three distinct layers

Germ layer& One of three distinct layers of cells that arise in the inner cell mass, the ectoderm, mesoderm, and endoderm, each of which develops into a distinctly different tissue in the embryo.

胚胎发育到原肠胚时的细胞层，分为内胚层、中胚层、外胚层，各胚层将发育成一定的组织器官。

Not unlike other major subsystems in the Linux kernel, the SCSI subsystem exists as a layered architecture with three distinct layers.

与Linux内核中的其他主流子系统不同，SCSI子系统是一种分层的架构，共分为三层。

This film has three distinct layers: an outer, oily layer to prevent evaporation; a middle layer of lacrimal fluid, the main ingredient of tears; and an inner, mucous layer.

泪薄膜由三个不同的层面组成：外层是防止蒸发的油脂层，中层是眼泪的主要成分泪腺液体，内层是粘膜层。