FORMATION OF THE LAYERS OF THE BLASTODERM. 655 



branes surrounding it, each layer being developed into certain 

 tissues and forming these only. 



Thus from the epiblast, or outer layer, arise the epidermis of 

 the skin, and the brain and spinal cord, and certain parts of the 

 organs of special sense ; whilst it also aids in the formation of the 



FIG. 250. 



Zf. 



Sections of the ovum of a rabbit, showing the formation of the blastodertnic vesicle. 

 (E. Van Beneden ) o, 6, c, d, are ova in successive stages of development, z.p. Zona pel- 

 lucida. ect. Ectomeres, or outer cells, ent. Entomeres, or inner cells. 



chorion and the amnion. From the mesoblast are developed the 

 skeleton, the connective tissues, the muscles, the nerves, in 

 addition to the vascular system and the supporting tissue of the 

 glands ; one kind of tesselated cells arise from this layer, viz., 



