Plexus, of Auerbach, [447]

Plex"s, of choroid, [38], [45], [49], [103]

Plex"s, of hypogastric, [3]

Polychæta, [357], [395]

Pores, abdominal, [430]

Porifera, [473]

Pouch, formation of gill, [165], [166]

Prestwichia, [24], [25], [249], [351]

Principle of concentration and cephalization, [51]

Prini"ple of embryology, [455]