Spicule Formation by Isolated Micromeres of the Sea Urchin Embryo

摘要: Micromeres are isolated at the 16-cell stage from three species of Japanese sea urchins, Hemicentrotus pulcherrimus, Pseudocentrotus depressus , and Anthocidaris crassispina cultured in water containing a small amount horse serum. In all used, micromeres first divide unequally as they do vivo. The pattern number subsequent cleavages also same vivo, although not necessarily clear cases, since border adjacent cells become invisible each resting some batches embryos. After cleavage, passing through when contours individual cell obscure, decendants form aggregates similar to group primary mesenchyme blastula. Within such aggregates, spicular rudiment appears which develops either into triradiate spicule normal gastrulae or rod. grows three-dimensional skeleton is very pluteus skeleton, only its final shape size including species-specific characters but developmental course crystallographic nature. rod, on other hand, one-dimensional two-dimensional skeleton. These skeletons probably correspond part complete