261 



PENTADESJIIS. 



PERCID.E. 



P. breeii, of Forbes and Goodsir, is the only species. It was dis- 

 covered in the Shetland seas, adhering to the stems of Laminariw. 

 It links the family of Psolidce with Pentactce. It is about half an inch 

 in length, of an ovate form, with both its extremities bent upwards. 

 The body is pinkish-white, with minute papilla?. The tentacula are 

 long, pedicled, and digitate at the extremity. It is sluggish in its 

 movements, but moves its tentacula freely. 



Cucamaria has the body regular, more or leas pentangular, with 

 five longitudinal rows of approximate suckers; ten tentacula; dental 

 apparatus composed of nearly square plates. 



The species are called Sea-Cucumbers. They are the most typical of 

 the Ifolothwiadre, and their popular name is very expressive of their 

 usual form. They have all of them the power of changing their 

 shape, so that sometimes they are very long, and others are oval or 

 round. They usually live among sea-weeds or in mud, and are sup- 

 posed to seize their prey by their large tentacula. They are found 

 very generally throughout the seas of the globe. The following are 

 the British species described by Professor E. Forbes in his ' History of 

 BritUh Star-Fishes ' : 



C.frondota (Holothurla frondosa, Gunner), the Great Sea-Cucumber. 

 It hag been principally found off the coasts of Scotland. 



C. pentodes (Holothuria pentacta, Miiller), the Angular Sea-Cucum- 

 ber. It has been taken on the coasts of Devonshire and Dorsetshire, 

 and is found in the seas of France and Norway. 



0. communie, Common Sea-Cucumber. Great numbers of these 

 animals have been observed off the coast of Fifeshire, and been 

 dredged in the north and south of Ireland, by Mr. W. Thompson and 

 Dr.BalL 



C. furiformit, the Long Sea-Cucumber. This is the longest of all 

 the specie* in proportion to its thickness. 



C. hyalina, the Glassy Sea-Cucumber. It is remarkable for its 

 hyaline glassy appearance. It inhabits the Shetland seas. 



C. Drummandii, This species was named after Dr. Drummond, 

 who discovered it in Belfast Bay. 



C. llyndmanni is named after Mr. Hyndman, who dredged it in 

 Belfast Bay. It has been since taken in large numbers off the western 

 coast of Ireland. 



C. fucicola, the Tangle Sea-Cucumber. It has been found in the 

 Shetland seal. 



Omu (Forbes and Goodsir) has the hody regular, cylindrical, 

 pentagonal, with five rows of distant suckers on the angles ; tentacula 

 ten ; dental apparatus very short. 



Professor E. Forbes describes two species of this genus, which he 

 calls, on account of its size as compared with the Sea-Cucumber, the 

 Sea-Uirkin. The two British species are 0. branneui and 0. tactea, 

 distinguished by their colour, the latter being milk-white, the 

 former brown. 



PENTADESMIS, a genus of Plants belonging to the natural order 

 Clutiacccc. P. J3utyrace<i is a tree found in Sierra Leone, from which 

 a fatty substance is obtained, which has given rise to its name of the 

 Butter-Tree and Tallow-Tree. It has an ovate fleshy fruit, about as 

 large as a citron, and its stamens are collected into five parcels, 

 whence its botanical name. 



PENTALASMtS. [CmmrEDiA.] 



PENTAPLATARTHKUS. [PAU 



PENTREMITKS. [ K.VCRI.MTES.] 



PEONY. [P-BONIA.] 



FEPO, a kind of fruit of which the Gourd is the type. It has an 

 inferior seed-vessel, filled with pulp inclosed within a hard pericarp, 

 and furnished with parietal placenta!. [FuuiT.l 



I'KITEK. [PIPEK; PIMENTO.] 



PEl'I'EHMINT. [MEXTHA.] 



I'KITKU-MOTH. [BlOTON.] 



PEPSIN, a substance found in the gastric acid of man and the 

 lower animals. If the glandular portion of the stomach is treated 

 with extremely dilute acids a substance is thrown down from the 

 fluid by corrosive sublimate, which Schwann firat called Pepsin. 

 Wasmann afterwards obtained pepsin in a purer form. He pro- 

 ceeded in the fallowing manner : The glandular layer in the stomach 

 of the pig, which extends chiefly from the greater curvature towards 

 the cardia, was carefully detached aud washed, without being cut up, 

 then digested with distilled water at a temperature of from 80 to 

 35. After some hours the fluid was poured away, the membrane 

 was again washed in cold water, and then digested in the cold with 

 about ix ounces of distilled water, and repeatedly washed, till a 

 putrid odour began to be developed. The filtered fluid was trans- 

 parent, viscid, and without any reaction ; it was now precipitated with 

 acetate of lead or corrosive sublimate ; the precipitate was carefully 

 washed and decomposed with sulphuretted hydrogen ; the pepsin was 

 then precipitated by alcohol from the watery solution in white flocks. 



The pepsin thus obtained, forms, when dry, a yellow, gummy, 

 slightly hygroscopic mass ; in its moist state it is white and bulky ; it 

 dissolves readily in water, and always retains a little free acid so as 

 to redden litmus; it i precipitated by alcohol from its watery 

 solution ; mineral acids induce a turbidity in a solution of neutralized 

 pepsin, which disappears on the addition of a small excess of the acid ; 

 but if there be a considerable excess of the acid, there is a flocculent 

 deposit. It is only imperfectly precipitated by metallic salts, and not 



at all by ferrocyanide of potassium. It has been asserted that pepsin 

 is coagulated by boiling, but Frierichs has shown that the coagulation 

 is merely dependent ou its admixture with albumen. This substance 

 possesses the converting power so strong that, according to Wasmanu, 

 a solution containing only l-60,000th part of this substance dissolved 

 albumen in six or eight hours. Similar experiments have been made 

 by Pappenheim, Valentin, and Elsasser. 



