Gametogenesis, Fertilization and Cleavage in the Trematode, Zygocotyle lunata (Paramphistomidae)

Abstract

Morph. of the chromosomes (2n = 14) is descr. in somatic tissue cells, early blastomeres, spermatogonia and oogonia. Behavior of the chromosomes during spermatogenesis and oogenesis is descr. from specimens varying in age from 23 days (immature) to 394 days, obtained from rats and ducks. Study of the relation between cytoplasmic inclusions of oocytes and nutrition of the ovum indicates that the developing ovum receives in its cytoplasm no abortive or degenerating oocytes from the ovary. Fertilization in the oviduct activates the oocyte to undergo the meiotic divisions, after which a resting female pronucleus is formed contiguous with a male pronucleus which becomes organized rapidly after the polocytes are formed. These stages and the ensuing early cleavages, up to the 5-cell stage in which condition the eggs are shed, occur at definite and constant levels in the uterus of the worm.