338 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
In the matter of anchorage the oyster has certainly proved very adaptable. Every 
oyster of a raccoon reef, as Prof. Ryder has pointed out,* owes its position in life to 
its ancestors. When in its swimming stage every natural obstacle stood iu its way; 
they alone extended a friendly shell for it to cleave to — they who in their turn were 
fastened to their ancestral shells, and so back indefinitely. In no place, perhaps, may 
this interesting pliylogeny be better examined than in South Carolina. Eight superin- 
cumbent generations have been counted upon a single shell, i. e., No. 2 attached to No. 
1, No. 3 to No. 2, etc. Should the muddy floor below be of medium softness the cluster 
is found to be a more permanent one, for increase in the weight of the growing load 
presses the cluster down and keeps it firmly rooted, and the sinking ancestral shell 
may in time disintegrate without injuring the stability of the bunch. On the other 
hand, should the character of the bottom prevent the basal shell from sinking and the 
bunch from thus becoming rooted, the cluster is apt to be capsized by storm or tide 
and rolled up on the beach to perish. Should the bottom, again, be of medium soft- 
ness, the anchorage becomes a curiously firm one, owing to the conditions of oyster 
growth. All the individuals of a cluster tend to bend out of their normal direction, 
and to assume in their growing tips a vertical position.! The basal oyster tends to 
become flat in its position, or is pressed somewhat slantwise into the bottom. So 
firmly may a bunch become thus established upon a flat, sunken shell, that it is some- 
times extremely difficult to dislodge. 
In economizing space the adaptability of the bunching form is noteworthy. A tall 
cluster, whose free end occupied an area of about a square foot, was found to repre- 
sent the shells of 186 oysters. So crowded sometimes are the individuals of a cluster 
that their shape will be as irregular as the space they are allowed to grow into. 
Sometimes, growing vertically, side by side, they become of the proportions of a razor 
shell ( Solen ), curious in the delicate fluting of their exposed tips. The basal shells, 
less crowded, become with age stout, broad, and heavy. The extreme lightness of 
the terminal shells appears to be unvarying, caused partly by their crowded quarters 
and partly by their out-of-water position. This provision of lightness of terminal 
shells is admirably designed to give a living to the maximum number of individuals 
with a minimum chance of overturning the entire cluster. 
The origin of the clustering condition is due undoubtedly in the main to the gen- 
eral soft, muddy character of the oyster’s ground. It is a building process where the 
oyster has had for ages to manufacture a place sufficiently firm whereon to anchor its 
fortunes. To do this it has had to drive into the mud, like irregular piles, the shells 
of ancestors, near and remote. There can be but little doubt that the beginnings of 
an oyster reef were of the smallest; a single firm point projecting above the softest 
mud flat, that has proved sufficient for the attachment of a .single cluster, will in time 
give rise to a reef. The shells dropping and sinking around the primitive cluster will, 
in time, become the nuclei of congregations of other clusters. 
* Maryland Fisli Commission, 1881, p. 27. 
t Many instances liave been noted in capsized bunches where the tips of the individuals seeking the 
vertical position have succeeded in changing their direction of growth by an angle of 90 u . 
