LUMINESCENCE 



545 



Panceri (51), in a pioneer study, found that the piddock Pholas dactyius 

 releases a luminescent secretion into the exhalant siphon from three 

 restricted regions of the body, namely a narrow band on the anterior edge 

 of the mantle, a pair of bands in the exhalant siphon and two triangular 

 spots near the retractor muscles (Fig. 13.5). The glandular cells involved 

 are elongated, with long ducts, and contain distinct secretory granules. 

 Forster (22) has described nerve fibres which enter and ramify among the 



Fig. 13.6. A Luminous Nudibranch Phyllirrhoe bucephala, with Mnestra 

 parasites Attached. (After Panceri, 1873, and Ankel, 1952.) 



light-cells. The pelagic gastropod Phyllirrhoe bucephala is a beautiful 

 luminescent form in which light appears from scintillating points scattered 

 over the body (Fig. 13.6). Each point corresponds to a single glandular 

 cell or group of cells lodged in the epidermis (Fig. 13.7). The cells are 

 rather large and contain masses of granular material which can be secreted 

 to the exterior. A nerve fibre proceeds to each of the glandular light-cells 

 and forms a terminal swelling on the side of the cell body. This swelling 

 appears like a specialized form of neuro-effector junction and displays a 

 series of equally spaced rodlets at the boundary with the cytoplasm proper 



M.A. — 18 



