G8 M. R. CARRIKER, D. B. SCOTT, AND G. N. MARTIN, JR. 



to produce additional secretion after excision, or whether only that 

 already present at the time of excision is utilized, is not known. The 

 variability in degree of etching in different preparations suggests the 

 latter. 



Excised ABOs held in distilled water for a minute or more prior 

 to placement on the substrate produced very little or no etching, 

 and immersion for a longer period evoked the fomiation of a dense 

 halo of what appeared like secretory globules over the secretory disk 

 of the ABO. These globules were not mucus, since histochemical 

 tests disclosed no mucus cells in the secretory epithelium or in the 

 subepithelial region of the ABO. 



Excised ABOs rinsed in and placed in drops of saline buffer of pH 

 5.7, 7.4, 8.2, and 8.8 all produced etchings on shell. At the end of the 

 24-hour incubation period, the pH of all the Huids was consistently 

 7.5 or above. The degree of etching under the ABO at the initial 

 pH of 5.7 differed from that under the ABOs at higher pH's, prob- 

 ably because of the influence of the acid buffer. 



Most striking of all the tests performed with ABOs was the clear- 

 cut demineralizing action of ABO homogenate diluted 10-fold. The 

 pH of this ranged from 7.3 to 7.5. The most obvious etchings oc- 

 curred as a pronounced ring at the outside edge of the drop of homog- 

 enate. A 50-fold dilution of the same homogenate also produced 

 etching, although somewhat fainter, and also as a clear line around 

 the outer edge of the drop ( Fig. 18 ) . 



So far we have been unable to find any other tissues in the muricid 

 snail body which can etch shell in the manner of the ABO. Minced 

 and whole portions of pedal epithelium from various parts of the 

 foot, salivary glands, accessory salivary glands, and glands of Leib- 

 lein produced no effect whatever on the nacreous shell of M. fid- 

 vescens. Graham ( 1941 ) applied whole accessory salivary glands to 

 polished shell, and extracts of the glands to polished shell and to 

 finely precipitated CaCOa, and was likewise unable to obtain dis- 

 solution of the CaCOa. The gastropod mantle, on the other hand, 

 may be able to dissolve shell; Dugal (1939) notes the use of shell 

 by Mercenaria mercenaria to buffer the product of anaerobic gly- 

 colysis, and Watabe (1954) and Watabe et al. (1958) have seen 



