128 



THE SEA. 



of which the bivalve molluscs are by far the most important to man. In consequence 

 of their very softness and delicacy, Nature has provided them with a shell coat of 



calcareous mail. 



The sub-class Acephala, are as their 

 names indicate, headless molluscs, and 

 though sometimes partially naked, are 

 usually very well protected by shells. 

 When it is known that there are over 

 4,000 species of bivalve molluscs, the 

 impossibility of describing more than a 

 few typical and prominent examples will 

 be seen. 



The genus Teredo consists of marine 

 worm-like animals having a special and 

 STAR-FISH. irresistible inclination for boring wood, 



whatever its hardness. Ships have been 



thus silently and secretly undermined, till the planks have been either like sponges or 

 have crumbled into dust under the very feet of their crews. The holes bored by 

 these imperceptible miners riddle the entire interior 

 of a piece of wood, without any external indica- 

 tion of their ravages. Piles and piers have been 

 utterly ruined, and vessels have sometimes gone 

 to the bottom through them. At the be- 

 ginning of the last century half the coast of 

 Holland was threatened with inundation and prac- 

 tical annihilation because the piles which support 

 its dykes were attacked by the teredo, and hundreds 

 of thousands of pounds damage was done by this 

 wretched worm. It has been now discovered that 



the worm has a great antipathy to oxide of iron, and wood impregnated with it is secure from 

 its ravages. Other animals of the same group are capable of boring even rock. 



Another important bivalve is the well known 

 Solen or " razor-fish," varieties of which are common 

 all over the globe. " These molluscs," says Figuier, 

 " live with their shells buried vertically in the sand, 

 a short distance from the shore ; the hole which they 

 have hollowed, and which they never quit, sometimes 

 attains as much as two yards in depth ; by means 

 of their foot, which is large, conical, swollen in the 

 middle and pointed at its extremity, they raise themselves with great agility to the entrance 

 of their burrow. They bury themselves rapidly, and disappear on the slightest approach 

 of danger. 



" When the sea retires, the presence of the Solcn is indicated by a small orifice in the 



URCHINS IN A ROCK. 



SEA-CUCUMBER (Holothurici tubulosct). 



