ARTIFICIAL OYSTER CULTURE. 1095 



One must know how thick the full-grown oysters lie upon 

 the beds ; whether, in fact, there is a sufficient number to 

 secure an average fecundity to the bank. Upon banks 

 such as those in the Bay of Arcachon and near Cancale, 

 which are left dry during spring-tides, it is not difficult to 

 observe the number of oysters necessary per square meter, 

 in order to maintain the fecundity of the bank at its 

 highest point, for at such times they are so exposed that 

 they can all be counted. But those beds along the Ger- 

 man and English coasts, and in the open North Sea, 

 which, on the contrary, remain continually under water, 

 are much less favourably situated for the purposes of these 

 inquiries. 



(Mobius then proceeds to give an ideal picture of the 

 life of an oyster bank, in order to show that one may 

 become really very well acquainted with an oyster-bed by 

 means of a dredge, and says of the latter that) 

 It can also be used to estimate the thickness of oysters 

 upon a bed, if the distance passed over by the dredge 

 while it is taking oysters be measured. In the inspections 

 of the Schleswig-Holstein banks, during the last few years, 

 this has been accomplished in the following manner : At 

 those points where the dredge is dropped upon the bed, 

 an empty cask, attached by means of a rope to a heavy 

 weight, is cast overboard. The weight sinks to the bot- 

 tom and holds the cask securely anchored, floating upon 

 the surface of the water. Connected with the rope of the 

 cask is a measuring-line, which is wound upon a roller, 

 and which runs off as long as the vessel is going forward, 

 and the dredge drags over the bottom. The mouth of our 

 larger dredges is one meter in width. Thus, if we let the 

 dredge drag over the bottom until 100 meters of line have 

 run off, and find that we have then 50 oysters in the bag, 



