Figure 19.7 Induction during Vulval Development in Caenorhabditis elegans (A) In the nematode C. elegans (shown in false color here), it is possible to follow all of the cell divisions from the fertilized egg to the 959 somatic cells found in the adult. (B) During vulval development, a molecule secreted by the anchor cell (the LIN-3 protein) acts as the primary (1°) inducer. The primary precursor cell (the one that receives the highest concentration of LIN-3) then secretes a secondary (2°) inducer that acts on its neighbors. The gene expression patterns triggered by these molecular switches determine cell fates.