Developmental Timing in Fertilized Merogones of the Sand Dollar, Clypeaster japonicus

摘要: Pairs of nucleate and non-nucleate fragments prepared by manually bisecting unfertilized eggs Clypeaster japonicus were inseminated to obtain a pair egg fragments, one with diploid nucleus (zygote) the other male pronucleus (merogone). Haploid pronuclei in merogone always entered first mitosis (NEB) later than zygote partner. The delay NEB ranged from 6 24 min different pairs. interval formations karyomere cleavage furrow, durations second, third fourth cell cycles identical zygote-merogone Observations Colcemid-treated suggested that duration DNA synthetic period was prolonged merogone. From this observation wide variation time mitosis, contrast constant subsequent mitotic intervals, we suppose some critical event triggers transition development for start well-ordered sequences cycle sea urchin development.