446 G/.oss,!/n' 



Pronuclei, the ccrm-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 Beneijen, 

 1875.) 



[Prothy'alosonie] (see Hyalosome). an area in the germinal vesicle (of .-Iscar/s) 

 bv which the germinal spot is surrounded, and which is concerned in formation 

 of the first polar body. (Van Beneuen, 18S3.) 



Protoblast (Trpwros, first; /t^Aaards. a germ)- i- A naked cell, devoid of a mem- 

 brane. (KoELiKEK.) 2. A blastomere of the segmenting egg which is the 

 jxirent-cell of a definite part or organ. (Wilson. 1892.) 



Pro'toplasni (Trpwros. first; TrAacr/tu. 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.) 



Protoplast (TTpwro?. first; ttAoio-tos. 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. 



[Pseudochro'matin] (see Chromatin), the same as prochromatin. (Pfitzner, 

 1886.) 



Pseudonu'clein (see Nuclein). the same as the paranuclein of Kossel. (Ham- 



MARSTKN, 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. (RlrcKERT, 1894.) 

 Pyre'nin {wp-^v, the stone of a fruit ; /.i'. relating to the nucleus), the substance of 



true nucleoli. Equivalent to the paranuclein of Hertwig. (ScHWARZ, 1887.) 

 Pyre'noid (-n-vpyjv, 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 {a-irippua, 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 (cnripixa, seed; /JAao-rds, 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 {(nripp.a. seed; kvoti?, 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 {cnrippjn, seed ; kvto<;, hollow^ (a cell)), the cells arising from the 

 spermatogonia. The primary sperinatocytc arises by growth of one of the last 

 generation of sperm.atogonia. By its division are formed two secondary sper- 

 matocytes, each of which gives rise to two spermatids (ultimately spermatozoa). 

 (La Valette St. George, 1876.) 



