DEMINERALIZATION MECHANISM OF BORING GASTROPODS 69 



evidence of shell dissolution by the mantle in election micrographs 

 of the nacreous surface of oysters. 



Morphological Characteristics of Shell 

 Subjected to ABO Activity 



The appearance of complete muricid and naticid bore holes at low 

 optical magnifications is shown in Figs. 1 to 4. When contact and 

 projection microradiographs were made of bore holes in ground sec- 

 tions of shell 0.7 mm thick cut parallel to the original surface of the 

 shell (Fig. 5), there was evident what appeared like a relatively 

 wide partially demineralized region surrounding the periphery of 

 the hole. This zone was even more apparent in projection micro- 

 radiographs of sections of incomplete holes cut at right angles to 

 the original surface of the shell (Fig. 6). That the density difference 

 in the shell could not be accounted for on the basis of changes in 

 contour of the hole through the section was established by use of 

 stereoscopic projection microradiography. By this technic the con- 

 tour of the surface of the hole in the shell section as well as the 

 surrounding radiolucent zone were well demarcated and clearly dis- 

 tinguishable. We suggest that this partially demineralized band 

 represents the result of ABO secretory activity which penetrated 

 the shell to this degree. 



Preliminary experiments were conducted to determine whether 

 structural changes effected by ABO secretion in shell could be de- 

 tected by means of surface replicas examined under optical and 

 electron microscopes. Very shallow incomplete holes bored by Uro- 

 salpinx and Eupleura in the natural shell of living Crassostrea vir- 

 ginica in the laboratory were employed. Silver-shadowed negative 

 collodion replicas were prepared for optical microscopy, and collo- 

 dion-carbon positive replicas for electron microscopy. It was soon 

 learned that although some microscopic detail could be observed 

 on the surfaces of the borings themselves, excessive quantities of 

 organic detritus and loosened shell material consistently interfered 

 with the preparation of adequate replicas. Furthermore, the presence 

 of the organic periostracal layer on the external surface of the shell 

 surrounding the excavation prevented comparison of the altered 



