Portion of tissue consisting of loosely organized undifferentiated mesodermal cells that give rise to such structures as connective tissues, blood, lymphatics, bone, and cartilage[XAO]. A mesh-like cell arrangement, less compact than an epithelium[ZFA]. The part of the embryonic mesoderm, consisting of loosely packed, unspecialized cells set in a gelatinous ground substance, from which connective tissue, bone, cartilage, and the circulatory and lymphatic systems develop[BTO]. [ http://zfin.org/curator http://en.wikipedia.org/wiki/Mesenchyme http://purl.obolibrary.org/obo/BTO_0001393 ]