Slide 10 - section through an Embryo.  In the loosest, palest areas on the lateral aspect of the section, note the stellate mesenchymal cells with fine processes seeming to form a network in a pale, amorphous (fluid, in life) intercellular substance.  In older embryos a few fine fibers will also be seen, but mesenchyme, is predominantly a cellular tissue.  Although mesenchyme as such no longer exists in the adult, a number of primitive, mesenchyme-like cells do remain and can produce new connective tissue cells when needed for repair (as in wound healing).