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ZOOLOGY. 



rim inside. Two of the ten arms arise from the under side 

 of the head ; they are twice the length of the eight others, 

 and oval at the end. On each side of the head behind the 

 tentacles are the remarkably large eyes, which, though usual- 

 ly said to be more like the vertebrate eye than those of any 



other invertebrate, are really 

 constructed fundamentally on 

 the same plan as the eye of 

 the snail ; differing in several 

 important respects from that 

 of a Vertebrate, the resem- 

 blances between the two being 

 superficial, while the struc- 

 ture of the eyes of mollnsks is 

 quite unlike that of Crusta- 

 ceans, insects or Vertebrates. 

 The mantle loosely invests 

 the front of the body next to 

 the head, so that the water 

 passes in around the neck in 

 order to bathe the gills, which 

 are quite free from the visce- 

 ral mass. The mantle is beau- 

 Dtifully colored and spotted, 

 the change of color being due 

 to the change in form of the 

 pigment masses or cliromato- 

 j>Jio7'es, which are under the 

 influence of the peripheral 

 nerves. 



The mantle is supported by 



Fig ydl.-LoUriopallida; male. About a homy " pell" (Fig. 209), or 



pen-shaped thin support, ex- 

 tending from the upper side of the anterior edge of the 

 mantle to the end of the body. In the fr/tiit of the Medi- 

 terranean Sea this is thick, formed of limestone, and is 

 called the "cuttle-fish bone." 



The organs of digestion consist of a mouth, pharynx, 

 oesophagus, stomach and intestine. The mouth is situated 



