i'AVONlNA. 



[ o81 J 



PEDALIOX. 



always having llie hollow face cuated or 

 tilled up with superiuiposed chanibeilft.s, 

 forming a columnar chamber-structure. 



British species, P. corrugata (I'l. 24. 

 tig. 8), rare : abundant in tropical seas ; and 

 of larger size in some Cretaceous and Ter- 

 tiary strata. 



BiBL. Williamson, 7?ec, For.AQ; Carter 

 {Cvimlites and Orbitolinci), Ann. N. H. 3. 

 viii. 331, 457, 459 ; Carpenter, Introd. For. 

 299. 



' PAVONI'NA, D'Orb.— A Hyaline Fora- 

 minifer, compressed and liabelliform ; cham- 

 bers concentric, the last widest, with 

 numerous marginal apertures. It is a tlat 

 Bigenerine Textularia. Madagascar, Pacific, 

 and West Indies. 



BiBL. Brady, Ann. N. H. 4. xix. lOo ; 

 Qu. Mio. Jn. n. s. xix. 68. 



PAXIL'LUS, Fr. — A genus of Agariciui 

 (^Hymeuomycetous Fungi) with the margin 

 of the pileus involute, the gills decurrent, 

 auastomosing, and separable from the pileus 

 and without any trama. Paxillus involutus 

 is a very common species ; and to this the 

 characters of the genus more especially 

 apply. P. inmnoides occurs on sawdust in 

 cellars &c., and is closelv allied to Merulius. 



BiBL. Fr. Gen. Hym. 8; Berk. Outi. 

 t. 12. fig. 5: Cooke, Handh. 194. 



PEARLS. — These well-known bodies are 

 formed as secretions from the mantle of 

 bivalve mollusks, the best being obtained 

 from the Cej'lon pearl-oyster or mussel 

 (Avicula maryaritifera). They occur natu- 

 rally from the irritation produced by particles 

 of sand accidentally confined betAveen the 

 mantle and the shell ; and they are produced 

 artificially by wounding the mantle with 

 pieces of ii-ou wire, &c. Their structure 

 agrees with that of the shell of the animal 

 in which they are formed. Sometimes they 

 consist entirely of nacre or pearly matter, 

 arranged iu close concentric layers; at 

 others, the interior exhibits the prismatic 

 sti'ucture of sheU. When acted upon by a 

 dilute mineral acid, the lime-salt is removed 

 from the organic cast of the original, which 

 is left. They are sometimes found fossil. 



See Shell. 



BiBL. Hague and Siebold, Siebold <$• Kdl- 

 liker's Zeitschr. viii. 439 & 445 ; Carpenter, 

 Microscope. 



PEB'illNE is the name of a disease 



•which for the past twenty years has raged 



amongst the silkwoi-msin France, In 1853, 



the weight of cocoons produced in that 



country was 26,000,000 of kilogrammes ; iu 



1805 it had fallen to 4,000,000. The black 

 spots wliich cover the larv;e are a frequent 

 outward sign of the disease ; hence the 

 name pehrine, first applied to the plague by 

 Quatrefages. It also declares itself iu the 

 stunted and unequal growth of the worms, 

 in the languor of their movements, in their 

 fastidiousness as regards food, and iu their 

 premature death. The cause of the disease 

 is the presence in the internal economy of 

 the larvie of Gregariaida \ their number is 

 often enormous. They take possession of 

 the intestinal canal, and spread thence 

 through the rest of the body. In particular, 

 the silk -secreting organs, instead of being 

 filled with the clear viscous liquid of the 

 silk, are packed to distention by these cor- 

 puscles. Pasteur in 1805 made out the 

 fact that they might exist in an incipient 

 condition iu the eggs and larvae, although 

 it might be impossible to detect them. In 

 the moths, if either egg or larva from 

 which they come should have been at all 

 stricken, the corpuscles infallibly appear, 

 and there is no dilficulty in detecting them. 

 In eradicating the disease, Pasteur, there- 

 fore, showed that it was of the greatest 

 importance to secure eggs from healthy 

 moths, since the healthy appearance of the 

 eggs themselves was not sufficient to secure 

 immunity. The larvaj issuing from the 

 eggs of perfectly healthy moths may them- 

 selves become infected thi'ough contact 

 with diseased larvae, or through germs 

 mixed with the dust of the rooms in which 

 the silkworms are fed. 



BiBL. Pastern", Maladie des vers a sole; 

 Tvvidall, Nature, 1870 ; Balbiani, Jn. Anat. 

 18G6, 599 ; Robin, Micr. 948. 



PECTIN ATEL 'LA, Leidy.— A genus of 

 freshwater Polyzoa, order Hippocrepia, 

 family PlumatelUdfe. 



Char. Zoary massive, gelatinous, fixed, 

 investing ; orifices arranged in ii'regidar 

 lobate areolae upon the free surface ; ova 

 lenticular, with a ring and marginal spines. 



P. niaynlfica. Philadelphia. 



BiBL. Leidy, , Proc. Ac. Philadelphia, 

 1851 ; AUman, Freshwater Polyzoa, 81. 



PEDA'LION, Hudson.— A genus of 

 Rotatoria, family Hydatinfea, P. tnirum 

 has the trochal disk very large, and resembles 

 2'riarthj-a lonyiseta. ' The males are very 

 smaU, and deficient in most of the inrnal 

 organs ; freshwater. 



BiBL. Hudson, Mn. Mic. Jn. 1871, 1872; 

 Qu. Mic. Jn. 1872, 333; Lankester, Qu. 

 Mic. Jn. 1872, 338. 



