DEMINERALIZATION MECHANISM OF BORING GASTROPODS 67 



and again at the edge of the bubble of sea water. In deeper etchings 

 ( Fig. 8 ) the entire area under the gland and sea water was affected. 

 Contact of the distal secretory cap of the ABO with the substrate 

 produced the most active dissolution. Some of the demineralizing 

 agent must have diffused into the sea water around the ABO and 

 beyond the tube chamber to produce the peripheral etching (Fig. 

 16). Evolution of gas was not observed even at magnifications of 

 10 times during etching. That the etched area of shell is considerably 

 more fragile than the surrounding shell was demonstrated bv wiping 

 a coarse tissue paper across the etched shell of Murex fulvescens; 

 the paper left no mark whatsoever on the unaffected surface, but 

 deeply scratched the damaged region. This fact is further illustrated 

 by the trail of a lead pencil drawn across etched and nonetched 

 surfaces in Fig. 18. 



The demineralizing activity of ABOs of snails from mid-temperate 

 latitudes was accelerated with increasing temperatures in the range 

 of 5 to 30° C. However, ABOs heated approximately to 80 °C for 2 

 minutes produced only very faint etched lines at the edge of the 

 drop of sea water surrounding them. Etching of shell by excised 

 ABOs began the moment the organ was placed on shell, and pro- 

 ceeded for a variable period. Marked etchings were obtained in as 

 short a time as 3 hours. Although the majority of excised ABOs 

 etched shell, there was generallv a small minorit\' which etched onlv 

 slightly or incompletely, even under consistently uniform conditions. 

 This suggests that there may be variation in the capacity of individ- 

 ual snails to etch or that secretion may occur periodically in associa- 

 tion with the boring behavior; however, tests comparing the etching 

 capacities of ABOs excised from actively boring and from resting 

 snails have not been conclusive to date. Whether the organ continues 



Fig. 7. An optical micrograph made from a silver-shadowed negati\e 

 replica of the nacreous surface of the adductor muscle scar of the clam 

 Dosinia discus on which an excised ABO of a small moon snail, Polinices 

 dupUcatus, had been placed for 24 hours in vitro. Etching took place principally 

 under the periphery of the ABO. ( X 50. ) 



Fig. 8. A similar optical micrograph of the nacreous surface of the shell 

 of Miircx fulvescens on which an excised ABO of the naticid Siniim per- 

 spectivum had been placed for 24 hours in vitro. In this case damage to the 

 shell substrate occurred beneath the entire ABO. (X 50.) 



