jacket cells Ciliated somatoderm of an orthonectid
mesozoan.
Jacobson's (vomeronasal) organ Olfactory receptor
present in most reptiles; blind-ending sacs that open through
the secondary palate into the mouth cavity; they are used to sample
airborne chemicals.
jawless fishes (class Agnatha)Fishes that lack
jaws and paired fins: hagfishes (or slime eels) and lampreys.
Jejunum Portion of the small intestine located
between the duodenum and the ileum.
jet streams Powerful winds or currents of air that
circulate in shifting flows; similar to oceanic currents in extent
and effect on climate.
Johnston's organ Mechanoreceptor (auditory receptor)
Found at the base of the antennae of male mosquitoes and midges.
joule A unit of energy. One joule is the energy
expended in 1 second by a current of 1 amp flowing through a resistance
of 1 ohm.
juvenile hormone Hormone produced by the corpora
allata of insects; among its effects are maintenance of larval
or nymphal characteristics during development.
juxtaglomerular apparatus Complex of sensory cells
located in the afferent arteriole adjacent to the glomerulus and
a loop of the distal tubule, which produces the enzyme renin.