744 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [62] 
oysters which are now upon the beds not more than 421 ought to be 
taken away annually. Uponanumber of banks where the productiveness 
is less than this the number taken should be less. Upon the Huntje 
Bed, where the production is more than 421 per thousand, as many as 
484 for every thousand can be taken yearly without endangering or 
lessening the productiveness, since that number of medium oysters grow 
into marketable oysters every year. But although the productiveness is 
thus expressed by a proportional number, yet the absolute number of full- 
grown oysters which may be taken from a bed during any one season 
cannot be arrived at without further consideration. 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 su 
exposed that they can all be counted. But those beds along the German 
and English coasts and in the open North Sea, which, on the contrary, 
remain continually under water, are much less favorably situated for the 
purposes of these inquiries. I have often been told that “such beds 
could be best investigated by means of divers.” The general impressien 
is that the divers can see, through the glass in the front part of their 
helmets, everything which lies upon the sea-bottom. But this is erro- 
neous, for in those shallow coast-seas which have ebb and flood tides 
the water is so clouded by the floating particles of mud that very little 
light can penetrate to the bottom. But even in clear water a diver would 
not be in a condition to ascertain by sight the number of oysters, for 
whenever he steps he renders the water cloudy, by stirring up the lighter 
particles lying upon the bottom; and so he would have to depend prin- 
cipally upon his hands, and ascertain, by feeling, those oysters which 
could just as well be taken up by means of the dredge, for the dredge 
brings from the bottom not only some of the soil, but also a portion of 
its inhabitants. And if the contents of the dredge be placed in large 
vessels or aquaria, with sea-water, the animals will very soon assume 
their customary positions and motions, so that we can see, in quiet and 
clear water, just how they live at the bottom of the sea. An aquarium 
with the living inhabitants of an oyster-bank is thus a segment of the 
bank itself. : 
When, in imagination, I have united many such segments together, I 
can picture to myself the sea-bottom, with its inhabitants, as a diver 
would never be able to see it. I can see the ground covered with oyster- 
shells, and here and there among them a living oyster with open shell, 
out of which protrude the fringed borders of its mantle. Upon the upper 
valve polyps are growing with expanded heads, looking like delicate, 
many-rayed stars. Hermit-crabs, bearing their snail-shell houses, are 
crawling hither and thither over the rough surface, and groping about 
