Analysis of yolk syncytium behavior in Salmo and Catostomus

The formation and early behavior of the yolk syncytial layer (YSL) of selected representatives of the teleost orders Clupeiformes and Cypriniformes are described, contrasted, and correlated with normal embryonic staging sequences. Movements of the cytoplasmic syncytium in Catostomus commersoni have been mapped by implantation of chalk particles and correlated with the morphogenetic movements of the blastodisc. The chalk particle experiments show for the first time that YSL cytoplasm which reaches the yolk plug during epiboly is not a part of the syncytium when gastrulation begins. Furthermore, there is a distinct convergence of YSL cytoplasm toward the dorsal midline during epiboly which mimics the motion of the cells at this time.