Page:The New International Encyclopædia 1st ed. v. 09.djvu/882

* HEREDITY. 812 HEBEFOBD. given the name of germ plasm." This germ plasm exists in the nuclei of the reproductive cells. The word 'continuity' expresses the hypothesis that heredity depends on the fact that a minute quantity of this germ plasm lies unchanged in the nucleus of the reproductive cells during the growth of the plant or animal, and afterwards grows and gives rise to the germ cells. A further elaboration of Weismann's views is not here necessary ( see Use-Inheritance and Weismann- ism), bu^ to him we are mainly indebted for the view now generally held, that the germ plasm (chromatin) of the nuclear matter is the bearer of heredit}'. The hypothesis seems supported by the experi- ments of Boveri on the eggs of the species of two genera of sea-urchins. By cross-fertilization of whole eggs or bits of eggs of sea-urchins of differ- ent genera having nuclei, larvae are developed that share the larval forms of the parents of both genera. On the other hand, larvae arising from the enucleated bits of eggs have inherited the characters of the male genus only. Hence he claims to have demonstrated the law that the nucleus alone is the bearer of heredity. It may be observed that Hertwig, for the germ- plasm theory of Weismann, substituted the theory of the controlling inter-adjustments' of the embryonic cells, and later of the tissues and organs. HoMOCHRONOUs HEREDITY. A form of heredity called by Darwin "inheritance at corresponding periods of life," and by Haeckel "homochronous heredity." Darwin thus describes the phenome- non : "When the embryo leads an independent life, that is, becomes a larva, it has to be adapted to the surrounding conditions in its structure and instincts, independently of those of its parents; and the principle of inheritance at corresponding periods of life renders this possible." (lin/a- tion of Animals and Plants Under Domestica- tion. ) Again : "On this principle of inheritance at corresponding periods, we can understand how it is that most animals display from the germ to maturity such a marvelous succession of characters" (ib. ). Examples of this law are the complicated meta- morphosis of certain free, but more especially the parasitic worms, notably the flukeworms (see Trematoda) and the cestodes (see Ces- toda), the complicated metamorphoses of the echinoderms, of the mollusks, crustaceans, and of those insects with a complete metamorphosis, and more especially such insects as the Meloidie, Rhipiphoridie, and Stylopidfe, in which there is a hypermetamorphosis. It is not altogether improbable, says Packard, that the phenomenon of alternation of generations is primarily due to changes in surroundings, and hence of habits, resulting in new needs which were met by adaptation to the new surroundings, and that the different stages were fixed by ho- mochronous heredity. BiBLiOGRAPiiy. Brooks, The ioir of Heredity (Baltimore. 1883) ; Cope, Primari/ Factors of Orf/anic Evolution (Chicago. 1896) ; Darwin, Variation of Animals and Plants Under Domesti- cation (London. 2d ed.. 1875) ; Galton, TJereditary Genivs (London. 1869) ; id., Enfilish ^fen of Science (London. 1874) ; xA.. Inquiries into Human Faculty (London, 188.3) ; id.. Natural Inheritance (London, 1880) ; Hering. Das Gedachlniss als eine allgcmeine Funh'ion der organischen Mate- rie (Vienna, 1870) ; Jager, Zoologische Briefe (Vienna, 1876) ; id., Lehrbuch der Zuologie (Leip- zig, 1878J ; Lucas, Traitc pliilosophique et physi- ologique de I'heredite naturelle (Paris, 1847); Nilgeli, Meohanisch-physiologische Theorie der Ahstammungslehre (Munich, 1884) ; Ribot, Ij'her6dit6 psychologique (3d ed., Paris, Naval. London. 1875) ; Pearson. The Grammar of Sci- ence (2d ed., Loudon, 1900) ; "Mathematical Con- tributions to the Theory of Evolution," in the Transactions of the Philosophical Soeiefij (Lon- don, 1894-99) : "Data on the Problem of Evolu- tion of Man," in the Proceedings of the Royal So- ciety of London (London, 1898). A. Weissmann, Ueber die Vererbung (Jena, 1883) ; Papers on Heredity (Oxford, 1889) ; Amphimixus (Jena, 1891); The Germ Plasm (New York. 1S93) ; "The All-Sufficiency of Natural Selection," in Ilie Contempoi-ary Remew (London, 1893) ; -Vcwe Gedanken sur Vererbungsfrage (.lena, 1895) ; E. Haeckel, Die Perigenesis der PlaMidiile (Berlin, 1876). R. Virchow, "Descendenz und Pathologic," in Virchow's Arehiv, ciii., 1886; Y. Delage, La structure des protoplasn^es et les theories sur I'hdredite (Paris, 1895); Wilson, The Cell in Derelopmcut and Heredity (New York, 1900) ; Windle, "Malformations and Hered- ity," in Proceedings Birmingham' Philosophical Society (1888) ; Osborn, The Gartirripht Lectures (New York. 1892) ; "Present Problems in Evolu- tion and Hereditv," in Medical Record ( New York, 1892) ; "The Present Problem of Heredity," in Atlantic Monthly (Boston, March. 1891) ; Packard, "On the Inheritance of Acquired Char- acter in Animals with a Complete Metamorpho- sis." in Proceedings American Academy of Arts and Sciences (Boston, 1894). For the earlier bibliography of heredity, see Thompson. "History and Theory of Heredity," in Proceedings of the Royal Society (Edinburgh, 1889). See also the essays of Koelliker, IMaupas, Poulton, Driexh, Roux, Turner, Detmer. De Vries. Van Bemmelin. Vines, Le Dantic, Hamilton, Sommer, Amnion. Baldwin, Loeb. Nathusies, Pfeffer, Haacke. Tor- nier, Eigenmann. Lloyd, Morgan, and Bailey. HEREFORD^ her'e-ford. The capital of Here- fordshire, England, a Parliamentary and munici- pal borough of great antiquity, and an episcopal see; on the Wye. 51 miles south of Shrewsbury (Map: England, D 4). The chief building is the cathedral, dating from 1079, and the fourth church built on the site; it was restored in 1856- 63. The chapter-house contains the famous Map- pa Mundi — map of the world — of the thirteenth century. Other edifices are the bishop's palace, originally a Norman hall ; the Coningsby Hospi- tal, 1610; the corn exchange, and the Doric shire hall. Hereford has an endowed grammar school of the fourteenth century. It owns profitable mar- kets and real estate, gas, water, and electric- lighting plant; maintains a fire brigade, free library and museum, and the Castle green. Its industries and trade are chiefly agricultural. The see of Hereford was created in 673 ; the town was a fortified place in the reign of Athelstan. and numerous charters begin with King John. For its loyalty and sufferings during the Civil War, Charles I. bestowed the motto "Invictm fidelitatis prsemium." Population, in 1891, 20.- 300; in 1901, 21.400. Consult: Duncumb, His- tory and Antiquities of Hereford (Hereford,