532 THE ORIGIN OF VERTEBRATES 



Parapodopsis, foot glands, 422 

 Parathymus, 427 

 Parathyroids, 427 

 Parietal organ, 76 



Pecten of scorpion, 114, 359, 366, 371, 372, 373, 374 

 Pedipalpi, 190 

 Periblast, 471 



Peripatus, 396, 399, 400, 411, 421, 429 

 Petromyzon, alimentary canal, 405, 445 

 ,, auditory organ, 378 



,, branchial segments, 169 



,, life-history, 59 



olfactory tube, 219, 226 

 ,, pronephric duct, 402 



,, retina and optic nerve, 95 



,, skeleton, 125 



,, suctorial apparatus, 287, 304 



,, transformation, v. Transformation of the Lamprey 



Phagocytes, 420, 471 

 Pharynx of Amphioxus, 410 

 ,, Vertebrate, 440 



Phoronis, 439 

 Phrynus, brain, 53 



,, caudal brain, 450 

 ,, carapace and carapace removed, 250 

 ,, ccecal diverticula, 109 



,, evidence of segmentation of carapace, 249, 250, 341 

 ,, operculum, 191 

 ,, prosomatic appendages, 306 

 „ crossing of dorso-ventral muscles, 271, 277 

 ,, stridulating apparatus, 368 

 Phyllodoce, 395 

 Phyllopoda, 321 

 Pigment, in Ammoccetes, in position of atrial cavity, 412 



epithelial lining of central nervous system, 43, 457 

 choroid of vertebrate eye, 104, 107 



between glandular cells round brain of Ammoccetes, 211, 379 

 tapetal layer of retina, 70 

 white, of right pineal eye of Lamprey, 76, 80 

 Pineal body, 14, 15 

 „ eyes, 74, 233, 244 

 ,, ,, of Ammoccetes, 80, 78, 85 

 ,, gland, 63, 75, 456 

 Pits, epithelial, of diaphragms in Ammoccetes, 164 



,, ,, skin in Ammoccetes, 173, 200 



Pituitary body, 244, 246, 319, 321, 425, 430 

 Plasma-cells, 471 

 Plakodes, 283 

 Planarians, 475 



Plastron, formation of cranial walls from the, 86, 322, 341 

 of Limulus, 136, 142, 143 

 ,, Palaeostracan, compared to trabecule of Ammoccetes, 145, 377 



