78 



NUTRITION. 



213. Among the Mollusks, a few, like the cuttle-fishes, 

 have solid jaws or beaks closely resem- 

 bling the beak of a parrot 

 (Fig. 57) ; and they move 

 up and down as in birds. 

 But a much larger number 



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rasp their food by means of 

 a tongue coiled like a watch- 



Fig. 58. 



Fig. 57. 



spring, the surface of which is covered with innumerable 

 minute tooth-like points of a horny consistence, as in the 

 highly magnified portion of the tongue of Natica (Fig. 58). 

 214. The Articulata are remarkable, as a class, for the 

 diversity and complication of their apparatus for taking and 



dividing their food. In some marine worms, 

 Nereis, for example, the jaws consist of a 

 pair of curved, horny instruments, lodged in 

 a sheath (Fig. 59). In spiders, these jaws 

 are external, and sometimes mounted on 

 Fig. 59. long, jointed stems. Insects which masti- 

 cate their food have, for the most part, at least two pairs 

 of horny jaws (Fig. 60, 61, w), besides several additional 

 pieces which serve for seizing and holding their food. 

 Those which live on the fluids which they extract either 

 from plants or from the blood of other animals, have the 

 masticatory organs transformed into a trunk or tube for this 

 purpose. This trunk is sometimes rolled up in a spiral 

 manner, as in the butterfly (Fig. 64) ; or it is stiff, and 



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V 



Fig. 61. Fig. 62. Fig. 63. 



Fig. 64. 



folded beneath the chest, as in the squash-bugs (Fig. 62), 



