The Cell in Development and Inheritance

Iso'tropy (to-os, equal; rpoTrrj, a turning), the absence of predetermined axes (as applied to the egg). (Pfluger, 1883.) [Ka'ryaster] (Kapvov, nut, nucleus ; see Aster, 2), the star-shaped group of chromo- somes in mitosis. Opposed to cytaster. (Flemming, 1882.) Karyokine'sis (Kapvov, nut, nucleus; KtVr/crts, change, movement), the same as mitosis. (Schleicher, 1878.) [Karyo'lysis] (Kapvov, nut, nucleus ; A-ucrts. dissolution), the supposed dissolution of the nucleus during cell-division. (Auerbach, 1874.)

[Karyoly'tic figure] (see Karyolysis), a term applied by Auerbach to the mitotic figure in livino- cells. Believed bv him to result from the dissolution of the nucleus. (A^uerbach, 1874.) Karyonii'crosonie (see Microsome), the same as nucleo-microsome. Karyomi'tome (Kapvov. nut, nucleus ; /xtVtu/xa, from /jllto^, a thread), the nuclear as opposed to the cytoplasmic thread-work. (Flemming, 1882.) Karyomito'sis (Kapvov, nut, nucleus ; see Mitosis), mitosis, (Flemming,

Ka'ryoplasm (Kapvov, nut. nucleus ; 7rAao-/xa, a thing formed), nucleoplasm. The nuclear as opposed to the cytoplasmic substance. (Flemming, 1882.) Ki'noplasm (Kivelv, to move ■ 7rAacr/xa, a thing formed), nearly equivalent to archoplasm, but used in a broader sense to denote in general the more active elements of protoplasm from which arise fibril] ae, the substance of cilia, and (in plants) the peripheral " Hautschicht " from which the membrane is

formed; opposetl to the " troplioplasm '" or nutritive plasm. (Stkashi'RGER, [Lanthanin] (Aav^ctvetv, to conceal), equivalent to oxychromatin. ( Hi:idknhain, Leucoplas'tids (AevKo?, white : TrAaoro?, form), the colourless plastids of plant- cells from which arise the starch-formers (amyloplastids), chloroplastids, and chromoplastids. (Schlmper, 1883.) Li'nin (linum, a linen thread), the substance of the "achromatic"' nuclear reticu- lum. (SCHWARZ, 1887.)

Lininoplast, the true nucleolus or plasmosome. (Eisen, 1899.) Macrocentrosome, a term applied to the " centrosome " in Boveri's sense, i.e. to the larger body in which lies the central granule. (Zikgler, 1898.) Probably svnonymous with entosphere. Maturation, the final stages in the development of the germ-cells. .More spe- cifically, the process by which the reduction of the number uf chromosomes is effected. Metakine'sis (see Metaphase) (/xera, beyond {i:e. further) ; KLvvrjrrL^;. movement), the middle stage of mitosis, when the chromosomes are grouped in the equatorial plate. (Flemming, 1882.)

Metanu'cleus, a term applied to the nucleolus after its e.xtrusion from the germi- nal vesicle. (Hacker, 1892.) Met'aphase, the middle stage of mitosis during which occurs the splitting of the chromosomes in the equatorial plate. (Strasburger, 1884.) Met'aplasm (/xera, after, beyond; TrAacr/xa. a thing formed), a term collectively applied to the lifeless inclusions (deutoplasm. starch, etc.) in protoplasm as op- posed to the living substance. (Hansteix, 1868.)

Micel'la, one of the ultimate supra-molecular units of the cell. (N.ageli. 1884.) Microcentrosome. equivalent to the central granule or centriole of Bovcri. (Ziegler, 1898.) Microcen'trum, the centrosome or group of centrosomes united by a '• primary centrodesmus," forming the centre of the astral system. (Heidenhain, 1894.) Mi'cropyle (fjuKpo^, small: ttvXt], orifice), the aperture in the egg-membrane through which the spermatozoon enters. [First applied by Ti'Ri'i.v, in 1806, to the opening through which the pollen-tube enters the ovule. /. Rohert

