on coral reefs, under stones at low water, in the crevices of rocks, adlicring 

 to sea-weeds and other bodies, or imbedded in wood, coral, or limestone 

 rocks. In ponds and marshes they are of a dull and stagnant nature, and 

 live either floating on the surface or attached to weeds. In rivers they 

 float up and down with the tide, or adhere to plants growing on the banks. 

 And on liills and in forests they live upon the branches of trees, or creep 

 about the roots of shrubs and amongst the decayed and fallen leaves scat- 

 tered on the earth. The ]\Iollusca, therefore, live both in and out of water ; 

 they swim, dive, float, bore, leap, cHmb, prey upon each other, and appear 

 indeed to possess habits analogous in some way or other to all that have 

 been noticed in the higher orders of animals, except that of flying. 



One of the most remarkable features in the natural history of the Mol- 

 lusca is the solvent property of their juices. By httle or no expenditure of 

 muscular power they are enabled to effect great changes in their condition. 

 The Cowrey, after having arrived at maturity, has stiU the power of dissolving 

 a great portion of its shell, and renewing it. The Pholades pierce the hardest 

 limestone rocks, and increase in bulk without any apparent terebrating 

 force, being found with the most deUcate carving of their shell unin- 

 jured. Indentures are also produced by Snails in limestone walls, wliilst 

 in a state of quiescence. Many naturalists stiU adhere to the opinion that 

 the perforations of shells are due to some mechanical action, some rotatory 

 or oscillatory attrition ; and Professor Owen attributes the formation of 

 these cavities to the action of constant currents of water round the shells, 

 produced by minute vibratile cilia or hairs, covering certain parts of the 

 animal, which are in a constant state of activity in attracting the water ne- 

 cessary to its natural existence'^. That there may be a constant current 

 of water flowing around these imbedded mollusks for the promotion of vita- 

 lity and nourishment is highly probable, but the extraordinary progress 

 wliich is made, "with so much apparent ease, into the hardest substances, 

 could not be accomplished without the collateral agency of some powerful 

 solvent. The MoUusca, as already shown in speaking of the Cowrey, possess 

 extraordinary powers of partially dissolving their own shells ; the inner spiral 

 partitions of a Co7ie in an early stage of growth are thick and solid, but in 

 an adult specimen they are mostly absorbed to a degree of tenuity wliich 

 would not have given sufficient support to the primitive structure. In the 

 varicose genera of Gastropods, such as Miirex, the mollusk has the power 

 of removing any portion of the varices presenting an obstacle to its revo- 

 lution of growth. In the Murex cornutus, for example, tliis mode of ope- 

 ration may be traced, by observing, on the left side of the aperture, the 

 base of a spine wliich has been removed for the purpose of paving the 

 boundary of the aperture with the usual coating of enamel. 



* Eleventh Report of the Meeting of the British Association for the Advancement of Science. 



