PROGRESS IN BIOLOGICAL INQUIRIES, 1935 429 



part of a shell. Its mode of giiining- entrance to an oyster is to 

 cover the bill with its foot and under cover of this, rasj) away the 

 thin edge of the upper valve until a very narrow aperture is made. 

 At present it is thought that a narcotic secretion is poured into the 

 shell resulting in the narcosis and relaxation of the adductor muscle 

 of the oyster. The presence of a large amount of purplish colored 

 mucus found in attacked oysters along the frontal edge of the gills 

 and the lack of mechanical means of holding the shell open during 

 feeding seem to substantiate the observations, although further study 

 of the problem is necessary. A Thais can kill and eat an oyster 

 within 12 hours. In view of the relative ease and rapidity with 

 which large oysters may be opened it is evident that the thickness 

 of the shell is not a factor in the selection of food. Therefore, as 

 shown by experiments in the field, trapping cannot be carried out 

 successfully with baited traps. 



Studies along this northwest coast of Florida show that, if 1935 

 was a normal year, spawning of Thais extends from late May to the 

 early part of August, during which time temperatures are above 

 20° C. and salinities are over 20. There is a definite spawning 

 migration, and egg laying is usually done by groups of individuals 

 assembled in one place. Whenever possible capsules are deposited 

 in masses on objects Avell elevated above the bottom. Each of these 

 masses has been found to contain from 3,600 to 6,000 eggs. Develop- 

 ment proceeds in the capsules for at least 7 to possibly 14 days. 



The average size of the adults, both male and female, is 8 cm. 

 Attempts to follow the rate of growth have so far been unsuccessful. 

 EA'ery area, from fresh water flats at the head of the bay to 5 

 fathoms out in the Gulf, was searched for young forms a number 

 of times but out of several thousand specimens collected, less than 

 half a dozen were under 5 cm in total length. It has been thought 

 that last season was for some reason unfavorable for the survival 

 of young Thais. 



Beside the study of the distribution and habits of the borer, the 

 field work in this section also included cruises for collecting hydro- 

 graphic data for the practical purpose of obtaining a better under- 

 standing of the relationship existing between oysters, their enemies, 

 and the various environmental factors involved. Hydrographic 

 observations were confined to the oyster-producing areas of Apalachi- 

 cola Ba}', totaling about 130 square miles. 



Although the laboratory' is located in the pass between the Gulf 

 and St. Vincent Sound there is a large difference between the maxi- 

 mum and minimum salinities even during the dry summer months. 

 This wide range in salinities has a practical bearing on the oyster 

 industry, for extreme changes from salt to fresh, or vice versa, 

 render oysters unsuitable for the market. Oystermen frequently 

 find it necessary to transfer operations from one locality to another 

 in an attempt to locate oysters of marketable quality. It is be- 

 lieved tlial this situation might be greatly improved by setting aside 

 suital^le bottoms for the production of market oysters, while other 

 beds would be used chiefly for seed production. 



Examination of the oyster bars in this region has shown that the 

 destruction of the large productive beds in St. George Sound has 

 throAvn an added strain on bars in other localities. The majority 



