yaws Bacterial disease caused by the spirochete
Treponema pertenue, often transmitted by flies.
yeasts One of several species of ascomycete fungi
in which an extensive mycelium is not produced, so that the oganism
is usually unicellular.
yellow fever Virus disease transmitted by the mosquito
Aedes aegypti.
yellowcake The concentrate of 70 to 90 percent
uranium oxide extracted from crushed ore.
yolk plug The large yolk-filled cells that
protrude from beneath the ectoderm at the blastopore of the amphibian
gastrula.
yolk sac The stored food reserve (yolk) and its
surrounding membranes, which is found in embryonic reptiles, birds,
and mammals.