The Cambridge natural history . ctenidium (never two), some-times of secondary branchiae, variously placed, while sometimesno special organ exists. The prolongation of the foot into lateral epipodia or parapodia(possibly to aid in swimming), and the effect of the epipodiaupon the shell, according as they involve it completely orpartially, are among the most instructive features of theOpisthobranchiata. If the epipodia are developed on the 428 OPISTHOBRANCHIATA anterior portion of the body, and do not become reflected, theymay, as in most Pteropoda Thecosomata, not directly affect theshell. But
The Cambridge natural history . ctenidium (never two), some-times of secondary branchiae, variously placed, while sometimesno special organ exists. The prolongation of the foot into lateral epipodia or parapodia(possibly to aid in swimming), and the effect of the epipodiaupon the shell, according as they involve it completely orpartially, are among the most instructive features of theOpisthobranchiata. If the epipodia are developed on the 428 OPISTHOBRANCHIATA anterior portion of the body, and do not become reflected, theymay, as in most Pteropoda Thecosomata, not directly affect theshell. But when, as in the Tectibranchiata, the epipodia aremedio-lateral, and tend to envelope the shell, their effect may betraced by a series of forms varying in proportion to the amountof shell-surface covered by the epipodia. The two principal linesalong which modification takes place are the gradual reductionof the spiral nature of the shell, and the gradual lessening ofits solidity. Both these changes are the direct result of the.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
