416 INCLUSA; PHOLAS, TEREDO. 



being'distended with water, the animal suddenly contracts it ; 

 and thus a jet is produced through the anterior orifice, which 

 washes out the part of the cavity occupied by the animal ; but, 

 as many of the particles expelled by it are deposited before they 

 reach the mouth of the hole, the passage is found to be lined 

 nearer its entrance with a soft mud. 



960. The Pholades evidently prefer such beds, as are com- 

 posed of indurated clay, or soft lime-stones, to harder lime-stones ; 

 though they are occasionally found in the latter. Hence it might 

 be supposed that their action is always of the mechanical nature 

 just described ; but though it is certainly of this kind in many 

 instances (as is proved by the cylindrical form of the perforation, 

 as also by the rasp-marks on its interior), Pholades are some- 

 times found so imbedded, that they could not have turned in 

 their perforation. In some countries they are much prized as 

 food; especially along the Mediterranean coast. They possess 

 one remarkable property, which is not, however, confined to 

 them, but which is manifested in a degree by other Mollusca ; 

 this is their phosphorescence. It is said to be so strong, that 

 persons who eat them raw, and in an obscure or dark place, 

 seem to be swallowing phosphorus. The Pholades are pretty 

 generally diffused over the globe. They usually multiply 

 around any spot which they have begun to frequent ; the young 

 produced from the eggs probably boring near their parents. 

 Pholades are not very abundant in a fossil state ; but they are 

 occasionally found in tertiary strata, imbedded in the cavities 

 which they have themselves formed. 



961, The Teredo is a genus which presents many points of 

 interest to the Naturalist, as well as to those who are practically 

 affected by its destructive operations. This animal bears a 

 general resemblance to the Pholas ; and it carries on its anterior 

 part a pair of valves, which it uses in the same manner, as 

 perforators of the wood into which it bores. When quite 

 young, it establishes its habitation in submerged timber, such as 

 ships' bottoms, piles, &c., which it perforates in every direction. 

 With its increasing bulk, it enlarges its hole, advancing into the 

 wood ; but it does not draw the tubes of the mantle after it, for 

 they remain where they were, and deposit shelly matter, which 



