OBSERVATIONS ON THE LIFE-HISTORY OF THE COMMON CLAM. 
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dug out of the beds, clams measuring 2 or 3 cm. in length are generally found to have 
gone down 12 or 15 cm. (5 or 6 inches) from the surface, the extremely delicate and 
filmy siphons of the small individual becoming relatively larger and more muscular. 
There undoubtedly comes a period — probably not far from this time — when the clam 
ceases to come to the surface, and, except for some accident, remains forever buried, 
reaching up to the water only by means of the siphon tubes. Evidence of this is the 
fact that clams are frequently to be found between rocks in such a position that it 
would be impossible for them to move, having reached such a location when smaller. 
Then, too, shells, especially the larger ones, are frequently distorted and rendered 
asymmetrical by coming in contact, in growth, with an unyielding object, such as a 
stone. The shape in such cases conforms to the space in which movement is possible. 
This same distortion of the shell may be noticed in other burrowing lamellibranchs, 
like PetricoJa pholadiformis. In case of this latter form, and also in Pliolas tr uncat a , 
which are to be found buried along the edges of salt marshes, the burrow is seen to be 
surrounded by so dense a feltwork of roots from the marsh vegetation that it would 
seem entirely impossible that the adult animal could remove itself. It is a mystery 
how the young could ever force its way into such material. 
FIXATION IN THE BURROW. 
A peculiar habit, the utility of which is very evident, is the spinning of the byssus 
by the small clam as soon as it has succeeded in covering itself in the sand. As 
has just been stated, the small individuals bury themselves, and again appear upon 
the surface, and this is repeated several times. But whenever the creature goes into 
the sand, it apparently at once proceeds to pour out the secretion which forms the 
byssus thread, and attaches itself more or less firmly by this means. Fig. 3 represents 
a clam with a shell 2.3 mm. long, which has been removed from its burrow. The 
single byssus thread (b) is seen to branch, the ends of the branches being attached to 
three sand grains (s. g.). Actually the number of sand grains and pebbles to which 
attachment is made is usually much greater than represented. The extremity of the 
thread which is fastened to the foreign body is considerably widened, as shown in fig- 
ure. The character of the thread is the same, whether the creature is attached to several 
sand grains, to a single filament of Enteromorplia , or to other bodies. Fig. 2 represents 
a very small individual, 0.4 mm. in length (drawn on a larger scale than fig. 3), which 
was attached by several branches of the byssus to one short seaweed filament. 
In coming out of the burrow and moving to a new locality, the byssus is cast off 
at the gland in the foot and left behind, and a new one is constructed at the next 
descent. This is done within a few minutes. Clams, from the smallest which are able 
to cover themselves in the sand to those at least 13 mm. long, exhibit this peculiar 
habit of forming a byssus in the burrow. How much longer the byssus organ remains 
in functional activity and when it begins to atrophy have not been determined. 
The utility of this habit is well illustrated in a circumstance which recently came 
under observation at the house-boat laboratory, in the Kickemuit Narrows, belonging 
to the Eli ode Island Fish Commission. Suspended in the water was a box filled Avith 
sand taken from a neighboring clam-bed. In the sand had been sunken some glass 
dishes, about 3 inches in depth, which had also been filled Avith sand. Here a number 
of small clams Avere allowed to burroAv. On August 5 the region avus visited by a 
terrific windstorm, and everything connected with the house-boat was pitched about 
furiously for more than an hour. Upon examining the glass dishes afterwards, it was 
found that all the finer sand had been washed out of them, and but a few small pebbles 
