288 GLOSSARY. 



Patagium. (1) The expanded integument forming the wing of a 

 bat. (2) A vesicular body, one on each side, attached to the 

 prothorax of the Lepidoptera ; it is covered with hair. 



Paxillcs. Clusters of spines or bristles in the Echinoderms. 



Pecten or Marsupium. A plicate membrane of the eye, placed 

 in the vitreous humour anterior to the retina. 



Pectines. A pair of comb-like organs situated behind the two 

 posterior legs of scorpions. 



Pedicellarice. Small two- or three-pronged pincer-like bodies, 

 found on most Echinoderms. 



Pedicelli or "Ambulacra" or " Ambulacralfeet." The suckers of 

 Echinoderms. 



Pedicle or Pedicel. A diminutive peduncle, variously applied. 



Pedipalpi. The maxillary palpi of the scorpions, the large pre- 

 hensile claws. 



Peduncle. A foot-stalk, variously applied. 



Pelvis. The bony " hip-girdle " supporting the lower extremities. 



Pereion. The thoracic segments of the lower Crustaceans. 



Pereiopoda. The legs attached to the body (pereion) of the lower 

 Crustaceans. 



Periosteum, The fibrous membrane covering a bone. 



Perioslracum. The membrane covering the shell of the Mollusca 



Perisarc. The chitinous envelope of some Hydrozoa. 



Perisome. The calcified integument of an Echinoderm. 



Peristome. The part surrounding the mouth of an Actinozoon. 



Peritoneum. The serous membrane investing the intestines, and 

 reflected on the walls of the abdomen. 



Peritreme. The aperture or mouth of a univalve shell. 



Persistent types are those which have not undergone any notable 

 modification in geological time, and even exist at the present, 

 day ; they belong chiefly to the lower forms of life. There is 

 no "valid reason for the supposition that the earliest forms 

 known in the oldest fossiliferous rocks were the first to make 

 their appearance on our planet'" (Huxley}. Animals with 

 what Mr. Darwin calls " an inflexible organization " may al&o 

 be referred to this type. 



Persona. See Individual. 



Phalanges. The bones composing the digits. 



