THE ACEPHALOUS MOLLUSKS. IOI 
pair are used for the same purpose in the church of St. Eulala, 
at Montpellier. 
The mantle of the acephalas is a kind of membranous tunic, 
and is so large as to form folds; its edges are fringed. This 
mantle protects the mollusks, and in its turn it is protected by a 
shell. The animal sometimes possesses eyes and ears; but as it 
has no head, the eyes are placed on the margin of the mantle, and 
its ears are in its stomach! The Ze//ine, the Pinne, the Arcade, 
and the Petunculi, have distinct, though very small organs of 
vision, consequently they are very close-sighted, and are dazzled 
in the full light of day. The ears are little bladders, which con- 
tain a microscopic pebble, suspended in a drop of water. 
When we compare the organs of different species throughout 
the whole range of the animal kingdom, we find them passing 
from the most simple to the most complicated structures by the 
gentlest gradations. But all the organs of an animal may not 
be in the same state of development; some of them appear to 
have stopped in the upward progress, while others have pro- 
ceeded to a further state of perfection. Yet there is always a 
compensating harmony in these inequalities of development, so 
that a creature deprived of the use of one perfect organ always 
has the deficiency made up by the superior quality of another. 
In this manner the budget of nature is always perfectly balanced. 
It is among the acephalous mollusks that we find those terrors 
of the ship-master, the 7Zeredos. These Vandals attack every piece 
of wood within their reach, just as it is the propensity of certain 
insects to cover all the wood they are able with their larve. In 
months, or even in weeks, they will perforate a plank in every 
direction; the little miners having the singular instinct never to 
cut into another channel. The wood externally does not appear 
injured, but crumbles at atouch. Silently, unwearyingly, the teredo 
bores, until the pier suddenly sinks, or the planks of the doomed 
ship crumble beneath the feet of the sailors. 
In the beginning of this century, half the coast of Holland was 
threatened with the invasion of the sea, because the piles which 
upheld the dykes were attacked by the teredo; and it required an 
outlay of a large sum of money to secure the country from the 
