. The sea-beach at ebb-tide : a guide to the study of the seaweeds and the lower animal life found between tidemarks . mity with the change, the resultbeing the familiar spiral form of the usual gasteropod shell. This theory may not be satisfactory, but the asymmetry ofgasteropods is a problem to be solved, and a more interestingline of biological investigation could not be found. Let us now take a good example of a gasteropod and locate itsvarious organs; at the same time we may use the occasion torefer to more important modifications of these organs which willbe encountered later in the vari
. The sea-beach at ebb-tide : a guide to the study of the seaweeds and the lower animal life found between tidemarks . mity with the change, the resultbeing the familiar spiral form of the usual gasteropod shell. This theory may not be satisfactory, but the asymmetry ofgasteropods is a problem to be solved, and a more interestingline of biological investigation could not be found. Let us now take a good example of a gasteropod and locate itsvarious organs; at the same time we may use the occasion torefer to more important modifications of these organs which willbe encountered later in the various genera. The most availablegasteropod on the east coast of the United States for thispurpose is Fidgur, both on account of its large size and itsabundance. Buccinum may be used if the student is north ofCape Cod and therefore unable to secure a good living specimenof Fulyur; the anatomical differences between the two are slight. Note the siphon protruding forward from a notch in the consists merely in an elongation of a fold of the mantle,which is held in a manner to constitute a tube, through which. GASTEROPODS the animal draws in water to supply the gills, lying just backof the siphon and concealed under the mantle in the cavityalready spoken of as the mantle cavity. With the exception ofthat portion of the mantle which constitutes the siphon, no partof its nun-gin, it will be observed, can be seen, the edge of theshell completely hiding it from view. In some genera the siphon is exceedingly long—in fact, longerthan the body of the animal. In these cases the mollusk isgenerally fond of buryingitself in the sand and main-taining communication withthe world above only bymeans of this long, fleshytube. In some genera thesiphon is protected by anelongation of the shell, as in TJ • 7 • /TYI - T V-*--TTT\ HiifH»u»i wiilatum: si. siphon. Fascwlana (Plate LXX\ I). An extreme example of this is given in the figure on page 343,which represents a species of Mures,
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmarinea, bookyear1901
