GLOSSARY. 287 



Ovisac. The external bag in which some of the lower Crusta- 

 ceans carry their eggs for a time after they are extruded from 

 the ovary. 



Ovoviviparous. When eggs are retained until they are hatched. 



Ovum, egg, or germ. "A highly differentiated portion of the 

 parent organism." 



Palaozoic. The primary fossiliferous period in geology; it in- 

 cludes the Laurentian, Cambrian, Silurian, Devonian, Car- 

 boniferous, and Permian formations. 



Palingenesis. Recapitulative ontogeny. 



Pallium. The mantle or fold of integument on each side in the 

 Mollusca. 



Palpi. Jointed appendages of the mouth in Arthropoda. 



Palpocil. A hair-like process in the tentacles of some Hydroida. 



Paluli. Small detached rods round the columella of an Actino- 

 zoon. 



Pancreas. A conglomerate gland situated behind the stomach 

 and connected with digestion. 



Pangenesis. Mr. Darwin's hypothesis that countless ' ' gemmules " 

 are generated in every organ which, having the power of re- 

 production, are the cause of the appearance in offspring of 

 ancestral characters or of physiological peculiarities. 



Panspermism. The hypothesis that all organisms come exclu- 

 sively from preexisting living germs. 



Paraglosscs. Two delicate membranous organs placed behind and 

 above the labitnn in certain insects. 



Parapleurce. The flanks or sides of the thorax. 



Parapodia. The unjointed feet of the Annelida and of the larva 

 of many insects. 



Parapophyses. The lower articular transverse processes of certain 

 vertebrae. 



Paraptera. See Tegulce. 



Paratoids. Glandular tubercles, chiefly found above the tym- 

 panum in Batrachia. 



Parostosis. The fibrous matrix in which integumental bones are 

 developed. 



Parthenogenesis. Virginal reproduction. "Asexual reproduc- 

 tion either by fission, gemmation, or the process of internal bud- 

 ding" (Huxley}. 



