INDEX 



969 



Placental septa, 922 

 Placentation, definition of, 917 



human, 923 



types of embryonic tissues involved in, 

 917 

 Placodes, acoustic, 813 



lateral line, 813 



lens, 812 



nasal, 812 



taste bud, 813 

 Plasis, 547 

 Plasm, polar, 1 17 

 Plasma, 726 



seminal, 21, 32 

 Plastron, xix 

 Piatt, J. B., 603, 716 

 Platydactylus, formation of hypoblast in, 



361 

 Platypus (Ornithorhynchus), xx, character- 

 istics of egg, site of fertilization, 

 and place of sperm entrance into 

 egg, 205t 



cleaving eggs of, 324, 326 



corpus luteum of, 84 

 Plethodon cinereus, xvii 

 Pleural cavities, 857. 869 

 Pleurodeles, mesoderm extension (migra- 

 tion) in, 417 

 Pleurodont tooth, 607 

 Pleuropericardial membrane, formation of, 



868 

 Pleuroperitoneal membrane, 864, 868 



development of, 869 

 Plica semilunaris, 853 

 Plug, vaginal, 31, 33 

 Pluma, 571 

 Plumules. 573 



Pluripotent state, definition of, 377 

 Pneumatic duct, of air bladder, 643 

 Pocket (semilunar) valves, in aortic and 



pulmonary trunks, 759 

 Pohlman. A. G.. 762 

 Poison glands, in skin of fishes. 561 



of rattlesnake, Crotahis horridus, 616 

 Polar bodies, formation of in Deroceras 

 laeve (Limax campestris), 214 



in Haemopis, 214 



in Nephelis, 214 

 Polar plasm, 1 17 



Polarity of cytoplasm, theories of, 158 

 PoUstotreina (Bdellostoma) stouti, xvi 



gill arrangement in, 639 



kidney tubules of, 773 



mesonephric kidney of, 778 



yolk sac of, 908 

 Pollachius virens, pollack, cranial nerve 

 distribution of, 825 



PoUister, A. W., 297 



Polocyte, 145 



Polyembryony, definition of, 380 



in armadillo, Tatusia novemcincta, 383, 

 384 

 Polyestrous conditions, 94 

 Polyinvagination, during formation of sec- 

 ondary blastula in Echidna, 364 

 in gastrulation, definition of, 397 

 Polyphyodont condition, of tooth develop- 

 ment, 607 

 Polypteriis, male reproductive duct in, 18, 



799 

 Polyspermy, in Bryozoa, 259 

 in hen's egg, 253 

 in insects, 259 

 in pigeon's egg, 253 

 in Triton, European newt, 270 

 influence of first cleavage amphiaster on, 

 286 

 Pontine flexure, formation of, 823, 833 

 Porichthys notatus, development of phos- 

 phorescent organ in, 561 

 Post-anal gut, 471, 600 

 Post-branchial bodies, 878, 880 

 Post-embryonic period, xii 

 Postganglionic neuron, 836 

 Post-nuclear cap of sperm head, formation 



of, 149, 150 

 Potency, autonomous, 379 



versatility of, definition of, 379 

 definition of, 376 

 in relation to differentiation, 376 

 prospective, definition of, 379 

 Potency expression, definition of, 379 

 Potency release, definition of, 379 

 Potency restriction, as a characteristic of 

 cleavage and the blastulative 

 process, 377 

 Pre-cartilage stage, of cartilage formation, 



665 

 Precaval veins, development of in chick 



embryo, 745 

 Pre-chordal plate, and cephalic projection 



in various chordates, 449 

 Pre-chordal plate material, 512 



importance of in late gastrula, 414 

 Pre-chordal plate mesoderm, definition of, 



523 

 Pre-chordal (trabecular) plate area, of 



primitive skull, 671 

 Preformationism, emboitement, theory of, 

 57 

 in modern embryology, 57 

 intangible, Leeuwenhoek's concept of, 



213 

 past and present, 56 

 Preganglionic neuron, 836 