C. Schmidt has proposed a new view with regard to the nature 

 of the digestive principle. He regards it as a conjugated acid, 

 whose negative constituent is hydrochloric acid, with Wasmann's 

 non-acid, or coagulated pepsin, as an adjunct; and assumes that it 

 possesses the property of entering into soluble combinations with 

 albumen, glutin, chondrin, &c. According to him, it more nearly 

 resembles ligno-sulphuric acid than any other conjugated acid, and as 

 this becomes disintegrated into dextrin and sulphuric acid, so the 

 pepsin-hydrochloric-acid becomes separated at 100 into Wasmann's 

 coagulated pepsin and hydrochloric acid, aud in either case it is equally 

 impossible to reproduce the conjugated acid from its proximate 

 elements after their separation. Ou bringing the complex acid in 

 contact with an alkali, the adjunct -the substance which has been in 

 combination with the hydrochloric acid is precipitated. Schmidt 

 believes that he has ascertained that an artificial digestive mixture 

 which has expended its solvent and digestive powers, regains them on 

 the addition of free acid ; and that when hydrochloric acid is added, 

 the pepsin-hydrochloric-acid is expelled from its combination with 

 albumen, &c., and thus regains its former properties, while the newly 

 added hydrochloric acid enters into its well-known soluble combina- 

 tions with albumen, &c. By the repeated addition of hydrochloric 

 acid, a digestive fluid or this pepsin-hydrochloric-acid might preserve 

 its digesting power for ever, unless the fluid became saturated with 

 the dissolved substances, or the conjugated acid underwent decompo- 

 sition. 



(Lehmann, Physiological Chemistry, translated for the Cavendish 

 Society.) 



PERAME'LES. [BANDICOOT; MARSOPIATA.] 



PERCH. [PEECID&] 



PE'RCID.<E, or Percoldes of Cuvier, a family of Acanthopterygious 

 Fishes, of which the Common Perch may be regarded as the type. 

 They have the body covered with scales whose outer surface is more 

 or less rough, and the free margins of which are denticulated ; the 

 operculum and preoperculum are variously armed with spines, and 

 denticulated at the outer margin ; they not only have teeth in both 

 jaws, but the vumer and palatine bones are also furnished with them : 

 the number of rays to the branchiostegous membrane varies from five 

 to seven ; they never fall short of the lower nor exceed the higher 

 number. The flesh of these fishes is generally well-flavoured and 

 wholesome. They inhabit both salt aud fresh water. 



The first division of the Percoides, according to Cuvier, comprises 

 all those species which have the ventral fins placed under the pectorals, 

 five soft rays to the pectoral fins, seven branchiostegous rays, and two 

 dorsal fins. This section includes the following genera : 



1. Perca proper, in which the preoperculum is denticulated ; the 

 operculum is produced behind into a flattened spine; the infra- 

 orbitals are obscurely denticulated, and the tongue is smooth. The 

 Common Perch (Perca Jtuviatilis of Lirm.'eus) is the best example. Io 

 is a common fish in the fresh-waters of Great Britain. Closely allied 

 to this is the P. Jtalica of Cuvier and Valenciennes, a species found 

 in tolerable abundance in some parts of Italy; it differs from the 

 Perca Jtuviatilu in being of a shorter and deeper form, and is destitute 

 of the black bands. Several true perches are found in North America ; 

 species have also been discovered in Java and New Zealand : it is 

 highly p-obable therefore, from the extensive geographical range of 

 the Perches proper thus exhibited, that very many species still remain 

 to be discovered. 



2. Labrax (Cuv. and Val.) differs chiefly from the true Perches in 

 having the infra-orbitals destitute of denticulations as well as tho 

 suboperculum ; the operculum (which, as well as the preoperculum, 

 is entirely covered with scales) has two spines on the posterior part, 

 and the tongue is furnished with minute teeth. [LABBAX.] 



3. Lota (Cuv. and Val.), a genus also closely allied to Perca proper, 

 in fact differs only in having the infra-orbitals more deeply denticu- 

 lated as well as the numerals; large spines are observable on the 

 angle of the preoperculum ; the anterior dorsal is shorter and higher 

 than in the Perch ; the tongue is smooth, as in the last-mentioned fish. 

 The fishes of this sub-genus are usually of large size, good eating, 

 and are chiefly found in the rivers in the warmer parts of tho Old 

 World. 



4. Centropoitiut (Lacdp.) includes those perch-like fishes whose oper- 

 culum is produced behind, but the produced part is rounded at the 

 apex; in the fins and denticulated preoperculum they resemble tho 

 perch. In the only species of this genus hitherto discovered the head 

 is more pointed than in the preceding genera. [CKNinoPOMCS.] 



6. Leucioperca (Cuv. and Val.) differs from both the preceding genera 

 in having larger sharply-pointed teeth intermixed with the ordinary 

 small teeth ; the form of the body is more elongated, and the first 

 dorsal fin is large. The L. Sandra (Cuv. and Val.) is found in the 

 rivers and lakes of the north-eastern portions of Europe, and is known 

 to the Germans by the names of Sander, Sandel, or Sandat ; it is th 



