CHAPTER XI. 
ACEPHALOUS MOLLUSCA. 
‘‘Sigillatim mortales, cunctum perpetui.”—APULEIUS. 
Tuer Mollusca proper were divided by Cuvier into five great sub- 
classes :—1. Lame'libranchiata, or Acephalous Mollusca, often called 
Conchifera. 2. Brachiopoda. 3. Gasteropoda. 4. Pteropoda. 
5. Cephalopoda. 
The name Mollusca indicates the characters of this class which | 
most struck the ancients: they are soft—in Latin, mois. their flesh 
is cold, humid, and viscous. In consequence of their very softness, 
they are generally furnished with an apparatus of defence, or protec- 
tion, in the shape of a calcareous covering, called a she//, According 
to the species this test may represent a coat of mail, a buckler, or a 
tower. The mollusc is thus armed and defended against all attacks 
from without, nearly after the manner of a knight of the middle ages ; 
only the knight was not quite shut up in his armour, while the mollusc 
is attached to it by indissoluble organic bonds. “Such a life and 
such a habitation!” says Michelet. ‘In no other creature is there 
the same identity between the inhabitant and the nest. Drawn from 
its own substance, the edifice is the continuation of its fleshy mantle. 
It follows its form and tints. The architect has communicated its 
own substance to the edifice.” 
The shell of the Mollusca has been variously accounted for by 
naturalists. ‘We might regard the shell as the bone of the animal 
which occupies it,” says a celebrated French naturalist ; and then he 
gives expression to a very different view. ‘‘We may say as a general 
thesis that testaceous moltuscs are animals with whom ossification is 
thrown out on the external surface in place of the interior, as in the 
mammals, birds, reptiles, and fishes. In the case of the superior 
animals the bones lie in the depths of the body; in the shelled 
Mollusca the bones are placed on the superficies. It is the same 
system reversed.” 
Other zoologists reject as altogether untenable both these com- 
