109 



HOAZIN. 



HOLOTHURIADJE. 



110 



of cells, and develop from these their higher elementary parts, stands 

 firm ; though it must not be understood aa if cells, or their derivatives, 

 were the sole possible or existing elements of animals. In the same 

 way, Schwann's conception of the genesis of cells, though considerably 

 modified and extended, has not been essentially changed, since the 

 cell-nucleus still remains as the principal factor of cell-development 

 and of cell-multiplication. Least advance has been made in the laws 

 which regulate the origin of cells and of the higher elements ; and 

 our acquaintance with the elementary processes which take place 

 during the formation of organs must be regarded as very slight. Yet 

 the right track in clearing up these points has been entered upon ; 

 and a logical investigation of the chemical relations of the elementary 

 parts and of their molecular forces, after the manner of Danders, 

 Dubois, Ludwig, and others, combined with a more profound micro- 

 scopical examination of them, such as has already taken place with 

 regard to the muscles and nerves, and further, a histological treatment 

 of embryology, such as has been attempted by Reichert, Vogt, and 

 myself, will assuredly raise the veil, and bring us step by step nearer 

 to the desired though perhaps never-to-be-reached end." 



In accordance with the plan of this work, the Histology of each 

 separate organ of the body will be found in the general article devoted 

 to that organ. 



The tissues or textures of the body enumerated in the article 

 ANATOMY will Ix* found under their respective names; and in the 

 articles Tl&iUEa, VEGETABLE, and TISSUES, ANIMAL, will be found an 

 account of the relations and general physiology of the textures of 

 the body. 



Necessary aids to the study of Histology are the microscope and 

 books. Under the article MICROSCOPE, in ARTS AND Sc. Div., the 

 nature of that instrument and the mode of using it will be described, 

 aa well as the various forms adapted for histological purposes. 



We refer here to some of the more important works and papers to 

 be consulted on this subject. 



Kolliker, Manual of Human IIitology ; Sharpey, General Anatomy, 

 in Quain's Elements of Anatomy; Beale, The Microscope, and its 

 nil',, i in Clinical Medicine; Todd and Bowman, Physiological 

 Anatomy ; Gerber, Element! of the General and Minute Anatomy of 

 Man and the Mammalia; Qoodsir, Anatomical and Pathological 

 Observations; Hassall, Microscopic Anatomy; Bowman, On the Struc- 

 ture of Voluntary Muscle (Phil. Tram., 1840) ; Kieruan, On the Struc- 

 ture of (lie Liter (I'hil. Trans., 1835) ; Mandl, Manuel d'Anatomie 

 Genirale; Hobl, On the Vegetable Cell; Owen, Lectures on Comparative 

 Anatomy; Quekett, Lectures on Histology ; Schleiden, Principles of 

 Scientific Botany; Schleiden and Schwann, Microscopical Research** 

 I Sydeuham Society) ; Ctidofxtdia of Anatomy and Physiology ; Robin, 

 II- '^ire Xaturdle da Viyflaux Parasites; Carpenter, Principle! of 

 Physiology, General and Comparative. 



( Quarterly Journal of Microscopical Science.) 



HOAZIN. [CRACID*.] 



HOBBY. [FALCONID.E.] 



HOCCO, a name employed by Buffon, Latham, and others, to 

 ite some of the Curassow Birds. [CRACID.E.] 



HOE. [SQUALID.E.] 



HOG. [SuiD.E.] 



HOG-MEAT. [BOERHAAVIA.] 



HOG-PLUM. [Si'ONDiAtE.E.] 



HOLASTEIl, a genus of Fossil Echinidce, proposed by M. Agassiz 

 to include species once ranked as Spatangi. Spatangus subglobosus 

 (Leske), S. planus (Mantell), and 8. hemispheric** (Phillips), are 

 examples. The species occur almost exclusively in the Chalk Forma- 

 tion. [ECHI.VODERMATA.] 



HOLCUS, a genus of Grasses belonging to the tribe Avenece. It 

 has 2-flowered glumes, the lower perfectly awnless, the upper 

 usually stameniferous, with a dorsal awn ; the palere hardening on 

 the fruit. There are two British species of this genus. H. lanatus 

 has the upper glume obtuse, apiculate ; the awn smooth, except for a 

 short distance from the tip. ' It grows in meadows and pastures. //. 

 muliis has the upper glume acute, and the awn rough throughout its 

 whole extent. It grows in thickets or open places on a light soil. 

 The //. ccrnunt of \Villdenow, and the //. sorghum of Liumeus are 

 now referred to the genus Sorghum. [SOHOHCM.] Fraos refers the 

 MtAijTj of Theophrastus (' Hist. Plant,' viii. 1, 3, 7, 10) to these grasses, 

 and not to the Setaria Italica, as had been done by previous authors. 



( liiiliington, Manual ofltritish liotany ; Fraas, Synopsis Plant. Florae 



HOLKTUA, [THACHEARIA.] 

 HOLlliUT. [HirrooLossus.1 



il' iI.JGAKNA, a genus of Plants belonging to the natunil order 

 A xacardiacetr. The berries of //. longifolia are manufactured in India 



i well-known black varnish. 

 HOLLY. [Ii.EX.1 

 H'H.LY, SKA. [EiiYSGiuM.] 

 lIOf.i.Vh'JCK. [AI.TH.KA.] 

 HOLMKSITK. [CLi.vroNiTB.] 

 HO [.or; A NTH US. [Cii.v.iODON.] 

 HOLOCENTBUM (Agassis), the name of a genus of Fossil Ctenoid 



from Monti: linU. [Plan.] 

 MOLOCH JfTRUS, a genus of Fishes belonging to the family Scom- 



berid(f. H. niger of Lace'pede is the Centrolophus pompilius of Cuvier 

 and Valenciennes. [CENTROLOPHUS.] 



