primary mesoderm

例句：

1. 1.The development of the embryo is divided into three main stages: primary mesoderm, secondary mesoderm, and tertiary mesoderm.
   胚胎发育分为三个主要阶段：初级中胚层、次级中胚层和三级中胚层。
2. 2. During this stage, the primary mesoderm differentiates into various tissues such as muscle, bone, and cartilage.
   在这一阶段，初级中胚层分化为肌肉、骨骼和软骨等不同组织。
3. 3. The primary mesoderm is responsible for forming the body's basic structures, including the circulatorysystem, digestive system, and nervous system.
   初级中胚层负责形成身体的基本结构，包括循环系统、消化系统和神经系统。