156 THE HISTORY OF CREATION. 



perfect forms) to be morphologically the lowest among the 

 four higher tribes of animals. 



Whilst, for reasons already given, we exclude the Moss- 

 polyps, and Tunicates — which have hitherto been generally 

 classed with the tribe of Molluscs — we retain as genuine 

 MoUuscs the following four classes : Lamp-shells, Mussels, 

 Snails, and Cuttles. The two lower classes of Molluscs, the 

 Lamp-shells and Mussels, possess neither head nor teeth, 

 and they can therefore be comprised under one main class, 

 or branch, as headless animals (Acephala), or toothless animals 

 (Anodontoda). This branch is also frequently called that 

 of the clam-shells (Conchifera, or Bivalvia), because all its 

 members possess a two-valved calcareous shell. In contrast 

 to these the two higher classes of Molluscs, the snails and 

 cuttles, may be represented as a second branch with the name 

 of Head-bearers (Cephalophora), or Tooth-bearers (Odonto- 

 phora), because both head and teeth are developed in them. 



The soft, sack-shaped body in most MoUuscs is protected 

 by a calcareous sheU or house, which in the Acephala (lamp- 

 shells and mussels) consists of two valves, but in the 

 Cephalophora (snails and cuttles) is generally a spiral tube 

 (the so-caUed snail's house). Although these hard skeletons 

 are found in large quantities in a petrified state in aU the 

 neptunic strata, yet they tell us but little of the historical 

 development of the tribe, which must have taken place 

 for the most part in the primordial period. Even in 

 the Silurian strata we find fossil remains of all the four 

 classes of Molluscs, one beside the other, and this, con- 

 jointly with much other evidence, distinctly proves 

 that the tribe of Molluscs had then obtained a strongf 

 development, when the higher tribes, especially the 



