290 GLOSSARY. 



Plexus. A. network of nerves. 



Plica semilunaris. See Membrana nictitans. 



Plumules. The down-feathers. 



Pluteus. The larval form of the Echinoidea. 



Pneumatocyst. The air-sac contained in a pneumatophore. 



Pneumatophore. The air-sac or float attached to the proximal 



end of the coenosarc of the oceanic Hydrozoa. 

 Podex. The last segment of the abdomen in insects. 

 Podium. The muscular so-called foot of certain Mollusks. 

 Polian vesicles. Interradial sacs connected with the ambulacral 



system of Echinoderms. 

 Polymely. The monstrosity when one or more of the extremities 



are doubled, or when there is any supernumerary part. 

 Polymerism. A. multiplicity of parts. 

 Polypary. The chitinous sheath investing more or less the 



coenosarc in the Hydroida. 



Polyphyletic. When the descent is from more than one form. 

 Polypide. The zooid of the Polyzooid colony. 

 Polypite or hydranth. The "nutritive zooid" of the Hydroid 



colony. 



Polyplast. See Morula. 

 Pons Varolii. The commissure of the cerebellum connecting the 



two lateral lobes. 



Primitive groove. A straight shallow depression of the blasto- 

 derm, indicating the longitudinal axis of the future embryo. 

 Proccelous. Said of vertebrae which are concave only in front. 

 Proglottis. A reproductive segment of a Cestode. 

 Prognathous. Projecting jaws and teeth ; in man a sign of de- 

 gradation. 



Pronotum. The dorsal surface of the prothorax. 

 Propodite. The sixth joint of the leg of an insect. 

 Propolis. A substance collected by bees, composed of wax and 



resin. 



Proscolex. The earliest larval stage of a Cestode. 

 Prosthema. The upright leaf-like process on the nose of certain 



bats. 



Prosthenic. Having the maximum of strength in the fore ex- 

 tremity. 



