Fig. 9.

Secretory vesicles permit functional expansion without anatomical variation. Blue and white cells reflect the intracellular expression of blue and white gene products. The origin of the signal peptide directing proteins to the regulated secretion system/secretory vesicle (white arrow) permitted segregation of gene products into two distinct compartments: intracellular and intravesicular. The subsequent duplication and divergence of the blue gene (black arrow) could result in the acquisition of numerous new cell types through unique and combinatorial gene expression. Green—co-expression of blue and yellow, purple—co-expression of blue and red, brown—co-expression of blue, yellow, and red