Mammalia A class of warm-blooded animals that
have three characteristics not shared by other animals:
body hair; the production of milk for nourishment of
their infants by mammary glands (teats), which are
modified sweat glands; and the three middle ear bones
(malleus, incus, and stapes). Placental mammals have a
vascular-connected placenta formed between the
embryo and mother (e.g., humans, bears, whales).
Aplacental mammals do not (e.g., marsupials and
monotremes). Most mammals also have differentiated
teeth. Found on land and sea, there are around 5,000
species placed in 26 orders.
mange A partial or complete lack or removal of hair
resulting from various disorders or conditions. Also a
form of dermatitis caused by species of mites (for
example, Sarcoptes scabieicauses sarcoptic mange or
scabies). Also called alopecia.
mantle A membranous or muscular outer form of
tissue that surrounds the visceral mass in a mollusk and
secretes the shell and periostracum, the outermost layer
of shell that provides protection.
marine Refers to sediments or environments in seas
or ocean waters.
marsupial An aplacental mammal whose young are
born undeveloped and complete their embryonic devel-
opment not inside the body of the mother but, rather,
inside a maternal pouch called a marupium, located on
the outside of the body, in which the young attach to
the mother’s nipples. Kangaroos, wombats, bandicoots,
opossums, and Koala bears are examples. Found only
in Australia, Tasmania, New Guinea, and a few nearby
islands, except for the opossum, which is the only
North American marsupial.
Mastigophora A phylum composed of the most
primitive type of protozoans. Usually parasitic, they
have many flagella for movement, and some can form
pseudopodia, used for food engulfing or movement,
called flagellates. They live inside host organisms to
obtain nutrients and cause diseases such as trichomoni-
asis, giardiasis, trypanosomiasis, and leishmaniasis.matrilineal Societies in which descent is traced
through mothers rather than through fathers. Property
is often passed from mothers to daughters, and the cus-
tom of matrilocal residence may be encouraged. Many
Native American nations are matrilineal.matrix Often described as a scaffolding, support, or
cell growth director (intercellular); it is a complex net-
work of nonliving fibrous material of the connective
tissues that acts as structural support. Examples
include the skin, cartilage, bone, tendon, and muscle.matter Any substance that has inertia and occupies
physical space; can exist as solid, liquid, gas, plasma,
foam, or Bose–Einstein condensate.mean Astatistical method used to indicate a point
on the scale of measures where the population is cen-
tered. The mean is the average of the scores in a popu-
lation.mechanoreceptor A specialized sensory receptor
that responds to mechanical stimuli, e.g., tension, pres-
sure, or displacement. Examples include the inner-ear
hair cells, carotid sinus receptors, and muscle spindles.Mechnikov, Ilya Ilyich(1845–1916) RussianZool-
ogist Ilya Ilyich Mechnikov was born on May 16,
1845, in a village near Kharkoff in Russia to an officer
of the Imperial Guard, who was a landowner in the
Ukraine steppes.
Mechnikov went to school at Kharkoff and was
interested in natural history. He attended the University
of Kharkoff to study natural sciences. After graduating
at Kharkoff, he went to study marine fauna at
Heligoland, and then to the University of Giessen, the
University of Göttingen, and the Munich Academy. In
1865, while he was at Giessen, he discovered intracel-
lular digestion in one of the flatworms. At Naples heMechnikov, Ilya Ilyich 213