DEMINEEALIZATION MECHANISM OF BORING GASTROPODS 81 



to which crystals may be loosened in one apphcation of an active 

 ABO was indicated by the successive number of replicas necessarv 

 to reveal the topography of more intact shell beneath. Action of 

 ABO secretion on the organic matrix of shell, if any, is not yet 

 known. Since radular teeth can rasp through the surface layer (or 

 periostracum) of conchiolin on shell (Carriker, 1943) and through 

 the noncalcareous horny wall of the egg capsule of a gastropod 

 (Jensen, 1951), loosening of mineral crystals alone should be suf- 

 ficient to permit effective boring hv the snail. The duration of the 

 period (from a few minutes to almost an hour) during which the 

 ABO is extended by living gastropods on the shell of hving prey is 

 not inconsistent with the time required to obtain desp etchings by 

 excised ABOs in vitro. Likewise significant here is an earher observa- 

 tion ( Carriker, 1943 ) that snails rasp in the hole for relatively short 

 periods of time and generally only while shell flakes can be removed. 

 If it should subsequently be found that the conchiolin support for 

 the crystals is also weakened or destroyed, the removal of shell by 

 the radula would be seen to be facilitated that much more. 



The absence of acid in the secretion of the ABO and in ABO 

 homogenates, the strong effect of the active agent on calcarecus sub- 

 strates, and the near inactivation of the agent when heated to 80 °C 

 give support to the suggestion of Hirsch ( 1915) that one constituent 

 of this agent may be a kind of "calcase." Our studies also suggest 

 that a chelating agent, or a chelating agent and enzyme combined, 

 may be involved. The electron micrographs of nacreous shell surface 

 etched by versene support the chelating agent hypothesis as clearly 

 as does an electron micrograph bv Gregoire (1957) of a polished 

 transverse section of the nacreous shell of the snail Turbo etched 

 with sequestrene. It should be emphasized that the similarity of 

 electron micrographs of etchings by the neutral to slightly alkaline 



Figs. 32 to 37. A group of election micrographs made from pseudo replicas 

 on which loosened crystals were removed from the nacreous surfaces of shells 

 subjected to the action of HCl and versene. Note the similarity of the damaged 

 crystals to those in Figs. 20 to 25. ( X 6000.) 



Figs. 32 and 33. Crassostrea virginica, 5 seconds in 0.1 n HCl, pH 1.0. 

 Figs. 34 and 35. C. virginica, 48 hours in versene, pH 8.0. 

 Figs. 36 and 37. Murex fulvescens, 24 hours in versene, pH 8.0. 



