338 



GLOSSARY 



Leucoplas'tids (AcvKos, white ; TrAcurros, form), the colourless plastids of plant- 

 cells from which arise the starch-formers (amyloplastids), chloroplastids, and 

 chromoplastids. (SCHIMPER, 1883.) 



Li'nin (linum, a linen thread), the substance of the "achromatic" nuclear 

 reticulum. (SCHWARZ, 1887.) 



Maturation, the final stages in the development of the germ-cells. More spe- 

 cifically, the processes by which the reduction of the number of chromosomes 

 is effected. 



Metakine'sis (see Metaphase) (/xera, beyond (i.e. further) ; KIVI/TJO-IS, movement), 

 the middle stage of mitosis, when the chromosomes are grouped in the equa- 

 torial plate. (FLEMMING, 1882.) 



Metanu'cleus, a term applied to the egg-nucleus after its extrusion from the 

 germinal 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 (/uera, after, beyond; 7rAcxo-/xa, a thing formed), a term collectively 

 applied to the lifeless inclusions (deutoplasm, starch, etc.) in protoplasm as op- 

 posed to the living substance. (HANSTEIN, 1880.) 



Micella, one of the ultimate supra-molecular units of the cell. (NAGELI, 1884.) 



Microcen'trum, the dynamic centre of the cell, consisting of one or more centro- 

 somes. (HEIDENHAIN, 1894.) 



Mi'cropyle (/xt/cpos, small; 7rv\r), orifice), the aperture in the egg-membrane 

 through which the spermatozoon enters. [First applied by TURPIN, in 1806, 

 to the opening through which the pollen-tube enters the ovule, t. ROBERT 

 BROWN.] 



Mi'crosome (tuKpos, small ; trto/xa, body), the granules as opposed to the ground- 

 substance of protoplasm. (HANSTEIN, 1880.) 



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, probably comparable 

 with the cell-plate in plants, formed in the equatorial region of the spindle during 

 the anaphases of mitosis. (FLEMMING. 1890.) 



Mi'tome (/xi'rto/xa, from /xiros, a thread), the reticulum or thread-work as opposed 

 to the ground-substance of protoplasm. (FLEMMING, 1882.) 



[Mitoschi'sis] (/XI'TOS, thread; (r^av, to split), indirect nuclear division; mito- 

 sis. (FLEMMING, 1882.) 



Mito'sis (/xiros, a thread), indirect nuclear division typically involving: a, the 

 formation of an amphiaster ; b, conversion of the chromatin into a thread 

 (spireme) ; c, segmentation of the thread into chromosomes ; d, splitting of the 

 chromosomes. (FLEMMING. 1882.) 



Mi'tosome (turos, a thread ; <r<o/xa, body), a body derived from the spindle-fibres 

 of the secondary spermatocytes, giving rise, according to PLATNER, 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 Blitschli (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. 



Nucleic acid, a complex organic acid, rich in phosphorus, and an essential 

 constituent of chromatin. 



