MR. T. H. HUXLEY ON THE MORPHOLOGY OF THE CEPHALOUS MOLLUSCA. 65 
PLATE V. 
The first eleven figures are to be regarded as mere diagrams, illustrative of the 
archetypal form of the Mollusca and its more important modifications. 
The shaded portion is the haemal surface, the unshaded the neural surface. 
Figs. 2 and 3 are supposed to represent the development of an abdomen, and the 
changes of position thence undergone by the intestine and heart. 
Fig. 4 is a diagram of a Pteropod, corresponding with fig. 2. 
Fig. 5 is a diagram of a Cephalopod, corresponding with fig. 3 ; but in these, changes 
in the different parts of the foot have been also effected. 
Figs. 6 and 7, similarly are supposed to represent the development of a post-abdomen. 
Fig, 8. A diagram of Aplysia, corresponding with fig. 6. Atlanta corresponds exactly 
with fig. 7* 
Figs. 9, 10, 11, are imaginary sections of a Mollusk, a Fish and an articulate animal, 
respectively, to show the relations of the nervous, alimentary, vascular and 
appendicular systems. 
The Mollusk and articulate animal are in their normal position ; the fish is 
turned upon its back to correspond with them. * The pectoral fins. 
-I- The legs of the articulate animal. 
Figs. 12-15. The buccal apparatus or tongue of Patella. 
Fig. 12. From the right side. 
Fig. 13. From above. 
Fig. 14. The supporting cartilages. 
Fig. 15. The elastic plate which plays over them. 
Figs 16, 17 . The stomach of Pteroceras. 
