CLASS CEPHALOPHORA. 



never intersecting those of its neighbors, quickly destroys 

 the strongest timber. Its valves are very small, cover- 

 ing only a limited portion of the anterior part of the 

 body. 



CLASS CEPHALOPHORA (sef a lof 6 ra). 



To this class belong mollusks which are generally 

 capable of locomotion, moving about on their so-called 

 foot. Placed anteriorly is 



FIG. 59. 



the head, which generally 

 bears tentacles and eyes, 

 and is pierced by the open- 

 ing of the mouth. The ali- 

 mentary tract is well devel- 

 oped, and bears anteriorly 

 a series of characteristic 

 teeth, the odontophore 

 (o don'16 phor).* Though 

 in many forms the body is 

 protected by the investing 

 mantle only, the greater 

 number have a single hard, 

 limy shell, into which they can partly or wholly contract. 

 Representatives are found in the ocean, in fresh-water, 

 and on land. Some, therefore, are obliged to breathe air, 

 and are consequently provided with lungs. 



The present class has been designated by several 

 names : CEPHALOPHORA in that they bear a head ; UNI- 

 VALVES (u'nl valvz), because of the single valved shell ; 

 and GASTEROPODS (gas'ter 6 podz), because the foot sup- 

 ports a portion of the alimentary tract. 



F L 



Diagrammatic view of Cephalophorous Mollusk, 

 showing main points in its anatomy. 0, 

 Mouth, leading into the elongated alimentary 

 tract, which has opening into it, the duct 

 from, L. the Liver. Sg, The supra o?sophageal, 

 or cephalic ganglion, connected by nervous 

 rings with, Ig< the infra-oesophageal and, Pg, 

 the pedal ganglia. F, Foot or creeping diek. 

 S, Shell ff, Heart, the space surrounding 

 which is in communication with the exterior 

 through the tube, T. 



* Compare with, teeth of Clam-worm, page 30, 



