Fig. 4. Immunostaining with anti-escapin shows that escapin in the ink gland is expressed only in amber vesicles. Tissue is 100 µm thick vibrating microtome sections of ink gland of Aplysia californica. (A) Transmitted light illumination reveals the presence of amber (black asterisks), red-purple (white asterisk) vesicles, and an uncolored vesicle-like structure (arrow, highlighted in C). (B) Fluorescence image showing anti-escapin immunoreactivity. Note that only the amber vesicles are immunoreactive. The additional small area of immunoreactivity (arrow) might represent the cap of a vesicle whose bulk is located in the adjacent section. (C) Overlay of A and B. Note that red-purple vesicle and the uncolored vesicle-like structure (highlighted by dotted line) are unlabeled.