Figure 4.

The contractile network hypothesis. (a) Evolutionary precursor state with epithelial mechanosensory and mesenchymal cells with long interconnected contractile and conductive processes forming a tissue-wide network. (b) The first nervous system comprising mechanosensory neurons innervating a tissue-spanning elementary nerve net composed of multipolar interneurons. The nerve net neurons innervate a network of contractile myocytes. Red boxes on the cells represent conductive ion channels. Red lines indicate actomyosin filaments for contraction. (Online version in colour.)