HOLO'PTYCHIUS (Agassiz), the name of a genus of Fossil Ganoid 

 Fishes from the Carboniferous Limestone of Burdie House near Edin- 

 burgh, and other localities. [FiSH.] 



HOLO'STEUM (from o\os, all, and baiiov, a bone, an anti- 

 phrasis applied to this plant because it is soft aud unlike bone), a 

 genus of Plants belonging to the natural order Caryophyttacece, and the 

 sub-order Alsinece. It has 5 sepals; 5 petals, toothed at the end ; 



3, 4, or 5 stamens ; 3 styles ; a subcyliudrical many-seeded capsule, 

 opening at the end, with 6 teeth. The species of this genus are 

 herbs with nothing to recommend them for use or cultivation. One 

 species, H. umbellcttum, is British. It has umbellate flowers, pubes- 

 cent viscid peduncles, the pedicels reflexed after flowering, the leaves 

 acute, elliptical, or elongate. It is not a common plant, but has been 

 found on old walls and dry places at Norwich, Bury St. Edtuuuds, 

 Eye, and Yarmouth. (Babington, Manual of British Botany.) 



HOLOTHURIA. [HOLOTHURIAMJ.] 



HOLOTHU'RIAD^E, a family of Animals belonging to the order 

 Echinodermata. 



Linnaeus, in his last edition of the ' Systema Naturte' (the 12th), 

 gives the following definition of his genus Holothuria, which he 

 places under his Vermes Mollusca, between Tethys and Terebella : 

 " Body free, naked, gibbous ; vent (anus) terminal. Tentacles nume- 

 rous at the other extremity (tentacula plura in altera extremitate). 

 Mouth situated among the tentacles." He records 9 species. Gmeliu, 

 in his edition (13th), increases the species to 23. 



The following is Lamarck's definition of Holothuria : " Body free, 

 cylindrical, thick, soft, very contractile; with a coriaceous skin, which 

 is most frequently papillose. Mouth terminal, surrounded with ten- 

 tacula divided laterally, subramose, or pinnated. Five calcareous teeth 

 in the mouth. Vent at the posterior extremity." He gives 10 

 species of Holothuria ; but he separates other Holothurice of authors 

 into the genera Fistularia and Priapulus. These three genera are 

 preceded by Actinia, and followed immediately by Sipunculus. The 

 place therefore assigned by Lamarck to Holothuria, is among the 

 Radiated Animals, in his third section of which, the Fistulides, he has 

 arranged the tribe. 



Cuvier gives the Holothuria a position among the Pedicillated 

 Echinoderms, making them follow the Echinidce. Priapulus is 

 placed by him in the next order, the Footless Echinoderms. He gives 

 a good outline of the anatomy, referring to the excellent work of 

 Tiedemann. 



M. De Blainville's Echinodermata form the first class of kiaActinozoa, 

 and the first order of that class consists of the Holothuridca, which 

 are followed (' Actinologie," 1834) by the Echinidea, his second order. 

 M. De Blainville thus defines the Holothuridca : 



"Body more or less elongated, sometimes subvermiform, soft or 

 flexible on all sides, provided with tentaculiforin suckers, often nume- 

 rous, very extensible, completely retractile, and pierced by a great 

 orifice at each extremity. Mouth anterior, at the bottom of a sort of 

 funnel or prebuccal cavity, sustained in its circumference by a circle 

 of nbro-calcareous pieces, and provided with a circle of arbuseular 

 appendages, more or less ramified. Vent terminating in a sort of 

 cloaca opening externally by a large terminal orifice. Generative 

 organs terminating externally by a single mesial orifice at a little 

 distance from the anterior extremity, and nearly marginal." 



M. De Blainville observes that Bianchi appears to have been the 

 first who came to the conclusion that this form ought to be approxi- 

 mated to the Echini, and in fact names one species, JfeMmu coriaceus ; 

 an opinion which was adopted by Blumenbach and most of the 

 modern zoologists, when they made the Holothuria! a division of their 

 Echinoderus with the Echini and Asterice ; some however, following 

 the idea of Pallas, consider that they should be placed near the 

 Actinice. 



The author last quoted remarks that the organisation of these 

 animals is not yet completely known, notwithstanding the labours of 

 Bohatsch, Miiller, Vahl, Forskahl, Monro, Tiedemann, and Delle Chiaje. 

 In addition to these names we would call the attention of the reader 

 to the drawing and description of Holothuria tremula, Linn., left by 

 John Hunter. The drawing is beautifully engraved, and, with the 

 description, will be found in the 1st vol. of the Descriptive aud Illus- 

 trated Catalogue of the ' Physiological Series of Comparative Anatomy, 

 contained in the Museum of the Royal College of Surgeons in 

 London,' pi. iii. The following parts are distinctly made out, namely : 

 1, The mouth, in which the bristle is introduced. 2, Appendicula 

 caeca, which surround the mouth, or fauces, into which they enter, 

 and which Mr. Hunter supposes to be salivary glands and ducts. 3, 

 A large one, lower down, just at the beginning of the intestinal canal. 



4, The whole tract of the intestinal canal, which is of considerable 

 length. 5, The dilated part of the intestine, or rectum, or what seems 

 to answer the same purpose as the dilated part of the gut at the anus 

 in a bird. 6, The anus. The use of the parts to which we next have 

 to advert, though the parts themselves are most clearly demonstrated, 

 seems to have been more the subject of conjecture with Mr. Hunter. 

 7, Two branching bodies almost like a tree, which consist of a duct 

 with its branches, and which open into the dilated part of the rectum. 

 These Mr. Hunter suspects to be the kidneys, from their opening 



