Intra-uterine (L. intra, within; uterus, the womb), within the womb.

Irritability (L. irrito, excite), the property of responding to stimuli.

Linin (L. linum, flax), filaments of the cell-nucleus not readily stained by dyes.

Luetin Test (L. lues, pest), a test for syphilis; see [p. 188].

Mammals (L. mamma, breast), warm-blooded, hairy animals which suckle their young.

Maturation (L. maturus, ripe), the final stages in the development of the sex-cells characterized by two divisions in one of which the number of chromosomes is reduced by one-half.

Mendelian, Mendelism, referring to Mendel, the founder of a theory of heredity. See [p. 67].

Metazoa (Gr. meta, over; zoon, animal), all animals higher than the protozoa.

Mitosis (Gr. mitos, thread), indirect nuclear division, characterized by the appearance of a fibrous spindle and a definite number of chromosomes. The latter split to form daughter chromosomes which diverge to the poles of the spindle to form parts of the new nuclei.