OBSERVATIONS ON THE LIFE-HISTORY OF THE COMMON CLAM. 197 
quently this happened, I kept a large mat of Enteromorpha , covered with clams, Boating 
in running sea-water. Under the mass was spread some fine cloth. In the course of 
a week, great numbers — perhaps a fourth of all those attached — were found to have 
fallen from their support to the cloth, and these were of all sizes. Here they attach 
themselves, wander about, and again attach, until, apparently tired of the effort to 
find congenial surroundings, they remain inert, most of them without byssus threads, 
for long periods of time. 
MIGRATION TO THE MUD. 
As one would naturally suppose, this period is a critical one for the clam, as 
much so, probably, as any in its history, though it has to contend with other great 
dangers which threaten its existence both before and after it enters the mud. The 
eelgrass on which the Enteromorpha filaments grow most abundantly, in the localities 
examined, is to be found in shallow water, near the clam beds. In falling from their 
support, most of the clams would probably find a resting-place on the bottom, below 
the? lowest low-tide mark. That this actually happens may be easily demonstrated 
by taking a little of the mud in these localities and washing it through a fine sieve. 
When this is done the small clams are often found. But the clams do not depend 
entirely upon Enteromorpha for fixation. As before indicated, they may also attach 
to stones and other bodies in the water. In the early summer, in certain localities, 
the floating weed may bear no attached individuals, which are, however, to be found 
fastened to near-by stones on the bottom. Wherever they may be, they probably free 
themselves from time to time, and, being below the low-water mark, fewer may reach 
maturity than if they had been between the tide marks. This is a matter of inference. 
My a undoubtedly may live in bottoms which are never exposed. I know this to be 
true, for example, at the salt pond at Wakefield, Rhode Island, and in the river at 
Essex, Massachusetts, and probably many other such regions are known; but it is 
difficult to believe that regions below clam flats usually, or perhaps often, bear clams. 
Clam-diggers very generally seem to know nothing of their existence. 
It may be concluded, then, that of the great numbers of small clams which fall 
to the bottom below low-tide mark, few are able to reach a favorable position higher up 
on the beach, and the great majority are destroyed. In such localities individuals over 
6 or 7 mm. in length are seldom found. While the majority may thus perish, we may 
well believe that a few, on falling at certain times, are borne by tidal currents above 
the low-tide mark. They are to be found here burrowed into the sand, or attached 
to the sides of stones, close to the line where the stone touches the mud. This occurs 
most frequently on stones covered by rockweed ( Fncus ), and perhaps for the reason 
that hei’e the little clams find better protection from their most destructive enemies, 
the young star fish. It is probable that many of these small clams between the tide 
marks originally attached themselves in this position, never having been fastened to 
objects in the water below low-tide mark. 
This wholesale destruction of individuals below low-water mark is but another 
example of the tremendous struggle for life to which so many species of organisms are 
subjected in nature. Of the millions of swimming larvae that probably arise from one 
female during a breeding season, few become attached to suitable objects, the water 
currents carrying most of them away. Those which succeed in fastening themselves 
are killed in vast numbers by very small star-fish; and even after attaining a position 
in the sand and mud of a favorable locality, the shifting of the sand, the crowding ot 
individuals, the decay of organic material in the water, or the isolation of salt water 
