Shell-fish industries . ned currents than where tliere is little movement ofwater. As so often happens in nature, the seed is sownbroadcast. While in this case it can usually live only oncertain restricted tracts between tide lines, it falls indeep water and shallow alike, probably thousands oftimes more often where death is inevitable than wherefarther development is possible. During the swimming period there has been formedfar back on the under side of the foot a gland for secret-ing a transparent fluid which, on being ejected into thewater, hardens into a minute, tough thread known as the T
Shell-fish industries . ned currents than where tliere is little movement ofwater. As so often happens in nature, the seed is sownbroadcast. While in this case it can usually live only oncertain restricted tracts between tide lines, it falls indeep water and shallow alike, probably thousands oftimes more often where death is inevitable than wherefarther development is possible. During the swimming period there has been formedfar back on the under side of the foot a gland for secret-ing a transparent fluid which, on being ejected into thewater, hardens into a minute, tough thread known as the The Life History of the Soft Clam 293 Immediately on settling, the young clam at-taches itself by means of this thread to shells, sea-weeds,pebbles, or even to sand. It is now not much larger thanmany of the sand grains, and its body is so light thatif it were not anchored in some way, it would be rolledalong by the action of the water. When water move-ments cease, as at slack tide, it often casts off the byssus. Fig. 56.—Very small long neck clam(.4 millimeter), b, byssus; f, foot;s, siphon. Drawn from living speci-men, and begins to creep by means of its foot. What the ob-ject of this habit may be it is difficult to imagine, for thelittle creature, even if in search of a more favorable lo-cality, is able to move only very short distances. Aftera little exercise of this sort, it rapidly secretes and fast-ens another thread, but sometimes continues to creepabout to the length of its tether. The general appearance of this newly settled clamis illustrated in Figure 56. Foot (/) and siphon (s)Sire shown extended, and the byssus thread (b) with its 294 O^r Food MoUusks terminal branches, is represented. The outhne of theshell is very different from that of the adult, being nearlyround. The umbones also are very prominent. Probably not even the swimming stage is more crit-ical for Mya than this period of creeping, which is oflonger duration. If on a beach, where it has a c
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Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyo, bookyear1910
