3i6 



CHAPTER XL 



ACEPHALOUS MOLLUSCA. 

 "Sigillatim mortales, cunctum perpetui." — APULEIUS. 



The Mollusca proper were divided by Cuvier into five great sub- 

 classes : — I. Lamellibranchiata, 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, mollis : 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 shell. 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 v.^as 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. " 1\\ 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 celeljrated French naturalist ; and then he 

 gives expression to a very different view. "We may say as a general 

 thesis that testaceous molluscs 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- 



