Microchromosomic Chromocentra — 97 — Mitotic Division 



Milt. — Testes of fishes. 



Mimetism. — Mimicry, q.v. 



Mimic Genes. — Two or more non-allelomorphic genes which 

 produce similar or identical effects. 



Mimicry, — Resemblance of one species to a second species 

 due to natural selection. See Batesian — ; Mullerian — . 



Miscegenation. — Interbreeding as between different varieties. 



Misogamy. — Reproductive isolation. 



Mitochondria. — See Chondriosomes. 



Mitogenetic Radiation. — Radiation supposed to emanate 

 from certain growing tissues and to induce mitosis in other 

 tissues. 



Mitogenic Rays. — Mitogenetic Radiation, q.v. 



Mitome. — The protoplasmic reticulum as opposed to the ground 

 substance. 



Mitoschisis. — Mitosis, q.v. 



Mitosis. — The process of nuclear division in which daughter 

 nuclei are formed each having a chromosome complement 

 similar to that of the original nucleus. Mitosis is divisible into 

 the following stages: 



(i) Prophase. — Thin, double threads appear in the nucleus 

 and these contract and thicken. Each double thread is a chro- 

 mosome, split into two chromatids. At this stage there are 

 2n chromosomes (4n chromatids) present, 

 (ii) Prometaphase. — Where a centrosome is present this 

 now separates, the two halves moving to opposite sides of the 

 nucleus, but remaining 'joined' by the spindle. The nuclear 

 membrane disappears. 



(iii) Metaphase. — The chromosomes now arrange them- 

 selves in the equatorial plate. 



(iv) Anaphase. — Division of the centromeres now takes 

 place and the two halves of each centromere repel each other, 

 forcing the chromatids apart towards opposite poles of the 

 spindle. (The chromatids are now called 'daughter chromo- 

 somes'). The equatorial region of the spindle now elongates 

 (the 'stem body') thus moving the two sets of daughter 

 chromosomes still further apart. 



(v) Telophase. — The chromosomes elongate and take up 

 water becoming less and less easily discernible. Each group 

 becomes surrounded by a nuclear membrane and is now a 

 daughter nucleus with 2n chromosomes. 



Mitotic Division. — Mitosis, q.v. 



