In the human embryo described by Peters the mesoderm outside the embryonic disk is split into two layers enclosing an extra-embryonic coelom; there is no trace of an intra-embryonic coelom. At a later stage four cavities are formed within the embryo, viz., one on either side within the mesoderm of the pericardial area, and one in either lateral mass of the general mesoderm. – See more at: http://www.nexttec.tk/2015/08/development-of-body-cavities.html#sthash.VLFnFndl.dpufDevelopment of the Body Cavities | The Next Technology.