328 THE OCEAN WORLD. 



The luminosity which is so characteristic of the animal is in favour 

 of an electric current, which is almost always accompanied by 

 chemical decomposition, which would set free the hydrochloric acid of 

 the sea water. The small size of the entrance to the chambers of the 

 Pholas is accounted for by the increase of its size during its residence 

 there. De Blainville thought that a simple movement of the shell 

 incessantly repeated would suffice to pierce the stone, macerated by 

 the sea water which passed through the breathing apparatus. 



Mr. Eobertson, of Brighton, exhibited the living Pholas in the act 

 of boring through masses of chalk, and thinks the process entirely 

 effected by the simple mechanical action of the " hydraulic apparatus, 

 rasp, and syringe." 



" If you examine these living shells," says Gosse, " you will see 

 that the fore part, where the foot protrudes, is set with stony points 

 arranged in transverse and longitudinal rows, the former being the 

 result of elevated ridges, radiating from the hinge, the latter that of 

 the edges of successive growths of the shell. These points have the 

 most accurate resemblance to those set on a steel rasp in a black- 

 smith's shop. It is interesting to know that the shell is preserved 

 from being itself prematurely worn away by the fact that it is com- 

 posed of aragonite, a substance much harder than those rocks in which 

 the Pholas burrows. The animal," Gosse adds, " turns in its burrow 

 from side to side when at work, adhering to the interior by the foot, 

 and therefore only partially rotating to and fro. The substance is 

 abraded in the form of a fine powder, which is gradually ejected from 

 the mouth of the hole by contraction of the bronchial syphon." 



The Pholades are met with on every sea shore, and are plentiful in 

 the Channel ; on the French coast they are called Dails, and sought for 

 their fine flavour. As examples of the genus, we may quote Pholas 

 dactylus (Fig. 131) ; Pholas Candida, found in the Channel and 

 in the Atlantic Ocean, which lives buried in the mud or in decayed 

 wood ; Pholas crispata (Fig. 132), also found in the Channel; Pholas 

 papyracea (Fig. 133); and Pholas melanoura (Fig. 134). 



The bodies of many genera of Mollusca have the property of shining 

 in the dark, but none emit a light more brilliant than that of the 

 Pholades. Those who eat the Pholades in an uncooked state (which 

 is by no means rare, for the flavour of the mollusc does not require 

 the aid of cooking to render it palatable) would appear in the dark as 