Brown.] Mi'crosome (fxiKpoq, small : croj/xa, body), the granules as opposed to the ground- substance of protoplasm. (Hansteix, 1880.) Microsphere, the central region of the aster (centrosphere) at the centre of which lie the centrosomes. (Kostanecki and Siedlecki, 1896.) Middle-piece, that portion of the spermatozoon lying behind the nucleus at the base of the flagellum. (Schweigger-Seidel. 1865.) Mid-body ("Zwischenkorper ''), a body or group of granules, i)robal)ly comparable

with the cell-plate in plants, formed in the equatorial region of the spindle during the anaphases of mitosis. (Flemming, 1890.) Mi'tome (/xtrco/xa, from ^tVos, a thread), the reticulum or thread-work as opposed to the ground-substance of protoplasm. (Flemming, 1882.) [Mitoschi'sis (/xiro9, thread ; ax^C^i-v, to split), indirect nuclear division; mitosis. (Flemming, 1882.) Mito'sis (iJLLTo<;, a thread), indirect nuclear division typically involving: u, the

formation of an amphiaster: /\ conversion of the chromatin into a thread (spireme) : r, segmentation of the thread into chromosomes : (/. splitting of the chromosomes. (Flemming, 1882.) Mi'tosome (^tros, a thread; aCjfxa, body), a body derived from the spindle-fibres of the secondary spermatocytes, giving rise, according to Platxer, to the mid- dle-piece and the tail-envelope of the spermatozoon. Equivalent to the Neben- kern of La Valette St. George. (Platxer, 1889.)

Nebenkern (Paranucleus), a name originally applied by Butschli (1871) to an extranuclear body in the spermatid : afterwards shown by La Valette St. George and Platner to arise from the spindle-fibres of the secondary spermatocyte. Since applied to many forms of cytoplasmic bodies (yolk-nucleus, etc) of the most diverse nature. Nuclear plate, i. The equatorial plate. (Strasburger, 1875.) 2. The parti- tion-wall which sometimes divides the nucleus in amitosis.

Nuclein, the chemical basis of chromatin ; a compound of nucleinic acid and albumin or albumin radicles. (Miescher, 1871.) Nucleinic or nucleic acid, a complex organic acid, rich in phosphorus, and an essential constituent of chromatin. Nucleo-albumin, a nuclein having a relatively high percentage of albumin. Dis- tinguished from nucleo-proteids by containing paranucleinic acid which yields no xanthin-bodies. [Nucleochyle'ma] (x^^Ad?, juice), the ground-substance of the nucleus as opposed to that of the cytoplasm. (Strasburger, 1882.)

Nucleohy'aloplasma (see Hyaloplasm), the achromatic substance (Hnin) in which the chromatin-granules are suspended. (Strasburger, 1882.) Nucleomi'crosomes (see Microsome), the nuclear (chromatin) granules as opposed to those of the cytoplasm. (Strasburger, 1882.) Nu'cleoplasm. i. The reticular substance of the (egg-) nucleus. (Van Bene- dex, 1875.) 2. The substance of the nucleus as opposed to that of the cell- body or cytoplasm. (Strasburger, 1882.)

Nucleo-pro'teid. a nuclein having a relatively high percentage of albumin. May be split into albumin and true nucleinic acid, the latter yielding xanthin-bodies. CEde'matin (otSy^/xa, a swelling), the granules or microsomes of the nuclear ground- substance. (Reinke, 1893.) O'ocyte (Ovocyte) (ww, egg; kvto?, hollow (a cell)), the ultimate ovarian ^gg before formation of \he polar bodies. The primary oocyte divides to form the first polar body and the secondary oocyte. The latter divides to form the second polar body and the mature egg. (Boveri, 1891.)

Oogenesis, Ovogenesis (todv, (t%g ; yeVccrts, origin), the genesis of the ^gg after its origin by division from the mother-cell. Often used more specifically to denote the process of reduction in the female. Oogo'nium, Ovogonium (cudv, ^gg ; yovr;, generation), i . The primordial mother- cell from which arises the egg and its follicle. (Pfluger.) 2. The descend- ants of the primordial germ-cell which ultimately give rise to the oocytes or ovarian eggs. (Boveri, 1891.)

Ookine'sis (coov, egg; KLvrjai^, movement), the mitotic phenomena of the egg dur- ing maturation and fertilization. (Whitman, 1887.) O'vocentre, the egg-centrosome during fertilization. (FoL, 1891.) Oxychro'matin (o#i;s. acid ; see Chromatin), that portion of the nuclear substance stained by acid tar-colours. Equivalent to '"linin" in the usual sense. (Heidenhain, 1894.) Pangen'esis (ttS? (Trav-), all; yeVecrt?, production), the theory of gemmules, accord- ing to which hereditary traits are carried by invisible germs thrown off by the individual cehs of the body. (Darwin. 1868.) Pangens (ttS? (vrav-), all ; -yeVvys, producing), the hypothetical uhi mate supra-molec- ular units of the idioplasm, and of the cell generally. Equivalent to gemmules, micellae, idioblasts, biophores, etc. (De Vries, 1889.)

