. The Cambridge natural history. Zoology. 20 ORIGIN OF LAND OPERCULATES chap. Pulmonata, as a whole, as derived from the Tectibranchiate Opisthobranchs, while others^ go further and regard the Stylom- matophora as derived directly from the Basommatophora. Origin of the Land Fauna Gasteropoda. — (1) Operculate. On a 'priori grounds, one might predict a double origin for land operculates. Marine species might be imagined to accustom themselves to a terres- trial existence, after a period, more or less prolonged, of littoral probation. Or again, fresh-water species, themselves ultimately derived
. The Cambridge natural history. Zoology. 20 ORIGIN OF LAND OPERCULATES chap. Pulmonata, as a whole, as derived from the Tectibranchiate Opisthobranchs, while others^ go further and regard the Stylom- matophora as derived directly from the Basommatophora. Origin of the Land Fauna Gasteropoda. — (1) Operculate. On a 'priori grounds, one might predict a double origin for land operculates. Marine species might be imagined to accustom themselves to a terres- trial existence, after a period, more or less prolonged, of littoral probation. Or again, fresh-water species, themselves ultimately derived from the sea, might submit to a similar transformation, after a preliminary or intermediate stage of life on mudbanks, wet swamps, branches overhanging the water, etc. Two great families in this group, and two only, seem to have undergone these transformations, the Littorinidae and the Neritidae. The derivation of almost all existing land operculates may be referred to one or other of these Fig. 16. —Two rows of the radula of Littorina littorea L., X 72. The power of the Littorinidae to live for days or even weeks without being moistened by the sea may be verified by the most casual observer. In the tropics this power seems even greater than on our own shores. I have seen, in various parts of Jamaica, Littorina muricata living at the top of low cliffs among grass and herbage. At Panama I have taken three large species of Littorina (yaria^ fasciata, pulchra')^ on trees at and above high-water mark. Cases have been recorded in which a number of L. muricata, collected and put aside, have lived for three months, and L. irrorata for four months.^ These facts are significant, when we know that the land operculates almost certainly originated in a tropical climate. 1 Bergh, Zool. Jahrb. v. p. 1 f. 2 Calkins, Amcr. Nat. xi. p. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration a
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