284 RESPIRATION OF MOLLUSCA. 



came into existence from Infinite Wisdom, perfect, and 

 complete, and immutable ; and, notwithstanding all their 

 variations, ever suited with special adaptation to the ele- 

 ment and the place they were fore-ordained to inhabit. 

 " Their forms are His special invention and construction, 

 and their principle of life is also His special and commu- 

 nicated gift," is the just conclusion of an historian eminently 

 distinguished for his learning, his good sense, and his piety.* 



Now, the distinction which has been drawn between the 

 Mollusca with lungs and gills, however anatomically correct, 

 is not always physiologically true ; for although I am not 

 cognisant of any pulmoniferous species that can breathe 

 water, j or ever does so voluntarily, yet there are many 

 branchiferous ones that can and do respire the uncombined 

 air. A great number of bivalves are alternately submerged 

 and exposed to the air, according to the fluctuations of the 

 tide ; but then the animals are covered up with a wet soil, 

 or the concavity of the low r er valve enables the animal al- 

 ways to retain some moisture around its gills, and I believe 

 they do not open their shells freely unless when covered 

 with water.J Of the Cephalopods the Octopoda are said 

 to come ashore frequently, and live among the rocks for 

 days together ; and the Pteropods and the naked Gastero- 

 pods in general love to swim at the surface in calm weather, 

 particularly at the time of sunset, apparently to enjoy the 

 respiration of a lighter and more oxygenated medium. 

 There are other Gasteropods with gills which pass so large 

 a portion of their term of life completely out of the water, 

 that they seem to merit the appellation of amphibious. 

 The most remarkable of these is an Australasian species 

 of Neritina, which loves to forsake its native rivers or ponds 

 for the green shade of the trees, amid whose foliage it is 

 found abundantly. The Patellar and the Littorinae are also 

 good examples. Our common species of the latter genus 

 seem, indeed, to prefer spots where they can be covered 

 only at high water, and I have seen myriads of them, when 



* Mr. Sharon Turner. His Sacred History of the World, from which 

 the quotation is taken, I earnestly recommend to the attentive perusal of 

 students of natural history. 



t Peron seems to have believed that a species of Onchidium (a pulmoni- 

 ferous genus) found on the shores of New Holland, lived always in a state 

 of submersion, but there is no doubt of some mistake here. — See Audouin 

 and Milne-Edwards in their Litt. de la France, i. 118. 



J Kellia rubra spends the greater portion of its life out of the water, and 

 is often for at least a fortnight uncovered with it. — See Clark in Ann. and 

 Mag. N. Hist. Ser. 2, iii.455, and iv. 144. 



