Pro thyalosoma \Pro* thy`a*lo*so"ma\, n.; pl. {Prothyalosomata}.
[NL., fr. Gr. prw^tos first + "y`alos glass + ?, ?, body.]
(Biol.)
The investing portion, or spherical envelope, surrounding the
eccentric germinal spot of the germinal vesicle.
[1913 Webster]