CRYSTALLINE STYLE OF LAMELLIBRANCHS 99 



Upon examining mussels which had thus been exposed for about 

 six hours, it was found that the style was invariably present. 

 In many instances, however, it was quite soft and had begun to 

 undergo dissolution. 



The oysters attached to these mussels, provided they had been 

 exposed for an hour or more, failed to show any style present. 

 What, then, is the relation of the style to the feeding activities 

 of the oyster? As is well known, oysters occur naturally in 

 reefs, or barriers, built up through successive generations at- 

 taching themselves to those already present. Since the oyster 

 is able to exist for some time out of water, the upper limit of 

 the reef comes to lie between the mean low- and high-water 

 levels. Consequently, large numbers of individuals near the 

 top are exposed for several hours at each ebb tide. 



Toward the close of ebb tide I went out on such a reef and 

 opened oysters at the rate of one a minute for two and a half 

 hours, a period extending over the close of the ebb and the 

 early flood of the tide. Began at 9.05 a.m., at which time the 

 oysters around me were all or partly submerged. A style was 

 present in all that were opened. 



By 9.45 a.m. most of the reef about me was exposed, and the 

 oysters opened for the next hour were devoid of styles. Shortly 

 after 10.00 a.m. the tide began to return, and when it had risen 

 sufficiently to cover the oysters they opened and began siphoning 

 vigorously. By 11.00 a.m. the reef was practically covered, 

 and from then on till 11.35 a.m., when the experiment was con- 

 cluded, a style was present in every oyster opened. All the 

 bivalves taken during the entire period came from a spot less 

 than 20 feet square and nearly level, hence all were subjected to 

 practically the same period of exposure. 



Subsequent laboratory experiments confirmed these results and 

 revealed the fact that the style of the oyster may be dissolved 

 within an hour, often in much less time. Furthermore, a new 

 style may be built up within fifteen minutes from the time the 

 animal begins active feeding. 



There is, however, a great variation in the length of time 

 required for these processes, depending on the previous feeding 



