578 APPENDIX III 



Interphase, the resting stage that may occur between the first and second 



divisions. Should not be applied to the resting stage in general. 



Lundegdrdh, 191 2. 

 Inversion, the reversal of the linear sequence of the genes in one segment of a 



chromosome relative to the centromere. Sturtevant, 1926 {cf. Ch. VII). 

 Isogamy, morphological similarity of fusing gametes. 

 [Karyokinesis], Schleicher, 1878, mitosis, q.v. 

 [Karyology], nuclear cytology. 

 [Karyomere], a compartment or vesicle in the resting nucleus, usually 



containing one chromosome. 

 Leptotene, the single chromosome threads at the early stage of the prophase 



of meiosis, and by extension the stage itself, {v. Zygotene, Pachytene, 



Diplotene) v. Winiwarter, 1900. 

 Lethal Factors, factors which render inviable an organism or, by extension, 



a cell possessing them. 



Balanced , factors which lie in chromosomes of opposite 



gametes and do not frequently cross over at meiosis. The chromosomes 



concerned must be homologues except in a ring-forming interchange 



heterozygote. Muller, 191 8, 1930 h. 

 [Linin], a structural component of the nucleus. The term has been applied to 



the descriptions of various artefacts and has no definite meaning. 

 Localisation, the genetic property of restriction of pachytene pairing and 



chiasma formation to one part of the chromosomes — proximal or distal. 



D., 1931 c. 

 Macronucleus, the large vegetative nucleus of the Infusoria. 

 [Matrix], the space left round the solid part of a metaphase or anaphase 



chromosome when it contracts, by syneresis or otherwise, to reveal its 



characteristic or non-characteristic structure, following fixation. By 



extension applied to any analogous appearance at prophase or telophase 



or to the supposed cause of any behaviour that might result from any 



analogous differentiation. Sharp, 1935 ; cf. D., 1935 d. 

 Matroclinal Inheritance, that in which the offspring resembles the mother more 



closely than the father (as opposed to Patroclinal) . 

 Maturation, the formation of gametes or spores by meiosis. 

 Megaspore (Macrospore), a spore having the property of giving gametophytes 



with only female gametes (the embryo-sac). 

 Meiosis, a form of mitosis in which the nucleus divides twice and the chromo- 

 somes once. The prophase of meiosis is the prophase of the first of the 



two divisions. Farmer and Moore, 1905. 

 Merogony, development of part of an egg with the sperm nucleus, but without 



the egg nucleus, as in male parthenogenesis. 

 [Metabolic Stage], an unwarranted physiological description of the resting 



stage, q.v. 

 Metaphase, the stage of mitosis or meiosis in which the chromosomes lie in a 



plane at right angles to the axis of the spindle and half-way between the 



poles. Strashurger, 1884. 

 Microchromosomes, fragment chromosomes in the Hemiptera which do not 



form chiasmata and do not usually pair until metaphase. Wilson, 1905. 

 Micronucleus, the small, permanent, reproductive nucleus of the Infusoria. 

 Microspore, the spore which produces a gametophyte bearing only male 



gametes (the pollen grain). 

 Mitosis, the process by which daughter chromosomes are separated into two 



identical groups ; the diagnostic property of division of the nucleus. The 



term may be conveniently used in contradistinction to meiosis. Flem- 



ming, 1882. 



