Regional differences in the pattern of vitellogenesis in the painted frog Discoglossus pictus

During oocyte growth in the frog Discoglossus pictus two patterns of vitellogenesis are described. The first one consists of the transformation of multivesicular bodies into yolk platelets; the second is the result of a typical endocytotic process, as described in other species. The peculiarity in Discoglossus vitellogenesis consists of a regional difference of these features of vitellogenesis in vitellogenic oocytes: the multivesicular bodies transforming into yolk platelets are found only in the germinative area--the central portion of the animal half--whereas deep crypts with numerous endocytotic pits are found only in the vegetal half. The probable meaning of this regional difference in vitellogenic oocytes is discussed.