pineal or median eyes, 15, 63, 74, 456 



,, ,, pituitary body and coxal glands, 246, 319 



thyroid, 192, 194 



,, ,, segmentation, double, of head, 157, 234, 258 



„ ,, skeleton, cranial, 120, 153 



,, nervous system, central, 8 



,, notochord, origin from segmented region, 443 



,, olfactory apparatus, 218 



,, organs of vision, 68 



„ palaeontology, 20, 497 



,, pineal or median eyes, 74 



,, prosomatic musculature, 247 



,, respiratory apparatus, 148 



,, segmentation in head-shield, 339 



,, skeleton, 119 



Evolution, 8, 15, 20, 149, 482, 497 



