DEMINEBALIZATION MECHANISM OF BORING GASTROPODS 65 



48 hours in 10 per cent disodium versenate (pH 7.5-8.0) at room 

 temperature. 



Optical Microscopy, Electron Microscopy, 

 and Microradiography 



The methods described by Scott and Wyckoff (1946, 1956) were 

 employed in the optical and electron microscopic study of etched 

 substrate surfaces by means of shadowed replicas. Contact and pro- 

 jection microradiographs were made from sections of shells by the 

 various technics outlined by Scott et al. (1962). Figures 5 to 49 in 

 this paper are all negative prints; electron-opaque objects thus ap- 

 pear white, and shadows appear black. 



Observations and Results 



Activity of ABOs and ABO Homogenates 



Repeated pH determinations of the fluid clinging to normally 

 withdrawn and normally extended ABOs, excised ABOs, and ABO 

 homogenates of muricid snails gave a neutral or slightly alkaline 

 reaction, thus confirming similar observations of Ankel (1938), 

 Fischer (1922), and Hirsch (1915). Early inconclusive tests with 

 litmus paper by Schiemenz ( 1891 ) suggesting that the secretion is 

 slightly acid were not corroborated. We found that the pH of fluids 

 in incomplete bore holes was slightly alkaline, but this might be 

 attributed to a buffering action of dissolved CaCO.3. The pH of the 

 freshly prepared ABO homogenate ranged from 7.3 to 7.5 and re- 

 mained so for some 20 hours. More refined determinations of the 

 hydrogen ion concentration of the secretions of the ABO are in 

 progress, but it is doubtful whether these will disclose values sig- 

 nificantly different from those already obtained. 



As viewed directly at low optical magnifications, the characteristic 

 gross pattern of etching of shell surface produced by the excised 

 ABOs took the form of a pronounced chalky white disturbance in 

 the region immediately affected by the ABO, and a faint etching 

 beyond this under the drop of sea water. In light etchings (Fig. 7) 

 first damage occurred in a ring at the outer boundary of the ABO 



