Ecotype
A locally adapted variant of a species, differing genetically from other ecotypes of the same
species.
Ectoderm
The outermost of the three primary germ layers in animal embryos; gives rise to the outer
covering and, in some phyla, the nervous system, inner ear, and lens of the eye.
Ectoparasites
A parasite, such as a flea, that lives on the exterior of another organism.
Ectotherm
An animal such as a reptile, fish, or amphibian, that must use environmental energy and
behavioral adaptations to regulate its body temperature.
Eeffector cell
A lymphocyte (as a T cell) that has been induced to differentiate into a form (as a cytotoxic T
cell) capable of mounting aspecific immune response called also effector lymphocyte.
Ectothermic
Relating to an organism that regulates its body temperature largely by exchanging heat with
its surrounding environment.
Efferent
Carrying away from a center, applied to nerves and blood vessels.
Egg
A female gamete, which usually contains abundant cytoplasm and yolk; nonmotile and often
larger than a male gamete.
Ejaculatory duct
In the male, a duct from each testis that join to form the urethra.
Elasmobranches
Any of numerous fishes of the class Chondrichthyes characterized by a cartilaginous
skeleton and placoid scales: sharks; rays; skates
Elastin
Elastin is a protein in connective tissue that is elastic and allows many tissues in the body to
resume their shape after stretching or contracting. Elastin helps skin to return to its original
when it is poked or pinched.
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