396 PRINCIPLES OF ANIMAL BIOLOGY 



Phalanx (Ja' lanks) (pL, phalanges, fa Ian' jeez). Any one of the bones of the fingers 

 or toes in vertebrate animals. 



Pharynx (far' inks). In an earthworm, the thick-walled portion of the digestive 

 tract just posterior to the buccal pouch and in front of the esophagus. In verte- 

 brates, the portion of the digestive tract at the back of the mouth, into which the 

 gill clefts open. 



Phoronidea (fo' ro nid' e a). A small group of marine animals, of which Phoronis is 

 the only genus, of uncertain relationship to other animals. Sometimes placed in 

 a phylum with the Bryozoa and Brachiopoda. 



Photosynthesis (fo' to sin' the sis) . The construction of carbohydrates from carbon 

 dioxide and water by the energy of sunlight in the presence of chlorophyll. 



Phototaxis (fo' to taks' is). A response to light. 



Phototropism (fo tot' ro piz' m). The response of an organism to light. 



Phylum (fi' lum). One of a dozen or more major groups into which the animal king- 

 dom is divided; in general, the largest group of which it can be said that the 

 members are related. 



Physalia (fi sa' li a). A very complex colonial coelenterate, one of the siphonophores. 

 Physiology (fiz' i oV o ji) . The branch of biology which deals with the functions 

 of animals and plants, and the processes going on in them. 



Phytogeography (fi' to je og' ra fi). The science of the geographical distribution of 



plants. 

 Pineal body (pin' eal). A structure on the dorsal side of the brain in vertebrate 



animals. Because of its similarity, in development, to the embryonic stages of an 



eye, it is often called the pineal eye, and is believed by many to be a vestigial sense 



organ. 

 Pinna (pin' na). A genus of bivalve moUusks. 



Pinnule (pin' vie). A small feather-like or laterally lobed division or part. 

 Pinus (pi' nus). A genus of coniferous trees including the pines. 



Pisces (pis' seez). A class of vertebrate animals including the fishes. For definition 

 see Chapter XII. 



Piscivore (pis' si vore). A fish-eating animal. 



Pithecanthropus (pith' e kan' thro pus). An extinct ape-like and man-like animal 

 believed to stand in the early ancestry of man. 



Pituitary (pi tu' i ia ri). A glandular organ beneath the brain composed in part of 



nervous tissue. 

 Placenta (pla sen' ta). A vascular tissue dove-tailing into the wall of the uterus 



on one side and connected with the umbilical cord on the other, thus forming an 



intimate nutritive connection between the embryo and the mother in viviparous 



animals. 

 Planaria (pla na' ri a). A genus of flatworms, phylum Platyhelminthes. 

 Planorbis (pla nor' bis). A genus of snails. 

 Planula (plan' u la). A ciliated larva consisting of a solid ellipsoidal mass of cells, 



developed from the fertilized egg of a medusa or similar organism. 



Plasmodium (plaz mo' di um). The naked mass of protoplasm containing many 

 nuclei, formed by the fusion of many amoeboid cells in the Myxomycetes. 



Plasmolyze (plaz' mo lize). To withdraw water from (a cell) by placing in solutions 

 of higher osmotic pressure. 