Parachro 'matin (see Chromatin), the achromatic nuclear substance (linin of Schwarz) from which the spindle-tibres arise. (Pfitznkk, 1883.) Parali'nin (see Linin), the nuclear ground-substance or nuclear sap. (Schwarz Parami'tome (see Mitome), the ground-sub.stance or interfilar sub.stance of proto- plasm, opposed to mitome. (Flem.ming, 1892.) Paranu'clein (see Nuclein), the substance of true nucleoli or plasmosomes. Pyrenin of Schwarz. (O. Hertwig, 1878.) Applied by Kossel to "nucleins" derived from the cytoplasm. These are compounds of aibumin and paranucleic acid which yields no xanthin-bodies.

Par'aplasm {irapL beside; irXdajxa, something formed), the less active portion, of the cell-substance. Originally applied by Kupffer to the cortical region of the cell (exoplasm). but now often applied to the ground-substance. (Kl'I'FFFR, Periplast (irepL, around; TrXao-TOs, form), i. The peripheral j)art of the cell, including those parts outside the nucleus or ^'endoplast."" (Hl-xlev. 1853.) 2. A term somewhat vaguely applied to the attraction-sphere. The term daughter-periplast is applied to the centrosome. (Vejoovsky, 188S.)

Perisphere (Trepc, around), a term applied to the outer region of the attraction- sphere in nerve-cells, and opposed to an inner '• centrosphere."' (Lenhossek, Plasmocytes (7rAacr/xa, K\no%), colourless blood-corpuscles supposed to be free attraction-spheres. (Eisen, 1897.) Plas'mosome (7rAao-/xa, something formed {i.e. protoplasmic) ; adfxa, body), the true nucleus, distinguished by its affinity for acid tar-colours and other -plasma- stains.'' (Ogata, 1883.)

Pla'some (irXdafxa, a thing formed; o-to/xa, body), the ultimate supra-molecular vital unit. See Biophore, Pangen. (Wiesxer. 1890.) Plas'tid (TrXasrds, form), i. A cell, whether nucleated or non-nucleated. (Hackel, 1866.) 2. A general term applied to permanent cell-organs (chloroplasts. etc.) other than the nucleus and centrosome. (Schi.mper, 1883.) Plas'tidule, the ultimate supra-molecular vital unit. (Elssbekg, 1874; H.ackel, Plas'tin, a term of vague meaning applied to a substance related to the nucleo- proteids and nucleo-albumins constituting the linin-network (Zacharias) and the cytoreticulum (Carnoy). (Reixke and Rodewald. 1881.)

Pluri'valent {plus, more; valcre, to be worth), applied to chromatin-rods that have the value of more than one chromosome soisn strict u. ( H.uker. 1892.) Polar bodies (Polar globules), two minute cells segmented ort' from the ovum before union of the germ-nuclei. (Disc, by Carus, 1824; so named bv Robin. Polar rays (Polradien), a term sometimes applied to all of the astral rays as opposed to the spindle-fibres, sometimes to the group of astral rays opposite to the spindle-fibres.

Pole-plates (End-plates), the achromatic spheres or masses at the poles of the spindle in the mitosis of Protozoa, probably representing the attraction-spheres. (R. Hertwig, 1877.) Polyspermy, the entrance into the ovum of more than one spermatozoon. [Prochro'matin] (see Chromatin), the substance of true nucleoli, or plasmosomes. Equivalent to paranuclein of O. Hertwig. (Pfitzxer, 1883.) Pronuclei, the germ-nuclei during fertilization : i.e. the egg-nucleus (female pro« nucleus) after formation of the polar bodies, and the sperm-nucleus (male pro- nucleus) after entrance of the spermatozoon into the egg. (Van Beneden,

[Prothy'alosome] (see Hyalosonie). an area in the germinal vesicle {oi Ascaris^ by which the germinal spot is surrounded, and which is concerned in formation of the first polar body. (Van Beneden, 1883.) Pro'toblast (7rfjioro<;. first; ySAao-ro?. a germ), i. A naked cell, devoid of a mem- brane. (KoLLiKER.) 2. A blastomere of the segmenting egg which is the parent-cell of a definite part or organ. (Wilson, 1892.) Pro'toplasm (Trpcorog. first; TrAacr/xa. a thing formed or moulded). The active or '• living "■ cell-substance. By all earlier and some present writers applied only to the substance of the cell-body (equivalent to Strasburger's cytoplasm). By many later writers applied to the entire active substance of the cell (karyoplasm plus cytoplasm). (Purkinje, 1840; H. von Mohl, 1846.)

