446 GLOSSARY 



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, 



1875.) 



[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, 

 1886.) 



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, 

 1835.) 



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.) 