Pro'toplast (TrpoiTos. first: TrAacrro?, formed), i. The protoplasmic body of the cell, including nucleus and cytoplasm, regarded as a unit. Nearly equivalent to the energid of Sachs. (Hanstein, 1880.) 2. Used by some authors synony- mously with plastid. [Psetidochro'matin] (see Chromatin), the same as prochromatin. (Pfitzner, Pseudonu'clein (see Nuclein), the same as the paranuclein of Kossel. (Ham- marsten, 1894.) Pseudo-reduction, the preliminary halving of the number of chromatin-rods as a prelude to the formation of the tetrads and to the actual reduction in the number of chromosomes in maturation. (Ruckert, 1894.)

Pyre'nin (irvprjv, the stone of a fruit ; /.t\ relating to the nucleus), the substance of true nucleoli. Equivalent to the paranuclein of Hertwig. (Schwarz. 1887.) Pyre'noid (-n-vprjv, the stone of a fruit: like a nucleus), colourless plastids (leuco- plastids). occurring in the chromatophores of lower plants, forming centres for the formation of starch. (Schmitz, 1883.) Reduction, the halving of the number of chromosomes in the germ-nuclei during maturation.

Sarcode {crapL flesh). The protoplasm of unicellular animals. (Du Jardin, Sertoli-cells. the large, digitate, supporting, and nutritive cells of the mammalian testis to which the developing spermatozoa are attached. (Equivalent to "sper- matoblast" as originally used by Von Ebner, 1871.) Sper'matid (airepixa, seed), the final cells which are converted without further division into spermatozoa ; they arise by division of the secondary spermatocytes or " Samenmlitterzellen.'' (La Valete St. George, 1886.)

Sper'matoblasts (cnrepfxa, seed : /^Aacrro?, germ), a word of vague meaning, originally applied to the supporting cell or Sertoli-cell, from which a group of spermatozoa was supposed to arise. By various later writers used synonymously with spermatid. (VoN Ebner, 1871.) Sper'matocyst (a-rreppja. seed : KvarL'i, bladder), originally applied to a group of sperm-producing cells ("spermatocytes"'), arising by division from an " Ursa- menzelle"' or "spermatogonium." (La Valette St. George, 1876.)

Sper'matocyte (o-Trep/xa, seed; Kvroq, hollow (a cell)), the cells arising from the spermatogonia. The primary spermatocyte arises by growth of one of the last generation of spermatogonia. By its division are formed two secondary sper- matocytes, each of which gives rise to two spermatids (ultimately spermatozoa). (La Valette St. George, 1876.) [Spermatogem'ma] (cr7rep/xa, seed; geniuia. bud), nearly equivalent to spermatn- cyst. Differs in the absence of a surrounding membrane. [In mammals. La Valette St. Georcje. 1878.]

Spermatogen'esis {air^pfxa, seed; yeVcmi;. origin), the phenomena involved in the formation of the spermatozoon. Often used more specifically to denote the process of reduction in the male. Spermatogo'nium ("• Ursamenzelle'') (rr7rep/xa, seed; yovy. generation), the descendants of the primordial germ-cells in the male. Kach ultimate sper- matogonium typically gives rise to four spermatozoa. (La \'ai.f:ite St. George, 1876.) Sperniatome'rites {cnripixa, seed; /xepos. a part), the chromatin-granules into which the sperm-nucleus resolves itself after entrance of the spermatozoon. (In Petrojnyzo7i, Bohm, 1887.)

Spermatozo'id (see Spermatozoon), the ciliated paternal germ-cells in plants. The word was first used by von Siebold as synonymous with spermatozoon. Sperm-nucleus, the nucleus of the spermatozoon ; more especially apjilied to it after entrance into the egg before its union with the egg-nucleus. In this sense equivalent to the "male pronucleus"' of Van Beneden. (O. Hkktnvk;. Sper'mocentre, the sperm-centrosome during fertilization. (Fol, 1891.) Spi'reme {criT^.ip'qjxa, a thing wound or coiled; a skein), the skein or •• Knauel" stage of the nucleus in mitosis, during which the chromatin appears in the form of a thread, continuous or segmented. (Flemmixg, 1882.)